Analysis Of Stress And Deformation Characteristics Of Retaining Structure For Circular Secant Pile Deep Excavation

Circular diaphragm wall, one of supporting patterns for structures, has many advantages such as high integrity rigidity, good water-resistance, large working space and low cost. Especially, it has obvious “spatial arching effect, which can transfer earth pressure acting on the structure into hoop stress resulting in a limited structure deformation. Furthermore, the compression of concrete can be largely exerted at its interest. In actually circular diaphragm wall has been widely studied, the circular clutching borehole grouting pile is rarely explored in terms of its characteristics of stress and deformation. Moreover, field measurements provide database for validating the theoretical work and gain experiences for future construction. As a result of the “spatial arching effect” of the circular excavation, the characteristics of stress and deformation of retaining structure is complicated. Additionally, regional difference of excavation is remarkable. Therefore, it is necessary to explore the characteristics of stress and deformation of circular clutching borehole grouting pile at a particular location.Based on the field monitoring, stress and deformation characteristics of retaining structure for the circular occlusal pile deep excavation are analyzed and summarized in this dissertation. MIDAS/GTS is utilized in this study to analyze the differences compared with the actual project by developing a three dimensional entity modelling. The circular secant pile is simplified as a circular diaphragm wall based on the stiffness equivalent principle. According to geological characteristics of Nanjing, the influencing factors affecting stress and deformation characteristics of the retaining structure of circular excavation are evaluated.Field monitoring shows that irregular deformation occurs in the overall excavation and the horizontal displacement value of an inclinometer borehole located in the south part of excavation is great than that same type of circular deep excavation with a small diameter. The poor construction quality of the occlusion part between the reinforced concrete pile and adjacent concrete pile is indicated as a main reason by the numerical simulation. Because the reinforced concrete pile and adjacent concrete pile may embed and slide each other in the occlusion part. In addition, without considering foundation the building also has a certain effect on the value for the top circular deep excavation and the maximum lateral value. The effect on the value of the top circular excavation is large for the furthest monitoring point and there exist a turning point at a certain depth. The change of elasticity modulus for concrete pile is not the main reason that the horizontal displacement value of secant pile is large. The monitoring data shows that the maximum ground settlement value outside the circular deep excavation is 0.8 times the excavation depth and 0.4 times main influence zone. The circular bored piles are equivalent to the diaphragm wall by the equivalent stiffness principle. The results show that the change range of maximum radial displacement value for retaining structure is 5.5% and the hoop stress is 4.2%. The value of stress and deformation for diaphragm wall is less than scant pile. The diameter of circular excavation has most prominent effect on the characteristics of stress and deformation of retaining structures among the various influencing factors. At a given thickness of circular excavation, the “spatial arching effect” of retaining structure decreases with the increase of diameter of circular excavation. At a given diameter of circular excavation, the “spatial arching effect” increases with increasing the thickness of retaining structure.