Study On The Failure Mechanism Of Shaft Lining In Stable Surrounding Rock With High Pressure Pore Water

In recent years,with China's coal mining moves to the western region,a lot of shaft linings pass through deep and stable water-rich sandstone strata.Under the action of high pore water pressure,it is a difficult problem to design single-layer shaft lining rationally.To reveal the mechanism of high pressure pore water fracturing the shaft lining in stable surrounding rock is the basis of solving this problem.In this paper,the mechanism of fracturing the shaft lining caused by high pressure pore water in stable bedrock is studied by means of numerical simulation and physical model test.Firstly,the plane strain model of porous media was established,and the whole interaction process between surrounding rock,pore pressure and the shaft lining was simulated by FLAC3 D finite difference numerical simulation software.Some parameters that affect the deformation of the shaft lining and the equivalent water load behind the lining during the growth of pore water pressure are compared and studied.The failure forms of the shaft lining in the whole process of pore pressure recovery are simulated.It is concluded that the main failure mode of shaft lining is shear failure.Secondly,based on the similitude theory,the physical model experiment was carried out to study the interaction between shaft lining,surrounding rock and pore water pressure.The shaft lining similar material is developed and the mechanical properties of the rock similar material are mastered.In the test,the horizontal ground pressure and pore water pressure were independently loaded.Based on the results of numerical simulation and physical model test,it can be concluded that the deformation of the shaft lining can be divided into three stages in the process of pore water pressure recovery:1.The tight fitting stage between the surrounding rock and the shaft lining.In this stage,the deformation of the shaft lining is less affected by the increase of pore water pressure,and the influence coefficient of pore water pressure is significantly less than the porosity of the surrounding rock.2.The partial separation stage between surrounding rock and shaft lining.The influence coefficient of pore water pressure increases continuously in this stage.The separation of shaft lining and surrounding rock develops from point to local area.At this stage,the shaft lining may be subjected to greater non-uniform forces.3.The complete separation stage between the shaft lining and surrounding rock,and the shaft lining bears full water pressure.In this stage,if the pore water pressure keeps increasing,the deformation of shaft lining increases rapidly until the shaft lining is destroyed.Finally,through the analysis of numerical calculation and physical simulation of the failure process of the shaft lining,it is believed that the high pressure pore water in the stable rock formation is the main cause of the shaft lining's failure.The mechanism is as follows: in the second stage,local separation occurs between the shaft lining and surrounding rock,the equivalent external water load on the local area significantly increases,and the shaft lining is subjected to uneven shear failure.In the third stage,the surrounding rock is completely separated from the shaft lining,and the shaft lining is rapidly deformed and destroyed under the action of full water pressure.Based on this,the prevention and control measures of high pressure pore water damage are put forward,such as increasing radial stiffness of shaft lining,increasing the adhesion force between the shaft lining and the surrounding rock,reducing the porosity of the interface etc.