Analysis On Working Mechanism Of Lime Nail Composite Frame Prestressed Anchors

Lime nail composite frame with pre-stress anchor is a new supporting structure which is used to solve the problem of foundation pit support in soft soil area.The water swelling and drainage consolidation characteristics of lime nail is used to reinforce soil.The solidified lime nail and the frame anchor form a space support system,and the three work together to maintain the stability of foundation pit slope.The working mechanism of lime nail composite frame with pre-stress anchor in this paper is analyzed by the method of theoretical research and finite element analysis,the specific research contents and conclusions are as follows:(1)The research background,structure composition,construction equipment,construction process and working mechanism of lime nail composite frame with pre-stress anchor are introduced in detail.And the strengthening effect of lime nail on soil mainly includes: replacement,expansion compaction,absorption and drainage effect,load reduction effect of reinforced layer and so on.The consolidation process of the drainage plate can be divided into normal consolidation stage and expansion pre-stress consolidation stage.(2)Based on the elastic-plastic theory,the additional stress around lime nail and the calculation formula of plastic radius caused by the expansion of lime nail are obtained.Based on the equivalent relation between unit strain and displacement,the calculation formula of average consolidation degree of soil in the reinforcement area of lime nail is given.The temperature field of lime nail is obtained by Laplace transform,Fourier transform and inverse transform.Then the calculation formula of average degree of consolidation of soil is modified.Through the analysis of the force mechanism of the lime nail composite anchor rod,the calculation formula of uplift capacity of the lime nail composite anchor is obtained,and its correctness is verified by comparing with the numerical calculation result.Based on the principle of pore extruding,the result that the reasonable arrangement distance of lime nail is obtained,which provides an useful theoretical guidance for the application of the structure in engineering.(3)By using the finite element software ADINA,the 2D model of deep foundation pit excavation and support are established.By comparing the axial force of anchor bolt and the displacement of foundation pit of the two supporting structure:frame pre-stress anchor with lime nail and frame pre-stress anchor,the advantages ofthe new structure are verified.By establishing the uplift model of lime nail composite anchor in consolidated soil,the stress law and displacement law of the soil around lime nail caused by the expansion of lime nail are obtained,the uplift capacity and expansion amount of lime nail are also obtained.(4)By establishing the model of foundation pit drainage,the good drainage effect of lime nail is compared and verified;By establishing the uplift model of lime nail composite anchor in saturated soil and delimiting different infiltration rate of lime nail,the permeability of lime nail influences on the consolidation rate of lime nail is obtained.By comparing the numerical solution with the theoretical value,the correctness of the formula for the uplift capacity of the composite bolt in saturated soil is verified.