송배전관로 되메움재로서 콘크리트 재생 순환골재의 적용성 평가 연구

위지혜 高麗大學校 大學院 2011 국내석사

Recently, the utilization of recycled aggregates for backfilling a power transmission pipeline trench has been considered due to the issues of eco-friendly construction and a lack of natural aggregate resource. It is important to identify the physical and thermal properties of domestic recycled aggregates that can be used as a backfill material. This paper evaluated thermal properties of concrete-based recycled aggregates with various particle size distributions. The thermal properties of the recycled aggregates and river sand provided by local vendors were measured using the transient hot wire method and the transient needle probe method after performing the standard compaction test. After the standard compaction, the cracking effect occurs by the compaction energy. The cracking effect causes different compaction curve and thermal resistivity in the respective positions of compaction mold. The needle probe method considerably overestimated the thermal resistivity of recycled aggregates especially at the dry of optimum water content because of experiencing disturbance during inserting the needle probe into the specimen. Similar to silica sand, the thermal resistivity of the recycled aggregates decreased when the water content increased at a given dry density. Also, this paper evaluated some of the existing prediction models for the thermal resistivity of recycled aggregates with the experimental data, and developed a new prediction model for the recycled aggregates. To verify the laboratory test, the field test using pilot chamber was performed during a certain period of time. According to the results of field monitoring, recycled aggregates have smiliar thermal characteristic to river sand. Also, the result represents that recyceld aggregates maintain the stable water contents below the criteia of thermal resistivity, 100 ℃-cm/W. This paper shows that the recycled aggregate can be a promising backfill material substituting for natural aggregates when backfilling the power transmission pipeline trench.

지반강도정수의 변동성을 고려한 사면의 안정성 평가에 대한 연구

최은진 고려대학교 대학원 2016 국내석사

To interpret the stability of slopes, input soil parameters should be estimated as an average of conservative values ​​or test values from a deterministic point of view. Therefore, the calculated factor of safety is an index merely indicating the relative stability of a slope. It does not imply the actual risk level of the slope due to the uncertainty of soil parameters. With probabilistic analyses, the probability of failure and reliability index are available to quantify the stability or risk level of slopes. In this study, a safety factor is calculated, and the cause of the slope collapse is identified by analysing slope stability. In addition, the input data and condition of slope are achieved through the limited equilibrium method by performing a back analysis of slopes with a real slope failure case. The probabilistic analysis of slope stability using the Monte-Carlo simulation method is carried out for simple slope models with steepness parameters. The variability of input soil parameters is assumed to be distributed with user-specified mean values and standard deviations. Lastly, based on the probabilistic approach, the effect of variable probability of failure is identified with a real case study of slope failure and the reliability index.

보어홀 열저항 평가를 통한 병렬 U형 대구경 현장타설 에너지파일의 열성능 예측기법

김병연 高麗大學校 2016 국내석사

Ground source heat pump (GSHP) system utilizes geothermal energy for heating and cooling of buildings with the aid of the ground heat exchangers (GHEXs) by exchanging thermal energy with ground. Energy pile can be fully utilized by one of the ground heat source heat pump system and building foundation. However, a well-recognized effect for predicting thermal performance of energy pile systems is not available. Field thermal response test using ground heat exchanger and laboratory test using sample of test bed are conducted to evaluate thermal conductivity of test bed. In other to verify CFD numerical analysis model using COMSOL Multiphysics, thermal performance tests are conducted for ground heat exchanger and parallel U-type large diameter cast-in-place concrete energypiles. In this study, a series of the 3-D numerical analyses was performed to estimate the performance of and change in the ground thermal environment during operating a parallel U-type large diameter cast-in-place concrete energypile with 15 m in depth and 1.5 m in diameter. Load condition is applied to simulate artificial cooling/heating operation for six months (i.e., 3 months cooling – 3 months resting or 3 months heating – 3 months resting). For evaluating influence factors affecting the thermal performance and underground thermal environment, the thermal conductivity of ground, the initial ground temperature, the velocity of circulating fluid were considered in the model. To predict thermal performance of different type of borehole, borehole thermal resistance was evaluated. Verification of developed two-dimensional parallel U-type energypile model is carried out by comparing multipole method. Using this model, various shape of parallel U-type borehole thermal resistance is evaluated. In this model, borehole diameter, pipe diameter, shank spacing of pipes, thermal conductivity of concrete and number of parallel pipes are considered. Thermal performance prediction method to evaluate heat exchange amount from operating parallel U-type energypile from 3pairs to 10 pairs are contained in this paper.

해저터널에 급속동결공법을 적용하기 위한 고수압 동결챔버시험 및 수치해석적 연구

오민택 高麗大學校 大學院 2016 국내석사

The construction of the subsea tunnel that connects with neighboring countries is very important to the Korean peninsula, surrounded on three sides by the sea. The subsea tunnel may establish a transport network hub, as well as improve the accessibility of the state. Therefore, it is necessary to secure the domestic core technology for the design and construction elements needed for the construction of an subsea tunnel under the high water pressure. Commonly, grouting method is applied in tunnelling construction to prevent damage to soil and inflow of ground water. But it is difficult to apply conventional grouting method to subsea tunnelling construction in the high-pressure condition. In such a condition, the artificial freezing method can enable the tunnel excavation construction to form a watertight zone around the freezing pipes. For a proper design of the artificial freezing method, the influence of salinity on the freezing process has to be also considered. However, there are few domestic tunnel construction that applied the artificial freezing method and it is not clearly identified how the pressure and the salinity impact on the freezing of the soil. In this paper, the experiments were performed to identify the epidemiological characteristics of the frozen soil. Strength of frozen soil was evaluated through the uniaxial compression test and the change of thermal properties caused by freezing process was analyzed through the thermal conductivity measurement. Also, the geothermal chamber was designed and manufactured to perform the large-scale freezing test. The temperature in silica sand mixed with saline water was measured during the freezing process to evaluate the effect of salinity on the frozen rate, which is significant in designing the artificial freezing method in subsea tunnelling. In addition, a numerical analysis is conducted by using a finite element analysis program to verify the results of the chamber test and perform the parametric study.

헬리컬 파일의 형상과 지지력에 관한 연구

이종원 高麗大學校 大學院 2014 국내석사

The helical pile is a manufactured steel pile consisting of one or more helix-shaped bearing plates affixed to a central shaft. This pile is installed by rotating the shaft into the ground to support structural loads. The advantages of helical piles are no need for boring or grout process, and ability to install with relatively light devices. The bearing capacity of the helical pile is exerted by integrating the bearing capacity of each helix plate attached to the steel shaft. In this study, to estimate the bearing capacity of helical piles, 12 types of helical piles were constructed with different shaft diameter, plate configuration and the penetration depth. A series of field loading tests was performed to evaluate the effect of helical pile configuration on the bearing capacity of helical pile, constructed in three different shaft diameters (i.e. 73 mm, 89 mm and 114 mm). In the same way, the diameter of bearing plate was also changed from 400mm to 250mm with one or three plates. As well, the penetration depth was varied from 3m to 7.5m to analyze the relation between the penetration depth and the bearing capacity. There are various methods, which take both the steel shaft and the helix plates attached to the shaft into account to predict the bearing capacity of helical pile. In this study, three representative methods, individual bearing method, cylindrical shear method, and torque correlation method, are studied and compared to each other. The calculated result of each method is verified by the result of a series of loading tests. In addition, a parameter study is conducted, by performing finite element analysis using a nonlinear finite element analysis program, to determine the correlation between the bearing capacity and the configuration of helical piles with respect to the steel shaft and helix plate.

인공동결공법을 위한 사질 동결토 강도 특성 및 평가 방법

정상훈 高麗大學校 2019 국내석사

Recently, the technologies for rapid transferring various resources are receive attention as the industry develops and international exchanges become more active. For these reasons, subsea tunnels are emerging as the core technology of civil engineering. Due to the geographical characteristics of Korea, the construction of subsea tunnels will play a very important role in securing accessibility to other continents or countries. Due to the geological characteristics of the subsea tunnel construction, it is inevitable to be encountered with high water pressure condition. In high water pressure condition of subsea tunnel construction, it is hard to apply grouting method for preventing damage to soil and inflow of ground water. In this condition, the artificial ground freezing method can be the alternative method. The artificial ground freezing method is one of ground reinforcement methods that makes watertight zone around the freezing pipes and also increases the strength of the ground. For a proper design of the artificial freezing method, the strength characteristic of frozen soil has to be considered. According to previous studies, frozen soil strength increases with decrease of freezing temperature. However, frozen soil strength shows a complicated behavior depending on the confining pressure. The strength of unfrozen soil increases with increase of confining pressure, but strength of frozen soil can decreases with increase of confining pressure. This phenomenon caused by “Pressure-melting effect” of frozen soil. In this paper, frozen soil triaxial compression tests were performed to evaluate frozen soil strength characteristics. These triaxial compression tests were performed under various confining pressure and freezing temperature. During the test procedure, the confining pressure is applied after freezing soil sample. The test results of this study will compared with Lee(2018) test results, which applies confining pressure before freezing soil sample. Through comparison of the test results, this paper will evaluate the effect of confining pressure applying procedure on frozen soil strength characteristics. In conclusion, this paper will present proper frozen soil strength evaluating method for design of artificial ground freezing method.

하중조건 및 입도를 고려한 도상자갈 침하 특성 평가 연구

김기재 高麗大學校 大學院 2014 국내석사

Railway systems play a crucial role in the transportation infrastructure of a country, and are an essential component for sustaining economic development(Selig and Waters 1994). Due to ever increasing traffic congestions and rising fuel costs, the demand for faster rail has been increasing on a daily basis. This will impart more and heavier cyclic loads to the existing track, which will inevitably degrade and foul the ballast, resulting in a loss of track geometry and increased deformation. Thus, numerous research studies have been carried out to understand the behavior of ballast during cyclic loading. However, field measurements cannot provide a full insight into complex ballast behavior mechanisms when the discrete and heterogeneous nature of granular materials is considered. In this study, Laboratory experiments were conducted using Box test to assist in the understanding of ballast settlement and degradation. Furthermore, PFC 2D using the Discrete Element Method provides enough information from the particles scale level to help understand the settlement mechanisms that occur under complex cyclic loads. And, a simple procedure has been developed to generate clumps which resemble real ballast particles. The effect of particle size were evaluated about ballast using the laboratory experiment. In the result, the large settlement occurred in the upper limit of the particle size which consist small particles. And, the settlement of ballast increased with magnitude of load. The influence of particle shape(elongated shape, rounded shape, circle shape) on the heterogeneous stresses within an aggregate was investigated in box test simulations using the PFC 2D. As a result, the interlocking effect provided by the clumps(elongated shape, rounded shape) provides a much more realistic load-deformation response than the circle shape. Also, settlement behavior of ballast was investigated according to the change of porosity in specimen. As a result, initial rapid settlement observed in case of higher porosity in specimen. This influence contributed total settlement of ballast. Thus, porosity of specimen have been a contributing factor about settlement mechanism of ballast. Additionally, The settlement behavior of ballast was evaluated using the load combination of which control time of load magnitude and number of repeated load. As a result, the maximum magnitude of load and the period of load were confirmed to affect settlement behavior of ballast. The experiment result and numerical result of these various conditions will be able to use basic research about the settlement model of track consisted of ballast.

서해와 남해 연안의 해성점통의 공학적 특성 비교

정현석 高麗大學校 工學大學院 2013 국내석사

서해와 남해 연안 해성점토의 공학적 특성 비교 우리나라 남해연안과 서해연안 지반 차이의 원인을 조사하기 위하여 한강과 낙동강 하구에서부터 남해, 서해 연안의 퇴적현상을 연구하였다. 남해안의 부산신항(북위 35.1°)과 서해안의 인천신항(북위 37.5°)의 지반조사에서 알 수 있듯이 이 두지역은 위도상의 차이는 크지 않으나, 두 지역의 연약지반은 마치 지구 반대편에 위치한 것처럼 현저한 차이를 보인다. 이 두 해안 지반의 공학적 특성 차이에 대한 실험적 연구의 결과로부터, 지구를 중심으로 공전하고 있는 달이 한반도의 강하구의 퇴적에 대한 중요한 영향을 미친다는 것을 알게 되었다. 달의 인력은 한반도의 강하구와 접한 해안의 형상에 따라 전혀 다른 조류를 야기시키는 주된 원인이다. 이러한 대조적인 두 지역의 조류는 서해로 흐르는 한강과 남해로 흐르는 낙동강 하류의 퇴적에 직접적인 영향을 주게 되고, 몇 만년 이상 반복되어 지금의 서해와 남해 연안 해성토의 공학적 특성을 바꾸어 놓았다. 이 연구는 이러한 차이가 발생하는 원인이 지구로부터 384,400km 떨어진 달로부터 시작되고 있음을 알려준다. 그러한 현상은 아주 오래전부터 계속되어 왔으며, 달이 지구를 공전하고 있는 한 한반도 서해와 남해의 지반의 차이는 앞으로도 계속 될 것이다.

현장타설 에너지파일 설계를 위한 등가 열교환율에 관한 연구

민선홍 高麗大學校 大學院 2012 국내석사

Recently, considerable interest on energy piles has grown in the pile foundation industry to utilize geothermal energy for heating and cooling residential and/or commercial buildings. However, a well-recognized means for designing energy pile systems is not available. In other to verify the thermal and structural applicability of the cast-in-place concrete structure, physical properties of concrete cast in energy foundation structure were examined. Thermal conductivity of concrete with various curing conditions were experimentally estimated and compared. The hydration heat inside concrete of in-situ cast-in-place concrete pile (called energy pile) was observed in 4 weeks. Integrity of the interspace between the circulating pipe and concrete was assessed using equivalent permeability tests. In addition, Unconfined compression strength was measured for the concretr samples which were exposed to varying temperature cycles ranging from 50°C to 10°C. A test bed was constructed in order to evaluate thermal efficiency of the cast-in-place concrete energy pile. The energy pile is a large-diameter drilled shaft equipped with two types of heat exchange pipe installation, W-shape and S-shape. The drilled shaft reaches to the depth of 60 m whilst the heat exchange pipes were installed to about 30 m deep from the ground surface. The W-shaped and S-shaped pipe were installed in the opposite sections of the drilled shaft. In-situ thermal response tests (TRT's) were performed for both the types of heat exchange pipes. In addition, two closed-loop vertical ground heat exchangers of 40 and 60 m in depth were symmetrically constructed adjacent to the cast-in-place concrete energy pile at the distance of 1.5 m. The vertical ground heat exchangers were used to estimate effective ground thermal conductivity by performing TRT. To avoid underestimating the thermal transfer efficiency due to hydration heat inside the drilled shaft, the TRT's for the energy pile were performed after four weeks since the installation of the energy pile. CFD numerical analyses using FLUENT, a 3-D finite volume method program, were performed to simulate and compare with the field TRT. For design purpose of energy piles, a series of CFD numerical analyses was performed for the W type, multiple U type and coil type to obtain the relative heat exchange rate. These results can be used for energy pile design using PILESIM2. PILESIM2 is a design program which considers the pile configuration (such as pile diameter, length, number and space) and soil property (such as thermal conductivity and ground water condition). This can determine the optimal load of the energy pile through the cooling/heating simulation up to 50 years. However, because PILESIM2 is developed to design only the multiple U type and coaxial type, the relative heat exchange rate of various types normalized by that of the multiple U type can be used to adjust the design results of PILESIM2.

개별요소법(DEM)과 네트워크 모델을 이용한 불포화토의 열전달 거동에 관한 연구

한은선 高麗大學校 大學院 2012 국내석사

Thermal conduction of the particulate composites or granular materials can be widely used in porous materials, geotechnical engineering and etc. Especially, thermal conduction in soils has been highlighted in a geotechnical engineering such as geothermal energy, buried earth-structures, radioactive waste disposal, geological sequestration of carbon dioxide and hydrocarbon energy recovery (Yun and Evans, 2010). And it has been continued to develop “effective thermal conductivity” of medium by modelling energy relationship among particles in medium. The classical effective medium approximations for evaluating the effective thermal conductivity of particulate composites or granular materials can be broadly classified as: the Maxwell model (maxwell’s approximation based models; Maxwell, 1873), Self-consistent model (Landauer, 1952) and Different effective medium (Bruggeman’s asymmetric model (BAM), Bruggeman, 1935; Landauer, 1952). Such models will enable one to optimize the structure and arrangement of the material (Kanuparthi et al., 2008). It has been suggested that thermal conductivity of soils is dominated by soil properties and boundary conditions such as grain size and shape, mineralogy, porosity, coordination number, pore fluid characteristics, overburden stress and drainage conditions (Gangadhara and Singh, 1999; Singh and Devid, 2000; Tarnawaski et al., 2002; Weidenfeld et al., 2004; Yun and Evans, 2010). Thus, the multi-scale governing factors as well as the heterogeneity and complex configuration of particle skeleton often challenge the accurate estimation and interpretation of thermal conductivity in soils (Yun and Evans, 2010). This study focuses on the development of the effective thermal conductivity at the unsaturated conditions of soils using the modified network model approach assisted by synthetic 3D random packed systems (DEM method, Discrete Element Method) at the particle scale. To verify the novel network model, three kinds of glass beads and the Jumunjin sand are used to obtain experimental values at the various unsaturated conditions. The PPE (Pressure Plate Extractor) test is then performed to obtain SWCC (Soil-Water Characteristic Curve) of soil samples. In the modified network model, SWCC is used to adjust the equivalent radius of thermal cylinder at contact area between particles. And cutoff range parameter to define the effective zone is also adjusted according to the SWCC at given conditions. From the series of laboratory tests and the proposed network model, the modified network model which adopts a SWCC shows a good agreement in modeling thermal conductivity of granular soils at given conditions. However, thermal conductivity from the modified network model at the relatively dried zone (5~20% in degree of saturation) shows slightly higher values than experimental values. It seems that the equivalent radius of thermal cylinder at particles becomes smaller values at relatively dried zone. And an empirical correlation between the fraction of the mean radius (χ) and thermal conductivity at given saturated condition is provided, which can be used to expect thermal conducvity of the granular soils, to estimate thermal conductivity of granular soils.