Research And Application Of Assembled Fast Diagonal Bracing Structure In Foundation Pit

The safety of the foundation pit is the premise of the development of underground space.When the retaining structure of the foundation pit deforms heavily,appropriate emergency measures should be taken immediately to limit the further damage of the foundation pit.The steel tube inclined brace has good bearing capacity and can be arranged flexibly according to the deformation of foundation pit,so it is widely used in the emergency rescue of foundation pit.But at present,this method often needs to pour the concrete base,which has some shortcomings such as complicated process,long construction period and difficulties in subsequent processing.In view of the current problem of using steel pipe diagonal bracing in the foundation pit for emergency rescue,this paper puts forward a kind of the assembled oblique support structure,which uses a specially designed prefabricated base to avoid concrete pouring construction,and has the advantages of fast construction and convenient recovery.In order to effectively apply the assembled oblique support structure in engineering practice,this paper combined with a civil ai r defense deep foundation pit project in Changsha City,and conducted model tests and numerical analysis on the bearing performance,load transfer and failure mode of the prefabricated oblique support structure systematic research.The main contents are as follows:First of all,a model loading device is designed according to the force characteristics of the proposed assembled oblique support structure.On this basis,the two components（the diagonal brace and the bottom plate）and their combined form are respectively loaded.In the test,the difference in the bearing performance of each member under individual load and combined load was obtained,and the distribution of the axial force of the diagonal brace,the soil pressure on the bottom plate and the failure mode of the foundation soil under each working condition were analyzed;Secondly,a numerical analysis model of the assembled inclined braces was established by FLAC^3D,and the parameters in the model were calibrated by comparing the model test data.On this basis,the influence of the inclination angleαand the strength parameters of the foundation soil（c,φ）on the bearing characteristics of the inclined support is analyzed.The bearing mechanism of the the assembled oblique support structure is clarified from multiple angles such as bearing capacity,load transfer and failure mode of foundation soil.And give design suggestions for engineering application;Finally,the assembled oblique support structure was applied to the civil air defense deep foundation pit project in Changsha,according to the actual situation of high-risk foundation pit support section,the fabricated oblique support structure was designed.And the process and effect of using it to reinforce the foundation pit when large deformation occurred were analyzed.The results will be used in engineering practice.