Renny the Erlington Crosstown West TBM

Managing Muck on the Eglinton Crosstown West LRT Project

Tunneling under a dense urban environment comes with several challenges including: what to do with all the wet slurry displaced by the tunnel boring machines?

How is Waste Created from Tunneling?

In many tunneling projects, a large amount of liquid waste is generated. Bentonite-based drilling lubricants, lubricating foams and other additives are used to maintain pressure on the over-burden and reduce friction on the large rotating cutting heads located at the front of the tunnel boring machines.

// ** Advertisement ** //

The amount of lubricant used depends on the geology being tunneled through. The lubricant also facilitates the transport of the debris generated to the rear of the tunnel boring machine where it is transported by a conveyor system or mud car to the surface. When this waste arrives at the surface, it has the consistency of a slurry often referred to as tunnel muck.

Treated material with MetaFLO MF006 solidification reagent
Treated material with MetaFLO MF006 solidification reagent

How it Works

Using their environmentally friendly reagents, MetaFLO can turn tunnel boring muds and sludge into a stackable, solid material, making the disposal of the waste product much more efficient. Fast acting, requiring low dosages and environmentally friendly reagents make the work of such a large-scale project more efficient by turning the resulting slurry into a stackable solid quickly.

// ** Advertisement ** //

Once the slurry is solidified and meeting clean fill criteria, it can be transported in standard dump trucks and disposed of in a range of local clean fill sites. Without on-site solidification, the slurry would need to be transported by alternative trucks at lower capacity to a transfer station for further treatment with dry bulking amendments which increases transportation and handling requirements significantly.

Compared to traditional liquid waste management methods which can use vacuum trucks, MetaFLO reduces risk and boosts efficiency by creating a material where its customers can use standard dump trucks. This process uses 54 per cent fewer trucks and has none of the safety issues involved in transporting and disposing of liquid material.

// ** Advertisement ** //

“For many companies involved in infrastructure projects, low technology solutions such as sawdust, cement and lime for liquid waste management have been in place for decades, becoming their default solution,” said Andrew McNabb, president of MetaFLO Technologies. “New and improved processes, such as the application of MetaFLO’s reagents, are often overlooked, but they shouldn’t be. Our methods allow for more efficient liquid waste management at a lower cost, lower overall risk and less environmental impact.”

Understanding that each project requires a unique solution, MetaFLO offers several custom-blended solutions. MetaFLO supplies these products via a network of authorized distributors who work in a variety of industry sectors.

// ** Advertisement ** //

The Eglinton Crosstown West Extension, a 9.2-km extension of the Eglinton Crosstown Light Rail Transit in Toronto Ontario, uses MetaFLO’s MF006 product, which is well-suited for the solidification of water-based semi solids such as tunnel muck, directional drill cuttings, hydro-excavation material, mining waste, municipal waste and stormwater lagoons. Construction on the project began in 2021, with tunnelling starting in April 2022.

This product is known to the Eglinton Crosstown West Extension team as MUD TERMINATOR supplied by Di-Corp. Di-Corp is a Canadian-based, leading manufacturer and distributor of specialty chemicals, parts and accessories serving the energy, mining and drilling industries.

// ** Advertisement ** //
Erlington Crosstown West alignment map
Treated material with MetaFLO MF006 solidification reagent

Reagents – An Environmentally Sound Choice

By solidifying waste at the site, MetaFLO can help reduce the carbon footprint of a massive project like the Eglinton Crosstown West Extension project in sizable ways.

First, treating the slurry on site helps to reduce the overall number of trucks required to move the treated material to its final destination for beneficial re-use.

// ** Advertisement ** //

Before MetaFLO, transportation for disposal required on average, twice the number of trucks to move the liquid waste material. Reducing truck transportation by over half also reduces greenhouse gas emissions and valuable, operational time, representing a 63% reduction in greenhouse gas emissions, according to Argonne National Laboratory, and 33% cost savings on average.

“Disposal of a liquid material poses unique challenges including the risk of groundwater contamination. Inappropriate disposal of liquid material can potentially leach and contaminate water tables affecting everything from wildlife to food security. Compliance to environmental regulations are now being considered in all project planning, and MetaFLO reagents meet or exceed compliance criteria,” added McNabb.

// ** Advertisement ** //

Also, simply collecting all of the liquid waste onsite requires a sizable footprint, one that is reduced by collecting and treating the slurry on site: less space means less resources required.

The possible contamination of groundwater is always a concern. Contamination of groundwater can affect the overall microbial well-being of soil. Employment of MetaFLO’s reagents are environmentally neutral and do not impact soil acidity, alkalinity or natural microbial activity unlike traditional solidification amendments like lime, cement or sawdust.

// ** Advertisement ** //
Erlington Crosstown West slurry
Treated material with MetaFLO MF006 solidification reagent

Tailored Solutions

Since starting on the Eglinton Crosstown West Extension, MetaFLO and Di-Corp have worked closely with the construction team to fine-tune the reagent dosage and application methodology used on the project to meet the needs of changing ground conditions: not all muck is created equal.

“With tunnel boring significant distances, you’re encountering changing geology. On the Eglinton Crosstown West Extension, we’re encountering shale, sandy shale and clay with alluvial material with varying moisture content which may require dosage adjustments to optimize reagent consumption,” added McNabb.

// ** Advertisement ** //

Traditionally, the slurry is treated on the surface, where it emerges from below the surface on conveyors and is discharged into muck pits or cells. MetaFLO has worked with the construction team to introduce our reagent in-situ through the muck conveyance process. This reduces or eliminates the need to utilize excavators to mix in surface cells improving efficiency and saving time and money.

By introducing the dosing of the slurry as it travels to the muck containment cells, the slurry begins the process of solidification immediately, requiring minimal finishing reagent on the surface. The existing cross conveyor system, which moves the slurry to the surface, can then leverage each directional change transition point of the conveyor system as a point of slurry agitation, further accelerating the solidification process. The original treatment plan was changed, allowing the mechanical action of the cross conveyors to do the work, saving time – and money.

// ** Advertisement ** //

“Engineers want precision, consistency, and the ability to meet ever-changing needs. MetaFLO and Di-Corp have provided this for the Eglinton Crosstown West Extension,” said McNabb.

This article was submitted by MetaFLO Technologies.

// ** Advertisement ** //
EDITOR’S NOTE: This article original appeared in the April 2023 issue of TBM: Tunnel Business Magazine, a sister publication of Trenchless Technology Canada.
// ** Advertisement ** //
// ** Advertisement ** //

See Discussion, Leave A Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.