The effect of freezing and thawing cycles on the mechanical properties and slope stability of the waste dump
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摘要: 为了解冻融循环引起的排土场散体物料剪切强度劣化规律，采用自主研发的大型直剪仪开展冻融循环作用下土石混合体的剪切试验，得到不同冻融循环次数下的排土场土石混合体剪切强度劣化曲线，并通过CT扫描分析不同冻融循环次数下土石混合体内部细观结构演化特征；最后，开展考虑冻融循环影响的排土场边坡稳定性分析。研究结果表明，在低法向压力下，散体物料的剪切应力-位移曲线主要呈现应变软化型，且在剪切过程中伴随剪胀行为；随着法向压力增大，曲线逐渐向应变硬化型转变，剪切过程中主要呈现剪切压缩行为；冻融循环次数增加，会使曲线应变硬化行为明显，逐渐弱化剪胀行为，内聚力和内摩擦角逐渐减小。当冻融循环次数达到15次时，内聚力和内摩擦角的减小量分别为18.45 % 和9.42 %；冻融循环导致散体物料内部细颗粒冻胀挤压碎裂，致使细颗粒和孔隙间发生错位与重组；冻融循环引起的散体物料孔隙变化主要集中在前5次；当冻融循环次数达到15次时，排土场安全系数减小率约为7.6 %。研究结果可为寒区排土场稳定性分析提供参考。Abstract: To investigate the shear strength evolution of soil-rock material in waste dump induced by freezing and thawing cycle (FTC), the shear tests are conducted by a self-developed direct shear apparatus, and the effect of FTCs on the shear strength degradation curve of soil-rock material is obtained. Furthermore, the inner microstructure of soil-rock material induced by FTC is analyzed by computer topography (CT)scanning testing.Finally, the stability of waste dump after and before freezing and thawing is compared. The results show that the shear and displacement curves of soil-rock material present strain softening during low normal loading pressure. However, the shear and displacement curve development trend changes from strain softening to strain hardening, and the shear dilatancy happens during loading process. As the FTCs increase, the strain hardening behavior becomes more obvious and the shear dilatancy effect is weakened. In addition, both the cohesion and friction angles decrease as the FTCs increase. When the number of FTC increases to 15, the decrement of cohesion and friction angle is 18.45 % and 9.42 %, respectively. The reason is mainly attributed to the dislocation and regroup of fine rock particles induced by freezing crack.The change in porosity of soil-rock material mainly happens within the initial 5 freezing and thawing cycles. The safety coefficient decrement of waste dump is approximately 7.6 % as the FTCs increase from 0 to 15. The results can provide guidance for waste dump in cold regions.
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Key words:
- waste dump /
- cold region /
- freezing and thawing cycle /
- mechanical property /
- stability /
- direct shear apparatus
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图 5 不同冻融循环次数下散体物料的剪切力-剪切位移曲线
Figure 5. Shear stress-shear displacement curve of bulk materials under different freeze-thaw cycles
图 6 不同冻融循环次数下散体物料的垂直位移-剪切位移曲线
Figure 6. Vertical displacement-shear displacement curve of bulk materials under different freeze-thaw cycles
图 7 不同冻融循环次数散体物料的剪胀角-剪切位移曲线
Figure 7. Shear expansion angle-hear displacement curves of bulk materials under different freeze-thaw cycles
图 8 散体物料峰值强度与冻融循环次数关系
Figure 8. Peak strength of bulk materials under different freeze-thaw cycles
图 9 内聚力、内摩擦角与冻融循环次数的关系
Figure 9. Relationship between cohesion, internal friction angle and freeze-thaw cycle times
图 10 内聚力、内摩擦角损伤系数与冻融循环次数关系
Figure 10. Relationship between cohesion, internal friction angle damage coefficient and freeze-thaw cycle times
图 11 散体物料的三维重构图及三维横切面位置
Figure 11. Three dimensional reconstruction drawing and three-dimensional cross-section position of bulk material
图 12 不同循环次数后试样不同位置的孔隙率分布曲线
Figure 12. Porosity distribution curves at different positions of samples after different cycles
图 14 冻融循环后角岩排土场不同排土时期安全系数
Figure 14. The safety factor of different dumping periods of breccia waste dump after freeze-thaw cycle
表 1 试样不同位置横切面的CT重构图
Table 1. CT reconstruction of cross sections at different positions of the sample
冻融次数 试样1/5位置 试样2/5位置 试样3/5位置 试样4/5位置 0次 
5次 
10次 
下载: 导出CSV
表 2 试样不同位置横切面的CT重构孔隙网络图
Table 2. CT reconstruction pore network diagram of cross sections at different positions of samples
冻融次数 试样1/5位置 试样2/5位置 试样3/5位置 试样4/5位置 0次 
5次 
10次 
下载: 导出CSV
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