How high are the costs for tunnel boring? The cost of tunnel boring is significantly influenced by various factors, leading to a wide range in expenses. Generally speaking, the cost per meter can vary from several thousand dollars to hundreds of thousands or even millions of dollars. Below are some primary factors affecting the cost of tunnel boring:

　　I. Geological Conditions

　　1. Favorable Geological Conditions

　　When the rock is hard and stable with simple geological structures and little groundwater, tunnel boring becomes relatively easier. For instance, construction in solid granite layers involves lower difficulty levels, less equipment wear, and simpler support requirements. In such cases, the excavation cost per linear meter might be between several thousand to tens of thousands of dollars.

　　For short tunnels, due to shorter construction periods, overall costs tend to be lower. If a tunnel a few hundred meters long is under favorable geological conditions, total costs may range in the millions of dollars.

　　2. Complex Geological Conditions

　　Encountering weak surrounding rocks, faults, shattered zones, karst formations, and other poor geological conditions drastically increases construction difficulty. More supports and reinforcement measures are needed in soft rock areas, potentially employing methods like advance support, grouting reinforcement, which significantly raise material and labor costs. In karst regions, additional cave treatment is required to prevent collapses and water gushing.

　　Under complex geological conditions, the cost per linear meter can reach into the hundreds of thousands or even millions of dollars. For long tunnels with extremely complicated geology, total costs could exceed billions of dollars.

　　II. Tunnel Size and Cross-Sectional Shape

　　1. Size Impact

　　Larger cross-sectional areas result in higher boring costs. Railway tunnels, generally larger than road tunnels to accommodate tracks and related facilities, involve increased excavation, support, and lining work volumes. As an example, smaller section road tunnels have costs around tens of thousands of dollars per linear meter, while larger sections can reach hundreds of thousands of dollars.

　　Longer tunnels require more equipment investment, ventilation systems, and construction time, thus increasing costs. Typically, every added kilometer of tunnel length can increase costs by millions of dollars or more, depending on geological conditions and other factors.

　　2. Cross-Sectional Shape Impact

　　Different cross-sectional shapes also influence costs. Circular sections are reasonably stressed but harder to construct; horseshoe-shaped sections are more common and easier to build. Special shaped sections may necessitate customized equipment and techniques, adding to costs.

　　III. Construction Methods

　　1. Traditional Drill-and-Blast Method

　　Drill-and-blast method, applicable across various geological conditions, includes costs for explosives, drilling equipment, ventilation equipment, muck removal devices, as well as labor costs. This method has relatively low costs but slow progress, with significant impacts on the surrounding environment. Costs per linear meter can range from several thousand to tens of thousands of dollars, depending on geological conditions and tunnel size.

　　Short tunnels might opt for this economical choice. However, for long tunnels, extended construction periods lead to prominent issues in ventilation, drainage, and increased costs.

　　2. Shielding and TBM Method

　　Shielding and tunnel boring machines (TBMs) suit longer tunnel projects, especially prevalent in urban subway networks and large-scale water conservancy projects. These methods offer faster construction speeds and minimal environmental impact, yet come with high acquisition and maintenance costs for equipment.

　　The price of a shield machine ranges from several million to tens of millions of dollars, requiring skilled operators and maintenance teams. Moreover, these machines' adaptability is limited, demanding special modifications and treatments for complex geological conditions.

　　Tunnels constructed using shielding or TBM methods might incur costs per linear meter in the hundreds of thousands or higher.

　　IV. Equipment and Material Costs

　　1. Equipment Purchase and Leasing

　　Massive specialized equipment—drilling jumbos, loaders, excavators, ventilators, formwork templates—is necessary for tunnel boring. Purchasing such equipment is expensive, prompting major construction companies to buy key equipment while small firms or short-term projects lease them.

　　Leasing fees fluctuate based on equipment type, leasing duration, and market conditions. Typically, large equipment incurs higher daily rental charges, varying from thousands to tens of thousands of dollars.

　　2. Material Costs

　　Materials required for tunneling include steel, concrete, waterproof materials. Price fluctuations affect costs, where rising steel prices elevate tunnel support costs.

　　High-quality waterproof materials are crucial for ensuring tunnel watertightness, albeit at premium prices. Under specific geological conditions, specialized waterproof materials may be needed, further increasing expenses.

　　V. Labor Costs

　　1. Demand for Skilled Workers

　　Tunnel construction demands skilled technical workers, including drillers, blasters, support workers, and concreters. Wages for these workers are high, particularly in remote locations or harsh working environments, entailing additional subsidies and benefits.

　　Labor shortages may cause wage hikes, inflating construction costs. Typically, wages for technical workers constitute approximately 20% to 30% of total costs.

　　2. Management and Support Staff Costs

　　Management personnel, engineers, and logistics staff contribute to tunnel construction costs through their salaries and benefits. Accommodations, meals, medical services provided for construction crew add up to logistical expenses not to be overlooked.

　　VI. Other Factors

　　1. Environmental Requirements

　　Rising environmental awareness mandates stricter compliance during tunnel construction. Measures taken to reduce dust, noise, and wastewater discharge can inflate costs.

　　In ecologically sensitive areas, ecological restoration and environmental monitoring impose extra expenses.

　　2. Engineering Insurance and Risk Expenses

　　Tunnel construction entails risks such as geological disasters, collapse, and seepage. To mitigate risks, construction firms typically purchase engineering insurance, adding to costs.

　　For high-risk tunnel projects, risk expenses might comprise a certain percentage of total costs.

　　To summarize, tunnel boring costs are subject to multiple variables, with typical expenses ranging from several thousand dollars to hundreds of thousands or even millions of dollars per meter. When budgeting for tunnel projects, comprehensive consideration of geological conditions, tunnel dimensions, construction methods, equipment material costs, labor costs, among others, ensures both accuracy and reasonableness in budget estimates.