• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 봄 학술발표회 논문집
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• pp.471-477
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• 1999

A new stress, load and displacement controlled direct shear apparatus has recently been developed at the Hyundai Institute of Construction Technology This direct shear apparatus is capable of testing of rock joint under constant normal stiffness, constant normal stress or constant normal load boundary conditions. This paper describes this direct shear apparatus and illustrates results of shear tests at constant normal stress condition, constant normal load condition and constant normal stiffness condition with dental stones which have a same joint roughness and unconfined compressive strength.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1481-1486
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• 2007

Frictional laws are criticized with emphasis on their application to bulk metal forming simulation in this paper. Coulomb frictional law and constant shear frictional law are investigated in detail in terms of their effect on metal forming process. A friction sensitive bulk metal forming process, a long-pipe simultaneously shrinking and expanding process, is introduced and the problems of the constant shear frictional law are revealed comparing the predictions obtained by the Coulomb frictional law and the constant shear frictional law with the experiments. It is shown that the constant shear frictional law is improper in the case that the normal stress varies very much from position to position and that the normal stress is low compared with flow stress of the adjacent material. It is also shown that the Coulomb frictional constant is more or less affected by the normal stress.

• Geomechanics and Engineering
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• 제7권3호
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• pp.297-316
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• 2014

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, $D_r$ = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.

• 터널과지하공간
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• 제15권5호
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• pp.330-337
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• 2005

전단하중을 받는 암반의 전단특성은 절리면의 구조적인 특징뿐만 아니라 암반 주변의 경계조건에 의해서도 영향을 받는다. 암반블록의 경계조건은 절리면이 받고 있는 응력상태를 기준으로 4가지로 구분할 수 있다. 일반적으로 주로 사용되는 CNL 조건의 전단시험에서 얻어지는 전단강도는 다른 경계조건에서 얻어지는 것보다 낮은 전단강도를 나타내며 그 거동도 다른 것으로 나타났다. 본 연구에서는 일정수직하중(CNL) 시험결과를 정규화한 그래픽 방법을 이용하여 일정수직강성(CNS) 조건의 전단거동을 모사할 수 있었다.

• 한국자동차공학회논문집
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• 제4권2호
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• pp.69-79
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• 1996

Dynamic stress intensity factors are derives when the crack is propagating with constant velocity under longitudinal shear stress in orthotropic disk plate. General stress fields of crack tip propagating with constant velocity and least square method are used to obtain the dynamic stress intensity factor. The dynamic stress intensity factors of GLV/GTV=1(=isotropic material or transversely isotropic material) which is obtained in out study nearly coincides with Chiang's results when mode Ⅲ stress is applied to boundary of isotropic disk. The D.S.I.F. of mode Ⅲ stress is greater when α(=angle of crack propagation direction with fiber direction) is 90° than that when α is 0°. In case of a/D(a:crack length, D:disk diameter)<0. 58, the faster crack propagation velocity, the less D.S.I.F. but when crack propagation velocity arrive on ghear stress wave velocity, the D.S.I.F. but when crack propagation velocity arrive on shear stress wave velocity, the D.S.I.F. unexpectedly increases and decreases to zero.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 사면안정학술발표회
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• pp.145-154
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• 2003

When a nail pulled out in dense, granular soil, the soil in the vicinity of the nail tends to dilate, but its dilatancy results in a normal stress concentration at the soil/nail interface, thereby increasing the pull-out resistance of the inclusion. It is thought to be occurring within the resistance zone where the soil mass is at stationary state and the reinforcement are held in position by the soil, due to the friction or bond. In this paper, A series of direct shear and interface tests were conducted by using so called‘Constant Normal Stiffness Test Apparatus’which was modified and improved from the conventional direct shear box test rig. Unlikely the normal shear box test, this enables to simulate the different constraint effects of surrounding soil during shear under the conditions of constant stress and volume, constant normal stiffness. The aim of the research programme is to get better understanding of pull-out bond mechanism, thus to explore the possibility of evaluating the pull-out bond capacity of soil/reinforcement at the preliminary design stage from the laboratory test.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.281-288
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• 2000

In this study, we tried to determine failure criteria for joints of soft rock using ring shear test machine. The residual stress fellowing shear behavior was determined by the result of ring shear test and direct shear test. Ring shear test with the specimens which cover a large deformation range was adapted to measure a residual stress, and was possible to present the peak stress to present the peak stress to the residual stress at the same time. Residual stress is defined a minimal stress of specimens with a large displacement and the result of the peak residual stress is shown by a size of displacement volume. Therefore, the residual stress in soil was decided by shear stress of maximum shear stress - shear displacement(angle) based on the test result of a hyperbolic function ((equation omitted), a, b ＝ experimental constant). In this study, it was proved that the residual stress of rock joint can be determined by using of this method.

• Geomechanics and Engineering
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• 제20권3호
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• pp.221-232
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• 2020

In many tropical regions, soil structures often fail under constant loads as a result of decreasing matric suction due to water infiltration. Most of the previous studies have been performed by infiltrating water in the soil specimen by keeping shear stress constant at 85-90% of peak shear strength in order to ensure specimen failure during water infiltration. However, not many studies are available to simulate the soil behavior when water is infiltrated at lower shear stress and how the deformations affect the soil behavior if the failure did not occur during water infiltration. This research aimed at understanding both the strength and deformation behavior of unsaturated soil during the course of water infiltration at 25%, 50% and 75% of maximum deviatoric stress and axial strain by keeping them constant. A unique stress-strain curve expresses the transient situation from unsaturated condition to failure state due to water infiltration is also drawn. The shearing-infiltration test results indicate that the water infiltration reduces matric suction and increase soil deformation. This research also indicates that unsaturated soil failure problems should not always be treated as shear strength problems but deformation should also be considered while addressing the problems related to unsaturated soils.

• Geomechanics and Engineering
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• 제11권5호
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• pp.713-723
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• 2016

Shear wave velocities of three selected sandy soils subject to drained triaxial compression test were continuously measured using the bender elements. The shear wave velocity during isotropic compression, as widely recognized, increased as confining pressure increased and they were correlated well. However, during drained shearing, the mean effective stress could no further provide a suitable correlation. The shear wave velocity during this stage was almost constant with respect to the mean effective stress. The vertical stress was found to be more favorable at this stage (since confining stress was kept constant). When sample was attained its peak stress, the shear wave velocity reduced and deviated from the previously existed trend line. This was probably caused by the non-uniformity induced by the formation of shear band. Subsequently, void ratios computed based on external measurements could not provide reasonable fitting to the initial stage of post-peak shear wave velocity. At very large strain levels after shear band formation, the digital images revealed that sample may internally re-arrange itself to be in a more uniform loose stage. This final stage void ratio estimated based on the proposed correlation derived during pre-peak state was close to the value of the maximum void ratio.

• Geomechanics and Engineering
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• 제30권3호
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• pp.219-231
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• 2022

Geotechnical materials such as silt, fine sand, or coarse granular soils may be unstable under undrained shearing or during rainfall infiltration starting an unsaturated state. Some researches are available describing the instability of coarse granular soils in drained or undrained conditions. However, there is a need to investigate the instability mechanism of unsaturated silty soil considering the effect of degree of compaction and net confining stress under partially and fully drained conditions. The specimens in the current study are compacted at 65%, 75%, & 85% degree of compaction, confined at pressures of 60, 80 & 120 kPa, and tested in partially and fully drained conditions. The tests have been performed in two steps. In Step-I, the specimens were sheared in constant water content conditions (a type of partially drained test) to the maximum shear stress. In Step-II, shearing was carried in constant suction conditions (a type of fully undrained test) by keeping shear stress constant. At the start of Step-II, PWP was increased in steps to decrease matric suction (which was then kept constant) and start water infiltration. The test results showed that soil instability is affected much by variation in the degree of compaction and confining stresses. It is also observed that loose and medium dense soils are vulnerable to pre-failure instability i.e., instability occurs before reaching the failure state, whereas, instability in dense soils instigates together with the failure i.e., failure line (FL) and instability line (IL) are found to be unique.