Analysis Of Mechanical Properties And FLAC^3D Numerical Simulation On Single Supporting Point Of Double Pile-anchor Supporting System

The combination of single fulcrum double-row pile and bolt is a new kind of supporttechnology. Through reasonable design, double-row piles and bolt merger as a wholeand display their respective advantages in technology. It is effective in controllingdeformation and improving stability of foundation pit slope, it also has a goodeconomic performance. At present, the little research on this supporting structure, theserious lack of field test data, and the finite element analysis which are mostlyconsidered in accordance with the plane problem have resulted in a limited awarenessabout its deformation features.This article is based on the basic theory of double-row piles and anchor structure, andthen a kind of computation model and method is proposed. In addition, depending onthe combined support methods of double-row piles+single-layer bolt+soil nails inthe east slope of excavation engineering of No. D office building of Raycom InfoTech,FLAC software was used to establish^3D numerical model, and then through thecomputation according to the structure excavation supports and protections order, themechanical characteristics of support system was discussed. The results wereexpected to provide the reference for the similar projects.In this paper, the main research and results are as follows:（1） Structure stress analysisOn the basis of the existing double pile door driving rigid computing model, assumethat the front row piles subjected to horizontal force instead of the anchor pre-stress,the calculation model of single fulcrum double-row pile and bolt support structurewas established. Rankine soil pressure theory is used to calculate the earth pressure ofthe row piles. The force on the top of the front and rear piles was transmited through acontinuous beam, and then the links was set up between them. Equivalent beammethod was used to calculate the bolt’s reaction, a kind of computation method ofsingle-fulcrum double row pile-anchor supporting structure was proposed.By contrast with the calculation results of Lizheng software, the rationality of thiscalculation method has been proved.（2） FLAC^3Dnumerical analysisThrough model computation, the horizontal displacement of limited soil in thebuilding foundation rear is an arc-shaped. The lateral displacement of first pilingassumes “large center, small on both sides” tendency. However the lateraldisplacement of latter piling is reduces gradually from top to bottom. The bendingmoment of first piling has the obvious inflection point near the earth nail anchor rod,but the bending moment of latter piling change tendency assumes“counter-S”. Thesurface subsidence assumes “spoon” shape distribution behind the slope, result in the adjacent C office building occurred a tilt. The force characteristics of pre-stressedanchor: non-anchor segment is a constant force generally, while axial force of theanchoring segment showed an attenuation trend. Axial force of the soil nails waselliptical shape distribution（3） Engineering applicationsCombined with the field-measured data of excavation engineering of No. D officebuilding of Raycom InfoTech, the article illustrates the rationality and practicality ofthis support forms. Groundwater which introduced into the construction site has agreat impact on the horizontal displacement of pile top of supporting structure.Similar projects in the future should pay special attention.