| Rock-socketed piles are common and widely used.They are used as deep foundations in many engineering fields such as industrial and civil buildings,ports,power transmission,and bridges.It has high utilization value and great development potential,but the standard design is conservative and the research is not perfect.Relying on the project of"Research on the Bearing Characteristics and Design Methods of Rock-Socketed Piles in Mountainous Power Transmission Lines",this thesis takes two layers of soft rock overlying and equal-diameter rock-socketed piles as the research object,uses finite difference FLAC3D numerical simulation and uses secondary development of contact surface plastic shear The method of strain softening constitutive model,combined with the results of a certain literature field test,carried out research on the side friction resistance of each stage under uplift conditions,and discussed the correctness of the numerical simulation model,the applicability of the softening constitutive model,and the limit of lateral resistance Influencing factors and laws,as well as the mechanism of side friction.The main work and research results of the thesis are as follows:（1）The plastic shear strain softening constitutive model simulating the pile-rock interface was written in C++language,which was embedded into FLAC3D finite difference software,and the numerical simulation of rock-socketed pile pulling up was carried out with a field test data.The results show that the curves of pile top load displacement,pile axial force and pile lateral friction output by numerical calculation are basically the same as the field test results,and the error of ultimate bearing capacity is less than 5%,and the softening phenomenon in field test can be simulated effectively.（2）The determination method of limit side resistance and the main influencing factors were explored.The control single variable method was used to develop the numerical simulation test program and carry out the numerical simulation work,and the influence law of each factor was analyzed.The results show that the factors that influence the ultimate lateral resistance of rock-socketed piles in soft rock are rock strength,rock-socketed depth and pile diameter.The coefficient of the traditional empirical formula between the ultimate side resistance and the uniaxial compressive strength of rock is 0.4233.With the increase of rock-socketed depth,the ultimate resistance increases first and then decreases,and the optimal diameters ratio of rock-socketed depth is 5.5.With the increase of pile diameter,the ultimate lateral resistance of silty clay and strongly weathered section decreases,while the ultimate lateral resistance of moderately weathered section increases first and then decreases,and the optimal pile runoff value is 1.2 m.（3）Taking a typical example as the research object,the exertion mechanism of the lateral resistance of rock-socketed piles in soft rock is studied from four aspects:axial force and deformation of pile,stress and deformation and failure characteristics of rock and soil mass,normal and tangential behavior of contact surface,and distribution and variation of lateral friction resistance.In conclusion,the pile axial force,pile lateral friction resistance and rock mass stress generally increase first and then decrease with the uplift load.The pull-up load is transferred from top to bottom,and the lateral friction is also exerted from top to bottom,but the softening phenomenon is aggravated from top to bottom.The deformation of soil is the largest,resulting in tensile failure,and the shear failure of rock mass in the middle and bottom of pile side.Because of the circumferential strain,the friction resistance at the top and bottom of the pile side is low.The normal stress and shear stress of the contact surface are positive feedback to each other.The lower end of the pile side is 1 meter,and the normal stress of the contact surface increases sharply and there is "softening". |
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