Study On Three-dimensional Soil Arching Effect Of Cantilever Piles And Ground Resisting Force Acted On Its Build-in Zone

Cantilever pile is widely used in reinforcement to excavation and fill geotechnical engineering as a support structure with resistance to deep sliding because of its characteristics, such as strong resistance, reduction of land use, convenience and short-time spend about construction and so on. The design theory and construction technology of cantilever piles have been developed in many years, however, most of current methods are based on plane strain assumption. Therefore, there are some failure and deformation phenomena which occur in actual construction and application stages. This research work is being supported by grants from National Science Fund for Distinguished Young Scholars of China (NO.50625824), National Natural Science Foundation of China (NO.50878218), National Science and a subject which belong to Technique Foundation during the 11th Five-Year Plan Period of China (NO.2008BAJ06B04) and Transmigrant Allocation and Programming Department of State Council Three Gorges Project Construction Committee (NO.2008SXG02-2). The study which mainly relates to three dimensional arching effect of cantilever piles and ground resisting force acted on their build-in zone is made by survey in field engineering. The main work and research conclusions are as follow:(1) In order to more rationally account the level and range of soil arching effect, it is suggested that the mutations of earth pressure along the normal or thrust force direction should be considered to substitute for the ratio of loads on the pile and soil after investigation work has finished on site. A indoor trust-pile test is designed based on viewpoints above, and the major test is directed distribution characteristics of stress in soil and three-dimensional soil arching effects. The relationship between friction and direct soil arching effects is studied according to tesr results. It is proved that direct soil arching structure bears the most earth pressure load, and is more critical to impact on stability of soil mass between adjacent cantilever piles.(2) A indoor trust-pile test about buried piles is also design in order to comparision with the cantilever piles. The distribution of earth pressure and failure pattern of soil near the piles is analysed according to the test results. The contrast and analysis on the test results of soil arching effect are made by changing the spacings of cantilever piles and the property of soil. In addition, the formation, development and fade processes of soil arching effect are discussed. (3) A outdoor test about flexiboard sheet-pile walls used in reinforced fill foundation on inclined ramp is designed. The purpose of test is primarily to compair and analyse results of three-dimensional soil arching effect and distribution of earth pressure, when flexiboard is installed on frontal or dorsal surface of piles. In the interest of simulating the unloading process of soil between piles, the boards are taken out in test process. Subsequently, a simple static penetration device is made for evaluating solidity of undisturbed soil on shear failure line of arch spring, and ultimate shear-thicknesses of direct arch are analyzed. In addition, test analysis is made about the comparison testing results with calculation value of the simplified granary method and the unloading arch method to discuss the design method of earth pressure which acts on the board.(4) The soil near the arch springing is worst-case position, which is based on survey and analysis of cantilever piles in incised slope and testing results. The stress fields of slope in both initial and incised condition are obtained by mechanics of elasticity. Three-dimensional soil arching effect and cutting-unloading stability analysis model of soil between adjacent piles is established on the basis of geotechnical strength theory. It is discussed that there is a relation between range of arching effect and partial stability of soil between piles. Based on the analysis about integral soil stability near piles, the analysis method of maximal spacing is estabilished by considering self-weight stress and sliding thrust.(5) A calculation method which is considered space effect in cantilever'build-in zone is established by superposition principle, and this process refers to reference the trigonometric series method. Based testing results of compression stress which acts on the contact surface between pile and ground, friction effect of contact surface is analysed. It is suggested that constraint condition at bottom of pile is deem to be free, when the ground near the pile is composed of perfect rock. In order to verify the rationality of calculation model, the comparison between test results and calculation results which contain the trigonometric series and K method is made.(6) Finally, the strengthening facilities are discussed about soil mass between cantilever piles and ground near their build-in zone. The finite difference methods are established ahout soil between piles reinforced by anchors and ground in front of piles strengthed by steel-pipe piles. The elevation election and drilling length of anchors are analysed, and the interacting between steel-pipe piles and ground and their operating principle are also studied. On the basis of conclusions above, the optimum designs about two facilities are discussed.