Drilling and blasting method for tunnel excavation
The method of excavating rock through drilling, charging, and blasting is referred to as the drill and blast method. This method has evolved from the early days of manually drilling and hammering holes, and using detonators to detonate individual explosive packages one by one, to using rock drilling rigs or multi-arm drilling rigs to drill holes, and applying millisecond blasting, pre-splitting blasting and smooth surface blasting. Explosive technology such as blasting. Before construction, the excavation method must be selected based on geological conditions, section size, support methods, construction period requirements, construction equipment, technology and other conditions. The main excavation methods are: ① Full-section excavation method, the entire excavation section is drilled and blasted at one time, the excavation is formed, and comprehensively advanced. When the tunnel height is large, it can also be divided into upper and lower parts to form steps, blasted simultaneously, and tunneled in parallel. When geological conditions and construction conditions permit, the full-section excavation method is preferred. ② Guide tunnel method: first excavate a part of the section as a guide tunnel, and then gradually expand the entire section of the tunnel (Figure 1). This is a construction method mainly based on small and medium-sized machines when the tunnel section is large and it is difficult to excavate the full section due to geological conditions or construction conditions. The cross-section of the guide tunnel should not be too large, so that it can adapt to the ballast loading machinery, ballast removal vehicle transportation, Feng Shui pipeline installation and construction safety. The pilot tunnel can increase the free surface during excavation and blasting, which is beneficial to exploring the geological and hydrogeological conditions of the tunnel, and creates conditions for ventilation and drainage in the tunnel. According to the geological conditions, groundwater conditions, tunnel length and construction conditions, it is determined to use the lower pilot tunnel, upper pilot tunnel or central pilot tunnel, etc. After the pilot tunnel is excavated, the expansion excavation can be carried out after the entire length of the pilot tunnel has been excavated, or it can be carried out in parallel with the pilot tunnel excavation. ③Partial excavation method: when the stability of the surrounding rock is poor and support is generally needed, when excavating a large-section tunnel, a part of the section can be excavated first, and the support can be done in time, and then the excavation can be expanded gradually . Tunnel excavation using the drill and blast method usually starts with the first stage of drilling, goes through processes such as charging, blasting, ventilation, smoke dispersion, and ballast removal, and ends with the start of the second stage of drilling, as a tunnel excavation operation cycle. Try to compress the operation cycle time as much as possible to speed up the excavation speed. In the 1980s, some countries used the drill and blast method to excavate tunnels with a cross-sectional area of about 100m3 in medium-hard rock, with an average excavation speed of about 200m per month. China's Lubuge Hydropower Station project excavates a diversion tunnel with a diameter of 8.8m. The average monthly footage of a single working face reaches 231m, and the maximum monthly footage reaches 373.7m. Boring machine method The boring machine is a special equipment for full-section tunnel excavation (see color picture). It uses the squeezing and rolling effects of the cutters on the large-diameter rotating cutterhead to break the rock. The American Robbins Company began producing the first tunnel boring machine in 1952. After the 1970s, boring machines have developed rapidly. The excavation diameter range is 1.8~11.5m. In medium-hard rock, a tunnel boring machine is used to excavate large-section tunnels of 80 to 100 m3, with an average excavation speed of 350 to 400 m per month. The Chicago Sanitary Management District Tunnel and Reservoir Project in the United States excavates a 9.8m diameter tunnel in limestone, with a maximum monthly footage of 750m. The diameter of the American Orson water tunnel is 3.09m, excavated in shale, with a maximum monthly footage of 2088m. Tunnel boring machine excavation is faster than the drill and blast method, requires less labor, is safe in construction, has a flat excavation surface, and has low cost. However, the machine body is large and inconvenient to transport. It can only be used for excavation of long holes, and the diameter of the machine cannot be adjusted. , has poor adaptability to geological conditions and lithology changes, and has limitations in use. Tunnel excavation