紫色土表土结皮发育特征的试验研究

通过模拟降雨试验,探讨了紫色土表土结皮的发育特征。结果表明：有、无雨滴打击下,紫色土在30min内均形成稳定结皮层,厚度约7～8mm;淋移作用是紫色土形成结皮的主导作用,降雨打击使表土在降雨前期迅速形成致密薄层,抑制了淋移作用并使盖网处理的结皮容重略高;孔隙的剖面分布对入渗、抗剪强度有较大影响,表现在发生层总孔隙度低但分布均匀的盖网处理具有更强的入渗能力,且由于降雨初期未发生致密上层使其抗剪强度略低。

DEVELOPMENT OF SOIL CRUST ON THE SURFACE OF PURPLISH SOIL

Soil crusts hinder water infiltration rate, thus increasing runoff and triggering soil erosion.Purplish soil is one of the most important types of soil in China and readily erodible.To study how soil crust is formed helps us understand how soil erosion proceeds and construct a physical erosion model.In recent years, works have been reported on characteristics and models of soil erosion in the purplish soil region of China.However, st ill not much is known about format ion of soil crusts and its effect on soil erosion process in purplish soil.In order to understand development of soil crusts on the surface of purplish soil and acquire scientific data for erosion risk assessment, a group of experiments were conducted.In the laboratory, two treatments (uncovered and covered with nets) were designed for samples of purplish soil collected in Lizikou Catchment, Sichuan Province.They were subjected to simulated rainfall.Results show that the purplish soil developed a stable layer of crust, 7~8 mm thick in 30 minutes; mechanical illuviation is the main factor of soil crusting, which was weakened by raindrops that beat the surface soil stimulating formation of a thin compacted layer; distribution of soil pores affects water infiltration and shear strength, which was demonstrated in the covered treatment where the total porocity was low, but evenly distributed, while the water permeability was high, because no compacted layer was formed at the init ial stage of the rainfall, thus lowering shear strength.