Abstract
Earth pressure balance (EPB) shield tunneling in a silty sand stratum is frequently faced with the wear of rotary cutter disc, clogging, or even collapse of workface due to its noncohesive and discrete properties of silty sand material. Soil conditioning is an effective way to reduce the discrete and friction properties of silty sand and to increase its rheology and fluidity, thus improving the cutting performance of EPB machines. However, soil conditioning materials were generally prepared and injected based on past limited field experiences or lab tests which were far from reality. In this article, a ground suitability test system for simulating shield tunneling in a conditioned ground was specially developed and used in a series of tests to investigate the influences of key factors of soil conditioning on the shield cutting performance. In addition, a field experiment of shield tunneling in silty sand of Wuhan Metro was conducted for verification. The major findings were obtained as follows. (1) The proposed test system performed well in simulating and assessing the cutting performance of EPB shield in conditioned soils, and the test results agreed well with the field test. (2) The soil conditioning materials can significantly reduce the cutting torque of shield tunneling in silty sand by up to 60%–70%. (3) The optimal foam and slurry parameters are suggested in the paper for shield tunneling in silty sand, respectively. (4) The test results reveal that the slurry conditioning is better than the foam in decreasing the cutter torque in silty sand. To achieve the same effect of soil conditioning, the injection ratios of foam and slurry should be 45% and 10%, respectively, to achieve the torque reduction ratio of 60%. These findings can provide a practical reference for engineers to determine the best‐fit conditioning materials and construction parameters in the silty sand stratum.
Highlights
Tunnel engineering has played a very important role in the rapid development of infrastructure construction [1,2,3,4]
The shield tunneling in sand is prone to serious abrasion of cutter disk, downtime of advancement, and even collapse of the workface [12,13,14]. e use of soil conditioning material is an effective way to improve the applicability of earth pressure balance (EPB) shields in different geological conditions [15,16,17]
In order to realize the effect of soil conditioning on the shield cutting performance and to optimize the conditioning materials, a series of laboratory tests were conducted using a self-developed ground suitability test system. e effect of four key factors was comprehensively investigated on the shield cutting performance and verified by field experiment of a real tunnel project. e major findings were obtained as follows: (1) e ground suitability test system performed well, and the prediction of the cutter torque based on the test agreed well with the field test
Summary
Tunnel engineering has played a very important role in the rapid development of infrastructure construction [1,2,3,4]. Merritt [42], Peila et al [39], Rivas et al [45], and ewes and Budach [47] developed microscrew conveyor models for laboratory tests to investigate the performance of conditioned soils based on different screw speeds and tank pressures. E main test device was designed and manufactured to simulate the cutting and driving process of shield machine and automatically to measure and record the interactions between the cutter head and soils. E main device is composed of a propulsion system, cutter head, and soil chamber system used to simulate the driving process of EPB shield machine (Figures 5 and 6). Where T is the cutter torque of actual shield machine, T0 is the cutter torque from the simulation test, k is the similarity ratio of the cutter diameter between the test device and shield machine, and α is the calibration coefficient of the test system (α 1.1 ∼ 1.3)
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