Research On Calculation Method Of Lateral Bearing Capacity Of Large Diameter Rock-socketed Pile Based On Deformation Control

Rock socketed pile foundation has the characteristics of high loading capacity,small pile group effect and strong deformation resistance.These characteristics make rock socketed pile foundation widely used in high-rise buildings,long-span bridges,ports and offshore engineering.The lateral load from upper structures could be transferred to bedrock via rock-socketed pile based on the interaction between the pile and the surrounding rock mass.The interaction between the pile and the bedrock under lateral load is of great significance in engineering practice.The research on the calculation method of lateral bearing capacity of rock socketed pile is a very important.However,due to the complex non-linearity and anisotropy of rock mass,as well as the large bearing capacity of rock socketed piles and the difficulty of field tests,there are few studies published about the rock-socketed piles under lateral loading are made.The numerical simulation,theoretical method and laboratory test are enployed to study the calculation method of lateral lateral capacity of large-diameter rock-socketed piles in this thesis.The nonlinear nature of rock mass strength and the influence of joint spacing are revealed.A new indoor model test method is proposed to simulate the lateral bearing capacity of rock socketed piles in jointed rock mass.The stress distribution mode around the pile and the initial stiffness of p-y curve are studied.And the calculation method of ultimate resistance of rock mass per unit length is put forward.The p-y curve is established and a finite difference method is proposed.The main contents and research results of this paper are as follows:(1)The rock mass strength is summarized and analyzed.The applicable scale and influencing factors of the rock mass failure criterion are studied,and the influence of the joint spacing on the rock mass strength is analyzed.The influence of confining pressure on rock mass strength is investigated.The rock brittle-ductile transition under different confining pressure is studied.The strength of jointed rock mass is related to block size and joint filled.The strength of rock mass is affected by the rotation and relative slip of rock blocks.Based on Hoek-Brown strength,the formulas of the cohesion and friction of rock mass related to confining pressure are derived.The natural parameter m_i of rock mass,the uniaxial compressive strength of rock and confining pressure is considered for the cohesion and friction angle.(2)The complex joints are simplified into three group joints which perpendicularwith each other.The joints divide the rock mass into rock blocks with side length of S.And the artificial concrete block is used to simulate the rock blocks.The blocks are assembled into jointed rock masses in a specific way;Compressive strength test and existing methods are used to calculate blocks and rock mass parameters.Four sets of model tests with different joint spacing were carried out.The influence of joint spacing on the lateral bearing capacity of the pile,the initial stiffness of p-y curve and the lateral deformance of the pile is studied.(3)The stress distribution mode around the pile is researched.The numerical analysis method is employed to study the distribution of normal stress and shear stress around the pile.The empirical formulas for the distribution functions of normal stress and shear stress around the pile are proposed.The lateral displacement of the pile and the initial stiffness of the p-y curve are studied.The research is carried out from the aspects of rock mass modulus,rock uniaxial compressive strength,GSI,m_i,poisson’s ratio of rock mass and pile size.An empirical formula for the initial stiffness of p-y curve is proposed.(4)Based on the failure modes of shallow and deep rock,combined with the cohesion and angle of friction of rock mass and the stress distribution mode around the pile,the ultimate resistance per unit length of lateral bearing capacity of deep and shallow rock socketed piles is derived.Combined with the initial stiffness,the hyperbolic p-y curve is established.(5)The strain wedge model of lateral bearing capacity of rock socketed piles is derived from four aspects:nonlinear displacement assumption,cohesion and friction angle related to confining pressure,stress level and pile side friction.The stress level of strain wedge considers both cohesion and friction angle of rock mass.According to the distribution function of shear stress around the pile,the relationship between pile side friction and pile lateral displacement is derived.The p-y curve based on the strain wedge model is obtained by combining the lateral normal stress and lateral friction in front of the pile.(6)According to the research in this paper,the calculation method of lateral bearing capacity of rock socketed pile is put forward,the finite difference solution method of pile deflection differential equation is established,and a finite difference program is compiled by MATLAB to calculate the pile deflection differential equation established by p-y curve.