Dynamics Analysis And Experimental Research On The Rod-less Drilling Rig-Bored Pile Soil Interaction

Rod-less drilling rig has attracted more and more scholars and engineering and technical personnel of concern and research for its structure characteristics,but the study on the dynamic feature of the interaction between the rod-less drilling rig and soil is little.In the structure design,foundation is usually considered to be rigid,the rigid foundation assumption is reasonable for the working site to be the bedrock and the soild ground.But a large number of theoretical analysis and enginerring practice show that interaction between the structure and soil has a very important effect on the structure ‘s dynamic features under the condition of soft soil.The rod-less drilling rig and soil are researced as a whole in the paper,the influence of the dynamic stiffness of soil on the working chareacteristics of the rod-less drilling rig is considered.Through theoretical analysis and experimental study,the mechanism of dynamic interaction between structure and soil is studied,and also provided convenient,fast and suitable for practical enginerring calculation methods and guidance for the rod-less drilling rig,and as well provided a certain theoretical basis for structure's design considering struture soil interaction.On the basis of reading a lot of literitures at home and abroad,the research status of the structure soil interaction were summaried,and the structure soil interaction research methods were aslo summarized.The limitations and advantages and disadvantages were analyzed.Basic assumptions and computational analysis framework were proposed according to the interaction between the soil and the special structure of the rod-less drilling rig.Through the detailed analysis of the stress state in the process of auger bit drilling,the resistance force and resistance moment in the working process were got.And then the force in each direction of the support plate of the rod-less drilling rig was abbtained.In order to consider the effect of the pile hole on the stablity of the soil mass,the use of virtual of soil column to simulate the pile hole was first put forward in this thesis,and based on the generalized Mindlin method,the stability of the soil under the wall of the support plate was solved under the action of the prestress.On the basis of this,the dynamic equations of the rod-less drilling rig and soil system were established by using the lumped parameter method and the Lagrange method.The numerical manifold method was used for the characteristic of high precision in the same number of units.The thin plate and soil were modeled based on the zero order basis function and the first order basis function respectively.And then a 3D contact element with equal thickness was established to simulate the contact relationship between the thin plate and soil,the stiffness matrix of which was derived in detail based on the priciple of virtual displacement.The rayleigh damping to simulate the energy dissipation in the dynamic contact relationship between the thin plate and soil was introduced.The static and dynamic manifold contact procedure of the thin plate and soil were complied respectively.By comparing with experimental tests,the accuracy and the engineering practicability of the 3D contact element were verified.Considering the wave effect of soil in the vertical,transverse and torsional directions and its viscoelastic properties,and using the Voigt model to simulate the interaction of soil layers,the dynamic interaction model for rigid coupling of the support plate and soil was established according to the dynamic theory of soil.The analytical solutions of the vibration displacement in the vertical,transverse and torsional directions were obtained by using the Fourier and separate variable method.Analytical solution of the frequency response was obtained according to the displacement and stress continuity conditin of the contact surface.The semi analytical solution of the time domain response of the support plate under the action of half sine pulse excitation was got by using the inverse variation of Fourier and convolution theorem.By comparing with the field test results,the rationality of the basic hypothesis and the correctness of the derivation process were verified.The influence of different design and soil paremeters on the dynamic impedance of the support plate was analyzed detailly.The full scale prototype of the rod-less drilling rig was manufactured,and the field test research was carried out between it and the hole wall soil,by which a lot of useful experimental datas were obtained.The vibration displacements in vertical,transverse and torsional directions were got by solving each dynamic eqution.Then the correctness of the proposed dynamic model was verified.On the basis of this,the influences of the changes of drilling speed and feed rate on the dynamic characteristics were analyzed in detail.