疏水石 meaning in Chinese

drainage aggregate
gravel layer

The university was pro - active in making the well - being of the flame tree outside the station an important consideration in the improvement project . strict supervision was in place during the work so that the tree would not be affected . a gravel layer was added to provide protection for the root area of the tree
大学积极保育火车站外的一株凤凰木，该树亦被列入改善工程的重要考虑因素，严格监控在施工期间凤凰木不会受到工程影响，并特别用疏水石堆成保护层，保护凤凰木的根部。