Investigation On Ground Surface Settlement For Deep Foundation Pit Excavation In Soils Underlain By Rock

With development of urban construction, deep excavations of subways, civil air defences and high-rise building basements are more and more widespread in complex environment where buildings are thick and underground pipelines interconnected. The deep excavation works have certain impact on adjacent structures and municipal pipelines, so more and more attention has been focused on ground settlement induced by deep excavations.At present, almost all attentions were paid to deep excavation and ground settlement problems in soft soils. Less attention was paid to the ground settlement problems of the deep excavations in soils underlain by rock. If we applied those calculation models and methods of ground settlement induced by deep excavation mainly based on the experiences in soft soils directly in soils underlain by rock, the results might have large deviation because different regions have different earth conditions.Firstly, the applicability of finite element analysis software, PLAXIS2D, in deep excavations, has been analyzed. Secondly, the present ground settlement calculation formulas have been analyzed and improved on the basis of existing researches on the ground surface settlement. Then, selecting deep foundation pit engineering examples supported by pile-inner bracing structure system, influences of different factors on deformation of deep excavation were calculated and analyzed through finite element analysis software PLAXIS2D by taking Qingdao soils underlain by rock as an example. Finally, on basis of the preceding studies, the calculating formula of ground settlement has been established and verified in soils underlain by rock for deep excavation.The following conclusions can be drawn from this dissertation. (1) Finite element calculated results of excavation cases compared with the measured results show that selecting the appropriate soil constitutive model and consider the proper way to simulate deep excavation, finite element analysis, PLAXIS2D, has good applicability in simulation of deep excavation.(2) Two methods suited for soft areas ground surface settlements estimated are regarding the ground settlement curve as normal school curve or decentration distribution curve respectively. Improvement has been made for the two methods based on empirical relations obtained from engineering practice. Calculated results of project cases has shown that the improved methods for computing ground surface settlement are more simple and suitable, and it is better to compute the surface settlement regarding the settlement curve as a kind of decentration distribution curve.(3) Deep excavations in soils underlain by rock under different influence factors have shown that position of the maximum horizontal displacement of support pile is about (0.5 ~ 0.7) H (H regards the depth of excavation)away from the top of the pile and position of the maximum surface settlement is stably about 0.40H away from the foundation edge.Stable relationship also exists between the maximum horizontal displacement of support pile and the maximum surface settlement is that the maximum horizontal displacement of support pile is about 1.7 times of the maximum surface settlement.(4) Method of ground settlement estimation in soils underlain by rock is established regarding the surface settlement curve as decentration distribution curve model. Engineering examples show that it has certain applicability.