Study On The Consolidation Behaviors Of Dredged Fill In The Qianwan Area Shenzhen

With the rapid development of economic construction and the increasing lack of coastal land resources in China since 1990's, a lot of land reclamation projects have commenced to conduct for the remission on limited land, especially dredging and land reclamation was commonly used in reclamation projects. Double-layered soft clay foundation of dredged fill and marine deposit silt is characterized by high water content and void ratio, of which the engineering practice showed that Terzaghi consolidation theories based on small strain can not accurately predict the consolidation process, guide the design and construction. Consequently, It is very necessary for the systematic study on consolidation characteristics of dredged fill and consolidation behaviors of double-layered soft clay foundation.In this dissertation, based on the engineering background of"Qianwan Reclamation Soft Clay Foundation Improvement Projects Shenzhen China", consolidation characteristics of dredged fill and marine deposit silt and consolidation behaviors of double-layered soft clay foundation are studied in detail by means of in-situ tests, laboratory experiment, theoretical analysis, numerical analysis and so on. The main research achievements are shown as follows:Considering of self-weight consolidation deformation as the main effect during self-weight deposition, one dimension self-weight consolidation governing equation of dredged fill is established. The new equation includes the nonlinear relationship between effective stress, permeability coefficient and solid volume fraction, which are solved by the SFCCP computing program. The new equation can also provide a favorable prediction on physical mechanical indices for self-weight deposition. Some significant influence of initial compressibility, initial permeability and initial solid volume fraction on void ratio, solid volume fraction, self-weight effective stress, surface settlement and settlement rate is analyzed by the SFCCP computing program. It is showed that the void ratio results based on the new model are close to the results from in-situ tests, which the effectiveness and practicability of the analytical model are validated.One-dimensional incrementally-loaded consolidation and permeability tests are performed on dredged fill specimens in Qianwan area Shenzhen by GDS consolidation test systems from Zhejiang University. Permeability and compressibility characteristics of dredged fill are studied, it is shown that the relationships of permeability coefficient-void ratio and compressibility parameters-void ratio is nonlinear, which are taken into account variations of parameters. The optimal permeability coefficient-void ratio fitting relationship kv=ced and effective stress-void ratio fitting relationship e=a(p')b for dredged fill and marine deposit silt are summarized by the analysis of test results.Based on the Gibson one-dimensional finite-strain consolidation theory and Barron vertical sands axisymmetric consolidation theory, a vertical drains and finite-strain consolidation governing equation for double-layered soft clay foundation is established, and solved by the TSDTC computing program. The new program includes some factors of double-layered soft clay foundation, nonlinear compressibility and permeability relationship, multi-stage filling, radial and vertical drainage conditions, initial excess pore pressure distribution.The computing results of consolidation for Florida phosphate mining sludge are compared with the published literatures and the rationality of the computing program is validated accordingly. Consolidation behaviors of double-layered vertical drains foundation are analyzed by the TSDTC computing program. Several influential factors including nonlinear permeability relationship kv=ced fitting parameters, nonlinear compressibility relationship e=a(p')b fitting parameters, layer thickness ratio, multi-stage filling, initial excess pore pressure distribution are also studied as well.Compared with the classical consolidation theory, based on the observed data in situ, Qianwan Reclamation Soft Clay Foundation Improvement Projects Shenzhen China, it is showed that the consolidation settlement process obtained by the mentioned method in this dissertation is more reasonable.The research achievements in this dissertation will have theoretical values to understand the engineering properties of dredged fill, and also have engineering significance in guiding double-layered soft clay foundation improvement projects in land reclamation.