Mechanical Characteristics of Slight-Expansive Soil in Hefei and its Effect by Saturation Disturbance
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摘要: 为了研究合肥地区弱膨胀土遇水及扰动对其强度和变形等力学性质的影响，对合肥地铁7号线徽富路站深基坑内弱膨胀土的原状样及饱和扰动样，分别开展了50 kPa，100 kPa和200 kPa三种围压下常规饱和三轴压缩（CTC）和三轴拉伸（CTE）以及原状非浸水样双压力室三轴压缩试验。通过对比原状样与饱和扰动样的应力–应变、强度指标以及变形模量的差异，探讨了饱水扰动对膨胀土力学性质的影响，且采用XRD衍射测试了膨胀土的矿物成分及含量。试验结果表明：（1）合肥地铁7号线基坑土质为弱膨胀土，黏土矿物中蒙脱石含量占46%；（2）合肥地铁7号线基坑的弱膨胀土强度的降低主要表现为黏聚力的降低，原状样较扰动饱和重塑样黏聚力下降了56%，而内摩擦角的变化并不显著；（3）合肥地铁7号线基坑内弱膨胀土有超固结现象，表现为原状样具有剪胀软化特征；（4）合肥地铁7号线基坑弱膨胀土原状样遇水扰动后初始模量下降了20%左右，水的浸润大幅降低了膨胀土抗变形能力。Abstract: 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.
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表 2 膨胀土膨胀潜势划分
自由膨胀率$ {\mathrm{\delta }}_{\mathrm{e}\mathrm{f}} $/% 膨胀潜势 $ {40\le \mathrm{\delta }}_{\mathrm{e}\mathrm{f}} < 65 $ 弱 $ {65\le \mathrm{\delta }}_{\mathrm{e}\mathrm{f}} < 90 $ 中 $ {\mathrm{\delta }}_{\mathrm{e}\mathrm{f}}\ge 90 $ 强 
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表 3 试验方案
试验
编号取样深度
/m试验类型 围压
/kPa试验条件 1 13 双压力室三轴压缩（CTC） 50 原状样 2 100 3 200 4 18 双压力室三轴压缩（CTC） 50 5 100 6 200 7 13 单压力室三轴压缩（CTC） 50 饱和扰动样 8 100 9 200 13 13 单压力室三轴拉伸（CTE） 50 14 100 15 200
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