Response Analysis Of Cantilever Retaining Structure With The Influence Of Traffic Load

With the rapid development of the economy,the city's focus has shifted from the increasingly narrow space above the ground to the underground space.During the construction of many super high-rise buildings and subways,the deep foundation pits are in densely populated areas,and some are even adjacent to the main roads of traffic.Due to the vibration of the road and the unevenness of the road surface,the traffic load will be applied to the road surface in the form of waves.The long-term vibration load will have a very adverse effect on the stability of the foundation pit.In the actual project,the safety factor method is generally adopted when considering the influence of traffic load on the foundation pit retaining structure,that is,the equivalent static load is multiplied by the dynamic load coefficient,but the dynamic load coefficient is generally estimated by engineering experience and does not have accuracy.At the same time,with the unevenness of the road surface and the speed of the road,the dynamic load coefficient will also change accordingly.Therefore,it is meaningful to carry out the response analysis of the foundation pit retaining structure under different traffic loads.In this paper,large-scale indoor model test and PLAXIS 3D finite element software simulation analysis are carried out to study the influence of traffic load on the retaining structure of foundation pit.Based on the previous forms and simplified forms of traffic load,sinusoidal loads are used to simulate traffic loads.On this basis,the indoor model test scheme is designed.The test model box size is 3m×2m×2m(length×width×height),and the foundation pit retaining form adopts cantilever row pile structure,and the foundation pit is filled with silt.The height of the earth is 1.6m.In order to simulate the excavation process,a total of six layers of excavation are carried out.When the excavation is carried out to the design condition,a static load is applied to the top surface of the foundation pit,and after it is stabilized,a sinusoidal load is applied,and the dynamic load is sequentially changed at the two excavation depths.The frequency,amplitude,waveform and dead load are used to measure the pile strain(bending moment)and the pile side earth pressure under different working conditions.The parameters of the PLAXIS finite element simulation are determined based on the similarity ratio 1:20 on the basis of the indoor model test.The frequency,amplitude and dead load are increased from the three contrast conditions in the model test to the six contrast conditions,and the curve is performed.Fitting and recording the pile strain(bending moment)and the pile side earth pressure under different working conditions.Through the indoor model test,the following conclusions are drawn:(1)The excavation depth and its corresponding pile bending moment and the dynamic load coefficient of the pile side soil pressure show a linear proportional relationship.The larger the excavation depth,the larger the corresponding dynamic load coefficient.(2)The change of dynamic load frequency has little effect on the dynamic moment coefficient of pile bending moment and pile side earth pressure.When the frequency increases by 1 Hz,its corresponding dynamic load coefficient increases by about 0.01.(3)The change of dynamic load amplitude has a great influence on the dynamic moment coefficient of pile bending moment and pile side earth pressure.When the amplitude increases by 1kN(1.6kPa),its corresponding dynamic load coefficient increases by about 0.1.(4)The change of dynamic load waveform has little influence on the dynamic moment coefficient of pile bending moment and pile side earth pressure.The influence of waveform on dynamic load coefficient is consistent with the effective value of wave,and the dynamic load coefficient of wave load below the same parameter is the largest.The sinusoidal load is second,and the triangular wave load is the smallest.(5)The change of dynamic load dead load has great influence on the dynamic moment coefficient of pile bending moment and pile side earth pressure,the dynamic load coefficient will decrease with the increase of dead load,and the dynamic load coefficient and amplitude and dead load The expression can be fitted between the expressions.The following conclusions are obtained by PLAXIS 3D finite element software simulation:(1)The excavation depth is linearly proportional to the corresponding pile bending moment and the dynamic load coefficient of the pile side soil pressure.The corresponding excavation depth is corresponding to the dynamic load coefficient.The bigger.(2)For each 1 Hz increase in the frequency of the dynamic load,the corresponding dynamic load factor is increased by about 0.01.(3)For each 1kPa increase in the amplitude of the dynamic load,the corresponding dynamic load factor is increased by approximately 0.05.(4)The dynamic load dead load and its corresponding dynamic load coefficient show a linear inverse relationship,but with the increase of dead load,the corresponding dynamic load coefficient decreases to a lesser extent.The conclusions can provide reference for the stability analysis of the cantilever retaining structure under the action of traffic load,and can provide guidance for the selection of the dynamic load factor value when taking into account the action of traffic load in actual engineering.