Research On Working Mechanism And Design Method Of Piles In Row And Composite Soil Nailing Supporting Structure

Composite soil nailing supporting has been widely used in deep foundation pitengineering because of its fast construction, economic, and it overcomes thelimitations of the soil nailing and so on. Piles in row and composite soil nailingstructure is the structure which sets up a column of soil nailing between pilesretaining structure, it can be used to conctrol the deformation of the foundation andimprove the stability of foundation pit. At present, this supporting structure has beensuccessfully used in foundation pit engineering, but the theory is far behind theengineering practice, and the research is still blank about the supporting structure.Therefore, research about the structure properties of piles in row and composite soilnailing has important significance on the theoretical research and designoptimization of the supporting structure.The finite element analysis method plays outstanding in simulating theconstruction process of foundation pit excavation, and it can consider the contactbetween the supporting structure and soil better. In this paper, using the ABAQUSfinite element software to establish the piles in row and composite soil nailingstructure calculation model. The model simulate the construction process offoundation pit excavation, analysis the stress and deformation behavior and thestability of foundation pit about the piles in row and composite soil nailing structure.Also this paper deduction the calculation method of deformation and force about thesupporting structure. Draws the following conclusions:(1) Nail plays a role of "weak anchor" in the piles in row and composite soilnailing structure, the maximum axial force of the soil nail is near to the foundationpit wall in the supporting structure, and the force value of the nail head is larger;under the action of soil nailing "anchor force", the pile deformation is bendingdeformation, but the top of the deformation curve is reduct, piles in row above theexcavation surface bear positive bending moment and piles in row under theexcavation surface bear negative bending moment; (2) Considering the control of pile lateral deformation, the appropriate pilespacing is two times of the pile diameter, the maximum positive bending moment ofpiles appear at the2/3H from the top;(3) When the piles in row and composite soil nailing slope instability,supporting structure will overall overturning around the pile bottom, the soilcontains the soil nailing that behind the pile will overturning slide with it; increasingthe pile embedded depth, pile diameter, soil nail length or decreasing pile spacingcan increase the stability of foundation pit, but the effects of the pile diameter andthe pile spacing changing on the stability of foundation pit safety coefficient issmall;(4) This paper present the method of calculating the deformation and forceabout the piles in row and composite soil nailing structure, compare to the results ofthe numerical analysis, the design method is feasible.