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Determination of Support Systems According to Rock Classes-Tlemcen-Akkid Abbas High Speed Railway Project-Algeria

One of the biggest problems encountered in rock mass classifications for tunnels is which supports will be applied in case of passing with different units in the tunnel section. While a weak unit is encountered in the top heading of the tunnel section, bench and invert section can be found in the rock. In these cases, while the rock mass is determined according to the worst conditions, there may be differences in the support system. While heavy support system is required in the top heading invert excavation may not be performed if the invert section remains in the high qaulity rock mass. In addition, the problems encountered in tunnels excavated in weak untis are generally encountered as failures in the tunnel support systems due to the squeezing mechanism and stability problems encountered in the tunnel face. In weak units, long-term failures usually occur after the completion of the support systems. In shallow tunnels, the design of the support systems is more critical since arching cannot be achieved around the tunnel. Because allowing deformations may trigger deformations around the tunnel that affects up to the surface. In addition, the effect of a failure that may occur during excavation in the tunnel face may be reflected up to the surface and may affects all tunnel support systems. For this reason, support systems should be completed without allowing deformations in tunnels excavated on weak soils under shallow overburden. In addition, it is obligatory to make face support systems in order to prevent any collapse in the tunnel face. Within the scope of this study, T10 tunnel support systems and tunnel design excavated in Telmcen Akkid Abbas High Speed Railway Project is examined. As a result of the study, the stability of the tunne face and ceiling is extremely important in the determination of tunnel support systems in weak untis. In addition, the tunnel support system pressure should be at least 2-3 times higher than the critical support system pressure in order to prevent squeezing problems in the long term.