Tunnel excavation drilling blasting method

Rock excavation by drilling, charging and blasting is called drilling and blasting for short. In the early days, this method developed from manual drilling and hammering, using fire detonators to detonate individual explosive charges one by one, to drilling with a drill rig or dobby, using millisecond blasting, presplitting blasting and smooth blasting. Before construction, according to geological conditions, section size, supporting methods, time limit for a project requirements, construction equipment, technology and other conditions, the excavation method is selected. The main tunneling methods are: ① Full-face tunneling method, one-time drilling and blasting of full-excavated section, excavation and shaping, and full propulsion. When the tunnel is high, it can also be divided into upper and lower parts to form steps, synchronous blasting and parallel excavation. When geological conditions and construction conditions permit, full-face tunneling method is preferred. (2) Heading method: First, use a part of the excavation section as a heading, and then gradually expand the whole section of the excavation section (Figure 1). This is a construction method with small and medium-sized machinery as the mainstay when the tunnel section is large and it is difficult to adopt full-face excavation due to geological or construction conditions. The cross section of the pilot tunnel should not be too large, and it should be suitable for ballasting of ballasting machinery, transportation of ballasted vehicles, installation and construction safety of feng shui pipes. The free surface can be increased when the pilot tunnel is excavated and blasted, which is beneficial to find out the geological and hydrogeological conditions of the tunnel and create conditions for tunnel ventilation and drainage. According to geological conditions, groundwater conditions, tunnel length and construction conditions, determine the lower pilot tunnel, upper pilot tunnel or middle pilot tunnel. After the pilot tunnel excavation, the expansion excavation can be carried out after the full length of the pilot tunnel excavation, or it can be operated in parallel with the pilot tunnel excavation. (3) Division excavation method, in the case of poor stability of surrounding rock and general need of support, 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 gradually expanded. When excavating a tunnel by drilling and blasting, it is generally regarded as a tunnel excavation cycle from the first drilling sequence, through the processes of charging, blasting, ventilation, smoke dispersion, slag discharge and so on, to the end of the second drilling sequence. Try to compress the operation cycle time and speed up the excavation. In 1980s, some countries used the drilling and blasting method to excavate tunnels with a cross-sectional area of about1100m3 in medium-hard rocks, and the average tunneling speed was about 200m per month. In the Lubuge Hydropower Station project in China, a diversion tunnel with a diameter of 8.8m was excavated, with an average monthly footage of 23 1m and a maximum monthly footage of 373.7m The roadheader is a special equipment for full-face tunnel excavation (see color map). It uses the cutter on the large-diameter rotary cutter head to crush the rock by squeezing and rolling. American Robbins Company began to produce the first roadheader in 1952. After 1970s, roadheader developed rapidly. The excavation diameter ranges from 1.8 to11.5m. In medium-hard rock, 80 ~ 100 m3 large-section tunnel is excavated by roadheader, and the average excavation speed is 350 ~ 400 m per month. In the tunnel and reservoir project of Chicago Health Management Area, USA, a tunnel with a diameter of 9.8m was excavated in limestone, with a maximum monthly footage of 750m. The Austrian index water tunnel in the United States has a diameter of 3.09m and is excavated in shale, with a maximum monthly footage of 2088m m. Compared with the drilling and blasting method, the tunnel boring machine (TBM) has the advantages of faster excavation speed, less labor, safer construction, flat excavation surface and low cost, but it is bulky and inconvenient to transport, so it can only be used for long hole excavation, and its diameter is not adjustable, so its adaptability to geological conditions and lithological changes is poor, and its use is limited. Tunnel excavation