Research On The Fast-Speed Construction Technology Of Precast-Slab For Tunnel Invert

During construction of Jin-dong tunnel in Shanxi Province, the broken bits of exploded rock were transported with truck-trail system, which is a transportation system without-rail. In order to increase the construction speed to utilize the non-rail system effectively, a new construction technology of fast construction of tunnel invert using precast-slab has been proposed. The proposed the construction technology includes via casting a layer of'dry'type of concrete with a small collapsing degree at first and then paving the precast-slabs on the in-site-cast'dry'concrete. Since this kind of concrete has the advantage of small deformation and quick strength-gaining, it can be opening to the transportation of exploded rock soon after casting. Consequently, the construction speed is increased. However, some problems in this technology should be solved, i.e. the basic design concept and parameters of the precast-slab, the ingredients and mixing method of the'dry'type concrete, and the impact of the transportation vehicle on the precast-slab and the concrete under the slab etc.In this study, two approaches are employed on the precast-slab and'dry'concrete, respectively. For the precast-slab, the following steps are conducted: i) the analysis of stress and strain in the concrete precast-slab using finite element method (FEM); ii) the load test on the slab in laboratory; iii) measuring of the stress and deformation in the precast-slab under the transportation vehicle; iv) in-situ observation on the damage of the slab. Based on the results of the four steps, the damage degree (destroyed or not) can be judged. For the'dry'type of concrete, the following investigation steps are conducted: i) collapsing degree test, ii) determining the ingredients and mixing ratio of the'dry'concrete; iii) core sampling to observe damage degree. Based on the results of the three steps, the status of cast cancrete (destroyed or not) can be judged.