ABSTRACT
The 3,297m long Satsuma Tagami Tunnel, which is located at the southern end of the Kyushu Shinkansen railway line, passes beneath a residential tract that was developed by grading Shirasu plateau. At several construction sites on the Shirasu plateau there are sites where old valleys formed by deep rivers erosion were filled with Shirasu material. Shirasu is easily eroded by flowing water. In a saturated condition it becomes friable and will easily collapse. Shirasu fill has no welded structure and has lost the ability to consolidate. This paper presents a new pre-support method (pipe roof; pipe jacking plus water cutoff injection from within the pipes) that was developed and applied in these sites.
