How to choose a suitable tunnel boring machine according to engineering geological conditions? When choosing a suitable tunnel boring machine according to engineering geological conditions, the following aspects can be considered:

  I. Geological lithology

   1. Hard rock formation

   ① If the engineering geology is mainly hard rock, such as granite, basalt, etc., a hard rock tunnel boring machine (TBM) is a more suitable choice. Hard rock TBM has a strong cutting ability, which can efficiently crush hard rock and increase the excavation speed.

   ② The tool and cutterhead design of hard rock TBM is suitable for cutting high-hardness rocks, and can ensure long-term stable operation in hard rock formations.

   2. Soft soil and water-rich formations

   ① For soft soil, silty soil, gravel formations and water-rich formations, mud-water balance TBM is usually a better choice. Mud-water balance TBM balances the water and soil pressure of the face through mud pressure, which can effectively prevent problems such as soft soil collapse and water gushing.

   ② Its mud system can discharge the cut soil smoothly to ensure the continuity of construction.

  3. Composite strata

   ① When encountering composite strata with both hard rock and soft soil, it is necessary to comprehensively consider the characteristics of the two types of tunnel boring machines. A dual-mode tunnel boring machine can be used, which can switch between hard rock and soft soil modes to adapt to different geological conditions.

   ② Or according to the specific geological conditions, different types of tunnel boring machines can be used for construction in sections.

   II. Geological stability

   1. Stable strata

   ① For strata with good geological stability, hard rock TBMs or ordinary earth pressure balance shield machines can be selected. These tunnel boring machines can quickly excavate in stable strata and have less disturbance to the strata.

   ② The construction risk in stable strata is relatively low, and tunnel boring machines with higher construction efficiency can be given priority.

   2. Unstable strata

   ① If the stratum is unstable and prone to collapse, deformation and other problems, slurry balance TBM is usually a safer choice. Its mud pressure balance system can effectively support unstable strata and maintain the stability of the tunnel face.

   ② For unstable strata with particularly complex geological conditions, pre-reinforcement measures such as grouting and pipe sheds can also be considered to cooperate with tunnel boring machine construction.

   III. Groundwater situation

   1. Water-rich strata

   ① When there is a large amount of groundwater in the engineering geology, the mud balance TBM can better cope with it. Its mud system can effectively discharge groundwater while maintaining the stability of the tunnel face.

   ② For water-rich strata, waterproofing measures need to be considered, such as strengthening the waterproof design of the tunnel and using water-stopping materials.

  2. Less or no water strata

   In strata with less or no groundwater, hard rock TBMs or earth pressure balance shield machines can be selected. These tunnel boring machines are relatively easy to construct in dry strata and do not need to deal with large amounts of mud and water.

   IV. Tunnel length and diameter

   1. Long tunnels

   ① For long tunnel projects, construction efficiency is an important consideration. Hard rock TBM and slurry balance TBM usually have a higher excavation speed and can shorten the construction period.

   ② In addition, the construction of long tunnels also needs to consider ventilation, transportation and other issues, and these factors should be comprehensively considered when selecting a suitable tunnel boring machine.

   2. Large diameter tunnels

   ① For large diameter tunnels, slurry balance TBM and earth pressure balance shield machine may be more suitable. These tunnel boring machines can be customized according to the tunnel diameter and can meet the construction requirements of large diameter tunnels.

   ② Hard rock TBM is relatively less used in large diameter tunnel construction, but it can also be considered in some special cases.

  V. Project requirements and costs

   1. Project requirements

   ① Select a suitable tunnel boring machine according to the specific requirements of the project, such as the use function and accuracy requirements of the tunnel. For example, for projects with high accuracy requirements such as subway tunnels, slurry balance TBM or earth pressure balance shield machine may be more suitable.

   ② If the project has high requirements for environmental protection, it is also an important consideration to select a tunnel boring machine with less impact on the surrounding environment.

   2. Cost considerations

   ① Different types of tunnel boring machines have different equipment costs, construction costs, and maintenance costs. When selecting a tunnel boring machine, it is necessary to comprehensively consider the project budget and cost-effectiveness.

   ② Generally speaking, the equipment cost of hard rock TBM is relatively high, but the construction efficiency in hard rock formations is also high, which may reduce the total construction cost to a certain extent. The equipment cost and construction cost of slurry balance TBM are also high, but it has better adaptability in soft soil and water-rich formations.

   Selecting a suitable tunnel boring machine according to engineering geological conditions requires comprehensive consideration of multiple factors such as geological lithology, geological stability, groundwater conditions, tunnel length and diameter, engineering requirements and costs. In actual engineering, detailed geological surveys and technical and economic analyses should be carried out to select the most suitable type of tunnel boring machine to ensure the safety, efficiency and quality of tunnel construction.