Study On Surrounding Rock Deformation Control Technology Of Chamber In Water-Rich Strata

With the rapid development of underground resources exploitation and transportation network in China,many infrastructure projects inevitably need to be built in some areas with complex geological conditions.Especially for underground chamber engineering,due to its outstanding characteristics of’long service cycle and strict deformation control’,it has always attracted the attention of engineering builders.For a long time,water,as a dominant factor affecting the structural stability of underground engineering,is a key variable that cannot be ignored in the process of effectively controlling the deformation of surrounding rock.Therefore,it is of great engineering significance to carry out the research on the deformation and failure mechanism and support technology of surrounding rock of chamber under the action of underground seepage water.Based on the engineering background of Badong Tunnel of Zhengzhou-Wanzhou Railway crossing the water-rich fractured surrounding rock section,this paper adopts the research methods of theoretical analysis,numerical simulation and field test.From the perspective of the plastic failure characteristics of the surrounding rock of the water-rich tunnel,the geometric distribution of the plastic zone of the surrounding rock of the tunnel is analyzed,and the influence of pore water pressure on the plastic zone of the surrounding rock of the tunnel is studied.The rock mechanics tests under different water contents are carried out,and the control method of the surrounding rock of the tunnel based on the distribution of the plastic zone is proposed.The main research results are as follows:Based on the elastic-plastic mechanics theory,the mechanical model of circular chamber considering the influence of pore water pressure is established,and the approximate boundary equation of plastic yield range of surrounding rock is derived.According to the analysis of the respective variables in the boundary equation,the lateral pressure coefficientλcontrols the distribution form of the plastic zone;Whenλgradually increases from 1.0 to 2.4,the basic form of the plastic zone completes the evolution from’round→oval→round rectangle→hourglass→butterfly’;When the ratio of two-way principal stressλ≤1.5,the dissipation of pore water pressure pw to the surrounding rock surface has a small promoting effect on the development of plastic zone;under the influence of strong horizontal principal stress（λ≥1.8）,the existence of pore water pressure pw increases the gap between the effective vertical principal stress and the effective horizontal principal stress on the rock mass structure,and the development of plastic zone of surrounding rock is extremely sensitive to the change of pore water pressure,showing a relatively obvious expansion trend;The decrease of shear strength parameters（cohesion c and internal friction angleφ）of rock mass caused by hydraulic action makes the range of plastic zone increase continuously,and the geometric shape characteristics become more obvious.Through the mechanical experiments on the rock samples obtained from the field sampling,it is found that the rock samples under different water contents show obvious deterioration characteristics in compressive strength and deformation parameters.The uniaxial compressive strength and elastic modulus of rock show a nonlinear decreasing trend with the increase of water content.The residual strength and ductility of rock during compression are more prominent due to the water-rock interaction.In addition,with the increase of water content,the crack propagation and fragmentation degree of rock samples under compression failure are significantly increased.The analysis shows that the weakening effect of groundwater on rock mass structure is an important factor leading to large deformation and failure of surrounding rock.FLAC^3Dfinite difference software was used to conduct numerical simulation research on the construction technology of Badong Tunnel crossing the section of water-rich fractured surrounding rock,and the step-by-step combined support method of full-section advance curtain grouting pre-reinforcement combined with‘advance pipe shed+prestressed hollow grouting bolt+locking anchor pipe+shotcrete’was proposed.The field test shows that the scheme has good control effect in controlling the convergence deformation of surrounding rock.