• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.4
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• pp.431-442
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• 2013

Most of previous studies have insufficiently investigated the shear behavior and fracturing characteristics, experimentally in respect to the change of size of tooth-shaped surface asperity such as length and slope angle in a broad range. This study investigates the influence of the length and slope angle of a tooth-shaped surface asperity on the fracturing characteristics and the interface shear strength by using direct shear test apparatus. A total of 36 interface direct shear tests were conducted by changing the three types of slope angle of surface asperity, four type of length, and three types of normal stress. The shape of fractured surface after the test was quantified by using a three-dimensional surface roughness measurement apparatus. Through the experimental test results, the characteristics of fractured shape of surface asperity according to the normal stress were investigated. In addition, fractured length and height were quantified at each slope angle of surface asperity under a certain normal stress condition.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.467-472
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• 1998

The interface friction angle between soil and fibers is important to evaluate improvement of the shear strength on fiber mixed soils. Direct shear test and pullout tort conducted by an apparatus made specially for the purpose of this study, was analyzed to know how fiber and soils affect on interface friction angle. By the results, The value of interface friction angle of sandy soils is larger than that of clayey soils. As a diameter of fiber is large, the value of friction coefficient of sandy soil is increase and that of clayey soil is decrease. An interface friction angle of well graded soil is larger value than that of uniform graded soil

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1233-1240
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• 2005

As the geotechnical technologies have grown, the size of civil structures has become bigger than before, thereby requiring large-scale geotechnical testing equipments which can evaluate the mechanical behavior of large size testing materials such as gravel, crushed rock and so on. These kind of large testing equipments are usually used to evaluate the mechanical characteristics of large size material which are applied in the large infra structures like dam, seashore structure, coastal landfill, soil-structure interaction and seismic response of large-scale structure. In this research, state-of-the-art information in the field of geotechnical engineering was collected and summarized for such large-scale experimental equipments as large-scale geo-centrifuge, large-scale triaxial testing machine, large-scale direct shear testing apparatus and large-scale oedometer.

• Journal of Forest and Environmental Science
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• v.30 no.1
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• pp.113-119
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• 2014

To examine the soil reinforcement by the shrub with shallow root systems for slope stability, we developed insitu apparatus for direct shear test and conducted the insitu field tests for Lespedeza cyrtobotrya, a representative revegetation species for artificial hillslopes. The insitu field tests were conducted for two different soil conditions (the rooted soils and non-rooted soils) and we then compared the experimental values with those calculated from the Wu model. The results showed that the soil reinforcement derived from the insitu field tests ranged from 0.01525 to 0.1438 $kgf/cm^2$ while the one calculated from the Wu model ranged from 0.1952 to 0.2696 $kgf/cm^2$. Our finding suggests more field tests are needed to collect the related parameters in the model application thereby predicting the reliable soil reinforcement by the shrub root systems.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.15-23
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• 2015

An experimental study has been conducted to evaluate the effects of average and cyclic shear stresses on the undrained failure behaviors of dense marine silty sand by using the Cyclic Direct Simple Shear apparatus. The results show that when the average shear stress ratio is zero, symmetric cyclic shear deformation is the major component of deformation, and permanent shear deformation is relatively small. On the other hand, when the average shear stress ratio is larger than zero, asymmetric permanent shear deformation is the major component, and cyclic shear deformation does not change much as the number of cyclic loads increases. The average shear stress ratio has less effects on the number of cyclic loads needed to fail, as compared with the cyclic shear stress ratio. The proposed stress-dependent failure contour can effectively be used to assess the cyclic shear strength of soil beneath the foundation for the design of offshore structures.

• Geomechanics and Engineering
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• v.34 no.6
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• pp.637-648
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• 2023

When an earth pressure balance (EPB) shield machine bores a tunnel in gravelly sand stratum, the excavated natural soil is normally transformed using foam and water to reduce cutter wear and the risk of direct muck squeezing out of the screw conveyor (i.e., muck spewing). Understanding the undrained shear behavior of conditioned soils under pressure is a potential perspective for optimizing the earth pressure balance shield tunnelling strategies. Owing to the unconventional properties of conditioned soil, a pressurized vane shear apparatus was utilized to investigate the undrained shear behavior of foam-conditioned gravelly sands under normal pressure. The results showed that the shear stress-displacement curves exhibited strain-softening behavior only when the initial void ratio (e₀) of the foam-conditioned sand was less than the maximum void ratio (e_max) of the unconditioned sand. The peak and residual strength increased with an increase in normal pressure and a decrease in foam injection ratio. A unique relation between the void ratio and the shear strength in the residual stage was observed in the e-ln(τ) space. When e₀ was greater than e_max, the fluid-like specimens had quite low strengths. Besides, the stick-slip behavior, characterized by the variation coefficient of measured shear stress in the residual stage, was more evident under lower pressure but it appeared to be independent of the foam injection. A comparison between the results of pressurized vane shear tests and those of slump tests indicated that the slump test has its limitations to characterize the chamber muck fluidity and build the optimal conditioning parameters.

• Journal of the Korean Geotechnical Society
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• v.33 no.1
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• pp.79-91
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• 2017

An experimental study has been conducted by using the Cyclic Direct Simple Shear apparatus to evaluate the influence of average and cyclic shear stresses on the undrained shear failure behavior of marine silty sand considering various relative densities. The obtained results show that despite using different relative densities, similar trends were gained in the cyclic shear deformation. Moreover, the cyclic shear deformation is affected mainly by the average and cyclic shear stresses. The number of cyclic loads for failure is significantly affected by the cyclic shear stress ratio and relative density, and is less affected by the average shear stress ratio. The proposed three-dimensional stress-dependent failure contour can be used effectively to assess the soil shear strength considering various relative densities in the design of foundation used for offshore structures.

• Magazine of the Korean Society of Agricultural Engineers
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• v.31 no.3
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• pp.57-69
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• 1989

The study was carried out for the strength parameter of coarse grained Soil and slope stability analysis of earth dam. The test samples were taken fifteen kinds of soil from cohesive soil to coarse gravel. The degree of compaction of test samples for shear test and permeability test was chosen 95 percentage of maximum dry density. The results of this study are as follows ; 1.The maximum dry density(Yd) of coarse grained soil increase in proportion to coarse particles(P) with the relation of Y d= 1.609+0.0043P. 2.The coefficients of permeability(k) decrease by the increase of fine particles(n) with the relation of k=0.0426e-0 185n. 3.The cohesions of soil decrease by the increase of coarse particles, but internal friction angles are more increased in same condition. 4.The internal friction angles(${\Phi}$) decrease in inverse proportion to void ratio(e) with the relation of ${\Phi}$ = 73.068 - 69.268e. 5.The strength parameters( Ct ${\Phi}$t) by triaxial compression test are clearly smaller than that (Cd, ${\Phi}$d) by direct shear test in fine grained soil, but the differences between both parameters are a little in coarse grained soil.The relations of both parameters are as follows; Ct = O.544Cd + 0.04 ${\Phi}$t= 1.282${\Phi}$d-2306 6.In cohesive soil, the strength parameters( Cl ${\Phi}$l) by large size shear test apparatus are similar to the strength parameters(Cs , ${\Phi}$s) by small size shear test appratus, but Cs and ${\Phi}$s values are larger than Cl and ${\Phi}$l values from 10 percentage to 20 percentage in coarse grained soil. 7.The fine grained soil is inappropriate to high dam more than 20 meters and it must be taken coarse grained soil with high internal friction angle for high dam.

• Journal of the Korean Geotechnical Society
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• v.28 no.9
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• pp.23-30
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• 2012

This paper is research results of slope stability analysis associated with seepage infiltration for unsaturated soil in debris-flow occurrence slopes. Site investigations were carried out in two slopes, located at Inje in Kangwon province where debris flow occurred in 2006 and at Yangpyung in Kyeunggi province where it occurred in 2010. For unsaturated soil sampled at the zone of debris-flow initiation, soil water characteristic curves with tempe pressure cells and shear strength parameters with newly designed shear strength apparatus were obtained respectively. The commertially available software SEEP/W was used to analyze seepage infiltration in unsaturated soil, based on their properties obtained from test results and the actual rainfall data at the moment of debris flow occurrence, and slope stability analysis with the program of SLOPE/W, associated with results of seepage analysis, was performed to simulate slope failure. As results of this research, seepage infiltration to unsaturated soil due to intensive rainfall was found to cause increase of ground water table as well as degree of saturation. Through this research slope stability analysis for unsaturated soil, considering the actual rainfall characteristic, might be a reasonable method of investigating characteristics of debris flow behavior, in particular, the moment of debris flow occurrence.

• Journal of the Korean Geotechnical Society
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• v.21 no.6
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• pp.81-91
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• 2005

'Coarse grained material' refers to crushed stones or gravels, and the behaviour of soil containing coarse grained material is not easily defined using the conventional soil mechanics theory due to the influences of large particles, therefore large scale test is essential to investigate their effects. Previous studies have identified the major factors affecting the properties of coarse grained materials by using large scale shear testing apparatus, such as maximum particle size, water content, density and uniformity coefficients. In this paper, the effect of variation of maximum particle size and water content on shear strength was analyzed from the results of large scale shear test. In addition, the fiction coefficient at critical state per vertical load was estimated using the equation proposed by Wood (1998). The sample for the test was obtained from the local quarry sites. Tests results show that the shear strength for 50.8 m maximum particle size is relatively larger than that of 76.3 m and air-dry sample has larger shear strength than saturated sample. In the meantime, the friction coefficient at critical state shows $1.0\sim1.6$ according to the test conditions.