Friction and degradation of rock joint surfaces under shear loads

Abstract

SUMMARYThe morpho-mechanical behaviour of one arti"cial granite joint with hammered surfaces, one arti"cial regularly undulated joint and one natural schist joint was studied. The hammered granite joints underwent 5 cycles of direct shear under 3 normal stress levels ranging between 0.3 and 4 MPa. The regularly undulated joint underwent 10 cycles of shear under 6 normal stress levels ranging between 0.5 and 5 MPa and the natural schist replicas underwent a monotonics shear under 5 normal stress levels ranging between 0.4 and 2.4 MPa. These direct shear tests were performed using a new computer-controlled 3D-shear apparatus. To characterize the morphology evolution of the sheared joints, a laser sensor pro"lometer was used to perform surface data measurements prior to and after each shear test. Based on a new characterization of joint surface roughness viewed as a combination of primary and secondary roughness and termed by the joint surface roughness, SR , one parameter termed &joint surface degradation', D , has been de"ned to quantify the degradation of the sheared joints. Examinations of SR and D prior to and after shearing indicate that the hammered surfaces are more damaged than the two other surfaces. The peak strength of hammered joint with zero-dilatancy, therefore, signi"cantly di!ers from the classical formulation of dilatant joint strength. An attempt has been made to model the peak strength of hammered joint surfaces and dilatant joints with regard to their surface degradation in the course of shearing and two peak strength criteria are proposed. Input parameters are initial morphology and initial surface roughness. For the hammered surfaces, the degradation mechanism is dominant over the phenomenon of dilatancy, whereas for a dilatant joint both mechanisms are present. A comparison between the proposed models and the experimental results indicates a relatively good agreement. In particular, compared to the well-known shear strength criteria of Ladanyi and Archambault or Saeb, these classical criteria signi"cantly underestimate and overestimate the observed peak strength, respectively, under low and high normal stress levels. In addition and based on our experimental investigations, we put forward a model to predict the evolution of joint morphology and the degree of degradation during the course of shearing.Degradations of the arti"cial undulated joint and the natural schist joint enable us to verify the proposed model with a relatively good agreement. Finally, the model of Ladanyi and Archambault dealing with the proportion of total joint area sheared through asperities, a , once again, tends to underestimate the observed degradation.

Direct assessment of structural resistance against pressurized fracture

“…The simplest functional dependence which can be hypothesized is illustrated by Figure 3(a): when the permanent crack opening displacement w p n ; see relations (2), is smaller than some critical value w l n ; then the fluid pressure p increases linearly from zero to the hydrostatic value p l ; beyond w l n ; p is kept constant. This piece-wise linear relationship can be described as a LCP, for given p l ; by introducing the auxiliary variable l p as follows: Observe that the parameter w l n permits to modulate the pressure distribution inside the crack.…”

“…In the case of low bulk permeability (e.g. in concrete dams, of specific interest herein), this hydraulic loading depends primarily on the efficiency of the drainage system but also on interacting phenomena such as dilatation and degradation of the fracturing surfaces, which increase the joint aperture and, therefore, its permeability [1][2][3][4][5].…”

“…Wearing due to cycling loading, see e.g. Reference [2], and the modelling of the fluid flow along the fracture, as done in Reference [6], are considered as marginal aspects to the main purpose of this work, which is restricted to steady-state quasi-static situations.…”

Effect of swelling mineral on geotechnical characteristics of clay soil

“…Several mineralogical researches on natural soils show the considerable presence of swelling clay and non-swelling clay in addition to the presence of bentonite and silt [4,5,6,7,8,9]. Therefore, the objective of this study is to highlight and quantify the influence of swelling minerals on the different properties of studied soils.…”

Dynamic modelling of a mining-induced fault slip

“…In addition to the shown shear strength models, other shear strength models taking into account the surface roughness have been proposed (Homand, Belem, & Souley, 2001;Kulatilake, Shou, Huang, & Morgan, 1995;Lee, Hong, Bae, & Lee, 2006) as a result of detailed examinations of joint surface roughness 16 and its change dependent upon sliding movements. However, it is to be noted that considerable attention is required when the shear strength models are applied to fault stability analysis.…”