• 한국지반신소재학회논문집
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• 제19권1호
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• pp.93-101
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• 2020

흙의 비선형적 거동특성을 예측하기 위해 비교적 간편하고 예측의 정도가 높은 것으로 평가되는 탄·소성 쌍곡선모델을 선정하였다. 모델의 특성을 알아보기 위해 구성모델에 관련된 함수를 정식화하여 토질매개변수 결정 및 거동해석 프로그램을 개발하였다. 상대밀도 변화에 따른 백마강모래의 배수삼축압축시험 결과로부터 각각의 토질매개변수를 결정하였고 상대밀도에 따른 토질매개변수의 변화 특성을 분석하였으며 각각의 조건에서 결정된 토질매개변수를 이용하여 응력-변형률 거동을 예측하였다. 그 결과 축변형률에 대한 축차응력은 각각의 상대밀도에서 측정치와 예측치가 양호하게 일치하는 것을 확인하였고 축변형률에 대한 체적변형률의 관계에서 상대밀도가 작은 경우는 측정치와 예측치가 일치하는 경향을 보이나 상대밀도가 큰 경우에는 구성모델의 한계로 인해 체적변형률의 예측치가 측정치보다 다소 작게 나타나는 것을 확인 하였다.

• 한국지반공학회논문집
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• 제22권7호
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• pp.73-83
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• 2006

조립토 다짐말뚝의 거동특성은 주로 말뚝의 횡방향 팽창을 억제하는 연약한 원지반의 횡방향 구속응력에 의해 지배된다. 따라서 조립토 다짐말뚝의 지반 보강 능력은 원지반의 비배수 전단강도가 $15{\sim}50kPa$ 정도인 경우에 가장 효과적인 것으로 알려지고 있으며, 보다 연약한 지반에서는 구속압력이 충분하게 발휘되지 않으므로 적용성이 크게 저하된다. 본 연구에서는 연약지반에 대한 조립토 다짐말뚝의 적용성 확대를 위해 등입도 투수성 콘크리트 보강 조립토 다짐말뚝 공법을 제안하였으며, 등입도 투수성 콘크리트와 쇄석 및 연약 점성토로 구성된 복합 공시체의 대형삼축압축시험을 통해 제안된 공법의 효율성을 입증하였다. 또한 본 연구에서는 제안된 공법의 실무 적용성 확보를 위해 침하량 산정기법을 제안하였으며, 제안된 침하량 산정기법의 검증을 위한 목적으로 3차원 유한요소해석을 실시하여 해석결과로 분석된 말뚝의 침하량과 제안식에 의해 산출된 침하량을 상호 비교 분석하였다. 추가적으로 본 연구에서는 다양한 변수분석을 수행하여 설계변수의 영향정도를 평가하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제14권1호
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• pp.109-116
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• 2010

물유리계 그라우팅 공법은 침투주입 그라우팅으로 자주 적용되고 있으나, 시간경과에 따른 내구성 저하와 환경에 부정적 영향에 대한 문제가 부각되고 있다. 이에 마이크로시멘트계 무기질 재료의 ENG 공법이 이러한 물유리계 그라우팅 공법의 문제점을 극복하면서 우수한 침투성을 목표로 하여 개발되었다. ENG의 적용성을 파악하기 위해 체적변형시험, 용탈실험, 일축압축실험, 실내 투수실험 및 현장투수실험 그리고 중금속검출실험을 실시하였다. 그 결과 체적변형, 용탈량, 일축압축강도는 물유리 공법보다 월등히 우수하였으며, 투수실험에 있어서도 차수효과가 나타났다. 또한 중금속 검출량도 미미하여 환경에 부정적인 효과도 적을 것으로 판단된다.

• 한국농공학회논문집
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• 제57권3호
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• pp.93-100
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• 2015

The object of this paper is to study the shear characteristics of the weathered granite soil. To this end, a series of consolidated undrained triaxial compression tests are carried out to investigate the shear parameters-cohesion and internal friction angle-for the degree of saturation and degree of weathering. From the results, it is found that the shear parameters of weathered granite soil are influenced on the degree of saturation, degree of weathering and disturbance. Especially, internal friction angle is more influenced on the upper factors than cohesion. And shear parameters are more acted on the degree of saturation than the degree of weathering in the test range. It is, therefore, recommended that must be considered the conditions of granite soil-degree of saturation, degree of weathering and disturbance etc-in case of the calculation of bearing capacity, stability analysis and other designs with shear parameters.

• 대한토목학회논문집
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• 제31권4D호
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• pp.571-576
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• 2011

일반적으로 도로구조물들은 포화상태라는 가정 하에 설계되고 있으나 실제 도로구조물의 재료인 입상지반재료는 대부분 불포화 상태에 존재하고 있다. 이러한 부분을 반영하기 위하여 본 논문에서는 다져진 입상지반재료를 대상으로 삼축압축시험과 함수특성곡선 시험 결과를 활용하여 다양한 조건에서의 불포화 전단강도를 추정하였다. 이를 바탕으로 비선형 모형을 활용한 2차원 유한요소해석을 실시하고 Mohr-Coulomb항복조건을 통하여 항복하중을 규명하였다. 또한, 입상재료의 항복하중에 대한 도로구조물 표층두께의 변화에 따른 영향을 확인하였다. 해석 결과 입상지반재료의 불포화토 이론을 고려하여 포장 혹은 비포장 도로의 지지력을 예측할 수 있음을 보여주고 있다.

• Geomechanics and Engineering
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• 제7권3호
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• pp.317-333
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• 2014

The study of the mechanical behavior of rockfill materials under three-dimensional loading conditions is a current research focus area. This paper presents a microscale numerical study of rockfill deformation and strength characteristics using the Combined Finite-Discrete Element Method (FDEM). Two features unique to this study are the consideration of irregular particle shapes and particle crushability. A polydisperse assembly of irregular polyhedra was prepared to reproduce the mechanical behavior of rockfill materials subjected to axial compression at a constant mean stress for a range of intermediate principal stress ratios in the interval [0, 1]. The simulation results, including the stress-strain characteristics, relationship between principal strains, and principal deviator strains are discussed. The stress-dilatancy behavior is described using a linear dilatancy equation with its material constants varying with the intermediate principal stress ratio. The failure surface in the principal stress space and its traces in the deviatoric and meridian plane are also presented. The modified Lade-Duncan criterion most closely describes the stress points at failure.

• Computers and Concrete
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• 제26권3호
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• pp.227-237
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• 2020

Strain rate investigations are needed to calibrate strain-rate-dependent material models and numerical codes. An appropriate material model, which considers the rate effects, need to be used for proper numerical modeling. The plastic concrete cut-off wall is a special underground structure that acts as a barrier to stop or reduce the groundwater flow. These structures might be subjected to different dynamic loads, especially earthquake. Deformability of a structure subjected to dynamic loads is a principal issue which need to be undertaken during the design phase of these structures. The characterization of plastic concrete behavior under different strain rates is essential for proper designing of cut-off walls subjected to dynamic loads. The Cowper-Symonds model, as one of the most commonly applied material models, complies well with the behavior of a plastic concretes in low to moderate strain rates and will be useful in explicit dynamics simulations. This paper aims to present the results of an experimental study on mechanical responses of one of the most useful types of plastic concrete and Cowper-Symonds constant determination procedures in a wide range of strain rate from 0.0005 to 107 (1/s). For this purpose, SHPB, uniaxial, and triaxial compression tests were done on plastic concrete samples. Based on the results of quasi-static and dynamic tests, the dynamic increase factors (DIF) of this material in different strain rates and stress state conditions were determined for calibration of the Cowper - Symonds material models.

• 한국농공학회논문집
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• 제51권6호
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• pp.69-76
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• 2009

Soils exhibit creep behavior in which deformation and movement proceed under a state of constant stress or load. In Korea, weathered soil is abundant and occupies around one-third of the country. Weathered soil is visually described as a sandy or gravelley soil, but the behavior is quite different from the behavior of usual sand and gravel. In particular, the permeability of weathered soil is similar to sand, but the durability of settlement is similar to clay. Therefore analysis of time-dependent behavior of weathered soil is very important. In this study, Creep tests with weathered soils were carried out under constant principal stress differences of various stress levels which were experimentally obtained by triaxial compression test. The results of these tests showed the creep behavior for which the deformation increased with time, and the results are consistent with phenomenological model by creep equation of Singh-Mitchell.

• 산업기술연구
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• 제24권B호
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• pp.107-116
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• 2004

This thesis is results of experimental works on the behavior of the cut-and-cover tunnel. Centrifuge model tests were performed to simulate the behavior of the cut-and-cover tunnels having cross sections of national road and subway tunnels. Model experiments were carried out with changing the cut slope and the slope of filling ground surface. Displacements of tunnel lining resulted from artificially accelerated gravitational force up to 40g of covered material used in model tests, were measured during centrifuge model tests. In model tests, Jumunjin Standard Sand with the relative density of 80 % and the zinc plates were used for the covered material and the flexible tunnel lining, respectively. Basic soil property tests were performed to obtain it's the property of Jumumjin Standard Sand. Shear strength parameters of Jumunjin Standard Sand were obtained by performing the triaxial compression tests. Direct shear tests were also carried out to find the mechanical properties of the interface between the lining and the covered material. Compared results model tests estimation with respect to displacements of the lining.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.1796-1801
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• 2007

Piezocone penetration testing(CPTu) results such as cone resistance$(q_c)$, sleeve friction$(f_s)$, and pore pressure(u), have been carried out at 5 sites in Honam high-speed railway areas of Korea, in order to continuously estimate the characteristics of soil layers and the undrained shear strength$(S_u)$ in a soft ground. For the applications of the conventional CPTu results to undrained shear strength, the cone factors$(N_{kt})$ were deduced based on Field vane tests, and Monte-Carlo Simulation(MCS). Moreover the correlations of the undrained shear strength of CPTu by soil depths were compared and revised with the results of triaxial compression(UU test), field vane and Dilatometer tests(DMT). The depths of soft foundation at 5 sites in Honam high-speed railway areas were calculated based on the results of the various field tests in addition CPTu. The applicability of CPTu for a soft foundation criterion referred to the criteria of high-speed railway and related agencies in Korea was evaluated.