Date

10 May 1984, 9:00 am - 12:00 pm

Abstract

Case histories of three Indian tunnels indicate that squeezing conditions are created due to plastic flow of rock masses under the influence of high cover pressures. These examples emphasize that a tunnel experiencing squeezing conditions must be allowed to deform to optimize support costs and avoid delays. Allowance for desirable tunnel deformations must, therefore, be made while planning the size of excavation.

Field data has shown that a flexible support system of compressible backfill and steel ribs may be used as an alternative to shotcrete support which is unpractical in Indian tunnels excavated largely by conventional methods. Instrumentation indicates that large broken zones are associated with late stabilization and that the coefficient of volumetric expansion of failed rock masses is significantly lower than believed so far. Comparison of measured rock pressures with those estimated from available methods shows that the elasto-plastic theory may provide reliable predictions provided that the strength parameters of rock masses are known precisely.

Department(s)

Civil, Architectural and Environmental Engineering

Meeting Name

1st Conference of the International Conference on Case Histories in Geotechnical Engineering

Publisher

University of Missouri--Rolla

Document Version

Final Version

Rights

© 1984 University of Missouri--Rolla, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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May 6th, 12:00 AM

Squeezing Problems in Indian Tunnels

Case histories of three Indian tunnels indicate that squeezing conditions are created due to plastic flow of rock masses under the influence of high cover pressures. These examples emphasize that a tunnel experiencing squeezing conditions must be allowed to deform to optimize support costs and avoid delays. Allowance for desirable tunnel deformations must, therefore, be made while planning the size of excavation.

Field data has shown that a flexible support system of compressible backfill and steel ribs may be used as an alternative to shotcrete support which is unpractical in Indian tunnels excavated largely by conventional methods. Instrumentation indicates that large broken zones are associated with late stabilization and that the coefficient of volumetric expansion of failed rock masses is significantly lower than believed so far. Comparison of measured rock pressures with those estimated from available methods shows that the elasto-plastic theory may provide reliable predictions provided that the strength parameters of rock masses are known precisely.