Factors Affecting TBM Cutter Tunneling Efficiency

Ⅰ. Mechanical factors affecting the tunneling efficiency of TBM cutters

Under the same machine conditions and geological conditions of TBM, the correct selection of tunneling parameters is the main factor determining the safety, speed and economy of tunneling.

There are 8 main driving parameters of TBM:TBM cutter head speed, cutter head torque, motor current value, propulsion force, propelling cylinder pressure, actual tunneling speed, penetration (footage per revolution) and propulsion speed potentiometer selection value .

After selecting the cutter head speed, the only direct control is to select the advance speed. The excavation is controlled by adjusting the propulsion speed. Due to the different rock conditions, the torque and propulsion required for driving are also different, and the actual driving speed achieved is also different.

Under the same driving speed, the penetration degree of the TBM cutter head at high speed is half of that at low speed, and the cutter head torque and propulsion force, which are proportional to the penetration degree, are relatively small.

However, when the cutter head is running at high speed, the disturbance to the weak surrounding rock is relatively large, which may cause instability and collapse of the surrounding rock. In this case, the main choice for the rotation speed of the cutter head is low speed.

The machine factors that are generally considered to affect the performance of the tunnel boring machine include the propulsion force of each TBM cutter, the degree of wear of the cutter, the cutter spacing, cutter diameter, torque, rotational speed, cutter head diameter and curvature, TBM propulsion force, rear supporting equipment, the ability of the machine to handle large rocks, and the stability of shock and vibration resistance, etc.

Ⅱ. Geological factors affecting the tunneling efficiency of TBM cutters

1. The strength of the rock

TBM is designed by taking advantage of the fact that the tensile strength and shear strength of rock are significantly smaller than the compressive strength. The compressive strength is one of the key geological factors affecting the tunneling efficiency of TBM.

2. Wear resistance of rock

The engineering practice of a large number of TBM construction tunnels in the world shows that the wear of the TBM roller cutter has a great impact on the tbm excavation efficiency and the economy of the excavation.

However, it is not enough to judge and predict the cutter wear only according to the compressive strength of rock, and the hardness of rock and the size and quantity of quartz particles contained in rock should be considered. 

3. Integrity of the rock

The development degree of the structural plane of the rock mass (joints, bedding, lamellae, and small faults), that is, the degree of fissure of the rock mass or the integrity of the rock mass has a great relationship with the excavation efficiency, which is another important geological factor affecting the working efficiency of TBM cutters. 

For rock masses with the same or similar compressive strength, hardness and wear resistance of rock, the development of structural planes is different, and the net excavation speed of TBM will be significantly different.

4. Other factors

(1) Influence of fault fracture zone on TBM tunneling efficiency

During the excavation of the TBM cutter, when the amount of ballast is greatly increased, the excavation speed is accelerated, the thrust is reduced, and the support reaction force is reduced, etc., it can basically be determined that the TBM has encountered a fault.

(2) Influence of water and mud inrush on TBM tunneling efficiency

Due to the characteristics of large water volume, high water pressure, and strong suddenness, sudden (inrush) water often leads to instability of surrounding rocks, collapses, and even flooding of tunnels, endangering the safety of construction personnel and equipment in the tunnel.

In the whole tunnel and underground engineering, the tunnel constructed by TBM cutter may only be a small part, but it must not be ignored because of its small size.