1·Various trenching methods and pipe geometries are used.
各种方法和管道几何挖沟使用。
2·At that time, there were many liberated black slaves that left the farm and the hometown to do the unfamiliar work, like building railroads and trenching and so on.
在那个时候，有许多解放黑奴说，离开了农场和家乡做了陌生的工作，如建设铁路和挖沟等。
3·Disturbance of the bedrock changes drainage and runoff patterns, which may increase the rate of erosion. Trenching is the exploration activity that most disturbs bedrock.
干扰的基岩排水和径流的变化模式，这可能增加侵蚀率。挖沟是勘探活动，大部分干扰的基石。