The efficiency of a single shield TBM depends largely on the formation conditions in which it is located. Different formation types can have a significant impact on the performance of the TBM. The following is an overview of the TBM efficiency in several typical formations:

   I. Hard rock formation

   1. TBM efficiency: In hard rock formations, single shield TBMs can usually achieve high TBM efficiency. Hard rock has good self-stability and low groundwater content, which enables the TBM to continuously excavate at a faster speed while reducing the need for support.

   2. Notes: Although the TBM efficiency is high, the cutters in hard rock formations wear faster and need to be replaced regularly, which may result in short downtime.

  II. Soft rock formation

   1. TBM efficiency: In soft rock formations, the TBM efficiency may be affected to a certain extent. Soft rock has poor self-stability and may require more frequent support measures, such as shotcrete and steel arch installation, which will reduce the excavation speed.

   2. Notes: Groundwater management in soft rock formations is also a challenge, but groundwater may have a certain impact on excavation, and corresponding drainage and water-stopping measures need to be taken.

   III. Broken Zone and Fault Zone

   1. Excavation Efficiency: In broken zones and fault zones, the instability of the formation is extremely large, and the excavation efficiency will be significantly reduced. These areas may be accompanied by a large amount of gushing water and loose materials, requiring frequent temporary support and formation reinforcement.

   2. Notes: When excavating in these areas, the safety risk is high, and the formation conditions need to be closely monitored and emergency plans prepared.

   IV. Clay and Sandy Formations

   1. Excavation Efficiency: In clay and sandy formations, clay with high viscosity may adhere to the cutter and shield of the tunnel boring machine, affecting the excavation speed. The excavation efficiency of a single shield tunnel boring machine is usually not high. In addition, these strata are prone to collapse and quicksand, and special stratum control measures such as mud wall protection and grouting are required.

   2. Precautions: Groundwater management in these strata is particularly important, and improper treatment may lead to serious ground subsidence.

  V. Mixed strata

   1. Excavation efficiency: In mixed strata, excavation efficiency is affected by many factors. Mixed strata may contain multiple components such as hard rock, soft rock, and clay. The tunnel boring machine needs to adapt to different stratum characteristics, which may lead to unstable excavation speed.

   2. Precautions: When excavating in mixed strata, it is necessary to flexibly adjust the excavation parameters and support strategies according to actual conditions.

   In general, the excavation efficiency of single shield tunnel boring machines in hard rock strata is the highest, while the excavation efficiency in soft strata, broken zones, fault zones, clay and sand strata, and mixed strata will be affected to varying degrees. In order to improve the excavation efficiency, it is necessary to select appropriate excavation strategies and equipment configurations according to specific stratum conditions, and strengthen on-site management and geological forecasting.