下垫层 meaning in English

base course
cushion
underlayer
underlying bed

Flow of block avalanche soils is caused by the resistance reduction due to pore water pressure . the supernormal pore water pressure between the block avalanche soils and underlay reduces the weight of block avalanche soils as well as the resistance between the block avalanche soils and underlay
块状崩塌土快速加载使其与下垫层之间出现超载孔隙水压力，且不能及时消散，减小了块体的有效重量，达到了减阻作用，其流动化机理为压差减阻。