The Study Of The Mechanism Of Nail-soil Interaction In Soil Nailing Structures

Soil nailing, a kind of in-situ soil reinforcement technology, has been widely used in deep foundation pit and slope engineering. But the related theories have lagged far behind the practice. In recent years, although many scholars pay attention to the mechanisms of nailed walls and received achievements abundantly, few of them have noticed the importance of analyzing the mechanism of soil-nail interactions in soil nailing structures. There have been five explanations on the mechanisms of soil-nail interactions. The first one considered that the nails constitute the bearing skeleton of soil nailing structure. The second one is that nails increase the strength of the in-situ soils. The third one is that soil and nails are all the undertaker of the gravity and overburdens . The fourth one is that nails decreased the stress concentration in soils. The fifth is considered that nails restraint the distortion of the slope surface. Based on above of explanations, scholars proposed some of theories on soil-nail structures, just as apparent cohesion theory, soil arching theory, the transverse resistance of shearing force theory etc. Based on the work of predecessors, this paper studies the nail-soil interaction mechanisms deeply and proposed some new explanations on it. The paper mainly discusses the followings:1. Basing on some of the soil-nail pull-out resistance model tests and predecessors'works, the paper improved the method to calculating soil-nail axial force and the shear stress on the interface of soil and nails. A project case was used to test the applicability of the formula.2. In the paper, it is assumed that the soils are Mohr-Coulomb materials and nails is rigid body, concerning the soil was pressed through the interval of two nails due to gravity and overburdens. In the process because of extrusion, plastic deformation occurs in the soils. Basing on the plastic deformation model, the paper introduced the formula for calculating the vertical stress in composite soils.3. Improved the traditional method on calculating the vertical average stress. The method based on level minor principal stress arching theory never concerned about the impacts due to the level displacement of soils. The paper considered that points and introduced the formula. Also the paper deduced the formulas for calculating the level stress. The method concerned the plastic deformation of soils and the coupling action between vertical stress and horizontal stress.4. Assuming the soil is visco-plastic Bingham material, nails anchored in the stable area of slopes firmly and provide shear resistance to the soils that have level velocity running to the excavation side. Based on the soil visco-plastic flow model, the paper introduced the method to calculate level average stress.