• Geomechanics and Engineering
• /
• 제37권4호
• /
• pp.341-358
• /
• 2024

This paper reports several plane-strain trapdoor tests conducted to investigate the effects of reinforcement on soil arching development under localized surface loading with a loading plate width three times the trapdoor width. An analogical soil composed of aluminum rods with three different diameters was used as the backfill and Kraft paper with two different stiffness values was used as the reinforcement material. Four reinforcement arrangements were investigated: (1) no reinforcement, (2) one low stiffness reinforcement R1, (3) one high stiffness reinforcement R2, and (4) two low stiffness reinforcements R1 with a backfill layer in between. The stiffness of R2 was approximately twice that of R1; therefore, two R1 had approximately the same total stiffness as one R2. Test results indicate that the use of reinforcement minimized soil arching degradation under localized surface loading. Soil arching with reinforcement degraded more at unloading stages as compared to that at loading stages. The use of stiffer reinforcement had the advantages of more effectively minimizing soil arching degradation. As compared to one high stiffness reinforcement layer, two low stiffness reinforcement layers with a backfill layer of certain thickness in between promoted soil arching under localized surface loading. Due to different states of soil arching development with and without reinforcement, an analytical multi-stage soil arching model available in the literature was selected in this study to calculate the average vertical pressures acting on the trapdoor or on the deflected reinforcement section under both the backfill self-weight and localized surface loading.

• Geomechanics and Engineering
• /
• 제23권5호
• /
• pp.481-491
• /
• 2020

Piles installed in row(s) are used as an effective technique to improve the stability of soil slopes. The analysis of pile-stabilized slopes require a reliable prediction of lateral resistance offered by the piles. In this work, an analytical solution is developed to estimate the lateral resistance offered by the stabilizing piles in sand and c - 𝜙 soil slopes considering soil arching phenomenon. The soil arching in both horizontal direction (between the neighboring piles) and vertical direction (in the active wedge in front of the pile row) are studied and their effects are incorporated in the proposed model. The shape of soil arch is assumed to be circular and principal stress trajectories are defined separately for both modes of arching. Experimental and numerical studies found in literature were used to validate the proposed method. A detailed parametric analysis was performed to study the influence of pile diameter, center-to-center spacing, slope angle and angle of internal friction on the lateral pile resistance.

• Geomechanics and Engineering
• /
• 제31권1호
• /
• pp.71-86
• /
• 2022

In Taiwan, an efficient approach for enhancing the stability of colluvium slopes is the drilled shaft method. For slopes with drilled shafts, the soil arching effect is one of the primary factors influencing slope stability and intertwines to the failure mechanism of the pile-soil system. In this study, the contribution of soil arching effect to slope stability is evaluated using the FEM software (Plaxis 3D) with the built-in strength reduction technique. The result indicates the depth of the failure surface is influenced by the S/D ratio (the distance to the diameter of piles), which can reflect the contribution of the soil arching effect to soil stability. When α (rock inclination angles)=β (slope angles) is considered and the S/D ratio=4, the failure surface of the slope is not significantly influenced by the piles. Overall, the soil arching effect is more significant on α=β, especially for the steep slopes. Additionally, the soil arching effect has been included in the proposed stability charts. The proposed charts were validated through two case studies, including that of the well-known Woo-Wan-Chai field in Taiwan. The differences in safety factor (FoS) values between the referenced literature and this study was approximately 4.9%.

• Geomechanics and Engineering
• /
• 제11권6호
• /
• pp.879-896
• /
• 2016

A new earth pressure equation considering the arching effect in $c-{\phi}$ soils was proposed for the accurate calculation of earth pressure on circular vertical shafts. The arching effect and the subsequent load recovery phenomenon occurring due to multi-step excavation were quantitatively investigated through laboratory tests. The new earth pressure equation was verified by comparing the test results with the earth pressures predicted by new equation in various soil conditions. Resulting from testing by using multi-step excavation, the arching effect and load recovery were clearly observed. The test results in $c-{\phi}$ soil showed that even a small amount of cohesion can cause the earth pressure to decrease significantly. Therefore, predicting earth pressure without considering such cohesion can lead to overestimation of earth pressure. The test results in various ground conditions demonstrated that the newly proposed equation, which enables consideration of cohesion as appropriate, is the most reliable equation for predicting earth pressure in both ${\phi}$ soil and $c-{\phi}$ soil. The comparison of the theoretical equations with the field data measured on a real construction site also highlighted the best-fitness of the theoretical equation in predicting earth pressure.

• 한국지반공학회논문집
• /
• 제26권11호
• /
• pp.89-98
• /
• 2010

성토지지말뚝시스템을 적용하여 연약지반 상에 성토를 설계 시공하고자 할 경우 말뚝지지 성토지반 내에 지반아칭이 발달할 수 있도록 한계성토고를 설계하는 방법이 마련되었다. 먼저 말뚝캡보의 간격이 비교적 넓은 경우를 대상으로 일련의 모형실험을 실시하여 성토단계에 따른 성토하중의 하중전이거동을 조사하고 성토지반 속에 지반아칭이 충분히 발달되기 시작할 때의 성토고를 실험적으로 관찰하였다. 모형실험결과, 하중전이거동은 말뚝지지성토지반 내에 지반아칭이 발달될 수 있느냐 여부를 결정지을 수 있는 성토고에 영향을 많이 받음을 알 수 있었다. 저성토단계에서는 성토지반 속에 지반아칭이 아직 발달되지 못한 관계로 펀칭전단파괴모드에 의하여 성토하중이 말뚝캡보에 하중전이가 진행되었고 고성토단계에서는 지반아칭이 발달하여 지반아칭파괴모드에 의하여 하중전이가 진행되었다. 이들 저성토단계와 고성토단계에서 측정된 연직하중의 실험치는 각각의 파괴모드에 의한 하중전이 메커니즘에 근거하여 이전 연구에서 유도 제시된 이론식들로 산정된 예측치와 좋은 일치를 보였다. 또한 모형실험결과 저성토단계의 펀칭전단파괴모드에 의한 하중전이 메커니즘에서 고성토단계의 지반아칭파괴모드에 의한 하중전이 메커니즘으로 변화하는 시점의 한계성토고가 존재함을 확인 할 수 있었다. 성토지반 속에 지반아칭을 충분히 발달시키려면 성토를 이 한계성토고 보다 높게 설계 시공하여야 함을 알았다. 또한 펀칭전단과 지반아칭에 의한 하중전이 메커니즘에 의거 유도 제안되었던 전이하중 산정 이론식을 같게 놓음으로서 한계성토고를 산정할 수 있는 이론식을 유도할 수 있었고 이 이론식으로 한계성토고의 실험치를 잘 예측할 수 있었다.

• Geomechanics and Engineering
• /
• 제24권6호
• /
• pp.599-610
• /
• 2021

Conduits are commonly installed below the ground for utility conveyance around the world. Vertical load on a buried conduit is an important parameter that needs to be known to ensure its safe design and installation. Consideration of soil arching in load calculations helps achieve a more realistic and efficient design. In the past, considering the arching effect, the design charts have been presented for use by practicing engineers to calculate the vertical load on the conduit buried below the level ground. There are currently no design charts for calculating the vertical load on the conduit buried under a sloping ground. In this paper, an attempt has been made to present the derivation of a generalized analytical expression considering that the soil mass overlying the conduit has a sloping face and the arching phenomenon takes place. The developed generalized expression has been used to present some design charts considering specific values of slope geometry, soil properties and burial depths. Furthermore, analytical results for specific soil parameters have been compared with the results extracted from a commercial software PLAXIS 2D, for a developed numerical model and an independent study.

• Geomechanics and Engineering
• /
• 제8권6호
• /
• pp.829-844
• /
• 2015

In the current paper the results of a numerical simulation that were verified by a well instrumented experimental procedure for studying the arching effect over a trapdoor in sand is presented. To simulate this phenomenon with continuum mechanics, the experimental procedure is modeled in ABAQUS code using stress dependent hardening in elastic state and plastic strain dependent frictional hardening-softening with Mohr Coulomb failure criterion applying user sub-routine. The apparatus comprises rectangular trapdoors with different width that can yield downward while stresses and deformations are recorded simultaneously. As the trapdoor starts to yield, the whole soil mass deforms elastically. However, after an immediate specified displacement, depending on the width of the trapdoor, the soil mass behaves plastically. This behavior of sand occurs due to the flow phenomenon and continues until the stress on trapdoor is minimized. Then the failure process develops in sand and the measured stress on the trapdoor shows an ascending trend. This indicates gradual separation of the yielding mass from the whole soil body. Finally, the flow process leads to establish a stable vault of sand called arching mechanism or progressive collapse of the soil body.

• 대한토목학회논문집
• /
• 제28권2C호
• /
• pp.133-141
• /
• 2008

토목섬유보강 성토지지말뚝시스템에서 지반아칭에 의한 하중전이 특성을 규명할 수 있는 이론해석법을 개발하였다. 이론해석 결과, 성토지지말뚝에 토목섬유가 복합시공되면, 말뚝의 효율이 증가하였으며, 효율의 증대효과는 지반아치가 완전히 발달하기 이전인 저성토 구간에서 특히 두드러지게 나타났다. 또한, 이론해석법에 의한 하중전이는 말뚝의 간격, 성토고, 지반정수 및 토목섬유에 크게 영향을 받고 있다. 즉, 말뚝의 간격이 증가하면 말뚝의 효율은 감소하며, 성토고, 성토지반의 내부마찰각 및 토목섬유의 강도가 증가하면 효율이 커지게 된다. 이와같은 해석결과는 본 제안식이 토목섬유보강 성토지지말뚝시스템에서의 지반아칭효과를 잘 설명해주는 합리적인 해석법임을 나타내고 있다.

• 한국지반공학회논문집
• /
• 제23권6호
• /
• pp.53-66
• /
• 2007

말뚝과 토목섬유로 지지된 성토지반의 아칭효과를 규명하기 위하여 일련의 모형실험을 실시하였다. 모형실험에서는 단독캡 말뚝을 상하이동이 가능한 철판 사이에 일정간격으로 설치하고, 토목섬유를 포설한 후 성토를 실시하였다. 모형실험에서는 침하판을 하강시킴으로써 연약지반의 침하를 모사하였으며, 침하판이 하강함에 따라 성토지반에 지반아칭이 발휘되었다. 성토지반과 토목섬유의 변형거동은 카메라로 관찰하였다. 또한 계측시스템을 통하여 말뚝캡에 작용하는 하중과 토목섬유의 인장변형률을 측정하였다. 모형실험결과 연약지반부의 침하가 발생할 때, 지반아칭효과로 인하여 말뚝으로 전이되는 성토하중이 급격히 증가하는 것으로 나타났다. 이때 토목섬유가 설치되지 않은 경우는 말뚝에 작용하는 하중이 최대값에 도달한 후 감소하는 반면, 토목섬유로 복합지지된 경우는 침하에 따라 말뚝하중이 점진적으로 증가하면서 일정한 값으로 수렴한다. 이것은 토목섬유에 의한 보강이 성토지반의 변형 억제에 효과적임을 나타내는 것이다. 한편, 침하유발시 말뚝캡 사이의 토목섬유는 원호형태로 변형을 일으키는 것으로 나타났다. 말뚝과 토목섬유로 지지된 성토지반에서 말뚝캡으로 전이되는 성토하중은 지반아칭효과와 토목섬유의 인장변형률을 고려함으로써 모형화할 수 있다.

• Structural Engineering and Mechanics
• /
• 제9권1호
• /
• pp.69-88
• /
• 2000

A relatively simple model of a buried structure response to a surface loading that can simulate a possible opening and closure of a gap between the soil and the structure is presented. Analysis of the response of small and medium scale buried roof slabs under surface impulsive loading shows that the model's predictions are in fairly good agreement with the experimental results. Application of the model to a study case shows the relative influence of system parameters such as, the depth of burial, the arching coefficient, and the roof thickness, on the interface pressure and on the roof displacement. This model demonstrates the effect of a gap between the structure and the soil. The relative importance of including a gap opening and closure in the analysis is examined by the application of the model to a study case. This study results show that the deeper the depth of burial, the longer the gap duration, and the shorter the duration of the initial interface impact, while the higher the soil's shear resistance, the higher the gap duration, and the shorter the initial interface impact duration.