Numerical Simulation Of Foundation Pit Deformation In Seasonal Frozen Soil Area

The deep winter foundation pit needs to consider the influence of soil frost heaving.When the horizontal frost heaving force is large,the supporting structure of the foundation pit will be deformed by horizontal displacement,base uplift and surface settlement.When the deformation is serious,the foundation pit will collapse.The stability of the foundation pit supporting structure poses a serious threat.This article takes a deep foundation pit project in Beijing as an example,sums up the theoretical analysis of the foundation pit frost heave theory and the supporting structure affected by the frost heave phenomenon by referring to the data and combining the research status at home and abroad,and elaborated the foundation pit deformation mechanism and monitoring method in detail.It is concluded that the main deformation forms of deep foundation pits are surface settlement,deformation of enclosure structure and base uplift,and the three deformations are related to each other.According to the actual measured data of this foundation pit project,the measured data is divided into excavation stage,The three different construction phases of frost heave phase and underground main construction are analyzed respectively for the three different construction phases.The model is established according to the actual situation of the foundation pit engineering,the temperature field of the model is calculated and the mechanism analysis of the freezing depth of the foundation pit is carried out.Then the temperature field is used as the initial temperature condition and imported into the model.Finally,the ABAQUS numerical simulation software is used to perform the thermodynamic coupling calculation.In this paper,the displacement field cloud map is used for data output and the data change curve is drawn to complete the comparative analysis.Then,the horizontal path is made at the depth of 2m behind the wall,and the horizontal and vertical stresses of the nodes on the path are extracted.The stress field cloud map is output according to the stress The distribution of the field cloud map draws the horizontal stress and vertical stress distribution curves of the foundation pit,completes the extraction output and deformation mechanism analysis of the maximum deformation value of the eastern and western slopes of the foundation pit in the model,and finally compares the simulated calculation values at the same point with the measured values.The reliability of the model is verified,and through the above analysis,the conclusion is as follows:(1)Based on the actual situation of the foundation pit project,the soil body was frozen in January and February and then thawed in March.The maximum freezing depth of the soil body during freezing was 3.6m and 3.2m,respectively.The soil body of the side wall of the foundation pit is subjected to negative temperature in both directions of the upper surface of the soil body and the side of the pile,and two-way freezing occurs,and the freezing depth increases significantly.(2)The soil around the foundation pit and the soil at the bottom of the pit are only affected by the negative temperature of the upper surface,and the freezing line and the surface of the soil layer are kept horizontal.At this time,the soil is frozen in one direction.The soil at the top and bottom of the pile side is cooled by the upper surface and the left side.The freezing line is curved and has a certain angle with the surface of the soil.At this time,the soil is frozen in two directions,and the freezing depth increases significantly.(3)Since the anchor is located 5-5.5m below the top of the pile,there is no effective constraint at the top,the upper part of the supporting pile is cantilevered,and the lower part is convexly deformed.The maximum deformation of the supporting pile is located at the top of the pile.Under the action of frost heave force,the displacement of the top of the pile in January is increased by 4.42 mm and 9.10 mm from the east and west slopes in March.The freezing effect has a significant effect on the displacement of the supporting pile The conclusion that the effect of displacement increases as the depth of pit excavation increases is more obvious.(4)Horizontal frost heave force is positively correlated with depth and increases with depth,and negatively correlated with ambient temperature.The lower the ambient temperature,the greater the frost heave force.Because the soil on the side of the pile is subjected to two-way freezing,the temperature contour is curved,and the horizontal freezing distance near the base decreases,so the frost heave force tends to decrease near the base.(5)The effect of frost heave of the soil on the supporting structure mainly occurs in the early stage of frost heave.As the amount of frost heave of the soil is basically stable,the horizontal displacement of the supporting structure tends to be stable.