The Variable Stiffness Analysis And Design For Balance Settlement Of The Circular RAFT Foundation

The contact pressure between soil and the flexible foundation under uniform load is uniformly distributed.The additional stress of subsoil under the contact surface is large inside and small outside.The settlement of the rigid foundation is uniform and the contact pressure is small inside and large outside.The stiffness of the soil storage tanks is between that of the flexible foundation and the rigid foundation,and so is the characteristic of settlement.Because the initial vertical rigidity of the natural ground or the foundation soil through a uniform treatment(such as uniform pile)is evenly spaced,the settlement characteristic of the circular raft foundation under uniformly distributed loads is large inside and small outside.The non-uniform settlement is ignored by the traditional design method of the oil tank foundation.According to the traditional design,the foundation is rigid and the foundation soil is uniformly treated.With the development of the oil tank,the load and the bearing areas are getting larger,and many tanks are built on the soft foundation soil in the coastal area.So it is very difficult to avoid the non-uniform settlement.The over-consolidated clays model(the UH model)model proposed by Yao et al.is able to describe the shear dilatation/contraction,strain hardening/softening,density dependent and path dependent behavior and so on.And the author has succeeded in combining the UH model and the finite element analysis software ABAQUS.In this paper,the author adopts the UH model as the soil constitutive model and builds 3D finite element analysis model for analysis.Based on the analysis of the force and settlement characteristic on the flexible foundation,the rigid foundation and the normal stiffness foundation,the author researches the sensitivity of main influencing factors for the non-uniform settlement of the oil tank foundation.And then the variable stiffness balance method is introduced to the oil tank foundation design.Through changing the distribution of the soil stiffness under the foundation,the author researches the non-uniform settlement characteristics of the oil tank foundation influenced by the variable stiffness balance method.At last,the variable stiffness method of non-uniform piles is simulated.And the author also expects that the research can provide reference for practical design.