• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2010년도 춘계 학술발표회
• /
• pp.314-323
• /
• 2010

Recently, granular soils having a large particle size are frequently used as a filling material in the construction of foundation, harbor, dam, and so on. The shear behavior of this granular soil plays a key role in the stability of structures. For example, soil particle crushing occurring at the interface between structure and soil and/or within soil mass can cause the disturbance of ground characteristics and consequently induce an issues in respect of stability of structures. In order to investigate the shear behavior according to an existence and nonexistence of particle crushing, numerical analyses were conducted by using the DEM(Discrete Element Method)-based software program PFC(Particle Flow Code). Using the crushing model and non-crushing model which were created in this study, numerical analyses of ring shear test were conducted and their results were analyzed and compared. In general, landslide and slope stability are accompanied by a large displacement and consequently not only a peak strength but also a residual strength are very important in the analysis of landslide and slope stability. However the direct shear test which has been commonly used in the determination of shear strength parameters has a limitation on displacement therefore the residual strength parameters can not be obtained. The characteristics of residual shear behavior were investigated through the numerical analyses in this study.

• 한국지반환경공학회 논문집
• /
• 제18권2호
• /
• pp.29-37
• /
• 2017

집중호우로 인하여 산악지반에 발생하는 토석류의 거동은 대상지반 세립분의 전단강도 및 유변학적 특성들에 의하여 영향을 받기 때문에, 두 특성에 대한 정수는 토석류 거동을 파악하는데 매우 중요한 요소이다. 본 연구에서는 직접전단 실험을 통하여 세립분의 전단강도 및 유변학적 정수를 평가하고자 하였다. 건조상태와 액성한계상태로 조성된 두 가지 세립분 시료에 대하여 직접 전단실험을 수행하였으며, 연직응력에 따른 전단강도를 측정하여 점착력과 내부마찰각을 산정하였다. 또한 액성한계로 조성된 시료의 잔류전단강도를 획득하기 위하여 전단변형률속도와 전단방향을 변화시켜 반복전단실험을 수행하였다. 실험 결과, 액성한계상태의 시료는 건조 상태 시료에 비해 내부마찰각은 작지만 점착력은 더 큰 것으로 나타났으며, 잔류전단강도를 통해 산정한 내부마찰각과 점착력은 첨두전단강도에 의해 산정된 결과보다 작은 것으로 나타났다. 반복전단 결과, 전단변형률속도와 잔류전단강도는 선형적인 관계를 보였으며, 전단변형률속도-잔류전단강도 관계의 기울기로써 결정되는 점성은 약 $73.60Pa{\cdot}s$로 산정되었다. 본 연구는 직접전단 장비가 산악지반 토석류 거동과 관련된 세립분의 전단강도 및 유변학적 정수 산정에 효과적으로 활용될 수 있음을 보여준다.

• 터널과지하공간
• /
• 제4권3호
• /
• pp.274-286
• /
• 1994

Direct shear tests were on ducted in a laboratory setting in order to investigate the shear strength and deformation behavior of rock joints. Also, the characteristics of acoustic emissions (AE) during shearing of rock joints were studied. The artificial rock joints were created by splitting the intact blocks of Hwangdeung granites and Iksan marbles. Joint roughness profiles were measured by a profile gage and then digitized by Image analyzer. Roughness profile indices(Rp) of the joints were calculated with these digitized data. Peak shear strength, residual shear strength, shear stiffness and maximum acoustic emission(AE) rate were investigated with joint roughness. The peak shear strenght, the residual shear strength and the shear stiffness were increased as roughness popfile index or normal stress increased in the shear tests of granites. In the tests of marble samples, the shear deformation characteristics were not directly affected by joint roughness. As the result of two directional shear tests, the shear characteristics were varied with shear direction. AE count rates were measured during the shear deformation and the AE signals in several stages of the deformation were analyzed in a frequency domain. The AE rate peaks coincided with the stress drops during the shear deformation of joint. The dominant frequencies of the AE signals were in the vicinity of 100 kHz fo rgranite sample and 900 kHz for marble samples. The distribution of amplitude was dispersed with increasing normal stress.

• 한국지반환경공학회 논문집
• /
• 제11권9호
• /
• pp.5-14
• /
• 2010

본 연구는 성토지반이나 사면에서의 강우 침투 시 포화도 변화에 따른 전단강도 특성을 규명하고자 대전지역 도로공사현장을 대상으로 성토재로 쓰이는 화강풍화토에 대하여 포화도 변화에 따른 전단강도특성을 분석하였다. 다짐함수비를 달리한 시료에 대해 직접전단시험을 실시하여 분석한 결과 최적함수비와 건조측 다짐함수비에서 점착력과 전단저항각이 가장 크게 나타났으며, 다짐함수비가 습윤측으로 갈수록 점착력이 감소하는 경향을 보였다. 또한, 다짐함수비별 시료에 대하여 포화도 변화에 따른 전단특성을 연구한 결과 침투한 물에 의해 포화도가 증가할수록 점착력은 50% 이상 감소하는 경향을 보였으나, 상대적으로 전단저항각의 감소폭은 $1{\sim}2^{\circ}$정도로 작았다. 또한, 잔류전단강도정수에 대한 포화도 변화의 영향은 실용적 차원에서 효과를 기대하기가 어려울 것으로 판단된다. 즉, Mohr-Coulomb의 파괴규준에서 포화도 변화가 잔류전단강도 변화에 미치는 영향은 미미한 것으로 판단된다.

• 터널과지하공간
• /
• 제7권1호
• /
• pp.31-38
• /
• 1997

Residual shear strength should be taken into consideration as well as peak one when analysing stability of slopes constituted by weathered rock or overconsolidated soils since such materials could be subjected to progressive failure mechanism. When landslide of a slope is related to progressive failure phenomenon, the failure might occur even though shear strength of the slope materials does not reach their residual shear strength over the whole slip surface. Therefore, stability of the slope concerned may be overstimated or underestimated when using only its peak or residual shear srength parameters. Mechanical description for progressive failure phenomenon is given by Bjerrum(1967). In parameters. Mechanical description for progressive failure phenomenon is given by Bjerrum(1967). In this study, his theory has been extended to estimate the distance of failed zone for a plane slope and the results calculated by this extended equatio has been compared with that obtained by numerical modelling using FLAC. In addition, stress state on the slip surface has been, in detail, analysed to understand failure mechanism when a limited progressive failure occurs. Effects of mechanical and hydraulic factors on progressive failure have also been analysed.

• 지질공학
• /
• 제33권4호
• /
• pp.717-724
• /
• 2023

잔류전단강도(residual shear strength)는 산사태와 토석류 해석시 사용되는 중요한 인자이다. 잔류전단강도는 흙이 전단될 때 발현되는 최소 전단응력으로 산사태 발생시점에서의 전단강도이다. 본 연구는 링전단시험장치를 사용하여 주문진 모래에 대한 잔류전단강도를 측정하였다. 거칠기 효과를 검증하기 위하여 링전단상자를 거친면(rough surface)과 매끈면(smooth surface)으로 달리 제작하여 흙 시료가 전단될 때 거칠기(roughness)에 따른 전단특성을 조사하고자 하였다. 시험은 조립상태, 배수조건에서 전단속도를 0.01, 0.1, 1, 10, 50, 100 mm/s로 달리 적용하여 각 전단속도에 따른 전단응력을 측정하고, 각 시험단계별 잔류전단강도를 측정하였다. 실험결과에 따르면, 일반적으로 전단강도는 전단속도가 증가하면 증가한다. 또한 전단시간이 길어질수록, 전단속도가 증가할수록, 링전단상자 하부링에서 더 많은 미립분이 쌓인다는 것을 확인하였다. 이러한 결과로 입자 파쇄량이 증가할수록 산사태 발생이후 토석류 확산시에 유동성을 증가시키는 원인으로 판단할 수 있다.

• Geomechanics and Engineering
• /
• 제36권2호
• /
• pp.145-156
• /
• 2024

The mechanical properties of the concrete-frozen soil interface play a significant role in the stability and service performance of construction projects in cold regions. Current research mainly focuses on the precast concrete-frozen soil interface, with limited consideration for the more realistic cast-in-place concrete-frozen soil interface. The two construction methods result in completely different contact surface morphologies and exhibit significant differences in mechanical properties. Therefore, this study selects silty clay as the research object and conducts direct shear tests on the concrete-frozen soil interface under conditions of initial water content ranging from 12% to 24%, normal stress from 50 kPa to 300 kPa, and freezing temperature of -3℃. The results indicate that (1) both interface shear stress-displacement curves can be divided into three stages: rapid growth of shear stress, softening of shear stress after peak, and residual stability; (2) the peak strength of both interfaces increases initially and then decreases with an increase in water content, while residual strength is relatively less affected by water content; (3) peak strength and residual strength are linearly positively correlated with normal stress, and the strength of ice bonding is less affected by normal stress; (4) the mechanical properties of the cast-in-place concrete-frozen soil interface are significantly better than those of the precast concrete-frozen soil interface. However, when the water content is high, the former's mechanical performance deteriorates much more than the latter, leading to severe strength loss. Therefore, in practical engineering, cast-in-place concrete construction is preferred in cases of higher negative temperatures and lower water content, while precast concrete construction is considered in cases of lower negative temperatures and higher water content. This study provides reference for the construction of frozen soil-structure interface in cold regions and basic data support for improving the stability and service performance of cold region engineering.

• Geomechanics and Engineering
• /
• 제28권1호
• /
• pp.35-48
• /
• 2022

The effect of discrete polypropylene fibre reinforcement on shear strength parameters, tensile properties and isotropic index of stabilized compacted residual subgrade was investigated. Composites of compacted subgrade were developed from polypropylene fibre dosage of 0%, 1%, 2.5% and 4% and 3% cement binder. Saturated compacted soil benefited from incremental fibre dosage, the mobilized friction coefficient increased to a maximum at 2.5% fibre dosage from 0.41 to 0.58 and the contribution due to further increase in fibre dosage was marginal. Binder stabilization increased the degree of isotropy for unreinforced soil at lower fibre dosage of 1% and then decreased with higher fibre dosage. Saturation of 3% binder stabilized soil decreased the soil friction angle and the degree of isotropy for both unstabilized and binder stabilized soil increased with fibre dosage. The maximum tensile stress of 3% binder stabilized fibre reinforced residual soil was 3-fold that of 3% binder stabilized unreinforced soil. The difference in computed and measured maximum tensile and tangential stress decreased with increase in fibre dosage and degree of stabilization and polypropylene fibre reinforced soil met local and international criteria for road construction subgrade.

• 한국지반공학회논문집
• /
• 제19권2호
• /
• pp.27-38
• /
• 2003

본 연구에서는 불포화토의 전단강도 특성과 이를 예측하는 모델에 대해 다루었다. 특히, 순연직응력(net normal stress)이 흙수분 특성곡선에 미치는 영향과 불포화토의 전단강도 발현에 미치는 영향에 대해 중점적으로 연구하였다. 이를 위해서 국내에 산재해 있는 화강풍화잔적토를 시료로 하여 불포화삼축압축 시험과 SWCC 시험 등을 실시하였으며, 특히, 순연직응력을 일정하게 유지시킨 상태에서 SWCC를 구할 수 있게 끔 기존의 장비를 개량하였다. 불포화토의 전단강도 시험결과와 기존의 강도예측모델에 의해 예측된 강도포락선을 비교해 본 결과, 흙수분 특성곡선과 흡인력 (matric suction)을 한 축으로 하는 강도포락선의 기울기가 순연직응력에 따라 변화함을 발견할 수 있었다. 따라서, 보다 정확하게 불포화토의 전단강도 포락선을 묘사하기 위해서는 흡인력에 미치는 순연직응력의 영향이 고려되어야 하는 것으로 나타났다. 본 논문에서는 기 언급한 내용에 근거하여 수정된 불포화토 전단강도 예측모델을 제안하였다.

• Geomechanics and Engineering
• /
• 제14권4호
• /
• pp.387-398
• /
• 2018

The present study evaluates the interface shear strength between sand and different construction materials, namely steel and concrete, using direct shear test apparatus. The influence of surface roughness, mean size of sand particles, relative density of sand and size of the direct shear box on the interface shear behavior of sand with steel and concrete has been investigated. Test results show that the surface roughness of the construction materials significantly influences the interface shear strength. The peak and residual interface friction angles increase rapidly up to a particular value of surface roughness (critical surface roughness), beyond which the effect becomes negligible. At critical surface roughness, the peak and residual friction angles of the interfaces are 85-92% of the peak and residual internal friction angles of the sand. The particle size of sand (for morphologically identical sands) significantly influences the value of critical surface roughness. For the different roughness considered in the present study, both the peak and residual interaction coefficients lie in the range of 0.3-1. Moreover, the peak and residual interaction coefficients for all the interfaces considered are nearly identical, irrespective of the size of the direct shear box. The constitutive modeling of different interfaces followed the experimental investigation and it successfully predicted the pre-peak, peak and post peak interface shear response with reasonable accuracy. Moreover, the predicted stress-displacement relationship of different interfaces is in good agreement with the experimental results. The findings of the present study may also be applicable to other non-yielding interfaces having a similar range of roughness and sand properties.