Polymer technology reduces costs and waste generated by the move underground
By Andrew McNabb
More frequent and extreme weather events are knocking down electrical lines and shutting down entire electrical grids. This loss of power can cost billions of dollars. In the United States, estimates indicate that short interruptions alone cost $60 billion annually, and in Canada, $12 billion. Wildfires ignited by overhead transmission lines have been linked to numerous deaths, destruction of property and hundreds of thousands of acres being burned.
Preventing wildfires and minimizing disruption and losses from severe and frequent extreme weather events such as hurricanes, tornados, and massive snow and ice storms are causing more and more utilities to consider hardening their infrastructure by moving it underground.
What’s one solution gaining traction? According to Samuel Ariaratnam, a nationally recognized expert in trenchless technology and a professor and Beavers-Ames Chair in heavy construction at Arizona State University, utility companies are beginning to move their power lines underground. Putting electrical utilities underground not only protects the power systems, making them more reliable, but also protects the communities and surrounding environment. This is not a panacea for all power security issues but a significant step towards addressing this liability.
Moving utilities underground is not an inexpensive solution and many municipalities are wary of making such a change given the price tag. Investing in such an endeavor, however, will yield substantial long-term savings by preventing emergencies that result from power outages and damage to above-ground systems. This will also result in diminished maintenance, repair and replacement costs.
Pacific Gas & Electric (PG&E) has announced plans to spend $20 billion over 10 years to bury 10,000 miles of power lines in wildfire-prone areas of California.
What it takes to move underground
Moving electrical utilities underground creates a different, but manageable, set of infrastructure challenges. Moving utilities underground can be done using both traditional open-cut and trenchless methods, such as horizontal directional drilling (HDD). Trenchless equipment has also been found to emit significantly fewer emissions compared to the equipment used in traditional, open-cut construction. This type of tunneling, although very efficient, does generate liquid waste that requires proper disposal. Liquid waste can be tough to manage and can be a potential safety issue for personnel and the environment in its liquid state.
For PG&E, all liquid waste generated from underground construction and integrity testing was being transported back to its own sites by vacuum excavation trucks. Contractors off-load the liquid slurry material and collect it in large tanks, allow the solids to settle out, remove the surface water, and add a dry bulking material to solidify the residual slurry. Conventional, dry bulking amendments used added as much as 200 percent in waste volume and released fluids during transportation. This methodology incurred significant cost and risk to the utility company.
Utility companies facing similar liquid waste management challenges now have other options. PG&E chose a more cost effective and environmentally friendly solution to this liquid waste problem: polymer-based solidification. The California-based utility opted to use MetaFLO’s proprietary polymer reagents to turn its liquid waste into a dry, stackable solid that was transport ready. MetaFLO’s polymer reagent significantly reduced labor and transportation costs and created a more efficient and safer work site. The time required to meet the solids criteria for disposal decreased and the total volume of waste transported off the site was reduced. This meant fewer trucks on the road, and lower GHG emissions.
Furthermore, depending on the type of liquid waste being solidified, the resultant solid can also be a candidate for beneficial reuse. It can be used as clean regenerative fill material, or used as fill material that can be applied as day-cover at local landfills.
Making the big move
Moving utilities underground is a significant project that comes with a variety of cost implications and challenges. A step in the right direction is to ensure that any liquid waste generated is being remediated in an efficient, cost-effective and more environmentally friendly manner though the application of polymer solidification technology solutions.
Innovation in Tunnel Spoils Management
Tunnel construction is underway in every population centre around the world and the need is only going to grow as densification and urban migration outpace urban planning, outdated underground infrastructure and capacity.
A report by the United Nations Department of Economic and Social Affairs estimates that by 2030, the world could have 43 so-called megacities (up from 31 today) – those with more than 10 million inhabitants – most of them in developing countries. Both the United Nations and the International Organization for Migration estimate that around 3 million people are moving to cities every week.
Jurisdictions each have their own unique set of development priorities, however, there are universal commonalities for underground tunnel construction that include:
- Transit expansion to address urban densification realities, workplace productivity and urban emissions criteria.
- Secure water and sewage movement in and out of population centres to replace and enhance aging infrastructure, address urban growth demands and climate change impact mitigation
- Commercial requirements for the flow of goods and services in and out of congested areas
Innovative technology has broadened tunnel application significantly:
- Improved geotechnical analysis provides better understanding of the ground conditions
- Concrete linings allow for better bore wall stabilization and improved safety
- Sensors can identify obstacles for better efficiency and less damage to existing infrastructure
Depending on ground conditions, the soil removed from the tunnel can be quite liquid. A mixture of clay and soil conditioners are utilized at the face of the tunnel boring machine (TBM) to lubricate, stabilize and extract cuttings out of the tunnel. This resultant slurry creates a problem for disposal.
Spoils solidification with environmentally friendly polymers from MetaFLO Technologies provide an innovative and effective method to efficiently dry the wet spoils at the surface. Using purpose-specific mixing technology, engineered to match spoils output, MetaFLO’s polymer can simply be incorporated into the spoils and immediately transported to a receiving site requiring clean, dry fill in reasonable proximity of the tunnel site.
Planning is the key to a successful tunnel spoil’s management program – and the benefits can be significant:
- Reduced operational footprint in congested urban sites to manage spoils quickly
- Improved transportation efficiency to remove dry material from project sites
- Solidified spoils that meet regulatory criteria to go directly to clean fill sites
- Lower GHG emissions, improved urban logistics, responsible excess soil management
MetaFLO Technologies can work with tunnel operations personnel to help put together an effective plan to address the challenges of dealing with wet spoils.
Andrew McNabb is President & COO, MetaFLO Technologies Inc. McNabb has worked with polymer technology for more than 10 years. His combination of lab and field experience across a broad range of industries has made him a uniquely qualified expert on the application of this technology for optimal results.