Application of the pipe jacking method as a means of drainage from landslide dam

Wataru SAKURAI, Ryo SAKAI, Yasuyuki OOTUKA, Hiroaki AOKI, Hideki NAGAHARA and Yoshinori ARAKI

When it was hit by Typhoon No. 12 in September 2011, a huge landslide dam was formed in the riverbed in Kuridaira district of Totsukawa Village in Nara prefecture, Japan. In October 2011, emergency counter measures were initiated, and an overflow channel that was used for the temporary drainage of the dam pool was constructed. However, during Typhoon No. 17 in September 2012, the flood waters eroded the channel and broke approximately two]thirds of the length of its banks. Fixing or reconstructing the drainage became urgent, so the drainage would last until the next flood season. A section of underground drainage pipes located 10]meters beneath the broken channel was used. There are two different methods of pipe construction: the pipe jacking and the cut and cover method. Due to the building period and to promote economic efficiency, the pipe jacking method was adopted. Despite possible construction challenges, such as vulnerable ground conditions and disturbance from tree trunks buried in the collapsed soil, a section of pipe 160 meters in length was installed within a one]month period, which was half the time the original estimate stated it would take. The construction process presented here was recognized as an efficient way to drain landslide dams.