Study On The Action Mechanism Of Prestressed Anchor Composite Soil Nailing Wall Support Structure

Prestressed anchor composite soil nailing wall has advantages of low price,easy construction and better stability,so it is widely used in supporting of foundation pit engineering.However,due to the complex relationship between the supporting structure and the soil,there always exits the problem of unclear understanding of the working mechanism of the composite soil nailing wall,as a result,some safety accident occurs due to excessive cost savings,or in pursuit of stability blindly some project makes a big waste.Based on the previous research,this article discusses the interaction between prestressed anchor,soil nailing and soil by means of theoretical analysis and numerical simulation to make reasonable recommendations and reference conclusions for foundation pit engineering designs.In this paper,the mechanism of the action of anchor and soil nail is analyzed theoretically at first.The whole mechanism of soil nailing wall and the process of soil nailing are expounded,and the theory of friction tendon and quasi-cohesion are introduced,then analyses anchor 's mechanism of force.Secondly,based on the design of foundation pit support in Lanbo D area,this article simulates the deformation characteristics of the foundation pit by Midas / GTS software.The horizontal displacement curve of the pit wall shows horizontal displacement presents "bulging type" along the depth of the foundation pit,which means the displacement of the upper and the bottom is less than lower part in horizontal direction.The displacement appears inflection at the position of the prestressed anchor,which means the prestressed anchor can limit the displacement;and if the position is different,the displacement is also not the same.Thirdly,the axial force curve of soil nail and anchor cable is drawn acoording to four dividing working conditions,and the article compares the variation of axial force of soil nail before and after the application of prestressed stress.It is found that the application of the prestressing force of the anchor cable has much influence on the axial force of the adjacent upper part of soil nailing,and it has less effect on the further upper soil nailing but has little effect on the lower soil nailings.Also,the restraint effect is distinct because of the different position of prestress anchor,if the position of the prestress is closer to the upper part of the soil,the axial force of adjacent upper soil nailing decreases more,the effect on constraint of the slope displacement is greater,on the contrary,the effect will be less.The anchorage cable has a great influence on the axial force and its transmission characteristics,but the soil nailings have little effect on the anchor cable.Therefore,the design concept of "weak nail,strong anchor" is proposed,which means we can regard the soil with nailings as reinforced soil,and think of prestressed anchor as the external force applied to the composite soil,and in this way analyze composite support system.Finally,based on the engineering example,the article optimizes primary design scheme with the design concept of "weak nail,strong anchor".After Li Zheng software checking and numerical simulation of deep foundation pit,the stability of the optimized scheme meet the relevant specification requirements.