Study On Three-Dimensional Mechanical Behaviour Of Rock Mass On High-Steep Slope Under Bridge Load And Determination Of Bridge Foundation Position

The bridge foundation position on high-steep slope has great effect on stability of slope and bridge; it also affects the technical index and cost of bridge. With the rapid development of computer technology and geotechnical theory, the methods of bridge foundation position determining is an urgent need by engineering construction. In this paper, the mechanical behavior of rock mass of high-steep slope under load is analyzed systematically by three-dimensional numerical analysis and three-dimensional model test. The regularity of mechanical behavior of rock mass under load is indicated, and the comparison between 3-D and 2-D results is studied. The methods of bridge foundation position determining in three-dimensional conditions are put forward, and the present design theory is improved. The research work involves several aspects as follows:1. Large FEM analysis software ANSYS is applied to three-dimensional finite element analysis of the stress and deformation characters of rock mass under load. The influence factors of rock mass mechanical behavior are analyzed. The influence factors include slope angle, slope height, load intensity, bridge foundation position, bridge foundation size etc.2. To obtain the physical and mechanical parameters of transversely isotropic,numerical simulation test of typical equivalent unit is researched by RFPA. The mechanical behavior of bedded rock mass is studied with method of transverse isotropy, and the model for typical equivalent unit is used to simulate the bedded rock mass. The most advantageous/disadvantageous bedding angle and bedding plane angle are put forward, also the most advantageous/disadvantageous fracture orientation in the relaxed-tension rock mass.3. The special high slope is the slope with angle slope surface. The regularity of the most dangerous surface position of special high slope is analyzed. The influence factors include load intensity, bridge foundation size, bridge foundation position, top surface angle etc.4. The comparative analysis of mechanical behavior of rock mass of high steep slope under load between 2-D and 3-D is analyzed in detail. With the changing influencing factors, such as load intensity, bridge foundation position, unloading crack characters etc, the variation of two-dimensional calculation error is studied.5. The basic distance of bridge foundation on high steep slope is determined as follow:General high-steep slope:S_a=0．080649·α^0.9511·L^0．4306·[(1-0．8101^B)·q]^0.4868Special high-steep slope:S_a=0．339663·α^0．6701·L^0．4355·β^0.0286·[(1-0．8588^B)．q]^0．398While considered the rock mass quantity, the distance of bridge foundation on homogeneous slope is determined as S_f=S_a·k_sr.The distance of bridge foundation on stratification slope is determined as S_f=S_a·k_sφ·k_sr·k_ω.Concise tablesfor bridge foundation position on high-steep slope are compiled for the road engineering designers referencing and querying conveniently.6. The shape and position of 3-D critical slip surface of high-steep slope under load are analyzed based on the stress effect coefficient. The effects of influence factors on the shape and position of 3-D critical slip surface are further analyzed, and the variation of critical slip line of high-steep slope under load is summarized in this paper. The range of 3-D critical slip surface on high steep slope is determined as follow:General high-steep slope:Special high-steep slope:7. The model test is designed on the basis of numerical analysis results. The mechanical behavior and failure mode of rock mass of high-steep slope under load is simulating by the principle of model test. The comparison of the model test results and numerical analysis results is studied.8. Take Mashuihe river bridge project as an example, the bank slope stability is surveyed through field investigations firstly, the bridge foundation position is determined by method of this paper. The mechanical behavior of rock mass under load is analyzed detailedly. The results show that the slope is stable under load at the bridge foundation position determined by method of this paper, and the position of bridge foundation is rational. For verifying the rationality of the method determining bridge foundation of this paper, the displacement character and failure pattern of the slope are studied with 3-D geological model test, The results show that the displacements of the slope under load are small, which have no influence on the stability of the slope. Verification with several methods shows that the methods determining position of bridge foundation and the stability analysis method of jointed rock mass are rational.