Abstract
Soil slope stability in seasonally frozen regions is a challenging problem for geotechnical engineers. The freeze-thaw process of soil slope caused by the temperature fluctuation increases the difficulty in predicting the slope stability because the soil property is influenced by the freeze-thaw cycle. In addition, the frozen soil, which has ice crystal, ice lens and experienced freeze-thaw process, could present stronger heterogeneity. Previous research has not investigated the combined effect of soil heterogeneity and freeze-thaw cycle. This paper studies the influence of soil heterogeneity on the stability of frozen soil slope under freeze-thaw cycles. The local average subdivision (LAS) is utilized to model the soil heterogeneity. A typical slope geometry has been chosen and analysed as an illustrative example and the strength reduction method is used to calculate the factor of safety (FOS) of slope. It has been found that when the temperature is steady, the FOS of the frozen soil slope is influenced by the spatial variability of the thermal conductivity, but the influence is not significant. When the standard deviation and the SOF of the thermal conductivity increase, the mean of the FOS is equal to the FOS of the homogeneous case and the standard deviation of the FOS also increases. After the frozen soil goes through freeze-thaw process, the FOS of the frozen soil slope decreases due to the reduction in the cohesion and the internal friction angle caused by the freeze-thaw cycles. Furthermore, the decreasing ratio of the FOS becomes more scattered after the 5th freeze-thaw cycle compared to that of the FOS after the 1st freeze-thaw cycle. The larger variability of the FOS could induce inaccuracy in the prediction of the frozen soil slope stability.
Highlights
In China, the permafrost area is 2.15 × 106 km2, about 22.4% of the country area, and the seasonally frozen soil area is 53.5% of the country area
In order to further investigate the influence of freeze-thaw cycle on the heterogeneous frozen slope stability, similar to the homogeneous case, the effective cohesion decreases from 12 to 10 kPa and the effective internal friction angle increases from 15◦ to 16◦ after the first freeze-thaw cycle
The local average subdivision (LAS) method is used to model the heterogeneity of the thermal conductivity and the strength reduction method is utilized to calculate the factor of safety (FOS) of the frozen soil slope
Summary
In China, the permafrost area is 2.15 × 106 km, about 22.4% of the country area, and the seasonally frozen soil area is 53.5% of the country area. Zhou et al [14] conducted tests on the undisturbed and saturated samples of loess Their results showed that the cohesion decreases with the number of freeze-thaw cycles, while the internal friction angle increases for both the undisturbed and saturated samples. Yu et al [15] conducted tests on the saturated silty clay They found that after 5 cycles, the changes of the cohesion and internal friction angle gradually become stable. The influence of soil heterogeneity in the strength parameters (i.e., cohesion and friction angle) and the hydraulic parameters (e.g., the saturated hydraulic conductivity) on the slope stability has been considered since 1970s, such as Wu et al [18], Cornell [19], Tang et al [20], Vanmarcke [21], Gui et al [22], Griffiths et al [23], Liu et al [24,25], etc. An illustrative example is analysed to investigate the combined effect of soil heterogeneity and the freeze-thaw cycle
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