| In recent years,with the vigorous development of deepwater long-span suspension bridge engineering in China,caisson is widely used as a common anchorage form of suspension bridge.As a deep-buried large-scale foundation form,the distribution characteristics of side wall and basement soil reaction force of caisson under the combined action of main cable anchor tension and self-weight load are not only affected by the early dynamic subsidence process,but also by a series of construction processes such as bottom sealing and filling after subsidence,which need to be characterized and calculated precisely.Based on the north anchorage caisson project of Nanjing Xianxin Road crossing river channel,through theoretical analysis,finite element calculation and field monitoring,considering the influence of each construction process,this paper explored the distribution characteristics of the reaction force of the sidewall and foundation soil of the anchorage caisson after sinking in place.The main research contents are as follows :(1)In this paper,the Coulomb friction law was introduced to describe the friction effect of the base soil.Assuming that the displacement mode of the caisson is translational and rotational,the construction process was simplified as a equivalent load,and the static equilibrium and the displacement coordination equation of the contact surface were listed.The calculation formulas of the reaction distribution of the side wall of the caisson and the base soil,the displacement and rotation formulas of each point of the foundation,and the calculation formula of the critical load of the base sliding were derived under the conditions of no base sliding and sliding.This method was compared with the calculation method of horizontal displacement and action effect of rigid caisson foundation given in the specification to verify the engineering applicability of this method.(2)A full-scale finite element model was established based on the project,and the construction process was simulated by the activation / passivation grid element.It is found that the m method used in the theoretical calculation cannot accurately describe the distribution characteristics of the side wall soil reaction along the depth of the caisson,and the change of the side wall soil reaction with the construction process is mainly caused by the inclined displacement of the caisson.The distribution of foundation soil reaction is most obviously affected by pouring bottom sealing concrete.The caisson before bottom sealing can be simplified as a local elastic foundation deep beam,and can be simplified as a rigid box foundation after bottom sealing.(3)By sorting out the monitoring data of soil reaction in Xianxin Road north anchorage caisson,it is found that the measured distribution of soil reaction along the depth is close to the finite element calculation results,and the soil reaction near the bottom is reduced due to the existence of stress relaxation zone at the blade foot.The early dynamic subsidence process produces unpredictable disturbance to the foundation soil,and the numerical difference of the reaction force of the foundation soil at each measuring point is large and there is no obvious law.Affected by the excavation form of ’ big pot bottom ’,the soil at the bottom of the partition wall is loosened and weakened,and the soil at the bottom of the blade foot is compacted and strengthened.In the overall trend,the soil reaction force at the bottom of the blade foot is much larger than that at the bottom of the partition wall.The partition wall mainly plays a structural role and increases the overall stiffness of the caisson.The supporting effect of the bottom soil is limited,which is inconsistent with the finite element calculation results. |
