Study On The Behavior Of Double-Row Piles

Double-row piles structure is a new kind of braced diaphragm structure in excavation that was first used in 1990s. The double-row piles has a much higher lateral stiffness compared to the single row soldier piles, and can be designed in a cantilever manner without any struts, which makes it cost lower, excavate more conveniently and shorten the construction duration. However, there is little mature design method at present, and lack of systematic study on the mechanic behavior and applicability. This thesis carries out a detailed research on the double-row piles based on the literature and several engineering cases. The main work and conclusions are as follows:(1) The excavation sequences are simulated by ABAQUS, and the distribution of soil pressure, the stresses of the soldier piles and the deformation are analyzed. The influencing factors are studied, which includes the row spacing, embedment of the pile, rigidity of the linkage, stiffness of the pile, strengthen of the passive area and reinforcement between the piles. Suggestions of optimization are then put forward;(2) The soil arch between piles are simulated and researched. A simplified calculation method to determine the pile spacing is obtained based on the Hewlett theory and the entire stability of the soil mass between soldier piles, and is verified by engineering cases by other methods. The effect of the pile spacing is studied and rational range of the pile spacing is given;(3) Three dimensional finite element analysis are carried out to study the behavior of the ring beam, the influenced region in horizontal direction is found and the deflection of the pile considering the ring beam effect is also obtained;(4) The patterns of additional stress produced by the overload above the pit is drawn and described in detail, and the area of the most unfavorable position of the pit-in-pit is received; orthogonal experiments are conducted based on large quantity of numerical experiments, and the factors that effect the stability of the pit-in-pit are ranged in the order of sensitivity;(5) According to several case studies, the repeatability of the numerical modeling and the estimation of the impact of the pit-in-pit are confirmed;(6) Advice to the further study on the deep excavation.