Abstract
Earth Pressure Balance (EPB) shield machines are considered to be the most efficient tunneling method for Metro tunnels due to their adaptability to a great variety of ground conditions, higher construction efficiency, and providing a safer working environment. There are many guidelines available for EPB shield machine selection. However, these guidelines are very general and cannot be used directly for an upcoming project. This paper takes Chengdu Metro Line 6 in China as the engineering background; the studied area is typical of a water‐rich sandy and cobble stratum with high content of cobble. Three types of EPBs in the two continuous intervals exhibit significant differences in performance and encounter many difficulties such as wear of the cutter disc and tools, clogging, and severe surface settlement during the operation. These difficulties prevent the construction efficiency, increase the cost of the project, and cause delays in construction period. The causes of these difficulties are summarized by recording and comparing the operational parameters of the three types of EPBs. These parameters that are summarized include the advance rate, total thrust, torque, and the rate of rotation of the cutter‐head. In addition, the surface settlements are also compared. The results indicate that the opening rate, maximum opening size, and the opening position of the cutter‐head are key factors that affected the geological adaptability of the shield machine in water‐rich sandy and cobble strata. Among the three factors, the maximum opening size and opening position are the most important factors influencing the strata adaptability of the cutter‐head. To avoid frequent jams of the cutter‐head, the maximum torque should be not less than 6,500 kNm. The maximum opening size should not be less than 420 mm × 420 mm. The effect of increasing the central opening of the cutter‐head is that large cobbles and boulders can be discharged through the central opening when they cannot be discharged through the opening near the original position of the cobbles and boulders. This paper provides specific guidance on the selection of cutter‐head for shield machines in water‐rich sandy and cobble strata.
Highlights
With the rapid progress of urbanization, the problem of urban traffic congestion is becoming more and more prominent. e Metro has an important role in urban rail transportation because of its advantages in environmental protection, efficiency, and safety
The cutter-heads of Earth Pressure Balance (EPB) shield machines are impaired by severe wear and the formation of a mud cake, which have significantly reduced the speed of construction and significantly increased the cost of construction in the water-rich sand and cobble stratum that contains large boulders
Due to the difficulties associated with the construction of shield tunnels, Li et al [1] studied the wear of the disc cutter and proposed a model to predict the wear r in typical sandy cobble strata, and the clogging effect was studied through an energy method in a practical project [2]
Summary
With the rapid progress of urbanization, the problem of urban traffic congestion is becoming more and more prominent. e Metro has an important role in urban rail transportation because of its advantages in environmental protection, efficiency, and safety. Cao et al [3] analyzed the performance of a slurry TBM (tunnel boring machine) in sandy cobble ground through a case associated with Lanzhou metro, and they summarized the challenges of tunnelling and proposed corresponding countermeasures by recording and comparing the operational parameters. E performance of the shield machine is reflected mainly by its operational parameters such as its advance rate, thrust, torque, and the rotation speed of the cutter-head. Based on Xuzhou Metro Line 1, the adaptability of the EPB shield machine in clay strata was evaluated, and the reasonable excavation parameters were proposed [15]. By recording and comparing the operational parameters (advance rate, thrust, torque, and rotation speed of the cutter-head), the adaptabilities of the three EPB shield machines were evaluated. By recording and comparing the operational parameters (advance rate, thrust, torque, and rotation speed of the cutter-head), the adaptabilities of the three EPB shield machines were evaluated. en the key factors that influenced the adaptabilities of the three EPB shield machines, including consideration of the geological features of the area, were discussed. en, the specific basis was presented for the selection of the cutter-head of the EPB shield machine in the water-enriched sand and cobble stratum
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