Experimental Study On The Effect Of Pore Fluid Properties On The Clay Mechanical Characteristics

Considering the high water head and the pore fluid conditions of the marine environment faced by the submarine tunnel constructions, this study designed and maked the air pressure preparation device of remolded saturated kaolinite to research the effect of marine environment on the clay mechanical properties. The simulation experiment was carried out to prepare the uniform remolded kaolinite samples, controlling the soil precipitation process by effectively changing the pore water chemical properties,which ensured the formation of clay’s initial microstructures. During the triaxial tests, the back pressure controller isolator was installed to make sure that the environmentwhere the microstructureof claywas formedis consistent,not only during the precipitation process,but also back pressure saturation stage, consolidation stage and failure stage under the load of triaxial tests. By back pressure simulation of high water pressure in marine environment,a series of drained and undrained triaxial tests were carried out to search clay mechanical properties under high water pressure.On the basis of this, the influences of pore fluidproperties on the clay shear strength,stress-strain relationship, stress paths and pore pressure accumulation characteristics were investigated. Also this study tried to explain the effect of different pore fluid environment on the clay mechanical properties, from the recognition that the microstructure precipitationis affected by the pore fluid conditions.The drained and undrained triaxial tests under the high water head condition showed that the undrained shear strength of the specimen changed with the back pressure under the same effective consolidation stress, but the result is not linear. In consolidated isotropically triaxial drained shear tests, the influence of backpressure on mechanical properties,especially shear strength is relatively slighter than undrained shear tests, that is, the drainage condition weakened the influence of back pressure on shear strengthrelatively.The samples with the same backpressure and effective consolidation stress, the critical state lines(CSL) are unique, and those kaolin samples with the same effective consolidation stress and different back pressure, the final effective stress state falls on a straight line parallelled to the total stress path of the undrained shear processon the p’-q curve.The undrained triaxial tests of remolded kaolin samples prepared in different pHand salinity of pore fluid showed that, while pH=5 the electrostatic attractionbetween clay particles dominated to form the edge-face flocculation structure, leading to the larger initial void ratioe. So the shear strength and the strain modulus is lowerunder the low consolidation stress, and with the increase of consolidation stress, both shear strength and strain modulus are increased because ofthe clay particles rearrangement.when pH=9 the double-layer repulsion between particles dominated, leading to face-face dispersion or agglomeration structure. Under the lower consolidation stress, the smaller distancebetween clay particlesmaked the smaller initial void ratio e and larger shear strength.With the increase of the consolidation stress, both the shear strength and the initial tangent slope of the dispersion structure decreased. NaCl changed the interaction between clay particles,balanced the negative potential of the particles surface, and reduced the repulsion, so that the claymicro-structure changedfrom the dispersion to the edge-face flocculation. The shear strength was higher than pH=7, which were also proved in other mechanical properties including the stress path, pore pressure accumulation and compressibility.