Study On Optimization Of Seepage Field Of Suspended Water Stop Curtain And Design Of Pull-Out Resistant Pile For Foundation Pit Project

As new underground structures in the city are buried deeper and deeper,and the water table is getting higher and higher due to policies and other factors,many underground structures and the bottom of the pit are subjected to high pressure water buoyancy load,so it is necessary to analyze the characteristics of the seepage field of the pit and the force characteristics of the underground structure under water-rich conditions.In this paper,we summarize the shortcomings of the current design of structural buoyancy resistance and focus on two key issues,namely,the calculation method of water inflow in the "wall-well" interception and discharge pressure reduction system for pits with different strata and the optimization of the arrangement scheme of pull-out piles considering the risk of local damage to the foundation,and the main research contents are as follows:(1)In order to accurately calculate the different water-rich strata using suspended curtain design of the pit surge,according to the principle of groundwater dynamics,separately established a circular pit,strip pit seepage field mechanical model and derived the analytical equation for the calculation of the inflow of water;proposed with the radius of the pit,the thickness of the water layer and curtain insertion depth and other factors related to the influence of the seepage diameter coefficient,the value of the coefficient directly affects the results of the calculation of the water inflow;The use of numerical simulation forward and backward analysis fit to obtain the formula for the influence of the seepage diameter coefficient.The comparison shows that: the theoretical analysis of the results of each working condition and numerical results and field measurement data have good consistency,to verify the accuracy and reasonableness of the derived formula.Finally,the discussion of the different aspect ratio of rectangular pits under the law of change in the amount of water inflow,respectively,proposed a circular pit and strip pits in the calculation of water inflow formula in rectangular pits in the applicable aspect ratio boundaries.(2)As a permanent anti-floating measure for the structure,the arrangement scheme of the pull-out piles takes the overall anti-floating stability of the structure as the test condition and ignores the partial anti-floating stability of the bottom plate of the structure,which will result in a large differential deformation of the bottom plate of the structure when it is subjected to high water buoyancy load and thus increase its risk of damage.In this paper,in order to investigate the arrangement scheme of uplift piles to increase the local floating stability of the bottom slab under the premise of overall floating stability,a topological optimization theory with pile length as the design variable and pile end displacement as the sensitivity factor is proposed by combining the force mechanism of uplift piles and the basic idea of BESO method.The method is combined with the numerical software FLAC3 D to optimize the design of the pullout resistant pile model under the foundation slab,and the differential deformation and total strain of the foundation slab can be significantly reduced after optimization.In order to avoid the inherent defect of the topological theory of local optimal solution,the optimization results of the two models with different pile diameters and pile distances are compared,and the idea of uplift resistant pile arrangement considering the local anti-floating stability of the foundation slab is proposed.(3)The design decision of pullout pile parameters for the pullout pile-foundation slab system under multiple loads needs to consider not only the structural reliability of the solution,but also the construction difficulty,construction period and economic rationality.In order to obtain the evaluation system for the design parameters of the pull-out piles in the pull-out pile-foundation slab system,a two-dimensional numerical model of pull-out piles-foundation slab-soil was established based on the basic principle of hierarchical analysis method,combined with the actual parameters of the site in the cover excavation reversal area of Lot 02 B in the sub-center comprehensive transportation hub project.A multifactor comparison study was conducted to investigate the arrangement of the pull-out piles.According to the general situation in the actual project,in the total hierarchical ranking,the biggest weight among the influencing factors is the maximum uplift of the foundation slab,followed by the maximum differential deformation of the foundation slab,the total strain energy of the foundation,the total construction cost of the single-row pile and the construction period of the single-row pile.Therefore,for general projects,when considering the decision of the design scheme of the pull-out pile parameters,the safety and reliability of the structure need to be satisfied as a priority,and then other factors are considered comprehensively to finally obtain the pull-out pile arrangement scheme.