Experimental Study on Mechanical Behavior of Recompacted Unsaturated Expansive Clay
摘要
為了研究吸力變化對非飽和膨脹土變形和抗剪強度特性的影響,利用三套新研制的雙壓力室非飽和土三軸儀,進行一系列吸濕試驗、等吸力壓縮固結試驗和等吸力剪切試驗。試驗土樣取自鄂西北的中膨脹性土,采用靜力壓實方法制備試樣。試驗成果表明:該非飽和膨脹土在低圍壓吸濕過程中的體變性狀呈明顯的屈服特性,因此驗證了Barcelona膨脹土本構模型中SD屈服包線的存在。在等向壓縮固結過程中,該非飽和膨脹土的屈服應力隨吸力增加而增大,而屈服后的壓縮系數隨吸力增大而減少,表明吸力對土體具有硬化作用。該非飽和膨脹土的有效內摩擦角不隨吸力變化而變化,吸力對抗剪強度的貢獻(似凝聚力)隨吸力呈非線性增加,吸力對該膨脹土抗剪強度的貢獻明顯高于壓實高嶺土和砂性土。A laboratory testing program was carried out to investigate the mechanical behavior of a medium unsaturated expansive clay taken from Hubei. Statically compacted specimens were used in this testing program, which was performed using three newly developed double-cell triaxial systems for unsaturated soils. The stress paths adopted in the testing program included wetting under isotropic stress condition, isotropic compression and shearing under different values of constant suction. The test results showed that the recompacted expansive clay exhibited an elasto-plastic swelling upon wetting at a low confining pressure, indicating the existence of the Suction-Decrease (SD) yield locus. Within the suction range considered (0 to 200 kPa), both the yield stress and the post-yield stiffness increased with suction, suggesting a suction-hardening effect on the soil behavior. The slope of critical state hyperlines in (q, p) plane was independent on the value of suction within the suction range considered. The contribution of suction to shear strength for this expansive clay was more significant than that of a compacted kaolin.