In order to prevent the left and right tunnels from being excavated at the same section at the same time, which will have a great impact on the surrounding rock between the two tunnels, the right tunnel is excavated from the entrance and the left tunnel is excavated from the exit. Drilling and blasting method is used for excavation, and smooth blasting technology is used for excavation. The import and export are mainly equipped with 1 drilling rig, 1 excavator and 1 side dump loader for ballast. 6 15T dump trucks are slagged. Class III surrounding rock adopts short bench method, with bench length of10-15m; Class Ⅳ surrounding rock is constructed by full-face method.
Second, the initial support construction scheme:
Grade Ⅲ surrounding rock of the entrance (S2) is supported by advanced small conduit (grouting), advanced mortar anchor rod (S3), steel mesh shotcrete and steel arch, and Grade Ⅳ surrounding rock is supported by combined anchor rod and sprayed steel fiber concrete. The sequence of support construction is: advance support (advance small conduit, advance mortar anchor rod)? At the beginning of excavation, the anchor rod, steel mesh and steel arch are sprayed again to the design thickness. Before excavation, advance support shall be constructed, and after excavation, initial support shall be carried out. The advanced mortar anchor is drilled by drilling rig, injected by high-pressure grouting pump, and sprayed concrete is prepared by wet spraying technology in wet spraying machine. In the process of construction, advance geological prediction and monitoring measurement should be carefully implemented to ensure that tunnel construction does not collapse.
Third, the tunnel lining construction scheme:
The construction time of the secondary lining is determined according to the monitoring data. The tunnel lining in the third-grade surrounding rock area should follow the initial support properly, and the inverted arch and backfill should be carried out before the secondary lining. The secondary lining of grade Ⅳ surrounding rock can be appropriately delayed, and the construction can be carried out after the initial support is basically stable. Before lining, waterproof layer and plastic blind pipe should be constructed according to design requirements. The waterproof layer and plastic blind pipe are constructed by self-made trolley, and the waterproof layer is laid without nails and fixed by hot welding. The tunnel lining adopts walking hydraulic lining trolley for full-face construction, and the entrance and exit ends of the tunnel are equipped with 1 trolley respectively. Considering that the tunnel is located on the curve, the trolley length is 9m.
When the emergency stop area is fully lined with concrete, 30 15 movable arc steel formwork will be added in the trolley steel formwork, and the size will be reinforced and adjusted with special comb formwork. Pedestrians, traffic intersections and other reserved caves will be built with special steps. The concrete is S8(C25) waterproof concrete, which is transported by concrete mixer (more than 200m), pumped into the mould by delivery pump and mixed in the mixing station.
Tunnel construction is the abbreviation of NATM tunnel construction method. It is a reasonable construction method put forward by Austrian scholars in the long-term tunnel construction practice from the perspective of rock mechanics. It is a new engineering construction method formed by using the system composed of shotcrete technology, monitoring measurement and rock mechanics theory.
NATM: the abbreviation of NATM tunnel construction method. It is a reasonable construction method put forward by Austrian scholars in the long-term tunnel construction practice from the perspective of rock mechanics. It is a new engineering construction method, which is formed by the system of bolting and shotcreting technology, monitoring measurement and rock mechanics theory.
References:
Construction of Baidu Encyclopedia Entrance Tunnel