Study On Stability Of Narrow Foundation Pit In Deep Soft Soil Area

Most of China's coastal areas are soft soil areas.Due to the low shear strength of soft soils,the foundation pits in soft soil areas are prone to instability failure,including the overall stability of foundation pits and the stability of soil uplift at the bottom of the pit.The narrow foundation pits with significant effect on the size of foundation pits such as underground public pipe corridors and subways are designed according to the existing standard wide foundation pit design,and do not consider the favorable influence of the foundation pit width on stability,resulting in design theory and practice.Does not match,which leads to a certain waste of design and construction.This paper first summarizes the current research status and existing problems of the stability of deep foundation pits and the stability of pit bottom uplift in soft soil areas at home and abroad.For the characteristics of foundation pits in soft soil areas,the stability of foundation pits suitable for soft soil areas is given priority.The research ideas and the advantages and disadvantages of the design calculation method;then based on the Swedish strip method and the arc slip method in the limit equilibrium method,the influence of the foundation pit width is introduced,and the overall stability of the foundation pit considering the finite width limit condition is derived.The calculation formula of the stability and anti-lifting stability defines the wide pit and the narrow foundation pit according to different widths,and verifies the stability of the foundation pit established by the actual project of the foundation pit of the Lek station of the Guangzhou-Foshan line.Calculate the reasonable accuracy of the formula.Finally,the response law of different foundation pit width,support structure insertion ratio and soil properties to the overall stability and anti-lift stability of the foundation pit is analyzed.The following research results have been obtained:(1)The fundamental causes and laws of the stability and failure of the foundation pit and the stability of the foundation are discussed.The stability mechanism of the foundation pit is analyzed.The calculation methods of the overall stability and anti-lifting stability of different foundation pits and their basic conditions are compared and judged.At present,the applicable merits and demerits of various calculation formulas are preferred to select a reasonable calculation formula suitable for the stability of soft soil foundation pits.(2)Based on the Swedish strip method in the limit equilibrium method,the calculation theory and formula are analyzed.By analyzing the influence of the foundation pit width and the mutual coupling of the slip surface,the calculation of the overall stability safety factor suitable for the narrow foundation pit is deduced.Define the width boundary of wide and narrow foundation pits;And combine the actual engineering case,verify the reasonable accuracy by the current norm calculation formula and finite analysis software Midas GTS,and finally combine the pit width,the support structure insertion ratio,the soil layer properties The influence of different influencing factors on the overall stability response of narrow foundation pits in soft soil areas.(3)Based on the calculation formula of the anti-lifting stability of the arc sliding mode in the limit equilibrium method,by analyzing the influence of the foundation pit width and the mutual coupling of the slip surface,derivation of the formula for calculating the safety factor of anti-lifting stability suitable for narrow foundation pits.Combined with the actual engineering case,the accuracy is verified by the current normative formula and the finite analysis software Midas GTS.Finally,the response law of the anti-lifting stability of narrow foundation pits in soft soil areas is studied by combining different factors such as foundation pit width,support structure insertion ratio and soil properties.