Innovative Approach for Reducing Shallow Tunnel Liquefaction-Induced Uplift Using Variable-Length Stone Columns

Controlling tunnel uplift is one of the most important factors in shallow tunnels. The effectiveness of stone columns in preventing liquefaction-induced uplift under tunnels and deterring pore pressure growth is not well-known. Laboratory tests have been conducted to assess the advantages of stone columns in loose sands and to observe the patterns of mitigation vectors during liquefaction with and without stone columns. After analyzing laboratory models, simulations were conducted to observe the behavior of liquefied soil with underlying clay around the tunnels. Different stone columns were used to evaluate the dynamic response of a tunnel, including uplift under the tunnel and on the ground, using the validated model. The results showed a perfect similarity between the model and the laboratory test and revealed that without the using stone columns, liquefaction was uncontrollable in the loose soil, exposing high peak ground acceleration (PGA). The uplift decreased by up to 93% with the stone columns when compared with the unimproved model, and there was a dramatic increase in the exit of excess pore pressure near the columns. The patterns of mitigation vectors during liquefaction are altered by the stone columns around the tunnel. The shear strain under the tunnel also decreases by up to 74%. The maximum proper distance between the stone columns when comparing the different arrangements in this study is limited to 5 m. The results indicate that by increasing the modulus of elasticity in the columns, the under-tunnel uplift can be reduced by 66% if the columns are more aggregated above the tunnel. At the same time, the bending moment, axial forces, and shear forces increase significantly in the tunnel lining. A new understanding of the dynamic performance of tunnels located in liquefiable soils is provided by the results and can be utilized in practical applications.