• Smart Structures and Systems
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• 제25권4호
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• pp.433-446
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• 2020

In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile test and triaxial test. Then a model with dimention of 100 m × 100 m was built. A circular tunnel with diameter of 20 m was drillled in the middle of the model. Also, a rectangular tunnel with wide of 10 m and length of 20 m was drilled in the model. The center of tunnel was situated 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m and 60 m below the ground surface. these models are under confining pressure of 0.001 GPa, 0.005 GPa, 0.01 GPa, 0.03 GPa, 0.05 GPa and 0.07 GPa. The results show that the volume of colapce zone is constant by increasing the distance between ground surface and tunnel position. Also, the volume of colapce zone was increased by decreasing of confining pressure. The maximum of settlement occurs at the top of the tunnel roof. The maximum of settlement occurs when center of tunnel was situated 15 m below the ground surface. The settlement decreases by increasing the distance between tunnel center line and measuring circles in the ground surface. The minimum of settlement occurs when center of circular tunnel was situated 60 m below the surface ground. Its to be note that the settlement increase by decreasing the confining pressure.

• Computers and Concrete
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• 제21권2호
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• pp.189-197
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• 2018

A discrete element approach is used to investigate the effects of confining stress on the shear behaviour of joint's bridge area. A punch-through shear test is used to model the concrete cracks under different shear and confining stresses. Assuming a plane strain condition, special rectangular models are prepared with dimension of $75mm{\times}100mm$. Within the specimen model and near its four corners, four equally spaced vertical notches of the same depths are provided so that the central portion of the model remains intact. The lengths of notches are 35 mm. and these models are sequentially subjected to different confining pressures ranging from 2.5 to 15 MPa. The axial load is applied to the punch through the central portion of the model. This testing and models show that the failure process is mostly governed by the confining pressure. The shear strengths of the specimens are related to the fracture pattern and failure mechanism of the discontinuities. The shear behaviour of discontinuities is related to the number of induced shear bands which are increased by increasing the confining pressure while the cracks propagation lengths are decreased. The failure stress and the crack initiation stress both are increased due to confining pressure increase. As a whole, the mechanisms of brittle shear failure changes to that of the progressive failure by increasing the confining pressure.

• Geomechanics and Engineering
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• 제23권3호
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• pp.189-206
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• 2020

The accurate modeling of boundary conditions is important in simulations of the discrete element method (DEM) and can affect the numerical results significantly. In conventional triaxial compression (CTC) tests, the specimens are wrapped by flexible membranes allowing to deform freely. To accurately model the boundary conditions of CTC, new flexible boundary algorithms for 2D and 3D DEM simulations are proposed. The new algorithms are computationally efficient and easy to implement. Moreover, both horizontal and vertical component of confining pressure are considered in the 2D and 3D algorithms, which can ensure that the directions of confining pressure are always perpendicular to the specimen surfaces. Furthermore, the boundaries are continuous and closed in the new algorithms, which can prevent the escape of particles from the specimens. The effectiveness of the proposed algorithms is validated by biaxial and triaxial simulations of granular materials. The results show that the algorithms allow the boundaries to deform non-uniformly on the premise of maintaining high control accuracy of confining pressure. Meanwhile, the influences of different lateral boundary conditions on the numerical results are discussed. It is indicated that the flexible boundary is more appropriate for the models with large strain or significant localization than rigid boundary.

• Structural Engineering and Mechanics
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• 제18권2호
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• pp.151-166
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• 2004

The interaction between concrete core expansion and deformation of perimeter ties has been known to have a significant effect on the effective confinement of rectangular reinforced concrete (RC) tied columns. This interaction produces passive confining pressure to the concrete core. Most existing models for determining the response of RC tied columns do not directly account for the influence of flexural stiffness of the ties and the variation of confining stress along the column height. This study presents a procedure for determining the confined compressive strength of RC square columns confined by rectilinear ties with various tie configurations considering directly the influence of flexural flexibility of the ties and the variation of confining stress along the vertical direction. The concept of area compatibility is employed to ensure compatibility of the concrete core and steel hoop in a global sense. The proposed procedure yields satisfactory predictions of confined strengths compared with experimental results, and the influence of tie flexibility, tie configuration and degree of confinement can be well captured.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.888-895
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• 2006

In this study, anisotropically consolidated undrained shear(CAU) test was performed to examine the variation of the shear strength according to the stress history. The specimen having 30% relative density was homogeniously prepared, and 200KPa of back pressure was applied to increase the B value more than 0.95. To make NC specimens, the vertical stress was applied on the specimen by 100KPa, 200KPa and 400KPa, and to make OC specimens, the vertical stress was applied upto 400KPa and was reduced to 200KPa and 100KPa resulting in OCR 2 and 4 respectively. The test result indicates the shear strength for the OC specimens are slightly higher then that of the NC specimens at the same confining pressure. The elastic modulus varies according to the confining stress and considerably affected by preconsolidation stress.

• 한국지반환경공학회 논문집
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• 제13권11호
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• pp.51-60
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• 2012

동토지반의 기초구조물을 설계하는데 있어 기초의 안정성을 지배하는 설계정수인 동결토의 전단강도 및 동착강도를 측정하기 위하여 지난 50여 년 동안 많은 연구가 수행되어 오고 있다. 하지만, 아직까지 동결토의 전단강도 특성에 관한 많은 연구들은 토사 종류, 수직구속응력, 동결온도조건 등 여러 가지 영향인자 중 제한된 영향인자의 변화를 통해 수행되어 왔다. 동결토는 일반 토질과는 달리 토립자, 물, 공기뿐만 아니라 얼음을 포함한 4상으로 구성되어 있으며, 동토의 역학적인 성질의 변화는 일반적으로 온도, 수직구속응력, 동토의 구성물질에 따라 영향을 받는다. 이와 같은 동결토의 전단강도 특성을 측정하기 위하여 영하 30도의 저온환경에서도 동작이 가능하도록 설계된 동결토 직접전단시험기를 활용하였으며, 동토지역의 저온환경을 모사하기 위하여 대형 냉동챔버 내에 직접전단시험기를 설치하였다. 동결토의 전단강도 특성을 측정하기 위하여 비교적 균질한 입경분포를 지닌 주문진표준사 및 실리카모래와 입도분포가 좋은 화강풍화토를 활용하였다. 각각 세가지 시료에 대하여 전단시험은 세가지 동결온도 조건 및 수직구속응력 조건에서 수행되었으며, 그 결과를 바탕으로 동결온도조건 및 수직구속응력이 동결토의 전단강도에 미치는 영향을 분석하였다. 전반적으로 동결토의 전단강도는 동결온도가 낮아질수록 증가하는 경향을 보였으나, 수직구속응력에 의한 영향은 미미한 것으로 나타났다.

• 한국지반공학회논문집
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• 제19권2호
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• pp.49-55
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• 2003

본 연구에서는 연직말뚝과 경사말뚝에 대하여 수행한 압력토조 모형실험을 통하여 경사말뚝의 연직하중과 침하량 관계로부터 경사각도에 따른 압축지지력의 증가양상을 분석하였다. 실트질 모래로 형성된 상대밀도 50%의 포화지반에 경사각 0$^\circ$, 5$^\circ$, $10^\circ$, 15$^\circ$, 20$^\circ$의 모형 개단강관말뚝을 항타 관입하였으며, 압력토조내의 구속압력을 35, 70, 그리고 120 kPa로 변화시키면서 재하실험을 수행하였다. 연직 압축지지력은 경사각도가 커짐에 따라 증가하였으며 분석방법에 따라 증가율에는 다소의 차이가 수반되었으나 경사각 5$^\circ$, $10^\circ$, 15$^\circ$인 경우 지지력 증가율은 각각 111, 121, 127 ~ 140 % 정도를 나타내었다. 경사각이 20$^\circ$ 이상인 경우에는 말뚝 두부의 전도로 인하여 모형실험의 수행이 곤란하였다.

• Geomechanics and Engineering
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• 제5권3호
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• pp.241-261
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• 2013

The bearing mechanism of pile during installation and loading process which controls the deformation and distribution of strain and stress in the soil surrounding pile tip is complex and full of much uncertainty. It is pointed out that particle crushing occurs in significant stress concentrated region such as the area surrounding pile tip. The solution to this problem requires the understanding and modeling of the mechanical behavior of granular soil under high pressures. This study aims to investigate the sand behavior around pile tip considering the characteristics of sand crushing. The numerical analysis of model pile loading test under different surcharge pressure with constitutive model for sand crushing is presented. This constitutive model is capable of predicting the dilatancy of soil from negative to positive under low confining pressure and only negative dilatancy under high confining pressure. The predicted relationships between the normalized bearing stress and normalized displacement are agreeable with the experimental results during the entire loading process. It is estimated from numerical results that the vertical stress beneath pile tip is up to 20 MPa which is large enough to cause sand to be crushed. The predicted distribution area of volumetric strain represents that the distributed area shaped wedge for volumetric contraction is beneath pile tip and distributed area for volumetric expansion is near the pile shaft. It is demonstrated that the finite element formulation incorporating a constitutive model for sand with crushing is capable of producing reasonable results for the pile loading problem.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.1458-1465
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• 2010

A lot of dredging and reclaming projects are recently under way in Korea for the efficient use of limiting land space. Saemanguem area is special case of reclaiming by dredged soil. In case of a confined disposal of dredged soils by a pump dredger, generally coarse grained soils are separated from fines with dropping at the near part of the pump dredger. This kind of seperation of fine contents could be a factor of liquefaction by earthquake. In Korea, recently, earthquakes with magnitude of 3.0 or higher are distinctively increasing in 1990. In this study, cyclic shear characterics of Saemanguem Dredged sand depending on fine content were analyzed. A series of undrained cyclic triaxial test with cyclic stress ratio ($\sigma_d/{2\sigma_{{\upsilon}c}}'$) were performed on both isotropic consolidated specimen and sand with fine contents of 0%, 5%, 15%, 30%, 40% under the effective vertical stress of 100kPa and 50% and 60%, 70% of relative density for fine content of 0%, respectively. In the test results, cyclic shear strength increased by increasing of cyclic stress ratio($\sigma_d/{2\sigma_{{\upsilon}c}}'$) with increasing the relative density at the same number of cyclic under the effective confining pressure of 100kPa. It is almost highest the double amplitude(DA) 1%, 3%, 5%, 7.5% and 10% at fine content of 15% between Cyclic stress ratio($\sigma_d/{2\sigma_{{\upsilon}c}}'$) value at cyclic number five and fine content. Number of cyclic is 30 under the effective vertical stress of 100kPa, 70% of relative density for fine content of 15%. when the cyclic stress ratio at each relative density was compared at cyclic number five, the double amplitude(DA) 1%, 3%, 5%, 7.5% and 10%, and the pore-pressure ratio (${\Delta}u/{\sigma'}_c$) 0.95 value were compared; under the relative density of 70% and the effective confining pressure of 100kPa. The pore-pressure ratio (${\Delta}u/{\sigma'}_c$) 0.95 value showed a similar trend to the double amplitude (DA) 5% line.

• 한국운동역학회지
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• 제19권4호
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• pp.771-778
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• 2009

본 연구는 구두 굽 높이 변화에 따른 보행 시 족저압력을 비교, 분석함으로써 구체적인 데이터를 정량화하여 높은 굽을 착용함으로 인한 전족부의 압력 증가가 발에 미치는 영향을 알아보고자 한다. 본 연구에 사용된 구두는 선행연구를 바탕으로 여대생이 선호하는 구두 굽 높이 3cm, 7cm를 선택하였으며 여대생 10명을 대상으로 발을 전족부와 후족부로 나누어 수직힘, 최대압력, 평균압력을 측정하였다. 그 결과 전족부에서의 평균압력은 7cm 높이 구두가 높게 나타났으며, 후족부에서는 7cm 높이 구두가 낮게 나타났다. 통계처리 결과 전족부위에서는 3cm 굽 높이와 7cm 굽 높이의 최대압력 비교에서 유의한 차이가 나타났으며(p<.05), 후족부위에서는 수직힘, 최대압력, 평균압력 모두 유의한 차이가 나타났다(p<.05). 이상과 같이 구두를 착용함으로서 전족부의 최대압력이 높아지는 것은 물론이고 후족부위의 수직힘, 최대압력, 평균압력도 높아지는 것을 알 수 있었다. 이러한 현상은 전족부위에 높은 압력분포로 구속압이 증가하여 발가락의 변형을 유발할 수 있으며 후족부위에 압력증가는 장시간 착용 시 뒤꿈치의 통증을 유발할 수 있다. 따라서 굽이 있는 구두를 착용할 때 굽 높이가 7cm일 때 보다는 3cm일 때, 굽 높이가 낮을수록 전족부의 변형 예방과 후족부의 통증을 줄일 수 있을 것으로 기대된다.