Research On Stability Evaluation And Control Of Foundation Pit Excavation With Existing Masonry Retaining Structure

Masonry retaining structure is the kind of special shallow foundation structure,which has the shortcomings of material deterioration and is sensitive to construction disturbance.In the case of close to the foundation pit,masonry retaining structure is likely to be disturbed too much.It is easy to produce new cracks,or even crack and damage,which will lead to the instability of the foundation pit and the safety accidents.Therefore,how to effectively evaluate and control the influence of foundation pit excavation on masonry retaining structure,it is the key issue to ensure the safety and stability of foundation pit engineering.The major presents an example of a foundation pit and the establishment of three-dimensional finite element model of ABAQUS.The pressure and pull damage constitutive model is used to characterize the masonry material properties.The Mohr-Coulomg elastoplastic model is used to simulate the geotechnical liquid property.The paper presents the analysis of retaining structure,soil and masonry retaining wall in foundation pit and puts forward the standard evaluation of foundation pit stability.The paper also presents the reasonable preloading of anchor support,the reasonable excavation method of foundation pit and reinforcement method of retaining wall.At last,The paper presents the optimization of the scheme,and the analysis by combining field monitoring and numerical simulation.The major findings are summarized as follows:(1)In the process of optimizing the excavation of the foundation pit,the vertical displacement of the masonry retaining structure has a smaller displacement value at the wall toe,and has a larger displacement value at the top of the wall.The horizontal displacement of the masonry retaining structure alternates between the upper and the bottom of the wall.The Tension and compression stress is concentrated at the toe of the wall.(2)Based on the deformation control,the masonry material properties are simulated by the compressive tensile damage constitutive model and the maximum tensile strain cracking criterion.(3)Under the conditions of pile-anchor support,the lateral displacement of the retaining structure,the displacement of the stone retaining structure,the tensile damage coefficient and the surface deformation are basically negatively correlated with the magnitude of the pre-force.When the pre-force is uesd by 0.5 to 0.9 times the standard value of the axial force,it can control the deformation of the foundation pit and the existing stone masonry supporting structure,and reduce the risk of cracking of the stone masonry under tension.The use of ground beam slabs and pre-stressed anchor cables,which strengthen the stone masonry,can weaken the stress concentration at the toe of the wall and improve the damage of the retaining wall.The process of "supporting while digging " can restrain the deformation of foundation pits and retaining walls in a timely manner than the process of "supporting after digging".