The cost of using a tunnel boring machine (TBM) per kilometer varies widely depending on factors like the size of the tunnel, geology, depth, location, and project complexity. However, general estimates are as follows:

　　1. Smaller Tunnels (e.g., for utilities):

　　- Cost per km: $10–30 million.

　　- Typically for tunnels with diameters of 1-4 meters.

　　2. Medium-Sized Tunnels (e.g., subway systems):

　　- Cost per km: $50–100 million or more.

　　- Diameters in the range of 5-10 meters.

　　3. Large Tunnels (e.g., highway or railway):

　　- Cost per km: $100–250 million or higher.

　　- Diameters of 10 meters or larger.

　　4. Mega Projects (e.g., underwater or deep urban tunnels):

　　- Cost per km: $300 million to over $1 billion.

　　- Involves challenging geological conditions, significant safety measures, or complex logistics.

　　Breakdown of Costs:

　　- Machine Purchase or Rental: A TBM can cost $10–100 million, depending on size and technology.

　　- Operation: Labor, maintenance, and power costs add significantly to the overall expense.

　　- Support Infrastructure: Ventilation, spoil removal, and tunnel lining systems.

　　- Geological Risks: Unforeseen ground conditions can escalate costs.

　　For specific projects, accurate cost estimation requires detailed site analysis and feasibility studies.