Research On Coupling Theory And Test Of Stress-Damage-Seepage In Fractured Rock Masses And Its Engineering Application

Jointed rock mass is rich in a variety of internal defects such as micro-cracks, pores, fissures and other discontinuous macro-joints etc. The jointed rock mass usually possesses very complex mechanical properties and permeability characteristics because the existence of those defects will not only dramatically change the mechanical properties of the rock mass, but also seriously affect its permeability. On the one hand, fracture seepage water pressure will intensify the crack's opening, extension and the linking between each other, resulting in the change of stress field and damage field of rock mass; on the other hand, the stress level and the extension of rock mass fractures will lead the change of fractured rock permeability and the distribution of seepage field in rock mass. This kind of interaction described above is called the stress-damage-seepage coupling.In this paper, the process of the seepage in the stress-damage-seepage coupling state has been strongly researched. The studies reveal the law of fracture's initiation, extension and the linking of rock fissures, and explore the damage mechanism of the fractured rock in the stress-damage-seepage coupling state. The reasons of in-stabilized destruction of water-bearing fractured rock mass are explained as well. The proposed coupling theory has a great application prospect in the mining engineering, the dam construction and underwater tunnel project to prevent from water inrush.The achieved researches in this paper have been supported financially by the National Key Basic Research and Development 973 project (No.2007CB209402:Dynamic characteristics and controlling factors of the water-inrush in mine) and the related research project with SHAN DONG Gold Group CO LTD. This paper mainly includes the following research contents:(1) Research on theoretical analysis:The fracture mechanical properties of jointed rock mass under the seepage water pressure is studied by the combination of fracture mechanics and damage mechanics. For the open type of cracks, the law of crack's closure or initiation, the law of branch crack's propagation, and the penetration and fracture laws of rock bridges between the adjacent cracks are discussed under the pressure-shear stress and the presentation of water pressure. The theoretical basics on the rock fracture and damage under the coupling action of seepage water pressure and pressure-shear stress are established.(2) Research on mechanics test:A model is studied and designed to make the pre-crack cylindrical rock samples ((?)50mm×100mm) with a single crack or with a pair of cracks according to the real needs. A high-precision universal seepage experimental device is developed on the basis of 2000KN servo testing machine. The modified equipment can help to measure the rock permeability by using fixed-level method or flow method at high confining pressure and high pore water pressure conditions. The software PFC is used to simulate and analyze the failure process under pore water pressure of non-uniform medium such as rock mass containing holes, cracks and grain, etc. The accordance between the numerical results and the test results is studied. The full process of the crack's initiation, expansion, linking up and even the breakdown of the entire structure are displayed and observed graphically in the stress field and seepage field.(3) Research on constitutive relation:The damage evolution of fractured rock under the coupling effect of tensile, compressive and shear stress and seepage water pressure is studied. The damage constitutive equations of elasto-plastic fracture and the damage evolution equations for the jointed rock mass under the consideration of the osmotic water pressure are derived. The damage constitutive tensor equations of elasto-plastic fracture are established under the coupling action of seepage and stress.(4) Research on physical simulation:A test system to study mine water inrush mechanism and seepage characteristics in mining engineering is developed and designed. Based on the above derived constitutive equations, a three-dimensional fluid-structure interaction model for Shandong Sanshandao Gold Mine is constructed. Theoretical calculation and numerical simulation analysis of mine water inrush caused by under seabed mining-induced seepage in jointed rock mass. Barite powder, liquid paraffin, solid paraffin, sand and other materials are selected and mixed up with proper proportion to make a non-hydrophilic material, which is used to build the fluid-structure coupling similar physical model. The minimum safe mining roof thickness for Shandong Sanshandao Gold Mine is studied by the similar physical model test under the consideration of seepage-stress coupling. The results show that the developed test system has important theoretical significance and practical value both in micro-macro tests and theoretical studies of deep mining water inrush mechanism.(5) Research on numerical analysis:The seepage stress dual-medium coupling model is derived with both discrete medium and quasi-continuous medium. The theory, source files and application methods of Finite Element Program Generator (FEPG) are introduced in detail.According to the survey data of fractured joints, the Monte-Carlo simulation technique is used to generate fracture network, then the coordinates of control points for the crack plane are derived through the VB programming. The file of the coordinates is directly called by ANSYS. The whole fractured rock mass is divided into grids with ANSYS, then the meshed numerical model is imported into FLAC3D. The numerical procedures of the fluid-structure interaction analysis and calculation are developed by using FISH. The final numerical results are pulled out by TECPLOT software.(6) Research on engineering application:The interface program that transits SURPAC three-dimensional geological model into FLAC3D numerical model is developed, which makes the coupling of the SURPAC three-dimensional geological model and numerical simulation to be possible and help to build complex computational FLAC3D model quickly and easily. The use of FISH is then extended to stress-coupling calculations based on FLAC3D seepage in fractured rock. Post-processing is completed in the TECPLOT and SURFER, e.g. the FLAC3D results are input into TECPLOT software through the interface program FLACTOTECPLOT.dat. Moreover, the data can be switched to SURFER by small program developed in FISH, the visual contours of pore water pressure can be draw.