Stability Analysis Of Deep Foundation Pit In Linjiang Weak Formation

With the development of the foundation pit project,the foundation pit project has been applied to various geological conditions,the Linjiang soft foundation pit has also come along with it.Due to the large number of factors that affect the stability of deep foundation pits in Linjiang soft formation,many Scholars are more complicated to study.Based on the deep pit excavation project in Ciqikou,Chongqing,this paper investigates the stability of deep excavation in Linjiang Soft Foundation.Firstly,the dissertation introduces the two major forms of instability in foundation pits,analyzes the main factors of instability,then theoretically analyzes the stability factors such as anti-uplift,anti-percolation,anti-overturning,and anti-horizontal slip.The main research contents and conclusions are as follows:1.Systematically studied the related contents of composite water-proof curtains and pit bottom reinforcements,summarized analyzed the characteristics of anti-seepage measures and the characteristics application scope of pit bottom reinforcement.On this basis,the composite waterproof curtain adopted for the construction of the project is a high-pressure jet grouting pile that is lapped by high-pressure grouting.The reinforcement measures at the bottom are high-pressure grouting reinforcement.2.Using MIDAS/GTS finite element software to simulate the groundwater steady state seepage under the condition of non-water curtain and water stop curtain,it is concluded that the water stop curtain has changed the seepage law of groundwater and can effectively strengthen the stability of the foundation pit;Based on the analysis of steady seepage of different waterproof curtain depths and the depths of reinforcement at the bottom pit,it is proposed that the depth of the water stop curtain is in the range of 25m-29 m,the depth of reinforcement in the bottom of the pit is in the range of 6m-8m,so as to verify the reasonableness of this project.3.Through the simulation analysis of the stress seepage coupling of the excavation of the foundation pit of Ciqikou,the laws of the displacement of the bottom of the pit,the support structure's displacement,the axial force of the internal support,the axial force and displacement of the post's pile,the ground settlement and the seepage field are obtained;The numerical simulation of the permeability coefficient of the water curtain and the length of the retaining piles show that the seepage velocity tends to be constant when the water stop curtain coefficient is reached,indicating that the water stop curtain has good anti-seepage performance,and then the permeability coefficient is reduced to the foundation pit.Percolation has no effect.4.Comparing the data obtained from the numerical simulation of excavation pits with the conclusions and some on-site monitoring data,which are slightly different,but basically can reflect the relevant laws such as surface settlement,support structure displacement,supporting axial force,and verification.The rationality and feasibility of the model provide reasonable model parameters for the following.At the same time provide reference for similar geological engineering.5.According to the parameters of the above model,numerical analysis was conducted on the uplifting factors of the deep foundation pit in soft soil,the effects of changing soil parameters,excavation parameters,support structure parameters on the uplift of the bottom of the pit after the completion of the excavation were discussed.The obtained soil has a reduced body weight,increased elastic modulus,increased cohesion and friction angle,a small excavation width,a small depth,an increase in insertion ratio,a decrease in the support distance of the lowest layer and an increase in the thickness of the ground wall will pit bulge volume decreases.