Tensile strength of large-scale incipient rock joints: a laboratory investigation

Abstract

In this paper, a testing methodology was developed in the laboratory to measure the tensile strength of large-scale incipient rock joints. In the test, an expansive grout was used to develop the tensile force. Each test comprises two phases: Phase i test and Phase ii test. The Phase i test identified sample failure time, while the Phase ii test measured the corresponding tensile force arising from the expansive grout. Ostensibly homogeneous rock samples without incipient joints were firstly tested to establish the methodology. Tensile strength of block samples containing incipient rock joints was then measured using the established testing scheme. The test results have been compared with those obtained from conventional Brazilian and uniaxial tension tests as suggested by ISRM. The proposed approach is capable of giving a measure of tensile strength of large-scale incipient rock joints, although somewhat smaller strength than that from the standard approaches was occasionally measured in the preliminary tests on ostensibly homogeneous samples. Effects of stress concentration, sample scale, loading rate and expansive tensile force on the testing results were discussed. Furthermore, this simple and practical testing scheme is proposed for the measurement of the in situ tensile strength of rock and incipient discontinuities in the field, which if successful will provide a more scientific guidance on the rock mass classification and engineering design.

Stability Analysis of Fragile Rock Pillars and Insights on Fault Activity in the Negev, Israel

“…To better understand the swaying motion, we perform modal analysis (following Chopra, 2012, Chapter 17), using the elastic properties of the rock mass and geometry of the pillar. A complete analysis should account for intrinsic properties of elasticity, Poisson ratio, density, contact continuity at the base (Elmo et al, 2018) and incipient discontinuity tensile strength (Shang et al, 2018). These parameters vary naturally between rock masses and often are difficult to assess from surface mapping.…”

“…(e.g., Shang et al, 2018) this scenario suggests that for median spectral acceleration basal detachment is probable. For the M7.5 scenario and similar tensile strength assumption, the basal tensile stresses are below the incipient strength for the median spectral acceleration and marginally above the incipient strength lower bound for the single standard deviation value.…”

“…For rock pillars evolved from sedimentary rock mass, basal attachment along bedding planes is assumed (Shang et al, 2018). To assure we do not underestimate the stability of FGFs, we assume the pillar is attached even where colluvium obscures their base (e.g., FGFs 3029 and 4016 in Figure 1).…”

Study of the effect of pre-existing crack and water saturation on strength of rock-like

“…Through these studies, it has been observed that under the load conditions, the pre-existing crack is at the origin of the appearance and the propagation of the majority of the new cracks which transform into rock bridges. The existence of relatively small rock bridges at the discontinuities greatly increases their strength [24,25,26] which must first be broken before a rupture can take place.The above-mentioned studies also pointed out that, the propagation of cracks within a rock was a complex phenomenon and depended on the rock composition and the properties (geometry/ shape, orientation, and size) of the pre-existing cracks.…”

Experimental Study of the Mechanical Characteristics of a Rock‐Like Material Containing a Preexisting Fissure under Loading and Unloading Triaxial Compression

“…Rock discontinuities are fundamentally important to most rock engineering projects [2]. Shang et al addressed the issue of tensile strength of incipient discontinuities in rock and presented results from a laboratory test programme to quantify this parameter [3,4]. Xiao et al studied the mechanical and deformation behaviors of the fractured rock-like material with one single fissure under the conventional triaxial compression [5].…”