What are the advantages and disadvantages of using raise boring vs. conventional methods for creating ventilation shafts?

Raise boring and conventional methods are two distinct approaches to creating ventilation shafts in underground mines, each with its own advantages and disadvantages. Raise boring is a mechanical excavation method that involves drilling a pilot hole from the surface to the underground workings and then using a raise bore machine to enlarge the hole to the desired shaft diameter by pulling a rotating cutter head upwards. Conventional methods, on the other hand, involve drilling and blasting from either the surface downwards or from the underground workings upwards. The advantages of raise boring include safety. Raise boring is generally safer than conventional methods because it eliminates the need for miners to work in an unsupported excavation. There is no exposure to falling rock or other hazards associated with drilling and blasting. It also offers faster excavation speed. Raise boring can excavate shafts much faster than conventional methods, especially for large-diameter shafts. The process is continuous and automated, reducing the need for manual labor. The method creates smoother shaft walls. Raise boring produces smoother shaft walls than conventional methods, reducing the need for additional support or lining. The smooth walls also reduce air resistance, improving the efficiency of the ventilation system. There is less overbreak. Raise boring is more precise than conventional methods, resulting in less overbreak (excavation beyond the design dimensions). This reduces the amount of waste rock that needs to be removed and minimizes the disturbance to the surrounding rock mass. Limited vibrations are also an advantage. Raise boring generates less vibration than conventional methods, reducing the risk of damage to nearby structures or equipment. The disadvantages of raise boring include equipment cost. Raise bore machines are expensive to purchase or rent, which can be a barrier to entry for smaller mining operations. Site access must also be considered. Raise boring requires access to both the surface and the underground workings. This can be a challenge in some locations, especially if the surface is located in a remote or environmentally sensitive area. Geological limitations are an issue. Raise boring is not suitable for all geological conditions. It is most effective in competent rock masses that can support the weight of the cutter head. It is less effective in fractured or weak rock masses, which can cause the cutter head to become stuck. Shaft diameter limitations exist. Raise boring has limitations on the maximum shaft diameter that can be achieved. The maximum diameter is typically limited by the size and power of the raise bore machine. Mobilization can be difficult. Mobilizing the raise bore machine to the mine site can be a logistical challenge, especially if the mine is located in a remote area. Conventional methods offer some advantages such as lower equipment cost. Conventional methods require less specialized equipment than raise boring, which can make them more affordable for smaller mining operations. They are also more adaptable to varying geology. Conventional methods can be used in a wider range of geological conditions than raise boring. The drilling and blasting can be adjusted to suit the specific rock mass characteristics. There are also fewer shaft diameter limitations. Conventional methods can be used to create shafts of any diameter, limited only by the size of the excavation equipment and the stability of the rock mass. The disadvantages of conventional methods include reduced safety. Conventional methods are more dangerous than raise boring, as they expose miners to the risk of falling rock, explosions, and other hazards. Slower excavation speed is also an issue. Conventional methods are typically slower than raise boring, especially for large-diameter shafts. More support may be needed. Conventional methods often require additional support or lining to stabilize the shaft walls. This increases the cost and time required for shaft construction. Conventional methods cause more overbreak and increased vibrations. Conventional methods can result in more overbreak and generate more vibration than raise boring, increasing the amount of waste rock and the risk of damage to nearby structures.