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Evaluation of the Cut-and-Fill Mining Method in Segmented Rock Excavation—Heijinggang Broadcast
Evaluation of the Cut-and-Fill Mining Method with Segmented Rock Drilling and Blasting
The sublevel caving method with staged rock excavation is a widely used open-pit mining technique in metal mines. Its core process involves staged rock excavation and stage-by-stage ore extraction, combined with the use of pillar supports left in the open stope to stabilize the roof. The effectiveness of this method must be evaluated comprehensively in light of orebody conditions and production indicators, allowing for a thorough analysis of its strengths and weaknesses.
I. Applicable Conditions
The application of this method is subject to clear limitations regarding orebody conditions; its core applicable range is: stable ore and rock. Stability coefficient f ≥8) Ore bodies that are steeply inclined to extremely steeply inclined (dip angle of 45° to 90°) and medium-to-thick or thicker (thickness ≥ 5 m). The stability of the ore and surrounding rock is fundamental; if their stability is insufficient, the open-pit mining method will be difficult to sustain over the long term, easily leading to roof collapses and preventing the full realization of its operational advantages. As for thin ore bodies, excessive use of pillars to support the mine structure will result in a deterioration of economic indicators, making them unsuitable for this mining method.
II. Advantages
1. High mining intensity
The core reason is Mine room Multiple parallel working faces can be arranged inside, and rock drilling operations can proceed in parallel with ore transportation operations without interfering with each other, significantly boosting mining efficiency.
Practical Calculation Example: In a certain iron mine, this method is used for mining. The stope dimensions are 60 m along the strike, 15 m along the dip, and a stage height of 40 m. Three drilling workfaces are arranged, with each workface achieving a daily drilling efficiency of 120 m. The spacing between blast holes is 1.2 m, the row spacing is 1.0 m, and the hole depth is 5 m. Ore transportation A scraper is employed, with a daily hauling capacity of 8,000 tons. Rock-drilling operations are carried out in parallel with hauling operations, enabling the completion of rock drilling at three working faces per day (totaling 360 meters). The volume of blasted ore is calculated as follows: 360 m × 1.2 m × 1.0 m × 5 m = 2,160 m³. Given an ore density of 2.8 tons/m³, the daily ore recovery amounts to 2,160 × 2.8 = 6,048 tons. The recovery rate can exceed 6,000 tons per day, significantly surpassing that of conventional open-pit mining methods (typically ranging from 3,000 to 4,000 tons per day).
2. High labor productivity
The process characteristic of staged mining is the large number of free faces (each stage has its own independent free face). Multiple rows of blast holes can be arranged in a single blasting operation, reducing the number of blasting cycles and increasing the ore output per unit time, thereby enhancing labor productivity.
Practical Calculation Example: The iron ore mining team consists of 12 workers, divided into three work groups (each group with 4 workers), corresponding to three drilling faces. Each blast involves 10 rows of blast holes, with 15 holes per row. The charge per hole is 3 kg, and the blasting efficiency is 90%. The amount of ore blasted per blast = 10 rows × 15 holes × 5 m hole depth × 1.2 m row spacing × 1.0 m hole spacing × 2.8 t/m³ × 90% = 2,138.4 tons. The duration of each blast is 8 hours. The team’s labor productivity = 2,138.4 tons ÷ 12 workers = 178.2 tons per worker per shift—significantly higher than that achieved using the room-and-pillar mining method (typically ranging from 80 to 120 tons per worker per shift).
3. Low consumption of timber and explosives results in low mining costs.
This method does not require extensive timber support (the open stope relies on natural support from ore pillars, and the roadways only need simple bolt reinforcement). It features numerous free surfaces and high blasting efficiency, with lower explosives consumption compared to similar mining methods, thereby directly reducing mining costs.
Practical comparative calculations: For the same iron ore as mentioned above, under the staged drilling and blasting method, the consumption of explosives is 0.35 kg/ton, and the consumption of timber supports is 0.001 m³/ton. In contrast, when using the full-mine extraction method, the consumption of explosives rises to 0.6 kg/ton, and the consumption of timber supports increases to 0.008 m³/ton. Based on a daily mining output of 6,000 tons, the daily savings in explosives amount to 6,000 × (0.6 - 0.35) = 1,500 kg. At a price of 3 yuan/kg, this translates into daily savings of 4,500 yuan in explosive costs. Monthly savings in timber supports total 6,000 × 30 × (0.008 - 0.001) = 1,260 m³. At a price of 1,200 yuan/m³, monthly savings in timber support costs reach 1.512 million yuan. Overall, the total mining cost can be reduced by 12% to 18%.
4. Work Safety
Throughout the entire process, workers carry out operations such as rock drilling and charging exclusively within dedicated tunnels, eliminating the need to enter the open-pit area. This approach effectively avoids safety risks such as roof collapses and falling loose rocks in the open-pit zone. Meanwhile, the tunnel working environment is relatively enclosed and less susceptible to external disturbances, further enhancing operational safety. Based on the actual operational data from the iron ore mine mentioned above, no safety incidents related to the open-pit area occurred during the implementation of this method, and the incidence rate of safety accidents was more than 80% lower than that of similar mining methods.
III. Disadvantages
1. The workload for preparation is substantial, and the preparation time is lengthy.
This method requires extensive preliminary construction. Mining access roadway These include stage transport roadways, segmented rock-drilling roadways, shafts, and connecting roadways. The large volume of preparatory roadway construction and the lengthy construction period lead to extended mine preparation time, thereby affecting the schedule for the mine’s commissioning.
Practical Calculation Example: For the aforementioned iron ore deposit, the total length of the preparatory drifts is 800 m, with a cross-sectional area of 4 m² and a total engineering volume of 3,200 m³. The drifts are being excavated using a rock-drilling jumbo, with an advance rate of 8 m per day. Therefore, the construction period is calculated as follows: 800 m ÷ 8 m/day = 100 days. Just the preparatory excavation alone will take 3.5 months; adding equipment installation and commissioning, the overall preparation time could extend to 5 months. 6 months, which is longer than the preparation time for the shallow-hole stoping method (3). (4 months) extended by approximately 40%.
2. The proportion of ore in the mine pillars is high, and the loss and dilution rates are relatively high.
This method requires leaving a large number of mine pillars to support the void areas, with the mine pillars accounting for 35% to 60% of the total ore volume. Moreover, by the time the mine pillars are mined out, the roof of the void area has already lost some of its support, resulting in poor working conditions and high risks, which leads to... Mine pillar recovery rate Low, which in turn leads to higher ore loss and dilution rates.
Practical Calculation Example: For the aforementioned iron ore deposit, the total ore volume of a particular block is calculated as follows: 60 m (strike length) × 15 m (dip width) × 40 m (stage height) × 2.7 t/m³ = 97,200 t (approximately 97,200 tons). Assuming square pillars with dimensions of 6 m × 6 m and a spacing of 12 m, the number of pillars is calculated as: (60 ÷ 12 + 1) × (15 ÷ 12 + 1) = 6 × 2 = 12 pillars. The volume of a single pillar is 6 × 6 × 40 = 1,440 m³; thus, the total volume of all pillars is 12 × 1,440 = 17,280 m³. The ore mass contained in these pillars is 17,280 × 2.7 = 46,656 t. The pillar-to-ore ratio is 46,656 ÷ 97,200 = 48%, which falls within the reasonable range of 35% to 60%. However, the recovery rate of the pillars is only 30%; therefore, the amount of ore recovered from the pillars is 46,656 × 30% = 13,996.8 t. The ore loss amounts to 46,656 - 13,996.8 = 32,659.2 t, resulting in a total ore loss rate of approximately 32,659.2 ÷ 97,200 ≈ 33.6%. The dilution rate is about 18%, both of which are higher than those achieved by the shallow-hole stoping method (with a loss rate of around 20% and a dilution rate of around 12%).
IV. Summary
The core advantages of the cut-and-fill mining method with staged rock excavation lie in its high recovery efficiency, low production costs, and enhanced operational safety. This method is particularly well-suited for medium-to-thick ore bodies with stable rock conditions and varying dip angles—from moderately inclined to steeply inclined—and is especially ideal for large-scale mining operations. However, its main limitations include a long preparation period and significant pillar loss. Therefore, it is essential to comprehensively evaluate and balance these factors against the specific orebody conditions and production scale of the mine.
In practice, mineral pillar dimensions can be optimized—for example, by adopting circular pillars to enhance support efficiency and reduce the number of pillars—while improving pillar extraction techniques (such as combining backfilling with extraction) to minimize ore loss and dilution. At the same time, the construction schedule for preparatory roadways should be planned reasonably to shorten preparation time and fully leverage the advantages of the mining method. For mines with unstable rock conditions, thin ore bodies, or small-scale operations, this method is not recommended due to insufficient economic viability and safety considerations.
