Study On The Mechanical Properties Of Karst Rock Mass In Shanghai To Kuming High-speed Railway Dushan Tunnel And Its Application

Karst rock is a non-homogeneous, non-continuous and anisotropy mechanics medium, the mechanics characteristics of which is affected not only by strata combination and structural plane, but the different levels of karst, morphology and location of cave. In order to accurately reflect mechanical properties of rock mass, such as deformation and strength, as well as the relationship and law with cave size, location and shape, the paper take the engineering rock mass of Dushan tunnel which belongs to Guizhou section of the Shanghai Kunming high-speed railway as subject to analyses the mechanical properties of karst rock combining the method of indoor test, field bearing plate test, direct shear test with numerical simulation. The major research contents are as followed:1) Based on the actual situation of the Dushan tunnel, by analyzing engineering geological data and field geological survey, the basic conditions for the development of karst, the controlling factors of karst in deep buried tunnel and the characteristics of karst are analyzed.2) According to the statistical analysis of karst cave revealed by drilling in Dushan tunnel and combining with some other factors like potential hazard points where tunnel crosses, the skeleton and distribution of karst pipeline system, the development scale and depth of large karst reservoir water structure, fill, runoff and drainage system of groundwater system in tunnel site area, tunnel design and tunnel location features, tunnel is divided as form of karst development degree into four levels.3) Through indoor tests, the basic mechanical parameters of karst rock are obtained. Karst rock pressure P-W deformation curves are got through bearing plate test, thus the deformation characteristic of karst rock mass can be inferred as well as the deformation modulus and elastic modulus of karst rock mass. Through drilling hole in the rock mass, the influence of karst rate changing on the test result of bearing plate test can be inferred. Through the test results, it can be inferred that karst rock mass is more likely plastic elastic medium. Moreover, deformation modulus and elastic modulus of rock mass decreases with the increasing of karst rate. Through direct shear test, the shear strength indexes of rock mass in different karst development degree are obtained.4) Based on the field test, the numerical simulation of bearing plate deformation test and rock shear test using FLAC3D software is carried out to obtain the deformation parameters and strength parameters of the karst rock mass and their relationship with karst rate. By using RFPA2D software to study on the mechanical properties of karst rock mass under uniaxial loading, different forms and positions of cave and different karst rate of rock are stimulated to analyze the difference of stress distribution, deformation and failure among different kinds of situation. The mechanical properties of the karst rock mass are studied macroscopically and microscopically. It is applied in the Dushan tunnel rock mechanics characteristic research, thus the mechanical properties of Dushan tunnel karst rock in different karst rate have been got.The mechanical properties of the karst rock mass is applied to the karst water inrush disaster research. By stimulating a certain size cave ahead of tunnel face and analyzing the effect to the deformation of surrounding rock. Thus deformation characteristics of tunnel rock mass near cave in different karst rate are revealed and it can be a reference to determine the safe thickness of the rock.