The squeezing potential of rocks around tunnels; Theory and prediction

The Dangerous Condition of Ground during High Overburden Tunneling (A Case Study in Iran)

“…[20], based on the experience of tunnels in Japan, proposed to relate the strength of the intact rock σ ci to the overburden pressure γH by the same relation as (3), implying that the uniaxial compressive strength of the intact rock σ ci and that of the rock mass σ cm are the same. The fundamental concept of the method is based on the analogy between the stress-strain response of rock in laboratory testing and tangential stress-strain response around tunnels.…”

“…In this Table, ε a Θ is the tangential strain around a circular tunnel in a hydrostatic stress field [20], whereas ε e Θ is the elastic strain limit for the rock mass. …”

“…2, five distinct states of the specimen during loading are experienced, at low confining stress σ 3 (i.e., σ 3 ≤ 0.1σ ci ). The following relations, as defined, give the normalized strain levels η P , η s and η f [20].…”

A numerical study on squeezing of overstressed rock around deep tunnels

“…The rock flows which will result in the collapse of the medium and the displacement will be very large and it will be necessary to re-excavate the opening and install heavy support Squeezing class competency range The tunnel behaviour according to Aydan et al (1993) No squeezing RMi/  >1 The rock behaves elastically and the tunnel will be stable as the face effect ceases.…”

“…Table 2. Classification of the degree of squeezing by the tangential strain of tunnel periphery (after Aydan et al, 1993) Class No. Squeezing degree Symbol Theoretical expression Comments on tunnel behavior…”