The sprayed waterproofing membrane has high adhesion to a substrate, such as excavated rock surface and shotcrete. Because it is easily sprayed and bonded on the substrate, the sprayed waterproofing membrane is being considered as an alternative method of a conventional sheet waterproofing membrane. The sprayed waterproofing membrane has high adhesion to the substrate, such as excavated rock surface and shotcrete. Also, because of its ductility and flexibility with high elongation, it can prevent the substrate from a brittle failure. The purpose of this study is to evaluate the sprayed waterproofing membrane as a possibility of auxiliary support system. First, the sprayed waterproofing membrane was mixed and produced. Next, physical properties of the membrane were evaluated. After that, inner surfaces of shield segments were coated by the sprayed waterproofing membrane with a thickness of 3, 5 and 7 mm. Finally, full-scale loading tests were carried out to evaluate a structural reinforcement of shield segments. From the test, it was confirmed that the structural loading capacity of the shield segment could be improved by a coating of the sprayed waterproofing membrane.
The sprayed waterproofing membrane is a kind of new waterproofing materials recently developed as an alternative measure of a conventional waterproofing sheet (ITAtech, 2013). Contrary to the waterproofing sheet, it shows characteristics of high adhesion and fully bonds to the substrate, such as rock surface and shotcrete. Because of these features, the sprayed waterproofing membrane can form an integrated composite structure with a concrete lining and function as a single-shell structure (Makhlouf and Holter, 2008; Thomas, 2009; Holter, 2016; Chang et al., 2016a; Chang et al., 2016b). In other words, the thickness of the concrete lining closely associated with the construction cost reduction can be decreased during the tunnel construction or reinforcement work.
Also, issues about the repair and rehabilitation of deteriorated tunnel structures have been increasing recently in Europe. Particularly, in the case of cyclic reinforcements of existing tunnels, a new problem that inner sections of tunnels are gradually being reduced can emerge. Contrary to Thin-Spray-on Liner (TSL) developed for the use of rock support, the sprayed waterproofing membrane, as its name indicates, was initially developed for waterproofing, not for the support system. Moreover, any sources are not presented by ITAtech (2013) for the application of the sprayed waterproofing membrane as tunnel support or reinforcement. Nevertheless, because of its similarity to TSL in terms of a chemical composition and construction technique, various studies (Makhlouf and Holter, 2008; Ahn, 2011; Chang et al., 2015; Chang et al., 2016a; Lee et al., 2017) have attempted to review the applicability of sprayed waterproofing membrane as a new tunnel support system, not only for waterproofing.
The object of this study is to evaluate the structural reinforcement of the shield segment coated by the sprayed waterproofing membrane through a full-scale loading test. Once the sprayed waterproofing membrane was being coated and hardened on the inner surface of the shield segment, full-scale loading tests were carried out to evaluate the reinforcing effect by measuring the early-age cracking load and the failure load of the shield segment.
