Study On Hydro-Mechanical Coupling Of Fractured Rock Mass Based On DDA

With the rapid development of rock engineering at home and abroad, more and more energy, transportation, mining, water conservancy construction and national defense have been built in rock area at present, whose engineering design, construction, stability evaluation and rock reinforcement etc depend directly on the characteristics such as strength, deformation, permeability and failure law of rock.The groundwater movement in fractured rock mass is of discontinuity, heterogeneity and anisotropy due to its randomness, fuzziness and corresponding complex geo-mechanical environment. While the permeability of rock fracture is significantly affected by stress environment as the main permeability channel in rock It is well known that engineering excavation causes the distribution of internal stress field and deformation or damage of rock. However, rock mass deformation or destruction has changed the permeability of groundwater in rock. Accordingly, changes of permeability in rock further transform the stress field of rock mass, which reflects the coupling relationship between them. The interaction between stress field and seepage field influences and determines the stability of engineering body, the normal operation of the project, the safety of project activities and high low construction costs. Major crash at home and abroad shows the importance of studying the interaction among force of human engineering, in-situ stress and groundwater seepage force.Hydro-mechanical coupling of fractured rock mass has been not only a subject that many scholars are challenging, but also a hot issue in mechanical study. Based on the discontinuous deformation analysis, the paper has studied systematically and deeply the coupling mechanism between seepage and stress field of fractured rock mass with theoretical analysis, numerical simulation and experimental validation. The work in the present paper can be summarized in the following.1. From the aspects of the coupling of seepage and stress of fractured rock mass, the geological and permeable characteristics of fractured rock mass have been quantitatively analyzed. Hydro-mechanical coupling properties under the circumstances of normal stress, shear stress as well as three-dimension (3D) complex stress state are analyzed, which lay firm foundations for the further coupling study between seepage and stress field. 2. The paper reviews some of the basic concepts of the DDA method. Then, corresponding improved measures are presented in the following aiming at disadvantages of the original procedure code. At first, the displacement function is improved by using higher order block element corresponding to non-strain field, which provide a theoretical basis for enhancing the accuracy of DDA calculations. Then, contacts between blocks have been modeled using an augmented Lagrange multiplier method instead of the penalty method to prevent interpenetration of the blocks. Finally, the correctness of this program has been demonstrated through the classic example.3. The seepage matrix of fracture network flow has been solved by using mathematical model of two-dimensional fracture network seepage. The validity of the method has been verified by comparing with the experiment, which lays theoretical foundations for the further coupling study between seepage and stress field. And the seepage law of discrete media is studied through numerical analysis. It is found that main fracture plays a role in controlling the distribution of seepage field. The seepage free surface of fracture network is solved by using the modified initial flow method. Then, the reliability of the program is verified by comparing the numerical and analytical solution.4. Based on the mechanical theory of DDA and fluid flow analysis of fractured network, hydro-mechanical coupling analysis model is established in the paper. Moreover, the paper has studied the effect of the deformation of fractured rock mass on the groundwater flow, its failure characteristics of the degeneration under the action of seepage and stress field. At the same time, hydraulic aperture and fluid pressure in hydro-mechanical coupling are formulated. Finally, hydro-mechanical coupling with DDA method proposed in this paper is demonstrated to be reliable and effective through the classic model.5. The full length rockbolt and excavation have been implemented in DDA method. The simulation results indicate that the modified discontinuous deformation analysis (DDA) method is effective for the reinforcement of tunnel. Furthermore, the change of axial force is consistent with the deformation of tunnel, which proves that the modified discontinuous deformation analysis (DDA) method is reasonable and correct. It is found that, in general, the anchoring effect of the full lenth rockbolt is better than that of the point anchoring rockbolt.