Clay, triaxial system

To study hydromechanical coupling in deep stiff clays we need to supply mean stress relatively high linked to the in situ stress state. Thus, to perform triaxial tests on stiff clays with permeability measurement we use a special triaxial apparatus (high pressure cell) with two independent drainage line. We have developed also a system for local strain measurements composed of 7 LVDTs which are suitable for tests in oil (confining fluid) under high level of stress. Tests are performed on cylindrical specimens (up to 80 mm in height and 40 mm in diameter). 

An experimental set up (high pressure triaxial cell and local strain measurement system) and an experimental procedure have been developed in order to quantify the permeability evolution with deviatoric stress on clays of very low permeability. Developed techniques have been improved on concrete and sandstone. We are able to detect with precision strain localization and we are able to measure with the pulse method, permeability, at different stages of loading. A testing program on both Boom Clay and Opalinus is in progress. 

The type of microstructure transformation upon deformation depends on the stress state. For example, the clay compaction upon triaxial isotropic compression leads to system strengthening whereas the uniaxial compression in odometer is accompanied by a certain direction of structural elements in the plane normal to the compressing stress. Therefore, soils with the similar density and moisture but compacted under different conditions manifest different properties. 

This paper presents the characteristics of pore water pressure and deformation of undisturbed sandy clay in two different triaxial unloading methods with a static high-pressure triaxial test system. The results show that the pore water pressures of this undisturbed sandy clay were all decreased at... 

To get detailed data on soil properties, exploratory wells dug in the study area, made new loess, old loess and silty clay samples each 15 groups. Then, they were tested on the GDS advanced dynamic triaxial test system in State Key Laboratory of Continental Dynamics, Northwest University. Show in Figure 5. Finally, we got series of the effective cohesion and effective friction angle. Because of the variation of c which made the greater impact of slope stability than other parameters, we obtain the mean and standard deviation to used in Rosenblueth point estimate method. Table 1 summarizes the values of soil properties obtained from laboratory tests in the study area. 

The three scales are as follows the clay mineral is the microscale medium, which has a thickness of 10 m and a width of about 10 m the quartz grain, which constitutes the mesoscale, has dimensions of 10 -10 m the triaxial specimen used in the experiments has dimensions 10 m. Considering these scales, the parameter s for a smectitic bentonite is about 10 . Then we can introduce the following relations between the coordinate systems ... 

Let a , and be coordinate systems introduced in the macro-/meso-/micro-domains, respectively. We consider a triaxial test on the typical bentonite of Japan, Kunigel VI , using a specimen of about 10 m in diameter, which is the macrodomain, where the size of the quartz grains are about e = which is the meso-domain, and the size of clay stacks is about 10 m. Then we can set e=10 , and introduce the following relations ... 

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