A Geostatistical Solution to Estimating Groundwater Inflows in Deep Rock Tunnels with Validation Through Case Studies
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A Geostatistical Solution to Estimating Groundwater Inflows in Deep Rock Tunnels with Validation Through Case Studies Mark J. Vanarelli 1,2 Received: 23 January 2020 / Accepted: 23 September 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract Estimating groundwater inflows in rock deep tunnels is critical to the safety of personnel constructing the tunnel and the cost of construction. This paper presents two case studies for estimating steady-state groundwater inflows into deep rock tunnels. The case studies included the Chattahoochee and Nancy Creek tunnels. In this paper, statistical methods were applied to packer test data obtained from exploratory borings during geotechnical site investigations. A semi-empirical procedure was utilized for estimating groundwater inflows into these deep rock tunnels. It is the most widely used method/procedure in the tunnel industry. The Chattahoochee and Nancy Creek tunnels are deep rock tunnels which exhibit radial flow conditions. For the radial flow condition, a statistical analysis presented in this paper indicates that the semi-empirical procedure works well; however, variations in the procedure and/or an insufficient amount of testing could lead to underestimations of the inflow quantities. Packer test data plotted in histograms were observed in all cases to be log-normally distributed for the radial flow condition. Modeling using Monte Carlo simulations was observed to be an effective tool for removing irregularities in the distribution of the data and incorporating high-end permeability data to derive reasonable groundwater inflow estimates. This paper is based on the PhD thesis entitled “Improvements to the Current State of the Practice in Steady-State, Groundwater Inflow Estimates into Rock Tunnels based on the Application of Statistical Analysis Methods of Packer Test Data obtained from Exploratory Borings During Geotechnical Site Investigations.” Keywords Groundwater inflows . Deep rock tunnels . Radial flow
1 Introduction Various researchers have developed different approaches to estimating groundwater inflows into rock tunnels. These approaches consist of analytical, empirical, semi-empirical, and numerical methods. The accuracy of all these methods is highly dependent on the quality of field data that characterize the geological and hydrogeological systems above, below, and through which the tunnel is constructed. It appears from a review of the literature that each method has inherent limitations in the accuracy of their estimates. One of these methods/ procedures is evaluated in this paper and the results are presented herein [14]. The current state of the practice is to utilize Heuer’s 1995, semi-empirical procedure to estimate steady-state
groundwater inflow to rock tunnels based on the work of Goodman. Heuer’s procedure provides reasonable estimates of groundwater inflow with discrepancies of 0 to 200%. To account for these discrepancies, Heuer proposed in his 2005 paper to apply a correction factor or multiplier of 1.5 to his estimate o
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