Industry perspective | From "conventional" to "unconventional"

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Industry perspective | From "conventional" to "unconventional"

Original Title: Industry Viewpoint | From "Conventional" to "Unconventional" Construction Method, What Are the Developments and Innovations of Drilling and Blasting Method? Once upon a time, the drilling and blasting method of tunnel construction was called the "conventional" tunnel construction method, while the mechanized tunnel construction using TBM at that time was the "unconventional" innovative method. Today, the TBM technology has been mature and promoted, but the drilling and blasting method seems to be gradually declining. Today, mechanized construction has become the mainstream of tunnel construction, what are the developments and innovations of the drilling and blasting method? Let's hear from the experts at AECOM! Application of drilling and blasting method In today's infrastructure construction, TBM or other mechanical tunneling technology has become the mainstream, only in the mining industry, the drilling and blasting method is still the most common excavation method. However, the drilling and blasting method still has certain advantages under the working conditions of short-distance excavation, large-section tunnels and caverns, connecting passages, shafts, etc. Unlike the usual circular section of TBM, the construction section of the drilling and blasting method is more free,Mining Drilling Equipment, and the space waste of the construction tunnel is less. The strata in Europe are mostly composed of hard granite and gneiss, and the drilling and blasting method is very economical. For example, in Stockholm Metro, shotcrete is used as the final lining after the tunnel is excavated by drilling and blasting, and no other cast-in-place concrete lining is used; Norway has more than a thousand road tunnels (the largest number in the world) and hundreds of small hydropower tunnels, most of which are constructed by drilling and blasting. From 2015 to 2018 alone, the volume of rock mass constructed by drilling and blasting method reached 4,down the hole bit,200,000 m ³; Although mountain tunnels in the Alps are generally longer, the drilling and blasting method is still "popular". Unlike the drilling and blasting tunnels in northern Europe, most of the tunnels here are lined with cast-in-place concrete; The formations in the northeastern United States and the Rocky Mountains are similar to those in northern Europe, so the drilling and blasting method has also been used on a large scale: the New York subway, the Eisenhower Tunnel, the MacDonald Tunnel and the Second Avenue subway project, which was opened soon, combined the drilling and blasting method with the TBM method. Innovation of drilling technology After years of development, rock drilling tools have developed from the original hand-held drill or single-boom jumbo to today's fully automatic multi-boom rock drilling jumbo: its excavation mode can be fed back to the on-board computer in real time to calculate the excavation position and excavation mode, and carry out fully automatic, high-precision and rapid excavation. Expand the full text The advanced drilling jumbo can be switched freely between fully automatic and semi-automatic modes: In the full-automatic mode, after the excavation of a borehole is completed,dth rock bit, the drill bit automatically moves to the next position and starts drilling, and no operation is required in the whole process; Under some complex working conditions, it can be switched to the semi-automatic mode, and the operation of replacing the drill hole is handed over to the workers manually; With the help of the fully automatic function, the operator can handle more than three booms at the same time; In addition, the power of the drilling jumbo is gradually increased to a maximum of 40 kW, and the drill bit is changed according to different rock mass types, with a maximum drilling speed of 3.6 m/min. At present, the latest development trend of rock drilling jumbo is multi-functional integration, which can realize the functions of drilling, slag discharge, installation of grid steel frame and even shotcrete operation at the same time by adding equipment to a single machine. Innovation of blasting technology When the multi-arm drilling jumbo is used for drilling and blasting construction in the tunnel, an independent charging truck is generally used to charge the bulk emulsion explosive for the borehole, and two to three boreholes can be charged at the same time. The filling amount of the emulsion explosive is adjusted according to the drilling position: the bottom drilling of the excavation surface is generally filled with 100% of the amount, and the edge is filled with 25%, and so on. When bulk emulsion explosive is used, it is also necessary to add a packaged explosive rod as a lead, which is placed at the bottom of the borehole together with the detonator, and the lead is ignited to further detonate the emulsion explosive. The use of bulk emulsion explosives reduces the total loading time of the drill and blast method compared to conventional industrial explosives, and a loading truck with two operators can load 80-100 boreholes per hour. Slag tapping Wheel loaders and trucks are still the most common mucking tools in drilling and blasting tunnel construction, and the muck is transported to the shaft and lifted out. However, in a recent long-distance tunnel project in the Alps, the construction party has made innovations in mucking: The crusher is used to crush the larger rock and transport the muck directly to the surface through the conveyor belt. This method reduces the mucking time, especially for longer tunnels. This option frees up space at the top of the tunnel for in-tunnel construction. If the muck has good performance, it can also be directly used as construction aggregate in the tunnel. Under the working condition of large section or weak rock stratum, the drilling and blasting method can be combined with the New Austrian Tunneling Method. Taking the 86th Street Station of the Second Avenue Subway Project in New York as an example, the top of the tunnel is first divided into three times for drilling and blasting excavation, followed by drilling and blasting on both sides, and the tunnel section of 18m15m is completed. Pre-grouting In order to reduce the intrusion of groundwater during excavation, pre-grouting is generally adopted in the drilling and blasting method. Pre-grouting can be used for the entire tunnel or only in fixed formation conditions, such as fault zones and shear zones. In the process of pre-grouting, 4-6 drilling holes are usually drilled to measure the relationship between groundwater and the established grouting point, followed by cement or chemical grouting. A single round of pre-grouting typically consists of 15 to 40 boreholes (70-80 feet), depending on the size of the tunnel and the amount of groundwater expected. When excavation is complete, allow 15-20 feet of safe area after the previous round of excavation before proceeding to the next round of probing and pre-excavation grouting. Xiaobian language In addition, with the progress of drilling and blasting automation technology, the safety of drilling and blasting method has been significantly improved in recent years. Although the mechanized tunnel construction using TBM is more conducive to the long-distance tunnel with constant cross section, the shutdown in the process of TBM tunnel excavation will lead to a long time of shutdown, while in the drilling and blasting construction of multi-operation,overburden drilling systems, even if there is a problem at a certain point, the overall tunnel construction can still continue. As long as the drilling and blasting method is used correctly, it is still a feasible option even in the construction of long-distance tunnels. Editor: Guo Deyuan ☞ Wechat and magazine submission email: Return to Sohu magazine@tunneling.cn to see more Responsible Editor:. wt-dthtools.com

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