下承层 meaning in English

support layer/subgrade surface

Preparation for construction : the surface of the under layer should be even and firm , and in accordance with the design requirement , without loose material and flaccid site , and need to reroll 2 3 times within full - width range of the subgrade with vibrating roller before the construction , as well as test the compaction and defecting , to check whether there is unqualified point in the soil base
施工准备：施工前下承层表面要平整、坚实，符合设计要求，无松散材料和软弱地点，施工前要用振动压路机在路基全宽范围内复压2 3遍，同时进行压实度及弯沉检验，检查土基中是否有不合格点。