Site-Specific Mine Site Safety in North America

Show me a person who tells you that safety on a mine site is just plain common sense, and I’ll show you someone who doesn’t understand mine safety completely. Mine safety is not simply common sense. It is that, and a whole lot more. Most mines have their own set of mine-specific regulations and rules. Nearly all mines, in Canada, the USA, and Mexico, are required by law, to follow government-mandated requirements such as U.S. Department of Labor- Mining Health & Safety Administration (MSHA) and/or the Occupational Safety & Health Administration (OSHA). Canada and Mexico have their government agencies governing mining as well. Even with strict government regulations, most mines have safety regulations specific to each individual mine. Anyone who desires to visit a mine site needs to accept one thing- whatever the rules and regulations are for a particular mine- these regulations are serious business and are meant to be enforced.

Safety in Shotcrete Application in Underground Construction

Because of its durability, strength, and flexibility in application, shotcrete is often used for the construction and stabilization of tunnels and other underground structures. The fact that tunneling involves general construction risks as well as tunnel specific environmental risks, makes this type of application potentially quite dangerous, and must be treated with caution. Risks cannot be eliminated, but we can implement measures to lower the risk.

Outstanding Underground Project

Project Name:
Courthouse Commons Tunnel

Location:
San Diego, CA

Shotcrete Contractor:
Atkinson Construction

Architect/Engineer:
McMillen Jacobs Associates

Material Supplier/Manufacturer:
The Quikrete Company

Equipment Manufacturer:
Normet

General Contractor:
Holland Partner Group

Project Owner:
Holland Partner Group

Outstanding International Project

Project Name:
M4-M5 Link Tunnels

Location:
Sydney, Australia

Shotcrete Contractor:
Acciona Bouygues Samsung Joint Venture

Architect/Engineer:
Jacobs Aurecon Joint Venture

Material Supplier/Manufacturer:
Bekaert

Equipment Manufacturer:
Normet Asia Pacific Ltd

General Contractor:
Acciona Bouygues Samsung Joint Venture

Project Owner:
Jacobs Engineering Group

ASA Real-Time In-Situ Article

Construction of sprayed concrete lining (SCL) ground support across the world utilizes the construct, verify and rework cycle. This methodology typically requires survey verification of the as-built result against design for each stage of the ground support installation. However, processing and analyzing the measurement data is a time consuming and often intensive manual process.

Shotcrete Incorporated into ACI 318-19 Building Code

Since the shotcrete process originated well over 100 years ago, improvements in materials, equipment, and placement techniques have enabled it to become a well-proven method for structural concrete placement. The efficiency and flexibility of shotcrete have been used to great advantage in sizable structural projects, as the high-velocity impact inherent in the process provides the compaction needed to turn low-slump concrete into freestanding vertical and overhead placements with minimal formwork.

Performance of Synthetic Sheet Waterproofing Membranes Sprayed with Steel Fiber-Reinforced Shotcrete

The recent Position Statement #2, “Spraying Shotcrete on Synthetic Sheet Waterproofing Membranes,” published by the ASA Underground Committee, pointed out many aspects critical to successful performance and raised some potential issues affecting the placement.1 In the position statement, specific techniques are presented to prevent problems such as delamination, voids, or fallouts. In the discussion, the potential issue of steel fiber-reinforced shotcrete (FRS) causing damage and potentially puncturing the membrane was raised. From the experience of the committee and the available information, it was concluded that: • The forces acting on the fiber are not strong enough to push the fiber into the membrane; and • The fibers tend to orient parallel to the membrane on impact, thus reducing the risk of damage. In parallel, a research project on this subject had been undertaken at Université Laval’s Shotcrete Laboratory, with the results only recently available. This article presents the results of this investigation.2 It is intended to support ideas presented in the ASA position paper and to help in the decision-making process when dealing with waterproofing membranes and FRS in underground projects.

Fiber-Reinforced Shotcrete Applications and Testing Overview

The addition of fibers to concrete and mortars as reinforcement is not a new concept. The ancient Egyptians used straw to reinforce mud bricks for use in structures like the core walls of the pyramids. During the first century AD, the Romans incorporated horsehair fibers in the construction of structures like the Coliseum to help prevent drying shrinkage cracking of the concrete. In the modern era, the first scientific studies on the use of steel fibers to reinforce concrete date back to the 1960s and 1970s.1,2 The use of steel fiber-reinforced shotcrete (FRS) was first introduced in the 1970s.3 The first documented use of FRS was in 1973 by the U.S. Army Corps of Engineers in a tunnel adit project at the Ryrie Reservoir in Idaho. Soon thereafter it became well recognized that soil and rock excavations could effectively be stabilized with steel FRS and its use and acceptance increased globally. In the mid-1990s, the use of macrosynthetic fibers in shotcrete was developed and has increased with particular success in temporary support in underground mines where large deformation capacity is desired. Since the 1970s, thousands of projects have been successfully completed using fibers as reinforcement, including shotcrete, slabson-ground, composite steel decks, slabs-on-pile, and precast elements.

Maryland Purple Line Plymouth Tunnel

The Plymouth Tunnel is a 1020 ft (311 m) sequential excavation method (SEM) tunnel located in Silver Spring, MD, that makes up a portion of the Maryland Transit Authority’s (MTA) Purple Line light rail connecting the existing metro lines around Washington, DC. The Purple Line Transit Constructors (Flour/Lane/Traylor Joint Venture— PLTC) is the Lead Contractor with the Traylor personnel self-performing the excavation and lining work for the Plymouth Tunnel.

Can shotcrete be considered as structural concrete with wire mesh and rockbolts in tunnel linings?

Shotcrete is a placement method for concrete. It is routinely used for a wide variety of structural applications. It has been used for both initial and final linings in tunnels where it is commonly reinforced with wire mesh, fibers, or reinforcing steel. You may want to review our past Shotcrete magazine articles on tunnel shotcrete at https://shotcrete.org/archive-search/
using keywords such as “tunnel,” “underground,” and “linings.” Also, we have two position papers from our underground committee: “Spraying Shotcrete Overhead in Underground Applications,” and “Spraying Shotcrete on Synthetic Sheet Waterproofing Membranes,” that you may find informative. Also, ACI 506.5R-09, “Guide for Specifying Underground Shotcrete,” can provide insight into topics important for using and specifying underground shotcrete.