Applicability of Weighting Method as Measure for Existing Manholes against Uplifting during Liquefaction

It has been confirmed that manholes may protrude from the road surface due to the liquefaction of the ground during a large earthquake. When the uplifting of a manhole occurs, it may bring about not only dysfunctions, such as the loss of the ability of sewage to flow, but also displacements, such as that of the pipeline connected to the manhole, which makes drainage difficult. However, effective and economic measures against the uplifting of existing manholes are still in the developmental stages. This study proposes a weighting method that increases the self-weight of the manhole as a countermeasure against the uplifting of manholes during an earthquake. The applicability of this weighting method will be clarified by conducting case studies from the viewpoint of the safety factor for manhole uplifting and the quantity of manhole uplifting. As a result, it is shown that, regardless of the shape of the manhole and the groundwater level, the risk of manhole uplifting during liquefaction can be reduced by implementing this weighting method.