A study on large volume losses induced by EBPM tunnelling in sandy soils

Tunnelling-induced ground surface settlements can be described by a Gaussian distribution curve with two key factors; the displacement trough width and the volume loss. In most cases the volume losses are well-controlled with maximum settlements less than the allowable limits. However, there have been reports showing abnormally large ground surface settlement, in sandy soil, induced by Earth Pressure Balance Tunnel Boring Machines (EPB TBMs). This research reports field data obtained during the construction of the Metro Line 1 Ben Thanh – Suoi Tien Tunnels in Ho Chi Minh city, Vietnam. Data include ground settlement measurements, the geotechnical conditions and TBM operation parameters. The results show that in locations where large settlements had occurred there were common characteristics of high liquefaction index, large excess pore pressure and abnormally large tail void grouting. A novel equation is suggested to describe the relationship between the volume loss and the liquefaction potential index. This has been calculated using simple and commonly available geotechnical parameters for use in practice as an indicator for potentially large settlements caused by EBP TBM tunnelling in sandy soils.