Study On Tunnel Grouting Reinforcement Theory And Its Application In Fractured Rock

As a challenging research topic, reinforcement for fractured rock through grouting plays an important and key role in construction successful and operation safety of tunnel engineering. Researches in this domain can promote the development of mechanical theory, as well as propose solutions for tunnel construction in karst region and fracture zone. Standards and criterions can be built on the principles and technical supports obtained from these researches. These researches can also support tunnel constructions, as well as expand the scope of application in railway tunnel, subway, and other underground engineering. This paper is based on grouting theory. At the first stage, a fluid model for percolation grouting is built on the analysis of several classic percolation grouting theories. Relationships among parameters as well as their solutions of flow rate of grout, grouting pressure and permeability coefficient are deduced in the grouting procedure. The analyses of mechanical mechanism are carried out for percolation grouting and fracturing grouting. After that, testing parameters are set based on the analysis of grouting mechanism model. Grouting mechanism is studied, and the grouting effects are tested at the same time. Finally, the acceptance criteria of grouting volume, testing approaches for grouting quality, and results from this research are applied in practical engineering. Contributions of this research can be summarized as follows:(1) A fluid model for percolation grouting is built on percolation grouting theory. Solutions of flow rate of grout, grouting pressure and permeability coefficient are deduced in the process of grouting. The relationships in the process of multi-hole grouting are studied. It can be concluded that:a) For a given point, in the process of multi-hole grouting, its grouting pressure equals the superimposed value of single-hole grouting; b) When grouting holes are in circular distribution, the center of the circle can get the worst effect for reinforcement. Optimal quantity of grouting holes for uniform distribution is deduced in condition that the grouting pressure is under control.(2) Solutions for elastic-plastic zone caused by fluid compressing soil, the formula of radius in plastic zone, as well as final formula for grouting pressure calculation, are deduced.The energy dissipation method is employed to calculate the pressure of fracturing grouting in fractured rock. And a simultaneous sensitivity analysis is carried out for the impact parameters related to the design of grouting pressure.(3) The time travel curves of grouting pressure, time travel curves of grouting rate, as well as general laws for fracturing grouting are obtained from the study of fracturing grouting mechanical model experiment. Injection rate of cement, mechanical mechanism of grouting, and effects of reinforcement in rock and soil are analyzed. Results are successfully applied in practical engineering. Thus, the veracity and reliability of this research are validated.(4) A control testing method for grouting quality is presented through studying in grouting volume control theory. A grouting control standard and its applicable scope are set.(5) Analysis is carried out for the principle of existing testing approaches, general features, applicable scopes, and detection effects. An improved method is introduced for quality testing of tunnel grouting reinforcement, which is based on boreholing core, grouting volume and pressure control, analysising injection rate of cement, testing of boreholing core and geological radar detection.(6) From the grouting reinforcement case analysis, the design parameters,which obtained from fracturing grouting mechanical model experiment, are effective. Thus, the study of grouting theory and the analytical method of grouting mechanism developed by this research is validated, which can be referenced to other practical applications in the field of grouting reinforcement.