Drill Monitoring for Rock Mass Grouting: Case Study at the Stockholm Bypass
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ORIGINAL PAPER
Drill Monitoring for Rock Mass Grouting: Case Study at the Stockholm Bypass Jeroen van Eldert1 · Johan Funehag1 · Håkan Schunnesson1 · David Saiang1 Received: 18 February 2020 / Accepted: 12 October 2020 © The Author(s) 2020
Abstract In tunneling, rock mass grouting is a method applied to reduce water ingress. Grouting is influenced by rock mass conditions, especially apertures, frequency, and continuation of fracturing. These rock mass conditions can partly be determined by rock mass classification systems. At the Stockholm bypass, the Measurement While Drilling (MWD) Fracturing Index was applied to characterize the rock mass for grouting purposes, with a focus on adjusting the grout hole drill plan to minimize environmental impact. This study divided the rock mass in a 1.9 km tunnel into six categories based on rock mass conditions, identifying rock mass quality, apparent fracturing, and grout consumption. These categories were then compared with the mean fracturing index based on the coefficients of penetration rate and rotation pressure variations, as well as grout consumption at each grout umbrella. The fracturing index was 93% successful in assessing favorable and unfavorable rock mass conditions in the studied tunnel and 85% successful in determining grout consumption. Finally, a conceptual method was developed to reduce the grouting activities using the MWD fracturing index and water loss tests. The introduction of this conceptual method for grouting decisions could potentially reduce 59% of the umbrellas found in the case study. Keywords Tunneling · Measurement While Drilling (MWD) · Rock mass grouting · Rock mass quality · Rock mass classification
1 Introduction Rock mass grouting is an integral part of tunnel excavation in Scandinavia. The grout hole drilling and grouting is a time consuming and costly process. The grouting procedure has a considerable impact on the environment, both energy consumption (for drilling and production of cement) and the introduction of foreign material in the rock mass (cement). The Swedish traffic administration (Trafikverket) strives to minimize the environmental impact of infrastructure projects, both during construction and operation. The purpose of this paper is to investigate the capability of Measurement While Drilling (MWD) technology to aid in Trafikverket’s commitments on reducing drilling and cement use while following the environmental regulations on water * Jeroen van Eldert [email protected] 1
Division of Mining and Geotechnical Engineering, Department of Civil, Environment and Natural Resources Engineering, Luleå University of Technology, Luleå, Sweden
ingress into the tunnels. Therefore, the grout consumption was compared with the MWD Fracturing Index (FI) of the rock mass while considering the observed rock mass conditions. This study concentrates on determining the rock mass conditions for grouting purposes by MWD recordings. It does not investigate the optimal grout umbrella design, neither the optimum grout mixtures, e.
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