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Suppressing tunnel subsidence: "Preload Shell Method"

When constructing structures for civil engineering works (such as roads, railways, and waterways), excavation work occurs for tunnels, shields, shafts, and culverts. During excavation, the geological conditions of the ground, the soil cover, and the functional characteristics of the load change, resulting in complex loads on the tunnel. To support these loads, support structures are used. Support structures are installed before the load is applied, but a gap arises between them and the ground, and if this gap is not filled, the ground will settle. To suppress this settlement early and stabilize the tunnel, support members that smoothly and quickly transmit the load to the support structures and the ground are necessary. A groundbreaking settlement suppression method developed for this purpose is the "Preload Shell Method," which involves setting a bag (jacket) between the ground and the support structure and filling the bag with non-shrink mortar, thereby integrating the support structure and the ground to ensure reliable support capacity.