DETERMINATION OF SUPPORT REACTION CURVE FOR STEEL-SUPPORTED TUNNELS

Based on the analysis of instrumentation data obtained from several tu nnels in India, an empirical approach has been proposed for determinat ion of the support reaction curve for tunnels supported with the steel rib-backfill support system. Expressions have been obtained for deter mining the stiffness of this support system with three types of backfi lls-concrete, tunnel muck, and gravel. These expressions show that the steel rib-backfill support system exhibits a non-linear behaviour und er pressure, unlike the normally assumed linear elastic behaviour due to the continuously changing backfill stiffness. The backfill, though not the main load carrying element, significantly influences the behav iour of the support system under pressure. The behaviour of three type s of backfills-concrete, gravel, and tunnel muck-under pressure, has b een studied. The concrete backfill provides a stiffer support than the other two types of backfills and is, therefore, preferable for the el astic ground condition. The tunnel-muck and the gravel backfills may b e more suited to the moderately squeezing and the highly squeezing gro und conditions, respectively, as the latter is relatively more flexibl e.