冻融循环和土壤性质对东北黑土抗剪强度的影响

为了揭示东北黑土区季节性冻融循环作用和土壤性质对土壤可蚀性的影响,采集黑龙江省宾县典型薄层黑土区(BX)和克山县典型厚层黑土区(KS)0—20cm的耕层土壤,通过室内冻融循环模拟和土壤直剪试验,分析了冻融作用和土壤性质对土壤抗剪强度的影响。结果表明:(1)经历1次冻融作用后BX和KS 2种供试土壤抗剪强度分别减小3.9%和9.2%,二者黏聚力分别减小15.2%和29.4%,内摩擦角分别减小1.4%和3.6%。经历7次冻融作用后,BX和KS2种供试土壤抗剪强度分别减小9.1%和15.1%,土壤黏聚力分别减小40.7%和74.5%,土壤容重分别减小6.7%和9.2%。受土壤有机质、水稳性团聚体、黏粒含量等的影响,KS土壤抗剪强度、黏聚力、内摩擦角和土壤容重的减小幅度皆大于BX供试土壤。(2)2种供试土壤抗剪强度皆随冻融循环次数的增加呈先逐渐减小后趋于稳定的变化趋势;第1次冻融循环对土壤抗剪强度破坏最大,经历1次冻融循环后2种土壤抗剪强度和黏聚力的减小量分别占7次冻融循环土壤抗剪强度和黏聚力总减小量的43.4%和61.0%,37.3%和39.4%。(3)土壤抗剪强度与土壤容重和团聚体平均重量直径(MWD)呈极显著的正相关,而与冻融循环次数呈极显著的负相关。

Effects of Freeze-thaw Cycles and Soil Properties on Mollisol Shear Strength in Chinese Black Soil Region

In order to reveal effects of seasonal freeze-thaw cycles and soil properties on soil erodibility in the black soil region of Northeast China, the effects of freeze-thaw cycles and soil properties on soil shear strength were analyzed through indoor freeze-thaw cycle simulation and direct shear tests in laboratory. Two different tested soils were collected from top soil (0-20 cm plough layer) at typical thin-layer black soil region (BX) in Binxian County and typical thick-layer black soil region (KS) in Keshan County of Heilongjiang Province. The results showed that:(1) Freeze-thaw alternations reduced soil shear strength, cohesion and internal friction angle for both tested soils (BX and KS). After one time of freeze-thaw cycle, soil shear strength of BX and KS tested soils decreased by 3.9% and 9.2%, the soil cohesion decreased by 15.2% and 29.4%, and internal friction angle decreased by 1.4% and 3.6%, respectively. After seven times of freeze-thaw cycle, soil shear strength of the two tested soils decreased by 9.1% and 15.1%, soil cohesion decreased by 40.7% and 74.5%, and soil bulk density decreased by 6.7% and 9.2%, respectively. Due to the differences in the contents of soil organic matter, soil water stable aggregate and clay content, the decreasing extent of shear strength, cohesion and internal friction angle of KS tested soil were all greater than those of BX tested soil. (2) Soil shear strength decreased gradually and then tended to be stable with the increasing of freeze-thaw cycles for both tested soils. Moreover, the first freeze-thaw cycle had the greatest damage to soil shear strength, the decrement of soil shear strength after the first freeze-thaw cycle for both BX and KS soils occupied 43.4% and 61.0% of the total decrement of soil shear strength after seven freeze-thaw cycles, respectively; the decrement of soil cohesion after the first freeze-thaw cycle accounted for 37.3% and 39.4% of the total decrement of soil cohesion after seven freeze-thaw cycles, respectively. (3) Soil shear strength had significant positive correction with soil bulk density and mean weight diameter of soil aggregates (MWD), while it had significant negative correction with freeze-thaw cycles.