Upper bound solution to the support pressure of tunnels excavated in weak Hoek–Brown rock masses
摘要
Determining a reliable value of the support pressure is necessary to prevent tunnel instability during excavation in weak rock masses. There are a few appropriate analytical solutions, most focused on tunnels excavated in soils. The present study proposes a method for determining the support pressure required to stabilize tunnels excavated in weak rock masses. The upper bound limit analysis method was applied for a rock mass obeying the Hoek–Brown failure criterion. Based on the findings, improving the strength of the rock masses results in decreasing the required support pressure. Increasing the Hoek–Brown parameters mi from 5 to 20, GSI from 10 to 25, and σci from 1 to 10 MPa, results in a maximum reduction of the tunnel support pressure by 62%, 56%, and 70%, respectively. In addition, increasing the ratio of horizontal to vertical insitu stresses from 0.4 to 1.2 reduces the maximum support pressure by about 59%. Moreover, increasing the disturbance factor from zero to 1 results in an increase of about 135% in the support pressure, while by increasing the tunnel width and the unit weight of the rock mass surrounding the tunnel, the maximum increase of 181% and 93% were observed in the support pressure.