Multistage Triaxial Testing of Rocks

Abstract

To determine the constitutive properties of the components in a rock structure, triaxial tests are commonly carried out on cylindrical test specimens. The conventional triaxial test (designated the single-stage triaxial test) involves obtaining a peak strength for the specimen and, after its breakage, a residual strength. In the multistage triaxial test, however, several peak and residual strengths can be obtained from a single specimen. This technique enables the experimenter to conserve samples and to obtain more consistent strength data by eliminating sample variabilities for the construction of failure envelopes. The feasibility of this test is examined by comparing strength results for single-stage and multistage tests in terms of the cohesion and the friction angle, which are calculated from the failure envelopes constructed by the two different types of test data. The feasibility is confirmed for Pierre shale and Raton shale, but is doubtful for Lyons sandstone, which is very brittle.

Importance of Water‐Clay Interactions for Fault Slip in Clay‐Rich Rocks

“…Slip was initiated by increasing axial displacement with a constant rate of 0.1 mm/min (causing increasing axial stress σ 1 ) under constant confining pressure P c . Multi‐stage triaxial testing was performed (Kim & Ko, 1979) for experiments of Test 1 involving confining pressures of 4–25 MPa (Table 1). The estimation of the non‐wetted frictional slip envelope was then used in Test 2 and 3 to define the initial stress conditions before fluid was injected. Non‐polar fluid (Test 2): Three friction experiments (Exp.…”

A Critical Review of Current States of Practice in Direct Shear Testing of Unfilled Rock Fractures Focused on Multi-Stage and Boundary Conditions

“…The literature suggests that the practice of multi-stage testing for triaxial and direct shear testing of both rock and soil has been followed since some of the earliest research on direct shear testing (e.g., [25,27,29]). Although there was early evidence that its use impacts the strength results of later stages (e.g., [27]), the overall use of a multi-stage technique was viewed as an advantageous way to obtain additional data from a specimen using only one sample for testing as opposed to multiple samples [25,29,30]. A similar claim was made by Muralha [15], who stated "it is not practical to use a joint sample to perform a single shearing under a constant normal stress.…”

Experimental Investigation and Micromechanical Modeling of Hard Rock in Protective Seam Considering Damage–Friction Coupling Effect

“…No obvious cracks are observed on the outer surface, and a good homogeneity is seen. The average density of the samples is 2.6 g/cm 3 .…”

“…In order to guarantee the safety and stability of the rock mass engineering, the mechanical properties of the engineering rocks need to be mastered. The high ground stress, high gas and low permeability conditions that exist in protruding mines at a depth of 1000 meters make protrusion accidents a frequent problem [3,4]. The rock (as shown in Figure 1) here is drilled and blasted out of the coal mine tunnels and made into standard rock samples.…”