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.
Highlights
Pre-grouting of fractured rock mass before excavation is essential to improving weak rock zones, such as faults or major joints, to ensure safe construction of underground structures [1,2,3]
The grout specimen displayed a gradual increase in shear wave velocity with curing time and the shear wave velocity reached 87.5% of its 28-day cured wave velocity within the first 7 days of curing
As the grout material filled the discontinuous joints, the joint filling and adhesive effects of the grout bound the rock disks into a single grouted rock column. This resulted in increased shear stiffness and decreased stress sensitivity
Summary
Pre-grouting of fractured rock mass before excavation is essential to improving weak rock zones, such as faults or major joints, to ensure safe construction of underground structures [1,2,3]. Grout injected into anisotropic and discontinuous rock media flows through the fracture network of the host rock, and the grout-filled discontinuities govern the deformation characteristics of the site [4,5,6]. After pre-grouting, the subsequent excavation results in large local non-linear strains within the grouted rock matrix. To determine the accurate shear deformation characteristics of the underground structure, the nonlinear stress- and strain-dependent properties of the grouted rock mass must be included in the safety analysis. Previous studies on rock grouting focus on the numerical simulation of grout flow in fractures [8,9,10] or field case studies [11,12,13,14] and less emphasis is placed on the actual deformation properties of the site after grouting
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