Monitor And Analysis Of Pile Bracing Strut Support System During Whole Construction Process

The construction technology progress of pile support structure is simple,and the effect of anti-deformation of foundation pit of pile support structure is also excellent.Pile support structure is widely used in subway station and other foundation pit engineering which are narrow with a neat pit and a great depth of excavation.There are many studies on the deformation and stability of the foundation pit.However,there is little research on the distribution and evolution of internal force in the row pile,especially the work of the force system formed by the envelope and the main structure in supporting process.Its working mechanism is not yet clear and there is a possibility that the internal force of envelope structure will increase.It describes several existing analytical methods of pile supporting structure and summarizes the characteristics of the methods.:The incremental method,whole method and classical method are used to calculate the example project in this study.This study makes Zhengzhou Metro Line 1 Phase II Henan University of Technology Station foundation pit engineering as its object of study,has monitored the internal and displacement of pile supported by pile support structure construction in the whole construction process and analyzed the distribution and evolution of the internal force of the supporting row.ABAQUS finite element software is applied to build three-dimensional finite element model for example project to simulate the excavation process of the foundation pit and the construction process of the main structure of the station and verify the rationality of theoretical analysis methods by comparing with the actual engineering test monitoring data.And the main conclusions of this study are as follows:(1)The calculation results of the example project used elasticity increment method: The results show that the maximum bending moment of the pile is 956.22kN?m and the maximum bending value occurs when the third support is removed,which is larger than the maximum bending value 628.09kN?m when the excavation is to the bottom of the pit.The results show that the maximum horizontal displacement of the pile is 12.12 mm and the maximum value occurs when the third support is removed,which is larger than the maximum horizontal displacement 9.78 mm when the excavation is to the bottom of the pit.It is more dangerous to remove the lower support of the foundation pit than to support the excavation to the bottom of the pit.(2)Classical method and elasticity method(full method and incremental method)are employed to do the calculations and the calculated results are compared to measured data.In the passive earth pressure area below the excavation surface of the foundation pit,the three kinds of results are mainly positive moment.The maximum bending moment calculated by the classical method(1295.33kN?m)is much larger than the incremental method(308.20kN?m),Indicating that the classical method in the calculation of pile support structure of the foundation pit excavation surface below the embedded section is not ideal.The results show that the calculation results of elasticity increment method are more consistent with the actual situation and there is a certain security reserves with good economy and applicability.(3)The actual monitoring results show that the internal force of the pile is zero near the excavation surface of the foundation pit.That is the anti-bending point of the pile bending moment.And the zero point of the internal force of the pile will decrease with the excavation of the foundation pit.The position of the anti-bending point of the measured pile is about 2 meters higher than the theoretical calculation.(4)The actual monitoring results show that the maximum negative bending moment above the excavation surface of the foundation pit is-658.31kN?m.The absolute value of bending moment above the foundation excavation surface is about 1.5 to 2 times as much as the maximum value of the embedded section below the foundation excavation surface.And anti-bending point of the pile bending moment also appears near the excavation surface of the foundation pit.Therefore,the reinforcement of the pile can be made as variable cross section.(5)The results of the numerical simulation of the horizontal displacement of the pile and the calculation results of just incremental method are in good agreement with the change of the measured results.The numerical simulation results(8.82mm)are close to the calculation results of just incremental method(9.78mm),which are larger than the actual measured value(5.39mm).(6)The results of numerical simulation show that the bending moment of the row pile reach the maximum value of-822.50kN?m during the dismantling of steel support of main structure of station construction.The numerical simulation results are in good agreement with the actual monitoring results.It is suggested that the monitoring frequency can be reduced after removing the last steel support.