Experimental Study On Nonlinear Characteristics Of Permeability And Compressibility Of Soft Clay

With the rapid development of economic and construction in coastal areas,The scale and technology of reclamation have achieved a vigorous development in China.Dredged silt is in a state of flow and its water content is much bigger than its liquid limit,which is underconsolidated soil.It has been found that the nonlinear characteristics of permeability and compressibility of dredge fill under lower stress are different compared with the higher stress.The practical application shows that the traditional small-strain consolidation theory to predict compressibility and permeability of dredge fill was usually unsuitable for clay slurry consolidated with effective stress.In this paper,relying on the construction of land reclamation in Tianjin,China,three specimens with different liquid limits are taken from three land reclamation sites,I.e.Lingang(TJLG),Nangang(TJNG),Donggang(TJDG)in Tianjin for the present studies.The 1-D consolidation and permeability tests are conducted in a new consolidation testing system(model GDSCTS)produced by GDS Instruments Pte Ltd,UK.The detailed contents are as follows:(1)Consolidation and permeability tests were conducted on soft clays with different liquid limit(41.50%,50.25%,46.75%)by GDS consolidation apparatus.The coefficient of permeability of soil specimen under the given consolidation pressure is obtained.(2)Regression fitting analyses on 4 common nonlinear permeability models and 3 nonlinear compressibility models were performed based on the test data.The preferred nonlinear function relationships for dredged fill in Tianjin Binhai district are obtained.(3)Comparing with the fitting parameters,soil samples with different liquid limits have different parameters for the same model.In order to find the universal law of permeability coefficient and compressibility with the soil property and void ratio,The void ratio was normalized by the liquid void ratio e_L,and the relationships of e/e_L with logkv and logp were established based on the test data through the Chapman-Richard curve fitting model.(4)The relationships of e/e_L with logkv and p were further verified using 29 groups of test data of permeability and 12 groups of test data of compressibility collected from China and abroad.Relatively good agreements are achieved.The obtained logkv vs.e/e_L and logp vs.e/e_L relationships can be simplified to bilinear equations with their intersection point on e/e_L= 1.3 and e/e_L= 1.0 respectively.The proposed relationships can be used as preliminary tools to calculate the compressibility and permeability of reconstituted marine clay encountered in land reclamation projects.