• Geomechanics and Engineering
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• 제13권5호
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• pp.825-844
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• 2017

This study aimed to find out the pullout capacity of inclined strip anchor plate embedded in anisotropic and nonhomogeneous fully saturated cohesive soil in undrained condition. The ultimate pullout load has been found out by using numerical lower bound finite element analysis with linear programming. The undrained pullout capacity of anchor plate of width B is determined for different embedment ratios (H/B) varying from 3 to 7 and various inclination of anchor plates ranging from $0^{\circ}$ to $90^{\circ}$ with an interval of $15^{\circ}$. In case of anisotropic fully saturated clay the variation of cohesion with direction has been considered by varying the ratio of the cohesion along vertical direction ($c_v$) to the cohesion along horizontal direction ($c_h$). In case of nonhomogeneous clay the cohesion of the undrained clay has been considered to be increased with depth below ground surface keeping $c_v/c_h=1$. The results are presented in terms of pullout capacity factor ($F_{c0}=p_u/c_H$) where $p_u$ is the ultimate pullout stress along the anchor plate at failure and $c_H$ is the cohesion in horizontal direction at the level of the middle point of the anchor plate. It is observed that the pullout capacity factor increases with an increase in anisotropic cohesion ratio ($c_v/c_h$) whereas the pullout capacity factor decreases with an increase in undrained cohesion of the soil with depth.

• Geomechanics and Engineering
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• 제28권4호
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• pp.397-404
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• 2022

Accurate prediction of the undrained shaft resistance is essential for robust design of bored piles in undrained condition. The undrained shaft resistance is calculated using the undrained adhesion factor multiplied by the undrained cohesion of the soil. However, the available correlations to predict the undrained adhesion factor have been developed using simple regression techniques and the accuracy of these correlations has not been thoroughly assessed in previous studies. The lack of the assessment of these correlations made it difficult for geotechnical engineers to select the most accurate correlation in routine designs. Furthermore, limited attempts have been made in previous studies to use advanced data mining techniques to develop simple and accurate correlation to predict the undrained adhesion factor. This research, therefore, has been conducted to fill these gaps in knowledge by developing novel and robust correlation to predict the undrained adhesion factor. The development of the new correlation has been conducted using the multi-objective evolutionary polynomial regression analysis. The new correlation outperformed the available empirical correlations, where the new correlation scored lower mean absolute error, mean square error, root mean square error and standard deviation of measured to predicted adhesion factor, and higher mean, a20-index and coefficient of correlation. The correlation also successfully showed the influence of the undrained cohesion and the effective stress on the adhesion factor. Hence, the new correlation enhances the design accuracy and can be used by practitioner geotechnical engineers to ensure optimized designs of bored piles in undrained conditions.

• Geomechanics and Engineering
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• 제18권4호
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• pp.427-437
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• 2019

Waste materials are being produced in huge quantities globally, and the usual practice is to dump them into legal or illegal landfills. Recycled tiles (RT) are being used in soil stabilisation which is considered as sustainable solution to reduce the amount of waste and solve the geotechnical problems. Although the stabilisation of soil using RT improved the soil properties, it could not achieve the standard values required for construction. Thus, this study uses 20% RT together with low cement content (2%) to stabilise soft soil. Series of consolidated undrained triaxial compression tests were conducted on untreated and RT-cement treated samples. Each test was performed at 7, 14, and 28 days curing period and 50, 100, and 200 kPa confining pressures. The results revealed an improvement in the undrained shear strength parameters (cohesion and internal frication angle) of treated specimens compared to the untreated ones. The cohesion and friction angle of the treated samples were increased with the increase in curing time and confining pressure. The peak deviator stress of treated samples increases with the increment of either the effective confining pressures or the curing period. Microstructural and chemical tests were performed on both untreated and RT-cement treated samples, which included field emission scanning electron microscopic (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and energy dispersive X-ray spectrometer (EDX). The results indicated the formation of cementation compounds such as calcium aluminium hydrate (C-A-H) within the treated samples. Consequently, the newly formed compounds were responsible for the improvement observed in the results of the triaxial tests. This research promotes the utilisation of RT to reduce the amount of cement used in soil stabilisation for cleaner planet and sustainable environment.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.940-947
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• 2005

In this study, model tests of soft silt soils(ML) and silt soils was polluted with wastewater and waste oil from factories($ML_p$). Distribution of displacement, bearing capacity comparing the test results with existing theoretical expressions and analyzing the test results, the following conclusions were obtained. It was found out that in soft silt soils the relationship of critical surcharge and undrained cohesion is $q_{cr}=4.14C_u$ and polluted silt soils $ML_p$ those are $q_{cr}=1.78C_u$, respectively and the relationship of ultimate capacities $q_{ult}=9.53C_u$ and undrained cohesion in polluted silt soils are $q_{ult}=4.39C_u$. Critical surcharge and ultimate capacity is less in polluted silt soils than in soft silt soils.

• 한국지반공학회지:지반
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• 제11권1호
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• pp.41-50
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• 1995

자연상태의 점성토는 Ko상태로 존재하며 하중재하시 주웅력방향에 따라 다르게 거동하는 이방적 특성을 갖는다. 그러나 실험실에서 점성토의 강도특성을 파악하기 위하여 실시하고 있는 실험은 실용성과 간편성 때문에 등방압밀 삼축시험이 보편적으로 사용되고 있다. 이 연구에서는 정규압밀점성토의 이방적 특성과 압밀방법에 따른 전단특성을 고찰하기 위하여 토괴의 형태로 채취한 불교란 점성토를 등방압밀 또는 Ko압밀시켜 정규압밀상태에 도달하게 한 후 비배수삼축압축과 신장시험을 실시하였다. 시험결과 주응력방향에 따른 강도의 이방성을 작인하였다. 등방압 밀은 압밀시 시료에 가해지는 Ko상태보다 높은 평균주응력과 흙의 이방적 구조의 파괴때문에 비 배수강도를 과대평가하며 이방성이 감소하고 응력-변형률과 발생 과잉간극수압이 영향을 받음을 알 수 있었으며, 과압밀점성토의 경우 과압밀비를 감소시킨다. 또한 내부마찰각은 신장시험이 압축시험보다 큰 값을 나타내지만 파괴시의 응력상태를 이용하여 회귀분석한 결과에 따르면 신장시 점착력과 함께 나타나는 내부마찰각은 압축시험과 거의 같은 값을 가짐을 알 수 있었다.

• 한국농공학회지
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• 제36권3호
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• pp.90-99
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• 1994

To investigate the undrained shear strength characteristics of marine soils with high water content, high compressibility and weak bearing capacity, a series of undrained triaxial tests with pore pressure measurements on undisturbed and disturbed Banwol marine clay in normally consolidated and overconsolidated states is carried out. The results and main conclusions of this study are summarized as follows : 1 . When the consolidation pressure is increased, the maximum deviator stress of disturbed and undistubed clay in normally consolidated state is increased. Pore pressure parameters and internal friction angle of undisturbed clay are greater than those of disturbed clay. 2. The relationship between pore pressure and axial strain of undisturbed clay in normally consolidated state can be expressed as a hyperbolic function like stress-strain relation proposed by Kondner. 3. In the pore pressure-axial strain relation of disturbed clay in normally consolidated state, failure ratio R'f is greatly deviated in the range of 0.7~0.9 proposed by Christian and Desai. 4. For overconsolided clay, when overconsolidation ratio (OCR) is increased, normalized maximum deviator stress is increased and maximum pore pressure is decreased gradually. 5. Cohesion of overconsolidated clay is greater than that of nomally consolidated clay and internal friction angle slightly is decreased. 6. Pore pressure parameter at failure (Af) of overconsolidated clay is varied with OCR, Af becomes negative values with increment in OCR

• 한국환경복원기술학회지
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• 제3권3호
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• pp.1-7
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• 2000

The aim of the work described in 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.

• 한국지반공학회논문집
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• 제30권2호
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• pp.65-76
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• 2014

해안지역의 연약지반을 개량하기 위하여 연약지반 위에 모래를 포설하거나 모래다짐말뚝을 시공할 경우 점토와 모래가 서로 섞이는 경우가 많으며, 풍화된 사면의 표층에도 모래나 자갈 섞인 세립토가 많이 존재한다. 본 연구에서는 이와 같은 혼합토에 포함된 모래 함유량의 증가에 따른 점토의 액소성한계 및 전단강도 변화에 대해 연구하였다. 먼저 카올리나이트와 벤토나이트에 모래 함유량을 0, 9, 17, 23, 29, 33, 또는 50%까지 증가시키면서 액소성한계시험을 실시하였으며, 모래 함유량이 증가함에 따라 액소성한계는 감소하는 경향을 보였다. 다양한 모래 함유량을 가진 카올리나이트와 벤토나이트에 함수비를 10% 또는 20%씩 단계적으로 증가시키면서 토베인시험기를 이용하여 비배수전단강도를 측정하였다. 동일한 모래 함유량을 가진 공시체의 경우 특정 함수비에서 비배수전단강도가 급격히 감소하였으며, 공시체 내 모래 함유량이 증가할수록 배수가 발생하면서 비배수전단강도는 감소하였다. 한편 동일한 조건의 혼합토에 대한 직접전단시험을 실시하여 모래 함유량의 증가에 따른 점토-모래 혼합토의 점착력 및 내부마찰각을 측정하였다. 점토 내 모래 함유량이 증가함에 따라 점착력은 감소하였으며, 내부마찰각은 증가하는 경향을 보였다.

• Geomechanics and Engineering
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• 제20권3호
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• pp.191-205
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• 2020

Soil shear strength parameters play a remarkable role in designing geotechnical structures such as retaining wall and dam. This study puts an effort to propose two accurate and practical predictive models of soil shear strength parameters via hybrid artificial neural network (ANN)-based models namely genetic algorithm (GA)-ANN and particle swarm optimization (PSO)-ANN. To reach the aim of this study, a series of consolidated undrained Triaxial tests were conducted to survey inherent strength increase due to addition of polypropylene fibers to sandy soil. Fiber material with different lengths and percentages were considered to be mixed with sandy soil to evaluate cohesion (as one of shear strength parameter) values. The obtained results from laboratory tests showed that fiber percentage, fiber length, deviator stress and pore water pressure have a significant impact on cohesion values and due to that, these parameters were selected as model inputs. Many GA-ANN and PSO-ANN models were constructed based on the most effective parameters of these models. Based on the simulation results and the computed indices' values, it is observed that the developed GA-ANN model with training and testing coefficient of determination values of 0.957 and 0.950, respectively, performs better than the proposed PSO-ANN model giving coefficient of determination values of 0.938 and 0.943 for training and testing sets, respectively. Therefore, GA-ANN can provide a new applicable model to effectively predict cohesion of fiber-reinforced sandy soil.

• Geomechanics and Engineering
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• 제10권5호
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• pp.617-633
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• 2016

A numerical study has been conducted to examine the improvement achieved in the ultimate pullout capacity of horizontal circular anchor plates embedded in undrained clay, by constructing granular columns of varying diameter over the anchor plates. The analysis has been carried out by using lower bound theorem of limit analysis and finite elements in combination with linear programming. The improvement in uplifting capacity of anchor plate is expressed in terms of an efficiency factor (${\xi}$). The efficiency factor (${\xi}$) has been defined as the ratio of ultimate vertical pullout capacity of anchor plate having diameter D embedded in soft clay reinforced by granular column to the vertical pullout capacity of the anchor plate with same diameter D embedded in soft clay only. The variation of efficiency factor (${\xi}$) for different embedment ratios and different diameter of granular column has been studied considering a wide range of softness of clay and different value of soil internal friction angle (${\phi}$) of the granular material. It is observed that ${\xi}$ increases with an increase in diameter of the granular column ($D_t$) and increase in friction angle of granular material. Also, the effectiveness of the usage of granular column increases with decrease in cohesion of the clay.