How to choose an economically appropriate TBM

As an important node of traffic network, tunnel plays an important role in the field of traffic and transportation. However, the construction and construction of tunnels is extremely vulnerable to multiple factors, especially in the geological environment. Geological environment quality is very important to tunnel construction. During excavation and construction, engineers must have a good understanding of the geological composition. From the point of view of construction, the choice of tunneling equipment and construction method is the key to make the whole scheme.

Geological conditions are a key factor in selecting TBMS
The type of engineering and understanding of geological conditions determine the best construction scheme of tunnel boring machine (TBM). Sometimes, in order to minimize the effects of geological complexity and transitions between different geological types, construction plans are adapted to the actual situation. However, the function of a tunnel often determines its cross section and horizontal orientation. As tunnel construction is often unavoidable under mixed geological conditions, certain buffer measures need to be taken, such as subdividing the tunnel alignment and dividing the tunnel sections with relatively consistent geological conditions together, so that the same construction method can be used in the tunnel sections.

How to choose an affordable TBM
Because TBMS will encounter different geological conditions in a single line, it is necessary to consider the treatment methods under various geological conditions, whose advantages and disadvantages depend on the actual geological conditions and design specifications. At the same time, composite geological buffer measures will also be included in the TBM specification.
TBMS are generally single-mode, classified as open or closed earth pressure balancing (EPB) or slurry shield machines. The shield tunneling machine is suitable for the section with similar geological conditions in the whole tunnel. The dual-mode or composite tunnel boring machine developed at present is used in tunnel excavation under the condition of soil rock mixed stratum, and the internal support is usually lined with precast concrete segments. Two-mode TBMS can also be divided into open and closed types. At the same time, earth pressure TBM and mud pressure TBM can be selected to switch between each other. In the construction of soft soil layer and transition zone, TBM uses closed mode; The TBM operates in an open mode in relatively stable formations and rocky areas. When open TBMS are used to excavate rocks and transition zones, detection and grouting are often used to control potentially unstable formations in order to prevent groundwater flooding.
As the performance of TBMS continues to improve, the drilling capability in mixed surface conditions is greatly improved and the risk is greatly reduced. However, the real issue is not the suitability and performance of TBMS in complex or mixed formations, but the selection of the right TBM equipment. This often depends on reliable geotechnical investigation, accurate geotechnical baseline profile and geotechnical parameter acquisition, adaptive TBM standards, adaptive TBM design under different geological conditions, and optimal operation of TBM equipment during tunneling. These factors will determine whether the tunnel can be successfully completed under complex geological conditions. The most important thing to realize is that TBM failures in mixed geological conditions can have serious consequences, including water seepage, subsidence, and even collapse. Correct geotechnical evaluation, proper TBM model and the vigilance of the operator to the change of geological conditions are the keys to the success of the project.