Determination of Support Reaction Curve for Steel-Supported Tunnels

Based on the analysis of instrumentation data obtained from several tunnels in India, an empirical approach has been proposed for determination of the support reaction curve for tunnels supported with the steel rib-backfill support system. Expressions have been obtained for determining the stiffness of this support system with three types of backfills-concrete, tunnel muck, and gravel. These expressions show that the steel rib-backfill support system exhibits a non-linear behaviour under pressure, unlike the normally assumed linear elastic behavlour, due to the continuously changing backfill stiffness. The backfill, though not the main load carrying element, significantly influences the behaviour of the support system under procure. The behaviour of three types of backfills-concrete, gravel, and tunnel muck-under pressure, has been studied. The concrete, backfill provides a stiffer support than the other two types of backfills and is, therefore, preferable for the elastic ground condition. ']'he tunnel-muck and the gravel backfills may be more suited to the moderately squeezing and the highly squeezing ground conditions, respectively, as the latter is relatively more flexible