Equivalent Load Height Determination Method for Shield Tunnel Vertical Load Based on Surrounding Rock Stress Change Rate

［Objective］ The applicability and accuracy of the load modes and calculation methods of shield tunnels under existing complex geological conditions are insufficient. It is necessary to determine the equivalent load height value of the shield tunnel vertical load based on the surrounding rock stress change rate. ［Method］ Based on the built shield tunneling project under similar stratigraphic conditions, a method for determining vertical load based on the critical stress change rate of surrounding rock load is proposed. Combined with the shield tunnel project of Nanning Metro Line 5, the vertical load value method of the cross-river shield tunnel passing through the earth-rock composite strata and the influencing factors on the vertical load change law are studied. ［Result & Conclusion］ Based on the built shield projects with similar stratigraphic conditions, a reference value of 2% is taken as the critical stress change rate of the surrounding rock load to determine the vertical load height value. The numerical calculation results show that the influence of burial depth on the equivalent load height is significant, while the influence of groundwater occurrence on the equivalent load height is relatively smaller.