Effect of Compaction Banding on the Hydraulic Properties of Porous Rock: Part I—Experimental Investigation

Abstract

The mechanical behavior and the influence of compaction banding on the hydraulic properties in soft porous rocks were studied. The tested rock was Calcarenite Tuffeau de Maastricht. In the frame of experimental investigations, triaxial and oedometric tests were conducted under dry and drained conditions. The results demonstrated that the rock is forming discrete compaction bands under high confining stresses and steep angle shear bands under low confining stresses. Permeability measurements during the oedometric and triaxial compression tests under drained conditions demonstrated that the axial permeability decreases with increasing axial strain. The maximum permeability decrease was three orders of magnitude for 40% of axial strain.

Compaction band localization in geomaterials: a mechanically consistent failure criterion

“…We rewrite (32) in terms of the elastic strain using index notation; thus, the instability condition becomes:…”

“…This feature, along with the positive definiteness of C e ijkl , allows us to state that: (34) εkl → εvp kl in the localization onset. Alternatively, we express the stress rate in (32) in terms of the total strain rate and the viscoplastic constitutive tensor as in (22), as follows: (35) σ : ε = εij C vp ijkl εkl = 0 , and, considering (7) and (34), expression (35) reads: (36) εij C vp ijkl εvp kl = λ εij C vp ijkl N kl = 0 , We then construct a tensorial quantity that becomes an indicator of the localization in a more robust way than the acoustic tensor, especially under isotropic conditions, which reads: (37) L ij := C vp ijkl N kl . Unlike typical approaches such as [7], the localization onset occurs when an eigenvalue of L becomes zero, and the localization direction is parallel to the eigenvector associated with the zero eigenvalue.…”

“…Similarly to the compaction band, the dilation band appears when radial plastic flowes N 22 = N 33 = 0 under the condition of having a positive plastic flow parallel to the principal stress. This stress path induces the following initial plastic flow, N dtx ij | t0 , and localization plastic flow, Our analysis framework seeks to explain the appearance of compaction bands in porous rocks processes in several laboratory tests [28,29,30,31,32]. Our numerical experiments induce localization under different triaxial compression conditions, using the Vermeer and Neher's [33] model, a modified overstress model based on Perzyna's viscoplasticity, that can be understood as a particularization of the constitutive framework of Section 2.…”

The Critical Indicator of Red-Bed Soft Rocks in Deterioration Process Induced by Water Basing on Renormalization Group Theory

“…When red-bed soft rocks encountering poor engineering conditions, Leuthold et al [21] conducted triaxial tests of porous soft rock under dry and wet environments to obtain the law of permeability variation and shear zone distribution. Jiang et al studied the shear mechanisms of red-bed soft rock through shear test and CT analysis [22]. On the other hand, basing on the image technology, many researches of SEM [23,24] (Scanning Electron Microscope), AE [25,26] (Acoustic Emission), CT [2,27] (Computed Tomography) are carried out.…”