pervious subsoil

透水底... ... ) lean concrete permeable base 贫混凝土透水基层 ) pervious subsoil 透水底土层 ) pervious subsoil 透水下层土 ...

... ) pervious subsoil 透水底土层 ) pervious subsoil 透水下层土 ) impervious clay blanket 不透水粘土层;不透水粘土铺盖 ...