CREG High-Pressure Hydro-Coupling TBM Constructing Hard Rock Tunnels

Hard Rock Tunnel Boring Machine (TBM) is the first choice for the construction of hard rock tunnels because it is a fast, safe, and environmental-friendly construction method.

TBM Specifications
Total installed power: 2160kW
Range of rotation speed: 0~8.5~14.5rpm
Breakout torque: 2022 kNm
Rated torque: 1348kNm
Cutterhead rotation speed: 15.8r/min
Advance speed: 100mm/min
Thrust force: 8970kN@320bar
Curve radius: 500m
Geology: Biotite granite, quartz conglomerate, quartz sandstone, siltstone, conglomerate, argillaceous siltstone, wall rock, etc.

As overburden increases, the ground stress of surrounding rock and the rock strength gradually rises. When the rock strength is more than 200MPa, TBM rock breaking efficiency would be sacrificed. To solve the problem of “hard and slow advance”, various auxiliary rock breaking methods are being studied.

CREG, as a worldwide underground solutions provider, developed the TBM with high-pressure water jet coupled with rock breaking technology on June 18, 2019. It was successfully applied at the Wan’an River Water Diversion Project in the Fujian Province of China, with a total tunnel length of approx. 14.936km and the excavation diameter of 3.83m.

The geology along the tunnel is mainly biotite granite, with the maximum uniaxial saturated compression strength of 226MPa and the average rock strength of 170MPa. The CREG TBM combines the high-pressure water coupling method and the traditional disc cutter rock breaking method, based on the principle that the high-pressure water jet with the nozzle reasonably installed on the cutterhead, is used to wedge the rock, so as to greatly improve the penetration capacity and rock breaking efficiency of the TBM disc cutter and achieve efficient driving.

According to the test data from the site, which includes thrust, penetration, torque of the TBM, when all disc cutters and high-pressure water jet method breaking rocks together, a comparison was made by taking the average value of each parameter, as shown in Table 1.

Table 1: Summary of average values of TBM driving parameters under different water pressures
High-pressure water pressure (MPa)	Thrust (kN)	Torque (kN·m)	Penetration (mm)	Field penetration index (kN/mm)	Torque penetration index (kN·m/mm)
Only disc cutters	5704	429	2.57	84.6	6.33
150	6100	584	3.25	71.4	6.79
200	6044	609	3.66	62.9	6.30
240	6122	640	4.07	57.6	5.97
270	6156	622	4.56	52.4	5.26

It is evident that the penetration of the TBM increases significantly, the torque of cutterhead increases slightly, and the field penetration index and torque penetration index decreases. Taking 270MPa high-pressure hydro-coupling rock breaking as an example, compared to the TBM with all disc cutters, the thrust of the TBM basically remains unchanged (the mean value increases by 7.9%), and its average penetration rises from 2.57mm to 4.56mm, with an increase of 77.4%.

Field penetration index (FPI) refers to the thrust requested by one disc cutter penetrating 1mm into the rock. The mean value of FPI is 84.6kN/mm when driving with only disc cutters, while it is 52.4kN/mm when driving with 270MPa high-pressure water jet, which means the thrust of one disc cutter to wedge 1m into the rock decreases by about 38.1%. Torque penetration index (TPI) refers to the force of rolling friction requested by one disc cutter penetrating the rock of 1mm. When driving with 270MPa high-pressure hydro-coupling, the TPI value decreases about 16.9% to 5.26kN·m/mm from the TPI value of 6.33kN·m/mm when driving with only disc cutters. The cutting effect on tunnel face is shown in Figure 1.