湿干冻融耦合循环作用下膨胀土裂隙演化规律

Evolution rules of fissures in expansive soils under cyclic action of coupling wetting-drying and freeze-thaw

裂隙的发生与演化是膨胀土在各种外部条件作用下的显著特征。针对北疆高寒地区膨胀土渠道边坡劣化问题,以渠基土每年经历通水、停水及冻结、融化过程为研究条件,开展了单向湿干冻融耦合循环作用下膨胀土裂隙试验。采用计算机断层扫描(CT扫描)及三维重建技术,对湿干冻融耦合循环作用下膨胀土试样内部裂隙演化特征进行定量描述,研究了不同湿干冻融耦合循环次数对膨胀土三维裂隙演化规律的影响。试验结果表明,湿干冻融耦合循环作用下的试样内部裂隙发育存在明显的区域性分布特征,裂隙的发育深度在5次循环后逐渐趋于稳定,对应于试样初始总高度的40%。对比不同循环次数作用下试样内部裂隙的发育形态可知,试样内部裂隙发育模式由循环初期浅层分散分布向后期深层汇聚偏转进行转化。采用切片裂隙率、弯曲度、分支数及死端点4个指标能较好地定量描述裂隙空间分布及连通性随循环次数的演化规律。研究成果对进一步揭示干湿冻融耦合作用下膨胀土渠道的劣化过程和破坏机制具有一定参考价值。

The occurrence and evolution of fissures are the significant characteristics of expansive soils under the action of various external factors. With regard to the deterioration of slopes of the canals of expansive soils in high and cold regions in the northern area of Xinjiang Uygur Autonomous Region, the tests on the fissures in expansive soils are performed under the unidirectional cyclic action of coupling wetting-drying and freeze-thaw considering the processes of the foundation soils of the canals witnessing water supply, water cut-off, freezing and thawing. By means of the CT scanning and 3D reconstruction techniques, the evolution characteristics of the internal fissures in expansive soils are quantitatively described under the cyclic action of coupling wetting-drying and freeze-thaw, and the influences of various coupling wetting-drying and freeze-thaw cycles on evolution rules of 3D fissures in expansive soils are investigated. The test results show that the internal fissures in the samples exhibit the development characteristics of obvious regional distribution. The growth depth of the fissures gradually tends to be stable after five cycles, corresponding to 40% of the initial total height of the samples. A comparison of development morphologies of the internal fissures in the samples under various cycles indicates that the development mode transforms from the shallow scattering distribution at the initial stage to the deep gathering one at the final stage. By using the four indices of porosity, bending, branching number and dead endpoints of slices, the evolution rules of the spatial distribution and connectivity of the fissures with the cycles can be quantitatively depicted more satisfactorily. The achievements of this study have certain reference values for further revealing the deterioration process and failure mechanism of canals of expansive soils under the coupling action of wetting-drying and freeze-thaw.