Experimental Research On Tunnel Lining Joints Temporarily Strengthened By SMA Bolts

Shield tunnels have been widely used in city metros. The joints of existing metro tunnel’sneighboring segments may open due to some factors, leading to some aftermaths such ascrushing of concrete near the joint edge, yielding of steel bolts and water leakage at the jointand so on. In this paper, a temporary strengthening method by using shape memory alloy(SMA) bolts is proposed. When the joint opening is too large, the preprocessed SMA bolts areinserted through the prepared holes in the neighboring segments and heated, which cangenerate closure force for the segmental joint by shape memory effect of SMA bolts, so thatthe joint opening is reduced and the proposed temporary strengthening method is to createfavorable conditions for the following permanent strengthening. The temporary strengtheningmethod was studied preliminarily in this article and main work as followed:1) The important essential data were provided to subsequent temporary strengtheningtests project through the recovery test of SMA rod. Test results show that, relatively highrecovery stress can be generated in the SMA rod whose prestrain is5.80%to under partialconstraint condition, and the maximum recovery stress is380MPa and occurs at a temperatureof160°C.2) A electric heating method for SMA rod was proposed and verified available throughheating tests, and the heating rates of two heating wires were compared in the tests. Testresults show that, the average heating rate related to the second heating wire is larger than thefirst heating wire, and the former can heat the SMA sample up to160°C in38min.3) Two full-scale tunnel lining joints temporary strengthening tests were carried out, theproposed temporary strengthening method was testified available in the tests. Test resultsshow that, the reduction percentages of the joint opening, the joint deflection, the concretestrain in compression zone, and the strain of steel bolts are37%~62%,21%~42%,87%~96%and67%~74%, respectively, by the strengthening method. And the less the jointopening is, the more significant the strengthening effect is.4) Several prime problems in engineering practice were preliminary discussed, and thecorresponding solutions were suggested to prove the availability of the proposed temporary strengthening method in engineering practice.