Study On Behaviour Of Composite Pile-wall-struts Retaining Structure For Deepened Excavations And Application In Soft Soil

In recent years,land resources have become increasingly tight,and underground projects have developed to a deeper and larger scale.In actual engineering,it is often the case that the number of underground structures is increased or the excavation sequence is adjusted under the condition that the envelope structure has been constructed,and the existing envelope structure cannot fully meet the needs of the deepened foundation pit in most cases.In order to avoid waste of resources,in the design and construction of deepened foundation pits,it is necessary to make full use of the existing envelope structure.Therefore,the coordinated work,deformation and internal force analysis of the combined structure formed by the existing and newly added envelope structures are urgently needed.Aiming at the above problems,this paper conducts comparative research through numerical analysis and practical engineering applications.The main work and conclusions are as follows:1.Using numerical analysis software,a 2D finite element analysis model of the composite retaining structures for the excavation of a soft soil layer is established,and the effects of the depth of the foundation pit,the location of the new retaining wall,the distance between the existing and new retaining walls,and the reinforcement of the soil between the piles on the deformation and the internal forces of the composite retaining structures,the ground subsidence outside the pit,and the uplift of the soil at the bottom were studied.The analysis found that the horizontal displacement,bending moment value,and surface settlement of the pit outside of the composite retaining structures all decreased with the increase of B(within 5d outside the foundation pit)which is the distance between the inner and outer rows of piles,it becomes stable when B?4 ?H(?H is the depth of the deepening of the foundation pit).Compared with adding piles in the pit,using piles outside the pit to control the horizontal displacement,bending moment and ground settlement of the retaining structure is more favorable;The consolidation of soil between piles can reduce the horizontal displacement of existing retaining piles,but it will cause the horizontal displacement of newly added retaining piles to increase slightly.2.Based on the above analysis conclusions,excavation of a basement for a complex basement on the soft clay ground of Hangzhou North,the design scheme of the combined pile supporting structure using piles in the pit is adopted.By establishing a model for finite element analysis and comparative analysis with the monitoring data of the foundation pit,the rationality and reliability of the combined pile-supporting support structure with piles in the pit is proved,which provides a reference for similar projects in the future.