Tunnel construction of different geology requires the use of different types of tunnel boring machines. The tunnel boring machines currently on the market are mainly divided into two categories: single mode and dual mode. As the name suggests, a single-mode tunnel boring machine has only one mode, such as mud-water (straight-discharge, air-cushion) shield machine, earth pressure balance shield machine, TBM (open type, shield type), etc.; while multi-mode tunnel boring The common machines mainly include the "muddy water + soil pressure" dual mode, the "earth pressure + TBM" dual mode, and the "muddy water + TBM" dual mode.

On August 27th, China Railway No. 820, the first three-mode shield machine that integrates muddy water, soil pressure and hard rock, was officially completed in China Railway China Tunnel United Heavy Equipment Co., Ltd. (hereinafter referred to as China Railway China Tunnel). The three-mode shield machine is not only suitable for the muddy water mode with large permeability coefficient, sensitive surface, soft upper and lower hard sections and unproven boulder formations, but also for the excavation of rock and soil layers with a high degree of weathering. Pressure mode, as well as the muddy water TBM mode of full-face hard rock and rock fracture zone.

The "China Railway No. 820" three-mode shield machine is jointly developed by Guangzhou Metro Group, China Railway Equipment Group, and China Railway China Tunnel. After the assembly is completed, it will be put into the Luogang to Shuixi section of the second phase of Guangzhou Metro Line 7. The section is 1086 meters long and the buried depth is about 19-73 meters. The complex composite stratum is the biggest problem encountered in the construction of this interval tunnel. The full-section hard rock stratum, soft soil layer, upper soft and lower hard stratum are densely distributed in the construction area. The shield machine needs to traverse the hard rock about 800 meters in length and the average rock strength is about 90 MPa. The proven rate of boulders in this section is as high as 66.7%. There are both hard rocks and boulders, which greatly increases the difficulty of construction.

Aiming at the geological environment of soft soil, boulder and hard rock between Luogang and Shuixi on Line 7, the R&D personnel of China Railway Equipment continue to improve the structure of the shield machine by strengthening the structure of the shield machine, increasing the rigidity of the cutter head structure and preventing stagnant discharge Ability to improve the adaptability of the shield machine to complex geological conditions.

Different from the previous dual-mode shield, the three modes of the three-mode shield can realize one-key conversion for different formations. The technicians can operate as long as they are in the main control room without entering the warehouse to disassemble parts, which greatly avoids a long time. The risks brought by the mechanical mode conversion operation.

In addition to the advantages of one-key switching, smooth slag discharge and mud pipeline slag discharge are also the advantages of the three-mode shield, which can achieve stepless and continuous discharge of slag and no dust in the working area, and reduce the wear of cutter head to a certain extent, which is effective It avoids the surface safety risks caused by the inrush water in the open tunneling of the subway project and the inability to close the earth bin during the tunnel construction process.

It is understood that after the shield machine is assembled, the next step will be system debugging and other work. According to the construction plan, the shield will be launched at the end of the year. Editor/Sang Xiaomei