Study On Supporting Structure Design Of Deep Foundation Pit Based On Deformation Control

With the development of urbanization,land resources are dwindling.There are dense buildings in the center of the city.The existed architecture not only have strict requirements for safety,but also are sensitive for displacement of adjacent foundation pits.Therefore,it is necessary to ensure the safety in foundation pits of new buildings,as well as,strictly control the deformation of adjacent existed architecture in the process of deep foundation pit construction.The combinative method of experimental analysis and numerical simulation in this paper,which is used to study the design of deep foundation pit support based on deformation control.Firstly,considering the control of deep foundation pits deformation based on temporal responses,had succeed in finding suitable grouting ratio for deep foundation pit support,which used sulphoaluminate cement as the cementitious base material to take relevant ratio experiment,bolt bearing performance experiment,as well.Under the test conditions,0.45 water-to-cement ratio of sulfoaluminate cement slurry,which was mixed with 1.83% polycarboxylate superplasticizer and 0.13%retarder,satisfied the requirements of bolt grouting on fluidity and strength.The slurry applied pre-stress and bearing capacity for anchor rod earlier,controlled the early deformation of the deep foundation pit at the same time.Secondly,the influence of deformation by pile-anchor retaining structures in the process of deep foundation pit construction was analyzed based on spatio responses.It was found that the displacement of long side was larger than that of short side.The horizontal displacement of pile head presented a "bow",the pile shifted to the inner side at horizontal direction of the foundation pit.The horizontal displacement of the pile at convex corners in foundation pit presented a rough "positive triangle".The surrounding surface settlement presented a "grooved".Finally,the related laws of the deep foundation pit based on deformation control were obtained by changing the design parameters of the support structure and the soil nail reinforcement between the piles.(1)Soil nails between the piles would not change the "bow" horizontal deformation of the soil.With the length of the soil nails increasing,the soil between the piles deformation gradually decreased,as well as,the maximum horizontal displacement of the soil between the piles was at the 1/3 depth of the foundation pit.The length of soil nails had a certain range in influence on the strength of the foundation pit soil.Changing the length of soil nails had a weak effect on the strength of soil between the piles after the length of soil nails in this project reached8 meters.(2)The horizontal displacement of the pile head and the pile,the ground aeposition around foundation pit would decrease with the increasing of the anchor cable prestress.Although increased the prestress,the influence of pit deformation was very weak after the prestress lock value reached 250 k N.Therefore,it is necessary to choose a reasonable prestress locking value for deep foundation pit design based on deformation control.(3)Increasing the pile length or reducing the pile spacing could effectively reduce the horizontal displacement of the pile and the ground aeposition around the foundation pit.The convex corners was obviously affected by the pile spacing and pile length.Under the conditions of this project,a design with 20 meters pile length and 1.2 meters pile spacing could provide a ideal supporting effect.