Study On Soil-Structure Interaction During Large Diameter Concrete Pipe Jacking

With the development and adoption of new technique and equipment, the diameter of jacking pipe grow up to be large scale gradually. It's inevitable that the influence of construction of large diameter jacking pipe was different with narrow pipe. So the traditional design methods of pipe was not suitable, and the working well which provided jacking force asked for higher requirement. Based on the South Line project of sewage treatment, the interaction between soil and pipe, between soil and caisson working well, were investigated respectively by numerical simulation in this dissertation. The major works and results of this dissertation were as follows:(1) Considering the characteristic of elastoplasticity of Shanghai soft clay, the performance of DN4000 jacking pipe was studied firstly. The variation of contact pressure between pipe and soil during construction was analyzed, and then the influence of soil parameters were discussed. At the same time, the existing computing methods were compared with results of numerical simulation, and the variation laws of earth pressure of the interface were summarized. The computed results were as follows: Reinforced concrete jacking pipe was belong to rigid pipe in Shanghai soft clay. Soil arch effect in the construction would decrease soil stress above and below pipe, while increased soil stress of two sides. Soil arch effect was strengthened with increasing of cover depth, and the distribution of contact pressure was very uniform. Active earth pressure was conservative to calculate lateral pressure in Chinese standard, so it's more reasonable to change the active earth pressure coefficient to be at rest.(2) Then the performance of rectangular and circular caisson under impellent were studied. The shortages of existing computing methods were pointed out, and the regularities of earth pressure distribution under different stress state were analyzed. The computed results were as follows: Under the counterforce on the rectangular caisson working well during pipe jacking, the displacement curve of back wall showed as parabolic while the soil was compressed all behind the back wall. The relation between displacement and earth pressure was used to calculate the earth counterforce. The soil behind back wall deformed entirely and reached to passive state at limiting state, and the vertical earth counterforce was calculated according to Rankine's passive earth pressure theory. The slide mass behind back wall of rectangular caisson was like a cambered sphenoid, and its flat shape was elliptic. While the slide mass behind back wall of circular caisson was like a sphenoid, and its flat shape was semi-circle.(3) The differences and reasons of various design methods was compared at home and abroad finally. Combined with results of finite element, the computing methods of earth pressure of pipe and caisson are optimized in rectilinear pipe line construction. Based on Chinese jacking pipe standard, the value and load model of vertical and lateral earth pressure, and subgrade counterforce were adjusted, which induced two new design models of jacking pipe. Both of the two models were more corresponding with field practice of pipe, and they could minish computed bending moment of pipe. Accordingly, the ratio of reinforcement could be reduced. At the limiting state, horizontal distribution of earth pressure was proposed for rectangular and circular caisson: The counterforce distribution of back wall was ladder-shaped for rectangular caisson, while the increment distribution of counterforce of back wall was centripetal cosine-shaped for circular caisson.