<p>The squeezing of tunnels is a common phenomenon in poor rock masses under high in situ stress conditions. The critical strain parameter is an indicator that allows the degree of squeezing potential to be quantified. It is defined as the strain level on ...

A review of underground openings, excavated in varying rock mass types and conditions, indicates that the initiation of brittle failure occurs when the damage index, Di , expressed as the ratio of the maximum tangential boundary stress to the laboratory unconfined ...

<p>A criterion for identifying the squeezing potential of tunnel is proposed. Tunneling conditions, classified as slightly or non-squeezing, moderately squeezing and highly squeezing, were identified by relating the strength-stress (cr,m/Po) ratio to the development ...

Stress-strain curves for brittle rocks show three characteristic stress levels: crack initiation, long-term strength, and peak strength. Damage-controlled testing at low confining stresses has shown that the long-term and peak strengths are sensitive to the ...

<p>Jointed rock masses comprise interlocking angular particles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials. The strength of such rock masses depends on the strength of the intact ...