Abstract: Due to the special mechanical properties of fluvioglacial deposits, traditional tunnel pressure calculation formula does not suit for fluvioglacial deposits tunnel. In view of this, a modified Terzaghi’s loose soil pressure calculation formula suitable for fluvioglacial deposit tunnel is deduced. First of all the change rule of lateral pressure coefficient is derived by theoretical derivation, and then the stress distribution at different buried depths are compared by numerical simulation, and also the soil arching effect is analyzed. Furthermore, the modified formula is compared with the original Terzaghi’s loose soil pressure formula and the formula in China’s Railway Tunnel Design Standard. Results conclude that the tunnel pressure calculated by the Standard formula would be higher than actual value; whereas the modified Terzaghi’s loose soil pressure formula could well reflect the actual pressure of fluvioglacial deposit tunnel.

Key words: fluvioglacial deposits, loose soil pressure, soil arching effect, lateral pressure coefficient, dividing line standard for deep-and-shallow-buried tunnels