Experimental Study Of Strength Characteristics And SWCC Of Unsaturated Loess Xining Region

The paper, taking unsaturated loess in xining area for studying. Conventional triaxial tester, strain controlled direct shear apparatus, GEO-Experts stress related SWCC pressure plate system and electron microscope scanner were used. The paper carried out triaxial shear tests under undrained conditions, direct shear test, SWCC tests and loess microstructure analysis test. The main contents and conclusions are follows:(1) The conventional triaxial tester were be used for remolded unsaturated loess under undrained shear tests, discussing the principal stress-strain curve characteristics of different initial conditions remolded unsaturated loess under at different confining pressures, as well as variations between shear strength parameters with the moisture content and dry density; results showed that: the types of damage of the stress-strain curve changed with confining pressure, dry density, and moisture content.Take the shear test with the same initial conditions in triaxial shear test, comparing results with triaxial test obtained the approximately same regular pattern. That dry density had a greater impact on the cohesion and internal friction angle. The moisture content had a greater impact on cohesion than the influence on internal friction angle.(2) The use of GEO-Experts stress-related soil and water characteristic curve pressure plate apparatus for suction of unsaturated substrates experiment found that undisturbed unsaturated soil-water characteristic curve at different depths. Test results revealed that: the soil water characteristic curves obtained from dehumidifying process and absorbent process can not completely overlap. With the increase of soil matric suction, volumetric water rate was reduced, whether dehumidifying or absorbent process. Shallow soil distribution, the changes of volumetric water rate in soil water characteristic curves in the dehumidifying and moisture absorption process are larger.(3) Scanning electron microscopy(SEM) are used to observe and analysis the grain composition, soil granule shape, arrangement characteristics, the particle surface characteristics, cementation between soil particles, pore characteristics of the undisturbed loess at different depth found that, soil skeleton gradually tend to be more closely with increasing depth. Form of contact between particles also is affected by the arrangement of the skeleton particles. The use of PCAS analysis system for quantitative analysis found that pore distribution rule of soil samples is irregular, and the soil pore arrangement characteristic is similar. Particles and pores morphology belong to more complex and slender. The perimeter of the particle and pore surface integral dimension values will change along with the increase of soil depth, the deeper soil, the higher degree of aggregate soil particles, the smaller pores.