Corrosion Level of Rock Bolts Exposed to Aggressive Environments in Nordic Road Tunnels

Cristobal Javier Manquehual,Pål Drevland Jakobsen,Amund Bruland

doi:10.1007/s00603-021-02547-3

Cristobal Javier Manquehual, Pål Drevland Jakobsen + Show 1 more

Open Access

https://doi.org/10.1007/s00603-021-02547-3

Copy DOI

Abstract

For road tunnels in most Nordic countries, temporary rock support installed during tunnel excavation usually becomes a part of the permanent rock support. Rock bolts are the most common rock support measure in road tunnels excavated in hard rock, and their conditions over the period of tunnel operation play a significant role in the safety of these tunnels. The rock bolt types and aggressive environmental conditions considered in this research are focused on those used and observed in Norwegian and Swedish road tunnels. Findings elsewhere in similar environments are included to highlight the different kinetics of degradation. Based on the collected data, the corrosion levels in these road tunnels are comparable to those in the most polluted industrial areas. Aggressive groundwater conditions for rock bolts include a groundwater pH below four (which can be caused by sulfuric acid formation due to the oxidation of the mineral pyrite in the rock), marine groundwater, and flowing groundwater with a high concentration of dissolved oxygen. Furthermore, chloride-bearing deicing salts commonly used on roads located in cold climate regions during winter can promote corrosion in rock bolts from the tunnel room. For these environments, this research proposes a lognormal probability function to quantify the expected steel corrosion level for 25, 50, and 100 years of exposure time. The corrosion protection given by cement grouting, hot-dip galvanizing and epoxy coating are also addressed to explore their contributions to the lifespan extension of rock bolts in acidic and chloride-rich environments.

Highlights

Rock bolts can be used in underground structures as rock support for several purposes
The rate at which this rock bolt corrosion proceeds depends on the chemical composition of the steel, the type of anchorage system, the type of corrosion protection, the quality control during installation, the environmental conditions where they are exposed and any increase in stress demand caused by the rock mass over time (Hadjigeorgiou et al 2020)
The uniform corrosion rates on steel caused by flowing groundwater in some Australian mines studied by Villaescusa et al (2007) gives corrosion rates that can be categorized as extreme corrosivity level CX

Summary

Introduction

Rock bolts can be used in underground structures as rock support for several purposes. Regardless of the reason for utilizing rock bolts in underground structures, they are usually made of carbon steel and are susceptible to corrosion. This chemical process causes steel to lose its cross-sectional area and form corrosion products on its surface due to interactions with the environment. The rate at which this rock bolt corrosion proceeds depends on the chemical composition of the steel, the type of anchorage system, the type of corrosion protection, the quality control during installation, the environmental conditions where they are exposed and any increase in stress demand caused by the rock mass over time (Hadjigeorgiou et al 2020)

Objectives

Findings

Discussion

Conclusion