In tunnels, mine mining, or large-scale infrastructure construction sites, when facing rock layers with high hardness, how to achieve efficient and safe blasting or excavation? During this process, drill jumbos play an important role, and their operating effect largely depends on the precise design of hole layout plans and scientific drilling methods. As a key piece of equipment in modern engineering construction, the hole layout plans and drilling strategies of drill jumbos have a direct impact on construction efficiency, blasting results, and operational safety.
I. Design Logic of Hole Layout Plans: Balancing Science and Practicality
The design of hole layout plans must follow three core principles to ensure the feasibility and safety of the overall plan.
Uniform Distribution and Balanced Force: Drill holes should be evenly arranged along the tunnel excavation contour line, mainly divided into three types: "peripheral holes", "cutting holes", and "auxiliary holes". Among them, peripheral holes are responsible for outlining the excavation boundary to help the tunnel take shape neatly; cutting holes are located at the center of the cross-section and serve as the initial breakthrough point for blasting, requiring priority to break the core rock to form a free surface; auxiliary holes fill the area between cutting holes and peripheral holes to further expand the rock breaking range. If the drill holes are unevenly distributed, it may lead to incomplete rock breaking, and even cause deformation of the tunnel contour, posing safety hazards.
Parameter Adaptation and Rock-Based Adjustment: There are significant differences in compressive strength between different rocks. For example, the compressive strength of granite can reach more than 150MPa, while that of shale is only 30-50MPa. Hole layout parameters must be adjusted accordingly based on rock characteristics. Taking hole spacing as an example, the spacing of peripheral holes in hard rock is usually controlled at 40-60cm, while in soft rock, it can be relaxed to 60-80cm; the depth of drill holes must also match the requirements of blasting footage. If a single blasting is planned to advance 1.5 meters, the depth of cutting holes needs to be 10-20cm deeper than that of peripheral holes to reduce the occurrence of "under-excavation" (rock not excavated to the required position) or "over-excavation" (excavation exceeding the design scope).
Safety First and Risk Avoidance: Hole layout plans must avoid weak areas in the tunnel, such as rock sections with developed fractures, to prevent rock surface collapse during drilling; at the same time, the positions of drill holes must maintain a safe distance from facilities such as steel supports and pipelines in the tunnel to avoid damage to equipment. A qualified hole layout plan must undergo three verification processes: geological survey, mechanical calculation, and simulated blasting, with errors controlled within 5cm; otherwise, it may have an adverse impact on blasting results.
II. Core Drilling Methods of Drill Jumbos: Adapting to Different Engineering Scenarios
With a precise hole layout plan, it is also necessary to match it with scientific drilling methods of drill jumbos to transform the design plan into actual construction results. According to differences in engineering scenarios, mainstream drilling methods can be divided into three types: "full-face excavation method", "bench excavation method", and "center diaphragm method (CD method)", each corresponding to different hole layout strategies and operation points.
Full-Face Excavation Method: Suitable for Hard Rock Tunnels, Pursuing Efficient Construction
In the construction of long tunnels with hard rock and stable geology, the full-face excavation method is widely used. Drill jumbos complete the drilling and blasting of the entire tunnel cross-section at one time according to the hole layout plan, which significantly improves efficiency compared with traditional manual drilling. During operation, the jumbo first uses a laser positioning system to accurately project the drill hole coordinates on the hole layout plan onto the rock surface, ensuring that the position and angle error of each drill hole is less than 3°; the drilling sequence must strictly follow the principle of "first cutting holes, then auxiliary holes, and finally peripheral holes". Cutting holes often adopt the "wedge cutting" or "parallel hole cutting" method. For example, wedge cutting requires 2-4 drill holes to be inclined at a 45° angle toward the center to form a wedge-shaped space, creating a free surface for subsequent blasting.
Bench Excavation Method: Suitable for Soft Rock or Large-Section Tunnels, Focusing on Construction Safety
When the tunnel cross-section is large (such as highway tunnels) or the rock is soft and prone to collapse, the bench excavation method can better demonstrate its advantages. This method divides the tunnel cross-section into two layers: upper bench and lower bench. The drill jumbo first completes the hole layout and drilling of the upper bench. After blasting, the upper rock is excavated first, and then the lower bench construction is carried out, forming a "layered advancement" operation mode.
The hole layout plan for this method must pay special attention to the "matching of bench height and hole depth". The height of the upper bench is usually 3-5 meters, and the depth of drill holes needs to be 0.5 meters deeper than the bench height to ensure the bench surface is flat after blasting; at the same time, the peripheral holes of the upper bench need to be inclined outward by 3-5° to form a "pre-split surface", reducing the disturbance of blasting to the rock of the lower bench. During the construction of a certain highway tunnel, after adopting the bench excavation method, the risk of tunnel collapse was effectively controlled, and it could better adapt to the switching of different geological sections. For example, when moving from a hard rock section to a soft rock section, only the hole spacing of the lower bench needs to be adjusted without changing the overall construction process.
Center Diaphragm Method (CD Method): Suitable for Complex Geology, Enhancing Deformation Control
In the construction of tunnels with complex geology and poor rock surface stability (such as tunnels crossing fault zones), the center diaphragm method (also known as CD method) is an important choice to ensure safety. This method divides the tunnel cross-section into two parts: left and right, with a temporary center diaphragm support set in the middle. The drill jumbo first performs drilling and blasting on the left cross-section according to the hole layout plan. After completing the support, it conducts the construction of the right cross-section, which is equivalent to "dividing the tunnel into blocks" and conquering them one by one.
The hole layout plan for this method must focus on designing the "drill hole parameters near the temporary center diaphragm". The spacing of peripheral holes needs to be reduced to 30-40cm, and the drilling angle is inclined outward to avoid damage to the center diaphragm during blasting; at the same time, the excavation length of each block is controlled at 2-3 meters, and the method of "short footage and quick support" is adopted to prevent rock surface collapse due to long-term exposure. When a certain water conservancy tunnel crossed a fault zone, the center diaphragm method was adopted, and combined with precise hole layout and controlled blasting, it successfully dealt with 5 small-scale rock surface slides and ensured construction safety.
From the precise design of hole layout plans to scientific drilling methods, and then to continuous intelligent upgrading, drill jumbos have become an important force in modern engineering construction with the characteristics of "precision, efficiency, and safety". In more and more tunnels, mines, and infrastructure projects, they are overcoming the construction difficulties brought by hard rock surfaces through professional drilling operations, providing support for the smooth progress of engineering construction.
