Analysis Of Dynamic Influence Of The Traffic Load On Double-row Pile Supporting Structure

In recent years,with the rapid development of social economy,the shortage of urban land has become an increasingly prominent problem.The development focus of urban buildings gradually shift from the ground to the underground,which lead to both the scale and the depth of deep excavation are increasing.Considering the complex surround environment,the narrow construction site,the strength of the supporting structure for deep excavation is required to be very high.Among all the supporting forms,double row pile is a common supporting structure.It has been widely used due to its strong deformation and coordination capacity as well as its convenient construction.Many deep excavations are located in urban traffic intensive areas,and some of them are even adjacent to the main traffic roads.Compared with static load,the influence of traffic load on the supporting structure of deep excavation is more complicated.However,in practice,the influence of dynamic characteristics of traffic load is not fully considered because the influence is usually assessed by static load or equivalent static load multiplied by safety factor.Existing studies on traffic load show that dynamic load frequency,amplitude and vehicle load can all exert certain effects on the supporting structures.Present research adopted indoor model tests and numerical analysis to systematically study the influence of traffic load on the internal force and deformation of double-row pile supporting structure.Main research contents are as follows:(1)Literature review and analysis were done to learn the research basis and present progress of previous studies on the influence of traffic load on supporting structures of deep excavation through reading literatures on traffic load,double-row pile supporting structure and influence of traffic load on these structures.This part provided guidance for the selection of traffic load models,the formulation of indoor model test schemes and the PLAXIS 3D finite element analysis.(2)Indoor tests of the effects of dynamic loads on double-row pile supporting structure at different excavation depths were carried out.All tests were designed reasonably based on the similarity principle of model test.The size of the model box is:3m×2m×2m(length×width×height);PVC piles were used to work as double-row piles.The length of the piles was 1.5m and the diameter was 32mm;the connecting beam i s made of wooden boards with a size of 200cm×18cm× 1.5cm(length×width× height);The loading plate is a steel plate with a size of 150cm × 110cm×2cm(length×width×height),and the loading plate is 20cm away from the rear row pile;silty soil was compacted in layers which was 1.6m in thickness.The experiment didn't start until the filling standing for a week.Tests in different excavation depths including 15cm,30cm,45cm and 60cm were done to study the changing law of internal force and displacement of the supporting structure with the change of depths.(3)Model tests on the influence of dynamic load on double-row pile supporting structure were carried out.To examine the influence of different load values,load frequencies,load amplitudes and load wave forms on the supporting structure,load values of 10kN,12kN,14kN and 16kN were put into tests;load frequencies of 2Hz,4Hz,5Hz were chose;load amplitude of 1kN,2kN,3kN were selected;load wave forms of sine waves,triangle waves and square waves were tested.(4)Numerical analysis was studied based on indoor model tests.Soil hardening model was adopted in the finite element soil model where equivalent board were used to simulate the front and rear rows of pile and the connecting beams.Influences of different excavation depths,median values,frequencies and amplitudes of dynamic loads on the double-row pile supporting structure were tested to compare with that of indoor model tests.In addition,influences of different dynamic load locations were also examined.(5)Numerical analysis based on project cases was conducted.First,the results of numerical analysis were compared with data tested in field experiments to verify the analysis results.The influence of different excavation depths,median values,frequencies and amplitudes of dynamic loads on the double-row pile supporting structure were examined by the finite element model which is more practically fitted.which is more suitable for engineering practice.The conclusions draw from this research conducted to examine the influence of dynamic load on the double-row pile supporting structure by comparing indoor model tests and numerical analysis can enrich the engineering design theory on the double-row pile supporting structure of deep excavation and provide reference to the design of double-row pile supporting structures when traffic load is taken into considered.