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• Development of Environmental Simulator and Advanced Construction Technologies Over TRL6 in Extreme Conditions Development of Environmental Simulator and Advanced Construction Technologies Over TRL6 in Extreme Conditions ▲ Senior Research Fellow Shin Hyu-soung, KICT Department of Future & Smart Construction Research Prologue In May 2021, South Korea became the 10th participating country in the “Artemis Accords” project, an international piloted lunar exploration program led by NASA. As not only the United States but also Europe, China, Japan, and India have announced plans for lunar exploration, it feels as if the dream of space construction which had previously seemed far away has become more concrete. Furthermore, looking at Korea, which has not yet performed a concrete mission, it even makes one feel impatient to think that Korea may be falling behind again. The recent discovery of large amounts of ice in the lunar poles has accelerated the competition for lunar exploration. This is because ice not only can provide fuel for rockets, but also water and oxygen, which are essential for sustaining the life of astronauts. The Moon's gravity is only one-sixth that of the Earth's, which makes it easier to get out of the gravisphere with relatively little fuel. Therefore, the usability of the Moon as a stopover is growing, because space missions can depart from the Earth, recharge their fuel on the Moon, and take off to deep space such as Mars. In addition, since the Moon is close to the Earth, it is a good place to prepare various technologies to be used in outer space and on other planets and to conduct various scientific studies, which further increases the value of the Moon. All of these are reasons why many countries around the world intend to build bases on the Moon and use them for the long-term residence of astronauts. The Korea Institute of Civil Engineering and Building Technology (KICT) has been leading space construction research through the BIG Project since 2016. To strategically respond to the shifts in the space development paradigm caused by the efforts of nations around the globe, such as space base construction and resource development, this study aims to secure core construction technologies applicable in outer space, an ultra-extreme environment. Centering on the achievements of the 6th year (2021) of the study, this article aims to introduce the development status of the four core technologies in detail: Development of a full-scale chamber for realizing extraterrestrial planetary ground environment and verification technology; infrastructure construction technology using extraterrestrial planetary local materials; technology for the informatization of space for construction on the ground of planets; as well as the development of planetary ground investigation equipment and the planetary underground informatization technology. Development of a Full-scale Chamber for Realizing Extraterrestrial Planetary Ground Environment and Verification Technology The Full-Scale Dusty Thermal Vacuum Chamber (DTVC), which simulates the extreme lunar surface environment, is used to minimize the risk of failure in the real extraterrestrial space environment by verifying various technologies and equipment developed for lunar exploration. This DTVC was made in 2017 and installed in the Future Convergence Building, and was completed in 2019 after undergoing a stabilization test. The internal scale of DTVC is 50 m3, and it can simulate the temperature (from -190 ℃ to +150 ℃) and vacuum conditions (exclusive of ground: 10-6 mbar, Inclusive of ground: 10-4 mbar) of the lunar surface, and a large amount of lunar simulant is put inside the chamber to evaluate the impact of cosmic dust, etc. (Figure 1). The Dirty Thermal Vacuum Chamber (DTVC)'s performance in creating vacuum and temperature environments has been secured through studies in Years 1 through 5. In 2021, studies were carried out for the simulation of ground temperature conditions according to the lunar night and day conditions; the measurement of the thermal conductivity of the ground according to the vacuum pressure for creating the ice ground; as well as the system for simulating electrostatic charging environments on the lunar surface and its measurement study. As the lunar surface has no atmosphere, the temperature near the equator can rise to 120 °C during the day, and can drop to as low as -170 °C at night. However, since the thermal conductivity of lunar simulant is low in a vacuum environment, the temperature change of the soils below 10 cm depth is not large, and the low-temperature state is maintained. The soil temperature according to the depth in the low/high-temperature environment of the full-scale chamber constructed based on these data was measured (Figure 2), and further study will continue to improve the performance of simulating the temperature of the ground. In addition to temperature and vacuum, the characteristic lunar surface environmental condition is electrical, which shows a positive potential of less than +20 V under the influence of sunlight during the day and a negative potential of hundreds to thousands of V at night under the influence of the Earth's plasma (Figure 3). This characteristic is considered a threat to the long-term residence of astronauts and equipment on the lunar surface, and it is necessary to understand and develop technologies to address it. To simulate this electrical environment in the DTVC, an electrification environment simulation system using ultraviolet lamps and electron beams was built in a small vacuum chamber (Figure 4). Based on the electrical data on the lunar surface, a similar environmental simulation and a measurement method were devised. In this year, the 7th year of the DTVC, a study on ground cooling in the chamber and measuring the potential of the ground charged with static electricity in an electrical electrification environment will be conducted. Through such research, it is planned to advance the environmental simulation performance of the DTVC and develop it into a more reliable construction technology verification facility in the lunar environment. Infrastructure Construction Technology Using Local Materials of Extraterrestrial Planets To build a lunar base, construction materials are needed. As the cost of transporting such materials from the Earth to the Moon would be astronomical, it is essential to develop a technology that makes it possible to produce construction materials using resources available on the Moon. To this end, a study is being conducted to solidify the “Lunar Simulant,” local resources available on the Moon, through a microwave-sintering technology in order to use it as a construction material. Sintered pellets of lunar simulants are created when lunar simulants (KLS-1) are densified at a temperature of 1,080°C or higher through the microwave-sintering method, and the density and compressive strength of the sintered pellets are increased as the sintering temperature rises. The thermal expansion characteristics of all materials used in the construction of the lunar base are very important, as repeated contraction and expansion of construction materials with the extreme temperature change of the Moon can cause cracks in the structure. The thermal expansion coefficient of the sintered pellets of lunar simulants produced by the microwave sintering method is about 5 × 10-6 °C-1 within a range similar to the lunar surface temperature (from -100 to 200 ℃), which was confirmed as similar to the thermal expansion coefficient of actual lunar rock. In addition, the thermal expansion coefficient of the sintered pellets of the lunar simulants did not change significantly even after processes of heating-cooling-reheating, so it was confirmed that the microwave sintered lunar simulant had high thermal resistance even under the Moon’s extreme temperature changes. To use the sintered pellets of the lunar simulant as a lunar base construction material, it is first necessary to review their homogeneity. In this study, the porosity was estimated through the Statistical Phase Fraction (SPF) method using X-ray CT images of the sintered pellets of lunar simulant to evaluate the homogeneity based on the porosity distribution of the material. It was confirmed that the total porosity of the sintered pellet of lunar simulants, estimated by the SPF method, was almost identical to the porosity calculated through the density analysis. Through estimating the local porosity of the local sintered pellets by dividing the CT image of the sintered pellet of lunar simulants into unit cells with a constant volume, it was confirmed that the mean porosity of 1,080 ℃ and 1,100 ℃ sintered pellets of lunar simulants were 30.4±2.1% and 27.1±2.9%, respectively, and distributed in the ranges of 26-40% and 20-36%. At the same height, the porosity decreases from the outside to the inside of the sintered pellet. This is due to the characteristics of microwave heating, which has a higher internal than external temperature, and it can be seen that a denser structure is formed in the center of the sample. Currently, sintered block of lunar simulant is being manufactured to increase its utility as a construction material, and to apply microwave sintering technology to a real lunar high vacuum environment, microwave vacuum sintering equipment must be built and sintering experiments conducted. Technology for Informatization of Space for Construction on Extraterrestrial Planetary Ground To select the optimal site for the construction of a lunar base, a lunar topography survey is essential. However, Global Positioning System (GPS) is not available on the Moon, and the Moon's Permanently Shadowed Regions are low illuminance areas without sunlight. Therefore, this study aimed to develop a real-time 3D topographical information technology based on an unpiloted vehicle that can be used to construct the high-precision 3D topographic map required for design and construction on the lunar surface. In this study, research was conducted to acquire real-time three-dimensional topographic information in low illuminance and GPU-shadowed environments by using a sensor combination of a stereo camera mounted on an unpiloted vehicle and an Inertial Measurement Unit (IMU). In particular, a self-supervised CNN-based image enhancement module was developed to maximize mapping performance in a low illuminance environment, and mapping performance with a mean error of less than 7 cm in a low illuminance environment was secured. In addition, simulated planetary topography consisting of craters, rocks, hills, soil, and gravel areas was built in the KICT's indoor simulated terrain laboratory and SOC Demonstration Research Center (Yeoncheon), and verification experiments for unpiloted topography informatization technology were conducted (Figure 7). The research was conducted on object recognition in images of constructed simulated extraterrestrial planetary topography, region classification, and evaluation of the similarity of the same object in other images. To automatically classify objects and regions of interest in the targeted areas, a topography and terrain feature recognition and region classification technique using Mask R-CNN, an open source program for deep learning region recognition, was developed. We also developed a matching method for identical object and terrain features in multiple images using the Triplet network, and completed a major object matching system between aerial photos and unpiloted-vehicle topographic images (Figure 8). In the future, we plan to develop a GIS-based unpiloted topography informatization technology system by improving the accuracy of unpiloted topography informatization technology and artificial intelligence object matching technique and combining them. Development of Extraterrestrial Planetary Ground Investigation Equipment and Extraterrestrial Planetary Underground Informatization Technology Moon explorations, which had stalled for a while after humans first successfully landed on the Moon, began to become active again when the existence of ice at the lunar poles was confirmed. To analyze the ice and underground resources that exist at the poles of the Moon, drilling equipment must be mounted on the exploratory Lander or Rover. In order to transport and operate such equipment on the Moon, an extreme environment, requirements in terms of small size, light weight, low power, high efficiency, and high performance have to be met. In this study, a prototype of drilling equipment that can be operated in atmospheric pressure and low temperature environments was first developed. In addition, in consideration of transportation needs, miniaturization of 0.27 m3 grade, weight reduction of 18.5 kg grade, and low power consumption of 44.4 W grade were secured. Prototype drilling equipment was pre-verified using artificial ice in the freezing chamber, and a field study was conducted under low power, low reaction, and waterless conditions for sea ice and frozen soils around the Jang Bogo Research Station to evaluate the drilling performance and identify problems in drilling the sea ice frost heaving (Figure 9). By performing the drilling performance and reliability evaluation under various local conditions, it was confirmed that drilling failure due to slip of the bit-cutting area occurred when the vertical reaction was 25 N or less, and drilling failure due to jamming occurred when it was 125 N or more. In the range of vertical reaction of 50 to 100 N and rotation speed of 25 to 125 rpm, drilling reliability of at least 60% was secured. Epilogue The construction of a space base, a dream of humankind for decades, is gradually becoming a reality. Space powers are competing with each other in terms of piloted lunar exploration and base construction plans to be the first to occupy the Moon. Relatively speaking, Korea's space development research lags far behind. However, the space construction field, which has just taken its first steps, has relatively low entry barriers compared to other space fields. As such, simply by securing the core technologies Korea can enter the ranks of advanced countries at the forefront of space exploration. It is hoped that the space construction technology developed by the KICT will be the first core technology to open the gates, and that it will leap forward as an institution leading the global space construction field in the future. Department of Future&Smart Construction Research Date2022-09-27 Hit 1662
• Special Bridge Safety Inspection Technology Utilizing Robots Special Bridge Safety Inspection Technology Utilizing Robots ▲ Senior Researcher Seo Dong-woo, KICT Department of Structural Engineering Research Prologue Most of the structures currently constructed as special bridges in Korea (collectively referring to cable-stayed bridges on which the measurement system is built) are constructed in the form of cable-stayed bridges or suspension bridges. Since the service life required for special bridges is more than 100 years, the stability, durability, and usability of the structure must be secured (KSCE, 2006). Damage to cables, which is one of the key deficiencies in special bridges, is a major factor reducing bridge safety and shortening service life. Cable damage is caused not only by environmental factors (climate, load, earthquake, etc.) but also by unpredictable accidents such as fire or collision. If a bridge in public use must suspend its operation due to cable damage, the economic and social losses are enormous (Na et al., 2014). In Korea, there was an accident in which one out of a total of 144 construction materials was completely broken and two were partially damaged by a cable fire at Seohae Bridge (cable-stayed bridge) (Gil et al., 2016). Although studies aiming to develop various inspection technologies for the safety and maintenance of cables are being conducted, there is a limit to the applicability of these technologies to special bridges, especially to cables, which are large facilities, due to limitations in the mobility and accessibility of equipment. To address this, efforts to develop a cable inspection robot capable of non-destructive testing are ongoing (Kim et al., 2014). To apply the inspection robot to cables, it is necessary to secure its field usability by using a wireless system and minimizing dead-weight. In this article, I would like to introduce a cable inspection robot equipped with an electromagnetic sensor to improve the driving stability, which was pointed out as a disadvantage of existing inspection robots, and to detect whether the inside of the cable is damaged. Design and Specifications of Cable Inspection Robot In making the cable inspection robot, we focused on the applicability of large diameter cables over 200 mm and securing the robot's driving stability. Figure 1 shows the 3D image of the cable inspection robot and its main devices. The dimensions of the robot are 510 mm × 610 mm × 710 mm, and the weight is reduced to 12.8 kg. In addition, to improve durability, the frame of the robot was made of aluminum. A high-resolution IP camera (1920 × 1080 pixels) was installed to take pictures of the exterior of the cable, enabling real-time cable shot images to be transmitted with a wireless Wi-Fi router. Furthermore, the movement distance of the robot could be calculated using an acceleration sensor and a rotary encoder. Three driving motors (IG-32GM, DC12) and urethane wheels were installed so that the robot can move on the cable while minimizing its shaking during climbing. In addition, a variable diameter adjustment part (140-300 mm) was made to improve the adhesion between wheel and cable. The wireless remote control of the robot uses IEEE 802.11 an/ac 5 GHz 2×2 MIMO to achieve a communication distance of 10 km and a data transmission rate of up to 867 Mbps. Damage to the steel wire of cables is detected with an electromagnetic sensor. As shown in Figure 2, the principle applied is that the polarity is divided again at the damaged area when the cable breaks or gets damaged. As shown in Figure 3, the sensing device mounted on the inspection robot for cable damage detection consists of pipe diameter adjusting units that can be adjusted according to the cable diameter and a roller for moving on the cable surface. Also, the electromagnetic sensor for detecting cable damage is inserted in the middle of the roller part. Performance Evaluation of Cable Inspection Robot Indoor and outdoor tests to evaluate the driving performance of the cable inspection robot were conducted as shown in Figure 4. One cable-stayed bridge with a history of cable accidents was selected as a test bed bridge for field tests of bridges currently in public use. The bridge is a short-span earth-anchored steel composite cable-stayed bridge with a span length of 400 m and a width of 23.9 m, on a four-lane road (two ways). The field cable (200 mm) had an inclination angle of 27.3 degrees, and the indoor test was conducted at 45 degrees. With the verification test, the climbing speed (19 cm/s) and the descent speed (20 cm/s) were evaluated, and it was confirmed that the robot is effectively controlling its speed when the speed increases due to slipping that may occur during the descent. It was also confirmed that the driving speed was constant regardless of the inclination angle. In addition, real-time images of the cable surface were taken with three cameras in the field test, and as shown in Figure 5, it was confirmed that visual inspection of the cable was possible. No communication-related problems occurred during the performance verification test. The cable damage detection test was conducted indoors. The cable specimen used in the indoor test is a type of cable currently used in bridges, and the inner cable consists of 20 pieces of one bundle composed of seven 1.57 mm strands. For the cable sheathing, the same High-Density Polyethylene (HDPE) tube used in the driving capability test was used. To detect cable damage, damage types were artificially simulated as shown in Figure 6. Cut damage was subdivided according to the degree of cross-sectional cut into 30%, 50%, and 100% cut (break). For disengagement damage, the case where the cable protruded to the outside in a tidy state was reproduced. For disconnection, one cable was made short. Figure 7 shows the results of the test conducted indoors. In the graph, the X-axis is time and the Y-axis is the electromagnetic sensor measurement. It can be seen that the phase of the electromagnetic sensor measurement changed by 180 degrees at the point where damage (cut) took place. On the other hand, it was confirmed that the phase of the electromagnetic sensor measured value did not change during disconnection, but the magnitude of the magnetic field increased. To secure the reliability of the experimental results, it is considered that additional experiments are needed, with more diverse damage types and repeatability than those conducted in this study. Epilogue This article introduced the development of a cable inspection robot capable of measuring large-diameter cables over 200 mm. The developed cable inspection robot has expanded its field applicability by improving its driving ability, driving stability, and wireless communication performance. The possibility of detecting damage to the inside of the cable using an electromagnetic sensor was verified through an indoor test. However, it is considered necessary to further improve inspection efficiency by developing an analysis algorithm that in addition to detecting the presence of cable damage can determine the degree and type of damage through additional tests. If facility maintenance technology using inspection robots is continuously advanced and applied, it is expected that it will greatly contribute to facility safety management. This cable inspection robot was developed with budget support by the Ministry of Land, Infrastructure, and Transport. It has been handed over to the Korea Authority of Land & Infrastructure Safety and is being used for the maintenance of general national highway special bridges. Department of Structural Engineering Research Date2022-09-27 Hit 771
• Modular Multifamily Housing in Korea and its Future Role Modular Multifamily Housing in Korea and its Future Role ▲ Research Specialist Boo Yoon-sub, KICT Department of Building Research Prologue One of the eco-friendly construction methods, in modular construction, modules produced at a factory are used to complete a construction project on site. At the same time as on-site construction such as bed excavation and foundation construction are carried out, the module is made at an off-site factory dedicated to modular fabrication and brought to the site for assembly. Accordingly, the modular construction method has the substantial advantage of being able to reduce the construction period by almost half because external factors that can delay the construction schedule on-site, such as particulate matter and civil complaints, are minimized. Modular construction can be divided into two types: the floor-by-floor method, in which modules are stacked on site, and the infill method, which involves installation as if inserting into a structure equipped with column-beam-slab (Figure 1). Based on the materials constituting the modules, the modules can be classified into steel-framed modules and concrete-based modules. Steel-framed modules have advantages such as high strength, high durability, and excellent machinability, because modular beams, columns, etc. are fabricated using high-quality steel. However, unlike concrete modules, the steel-framed module requires separate details to secure fire resistance. In addition, compared to concrete modules, the production cost is relatively high, and it is necessary to solve the problem of being somewhat vulnerable to vibration. Concrete modules have the advantages of high strength, fire resistance, excellent anti-vibration, and economic feasibility, as floors, wall units, etc. are fabricated using precast concrete (PC). However, since they are heavier than steel-framed modules, there is a difficulty in lifting for high-rises, which must be overcome for high-rise modular construction with more than 20 stories (Table 1). Trends in Modular Multifamily Housing in Korea Modular multifamily housing in Korea mainly uses steel-framed modules. As a national R&D demonstration project, the Korea Institute of Civil Engineering and Building Technology (KICT) promoted the public housing project of a Modular Demonstration Complex in Gayang-dong in Seoul (2017) together with the Seoul Housingㅍ& Communities Corporation (SH). It also constructed the Modular Demonstration Complex in Dujeong-dong in Cheonan (2019) jointly with the Korea Land and Housing Corporation (LH). Both were supplied as the first multifamily public housing to comply with housing performance standards. After that, public sector bodies such as local governments provided modular housing with six stories or less above the ground as rental housing. The KICT is conducting a mid to high-rise modular public housing demonstration project (hereinafter referred to as “Gyeonggi Happy Housing”) in Yeongdeok-dong, Yongin, Gyeonggi-do in collaboration with the Gyeonggi Housing & Urban Development Corporation (GH). Gyeonggi Happy Housing, which at 13 stories (106 households) is the highest-rising public housing project in Korea, plans to apply the achievements developed by the mid to high-rise modular research group, such as design engineering, off-site construction method, and on-site management. The three-hour fire resistance pointed out as a disadvantage of the steel-framed modular housing above was secured for the first time in Korea through an accreditation test by an accredited institution, and on-site construction is underway with the goal of completion at the end of 2022. The SH is carrying forward a 12-story modular public housing project in Garibong-dong, Seoul (246 households), and a 10-story modular public housing project (512 households) in downtown Seoul. The LH provided public silver housing (152 households) in Ongjin-gun, Incheon by applying the modular construction method, and pushing ahead with the modular public housing project in Sejong City, etc. The government is considering early move-in by converting part of the public housing in the third new city to a modular construction method. For concrete modules, KC Industry, a private company, jointly developed a PC box-type module with the KICT and built a modular building for promotion purposes at its headquarters in Yeoju and its branch in Jeju. It entered the housing market focusing on private housing with one to two stories. In addition, it is expected that the PC box-type modular housing will be able to be supplied as low-rise multifamily public housing of five stories or less, as it has secured structural safety and residential performance. Role of Modular Multifamily Housing For modular public housing, it is most important to resolve the problem of lack of public understanding in relation to off-site construction, and dispel misconceptions about poor residential performance compared to reinforced concrete (RC) construction. After the completion of the Gyeonggi Happy Housing promoted by the KICT as well as the modular multifamily public housing promoted by the public sector, through a thorough review of housing performance, it is necessary to inform the public that modular housing can also secure residential performance equivalent to that of RC multifamily public housing. In addition, it is necessary to pioneer a housing market that applies a modular construction method. Since 2015, the housing crisis has been exacerbated due to a decrease in the number of authorizations and permissions for housing construction, a surge in the number of households caused by the concentration of population in metropolitan areas and division of households, and a shortage of high-quality housing stock. The current housing policy focuses on large-scale housing supply that can be expected after the passage of at least five years, such as large-scale housing site development, reconstruction, and redevelopment. As such, it is difficult to satisfy the current demand for housing, such as for single or two-person households in downtown areas. If local governments and local housing corporations provide a fast and timely supply of modular public housing to small publicly owned sites, it will be possible to flexibly respond to the issue by utilizing the modular construction method to fill the gaps that are not affected by the housing policy. Department of Building Research Date2022-09-27 Hit 1124
• Development of Nondestructive Evaluation Technology for PSC Structures (PSC Stethoscope) Development of Nondestructive Evaluation Technology for PSC Structures (PSC Stethoscope) ▲ Senior Researcher Park Kwang-yeun, KICT Department of Structural Engineering Research The Aging of PSC Structures and Need for External PS Tendon Nondestructive Testing Whether at home or abroad, in countries where civilization has progressed rapidly, a number of bridges containing the essence of civil engineering technology have been built, allowing logistics and passengers to quickly cross rivers and valleys. In South Korea as well, befitting a civilized country, many bridges have been built and are playing numerous roles. These bridges enable convenient crossing of the Han River to bind the Gangbuk and Gangnam areas into a single city, overcome mountain valleys to greatly increase accessibility to mountainous regions, and connect islands to the mainland. It is found that 38% of these bridges were built using pre-stressed concrete (PSC) structures. Given the fact that a large number of bridges have been built since the 1980s and 1990s when Korea's economy grew rapidly, it can be assumed that the development of safety diagnosis technology for PSC structures older than 30 years is urgent. As the name suggests, the pre-stressed tendon (PS tendon) plays the most critical role in the PSC structure. PS tendons can be broadly classified into external PS tendons and internal PS tendons. For example, regarding external PS tendons, there was a case of enormous economic and social loss in 2016 due to corrosion of external PS tendons on Jeongneungcheon Viaduct, the inner ring road in Seoul, raising public awareness of the need for safety diagnosis (Figure 1). State of External PS Tendon Nondestructive Testing Technology Taking the Jeongneungcheon Viaduct case as an opportunity, the Korea Institute of Civil Engineering and Building Technology (KICT) conducted the KICT Blind Test (2016), targeting domestic and foreign nondestructive testing technologies to investigate the technology that can assess the integrity of external PS tendons. The integrity of the external PS tendon can be checked using three indicators: sectional damage, stress, and voids. However, for stress, no organization possessed the related technology, regardless of location at home or abroad, and for voids, only one French company (Advitam) applied for and demonstrated a detection rate of about 73%. Among the three indicators, cross-sectional damage is the most important and direct indicator. Of the ten local and foreign companies that applied for related nondestructive technology, only two companies, Tokyo-Rope of Japan and Instron of Russia, showed valid results, and none of the Korean companies demonstrated valid results. As for the technology of the two companies, which showed valid results, we came to the conclusion that it would be difficult to apply it in the field unless the cost, usability, size, and weight of equipment were improved. Development of Nondestructive Evaluation Technology for PSC Structures (PSC Stethoscope) For this reason, the KICT initiated a study to develop a proprietary technology that can inspect cross-section damage, stress state, and voids by conducting nondestructive testing of external PS tendons. The cross-sectional damage and stress use the magnetic properties of the external PS tendon made of metal, and the presence or absence of voids is inspected by applying radar technology. In this article, I would like to briefly introduce a technology for nondestructive testing of sectional damage, which is the most important indicator to assess the integrity of PS tendons. Underlying Concept of Nondestructive Testing Sensor Figure 2 shows the conceptual diagram of the developed electromagnetic sensor installed on the external PS tendon. Although the external PS tendon (the red-brown part in Figure 2) is actually paved with ducts and grouts, the magnetic properties of the duct and grout are almost the same as that of air (or vacuum). Therefore, it can be assumed that there is no magnetic property. The electromagnetic sensor is largely made up of three parts: the primary coil (yellow part in Figure 2), the secondary coil (orange part in Figure 2), and the fixing frame (purple part in Figure 2). The fixing frame is made of plastic that does not respond to magnetic fields. The primary coil is a kind of electromagnet that generates a magnetic field inside the sensor by flowing electricity, and the magnitude of the generated magnetic field is a function of the cross-sectional area of the external PS tendon, a metal component that penetrates the inside of the sensor. The secondary coil is wound to wrap the external PS tendon several times, and if the magnetic field inside the sensor is changed by varying the current applied to the primary coil, an induced current proportional to the magnetic field change is generated in the secondary coil. Using this principle, when AC electricity having a sine wave shape of constant amplitude is passed through the primary coil, AC electricity having an amplitude positively correlated with the cross-sectional area of the external PS tendon is induced in the secondary coil. Therefore, the cross-sectional area of the external PS tendon can be estimated by analyzing the amplitude of the induced AC electricity. The cross-sectional area of the metal component decreases when the external PS tendon is broken or rusted (iron oxide does not respond to a magnetic field). So, it is possible to estimate corrosion and break from the reduction in the cross-section. Development of Sensors Optimized for Field Work As can be seen from Figure 2, the sensor using this principle should have a closed circuit that wraps the external PS tendon. Tokyo-Rope of Japan and Instron of Russia, who were introduced earlier, also share the concepts and basic ideas mentioned above (of course, if you look at the details, they are quite different). However, Japanese and Russian technologies require winding work or equivalent work at the site, as shown in Figure 3, to make a closed circuit wrapping the external PS tendon, which takes a considerable amount of time. Consequently, workability is poor. In addition, since the sensor condition changes every time it is installed, the reliability of the sensor is lowered, and it is disadvantageous to work in the narrow passageway inside the bridge because all the sensor parts must be carried separately to be moved. On the other hand, the electromagnetic sensor developed by the KICT is divided into two, as shown in Figure 4, so with a little mastery, it can be installed within one to two minutes. Furthermore, it was ensured that the reliability of the sensor does not decrease, no matter how many times it is repeatedly installed, by composing the main junction with a highly reliable ready-made connector. The total weight is 5 kg and each side weighs about 2.5 kg, so it is not too heavy for a person to carry. If this sensor is installed as shown in Figure 5 and scanned at an appropriate speed along the external PS tendon, the change in the cross-sectional area can be inspected by performing a nondestructive test for the concerned section. Decision-making Technology Using Signal Processing and Artificial Intelligence Figure 6 shows the results applied to the specimens made to test the developed non-destructive equipment. The cross-sectional area simulating the damage as well as the damaged section are schematized at the top of the Figure. The result, measured by the same process as in Figure 5, is shown as the green line in Figure 6, but it is difficult to distinguish with the naked eyes because the amplitude change is insignificant. When the measured signal goes through several stages of signal processing, such as amplitude demodulation, to help assess the integrity of the external PS tendon using the measurements from the magnetic sensor, the result shown in the red line in Figure 6 can be obtained. In the red line, it can be seen that the change according to the damage to the PS tendon is clearly distinguished. However, a lot of experience is needed to distinguish whether these changes are caused by damage or noise. In addition, it is difficult to obtain information about the extent of the damage. To solve this problem, we developed an algorithm that uses a shallow FRP nerve sensor to specify the location of the damage, as shown in the blue dot in Figure 6, and predicts the ratio of the damage cross-section and even the length of the damage. Moreover, a number of specimens, as shown in Figure 7, were made and used to study artificial intelligence. Epilogue The KICT has developed a technology for nondestructive testing of the external PS tendon, a major element of the PSC structure, to prevent situations such as the Jeongneungcheon Viaduct that occurred in 2016 from being repeated. This technology uses the principle of nondestructive testing of the cross-sectional area made of metal with the application of electromagnetism and enables the repair and reinforcement of the PSC structure by detecting breaks and corrosion of the external PS tendon in advance. We not only developed sensors but also developed technology to help decision-making by improving the usability of sensors and applying signal processing and artificial intelligence to measured signals. The usability of the sensor is continuously improving through close communication with the companies currently in demand. Also, in the case of signal processing and artificial intelligence to help decision making, the algorithm is being enhanced and the accuracy is increased by adding learning data. We are also developing technology for the nondestructive testing of cables in cable bridges using the same principle. If the technology introduced here is completed and enters the bridge maintenance market, it will be possible to prevent huge economic losses through preemptive maintenance of bridges and to help avoid social losses caused by inconvenience to many people. Department of Structural Engineering Research Date2022-06-27 Hit 722
• Development of Technology to Assess Water Shortage Risk and Secure Water for Small-Medium Rivers in Response to Drought Development of Technology to Assess Water Shortage Risk and Secure Water for Small-Medium Rivers in Response to Drought ▲ Research Fellow Kim Chul-gyum, KICT Department of Hydro Science and Engineering Research Prologue Drought in Korea takes place every five to year years, statistically, and recently its occurrence and damage have become more frequent due to climate change. Aggravation of water shortage in the future, which is predicted according to climate change and increase in water consumption, will adversely affect water quality and aquatic ecosystems as well as water supply problems. In particular, the watersheds of small-medium rivers have a low ability to respond to water shortages from the drought and face repeated deterioration of the water quality and ecological environment due to water shortages. Furthermore, it is difficult for them to secure water supply through dams or reservoirs and control the flow of the rivers. Accordingly, measures for continuous water management, considering stable water security and water quality, are required for them. For effective drought response, accurate analysis and assessment of available water resources, along with rainfall prediction, and efficient water supply that can reduce the risk of water shortage based on this are required. As one of the alternatives for securing water, the reuse of sewage re-treated water is attracting attention, but the actual recycling rate is less than 20% due to concerns about the quality of reused water and aesthetic rejection. Accordingly, in order to increase the utilization rate of reused water, it is necessary to further strengthen the treatment level for water quality, while securing a safe level of water quality for various new hazardous substances that are not yet subject to regulation. In addition, in the case of small-medium rivers, eutrophication or algae is more likely to occur due to nutrients in the effluent because the amount of water discharged from the sewage treatment plant accounts for a large proportion of the river flow during drought. Therefore, it is necessary to highly upgrade the water quality treatment level for the water discharged from sewage treatment plants in order not only to secure the water quality safety of reused water but also to protect river water quality during drought. In order to solve the problems in terms of quantity and water quality that can occur in the watersheds of small-medium rivers during drought, in this study the Korea Institute of Civil Engineering and Building Technology (KICT) developed detailed technologies in three major areas, as shown in Figure 1. In the field of prediction/forecasting, we developed a technology for predicting the weather, amount of evapotranspiration, volume of runoff, etc. In the field of analysis/assessment, we developed a precision spatiotemporal hydrological analysis technology that reflects the complex water use system and physical characteristics of the watersheds of small-medium rivers; this assesses water resources availability and risk of water shortage. To secure water, we developed an advanced treatment technology for water reuse in sewage treatment plants and economical treatment technology that are superior to previous treatment processes. We also developed a technology that can dramatically reduce sludge and eutrophication-inducing substances generated in the sewage treatment process. Long-term Prediction Technology for Weather and Hydrologic Volume From a meteorological point of view, long-term prediction on a time scale ranging from one month to several months is essential information for securing and managing stable water resources and securing agricultural productivity in response to meteorological disasters, such as drought, flood, heat waves, and cold waves. Long-term prediction is mainly made by statistical models and climate models. However, it has not yet secured a sufficient level of predictability, and it is an area where attention and research have been continuously focused on in recent years. The Korea Meteorological Administration also provides forecast data for one to three months on precipitation and temperature using the results of the global climate model, which is a dynamical model. However, due to the geographical characteristics of the Korean Peninsula, sudden heavy rains or typhoons and abnormal climatic conditions have become more frequent than in the past. That is why it is not easy to accurately predict the weather. In this study, we developed a statistical model that can predict the monthly precipitation and temperature for the next one to twelve months in the Han River Sphere. We configured the prediction mode by flexibly selecting the optimal predictive parameters according to the prediction month based on the teleconnection between prediction target meteorological parameters (precipitation, temperature) and global climate patterns, making it possible to reflect meteorological and climate variability according to future climate change, etc. The forecasted monthly weather information is converted into the daily data for each major point by using the statistical downscaling technique, and the converted daily data are linked with the hydrological model. In this way, the forecasting results for hydrological parameters, such as the amount of evapotranspiration or volume of runoff, for the next 12 months also can be derived in the same way as the weather forecast period. Predicted weather and hydrologic volume information are provided through a web-based system as shown in Figure 2. Currently, monthly forecast information is being provided for the monthly precipitation, average temperature, and reference amount of evapotranspiration in the Han River Sphere, as well as the volume of runoff in the Chungju Dam watershed and the Gyeongancheon watershed. In addition, the forecast results ranging from December to the latest forecast results are being provided. Moreover, the forecast results ranging from those for January to December 1991, which were predicted based on December 1990, to the latest forecast results are provided. Precision Hydrologic Analysis and Assessment Technology for Small-Medium Rivers Watersheds Compared to the wide-area water supply regions around large rivers, water supply stability in small-medium river watersheds is relatively vulnerable during drought. Therefore, reliable prediction of the volume of runoff or available water resources is required in order to prepare comprehensive measures, such as the efficient operation of water supply facilities, assessment of water supply risk, and optimal use of available water resources. To this end, in this study we developed a water shortage risk assessment and water resources capacity assessment technology that reflects the detailed water use system (groundwater intake/drainage, sewage/wastewater discharge, etc.) and hydrological environment characteristics in watersheds during drought (Figure 3). By utilizing the developed technology, we have identified the impact of underground water intake on the accuracy of the prediction of the volume of runoff of the river watersheds for the first time in Korea. In addition, we laid the foundation for practical use to support the policies of the Ministry of Environment and local governments for the water management during drought by securing more than 70% predictive accuracy for the developed technology for each sphere of the medium-sized rivers, including Han River, Nakdong River, Geumgang, Yeongsan River, and Seomjin River. Furthermore, we developed a dynamic water resources assessment tool (DWAT), a program to assess the hydrological volume for small-medium rivers, and released it on the World Meteorological Organization (WMO) website in 2019. In June 2019, the WMO Hydrological Assembly decided that the DWAT would support the pilot project of "Global Hydrological Status and Forecasting System (HydroSOS)." In 2021, the DWAT was applied to sites in four Member States (Colombia, Argentina, the United Kingdom, and river watersheds in Bhutan). The research team continues to provide technical support related to the application and education of the DWAT through the WMO Technical Advisory Project (Figure 4). Technology for Advanced Treatment of Recycled Water Based on Advanced Oxidation Reuse of water refers to recycling the sewage and wastewater, heavy water, or stormwater that have been retreated through an appropriate water treatment technology, as water that meets the purpose of use. Reuse of water, in addition to reducing the amount of water source used, also offers benefits such as a cutdown of discharge of pollutant loads to public waters. Consequently, the need for the reuse of water is growing in terms of improving water scarcity and creating a healthy water environment. Meanwhile, it was found that new and trace pollutants/contaminants which are of concern as being hazardous to the human body or ecosystem, such as chemicals and pathogenic microorganisms, may remain in the reuse water. Accordingly, a technology for producing recycled water that can ensure the safety of reused water is required. In this study, we developed a UV-based advanced oxidation treatment process that can effectively treat residual trace organic pollutants by utilizing the TOC item newly added to the effluent water quality standards from 2020 as an index. We also secured the technology for recycling re-treated sewage water. By reducing the TOC concentration to 2.3-4.4mg/L in the secondary treated water of sewage, we have developed a process that can re-treat the sewage water, which has gone through secondary treatment, up to the level of Ib to III grade (the level that can be used as water for residential water) on the river living environment of the TOC standards. Furthermore, we secured a preemptive response technology for the treatment of unregulated new pollutants as well in order to secure the safety of recycled water, which is not currently regulated. For this, the ozone treatment process developed using a vortex-type microbubble generator was applied to 23 pharmaceuticals, including antibiotics, which are highly likely to be regulated in the future. As a result, it was confirmed, as shown in Figure 5, that pharmaceuticals can be reduced by more than 80%, and perfluorooctanesulfonic acid (PFOS), a representative material of perfluorinated compounds, can be cut down by 43%. Technology for Reuse of Sewage-treated Water with Low Energy In order to promote the use of recycled water, it is necessary to secure the safety of water quality and to develop an economical water supply plan. Korea reuses about 1 billion m3, which is 14.7% of the total sewage water treatment volume, and it is mainly used for washing water in the treatment plant, water for other uses, and water used to maintain the level of river water (74% of off-site water) (Ministry of Environment, 2015). This is because sewage-treated water effluent can be utilized directly without further treatment. In Korea, the ozone-based advanced oxidation process and membrane-based reverse osmosis (RO) process are mainly used for treatment processes for use as industrial water and agricultural water. In the case of the RO process, where membrane technology is widely used, 44% of the cost of operation and management is shown to be the energy cost for maintaining a high pressure of 12-19 bar or higher. On the other hand, the capacitive deionization (CDI) process used for seawater desalination is a technology that adsorbs ionic substances in the water onto an electric double layer, generated through electricity applied to a porous electrode composed of a dual-module, and treats them. It is known that its ion removal rate is lower than that of the RO process but the energy consumption is comparably lower. In this study, we developed a low-pressure membrane (UF)-CDI process linking an ultrafiltration membrane and CDI to derive an optimal process that can treat water meeting the target water quality level and save energy. It was compared with the target TOC concentration of 5 mg/L and confirmed that it was possible to treat up to a level of 3.62 mg/L. And in terms of energy, it was analyzed that the maintenance cost could be reduced by about 30% or more compared to that of the conventional RO process (Figure 6). Hence, it will increase the treatment efficiency of recycled water along with the ozone/ultraviolet advanced oxidation treatment process and secure sufficient water quality safety, thereby contributing to reducing the rejection of recycled water and increasing its utilization rate. Technology for Removal of Phosphorus in Water without Generation of Sludge and Recovery The nutrients contained in the sewage treatment water, including phosphates, cause eutrophication in rivers and dams, resulting in deterioration of water quality. Conventionally, the removal of phosphate contained in water has been centered on chemical treatment methods, such as rapid stirring - slow stirring - precipitation using ferric salts or aluminum. This method has a problem in that the cost of treating sludge is high due to the excessive generation of chemical sludge. Accordingly, several researchers are trying to remove phosphorus without generation of sludge by using iron components, such as iron ore, slack, and zero-valent iron, as an adsorbent for phosphate removal, but the removal efficiency is not high and the reaction time is excessively long (more than four hours). In this study, we developed the world's first sludge-free phosphate-removing and adsorbing new material to solve this problem and derived an optimal method to produce fertilizer using the removed phosphate (Figure 7). To assess the performance of the developed adsorption material, the adsorption/desorption process was repeated about 65 times. As a result, the component in the treated water was not detected at all, or it was found to be less than 0.03 mg/L, which is about 1/10 of the current water quality standard. In addition, in terms of maintenance, the net construction cost is similar to that of the conventional process (PAC+DAF)1) based on the treatment capacity of 1,000 m3/day, but the chemical agent consumption cost is found to be 1/30. It was analyzed that the economic feasibility was also excellent as 240 kg of phosphate fertilizer per month could be produced as a by-product. Technology for Crystallization of MAP to Recover Phosphorus and Nitrogen from Side Streams of Sewage Treatment Plants The average amount of water discharged from public sewage treatment plants in Korea is about 19 million m3 per day as of 2015. For watersheds of small-medium rivers like Gyeongancheon Stream, this represents a good amount of water resources, accounting for more than 70% of the quantity of flow during the low-water season. However, nutrient substances such as phosphorus and nitrogen remain in the effluent, which is highly likely to cause eutrophication and algae growth in rivers and lakes. Meanwhile, the side streams (or reject water) containing high concentrations of phosphorus and nitrogen from the sewage treatment plant are returned to the grit chamber and this rapidly increases the load of phosphorus and nitrogen in the subsequent biological treatment process, thereby ultimately lowering the water quality of the effluent. In this study, we developed a new process for crystallization of MAP (Magnesium Ammonium Phosphate) that can dramatically remove and recover nutrients, such as phosphorus and nitrogen in side streams, generated from sewage treatment facilities. In addition, the recovered MAP crystals can be used as a controlled release fertilizer (Figure 8). Design and optimal operating parameters were derived through the operation of a demonstration plant for the developed MAP crystallization process, and the basis for practical use was established through operation and maintenance manuals. The new MAP crystallization process secured more than 90% efficiency in removing phosphorus (PO4-P) in side streams by using sewage sludge incineration ash and recovering high-concentration effluent. And it raised the efficiency of removing nitrogen (NH4-N), which was on average 20% in the conventional MAP crystallization process, to more than 80%. Furthermore, it minimized the cost by using a single MgO chemical agent in the treatment process, and sufficient economic feasibility was secured for practical use by recovering MAP crystals that can be used as fertilizers. The developed new process will dramatically cut down the amount of phosphorus and nitrogen, which are circulating at high concentrations in the side streams, thereby reducing the load on the follow-up treatment processes and ultimately contributing to the protection of the water quality of the river to which it is discharged. Epilogue After five years of close study, core technology was secured for drought countermeasures in watersheds of small-medium rivers (Figure 9). In the field of prediction/forecasting, we laid the foundation to enhance the utility of preemptive drought forecasting and prediction information by developing quantitative forecasting technology for meteorology and hydrology and establishing a web-based service system that can provide long-term forecasting results. For analysis/assessment, we developed technology for precise spatiotemporal hydrological analysis and assessment, laying the groundwork for decision support for local governments in Korea to establish drought countermeasures. In addition, we established the foundation for global application and technical support by distributing it to major overseas WMO member states. In the field of response/security, we sought preemptive response to unregulated hazardous substances, provision of technical support for water treatment facilities, and enhancement in the value of the use of alternative water resources by developing advanced and low-energy treatment processes for the use of sewage recycled water. Moreover, we laid the foundation for not only protecting river water quality but also generating profits through the recycling-to-resources, via the sludge-free nutrient reduction technology as well as the recovery and crystallization technology. Regarding long-term forecasting technology, we continue to provide meteorological and hydrological forecasting information for the Han River Sphere through our website. The technology for hydrological analysis and assessment has been adopted as the main model of WMO and technical support is being provided to several member states. The reuse-water production technology is being considered for the application to the process improvement project of the wastewater treatment plants by the companies to whom the technology was transferred. The nutrient material treatment technology is also in the process of technical explanations and consultations at the working group level with related companies for each core process. The various detailed technologies developed in this study will be able to contribute to creating a healthy water environment, as well as securing stable and safe water resources for the watersheds of small-medium rivers, which have been relatively vulnerable to drought response. Department of Hydro Science and Engineering Research Date2022-06-27 Hit 686
• Trends in Extraterrestrial Planetary Resource Exploration and International Technology Trends in Extraterrestrial Planetary Resource Exploration and International Technology ▲ Research Specialist Ryu Byung-hyun, Department of Future & Smart Construction Research Prologue Since the Space Age began in the 1960s, there have been 60 lunar missions, eight of which have been human piloted or crewed missions. Apollo 11 was the first crewed mission to land on the moon in 1969, and later Apollo 15 brought rock samples back from the surface, putting more weight on the hypothesis that the moon was born from a massive collision with Earth. Human understanding of the extraterrestrial universe has been broadened through such lunar exploration, with human interest in Mars growing even further since. In 1997, Mars Pathfinder was the first mission to land a mobile rover on the surface of Mars, with photos sent from the rover attracting great public attention and further promoting the Mars exploration. However, as the Mars exploration became more challenging, humankind has begun to show interest in lunar exploration once again. The reason that governments and enterprises of each nation are actively engaged in lunar exploration in the space development competition is that the moon is not a mere subject of mystery but is closely related with the future of humankind. Our terrestrial resources are naturally and gradually being depleted due to their natural scarcity, even though the rate may vary depending on how quickly they are consumed. The anticipation that humankind could continue to subsist solely on Earth's resources indefinitely is now long gone. Instead, humankind has been devising ways to conserve resources while producing various solutions such as the development of alternative energy and alternative materials. On the other hand, humanity is also pondering how to make use of extraterrestrial resources. Many of the objects in space are astronomically distant from us, with only a few countries having the means of transportation, and the costs are likewise astronomical. Tapping into extraterrestrial resources was thus merely a topic of the imagination in the past. Recently, however, new ideas have been emerging to tap into the virtually unlimited resources of outer space. Discovery of Extraterrestrial Planetary Resources The discovery of extraterrestrial planetary resources dates back to when the samples that the Apollo spacecraft brought back from the moon were analyzed. Since that moment, when helium-3 was discovered in these rocks brought back to Earth, the amount of helium-3 in the lunar rocks was investigated, and the resources from each lunar landing site began to be estimated. The US had collected 382 kg of return samples from the lunar sea and high mountain regions of the moon through its Apollo program (Lucey et al., 2006), and Russia also analyzed 170.1 g of lunar samples (Wikipedia, 2017b) brought back to Earth, enabling them to understand the soil and rocks on the lunar surface. This was done to estimate where and how much of the resources were distributed on the lunar surface based on the lunar samples. Later, there was a new discovery from the Clementine mission of iron and titanium, forming the mineral map for the moon. The discovery of permafrost also suggested, for the first time, the possible presence of water on the moon. Launched in 1998, the Luna Prospector mission mapped the water as well as thorium and potassium, the natural radioactive elements, using epithermal neutrons. Most of the findings from these past missions were obtained by remote sensing, and they played a major role in creating maps that provide an understanding of the resources on the lunar surface. The gamma-ray spectrometers used in the Luna Prospector and Kaguya missions enabled the provision of maps of several major elements, and the gamma-ray spectrometer of the Kaguya mission produced, for the first time, the map for uranium. After remote sensing by the orbiter, Chang'e-3 was able to perform elemental analysis on the lunar surface using an x-ray spectrometer, but continued analysis was not possible due to the difficulty of rover survival. This phase of human discovery of resources on the moon and the estimation of their distribution is evolving into an on-site extraction experiment to confirm and utilize the findings on the lunar surface in the future. We are turning into reality our dreams of starting resource exploitation activities that would allow us to settle on survivable area on the moon, utilize local lunar resources, and provide energy resources, such as helium-3, which will be needed on Earth in about 10 years. Resources in Lunar Poles The Lunar Crater Observation and Sensing Satellite (US LCROSS) and Lunar Reconnaissance Orbiter (LRO) missions to the Moon were launched in June 2009. Following the new findings obtained as a result of the LCROSS collision with Cabeus, a crater at the moon's southern pole, the possibility newly presented itself for humanity's future utilization of the resources of the lunar poles. LCROSS announced that it had discovered water in the lunar southern pole, which is a requirement for humankind to build a lunar base. LRO has laid the foundation for the construction of a lunar base by orbiting the moon at an altitude of 50 km, focusing on the search for resources, including water, and scanning the lunar radiation environment. Based on the findings obtained using the Diviner Spectrometer mounted on the LRO, volatile substances and rare metals as well as water, brought by comets and asteroids, were estimated to have been deposited in permafrost on the lunar surface for billions of years since the moon was formed, and these materials were found to have been eroded at a loss rate of 1 mm per billion years (Paige et al., 2010), signifying the importance of the utilization of lunar permafrost resources (Colaprete et al., 2010; Gladston et al., 2010). These new findings provided an opportunity for major countries including the United States to seriously consider their plans for the construction of lunar bases as intermediate bases and the utilization of lunar resources in planning for the long-term exploration by humans of planets in more distant solar systems, as well as Mars. As a result of the LRO/LCROSS lunar missions, it was discovered that the lunar southern pole, a permafrost region, contains several volatile substances and has high content of rare metals such as gold, silver, and mercury. These substances are believed to have been brought from outside the moon (Gladstone et al., 2010). Drilling for Extraterrestrial Planetary Resources Recently, it has been revealed that water is present in the form of ice on extraterrestrial bodies such as the moon, and extraterrestrial resource exploration projects are being actively conducted centering on National Aeronautics and Space Administration (NASA) and China Association for Science and Technology (CAST). Furthermore, the European Space Agency (ESA) has announced the construction of the Moon Village and is leading the international cooperation necessary for the development of core technologies. In 2018, a team of researchers at the University of Hawaii discovered ice traces in the “Permanently Shadowed Regions” at the northern and southern poles of the moon. It has been speculated for a long time that water or ice has existed on the moon, but the research team at the University of Hawaii was the first to present conclusive evidence of this. The existence of water components has been identified in the past, but this was the first time that the molecular (H2O) form of water has been discovered. As the existence of usable water became clear during the lunar missions, the lunar explorations prepared by different countries were also able to gain momentum. Water in ice or liquid state cannot exist on the surface of the moon because its temperature rises to 130°C or higher when exposed to sunlight, which causes it to evaporate. Permanently shadowed regions in the surface craters of the south pole of the moon, which never receive direct sunlight, were thought to have ice because the temperature is believed to always be kept below -180°C. Based on this, scientists have speculated that water may exist in these regions. In 2009, NASA confirmed the presence of water by deliberately crashing the LCROSS spacecraft on the southern pole of the moon. However, it was not clear whether this was an actual form of water or of other substances (Li S, Lucey PG, Milliken RE et al., 2018). Water can be detected using infrared light, but so far only the 3㎛ wavelength band has been employed. With this wavelength, the water molecule could not be clearly distinguished from the hydroxyl group (-OH) bound to the mineral. If hydrogen and oxygen are present but merely as components in the state of attachment to a mineral rather than in the form of water, other additional processing is required to make use of it from this state. So far, it has been speculated that water in the form of water molecules is present in the regions of the lunar southern pole at a concentration of about 100 - 400 ppm. Whether water exists there depends on the surrounding topography, and it has been analyzed that this does not mean that water is present throughout the region. As this type of water exists in vitrified soil or between gravels, it is assumed that it remains even in the extreme environment of the moon. In addition, it was analyzed that there are many places where water can remain in the form of ice at the northern and southern poles. A team of scientists led by Professor Paul Hayne of the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder, USA said in a study published in the Nature Astronomy journal on the same day that “Permanently Shadowed Regions,” which may serve as ice reservoirs or cold trap at the moon’s northern and southern poles, measure at approximately 40,000 m2, or about six times the size of a football field (P. Hayne, O. Aharonson, N. Schörghofer, 2020). As the presence of water at the southern pole became evident, nations are pushing ahead to explore this area competitively. On the moon, the southern pole has more uneven surfaces compared to those of the equator, and communication is difficult, making exploration even more challenging. However, because of the presence of water, which is essential for life and can be used for exploration, different countries have designated the southern lunar pole as an exploration target. The United States announced the "Artemis Program" to send crewed spacecraft to the moon by 2024 and designated the southern pole as a landing point. China is also planning a "Chang'-e 7" mission to the Moon in 2024. NASA and CAST are scheduled to bring soil samples from extraterrestrial planets back to Earth through their extraterrestrial resource exploration projects. To accomplish this, it is necessary to develop drilling equipment that can be stably operated in extreme space environments. An extraterrestrial drill is equipment that can collect not only extraterrestrial planetary surface samples but also underground samples during the drilling process. It should thus be developed in an ultra-lightweight and compact form that enables uncrewed operation with low power and high efficiency in the extreme environment of space as well as transportation from Earth to the extraterrestrial bodies. The Korea Institute of Civil Engineering and Building Technology (KICT) is developing a drill for extraterrestrial resource exploration by reflecting this trend of international space missions, and intends to devise a method for evaluation that can directly estimate the uniaxial compressive strength of the ground that resists destruction by using the drilling information of the drilling equipment. In this regard, we would like to introduce here a series of processes of performance verification for a drilling rig, the development of bits, and the derivation of evaluation techniques, all through laboratory experimentation as basic research. Trends in Extraterrestrial Planetary Geotechnical Survey Technologies NASA succeeded in drilling into the lunar surface for the first time after a crewed lunar landing with the Apollo 15 mission in 1971. The drilling equipment used was called the Apollo Lunar Surface Drill (ALSD) and was a battery-powered portable drill used for drilling by the Apollo 15 crew. NASA's drilling equipment has been advanced dramatically through research and development, and its representative drilling equipment is the icebreaker drill developed by Honeybee Robotics, Ltd. This icebreaker drill was developed to search for signs of life in the ice-rich regions of Mars. Considering the conditions, such as lower gravity and atmospheric pressure compared to those of Earth, finite electrical energy, and an environment where it is difficult to use cutting oil, this equipment set its performance target of achieving 1 m deep drilling depth within one hour at power of 100 W and thrust of 100 N or less. It succeeded in achieving this performance target in a vacuum chamber experiment with an environment similar to that of Mars. The icebreaker drill consists of a deployment boom, Z-stage, rotary-percussive drill head, auger, drill bit, and sampling system. The deployment arm is a 3-DOF (Three Degrees of Freedom) cantilever that moves the Z-stage to the drilling point. The Z-stage is composed of a rail that moves in a straight line, a table and pulleys that move in a straight line, and cables, and is a device that transports an auger and drill bit in a straight line in the drilling direction. The rotary-percussive drill driving unit applies a rotary percussion to the auger drill bit to provide the torque and thrust required for drilling. The auger implements cutting material transport and sample collection functions. The drill bit is a cutter placed at the end of the auger. The icebreaker drill bit has an embedded temperature sensor and electrical conductivity sensor to monitor the temperature of the drilling environment around the drill bit and the physical condition of the materials being cut in real time during drilling. The sample extraction unit consists of a device for extracting the cut materials attached to the auger groove. After the Chang'e 3 mission's successful landing on the moon for the third time in the world in 2013, CAST launched the Chang'e 5-T1 (嫦娥五号T1), an uncrewed spacecraft that would bring samples from the moon back to Earth in 2020. Chang'e 5-T1 was launched from the Wenchang Space Launch Center in Hainan province, China, and landed on the "Ocean of Storms," a plain in the northwestern region of the moon, and collected about 2 kg of soil and rock samples. It then launched again from the lunar surface and made its way back to Earth. In December 2020, the Chinese National Space Agency (CNSA) announced that a capsule containing soil collected from the moon by Chang'e 5-T1 had landed in Inner Mongolia. China thus became the third nation to have brought lunar soil to Earth, after the United States and the Soviet Union. Chang'e 5-T1 has succeeded in bringing lunar soil back to Earth for the first time in 44 years since the Soviet Union's uncrewed Luna 24 mission in 1976. For lunar drilling research, China has been manufacturing a drilling test bed since 2016 based on Zhang Tao et al. (2016) and conducted experiments on drilling equipment to be applied in its mission to explore lunar resources. Mechanically, it is composed mainly of a body frame, a rotary mechanism, a penetrating mechanism, and encoders. The body frame is a structure that supports the rotary mechanism and the penetrating mechanism. The rotary mechanism is the unit that causes a drill tool to rotate, and the penetrating mechanism is the unit that forces the drill tool to drill into the lunar surface and sample the lunar soil. The encoder unit is composed of two encoders, which have the respective functions of measuring the rotational velocity of the rotary mechanism and the drilling speed of the penetrating mechanism. Status of KICT’s Development of Extraterrestrial Planetary Drilling Equipment The world's space powers are competing fiercely for resource exploration by developing drilling equipment that can be used in the environments of space. Accordingly, the Korea Institute of Civil Engineering and Building Technology (KICT), as a latecomer, began developing drilling equipment for the exploration of extraterrestrial resources in 2016. Currently, we are manufacturing prototypes of drilling equipment and conducting performance tests under various extreme environmental conditions. Mechanically, this equipment is composed mainly of a body frame, a driving unit, and a rotary unit. The body frame maintains the vertical position of the drill and supports the driving unit and the rotary unit. The driving unit consists of a vertical motor capable of vertical transport and a gearbox for speed control. The rotary unit consists of a bit-auger rotary motor, a bit-auger connection part, and a gearbox for rotation speed control. The auger serves to transport the cut materials and collect samples. The bit refers to a cutter installed at the end of the auger. One of the characteristics of this drilling equipment is that it has an integrated load cell, which can simultaneously measure reaction force and torque. In addition, the drilling speed can be estimated by the number of revolutions of the vertical motor, as it moves along the timing belt attached to maintain the vertical feed and vertical position of the drilling equipment. An encoder-coupled planetary reduction DC induction motor is mounted, capable of precise control of 48.6 W output for rotation of the auger, with a gear reduction ratio of 1:230. The output shaft of the motor is connected in the order of a reduction gear, a drive shaft, a torque meter, a drill bit clamp, and a drill bit. The driving force of the motor is used to cut and crush the center of the specimen by rotating the drill bit at the bottom. The motor is driven with a power of 24 V, rated current of 2,850 A (ampere), and rated speed of 3,550 rpm, and drills while rotating at a constant speed under the rated load. Department of Future&Smart Construction Research Date2022-03-28 Hit 1398
• Using Robotic Technology to Inspect Underground Spaces Using Robotic Technology to Inspect Underground Spaces ▲ Senior Research Fellow Lee Seong-won and Research Specialist Shim Seung-bo, Department of Geotechnical Engineering Research Complex and Diverse Underground Spaces The underground space of the city is a familiar place. It has huge shopping malls, serves as a passageway for transportation, and becomes a workplace as well. With the full utilization of underground spaces, the range of human activity has been expanded greatly, but is also naturally accompanied by risks. There are various risk factors such as collapse or flooding that accompany the underground space. The Department of Geotechnical Engineering Research at KICT is researching geotechnical engineering technologies that are essential to civil engineering construction, such as for tunnels and underground spaces, structural foundations, slopes, soft ground, and earthquakes. “Based on our current progress in research and development, the Department of Geotechnical Engineering Research is working with a focus on four major research subjects. To be specific, when constructing earthworks and foundation structures, they are classified under “development of technologies for automation of quality control,” “development of technologies for advanced management of three-dimensional infrastructure,” “development of technologies for securing safety of earthquake response facilities,” and “development of technologies for utilizing large underground spaces.” Members of the department are dedicated to the research based on expertise in their respective field. With our cutting-edge research achievements, we are leading the development of technologies for South Korea’s underground spaces.” With industrialization progressing in earnest, Korea's underground spaces are also becoming more and more complex. As the highways were built, tunnels through mountains were also constructed in various places, and recently the world's fifth longest undersea tunnel was opened in Boryeong. Research Specialist Sim Seung-bo explains that the underground space in Korea can be largely classified into railway tunnels, road tunnels, undersea tunnels, and utility-pipe conduit tunnels based on characteristics such as shape, size, and use. “The longest high-speed rail tunnel in South Korea is the Yulhyeon Tunnel, which is 50.25 km long and connects Suseo Station in Seoul to Jije Station in Pyeongtaek. The recently completed Boryeong Undersea Tunnel is one of the undersea tunnels, stretching to a length of 6.93 km. Finally, the most important tunnel is the utility-pipe conduit tunnel. This tunnel contains systems accommodating electricity, communication, heating, water, and conduit pipes necessary for living in the city. This tunnel is called a “lifeline” because it acts like the blood vessels that distribute energy to the body. Such tunnels are classified as national security facilities and are kept inaccessible to the general public.” Utility-pipe Conduit Accidents Leading to Large-scale Disasters A fire that broke out in the communication tunnel under the KT Ahyeon branch building on November 24, 2018 was an accident that clearly demonstrated the importance of the utility-pipe conduit tunnel. As a result of the accident, approximately 79 m of the communications tunnel on the first basement floor was burned out, and the Internet, mobile phone, and the wireless communications services provided by KT in the western area north of the Hangang River in Seoul became unavailable. “Unlike other tunnels, the utility-pipe conduit tunnel takes up space even for the internal accommodation facilities, so the space for people to move is very narrow. That was why it took so much time to extinguish the fire, which soon led to a large-scale accident. Based on the total amount of damage at that time alone, KRW 8 billion in property damage and KRW 30 billion in compensations were incurred. On the day of the accident, text messages were sent out to inform people, but no one could know why their phones were not working because the KT network was cut off.” It was called a digital disaster situation, where financial transactions and payment systems were cut off as the high-speed internet was unavailable at the time, and an elderly person in his 70s who could not report to 119 for help ended up dying due to the severance of communications. As a result, the scale and impact of direct and indirect damages in our daily life and society from an accident in the utility-pipe conduit tunnel raised the awareness that it could potentially lead to a bigger and more serious disaster than previously anticipated. Accordingly, thorough inspection and management of underground spaces including utility-pipe conduits have become much more important. “In Korea, infrastructure built during the period of economic development and growth are gradually approaching the end of their life expectancy, resulting in more frequent accidents. Such accidents can inevitably increase with aging, which has prompted us to take a closer look at practical ways to protect the safety of our citizens from such risks.” Robotic Technology Enabling Autonomous Travel and Inspection Periodic inspection is the most important means to safely manage underground space facilities. In particular, management through regular precision inspection is required. The conventional inspection method is known to have been carried out in a human-centered manner. Precision inspection is an inspection method where the inspector visually checks the damage point, then measures and records the size of the specific point using a crack gauge or crack detection microscope. In this case, it is said that it is not easy to diagnose the condition objectively because it inevitably involves the subjective judgment of the inspector. In addition, there are disadvantages in that costs are continuously required to improve safety through maintenance by increasing the frequency of inspection. The research team has developed technology for an automated inspection robot that travels inside the tunnel in the place of workers to inspect damage points on concrete structures. “The development of technology for automated inspection robots is divided into three phases: The phase of developing the core technology for each constituent technology, the phase of integration between constituent technologies, and the phase of on-site testing. In Phase 1, damage detection technology using deep learning as well as damage measurement technology using stereo vision are developed. In Phase 2, an inspection scenario according to the measurement result is implemented by linking the uncrewed moving object and the robot arm. Finally, automated inspection robotic technology is completed through on-site testing so that precision inspections can be performed in a tunnel environment.” The biggest advantage of automated inspection robotic technology is that it can be used flexibly in maintaining underground spaces based on the convergence of multiple core technologies. The robot is applied with technology for an uncrewed traveling object that can autonomously travel inside the tunnel, technology for the robot arm that can avoid complex internal accommodation facilities, and technology for the artificial intelligence sensor that can detect and measure damage points. This inspection technology was developed to also enable remote control through a wireless network, enabling convenient application by administrators. "The utility-pipe conduit is an underground lifeline; it is a tunnel that jointly accommodates communications lines, utility lines, and heating and gas pipes. In the past, tunnels and pipelines were laid in a complex urban underground system according to their respective uses, such as communications, utilities, and gas pipelines. To facilitate joint accommodation, it is essential to cut the costs of operating and maintaining utility-pipe conduits. It is expected that operation and maintenance costs can be reduced through the use of automated inspection robotic technology and that various accommodation facilities can be safely and efficiently managed within the utility-pipe conduit tunnel.” Provision of Safe and Sustainable Infrastructure The research team plans to continue its research to provide safe and sustainable infrastructure to society. The team will continue to advance this research in various forms and ultimately contribute its best efforts to the perfection of uncrewed and automated technologies for the maintenance of underground facilities. “In our future society, the aging of our population will be accelerated thanks to the extension of average life expectancy, while the economically active population will decrease accordingly. Under such circumstances, the maintenance of infrastructure relying on the workforce is expected to become more difficult. In response to these issues, we plan to develop the necessary technologies for automation and uncrewed maintenance and to further develop the technologies needed to enable automated damage repair.” Department of Geotechnical Engineering Research Date2022-03-28 Hit 1096

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