底土层是位于心土层以下的土层。一般位于土层表面50-60厘米以下的深度。
劳克雷说，“鹭是通过慢慢移动来搅动底土层并找到食物的”。
"Herons do a shuffling behavior to stir up the substrate" and find food, said Lockley.
采用降低坑底土层渗透性的措施和选择最佳的降水深度能有效地控制坑外地表的沉降。
By reducing the permeability of soil at the bottom of pit and selecting optimal dewatering depth, the settlement of ground surface can be well controlled.
当土壤水吸力增大到一定值时，中间土层的土壤非饱和导水率反而大于底土层和表土层。
While the soil water suctions increased to some values, the unsaturated hydraulic conductivities in middle soil layers were higher than those in topsoil layers.
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