The total length of Qingdao subsea tunnel line is 7120m, of which the tunnel is 6170 m long. The tunnel is divided into four sections, including 3214.3m excavation construction for the third section. Different from the traditional tunnel construction method, Qingdao subsea tunnel adopts the combined supporting methods of shotcrete and multiple anti-corrosion anchor bolt, so as to ensure the stability of surrounding rock in the tunnel.
According to the geological survey, the chemical compositions of the groundwater in the sea and near the sea are similar with those of the seawater, which have corrosion to the rebar in reinforced concrete. In order to ensure the durability of anchor bolt in the initial support, Qingdao subsea tunnel adopts corrosion hollow anchor bolt in land areas and multiple anti-corrosion anchor bolt in sea areas.
The service life of anchor bolt embedded in rock and soil depends on its durability, while the biggest threat comes from corrosion. The anti-corrosion of anchor bolt is to adopt isolation and insulation measures, so that water and air in the cracks of the strata or rock are not in contact with anchor bolt as far as possible. The common isolation methods include grouting, coating, casing, etc.
Multiple anti-corrosion anchor bolt combines more than 2 kinds of the above anti-corrosion measures: using PE plastic sleeve for isolation and grouting for protection. After consolidation, it forms multiple anti-corrosion anchor bolt. If using the galvanized anchor bolt (three anti-corrosion structure), the anti-corrosion performance is more reliable.