Experimental Study On The Effects Of Orientation Of Principal Stress And Initial Sampling Water Content On The Static And Dynamic Shear Behavior Of Satuated Silt

The initial stress conditions of the soil elements of the foundation of buildings or marine structures are usually very complex. The value and direction of principal stress keep changing at the same time. The research about direction of principal stress has close relationship with sample preparation method and anisotropy. Besides, the object soil is usually sand or clay rather than silt that is easy to liquefy. On the other hand, sample preparation is a key step for soil laboratory test and different sample preparation methods will lead different of soil structure and the different of mechanics reaction behavior of samples under loading. Studying the effects of direction of principal stress will indicate the anisotropy lead by different sample preparation methods.By using the soil static and dynamic universal tri-axial and torsional shear apparatus, the tests were done on Shan-Dong Dong-Ying intact saturated silt and remolding saturated silt prepared by tamping method controlling three kinds of initial sampling water content. The consolidation conditions were three-directional anisotorpic consolidation of different initial angles of the principal stress. Under the mean principal stress and coefficient of intermediate principal stress were fixed, the stress-controlled undrained static shear tests and dynamic torsional shear tests were performed with different models of direction changes of principal stress. What's more, the static shear tests contained two models:the direction angels of principal stress changed or fixed. The effects of initial orientation of the principal stress, orientation of the principal stress during shear processes, initial sampling water content on static and dynamic stress-strain relations, the pore water pressure, the effective stress paths and strength of saturated silt were respectively studied.The result of static torsional shear tests under 5 kinds of initial direction angels of principal stress ao showed that:the stress-strain relationships of the intact silt were obvious strain-hardening and the samples made by Dry-Tamping(DTS w0=0%) were probably strain-hardening, the samples made by Moist-Tamping(MTS w0=5,10%) were signaficantly strain-softening. For same generalized shear strain, the generalized shear stess of intact sample and DTS all decreased and MTS was little affected by initial direction angels of principal stress as the direction angel of principal stress increased. During the torsional shear process, the intact silt experienced the translation from shear-contraction to shear-dilatancy. DTS had the obvious phase-transformation state from shear-contraction to shear-dilatancy. There wer only shear-contraction displayed in MTS.Under 3 kinds of initial direction of principal stress, the result of static shear tests of fixed direction of principal stress showed that:initial sampling water content decided the stress-strain relationship strain-strengthening or strain-softening, and influence the grade of strain-softening of MTS. With the propernitial sampling water content, initial structure anisotropy will be eliminated. The shear strength of DTS was significantly higher than that of MTS, but the shear strength of MTS was little affected by the initial sampling water content. Besedes, the shear strength of remolding sample decreased as the direction angel of principal stress increased.The result of dynamic torsional shear tests under 3 kinds of ao indicated that: with the same initial direction of principal stress and number of cycles, the dynamic strength of DTS was apparent higher than that of MTS. For the samples made by same initial sampling water content, the dynamic strength decreased as the direction of principal stress increased.In addition, MTS had the larger reduction in dynamic strength. The um/p0'-N relationship relied much on initial sampling water content. The development model of DTS was much close to the arcsine curve which was proposed by Seed. The initial direction of principal stress had some influence on the development rate of um/p0'.At last, generally study the effect of different stress paths on the shear characteristic of saturated remolding silt. It showed that: stress path had a very considerable affect on the residual strength of the saturated remolding silt. Flow-slide deformation and cyclic mobility in the dynamic shear tests respectively matched well with strain-softening and strain-hardening in the static shear tests. Relative to the static shear tests, the dynamic torsional shear tests had a significant influence on the cumulative effect of pore water stress for DTS. However, that of MTS was little affected by different stress paths.