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采用空心圆柱仪对上海原状软黏土进行了不排水剪切试验,研究了主应力轴旋转条件下中主应力系数对饱和软黏土变形与强度特性的影响。采用等压固结模式对软黏土空心薄壁试样进行固结,并在3种不同主应力轴旋转角度下,对试样进行不同中主应力系数的不排水剪切试验。试验前提为剪切过程中平均应力、中主应力系数与主应力轴旋转角度均保持不变,而偏应力逐渐增大,直至试样破坏。试验结果表明:在不同中主应力系数下,天然软黏土的变形与强度特征存在明显的差异,在3种主应力轴旋转角度下,随着中主应力系数的增加,临界应力比均呈降低趋势,相应的峰值剪切强度减小;在主应力轴旋转角度为0°时,中主应力系数为0.25和0.50的试样均出现了轻微的应变局部化现象,剪应力在达到峰值后呈逐渐降低的趋势;在主应力轴旋转角度为90°时,中主应力系数为0.50和0.75的试样所对应的状态为内外压不等的非轴对称拉伸状态,二者的峰值剪切强度比较接近,而中主应力系数为1.00的试样对应的为内外压相等的轴对称拉伸状态,其峰值剪切强度相比前二者降低了25%;在内外压相等的加载条件下,主应力轴旋转角度由0°增加为90°的同时,中主应力系数由0增加为1.00,试样破坏时对应的临界应力比与不排水剪切强度均逐渐降低。
Undrained shear tests were carried out on the intact soft clay in Shanghai with a hollow cylinder to study the effect of the middle principal stress coefficient on the deformation and strength characteristics of saturated soft clay under the rotation of the main stress axis. The isobaric consolidation mode was used to consolidate hollow thin-walled samples with soft clay and the specimens were subjected to the undrained shear tests with different middle-principal stress coefficients at three different rotation angles of principal stress axes. The test premise for the average shear stress, the main stress coefficient and the main stress axis rotation angle remain unchanged, while the partial stress gradually increased until the specimen damage. The results show that the deformation and strength characteristics of natural soft clay are obviously different under different middle principal stress coefficients. Under the rotation angle of three main stress axes, the critical stress ratio decreases with the increase of middle main stress coefficient And the corresponding peak shear strength decreases. When the rotation angle of the principal stress axis is 0 °, slight strain localization occurs in the specimens with medium principal stress coefficient of 0.25 and 0.50, and the peak shear stress Gradually decrease. When the rotation angle of the principal stress axis is 90 °, the specimens with the intermediate principal stress coefficients of 0.50 and 0.75 correspond to the non-axisymmetric tension with different internal and external pressures. The peak shearing The strength is relatively close, while the sample with medium principal stress coefficient of 1.00 corresponds to the axisymmetric tensile state with equal internal and external pressure, the peak shear strength is reduced by 25% compared with the former two. Under the same loading conditions , The principal stress axis rotation angle from 0 ° to 90 ° at the same time, the main stress coefficient increased from 0 to 1.00, the corresponding critical stress ratio and undrained shear strength decreased.