Analysis of Nonlinear Consolidation Characteristics of Soil Around Tunnels Considering Self-Gravity Stress

Considering the self-gravity stress of the soil around the tunnel, a two-dimensional nonlinear consolidation control equation for saturated soil was established, and solved using the alternating implicit difference method. The correctness of the solution was verified by comparing the degenerate solution with an existing analytical solution, and by comparing the calculated results with measured data. On this basis, the influence of changes in soil self-gravity stress and consolidation coefficient on the nonlinear consolidation characteristics of the soil around the tunnel was further explored. The results indicate that neglecting the self-gravity stress of the soil leads to a higher excess pore pressure and a lower rate of consolidation settlement, and leads to a lower final surface settlement. Under the influence of self-gravity stress, a smaller ratio of compression index to permeability index Cc/Ck results in a slower consolidation settlement rate of the soil, but does not affect the final surface settlement. When Cc/Ck=1.0, a smaller soil self-gravity results in a greater influence of the initial effective stress distribution on the consolidation rate and a higher final surface settlement. When Cc/Ck>1.0, the permeability coefficient plays a dominant role in the consolidation process, and the consolidation rate decreases as the gravity increases. In contrast, when Cc/Ck<1.0, the volume compression coefficient becomes more influential, and the consolidation rate increases with the increase of gravity, though the final surface settlement in both cases decreases with increasing gravity.