Matric Suction Creep Characteristics of Reticulated Red Clay

Jianzhong Li,Yuanli Yang 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.10

Matric suction creep is the creep of unsaturated soil caused by loading constant matric suction. Matric suction creep characteristics of reticulated red clay with constant net confing pressure and step-loading matric suction was studied using stress-controlling unsaturated triaxial test apparatus. Test and analysis results show that: (1) with constant net confining pressure, axial and radial strain of the clay caused by creep due to matric suction increases obviously; (2) the increments of axial strain of the clay, caused by creep due to matric suction under constant net confining pressure, is not the same as that of radial strain, and the absolute value of radial strain is bigger than that of axial strain; (3) creep strain produced by the same amount of matric suction decreases as the increasing of the matric suction during step loading creep, which means that matric suction makes the clay hard; and (4) the creep strain-time curves of both axial and radial creep can be simulated very well by exponential decay function, and the parameters of the function are matric suction depend obviously.

Creep Behavior of Unsaturated Reticulate Red Clay Under Matric Suction

Jianzhong Li,Yuanli Yang 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.2

In order to study unsaturated creep behaviors of reticulate red clay under matric suction, a series of isotropic creep tests with different matric suction level were carried out by using Geotechnical Digital Systems (GDS) unsaturated apparatus. Results indicate that creep strain caused by matric suction increases with the increasing of matric suction level and tends to certain stability over time. Based on the analyses of test results, a creep model for the unsaturated reticulate red clay under matric suction was established to predict the creep strain caused by matric suction. In the model, a new parameter M (matric suction level) was defined as a ratio of the matric suction to the net confining pressure, a hyperbolic function was adopted for the description of the strain-time relationship and an exponential function was employed for the strain-M relationship. Predicted results are in good agreement with the test results shows that the model can reasonably simulate the effects of matric suction on creep properties of unsaturated reticulate red clay.

새만금지역 준설토의 불포화 특성에 대한 실험적 연구

송영석(Song,Young-Suk),유승경(You,Seung-Kyong) 한국토목섬유학회 2011 한국지반신소재학회 논문집 Vol.10 No.3

본 연구에서는 자동 흙-함수특성곡선 시험장치를 이용하여 새만금지역에서 채취한 준설토의 모관흡수력과 체적함수비를 측정하였다. 측정결과를 토대로 Van Genuchten(1980)의 방법을 이용하여 흙-함수특성곡선(SWCC)을 산정하였다. 동일한 유효포 화도에서 건조과정의 모관흡수력은 습윤과정의 모관흡수력보다 크게 나타났다. Lu and Likos(2006)의 방법을 이용하여 모관 흡수력에 따른 흡입응력을 산정하고, 흙-함수특성곡선(SWCC)의 불포화 관련계수를 토대로 흡입응력특성곡선(SSCC)을 예측하였다. 건조과정의 흡입응력은 유효포화도가 증가함에 따라 증가하다가 감소하지만 습윤과정의 흡입응력은 유효포화도가 증가함에 따라 지속적으로 감소한다. 또한 동일한 유효포화도에서 건조과정의 흡입응력은 습윤과정의 흡입응력보다 크게 나타났다. 한편 van Genuchten(1980)의 방법을 이용하여 투수계수함수(HCF)를 예측하였다. 체적함수비가 증가함에 따라 불포화 투수계수는 증가하며, 동일한 모관흡수력에서 건조과정의 투수계수가 습윤과정의 투수계수보다 크게 나타났다. 흙-함수특성곡 선(SWCC)과 흡입응력특성곡선(SSCC)의 산정결과에 의하면 건조 및 습윤과정에서 흡입응력 혹은 모관흡수력에 대한 이력현상이 발생되었다. 이러한 이력현상은 흙입자 사이의 간극수로 인한 잉크병 효과에 의한 것이다. The matric suction and volumetric water content of dredging soils obtained from Saemangeum area were measured by the automated Soil-Water Characteristic Curve (SWCC) apparatus under both drying and wetting conditions. Based on the test result, SWCCs of the dredging soils were estimated by the van Genuchten(1980) model. The matric suction of drying process is larger than that of wetting process at a same effective degree of saturation. The suction stresses for various matirc suctions were estimated using Lu and Likos(2006) model and the Suction Stress Characteristic Curves (SSCC) were predicted using the independent parameter of SWCC. The suction stress of drying path was increased and decreased, while the suction stress of wetting path was continuously decreased with increasing the effective degree. Also, the suction stress of drying path is larger than that of wetting path at a same effective degree of saturation. The Hydraulic Conductivity Function(HCF) was also predicted by the van Genuchten(1980) model. The hydraulic conductivity was increased with increasing the volumetric water content. The hydraulic conductivity of drying path is larger than that of wetting path at a same matric suction. According to the results of SWCCs and SSCCs, the hysteresis phenomenon of suction stress or matric suction during both drying and wetting paths was occurred. The main reason of hysteresis phenomenon is a ink bottle effect of water among soil particles.

Experimental Study on the Mechanical Behaviour of Natural Loess Based on Suction-Controlled True Triaxial Tests

Fang Zheng,Shengjun Shao,Jiao Wang,Shuai Shao 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.8

Loess is mostly distributed in an unsaturated state in nature, and the complexity of the engineering properties of unsaturated soil is mainly due to the existence of matric suction. Therefore, matric suction must be considered in investigating the mechanical properties of unsaturated loess. However, soils are most often subjected to three principal stresses with different magnitudes in practical engineering. For the sake of examining and discussing the mechanical behaviour of unsaturated natural loess under a complex stress path, a suction-controlled true triaxial apparatus with a rigid-flexible boundary is used to test unsaturated natural loess under a complicated stress path. Four trials of isotropic consolidation tests are conducted on natural loess under suction-controlled conditions via the true triaxial apparatus. The consolidation yield characteristics of the natural loess under different matric suctions are investigated. Forty-eight trials of consolidated drained true triaxial tests under suction-controlled conditions are conducted on unsaturated natural loess to examine and discuss the influence of the matric suction and intermediate principal stress parameter (b-value). The consolidated drained trials are performed under a constant net mean stress and a constant matric suction with different intermediate principal stress parameters (b-values). Stress-strain curves and failure envelopes of the natural loess are also presented. The results indicate that the stress-strain-strength response of unsaturated natural loess depends on the matric suction and intermediate principal stress parameter under true triaxial conditions.

낮은 모관흡수력 수준에서 불포화토의 Bishop 응력에 관한 연구

오세붕,김태경 한국지반공학회 2008 한국지반공학회논문집 Vol.24 No.7

In this study, the triaxial behaviour of an unsaturated soil was analyzed by Bishop stress descriptions. K0 stress paths and those final values were independent of matric suctions after describing by the Bishop stress. The failure criteria could be defined uniquely by the Bishop stress and were also independent of matric suctions. In the low level of matric suctions the failure criteria have a linear relationship and the estimated criterion fits the measured accurately. The variable χ for describing the Bishop stress was a constant theoretically under the low level of matric suctions. The suction stress could be defined at zero deviatoric stress in the failure criteria and increased linearly with respect to matric suctions in both the theory and the experiments.

모관흡수력과 구속압 변화에 따른 화강풍화토 응력-변형률 관계

서세관(Se-Kwan Seo),김재홍(Jae-Hong Kim),김유성(You-Seong Kim) 한국지반신소재학회 2014 한국지반신소재학회 학술발표회 Vol.2014 No.11

Experimental tests with various confined pressures and matric suctions in weathered granite soil was carried out by unsaturated triaxial compression test. The tests were performed to obtain the shear strength of unsaturated soils, for example, matric suction (0, 50, 100kPa) and effective confined pressure(50, 100, 200kPa) conditions. Experimental results show that the shear strength of soils increase when matric suction and effective confined pressure increase. The shear strength of unsaturated soil was affected by variation of the effective confined pressure than matric suction. As a result, when the soil strength is fixed matric suction 100kPa, the strength parameter of unsaturated soil could be investigated cohesion 20.3kPa and friction angle 24°.

불포화 사질토의 전단특성

임성윤 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.10

Since matric suction of unsaturated soil was related to soil and ground water contaminations, it is very important to analyze its mechanism that was represented by shear characteristics. In three phases of soil, a little air makes the condition of unsaturated soil on contract or shrinkage surface between water and air. Capillarity and suction in pore of unsaturated soil cause surface tension and surface force so it makes negative pore water pressure and increases effective stress as a result. Therefore, negative pore water pressure in partially saturated soil affects the soil structure and degree of saturation and it is important to evaluate accurately unsaturate flow and behavior. In this study, the shear strength characteristics of the seven sandy soils were investigated using consolidated drained triaxial tests with special emphasis on the effects of the negative pore pressure and the matric suction. These tests involved shearing under either a constant net confining pressure and varying matric suction or under a constant matric suction and varying net normal stress.

불포화토의 K0 압밀 삼축압축실험시 모관흡수력에 따른 정지토압계수 및 전단강도에 관한 연구

김태경,오세붕 한국지반공학회 2008 한국지반공학회논문집 Vol.24 No.5

In this study, the behaviour of an unsaturated soil was analyzed by performing K0 consolidated triaxial tests. Unsaturated triaxial tests were performed with matric suctions for weathered soils and stress paths under consolidation and stress-strain relationships under shear were obtained. As a result, the K0 value decreased as the matric suction increased. Besides, both isotropic and K0 conditions had similar shear strength envelopes at the same matric suction. Especially, strength parameters could be obtained by stress variables used in the critical state theory more reasonably than by those of Mohr circles at failure.

불포화토의 흙-수분 특성곡선에 관한 실험적 고찰

송창섭 ( Song Chang Seob ),김명환 ( Kim Myung Hwan ) 한국농공학회 2003 韓國農工學會誌 : 전원과 자원 Vol.45 No.6

The purpose of this paper is to investigate the soil-water characteristic curves for an unsaturated soil. To this ends, a series of suction measured test was conducted on the selected 4 kinds of soils taken from different sites of Korea, using modified pressure plate apparatus. Form the test results, the water contents, degree of saturation and volumetric water contents were analyzed with the suction. And the soil-water characteristic curves of unsaturated soil were drawn from the test results for various factors. The characteristic curves drawn with water content vs matric suction were classified certainly the difference in wet side but were not classified in dry side. The characteristic curves drawn with degree of saturation vs matric suction for unsaturated soil were shown the opposite inclination as compared with the former curve. But the characteristic curve with volumetric water content vs matric suction was described suitably not only in wet side condition but also in dry side. And it was found that the volumetric water contents of loose soil was high at the initial condition but that of dense soil was high at final condition (dry side).

강우재현 모형실험과 SWCC Cell 실험에 의한 화강암질 풍화토의 함수특성곡선

기완서 ( Wan Seo Ki ),김선학 ( Sun Hak Kim ) 대한지질공학회 2008 지질공학 Vol.18 No.4

강우재현장치를 제작하고, 강우 및 사면조건에 따라 강우재현 모형실험과 함수특성곡선실험(SWCC Cell Test)을 실시하여 불포화 특성에 관해 연구하였다. 그 결과를 이용하여 강우에 따른 침투거동 특성과 함수특성곡선 모델들의 불포화된 화강암질 풍화토에 대한 적용을 검토하였다. 강우재현 모형실험의 습윤과정(강우재현)과 건조과정(방치)에서 계측된 체적함수비와 모관흡인력을 비교한 결과 체적함수비는 2~5%, 모관흡인력은 3~10 kPa 정도 값의 차이를 보여 이력현상을 확인 할 수 있었다. 또한, 모관흡인력의 값이 체적함수비의 값에 비해 상대적으로 큰 차이를 보여 모관흡인력에 이력거동이 더 큼을 확인할 수 있었다. 강우재현 모형실험과 함수특성곡선실험에서 얻은 결과로부터 구한 함수특성곡선을 비교하면, 습윤과정과 건조과정에서 두 방법 모두 근접한 함수특성곡선을 얻을 수 있었으나, 두 방법 모두 습윤과정과 건조과정에서의 결과는 차이가 있었다. 이로써 불포화토의 특성을 고려한 보다 합리적인 설계나 안정검토에 함수특성곡선을 적용시킬 때에는 습윤과정에서는 습윤과정 함수특성곡선을 건조과정에서는 건조과정 함수특성곡선을 적용하는 것이 합당할 것으로 여겨진다. A simulated rainfall system was built, and the unsaturated characteristics were examined by execution of simulated rainfall system test and soil water characteristic curve cell test(SWCC Cell Test) under the various rainfall and slope conditions. With the results, the applicability of infiltration behavior under rainfall and soil water characteristic curve models to the unsaturated weathered granite soil was examined. At the results of comparison the volumetric water content and matric suction measured in the wetting process(under rainfall) with those in the drying process(leaving as it was) of the simulated rainfall system, the volumetric water content showed a difference of 2~5% and matric suction of about 3~10 kPa, indicating the occurrence of hysteresis. In addition, the difference was relatively larger in matric suction than in the volumetric water content, and this tells that the hysteresis behavior is larger in matric suction. When the soil water characteristic curve derived from measurements in simulated rainfall system test were compared with those from the soil water characteristic curve cell test, both methods produced soil water characteristic curves close each other in the wetting process and the drying process, but in both, there was a difference between results obtained from in the wetting process and those from in the drying process. Thus, when soil water characteristic curves are rationally applied to the design and stability analysis considering of the properties of unsaturated soil, it is considered desirable to apply the soil water characteristic curve of the wetting process to the wetting process, and that of the drying process to the drying process.