Study On The Design Method And Anchored Mechanism Of Pressure-type Anchorage Cable In Weathered Rock

Based on the National Science Foundation of China (50874085) titled "anchor reinforcement mechanism and design method of pressure diffusion cable in slope reinforcement" and the Guangdong Provincial Science and Technology Plan Project (63123)with title of "key technologies research on instability prediction and disposal of expressway steep slope". The displacement and stress distribution characteristics of pressure-type anchorage cable are studied by means of theoretical analysis and numerical calculation in weathered rock, which takes the part of highslope project of Er-guang Expressway within Guangdong province (from Huaiji to Sanshui) as the research background. Then, the design method of length of prestressed anchorage cable in weathered rock is also studied. The main contents of this paper are as follows:1 The weathered rock is regarded as transversely isotropy rock, and its elastic modulus and shear modulus changed exponentially. The displacement and stress expressions in transverse isotropy elasticity rock are deduced in cylindrical coordinates and cartesian coordinate system. According to the mechanical properties of weathered rock, and the distribution characteristics of shearing stress in transversely isotropy elastic rock which is under the circular symmetric loads.The research shows that these two methods results are in good accordance with each other.2 The influence of elastic modulus, shear modulus, possion ration and cable diameter of weathered rock on shear stress distribution at the interface between greating aroud pressure-type cable bolt and soil was studied. The research results shows that:(1) The shear stress in the contacting surface of the anchor section mainly distributes near to the load-bearing plate regardless of decency rock or Isotropic rock. Compared to the same condition of decency rock. The shear stress of the anchor section increases(decreases) with the increase(decrease) of the elastic modulus and the rate of change of the shear stress is also increases with the depth, and their change have the same rate, if the elastic modulus of the decency rock changes with a certain function. (2) The shearing stress at anchor section is distributed more centralized. With the decrease of cable diameter, and vice versa. And the type of shearing stress distribution curve type at anchor section will not change with anchor cable diameter, but the curve characteristic valus do.(3) The shearing stress in the anchor section interface changes with the shear modulus perpendicular to the rock mass crosswise layer in transversely isotropic of weathered rock, based on the assumption that the anchor cable hole radius is to be invariable. Generally speaking, the bigger the shearing modulus is the more centralized the shearing stress distributes on the anchor peak. Otherwise, the shearing stress distributes more evenly.3 This paper discussed the design method of the anchored length of the pressure-type anchorage cable in the weathered rock based on the above results researched. The assumption in traditional anchor cable design method is analyzed firstly. And the deficiency of the assumption of shear stress distributed uniformly is pointed out. Then, a modified design method is proposed in the paper based on distribution characteristics of shear strength of the pressure-type anchorage cable in the weathered rock and the research results from home and abroad. The modified method is more a conform to practical engineering.