The quality of the tunnel depends on the quality of the process, and the quality of the process depends on the quality of the excavation, initial support and drainage and drainage, etc. The better control of the initial support and drainage and drainage can strengthen the supervision, so the focus is on the quality of the excavation, which depends on the quality of the excavation The quality of drilling and blasting means that in theory, the quality of the initial support without subsequent over-excavation is guaranteed. Therefore, the quality of the tunnel depends largely on the quality of drilling and blasting.
(1) The crack should be penetrated and have a certain crack width on the ground. For medium-hard rock, the crack width should not be less than 1.0cm; the crack width of hard rock should reach about 0.5cm; but when the width of the crack on soft rock reaches more than 1.0cm, the shock absorption effect is not significantly improved, and some field tests should be done to Lee sums up experience.
(2) The unevenness of the pre-cracked surface after excavation should be greater than 15cm.
(3) The retention rate of blast hole traces on the pre-cracked surface should not be less than 80%, and the rock near the blast hole does not show serious blast cracks.
The construction of the tunnel and the gate are also very important. The excavation and support of the cave entrance, the slope, and the tunnel should be excavated and layered from top to bottom, and the outside of the cave, temporary prevention, and drainage must be carried out first to make the surface water smooth. Avoid surface water washing the slope.
When necessary, artificial slope repair is adopted to prevent over-excavation and reduce disturbance to adjacent sections of the opening; excavation exposed slopes shall be designed and protected in time to reduce the exposure and weathering of surrounding rocks, and support shall be followed closely. On the high side and the slope, if it is not timely, safety cannot be guaranteed, and a lot of manpower and resources will be wasted.
The construction of the Myeongdong must be inspected, and the geological status and foundation bearing capacity of the Myeongdong side wall foundation must be reviewed to meet the design requirements.
Requirements for the excavation of the body: excavation of the middle guide hole, after the completion of the support when the hole is faced, dig the groove according to the outline of the excavation of the middle guide hole, embed the first steel grid arch after the initial spray of concrete, and stand outside the hole The steel grille is connected to the whole with longitudinal steel bars. After hanging the steel mesh, the concrete is sprayed to form the opening scaffold. The first steel grille is used as the fulcrum. Small pipe, excavation after 4 hours of grouting. The excavation of the middle guide hole adopts two steps of excavation, and the soil excavated on the upper step is manually turned to the lower step, and then used a loader to transport and abandon the vehicle. After excavating on the step, support it in time, then dig down the step.
When excavating the tunnel, we should pay attention to the construction of power supply and drainage: install a 315kva transformer at the entrance and exit of the tunnel, use the local local power grid to supply power, and prepare a 220kw generator for backup. The power equipment uses three-phase 380v, and the lighting uses 220v. To ensure safety, all lines are equipped with leakage protection switches. The erection of lines and the installation of various electrical appliances must meet the relevant requirements of the "Technical Specifications for Highway Tunnel Construction".
Construction drainage is mainly to exclude groundwater and construction wastewater that may flow into the tunnel. The tunnel is 1.54% uphill from exit to entrance. The construction of the exit is along the slope, and the construction drainage uses natural slopes and uses plastic pipes to drain the water out of the cave. The entrance construction is reverse slope construction, and the construction drainage is to dig a sump in the excavation area and use the pump to pump out the hole.