Vertical Dynamic Characteristics Of Static Drill Rooted Nodular Pile And Its Application

As a new of pile foundation,static drill rooted nodular piles have been gradually promoted in coastal areas in recent years.The bearing capacity of the static drill rooted nodular pile under compression and tension have been investigated by scholars using a series of field tests,model tests and numeric simulations and lots of achievements have been conducted.However,there are few studies focused on the dynamic characteristics of this kind of pile foundation,which is hard to satisfy the engineering applications.In light of this,analytic methods,field tests and numeric simulations were employed to investigate the vertical dynamic characteristics of static drill rooted nodular piles,and the main research work and achievements are as follows:(1)In order to simulate the strong cohesiveness between the pile and inner cement soil,the surrounding fictitious soil pile model was proposed.The analytical solution in the frequency domain and semi-analysis in the time domain of pile top were derived by impedance function transfer method.A comparison between the solution presented in this paper and 3D finite element model was conducted to verify its reliability.Then a parameter study was conducted to investigate the influence of the pile and inner cement soil parameters on the complex impedance and velocity time domain response at pile top.At last,a field test was performed to investigate the influence of inner cement soil on velocity time domain response,and the key parameters in the calculation model were obtained by inversion.(2)Considering the interaction of the nodular pile and surrounding cement soil,a surrounding fictitious soil pile model was established in both vertical and radial inhomogeneous saturated soil.The analytical solution in the frequency domain and semi-analysis in the time domain of pile top were acquired by the impedance function transfer method and the shear complex stiffness transfer method,and the solution in this paper was verified by comparing with existing solutions.Then a parameter study was presented to investigate the influence of cement soil,surrounding soil and basement soil on the complex impedance and velocity time domain response at pile top.At last,a field test was also presented,and the key parameters in the calculation model were obtained.(3)Considering the influence of the welding seam on the dynamic response of assembly pile,an impedance transfer model in both vertical and radial inhomogeneous saturated soil was proposed.Compared with the measured curve,the existing model of the welding seam was amended.Then,a field test was carried out to investigate the influence of the interaction of pipe pile and cement soil on the velocity time domain response.Finally,a parameter study was presented to analyze the influence of the pile parameters and combining form of pipe and nodular piles on the complex impedance on pile top.(4)By fitting with curves in field tests,the 3D finite element models for pipe piles and nodular piles were established by software ABAQUS.Based on these models,at first,the influence of the size,distance of joints and the time of excitation on the time domain response of the pile were investigated,then the influence of the relative location of excitation and picking point on wave velocity and reflection amplitude were also studied,at last,field tests were performed on several kinds of nodular piles to research the relationship of wave velocity between measured and calculated curves,and some suggestions were carried out in low-strain integrity testing on nodular piles.(5)In order to investigate the influence of asymmetric defects of the nodular pile and the inhomogeneity of the cement soil on low-stain integrity testing,a 3D pile-soil finite element model was established by ABAQUS.By comparing with measured curves from field tests,the accuracy of the solution presented in this model was confirmed.Then some parameters including the length,width,relative location,filler's modulus of the defect and the time of excitation were studied.Finally,the inhomogeneity of the cement soil including size,depth and modulus were investigated to analyze their influence on the velocity time domain response.The above works developed the simulating of the pile-soil interaction by proposing the surrounding fictitious soil pile model,which is confirmed by field tests.The new results in this paper can be used in dynamic design and low-strain integrity testing for static drill rooted nodular piles.