• 한국환경복원기술학회지
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• 제7권2호
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• pp.46-51
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• 2004

In this paper, reinforcement of soil shear strength by bamboo(substitute materials simulating a root system) are evaluated by soil strength parameters(apparent cohesion(c) and internal friction angle(tan${\Phi}$)), using simple shear tester which clearly depicts shear deformation and controls soil suction. The results show that the internal friction angle does not change under various soil suction conditions but the apparent cohesion, which reach a peak in suction of 45cm$H_2O$ near critical capillary head, is effected by soil suction. And the reinforcement of soil strength by bamboo are expressed by apparent cohesion more than internal friction angle. In addition the increment of apparent cohesion by bamboo reached a peak in suction 45cm$H_2O$ too.

• Geomechanics and Engineering
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• 제16권6호
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• pp.599-608
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• 2018

This study investigates the feasibility of adopting the results of the UC (unconfined compression) test to assess the total cohesion of the unsaturated soil. A series of laboratory tests were conducted on samples of unsaturated lateritic soils of northern Taiwan. Specifically, the unconfined compression test was combined with the pressure plate test to obtain the unconfined compression strength and its matric suction of the samples. Soil samples were first compacted at designated water content and then subjected to the wetting process for saturation and the subsequent drying process to its target suction using the apparatus developed by the authors. The correlations among the matric suction, the unconfined compression strength and the total cohesion were studied. As a result, a simplified method to estimate the total cohesion using the unconfined compressive strength is suggested. The calculated results compare reasonably with the unsaturated triaxial test results. Current results show good performance; however, further study is warranted.

• Geomechanics and Engineering
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• 제33권3호
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• pp.301-315
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• 2023

Adopting cohesive soil as geocell-pocket infill materials is not fully accepted by researchers in the field of road engineering. The cohesion that may inhibit the lateral limitation of geocells is a common vital idea that exists within every researcher. However, the influence of infill materials' cohesion on geocell-reinforced performance is still not thoroughly determined. The mechanism behind this still needs to be studied in depth. This study initially discussed the relationship between subgrade bearing capacity, geocells' contribution to reinforced performance, and infill materials' cohesion (IMC). A law was proposed that adopting the soil with high cohesion as infill materials benefited the subgrade bearing capacity, but this was attributed to the superior mechanical properties of infill materials rather than geocells' contribution. Moreover, the vertical and lateral deformation of subgrade, coupling shear stress and confining stress of geocells, and deformation of geocells were deeply studied to analyze the mechanism that high cohesion can inhibit the geocells' contribution. The results indicate that the infill materials with high cohesion result in the total displacement of the subgrade toward to deeper depth, not the lateral direction. These responses decrease the vertical coupling shear stress, confining stress, and normal displacement of geocell walls, which weaken the lateral limitation of geocells.

• Geomechanics and Engineering
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• 제37권5호
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• pp.511-525
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• 2024

Micropiled raft has been used to support the existing and new structures or to provide the seismic reinforcement of foundation systems. Recently, research on micropile or micropiled raft has been actively conducted as the usage of micropile has increased, and the reinforcement effect of pile for the raft, the pile installation methods, and methods for calculating the bearing capacity of micropiled raft have been proposed. In addition, existing research results show that the behavior of this foundation system is different depending on the pile conditions and can be greatly influenced by the characteristics of the upper or lower ground depending on the conditions of pile. In other words, considering that the micropile is a friction pile, it can be predicted that the reinforcing effect of micropile for the raft and the bearing capacity of micropiled raft may depend on the cohesion of upper soil layer depending on the pile conditions. However, existing studies have limitations in that they were conducted without taking this into account. However, existing studies have limitations as they have been conducted without considering these characteristics. Accordingly, this study investigated the reinforcing effect of micropile and the bearing characteristics of micropiled raft by varying the cohesion of upper soil layer and the stiffness of pile which affect the behavior of micropiled raft. In this results, the reinforcing effect of micropile on the raft also increased as the cohesion of soil layer increased, but the reinforcing effect of pile was more effective in ground conditions with decreased the cohesion. In addition, the relationship between the axial stiffness of micropile and the bearing capacity of micropiled raft was found to be a logarithmic linear relationship. It was found that the reinforcing effect of micropile can increase the bearing capacity of raft by 1.33~ 3.72 times depending on the cohesion of soil layer and the rigidity of pile.

• Agricultural and Biosystems Engineering
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• 제6권2호
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• pp.59-64
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• 2005

In the study, the cone index, the cohesion and the internal resistant angle of soil were measured before and after tillage in order to suggest relative improvement in soil properties. The tillage methods tested in the study were five combinations of plow and rotary tillage operation and the experiments were performed on five selected test fields. The maximum tillage depth was 20 cm under the ground. The CIs for all the tillage operations were improved in comparison with those before tillage. The best combination of tillage operations for improving the CIs of soil was one plow operation followed by one rotary. After applying the tillage operations, the internal resistance angle reduced by 7-8 degree and the cohesion decreased up to about $1N/cm^2$ in comparison with those before tillage. We concluded that the cone index, the cohesion and the internal resistant angle of soil could be used as measures for representing the relative degree of tillage for a specific tillage operation. In addition, the study was useful as a basic research tool for developing an decision making system that determines an optimal tillage method with soil properties.

• 한국환경복원기술학회지
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• 제9권3호
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• pp.76-81
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• 2006

The reinforcement of soil shear strength by nylon net as substitute materials simulating a fine root system was evaluated by soil strength parameters(apparent cohesion(c) and internal friction angle(tan${\phi}$), using simple shear tester which clearly depicts shear deformation and controls soil suction. And the results of shear test by using bamboo as a substitute materials simulating a main root system and using nylon net as a substitute materials simulating a fine root system were compared. The reinforcement of soil strength by nylon net are expressed by apparent cohesion more than internal friction angle. In addition the increment of apparent cohesion by nylon net reached a peak in suction 60 $cmH_2O$. Different from with bamboo, the possibility of the change on internal friction angle(tan${\phi}$) caused by the soil water condition was shown in shear strain 20% condition. These results show that the mechanism of reinforcement by substitute materials simulating root system may be different in the condition of various soil water content.

• Geomechanics and Engineering
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• 제30권2호
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• pp.139-151
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• 2022

The mechanical properties of expansive soil are very unstable, highly sensitive to water, and thus easy to cause major engineering accidents. In this paper, the expansive soil foundation pit project of the East Huada Square in the eastern suburb of Chengdu was studied, the moisture content of the expansive soil was considered as an important factor that affecting the mechanics properties of expansive soil and the stability of the non-equal-length double-row piles in the foundation pit support. Three groups of direct shear tests were carried out and the quantitative relationships between the moisture content and shear strength τ, cohesion c, internal friction angle φ were obtained. The effect of cohesion and internal friction angle on the maximum displacement and the maximum bending moment of piles were analyzed by the finite element software MIDAS/GTS (Geotechnical and Tunnel Analysis System). Results show that the higher the moisture content, the smaller the matrix suction, and the smaller the shear strength; the cohesion and the internal friction angle are exponentially related to the moisture content, and both are negatively correlated. The maximum displacement and the maximum bending moment of the non-equal length double-row piles decrease with the increase of the cohesion and the internal friction angle. When the cohesion is greater than 33 kPa or the internal friction angle is greater than 25.5°, the maximum displacement and maximum bending moment of the piles are relatively small, however, once crossing the points (the corresponding moisture content value is 24.4%), the maximum displacement and the maximum bending moment will increase significantly. Therefore, in order to ensure the stability and safety of the foundation pit support structure of the East Huada Square, the moisture content of the expansive soil should not exceed 24.4%.

• 한국지반환경공학회 논문집
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• 제4권2호
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• pp.27-37
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• 2003

본 연구에서는 삼축 조건하에서 지오셀-흙 복합체의 응력-변형 거동과 지오셀에 의한 강도증가를 고찰하였다. 연구를 위하여 직경 50mm, 높이 100mm인 시료 중앙에 직경 50mm, 높이는 각각 35, 50, 70mm인 연성의 모형셀을 넣고 3개의 밀도 변화에 따른 일련의 삼축시험을 수행하였다. 시험결과 지오셀의 구속은 모래의 등가점착력을 유발시키는 것으로 나타났으나 점착력은 지오셀 재료의 특성에 관계되는 것으로 나타났다. 기존의 지반보강재에 의한 강도증가가 등가점착력의 유발만 나타난 것과는 달리 본 연구에서 사용된 탄성의 고무지오셀 재료는 등가점착력의 유발뿐만 아니라 내부마찰각도 증가시키는 것으로 나타났다. 지오셀-모래 복합재의 강도를 쌍곡선 모델에 적용시킨 결과 지오셀 복합재료의 거동이 일반 흙과는 거동이 다르므로 적용된 설계하중 범위에서의 첨두강도 결정이 거동을 묘사하는데 중요한 것으로 인식되었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.20-27
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• 2004

Reinforced twice than width of foundation with SIC under steel piles drived in cohesion soil and in the coal-limestone which heavily fractured. To analyze behaviour characteristic of steel piles, load transfer test was performed to steel piles attached with strain gauges to axial direction. After it passed 49days, dynamic load test was performed to set-up effect of steel piles bearing capacity. The results of test were compared to each other. According to the results, as the skin friction of steel pile was on the same condition, end bearing capacity of steel piles established on SIC solid of cemented milk in cohesion soil was three times than steel piles established on SIG solid of cemented milk in heavily fractured coal- limestone. After piles were driven and passes 49days, in case of piles on SIG solid of comented milk in cohesion soil the increaes of allowable bearing capacity was 442.9% and allowable bearing capacity of piles on SIG solid of cemented milk in heavily fractured coal-limestone increased 22.4%.

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