The Macro-micro Test Research Of Strength Properties Of Weak Expansive Soil In North Water Transfer Project

Expansive soil is a highly plastic clay composed of montmorillonite and illite which isstrongly hydrophilic clay mineral, and its typical characteristics is water-swelling,dehydration-shrinking,In addition, it also has multi-fissure and intensity attenuation. Due tothese peculiarities, the destruction of the buildings caused by expansive soil often haverepeatedly and long-term potential danger, and it causes serious disasters on human life. Inthis thesis, having a series of research to macro-mechanical properties and microstructure ofweak expansive soil of the North Water Transfer Project in Yu Zhou by direct shear residualshear apparatus, GDS unsaturated triaxial instrument, cyclic shear instrument and scanningelectron microscope. The main achievements in this thesis can be obtained as follows.(1) The statics tests are made on the undisturbed and remolded expansive soil by usingdirect shear residual shear apparatus. By analyzing shear stress-shear displacement curve ofexpansive soil in different states to obtain that the structural strength of undisturbedexpansive soil is an important factor affecting the shear stress-shear displacement curvehaving a peak. The change trend of residual strength is substantially the same as the peakstrength with structure changing. In different structural states and ambient conditions,basically showing that: undisturbed sample strength> remolded sample strength> unsaturatedundisturbed sample strength> saturated remolded sample strength. With the pressureincreasing, the strength difference between undisturbed sample and the other three samples isgetting smaller and smaller(2) The unsaturated property of expansive soils are analyzed by using GDS unsaturatedtriaxial instrument. The results show that: the shear strength of expansive soil depends not only on confining pressure, but also closely related to the size of the matric suction and shearstrength increases with confining pressure and matric suction increasing; cohesion non-linearincreases with matric suction increasing; but the matric suction was almost no effect on theeffective angle of internal friction.(3) The dynamical properties of expansive soils are analyzed by using cyclic simpleshear instrument, to draw consolidation pressure and vibration frequency on the impact of thedynamic shear modulus and damping ratio.(4)The expansive soils are micro-scanned by using Scanning electron microscopy, thenusing Matlab software to extract the parameters of the SEM images. To obtain microstructureand mineral composition of expansive soil on the impact of its expansion and contraction andphysical mechanical properties, the microstructures of expansive soils are analyzed from bothqualitative and quantitative.