冻融循环和土壤含水率对棕壤崩解特性的影响

Effects of Freeze-thaw Cycles and Soil Water Contents on Disintegration Characteristics of Brown Earth

以沈阳地区5~7 cm和25~27 cm 2个深度原状棕壤为研究对象,分析冻融循环次数和土壤含水率对棕壤崩解特性的影响。根据气象数据结合野外观测结果,共设计了5个冻融循环次数。控制土样质量含水率分别为10%、15%、20%、25%和35%。采用静水崩解,通过数显拉力计及测量软件测定崩解过程。结果表明:(1)棕壤崩解具有阶段性,包括快速吸水阶段、指数崩解阶段、阶跃崩解阶段和崩解完成阶段。其中指数崩解阶段是崩解过程的主要发生阶段,土样因拉扯或失去支撑接连崩落。该阶段的崩解速率和非毛管含水率对冻融循环次数的响应规律一致。根据拟合曲面,10%~15%的含水率区间存在最易崩解含水率,其最终崩解率最大。当土样含水率为25%和35%时,土样会跳过指数崩解过程直接进入阶跃崩解阶段。含水率35%条件下,5~7 cm和25~27 cm土样的最终崩解率很小,不超过6.93%和11.14%。(2)冻融作用会对含水率为10%和15%土样产生超固结效应,加速土壤孔隙的两极化分布,土样指数崩解阶段的崩解速率和非毛管含水率,最终在多次冻融后增加。冻融作用也会对含水率为25%和35%土样结构产生影响,扩张土壤孔隙造成内部沉降,以及降低吸水能力。土样指数崩解阶段的崩解速率和非毛管含水率,最终在多次冻融后减小。(3)25~27 cm土样孔隙差异性略大,较高的黏粒含量抑制了双电层对自由水的控制能力,最终崩解率偏高。冻融作用可将土壤抵抗由内到外发生侵蚀的能力,转化为抵抗由外到内发生侵蚀的能力。研究结果可为棕壤侵蚀研究提供数据支撑。

【Objective】Undisturbed brown earth soils from 5–7 cm and 25–27 cm depths in the Shenyang area of China were collected for this research.The effects of freeze-thaw cycles and soil water contents on the disintegration characteristics of the soils were analyzed.【Method】Based on meteorological data and field observation,five freeze-thaw cycles were designed.The weighed water contents of the soil samples were regulated to 10%,15%,20%,25%and 35%,respectively,and the disintegration process was measured.【Result】(1)The soil disintegration had four phases,including the rapid water absorption phase,exponential disintegration phase,step disintegration phase,and disintegration completion phase.In the four phases,the exponential disintegration phase was regarded as the main disintegration process.Importantly,during the exponential disintegration phase,the soil sample collapsed continuously due to pulling or losing support.Also,the disintegration rate in the exponential disintegration phase and non-capillary water content showed similar behavior as the increasing freeze-thaw cycle.According to the two fitting surfaces,there was a most easily disintegrating soil water content in the range10%-15%in which the total disintegration rate was largest.When the water contents were 25%and 35%,all soil samples skipped the exponential disintegration phase and directly entered the step disintegration phase.The total disintegrations of 5-7 cm and 25-27 cm soils were very small under 35%soil water content,and was no more than 6.93%and 11.14%,respectively.(2)Over-consolidation was observed on soil samples with 10%and 15%water contents,and the polarization distribution of soil pores was accelerated under the freeze-thaw cycles.The disintegration rate of the exponential disintegration phase and non-capillary water content of both soil samples was increased after continuous freeze-thaw cycles.Under the freeze-thaw cycles,the structure of soil samples with 25%and 35%water contents was destroyed,soil pores were expanded with an internal settlement,and the water absorption capacity was reduced.(3)The pore difference of 25-27 cm soil sample was slightly larger,the control ability of electric double layer to free water was inhibited by the higher clay content,which resulted in a higher total disintegration rate.【Conclusion】The ability of soil to resist erosion from inside to outside was transformed into the ability from outside to inside under freeze-thaw cycles.All the findings may serve as a data basis for brown earth soil erosion research.