Research On Space Effect Of Pile-internal Support Support System

With the rapid development of urbanization in China,the surrounding environment of deep foundation pit engineering is becoming increasingly complex,the safety problem that should be considered in the construction of deep foundation pit transits from the safety of foundation pit itself to not only the safety problem of foundation pit itself,but also whether the construction process of deep foundation pit will affect the surrounding buildings or whether the surrounding existing buildings will affect the safety construction of deep foundation pit engineering,this also increases the requirements for the stability of deep foundation pit support engineering.Based on a deep foundation pit excavation and support project,on the premise that the geological conditions of the construction site,the surrounding environment and the interaction between the construction site and the adjacent existing facilities have been identified,the horizontal displacement monitoring at the top of the pile,the vertical displacement monitoring at the top of the pile,the deep horizontal displacement monitoring of the soil,the vertical displacement monitoring of the column,the internal force monitoring of the support,the internal force monitoring of the pile,the settlement monitoring of the surface and the surrounding roads,the settlement monitoring of the surrounding buildings,the groundwater level monitoring and the inclination monitoring of the building are carried out,five monitoring data,including the horizontal displacement of crown beam top,the vertical displacement of crown beam top,the settlement of column,the change of groundwater level and the change of reinforcement stress,were collected and analyzed briefly;Then,according to the actual situation of the project,the model is simplified and assumed.According to the geological conditions of the study area and the relevant literature,the constitutive model and the analysis range are determined various parameters required to establish the model and the equivalent stiffness method are used to convert the row piles,the finite element software Midas GTS NX is used to establish the corresponding model.According to the actual construction process of pile foundation construction,earthwork excavation and support system construction,five excavation conditions of the model are set up,and the column pile constraints,boundary constraints and self-weight are added;Finally,the rationality of the model is verified by comparing the field observation data with the model calculation results,and the possible problems in the excavation process are predicted to a certain extent by the calculation results.This paper draws the following conclusions :(1)The surrounding environment of this study area is very complex.Some soil layers may have liquefaction and seismic subsidence,and the self-stability of the main soil layer that constitutes the sidewall of the foundation pit is poor.Therefore,the vertical excavation cannot be adopted,and the sidewall must be supported by slope excavation or reliable supporting structure.(2)In the process of foundation pit excavation,the horizontal displacement of crown beam top and the change of groundwater level are within the controllable range,and the vertical displacement of crown beam top and the vertical displacement of column pile are partially more than their deformation warning values,which need to cause attention and take corresponding control measures.(3)There is a certain difference between the simulated value and the measured value,but the difference value is relatively small,and the deformation law of the two is similar to a certain extent.Therefore,the established vertical Mohr-Coulomb constitutive model can reflect the actual deformation law of the foundation pit to a certain extent,and can provide reference for the safe construction of the foundation pit.(4)The deformation of the retaining structure is mainly concentrated in the middle and lower part of the four edges of the foundation pit composed of diaphragm walls,and the maximum displacement is 32.74 mm.In the process of foundation pit excavation,the displacement of foundation pit internal support system will exceed the deformation warning value,the maximum deformation is 119.43 mm;The uplift amount of soil inside the foundation pit increases with the increase of the distance from the retaining structure,and the maximum uplift amount is 136.86 mm.The construction of column piles inside the foundation pit can prevent the uplift of soil inside the foundation pit to a certain extent,and this trend becomes more obvious with the increase of excavation depth.