Novel mitigation techniques using base opening and permeable piles against sand liquefaction induced uplift for existing manholes

Abstract

Soil liquefaction induced manhole uplift causes significant disruptions to vital lifelines following major earthquakes. In the past decades, remediation measures have been proposed to tackle this problem for newly constructed manholes. Nonetheless, mitigation measures for existing manholes were rarely reported, which leaves existing manholes facing high uplift risk in future earthquakes. Aiming to address this problem, this study proposes a series of mitigation measures, including (1) opening a drainage hole at the manhole base, (2) installing a smooth permeable pile under the manhole, and (3) installing a permeable pile with spiral wings under the manhole. The experimental results revealed that these three methods can mitigate manholes uplift to different extents. The drainage opening can mitigate the manhole uplift by releasing the pore water pressure on the manhole invert and draining water into the manhole chamber. The smooth permeable pile can further mitigate the manhole uplift with more drained water and greater retained sidewall friction due to the lowered liquefaction degree in the surrounding soil as a result of the extended drainage effect. However, the additional pull-out resistance expected from the spiral wings was of little contribution in view of the slight uplift difference comparing to the smooth permeable pile. The above observations are also validated with theoretical force equilibrium.