下水管道维修和修复的难题提出了重要而又困难的挑战。因为下水管道处于地下,直到它受到灾难性的破坏以前一直容易被忽视,难以确定其受损程度,甚至难以判断它存在的问题。然而,下水管道一旦破坏和产生泄漏,就可能造成市民生活的重大混乱,所以必须经常地对它进行维修。对于... Sewer pipe repair and repair problems posed an important and difficult challenge. Because sewer pipes are underground, they were easily overlooked until they were catastrophically devastated, difficult to determine their extent of damage and even difficult to judge. However, once a sewer line is damaged and a leak is created, it may cause major disruption to the public’s life and it must be repaired regularly. for...