The effective stress law for the permeability of a limestone is studied
experimentally by performing constant head permeability tests in a triaxial
cell with different conditions of confining pressure and pore pressure. Test
results have shown that a pore pressure increase and a confining pressure
decrease both result in an increase of the permeability, and that the effect of
the pore pressure change on the variation of the permeability is more important
than the effect of a change of the confining pressure. A power law is proposed
for the variation of the permeability with the effective stress. The
permeability effective stress coefficient increases linearly with the
differential pressure and is greater than one as soon the differential pressure
exceeds few bars. The test results are well reproduced using the proposed
permeability-effective stress law. A conceptual pore-shell model based on a
detailed observation of the microstructure of the studied limestone is
proposed. This model is able to explain the experimental observations on the
effect of the total stress and of the pore pressure on the permeability of the
limestone. Effective stress coefficients for the stress-dependent permeability
which are greater than one are obtained. It is shown that the controlling
factor is the ratio of the different bulk moduli of the various constituents of
the rock. This ratio is studied experimentally by performing microhardness
tests.Comment: International Journal of Rock Mechanics and Mining Sciences (2008) In
pres
International audienceThe poromechanical behaviour of hardened cement paste under isotropic loading is studied on the basis of an experimental testing program of drained, undrained and unjacketed compression tests. The macroscopic behaviour of the material is described in the framework of the mechanics of porous media. The poroelastic parameters of the material are determined and the effect of stress and pore pressure on them is evaluated. Appropriate effective stress laws which control the evolution of total volume, pore volume, solid volume, porosity and drained bulk modulus are discussed. A phenomenon of degradation of elastic properties is observed in the test results. The microscopic observations showed that this degradation is caused by the microcracking of the material under isotropic loading. The good compatibility and the consistency of the obtained poromechanical parameters demonstrate that the behaviour of the hardened cement paste can be indeed described within the framework of the theory of porous media
International audienceThe experimental results of isotropic compression tests performed at 20°C and 90°C on a class G hardened cement paste hydrated at 90°C (Ghabezloo et al., 2008, Cem. Conc. Res. 38, 1424-1437) have been revisited considering time-dependent response. Within the frame of a viscoplastic model, the non-linear responses of the volumetric strains as observed in drained and undrained tests and of the pore pressure in undrained tests are analysed. The calibration of model parameters based on experimental data allows to study the effect of the test temperature on the viscous response of hardened cement paste showing that the creep is more pronounced for a higher test temperature. The effect of the hydration temperature on the time dependent behaviour is also studied by evaluating the model parameters for a cement paste hydrated at 60°C. The time-dependent deformations are more pronounced for hydration at a higher temperature
ABSTRACT:Water is an important weathering factor on rock discontinuities and in rock mass mechanical behavior. The increase of rainfall in frequency or in intensity highlights some problems on the rock slope stability analysis. The aim of this paper is the multi scale analysis of the chemical impact of water on rock (surface roughness and matrix). In this study we show how water induces degradation and thus may decreases the stability of the discontinuous rock mass. Water is known to have significant erosion and dissolution effects on rock surface or rock matrix. The chemical features of water such as temperature, pH or salinity make it a "good" candidate to rock degradation. This study has two main components. The first one is the study of water-solid chemical mechanisms and the other is the analysis of the mechanical response of the discontinuity modified by the water alteration. The stability of the rock mass is naturally a function of the type and the space distribution of discontinuities. The study aims also to evaluate the effect of water flow on the rock slope stability and it is performed at two space scales: laboratory (micro scale and macro scale) and in situ scales. The last one is still under investigation and will be presented.
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