Abstract
For an ultra-shallow buried double-arch tunnel with a large cross-section, the arching effect is difficult to form in surrounding rock, and grouting method is often adopted to reinforce the surrounding rock. Hence, examining the grouting reinforcement parameters is of great significance for potential failure and collapse prevention. The land part of Haicang undersea tunnel was selected as a case study; laboratory experiments, theoretical analysis, and numerical simulation were performed to determine the grouting solid strength and grouting reinforcement parameters. The effects of different water–cement ratios on slurry fluidity, setting time, bleeding rate, and sample strength were studied by laboratory experiments. A method was proposed to determine the shear strength parameters of grouted surrounding rock through the grout water–cement ratio and the unconfined compressive strength of the rock mass. Numerical simulations were performed for grouting reinforcement layer thickness and the water–cement ratios. The deformation and stability law of tunnel surrounding rock and its influence on surrounding underground pipelines were obtained considering the spatial effect of tunnel excavation and grouting reinforcement. The reasonable selection range of grouting reinforcement parameters was proposed. The initial setting time and bleeding rate of cement slurry increased with the increasing water–cement ratio, while the viscosity of cement slurry and sample strength decreased with the increasing water–cement ratio. The shear strength parameters of grouted surrounding rock were determined by the water–cement ratio of grout and unconfined compressive strength of rock mass before grouting. When the thickness of grouting reinforcement layer h = 1.5 m and the water–cement ratio of grout was suggested η = 0.85, the surface settlement, the deformation of the vault, and the deformation of the nearby pipeline all met the design. Moreover, the construction requirements were more economical. Research results can provide a reference for the selection of grouting reinforcement parameters for similar projects.
Highlights
To strengthen the bearing capacity of the rock mass and avoid possible risks in construction, various methods and measures are often adopted in the project, such as advance support, small pipe reinforcement, and grouting reinforcement to reinforce the surrounding rock [12,13,14,15,16,17]
The principle of grouting reinforcement technology is to use cement slurry, water glass, cement mortar, chemical grout, and other materials to fill the voids of broken rock masses effectively to improve the compactness, integrity, tension, compression, shear, and creep of the rock mass, so as to maintain the stability of rock mass [21]
The strength and stability of grouted surrounding rock formed after grouting reinforcement of broken rock mass is an important index to evaluate the effect of grouting reinforcement, and a key parameter to determine the deformation and the self-supporting capacity of the surrounding rock
Summary
Due to the influence and limitations of geographical location and surrounding environment, problems such as poor geological conditions, shallow burial depth, tight engineering land, complex surrounding environment, and strict control standards are common [1,2]. Found that when the water–cement ratio was 0.4 and 0.5, respectively, the peak and residual shear strength of grouted surrounding rock increased with the increasing normal stress. Through grouting experiments on fully weathered granite, Yang et al [28] studied the diffusion law of cement rule of different viscosity and the influence of grout viscosity on the reinforcement effect, and found that an increase of slurry viscosity strengthens compressive strength and shear strength. 3 of on fully weathered granite, Yang et al [28] studied the diffusion law of cement rule different viscosity and the influence of grout viscosity on the reinforcement effect, an found that an increase of slurry viscosity strengthens compressive strength and she strength.
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