Analysis of water ingress, grouting effort, and pore pressure reduction caused by hard rock tunnels in the Oslo region

Langford, Jenny; Holmøy, Kristin Hilde; Hansen, Tom Frode; Holter, Karl Gunnar; Stein, Eivind

doi:10.1016/j.tust.2022.104762

Cited by 8 publications

(5 citation statements)

References 20 publications

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“…Because they can ensure all-weather traffic during snowy, foggy, and windy seasons [3] and have little impact on shipping, they have become an important means of crossing rivers and seas. The construction of subsea tunnels demands the careful consideration of the significant challenge posed by sudden water inflow in the unique underwater environment [4]. Accurately predicting and reasonably evaluating water inflow are crucial in guiding the waterproofing and drainage design of subsea tunnels, as well as the stability analysis of the surrounding rock formations [5,6].…”

Section: Introductionmentioning

confidence: 99%

Research on a Grading Evaluation System for Water Inflow in Three-Hole Parallel Subsea Tunnels Considering Inter-Tunnel Influence

Han,

Yan,

Zhu

et al. 2023

Applied Sciences

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Water inflow analysis is critical for subsea tunnel construction. However, existing studies largely concentrate on the inflow issues pertaining to single-hole tunnels. To address current practical engineering problems, a three-hole parallel configuration is common for subsea tunnels, which may alter water inflow patterns due to the influence of their seepage fields. Herein, numerical simulations are conducted to investigate the water inflow characteristics of a three-hole parallel subsea tunnel. Specifically, the impact of various factors on the water inflow phenomenon, including the permeability coefficient of the surrounding rock, the depth of the seawater, the depth of the tunnel, the spacing between tunnels, and the relative size of the tunnels, are comprehensively studied. Furthermore, based on the principles of the analytic hierarchy process and fuzzy mathematics, an exhaustive assessment framework is developed to evaluate the water inflow of three-hole parallel subsea tunnels. The results indicate that there is a mutual influence between the three parallel tunnels, differing from the predicted water inflow, which is overestimated in a single-hole tunnel model. Therefore, the water inflow assessment for a three-hole parallel subsea tunnel system should account for the inter-tunnel influences. The findings of this study offer valuable insights for the design of waterproofing and drainage systems in three-hole subsea tunnels.

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Section: Introductionmentioning

confidence: 99%

Research on a Grading Evaluation System for Water Inflow in Three-Hole Parallel Subsea Tunnels Considering Inter-Tunnel Influence

Han,

Yan,

Zhu

et al. 2023

Applied Sciences

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“…X-ray diffraction, polarizing microscopy and scanning electron microscopy are important means for detailed analysis of the diagenetic process and microstructure of rocks [5,6]. On this basis, some scholars [7,8] have carried out analysis from the perspectives of Some scholars have conducted research on the failure characteristics of the Luohe Formation sandstone, primarily focusing on rock mechanics properties such as uniaxial compression, triaxial compression, and water-induced softening [3,4]. This research has provided some insights into the analysis of the surrounding rock failure mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Support Optimization of Open TBM Tunneling in Luohe Formation Sandstone by CT Test and Numerical Simulation

Kang,

Li,

Xie

et al. 2023

Applied Sciences

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As underground engineering extends into the western and deeper regions of China, more and more Luohe Formation sandstone layers will be encountered, which have weak cementation and high water content. It is a significant challenge to apply the open TBM, and the support system is crucial in determining whether TBM can excavate quickly and safely. Therefore, in order to optimize the support scheme, this paper analyzes the pore structure and porosity through CT scanning, the results indicate that the volume percentage of pores ≥34 μm is 2.3% and 1.5%, respectively, the large pore apertures are predominant, the surrounding rock has strong permeability, and there is a high risk of rock burst and roof collapse accidents, hence requiring reinforced support measures. On this basis, numerical simulations were conducted to evaluate the support effectiveness. The results show that replacing the “bolt + mesh” with a “bolt + cable + mesh + steel belt”, and replacing the top three bolts with 7.3 m anchor cables, can better control the deformation and provide sufficient thrust force for the TBM, ensuring excavation speed. After the implementation of this scheme at the Kekegai coal mine in Shaanxi, China, the TBM excavation speed increased by 70%, from the previous 10 m/day to 17 m/d, significantly reducing the project duration and construction costs.

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“…The pre-grouting efficiency is normally evaluated using various types of water ingress measurements performed in the tunnel. However, due to the uncertainties related to these measurements, new methods need to be explored to be able to assess the performance of the pre-grouting (Langford et al 2022). This paper explores the potential of using real-time pore pressure data to assess the effects of tunnelling on pressure levels during construction.…”

Section: Introductionmentioning

confidence: 99%

Time series modelling: applications for groundwater control in urban tunnelling

Stein,

Langford,

Kahlström

2023

Bull Eng Geol Environ

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Water ingress to tunnels may result in pore pressure drawdown and consolidation settlements in areas above tunnels founded on soft soil deposits, potentially causing damage to buildings and infrastructure. To limit pore pressure drawdown, requirements are set on water ingress to bedrock tunnels. To meet these requirements, pre-excavation grouting is often performed to reduce the hydraulic conductivity of the rock mass surrounding the tunnel. Real-time pore pressure monitoring may be used to document pore pressure drawdown during construction. However, the effect of tunnel water ingress can be difficult to distinguish from natural pore pressure fluctuations. This paper presents a tunnel case in Oslo, Norway, where time series modelling was applied to local pore pressure data using the transfer function model framework. The input to the models was daily meteorological data considering precipitation and evapotranspiration, and the output was simulated pore pressure levels with impulse response functions. The models were optimised with data from before tunnel excavation, and simulations were run during the tunnel excavation period. Simulated pore pressure levels were compared with observed pore pressure levels to assess tunnelling-induced drawdown. Model uncertainty ranges were used to produce upper, lower, and best estimates of the drawdown. The findings show that time series modelling with transfer function models may be used in tunnel projects to continuously assess the impact on the local groundwater environment, for better evaluation of the pre-grouting performance, and for quantifying both the temporary and long-term drawdown with increased accuracy.

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Analysis of water ingress, grouting effort, and pore pressure reduction caused by hard rock tunnels in the Oslo region

Cited by 8 publications

References 20 publications

Research on a Grading Evaluation System for Water Inflow in Three-Hole Parallel Subsea Tunnels Considering Inter-Tunnel Influence

Research on a Grading Evaluation System for Water Inflow in Three-Hole Parallel Subsea Tunnels Considering Inter-Tunnel Influence

Support Optimization of Open TBM Tunneling in Luohe Formation Sandstone by CT Test and Numerical Simulation

Time series modelling: applications for groundwater control in urban tunnelling

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