Study On Mechanical Behaviour Of Rock Mass On High-Steep Slope Under 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. The mechanical behavior characteristics of rock mass of slope under load are the basis of bridge foundation position determining and slope stability analysis. In this paper, the mechanical behavior characteristics of rock mass of high steep slope under load are analyzed systematically. The regularity of mechanical behavior characteristics of rock mass under load is indicated. The methods of bridge foundation position determining and stability analysis of slope based on mechanical behavior of rock mass are put forward. And the present design theory is improved.For numerical analyzing conveniently, a FEM program suitable to mechanical behavior analysis of rock mass of high-steep slope and discontinuity surface contact analysis is developed.To rock mass slope treated with homogeneous material, the stress and deformation characteristics of rock mass under load are analyzed in detail. The influence factors of rock mass mechanical behavior characteristics are analyzed. The influence factors include slope angle, slope height, load intensity, bridge foundation position, bridge width, slope type etc. The regularities of stress influence range of rock mass, rock mass stress of slope surface, bridge foundation displacement, additional stress of foundation base are denoted.To bedded rock mass, the mechanical behavior characteristics under load are studied with method of transverse isotropy. The main factors which influence the mechanical behavior of bedded rock mass include bedding angle and mechanical parameters. The influence regularities of bedding angle and mechanical parameters on mechanical behavior of bedded rock mass are denoted. The result shows that the most disadvantageous bedding angle is between 20° and 30°, and the difference of mechanical parameters indicates the influence degree of bedding angle on rock mass stress.The influence of relaxed crack of high steep slope on mechanical behavior characteristics of rock mass is studied. Especially the influences of the height of relaxed crack, the relative position between relaxed crack and bridge foundation on mechanical behavior of rock mass are analyzed in detail. The results show that if the height of relaxed crack is out range of the stress diffusion angle, the influence of relaxed crack can be ignored. The preferredposition of bridge foundation is behind of the relaxed crack. While the bridge foundation set before the relaxed crack, the both influence of slope surface and relaxed crack should be taken into account.The mechanical behavior characteristics of long-through structural plane on high steep slope are analyzed in detail. The stability of long-through structural plane is determined according to the contact stress of structural plane. The methods of stability analysis of jointed rock mass and determining method of potential failure surface of slope under load are put forward.The safe influence coefficient of stress is determined according to the relation between rock mass strength and influence coefficient of stress. According to the regularities of rock mass mechanical behavior characteristics of different influence factors, the basic distance of bridge foundation on high-steep slope is determined as follow:Sa=0.0309591a14823[(l-0.8655B)#6965While considered the rock mass quantity, the distance of bridge foundation on homogeneous slope is determined as S/=Sa-ksr. The distance of bridge foundation on stratification slope is determined as S/=Sa-ks^-ksr. The methods determining the bridge foundation position in special situation are put forward, such as polygonal line slope, relaxed crack slope, long-through structural plane slope and so on.Take Beipanjiang river bridge project as an example, the bridge foundation position is determined by method of this paper. The mechanical behavior characteristics of rock mass under load are analyzed in detail. The collapse stability and slip stability of jointed rock mass are analyzed. 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 model test, DEM and field monitoring. The results prove that the methods determining position of bridge foundation and the stability analysis method of jointed rock mass in this paper are rational.The bridge foundation position determining method put forward in this paper supports by abundant and clear theory. Applying this method to engineering practices, the economical value will be remarkable.