ABSTRACT

An old defective sewer pipe, when it is damaged, may eventually cause local subsidence or a cave-in in the road. Recently, the number of pipes which are older than the service life time of 50 years, has been rapidly increasing. Accordingly, incidents of a cave-ins are found to be more frequent in urban areas. In spite of the significance, full investigation of the road cave-in is often skipped as the urgent road restoration is usually prioritised. It is difficult to identify the real cause clearly because the eventual cave-in is likely to occur long after the initial formation of a cavity in soil. The congested underground lifeline structures also make it complicated.