Research On Engineering Problems Of Foundation Pit Excavation On Existing Rigid Support Structures

Accompanied by the acceleration of urbanization in China,the tense situation in urban construction land continues to deteriorate.Maximizing the use of underground space has become an urgent need for people.Deep foundation pit projects have emerged as the times require.The construction of foundation pits on the passive soil pressure side of the city’s small-scale slope treatment structure has become one of the engineering crises commonly faced by the urban construction in hilly areas in South China.The construction behavior on the passive soil pressure side mainly disturbs the original state of stress balance of the retaining structure of the slope,resulting in physical mechanical deformation of the retaining structure,which in turn causes functional failure of the retaining structure.Ultimately,it has a catastrophic effect on the safety of nearby buildings.With its great destructiveness and the gradual nature of disasters,the foundation pit projects has been highly valued by the engineering community for a long time.In this paper,the deformation of existent rubble retaining wall in foundation pit construction was analyzed by ABAQUS software based on the engineering of a deep foundation pit close to existent rubble retaining wall in Changsha,the influence of excavation on the integrity and stability of the built-up rubble retaining wall was discussed by analyzing the deformation law of which on the top of the foundation pit.First,the influence of different excavation depth,different pile spacing and distance between piles on the existent rigid retaining structures was analyzed;the second was to analyze the influence of different support forms,different bolt prestress and different excavation procedures on the existent rigid retaining structures.The main conclusions were as follows:(1)When the excavation depth of the engineering pile is 4.0 m,6.0 m,8.0 m in the bottom of the foundation pit,the maximum horizontal displacement of the retaining wall was 14.3 mm,18.6 mm and 20.2 mm respectively.When the distance between engineering piles is 2.0 m,4.0 m and 6.0 m,the maximum horizontal displacement of the retaining wall was 14.3 mm,13.4 mm and 12.8 mm respectively.When the distance between engineering pile and supporting pile is 1.5 m,3.0 m,4.5 m,the maximum horizontal displacement of the retaining wall was 14.3 mm,12.6 mm and 11.9 mm respectively.So the horizontal displacement of retaining wall increased with the increase of the depth of excavation or the reduction of the distance between engineering piles or the closeness of the supporting piles,but the increase range decreased gradually.(2)The maximum horizontal displacement of retaining wall with soil nailing wall was 20.7 mm,while the maximum horizontal displacement of retaining wall with prestressed anchor was 13.9 mm,which was 6.8 mm difference.The result showed that the prestressed anchor was better than soil nailing in controlling deformation.The greater prestress of the anchor,the smaller displacement of the retaining wall.However,when the prestress is more than 100 kN,the passive soil pressure was increasing and the effect of controlling the displacement of the retaining wall was gradually weakening.When support and excavation are carried out at the same time,the maximum horizontal displacement of the existent retaining wall was 13.6 mm lower than that first excavation and the second support,which was more favorable to the stability of the existent retaining wall in the excavation of the foundation pit.(3)The plan was determined by the deformation law of built rubble retaining wall,which plans are engineering pile excavation,the construction procedure of excavation and reinforcement scheme.Then the plan was evaluated by checking the integrity and stability of the existent retaining wall.Finally,the correctness of the evaluation and the feasibility of the scheme were verified by the field monitoring data.