Auxiliary Air Pressure Balance Mode for EPB Shield Tunneling in Water-Rich Gravelly Sand Strata: Feasibility and Soil conditioning

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.

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Application Ranges of EPB Shield TBM in Weathered Granite Soil: A Laboratory Scale Study

Applied Sciences ◽

10.3390/app11072995 ◽

2021 ◽

Vol 11 (7) ◽

pp. 2995

Author(s):

Tae-Hwan Kim ◽

In-Mo Lee ◽

Hee-Young Chung ◽

Jeong-Jun Park ◽

Young-Moo Ryu

Keyword(s):

Water Content ◽

Upper And Lower Bounds ◽

Shield Tunnel ◽

Particle Crushing ◽

Pressure Balance ◽

Soil Conditioning ◽

Weathered Granite ◽

Weathered Granite Soil ◽

Granite Soil ◽

Epb Shield

Soil conditioning is a key factor in increasing tunnel face stability and extraction efficiency of excavated soil when excavating tunnels using an earth pressure balance (EPB) shield tunnel boring machine (TBM). Weathered granite soil, which is abundant in the Korean Peninsula (also in Japan, Hong Kong, and Singapore), has different characteristics than sand and clay; it also has particle-crushing characteristics. Conditioning agents were mixed with weathered granite soils of different individual particle-size gradations, and three characteristics (workability, permeability, and compressibility) were evaluated to find an optimal conditioning method. The lower and upper bounds of the water content that are needed for a well-functioning EPB shield TBM were also proposed. Through a trial-and-error experimental analysis, it was confirmed that soil conditioning using foam only was possible when the water content was controlled within the allowable range, that is, between the upper and lower bounds; when water content exceeded the upper bound, soil conditioning with solidification agents was needed along with foam. By taking advantage of the particle-crushing characteristics of the weathered granite soil, it was feasible to adopt the EPB shield TBM even when the soil was extremely coarse and cohesionless by conditioning with polymer slurries along with foam. Finally, the application ranges of EPB shield TBM in weathered granite soil were proposed; the newly proposed ranges are wider and expanded to coarser zones compared with those proposed so far.

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Research on Chamber Earth Pressure of EPB Shield Considering Soil Arching Effect

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1065-1069.373 ◽

2014 ◽

Vol 1065-1069 ◽

pp. 373-377

Author(s):

Jing Cao ◽

Hai Xing Yang ◽

Bo Liang ◽

Hai Ming Liu

Keyword(s):

Earth Pressure ◽

Shield Tunnel ◽

Pressure Balance ◽

Soil Arching ◽

Shield Tunneling ◽

Arching Effect ◽

Soil Arching Effect ◽

Earth Pressure Balance ◽

Tunnel Depth ◽

Epb Shield

Chamber earth pressure is one of the significant parameters during the Earth Pressure Balance (EPB) shield construction processing. The soil arching effect is existence when the tunnel depth is enough. It is significant to consider the influence of arching effect to analyze the pressure in soil chamber in shield tunneling. In this paper, the influence of arching effect is considered to calculate the chamber earth pressure. Firstly, the soil is supposed as loose media, and the necessary buried depth of producing arching affects is deduced according to the loose media theory. Then, based on the characteristic of proper arching axis, the equation and the height of proper arch are obtained. At last, the calculation formula of minimum chamber earth pressure of EPB shield tunnel is deduced which can consider the effect of arching effect.

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Prediction of maximum surface settlement caused by earth pressure balance (EPB) shield tunneling with ANN methods

SOILS AND FOUNDATIONS ◽

10.1016/j.sandf.2018.11.005 ◽

2019 ◽

Vol 59 (2) ◽

pp. 284-295 ◽

Cited By ~ 31

Author(s):

Ren-Peng Chen ◽

Pin Zhang ◽

Xin Kang ◽

Zhi-Quan Zhong ◽

Yuan Liu ◽

...

Keyword(s):

Earth Pressure ◽

Surface Settlement ◽

Pressure Balance ◽

Shield Tunneling ◽

Maximum Surface ◽

Earth Pressure Balance ◽

Maximum Surface Settlement ◽

Epb Shield

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Soil Conditioning for EPB Shield Tunneling in Silty Clay and Weathered Mudstone

International Journal of Geomechanics ◽

10.1061/(asce)gm.1943-5622.0002119 ◽

2021 ◽

Vol 21 (9) ◽

pp. 06021020

Author(s):

Zeen Wan ◽

Shuchen Li ◽

Chao Yuan ◽

Shisen Zhao ◽

Manling Wang ◽

...

Keyword(s):

Silty Clay ◽

Shield Tunneling ◽

Soil Conditioning ◽

Epb Shield

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Risk Mitigation and Construction Control for Effective Underwater Recovery of an EPB Shield: A Case Study of the First Metro Tunnel in Tel Aviv

Advances in Civil Engineering ◽

10.1155/2020/6049608 ◽

2020 ◽

Vol 2020 ◽

pp. 1-15

Author(s):

Weiqiang Qi ◽

Zhiyong Yang ◽

Yusheng Jiang ◽

Zhiyong Liu ◽

Yinxin Guo ◽

...

Keyword(s):

Risk Mitigation ◽

Fine Sand ◽

Diaphragm Wall ◽

Screw Conveyor ◽

Shield Tunnel ◽

Pressure Balance ◽

Shield Tunneling ◽

Tel Aviv ◽

Metro Tunnel ◽

Epb Shield

Shield recovery in water-rich sand strata is a challenging issue in the field of shield tunnel engineering, especially when the end of the shaft cannot be reinforced by jet grouting or freezing or when the shield cannot be supported with a steel sleeve. Therefore, it is important to develop an effective recovery approach and adopt suitable techniques to control the risks. In this study, a new method based on filling the receiving shaft with water is proposed for the underwater recovery of an earth pressure balance (EPB) shield with zero end reinforcement from a metro tunnel in Tel Aviv, Israel. Several additional techniques are used to ensure safe recovery of the shield, including the design of a concrete cradle, drilling of pressure relief holes, control of excavation parameters, screw conveyor sealing, portal sealing, tail sealing, and grouting. Furthermore, according to the actual situation on site, filling the shaft with water to 1 m above the water level in the strata can prevent the fine sand from percolating into the shaft. Before the cutterhead approaches the underground diaphragm wall, the driving attitude should be strictly controlled, and the edge hob should be inspected for wear. The necessary thrust of shield tunneling in the underground diaphragm wall and shaft is calculated theoretically. In order to ensure the deformation control of the underground diaphragm wall and the smooth tunneling of the shield, the thrust of the shield excavating the underground diaphragm wall will not be larger than 12 000 kN, and the penetration degree will be limited to 3 mm/r. Qualitative observations and measurements of surface subsidence in the metro tunnel indicate that these risk mitigation techniques are effective and suitable for the underwater recovery of EPB shields in water-rich sand strata.

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