Mechanical Characteristics of Slight-Expansive Soil in Hefei and its Effect by Saturation Disturbance

To study the influence of water and disturbance on the strength and deformation of weak-expansive soil in the Hefei area, the undisturbed samples and saturated disturbed samples of weak-expansive soil in the deep foundation pit of Huifu Road Station of Hefei Metro Line 7 were subjected to conventional saturated triaxial compression (CTC) and triaxial tension (CTE) under three confining pressures of 50 kPa, 100 kPa and 200 kPa, and the undisturbed non-immersed samples were subjected to a triaxial compression test. By comparing the differences of stress-strain, strength index, and deformation modulus between undisturbed and saturated disturbed samples, the influence of saturated disturbance on the mechanical properties of expansive soil was discussed, and the mineral composition and content of expansive soil were tested by XRD diffraction. The test results show that: (1) The soil of the foundation pit of Hefei Metro Line 7 is cohesive weak expansive soil, and the montmorillonite content in clay minerals accounts for 46%. (2) The decrease of cohesion mainly manifests the decrease of strength of Hefei weak-expansive soil. The cohesion of the undisturbed sample is 56% lower than that of the disturbed saturated remolded sample, while the friction angle change is insignificant. (3) The weak-expansive soil in the foundation pit of Hefei Metro Line 7 has the phenomenon of over-consolidation, characterized by the dilatancy softening of the undisturbed sample. (4) The initial modulus of Hefei weak-expansive soil decreased by about 20% after water disturbance, and water infiltration significantly reduced the deformation resistance of expansive soil.