Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses

Abstract

Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10−5) and mid-strain (10−5 to 10−3) ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1) grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2) the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3) the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4) increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass.

Characterization of the Dynamic Properties of Clay–Gravel Mixtures at Low Strain Level

“…A similar tendency was observed by Meidani et al [11,16,17], and it can be explained by the large size and the high strength of the gravels. Thelarger the size of the gravels, the less contacting points in the CGM at the given volume, and the higher the strength, the better the gravels can transfer the shear wave than clay [39,40]. Hence, a greater referent shear strain appeared in the CGMs with the increase of gravel contents.…”

Non-Destructive Evaluation of Rock Bolt Grouting Quality by Analysis of Its Natural Frequencies

“…As a basic point for investigation of dynamical response, a frequency range needs to be determined. Taking into consideration Equations (7) and (8) and the relation between angular and ordinary frequency ω = 2π f , a following arises:…”

“…Since the visible trace length of a discontinuity can be a poor indicator of true persistence, some innovative methods, such as FERM given by Shang et al [6] may help to detect the internal connections of rock bridges that hinder the flow of grout. Although the grouted rock bolts can produce a higher degree of load transfer in comparison to the other types of bolts, the grouting procedures and characteristics of the bonds between the bar and the grout and with the rock mass are the least controlled in practice [7], while the rock mass grouting procedures remain a predominantly empirical practice [8]. The importance of grouting quality can be seen through the potential rock bolt failure mechanisms, where most significant mechanisms include pull-out failures at bar-grout (B-G) contact, as well on grout-rock mass contact (G-RM).…”

“…The product of bar diameter dBR (m) or borehole diameter dBH (m), installed rock bolt length l (m), and unit shear strength of bar-grout contact τB-G or unit shear strength of grout-rock mass contact τG-RM (kN/m 2 ), theoretically give the values of pull-out capacity at bar-grout contact RB-G (kN) and pull-out capacity at grout-rock mass contact RG-RM (kN), respectively. Since the pull-out resistance can be achieved only on the grouted portion of a rock bolt, it is of importance to properly Although the grouted rock bolts can produce a higher degree of load transfer in comparison to the other types of bolts, the grouting procedures and characteristics of the bonds between the bar and the grout and with the rock mass are the least controlled in practice [7], while the rock mass grouting procedures remain a predominantly empirical practice [8]. The importance of grouting quality can be seen through the potential rock bolt failure mechanisms, where most significant mechanisms include pull-out failures at bar-grout (B-G) contact, as well on grout-rock mass contact (G-RM).…”

Constitutive Model of Stress-Dependent Seepage in Columnar Jointed Rock Mass

“…The anisotropy of a jointed rock mass is mainly controlled by the intact rock mass and the joint [6][7][8]. For intact rock masses, the permeability coefficient is extremely weak, and the flow of water in it is negligible.…”