Systematic Study Of Soft Soil Deep Foundation Pit Supported By Spray Anchor And Cantilever Piles

With the rapid development of China's economy,culture and infrastructure,the limited space on the ground has spawned the development and utilization of underground space.Complex and diverse working conditions put forward higher requirements for foundation pit support methods,and the application of combined support in foundation pit engineering is increasingly frequent.Slope spray anchors and cantilever piles are widely used in engineering,and have the characteristics of simple construction and low cost.However,when the excavation site is poor in soil quality,the lower part of the spray anchor support and the top of the cantilever pile are prone to large displacement,so it cannot be applied to the high-grade foundation pit.By stratifying the two types of supports one by one,the position of large displacement is concentrated in the middle of the sump edge,and only the intersection of displacement curve of the single support happens,it can effectively reduce the horizontal displacement of the enclosure structure,then improve the level of pit category and reduce the cost.Due to the lack of application of this combination support and the lack of theoretical research,this paper conducts preliminary research.Aiming at the common deep foundation pits of high-rise,this paper uses the finite element software ABAQUS to simulate the excavation process of the foundation pit under the combined support of spray anchor and cantilever pile.It mainly includes the following research contents:1.Establish an excavation model with the help of a subway deep foundation pit project,and compare the simulation results with the measured data to verify the accuracy of the modeling method and parameter selection.2.Under the condition of soft soil,establish the foundation pit model under the combined support of spray anchor and cantilever pile to summarize the deformation law during excavation.Compare various aspects with traditional cantilever,such as the deformation value and maximum lateral stress and internal force of the retaining structure pile,then summarize the modified effect of the combined support.3.The single factor analysis is used to study the influence of multiple design parameters of spray anchor and cantilever pile on the deformation of foundation pit,and the influence law and reasonable value range are obtained.4.According to the different combinations of cantilever segment and spray anchor height,three feasible combinations are proposed,and the support effect is analyzed and economic evaluation is carried out.The research results show that the combined support of spray anchor and cantilever pile is superior to the traditional cantilever pile.The lateral pressure of the cantilever pile is reduced by the spray anchor support,so that the deformation value and internal force of the envelope structure are greatly reduced.The width-to-height ratio and strength of the reinforced soil,the modulus and depth of the pile,the reinforcement,the inclination,and the prestress of anchor have different effects on the deformation of the foundation pit,and all have reasonable value intervals;The three combined schemes not only ensure that the displacement of the envelope structure meets the pit specifications,but also reduces the direct engineering cost by 7% to 25%.Test has proved that the combined support of spray anchor and cantileve pile in this paper has certain theoretical significance and practical benefits,which can provide methods and reference for engineering.