Methodology for horizontal gravel pack wells in Brazilian deepwater. 巴西深水域中水平砾石充填井的方法。
In drainage of agricultural lands, a filter or gravel envelope is used to prevent the entrance of fine sand and silt into the drains. 在农田排水中常常采用砾石或过滤层来防止粉细砂和泥沙进入排水沟。
