Frozen curtain characteristics during excavation of submerged shallow tunnel using Freeze-Sealing Pipe-Roof method

doi:10.1016/j.rcar.2022.09.004.

Abstract

Abstract:

The Freeze-Sealing Pipe-Roof (FSPR) method, which has been applied for the first time in the Gongbei Tunnel of the Hong Kong-Zhuhai-Macao Bridge, is a new approach of tunnel pre-support that allows flexible adjustment of freeze tube arrangement and can be adapted to different environmental conditions. When the FSPR method is used to construct shallow burial submerged tunnels, the frozen wall to hold back groundwater during excavation will be weakened by air and water flows inside and outside the tunnel, and its waterproof performance needs to be further investigated. In this paper, a two-dimensional numerical model of the temperature field considering excavation and moving water boundary is established based on the preliminary design scheme and in-situ conditions and is used to analyze the variation in frozen curtain properties with various active freezing times during excavation. The results show that excavation has a weakening effect on both sides of the frozen wall, with a greater effect on the inner side, and a positive temperature appears in the local area inside the jacked pipe. The concrete fill in the jacked pipe obviously improves the freezing efficiency, and the tunnel excavation after 60 days of active freezing in the interval filling mode can ensure that the frozen soil thickness at the thinnest segment exceeds 2 m, i.e., the design requirement. In practice, the active freezing time can be extended appropriately to reduce the influence of river water flow above the tunnel. The study serves as a technical reference for the design and implementation of similar projects.

Key words: Freeze-Sealing Pipe-Roof method, submerged tunnel, soil excavation, temperature field, frozen wall thickness

Ye Niu,ZeQun Hong,Jun Zhang,Lei Han. Frozen curtain characteristics during excavation of submerged shallow tunnel using Freeze-Sealing Pipe-Roof method[J].Sciences in Cold and Arid Regions, 2022, 14(4): 259-266.

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Layer	Soil	Thickness (m)	Natural moisture	Density (g/cm³)		Natural void ratio	Internal friction angle	Elastic modulus (MPa)
Layer	Soil	Thickness (m)	Natural moisture	ρ	ρ_d	Natural void ratio	Internal friction angle	Elastic modulus (MPa)
(1)2	Plain fill	2.7	26.42%	1.96	2.72	0.78	-	-
(2)1	Silty clay (soft, plastic)	1.5	27.53%	1.96	2.72	0.78	11.64°	16.2
(2)2	Silty clay (hard, plastic)	5.1	26.73%	1.95	2.73	0.77	11.18°	18.0
(2)9	Silty clay (hard, plastic)	6.3	24.39%	2.02	2.72	0.68	16.00°	24.5
(3)2	Silty clay (hard, plastic)	4.3	24.20%	1.98	2.72	0.72	12.50°	21.8
(3)9	Coarse gravel soil	4.1	25.46%	2.01	2.73	0.70	13.00°	25.0
(6)6-2	Argillaceous sandstone	2.6	23.33%	2.01	2.74	0.74	25.00°	1.29×10⁴
(6)5-3	Sandstone	-	22.10%	2.41	2.75	0.66	54.70°	1.57×10⁴

Soil	Parameter
Soil	Temperature (°C)	Thermal Conductivity (W/(m·K))	Density (kg/m³)	Specific heat (J/(kg·K))	Enthalpy (kJ/m³)
Frozen soil	-28	1.74	1,870	1,650	0
	-10	1.74			55,714.4
	-4	1.74			115,302.2
Freezing point	-2.1	1.74	-	-	199,526.7
Unfrozen soil	18	1.42	-	-	247.954
Steel	-	44.70	7,850	459.8	-
Concrete	-	1.835	2,344	752.4	-
Air	-	0.0279	1	1,003.2	-

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