Material-handling innovations and challenges

By William Gleason, Editor When a major tunneling project commences in an urban area there is often a great deal of attention paid to the tunnel boring machine (TBM) that will be used to create the tunnel. These massive machines capture the attention of the general public and naming competitions are a great way to engage the public in a positive manner. What gets much less attention but is of great importance is what happens to the material that is removed from the earth by the TBM to create the tunnel. According to Shane Yanagisawa, principal at Osprey Engineers, muck removal and disposal is one of the more mundane but difficult tasks with every tunnel project no matter the size or end use of the tunnel. Advancements in conveyor-belt technology, such as retractable-belt technology, and vertical-belt- storage technology has allowed for more consistent production from TBMs and improved efficiencies. The introduction of multiservice vehicles (MSVs) and rubber-tired transportation vehicles has also helped increase efficiencies in regard to the removal of muck as well as the delivery of materials to the tunnel face. However, the issue of muck remains a challenge. Increased environmental concerns add another level of complexity to the process. T&UC recently reached out to material-handling experts at Kiewit, including Abner da Silva, Kiewit underground tunnel superintendent; Christof Metzger, Kiewit underground construction manager; Kurt Kroner, environmental compliance manager, CP2 project and Tee Galbraith, Kiewit logistics coordinator at Fermi to learn more about the innovations and challenges in material handling and muck removal and disposal. T&UC: What are the primary challenges regarding material (muck) handling in the tunneling and underground construction industry? da Silva: The transportation of tunnel muck presents a number of challenges in urban areas, especially in densely populated areas. Heavy trucks can contribute to the worsening of the traffic, they bring an extra risk on public roads, pollution and if not cleaned properly, they can bring dirt from the site onto public areas. Hence, a comprehensive planning of the transport routes, identification of adverse conditions and its impacts (are needed). For example, is there a stadium near the job site? How is it going to be on game days? A contingency plan needs to be in place to minimize problems and risks when handling muck. In addition, in soft-ground tunneling, the soil needs to be conditioned with products to reduce cutterhead torque and friction, improve face stability, reduce torque on the screw conveyor, and reduce adhesion to metal surfaces, among other benefits. Different types of products can be used in the same tunnel project, depending on the geology of the face, and the treated soil can have a different consistency from the in situ soil. The tunnel spoil will then need to be tested to determine potential reuse and/or disposal as waste according to its classification. Tunnel construction in Rio de Janeiro, Brazil. (Photo: Henrique Freire/GERJ.) T&UC: How many projects use conveyors versus muck cars and how has that changed in the past 10 years? Metzger: It may not have changed significantly within the last 10 years. It is a project-specific decision process, and many factors need to be considered. Both methods come with advantages and disadvantages. Whether a conveyor belt is used or not, it does not change the need for a different, and in the case of a conveyor belt usage, additional logistic concept. The TBM will need material supply and tunnel liner segments, and the crew also needs to be brought in to the TBM. The conveyor belt assembly is often a critical path operation. For this reason, a conveyor belt needs to bring performance-related advantages. A rail-bounded system or the use of muck cars can be used universally. Here are some considerations for the use of conveyor belts: Length of the tunnel: In most cases the effort to assemble and remove a conveyor belt is not economical, and muck cars might be a more economical approach. However, the longer the tunnel, the more advantages a conveyor belt will bring to the table. Alignment, especially tight and changing radii: Conveyor belts can cause challenges in curves, especially S-curves. A train is guided by tracks. Access to the tunnel: If shafts are in place, a vertical conveying system needs to be installed. Using a train and muck cars will require a cycle study to get the muck cars dumped on time. A vertical conveyor promises a higher performance based on the continuous operation. In that case, it is much easier to feed the vertical conveyor with a tunnel conveyor as transferring the muck material from tracks to the belt. U.S. Mine Safety and Health Administration (MSHA) requirements. In gassy conditions, equipment may need to be explosion proof. Both systems need to be checked for their pros and cons accordingly. Emission: Conveyor belts are usually “clean air” equipment. In the case of locomotives, the difference between e-locomotives (battery) and diesel will make a significant difference. Diesel locomotives will require a more extensive ventilation as well. Material being dumped at Rondout. T&UC: Multiservice vehicles (MSV) are not yet widely used in North America, what are the possibilities for more MSV usage? Metzger: The availability of MSVs in North America is limited. The more projects utilizing this approach, the more used equipment will be on the market allowing for the option to become more competitive. MSVs are not a shelf product ,and are typically manufactured to meet the specific project requirements. This results in a relatively long lead time. A growing demand will end up in a wider product portfolio and may reduce the specific design phase and lead time. The big advantage for MSVs is the capability of managing steeper grades and tighter radii. The more projects on the market with steeper grades, the higher the demand for MSVs will be. Generally, it will still be a project-to-project decision. T&UC: In what situation are MSVs a better choice than a rail car system? da Silva: MSVs are a better option when there is site layout restriction, steep ascents/descents, and when other activities need to be performed in the invert of the tunnel concurrently with the excavation; since they don’t need a track system and have excellent mobility, they can avoid the double handling of material, saving time and cost. As an example, in the new metro line for the Olympic Games in 2016 in Rio de Janeiro, Brazil, the tunnel was excavated using an earth pressure balance (EPB) TBM supported by MSV and a belt conveyor system. The ability to pour roller-compacted concrete in the invert of the tunnel as the TBM excavated was crucial to delivering the project on schedule. The metro line was operational in only four months after the TBM hole through — it wouldn’t be possible to achieve such a tight schedule if a rail track system supporting the TBM had yet to be removed after the hole through, pour roller-compacted concrete, and then perform the works for the permanent rail system. T&UC: What innovations are you aware of that are taking place in material handling? da Silva: The use of vertical conveyor belts to dispose of muck in shafts. The Shoreline project in Ohio is using a vertical conveyor belt with buckets to transport the material out of the shaft. The alternative to using muck buckets requires a complex hoist system to be efficient. While conveyors can often be used for changes in elevation, it requires a specific amount of floor space per increase in elevation. The vertical belt conveyor rises straight up to the surface, fully enclosed, with a minimal ground footprint. T&UC: Environmental considerations play a crucial role in the planning and execution of underground construction projects. How have these considerations altered your work on recent and/or current projects? Kroner: Proper planning and early strategic positioning on environmental issues have offset impacts. Owners now invest in extensive characterization of soil and groundwater conditions to establish environmental baselines. Rather than confine the risk to the contractor or delivery team, the environmental scope can be well defined and supported by ample environmental data. Owners also engage with regulatory agencies early to establish agreements and to obtain permits for the handling of groundwater and soil. This preplanning helps mitigate cost and schedule impacts by having conditions and requirements well defined. Most projects now have a specification requirement for an environmental compliance manager. This level of expertise is necessary whether specified or voluntarily provided by the contractor to navigate the voluminous data available and to strategically plan. This environmental professional will direct the project using available and new data. The BART Silicon Valley Extension Phase 2 project performed prebid environmental investigations along the project alignment and worked collaboratively with regulatory agencies to review and approve procedures for the management of potentially contaminated materials generated during construction. The procedures contained thresholds for excavated material reuse and export. Areas containing contaminants requiring special handling were fully characterized to allow assessment by the project team for ensuring worker health and safety, and to properly estimate offsite disposal options. By engaging in capable and knowledgeable environmental support early in the process, the environmental risks could be effectively managed and be an overall benefit to the owner and contractor. T&UC: What are the greatest environmental challenges regarding material handling? Kroner: Worker health and safety. The environmental investigations performed along the project alignment reveal not only a great deal of information to develop disposal costs but also the necessary worker health and safety requirements. The environmental soil sampling data identify contaminant concentrations in the soil from previous industrial activities, and also naturally occurring substances such as asbestos, silica and arsenic. Engineering controls, primarily ventilation, are necessary to minimize employee exposures. Personal protective equipment designed for the known contaminants is specified for workers that come into direct contact with excavated materials. Monitoring is performed to verify the effectiveness of the control measures and to make adjustments to ensure that work is performed within permissible exposure levels for substances present during construction. Material disposal. Material disposal is constrained by many factors including truck count restrictions, trucking hours, fuel cost, labor issues, distance, weather closures, disposal costs and environmental screening. Screening of the soil is important to secure disposal at sites that are most desirable based on vicinity, cost and sustainability. If the environmental baseline data are insufficient to classify the soil for disposal, additional sampling will be required prior to construction or during construction. Early discussion with landfills and disposal sites is necessary to determine if lower-cost options can be utilized. If sampling is required during excavation, a sampling program must identify sample turnaround time and adequate soil holding areas while results are pending. Alternative disposal sites must also be ready if disposal is rejected due to exceedance of the screening criteria. Sustainable disposal options, such as quarry reclamation, wetlands creation and landfill capping may have strict soil screening criteria that will need to be evaluated to determine if project soils can be considered. T&UC: Can you explain the material-handling innovations taking place at the LBNF project at Homestake Mine in South Dakota, and those at the Rondout Project in New York? da Silva: At Rondout the spoil was loaded on muck cars and hauled from the tunnel to the shaft by train. The shaft is 300 m (900 ft) deep and a comprehensive hoisting system was developed to transport personnel and material supply and fly out the spoil of the excavation. The collarmounted, base-frame structure was able to fly out a 20-cu yd loaded muck box, dump it on the surface, fly it back down and set it back on the train car all in seven minutes. Each train composition had seven muck cars making the total cycle in less than an hour, enough to keep up with the excavation. Galbraith: At Fermi LBNF, the project required the refurbishment of the material hoisting and handling system largely idle since the early 2000s. Underground, the work involved the rehabilitation of an ore pass to and loading pockets at the 5,000-ft level. On the surface, the project team refurbished the surface crusher system and then installed a 1,700-ft conveyor system crossing an active highway to the previous mines open pit. The system is designed to handle a maximum of 2.7 kt/d (3,000 stpd) and has processed approximately 453 kt (500,000 st) to date.

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