• 한국지반공학회논문집
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• 제40권5호
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• pp.59-76
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• 2024

지반은 구조물로부터 장기간 다양한 형태의 반복하중을 받으며, 구조물의 안정성 확보를 위한 유효수평응력의 변화 예측이 필요하다. 본 연구는 장기간 반복하중을 받는 입자성 물질의 정지토압계수, 간극비, 전단파 속도의 변화를 실험을 통해 파악하였다. 기존 연구의 압밀셀을 개조하여 수평응력 및 전단파를 측정하기 위한 시스템을 구축하였고, 주문진 표준사를 다양한 상대밀도로 조성하여 초기 정하중, 반복하중, 추가 정하중, 그리고 하중 제하의 응력 이력 동안 일정 초기응력에서 다양한 응력 진폭으로 반복압축실험을 수행하였다. 실험 결과, 무한대에 근접한 반복압축에서 모든 시료의 간극비는 초기응력-진폭비 (= Δσ/σ_o)에 따라 감소하였으며, 시료의 최종 상태를 대변하는 최종 간극비 e_T로 수렴하였다. 반복압축 중 정지토압계수는 상대밀도에 따라 변화양상이 달리 나타났으며, Soil fabric의 변화와 Particle scale mechanism에 따라 결정되는 것으로 판단된다. 응력 이력 동안, 전단파 속도의 변화를 통해 반복하중을 무한대로 받는 시료의 정지토압계수를 예측하였으며, 측정한 값과의 교차 검증을 통해 높은 신뢰도를 보여주었다. 실험결과로부터 무한대에 근접한 반복압축조건에서 흙의 도로포장설계 정수인 회복탄성계수의 새로운 산정 방법과 기초 구조물의 최종 침하량 예측방법을 제시하였다.

• Geomechanics and Engineering
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• 제19권1호
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• pp.79-91
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• 2019

Renewed interest in the long-term pile foundations has been driven by the increase in offshore wind turbine installation to generate renewable energy. A monopile subjected to repetitive loads experiences an evolution of displacements, pile rotation, and stress redistribution along the embedded portion of the pile. However, it is not fully understood how the embedded pile interacts with the surrounding soil elements based on different pile geometries. This study investigates the long-term soil response around offshore monopiles using finite element method. The semi-empirical numerical approach is adopted to account for the fundamental features of volumetric strain (terminal void ratio) and shear strain (shakedown and ratcheting), the strain accumulation rate, and stress obliquity. The model is tested with different strain boundary conditions and stress obliquity by relaxing four model parameters. The parametric study includes pile diameter, embedded length, and moment arm distance from the surface. Numerical results indicate that different pile geometries produce a distinct evolution of lateral displacement and stress. In particular, the repetitive lateral load increases the global lateral load resistance. Further analysis provides insight into the propagation of the shear localization from the pile tip to the ground surface.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.281-292
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• 2008

Prefabricated Board Drains (PBDs) recently become more widely used than conventional sand drains in improving soft ground because the PBD is more time and cost effective. The performance of PBDs is affected by disturbance in the adjacent soil formation during inserting mandrels, the intrusion of fine particles into filter fabric, and necking of the drain by excessive lateral pressure especially occurring in very deep clay formation such as the Busan New Port site. In this study, the PBD with double-core is introduced, which seems to overcome the shortcomings of usual single-core PBDs. An in-situ test program was established in the Busan New Port site, in which a set of the double-core PBDs and the single-core PBDs was installed to compare the efficiency of each of the drains. The discharge capacity of the double-core and the single-core PBDs was compared for various confining pressures in the modified Delft test and the chamber test. A series of CRS consolidation tests was performed in order to obtain profiles of void ratio-effective stress and void ratio-permeability relationships in the Busan New Port site that are used as input date in performing a numerical program ILLICON. The numerically simulated settlements of ground surface in the test site are in good agreement with those of in-situ measurements. In addition, the performance of the double-core and single-core PBDs has been experimentally and numerically compared in this paper.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1992년도 가을학술발표회 논문집
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• pp.113-120
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• 1992

The construction of container terminal at Brani, Singapore required the improvement of soft clay layer having the thickness of about 6.5m, average moisture content of 79.4%, liquid limit of 90.4%, plastic limit of 21.8%, field vane strength of 10 to 25 KPa, pre-consolidation pressure of 225 to 60 KPa and compression index of 0.4 to 1.0. For the improvement of this layer, Colbon drains of 1.3m spacing in triangular pattern were installed to the bottom of the layer and surcharge of more than 11.25m high sand fill was later applied to the treated area. The settlement and lateral displacement of the ground were measured and the speed of surcharge filling was controlled, based on these readings. The removal of surcharge was determinied using the estimated time for the 90% degree of consolidation under the design pressure of 180KPa. The field and laboratory test results show that the soft clay layer has been improved substantially in its strength and consolidation characteristics: increase in strength of about 50KPa and pre-consolidation pressure and decrease in void ratio and compression index.

• 한국지반공학회논문집
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• 제21권1호
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• pp.15-27
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• 2005

이 논문에서는 앞서 수행된 국내의 화강풍화토의 실험 결과를 토대로 하여 화강풍화토의 함수특성곡선을 합리적으로 예측하기 위한 방법이 제안되었다. 이 방법은 인공신경망기법을 이용해서 Fredlund와 Xing의 함수특성곡선식의 계수들을 추정하도록 제안되었다. 이러한 계수들을 추정하기 위한 신경망 모델의 입력 자료로는 실험결과에서 함수특성곡선의 계수에 큰 영향을 미치는 것으로 확인된 입도분포곡선, 다짐함수비, 그리고 간극비가 사용되었다. Fredlund 와 Xing의 함수특성곡선식의 계수를 구하기 위해 본 연구에서 제안된 신경망 모델은 신뢰성 있는 예측결과를 보였으며 그 예측결과의 정확도가 이전의 다른 방법들에 비해 높게 나타났다.