Abstract
This paper analyzes the vertical ground movement during large-scale pipe roof installation and artificial ground freezing of Gongbei tunnel of the Hong Kong-Zhuhai-Macau bridge project. The transverse ground settlement during pipe roof installation is analyzed. The ground loss volume ratio and settlement trough width coefficient during pipe jacking are estimated based on the field measurement of ground settlement. The interaction of pipes during multiple jacking is investigated. The effect of frost heave control by pregrouting, limiting frozen soil thickness, and combination of the two methods is evaluated. The analysis shows that the ground settlement during pipe roof installation by jacking 37 pieces of 1620 mm steel pipes is relatively small with a maximum value of 2.2 cm. The reinforcement to ground provided by the fore-jacked pipes reduces the ground loss volume ratio and, consequently, the ground settlement during the follow-up pipe jacking. The artificial ground freezing generates a relatively large ground heave with a maximum value of 7.8 cm. Pregrouting plays a critical role in the frost heave control by reducing the heave by about 33%. Limiting the frozen soil thickness by heating pipes serves as an effective supplement to frost heave control by reducing the heave by about 9%. The combination of the two measures reduces the ground heave by about 42%. Findings from this paper provide valuable reference to the tunnel construction using pipe roof and artificial ground freezing as presupport.
Highlights
With the advancement of tunnelling technique and increasing traffic demand, more and more large cross-section tunnels have been built in recent years. e International Tunneling Association (ITA) defines the large cross-section tunnels with an excavation area larger than 100 m2
Hu reported that when the permeability of the soil decreases from 1.7 × 10−6 to 6 × 10−7 cm/s, the frost heave ratio reduces from 4.5% to 2% [21]. e previous studies mainly focused on the frost method, such as pregrouting or controlling temperature field, is usually applied to control the frost heave. e combination of multiple control methods is rarely applied in engineering practice
At the end of jacking the 37 pipes, the ground settlement curve at each cross section was in an approximate normal distribution along horizontal direction with the maximum value occurring above tunnel centerline, and the inflection point was located at the position with a horizontal distance of about 12 m from the tunnel centerline. e maximum ground settlement at the three sections ranged from 21.4 to 22.2 mm
Summary
With the advancement of tunnelling technique and increasing traffic demand, more and more large cross-section tunnels have been built in recent years. e International Tunneling Association (ITA) defines the large cross-section tunnels with an excavation area larger than 100 m2. E recently built Gongbei tunnel of the Hong Kong-ZhuhaiMacau bridge project has an excavation cross-sectional area of 336.8 m2 and burial depth of 4 to 5 m in interlayers of saturated clay/silt/sand. It applied a large-scale pipe roof in combination of artificial ground freezing as presupport. Is paper investigates the vertical ground deformation during the installation of large-scale pipe roof and artificial ground freezing using Gongbei tunnel as a case project.
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