Mechanism Of Grouting Spread And Reinforcement On Soft Medium In Fault And Its Application

With rapid development of economy in our country, requirements for mineral resources, water resources and traffic engineering are increasing dramatically. A serious of underground project, such as cross harbor tunnel, highway tunnel, deep mine and city subway, are under construction, with a trend towards areas of complex geological conditions and extremely high difficulty for construction. Soft medium filling fault is a widely existed bad geology in underground construction. With the influence of groundwater and excavating stress, the filling medium can be easily damaged and thus forming water channel and soft structural surface, leading to a serious of geological disasters such as water and mud inrush, collapse and instability, and surface subsidence. Because of this, soft medium filling fault is a main disaster source of underground construction. Grouting, as an effective controlling method, is widely used in the treatment of disaster of soft medium filling fault. However, due to the limit of undiscoverable process during grouting and the anisotropic property of grouted medium, the interaction between grout and rock mass is extremely complex, and grouting theory is far left behind engineering practice, with urgent need for further study. In this paper, a combination of theoretical analysis, modeling test, numerical simulation and field test are adopted. Typical soft medium are selected to study the mechanism of grout spreading in soft medium, according to non-linear compression model. Experiments and mathematical analysis has been done to establish the quantitative relationship of mechanical property of soil before and after grouting. Then, stability of the underground construction before and after grouting are analyzed and combined grouting method with segmented pressure increment are proposed. Engineering applications are conducted, which acquired a serious of achievement.(1) Different types of fault filling medium are sorted, according to physical structural characteristics, to study different grout pattern of spreading and reinforcement of different medium. Spreading occurrence conditions and the process of grouting reinforcement are revealed and main parameters representing grouting effect are acquired.(2)Typical kinds of soft medium soil are selected as study object. Based on non-linear compression model of soil and the coupling effect of the flow field of grout and the stress field of soil during grouting process, theoretical model of fracture grouting spread is established. The spatial distribution of the width of splitting channel is acquired and the relation among grouting pressure, width of channel and grout spread radius are analyzed. Compression modulus, porosity and permeability of soil are selected as evaluating indicator and a method is proposed to determine the effective grouting reinforcement radius and fracture grouting parameters.(3)A three dimensional large scale modeling test system of grouting in soft filling medium is established, which can return the original condition during grouting in the soft medium. Segment grouting simulation tests are conducted and real-time monitoring of multi-variant information is carried out. The process of grouting spread in soft medium are studied. Then, characteristics of grouting pressure and velocity variation during different stage of grouting spread a time-spatial evolution law of the pressure field during the grouting process are analyzed. Finally, mechanism of segment grouting reinforcement is acquired. According to excavation and sampling test, thickness variation of grout vein and spatial distribution characteristics are analyzed. Mechanical property and permeability quantitative relation before and after grouting are established.(4)According to the relation above, finite element model for foundation ditch excavation are established with numerical software. Stability of foundation ditch before and after grouting is comparatively analyzed to validate the selection of grouting parameters.(5)Compound grouting technology with section pressure increment is established. Principle for the compound grouting technology and design method are systematically elaborated. Research results have been successfully used in shangyuanmen subway of Nanjing province, which acquired notable effect and may offer reference to similar project with wild application prospect.