ABSTRACT
Figure 1 presents a schematic figure of the test apparatus used in this study. A rectangular soil container with dimensions of 300 mm in length, 50 mm in width and 220 mm in height and an opening at the base was employed. The dimensions of the opening were 5 mm in length and 50 mm in width. Model ground was prepared at certain initial water content, and tamped in place in the container to a depth of 200 mm. An overburden pressure which corresponded to that of stresses at 60 cm below ground surface was loaded by brass weights. A water tank was connected to the opening of the container and its water head was always
1 INTRODUCTION
Recently, cave-ins of roads have occurred quite frequently in urban areas in Japan. One of the major causes is considered to be cavities that develop in the ground due to outflow of soil through breakages in sewer pipes. According to the survey conducted by Ministry of Land, Infrastructure, Transport and Tourism (MLIT), Japan, the number of the caveins occurring above sewer pipes tends to increase, when their duration of service life time exceeds 30 years (MLIT 2009). As the sewerage systems constructed during the striking economic progress in the 1950's in Japan have deteriorated simultaneously, it is estimated that the number of cave-ins caused by the damaged sewer pipes would increase more and more in the near future.
