How to configure shield tunneling tools for different geological conditions

source：Shield tunneling tool Release Time：2015-01-04 16:31:27

1. Introduction

The configuration of shield tunneling tools is a very important part of shield tunneling tool design. Whether its configuration is suitable for the geological conditions of the application project directly affects the service life, cutting effect, excavation condition, excavation speed, and construction efficiency of the cutterhead of the shield tunneling machine.

2. Types of cutting tools and cutting principles

2.1. Cutting blade (toothed blade, scraper)

The cutter is a soft soil cutting tool arranged on both sides of the opening groove of the cutterhead. Its cutting principle is that while the shield machine advances forward, the cutter rotates with the cutterhead to generate axial (along the direction of tunnel advancement) shear force and radial (tangential direction of cutterhead rotation) cutting force on the soil in front of the excavation face. Under the rotation of the cutterhead, the cutting edge and the cutting head are inserted into the interior of the formation, continuously cutting off the soil in front of the excavation face. Cutting knives are generally suitable for loose formations such as sand, gravel, clay, etc. with particle sizes less than 400mm.

2.2. Advance Knife (Advance Knife)

The advance cutter is a tool used to cut soil first, and is arranged accordingly. The primary consideration in the design of the advanced knife is to collaborate with other tool combinations. The advance knife cuts the soil before the cutting knife cuts it, dividing the soil into blocks to create good cutting conditions for the cutting knife. The cutting width of the leading blade is generally narrower than that of the cutting blade, resulting in higher cutting efficiency. By using a pre cutting tool, the flowability of the cutting soil can be significantly increased, the torque of the cutting tool can be greatly reduced, the cutting efficiency of the cutting tool can be improved, and the wear of the cutting tool can be reduced. The use of advance knives is very effective in loose rock formations, especially in sandy gravel formations.

2.3. Shell shaped knife

The shell type cutter is essentially an advanced cutter. When a shield tunneling machine passes through sand and gravel formations, especially large particle sand and gravel formations, if a rolling cutter type cutter is used, the loose soil debris will cause significant deformation under the squeezing of the rolling cutter during excavation, greatly reducing the cutting effect of the rolling cutter and sometimes even losing its cutting and crushing ability. Arrange it on the front end face of the cutterhead ring, specifically for cutting sand and gravel.

2.4. Center knife (fishtail knife, double-edged or three bladed rolling cutter, conical knife, center sheep horn knife)

When excavating in soft soil layers, due to the inability to arrange a cutting blade at the center of the cutterhead, a larger fish tail knife (sheep horn knife) can be designed at the center to improve the cutting and mixing effect of the soil. Generally, the fish tail knife is advanced by about 600 mm. The design and configuration of the fishtail cutter are as follows: firstly, the shield machine is divided into two steps to cut the soil. The fishtail cutter first cuts the small circular cross-section soil in the center, and then expands to cut the entire cross-section soil, that is, the design of the fishtail cutter is not on the same plane as other cutters, that is, the fishtail cutter is arranged ahead of the cutters to ensure that the fishtail cutter cuts the soil first; The second is to design the root of the fishtail blade into a cone shape, so that the soil cut by the fishtail blade with the rotation of the cutterhead can be flipped on the basis of tangential and radial motion. This can not only solve the cutting problem of the central soil and improve the fluidity and mixing effect of the cutting soil, but also greatly improve the overall excavation effect of the shield tunnel.

1) Due to rapid changes in rock conditions (mostly developed fractured rock layers) or operational reasons (excessive directional adjustment or thrust), as well as unreasonable tool changes (significant differences in wear between adjacent tools), some tools are overloaded, causing the bearing end of the tool bearing tapered roller to peel off, and the peeled metal fragments and particles cause seal failure.

2) Due to poor foaming agent system of the cutterhead, the temperature of the bearings and lubricating oil is too high.

3) High strength large stones or broken front teeth and edge scrapers get stuck at the sealing of the tool end cover, causing the sliding seal to fail under impact loads.

4) The lifespan of tool bearings and floating seals has reached its limit.

5) During the tool repair process, the sleeve size does not meet the specifications or there are impurities mixed inside the tool.

1.5 Knife ring peeling off

Due to the wear of the cutting ring, fatigue cracks are generated on the surface, which gradually propagate and lead to micro fracture and wear peeling. From the inspection of the cutting tools, it can be seen that the peeling blocks of the general cutting tools are relatively small and do not affect the normal operation of the cutting tools.

1.6 Ring fracture or detachment

The inner side of the front and edge rolling cutters produced by Rick Company has a safety retaining ring welded in half, which facilitates the replacement of the cutting ring and prevents it from shifting. However, due to the centrifugal force, the force exerted by the cutting ring on the cutting body is directed towards the outer side, so the inner side generally receives less force. However, during the construction process, due to poor welding quality of the retaining ring or broken rocks in the front of the cutting disc, collapsed large stones often break or detach the retaining ring, until the cutting ring shifts, making it difficult to replace the tool.

1.7 Loosening, detachment, breakage, and tool dropping of tool bolts

The original records indicate that as the number of tool changes increases, the phenomenon of tool bolts becoming loose, detached, broken, or even falling off (collectively referred to as bolt problems) gradually becomes more serious. The main reasons for tool bolt problems are as follows:

1) The rapid tightening of cutting tools and the repeated use of U-shaped blocks cause a considerable portion of the mating surfaces to deform into a stepped shape under pressure. At the same time, too many repairs result in the two rapid tightening mating surfaces of a single knife not being on the same plane.

2) The tools and tool bolts are frequently reused, resulting in severe thread damage.

3) Due to the failure to clean all mating surfaces (such as quick tightening, U-shaped blocks, threads, and male and female pads) during the installation of the tool, bolt problems occurred during the excavation process.

4) Due to operational reasons, all bolts of the tool did not reach the specified pre tightening torque.

2 Preventive measures

1) Select and install cutting tools with different torques based on different geological conditions during the construction process.

2) During the construction process, the cutterhead foaming agent system should be continuously used while ensuring the effectiveness of the foaming agent system's functions, in order to achieve effective lubrication of the cutting tools, reduce the surface temperature of the cutting tools, and achieve soil improvement.

3) The main components of the cutting tool (such as bearings, end caps, shafts, etc.) that have been used continuously for more than three times need to be scrapped.

4) Establish a quality inspection system for the installation of cutting tools after completion, mainly checking whether the installation position of the tool shaft and tool tightening is correct, and whether the tool bolts are tightened.

5) During the construction process, timely selection of excavation parameters should be based on changes in geological conditions.

6) Establish a strict tool inspection system, inspecting tools every 100 to 150 rings (150m to 225m) in soft rock formations and every 20 to 50 rings (30m to 75m) in hard rock formations. Of course, in case of sudden changes in construction conditions, the inspection date for tools can be determined based on the specific situation at that time.

7) The whole knife and knife ring must be transported, unloaded, and lifted strictly in accordance with relevant regulations and methods, and must be handled with care, and various protective measures must be taken. The on-site installation of cutting tools must be carried out in accordance with their installation requirements and processes.

3 Conclusion

The article discusses the wear and tear forms, causes, and corresponding preventive measures of the cutting tool - rolling cutter - used in the shield tunneling process of Guangzhou Metro Line 3 (from Shiqiao Station North to Panyu Square Station shield tunneling section). The article provides some experience on how to maximize the service life of cutting tools in shield tunnels in the future.

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