Influence of Freezing-Thawing Cycles on Mechanical Properties of Tailing Soil at Yunnan-Guizhou Plateau
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摘要: 为研究尾矿力学指标在冻融循环过程中的弱化规律，基于冻融尾矿土的常规三轴固结不排水剪切试验，对冻融前后尾矿土的各项力学指标进行了分析. 首先对尾矿土试样进行开放条件下的冻融试验，设置0、1、5、10、15次冻融；然后对不同冻融次数下的尾矿土进行常规三轴固结不排水剪切试验，设置50、100、200、300 kPa 4组围压；最后基于试验结果，对抗剪强度、峰值抗剪强度及弹性模量等力学指标进行分析. 研究表明：冻融对尾矿土的力学性质影响显著，随着冻融次数的增加，其应力-应变关系曲线由应变软化型逐渐向加工硬化型发展；破坏形式由脆性剪切破坏转变为延性破坏，剪切过程中孔压负增长的趋势逐渐减弱至消失；抗剪强度指标、峰值抗剪强度及弹性模量逐渐降低，其中，尾矿土受第1次冻融的扰动最大，表现为有效凝聚力和有效内摩擦角分别降低了30.55%和6.33%；峰值抗剪强度下降比的平均值达42.66%，弹性模量下降比的平均值达33.61%；10次冻融后尾矿土的力学指标趋于稳定，从第10次到第15次冻融，有效凝聚力和有效内摩擦角分别降低2.94%和0.37%；峰值抗剪强度下降比的平均值和平均弹性模量下降比的平均值分别为2.53%和4.03%，建议采用冻融10次的力学指标作为工程设计的依据.Abstract: In order to study how the mechanical properties of tailing soil evolve during the freezing-thawing process in open environment, a series of triaxial consolidated undrained (CU) shear tests were carried out with different numbers of freezing-thawing cycles and confining pressures. In the tests, 0, 1, 5, 10 and 15 freezing-thawing cycles were set and the groups of confining pressures including 50, 100, 200 and 300 kPa were applied. Based on test results, the mechanical indexes, including the shear strength, the peak value of shear strength and elastic modulus are finally analyzed. The results indicate that the influence of freezing-thawing on mechanical properties of tailing soils is significant. As the number of freezing-thawing cycles increases, the stress-strain curves gradually transform from the strain-softening type into the work-hardening one, whereas the brittle failure pattern turns into plastic failure, and the negative growth of pore pressure during the shearing process becomes weak till disappears; the peak shear strength, cohesion, internal friction angle and elastic modulus gradually decrease; during the process, tailing soils are affected most by the first cycle of freezing-thawing, of which the effective cohesion and effective internal frictional angle is reduced by 30.55% and 6.33%, respectively; and the average reduction ratios of the peak shear strength and elastic modulus are 42.66% and 33.61%, respectively. The mechanical indexes of tailing soils tend to stabilize after 10 freezing-thawing cycles, and from 10 to 15 cycles of freezing-thawing, the effective cohesion and effective internal frictional angle are reduced by 2.94% and 0.37% respectively; and the average reduction values of the peak shear strength and elastic modulus are 2.53% and 4.03%, respectively. The mechanical indexes of 10 freezing-thawing cycles are proposed as the reference for engineering design.
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图 2 未经室内冻融处理的重塑尾矿土试样的电镜扫描图像
Figure 2. SEM images of remoulded tailing soil without indoor freezing-thawing treatment
图 3 冻融循环对试样体积的影响
Figure 3. Influence of freezing-thawing cycles on volume expansion of tailing soil
图 4 冻融循环次数对应力-应变关系曲线的影响
Figure 4. Influence of freezing-thawing cycles on stress-axial strain curve
图 5 冻融循环对尾矿土破坏形式的影响
Figure 5. Influence of freezing-thawing cycles on failure form of tailing soils
图 6 围压对孔压-轴向应变关系曲线的影响
Figure 6. Influence of confining pressure on pore pressure-axial strain curve
图 7 冻融循环次数对峰值抗剪强度的影响
Figure 7. Influence of freezing-thawing cycles on peak shear strength
表 1 尾矿土主要物理参数
Table 1. Mail physical parameters of tailing soils
比重 干密度/
（g•cm−3）孔隙比 液限 /% 塑限/% 天然含水
率/%塑限指数 /% 液限指数 可溶性盐
含量/%3.0 1.492 1.01 71 32 35 39 0.07 2～3 
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表 2 尾矿土X射线能谱分析结果
Table 2. EDS analysis results of tailing soil
% 项目 O C S Ca Si Fe Zn Al K Mg Mn 质量百分数 56.28 5.28 10.51 10.46 6.03 5.61 2.74 1.37 0.61 0.37 0.75 原子数目百分数 70.38 8.80 6.56 5.22 4.30 2.01 0.84 1.01 0.31 0.3 0.27
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表 3 不同冻融循环次数下有效黏聚力和有效内摩察角
Table 3. Effective cohesion and effective internal friction angle under different freezing-thawing cycles
N/次 c/kPa φ/（°） c'/kPa φ'/（°） 0 254.20 11.00 120.70 38.25 1 104.20 10.79 83.83 35.83 5 60.00 6.33 44.50 24.18 10 39.74 6.30 30.36 19.76 15 31.67 6.24 26.81 19.62
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表 4 不同冻融循环次数和围压下的弹性模量
Table 4. Elastic modulus under different freezing-thawing cycles and confining pressures
MPa N/次 围压 50 kPa 100 kPa 200 kPa 300 kPa 0 425 583 618 638 1 235 340 413 543 5 108 155 170 174 10 55 115 138 143 15 50 98 100 105
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