Study On Anchorage Mechanism Of Dispersed Pressure Anchor Cable And Relevant Technology

Rock or soil anchoring technology has extensive application in practical engineering, especially since the ninties of the20century, dispersed pressure anchor cable began its application and development in some engineerings of China. Although some study work on anchorage mechanism has been done, the recognized results have not yet obtained, which affected the further application of the anchor cable. Combined with the extensive attention the hot and difficult issues of the engineering profession, the anchorage mechanism of the pressure dispersed anchor cable has been studied by theoretical analysis, geomechanical model test and numerical simulation, the design calculation method has been studied and developed on the anchorage mechanism basis. The main achievements are as follows:(1) The features of mechanics and deformation of the cable system have been revealed.The pressure dispersed anchor cable transformes the tension load into the pressure of grouting body of the anchor cable unit through the bearing body, anchor cable system exhibits three stress characteristics:one, the radial expansion deformation of the grouting body will occur after the grouting body under pressure, and the hole wall of rock and soil will constrain the radial deformation to exert radial pressure on the grouting body, the radial constraint effect producing the friction resistance along the pulp-rock interface is the very important reason of the anchoring force improved; secondly, if the shear strength of the pulp-rock interface is insufficient or the anchoring segment length is shorter, and the load of each anchor cable unit is very bigger, the pressure on each anchor cable unit will influence each other in the transmission process, the stress superposition phenomenon will occur between the anchor units; thirdly, the tensile stress near the bearing body appears, when the tension and compression deformation of the grouting body deformation of the near units does not coordinate with each other, the grouting body will crack.(2) A set of new model test equipment has been studied and developed.The dispersed pressure anchor cable apply the tension load on the grouting body of each anchor cable unit in the form of pressure, the characteristics of the mechanics and deformation of each anchorage unit and the influence on each other are the important content of mechanism of anchorage. A set of new geomechanical model test apparatus and test method have been studied and developed, and the tension test can adopt the grading cyclic loading method in each bearing unit of the dispersed pressure anchor cable to study the mechanical characteristics of each anchorage unit and load transfer mechanism.(3) The calculation formula of the increased value of the anchoring force based on the radial expansion deformation of the grouting body has been studied and developed.According to the radial expansion deformation characteristics of the grouting body under pressure, the distribution laws of negative exponential function changes of the axial stress and shear stress of the anchor cable have been put forward, the maximum value of the axial stress or shear stress bearing is located at the bearing body, and reduced gradually with the grouting body length increased. Compared with tensile type anchor cable, the anchorage force of the dispersed pressure anchor cable increased because of the radial expansion deformation of the grouting body can be affected by radial confinement pressure while frictional resistance produced, the increased value of shear stress in accordance with the calculation formula τa-Pmtanφl(3S).(4) The length of anchorage segment of anchor cable unit has been studied and developed.The constraint on the radial expansion deformation of grouting body by the hard rock is very larger, the pressure of each anchor cable unit would not be affected in the transmission process, and the stress superposition phenomenon won’t produce also, the constraint on the radial expansion deformation of grouting body by the Soft rock is smaller, the stress between the anchor unit will influence each other, which is prone to stress superposition phenomenon. According the increased value φa of the shear intensity of grouting-rock interface and the inherent cohesion C between the grouting body and rock soil, these two part resistance of the cable unit all play out, and consider the structure of the safety coefficient Fs, under the condition of the stress superposition phenomenon eliminated,the calculation formula of the length of anchoring segment of unit la can be replaced by the following formula la=FsP/πD(τa+c).(5) The calculation method of grouting body based on compression deformation has been put forward.When the bearing body of the anchor cable element connects two elements which are before and after the bearing body, as applying the tension load on the bearing body of the anchor cable element through the bearing body, a pulling force is also applied on the the bottom of the hole or the anchor cable unit.when the grouting body deformation of the near units does not coordinate with each other, the grouting body which is contact with the bearing body will cause tensile crack and affect the the anchorage effect. Based on the feature of the tensile and compressive deformation, the deformation degree of the grouting body calculated by the grouting compressive displacement to has been put forward, the formula for the calculation is s0=S0=σ0la/3e≤[S0], and the theory reference to control the deformation and cracking of the grouting body has been provided.(6) The improvement suggestions about the existing design method have been proposed.This dissertation achieved good results about the anchorage mechanism of the pressure dispersed anchor cable, the reason of the anchorage force improvement, the transmission of the pressure of the anchor cable units, the stress and the deformation of the grouting body at the bearing body etc. The existing design methods have deficiencies in these aspects. On the basis of detailed analysis of the existing design methods in the foundation, the suggestions of improvement and supplement has been proposed.