The Deformation Characteristic Analysis Of Mini-sized Piles Pre-stressed Anchor Composite Soil Nailing Wall

With the development of urbanization, urban land is increasingly less,development and construction of underground works have become the need of thetimes. Full utilization of urban underground space will inevitably bring about largescale excavations and supports. It has been usually constructed in buildings of highdensity urban district, the narrow space, geological conditions and the complexity ofsurrounding environment, high difficulty of construction, thus the safety offoundation pit has become an urgent problem. Provided with convenient construction,reliable quality, low pit deformation，little impact on the environment, etc., compositesoil nailing technique has been increasingly widely used in deep excavation structure.So far, it has been have a define calculation and description for stability analysis ofcomposite soil nailing, but research on the deformation of feature is still relativelyless, at a preliminary stage, theory falls behind the practice, being no definite formula.This paper focuses on studying deformation characteristics of composite soilnailing wall with mini-sized pile and pre-stressed anchor, relying on Xiangtan CityHexi peacetime and wartime air defense engineering mini-sized pile pre-stressedanchor composite soil nailing supporting technology, intended to reveal mini-sizedpiles pre-stressed anchor composite soil nailing deformation characteristics, provideda reference for the design and construction of similar projects. The main contents andconclusions are as follows:（1）It has been described the soil nailing technique with composite soil nailingtechnique of production, development and application, summed up the results ofprevious studies, analyzed the significance of composite soil nailing deformationstudies.（2）According to the characteristics of the supporting structure, the use ofplanar truss structure elastic pivot method for mini-sized pile pre-stressed anchorcomposite soil nailing deformation analysis, selected engineering parameters, foundthe model of elastic pivot method, calculated the deformation of supporting structureunder the different working conditions. It resulted in excavation sidewalls horizontaldisplacement and surface subsidence increasingly growing with the excavation offoundation pit, the maximum horizontal displacement is located in the upper part andthe main effects of surface subsidence area is located in the range of1to1.5times thepit excavation depth. （3）The on-site monitoring data are compared with theoretical calculations,combined with site engineering geological conditions, construction conditions, todetermine mini-sized pile pre-stressed anchor composite soil nailing deformation lawthrough monitoring of the project design, the use of monitoring tools to obtainhorizontal and vertical displacement of the top pit surrounding surface subsidence.The results showed that the elastic pivot points are larger than the on-site monitoringresults, and the variation is basically unanimous. It means that rational explanation ofthe foundation pit design, and it verifies the elastic deformation of the pivot method toestimate reliability at the same time.（4）It will acquire the deformation of foundation pit under the different workingconditions, by using the finite element analysis software ANSYS appropriate choiceof parameters, creating a composite soil nailing and nailing two models of pure soil,the finite element results with the measured data comparison showed that due to theeffect of soil pressure, mini-sized piles produce tiny rotation, composite soil nailingsurface above the horizontal displacement of the excavation showed the oppositephenomenon with the following top pit smaller margin uplift, mini-sized piles andpre-stress anchor applied to the pit sidewall, horizontal displacement and landsubsidence have a greater impact, and it can effectively control soil deformation, butthe impact on pit bottom bulge is relatively less.