On Track in Toronto

Concrete Boom Pumps Overcome Unusual Jobsite Logistics to Keep Toronto-York Spadina Subway Extension Project Moving

Construction of the first subway station for the Toronto-York Spadina Subway Extension (TYSSE) project is right on schedule with the help of Putzmeister truck-mounted concrete boom pumps. They are being used to place an extremely harsh concrete mix with speed and precision, while oftentimes operating at a low boom height to meet air space restrictions of a nearby airport.

The $2.6 billion (CAN) project to construct a 5.3-mile (8.6-km) subway extension is the first Toronto Transit Commission rapid transit line to cross the City of Toronto boundary into The Regional Municipality of York — the fastest-growing region in the Greater Toronto area over the past decade.

The massive project is divided into six sections, with the $279 million Sheppard West Subway Station & Southern Tunnels (Sheppard West) as the first station of the extension and the first contract awarded — going to the joint venture of McNally Construction, Kiewit Construction and Aecon Constructors (MKA). MKA is responsible for constructing 1.6 miles (2.6 km) of twin-tunnel subway track, along with building an integrated subway/GO Transit rail station that includes a three-level, 110,000-sq ft (10,219 m²) structure.

Amherst Concrete Pumping Inc. (Amherst), headquartered in Toronto, is the exclusive concrete pumping contractor for Sheppard West. The pumping company, celebrating 50 years in business next year, has vast experience in placing concrete for residential and commercial construction, as well as tunnels, roads and bridges, and therefore selected to undertake a fast-paced, 18-month schedule to place 65,400 cu yd (50,000 m³) of concrete for the new station.

In Layers

The overall construction process is divided into 150-ft (45.7-m) long sections and built in layers rising out of the 50-ft (15.2-m) deep excavated hole. Varying sizes of truck-mounted concrete boom pumps from Amherst’s fleet are kept busy, pumping the concrete walls at a 3.5-ft (1.07-m) thickness around the hole’s perimeter, a thin concrete slab or mud coat at the bottom of the hole, as well as placing up to 1,570 cu yd (1,200 m³) of concrete per pour to create raft slabs. The raft slabs, at a 5-ft (1.5-m) thickness, are being utilized to establish the foundation because of a high water table.

For the substantially sized raft slab pours, Amherst typically dispatches three to four larger boom pumps — 52Z- and 63Z-meter models, capable of longer boom reaches up to 203-ft, 9-in. (62.10 m), so the concrete is placed exactly where needed. Plus, the models offer outputs up to 260 cu yd an hour (200 m³/hr) to maintain a fast pace. The pours are accomplished at night during off hours to ensure availability of concrete from the ready mix supplier, as well as avoid busy street and air traffic times.

By using a ground bearing concrete floor slab as part of its construction, the raft slabs are ready for walls. The crew then forms the 18-ft (5.5-m) high walls and a boom pump returns to pump between 200 to 525 cu yd (150 to 400 m³) of concrete, using a tremie pipe raised in 3-ft (1-m) lifts every hour. The next section pumped is the elevated subway platform level consisting of the platform, walls and an escalator. For the final section, the main floor and concrete walls are built, this time finishing above ground as this is the station’s entry level.

The structure is taking shape between two tunnels located just over a half-mile (1 km) apart from each other.

Restrictive Air Space

Amherst has been pumping concrete at the job site since fall 2011, using almost every boom pump size in its Putzmeister fleet. However, the manner in which pours were scheduled changed with the arrival of the new Putzmeister five-section 42Z-meter, a model unveiled at World of Concrete 2012, and the first of four 42Zs that Amherst ordered from the manufacturer.

“The 42Z’s low unfolding height and five-section boom allowed us to unfold the boom and operate under the 30-m (100-ft) height restriction of the nearby airport, while we could also attain longer boom reaches than possible with smaller-sized equipment,” says Paul Turney, equipment manager for Amherst. “Prior to this five-section 42Z-meter joining our fleet, we could only use larger sized boom pumps when planes could be routed to other runways.”

Upon arrival, the 42Z went right to work pumping concrete; its lighter weight, less than 66,000 lbs (29,937 kg), didn’t require overweight permits, eliminating costly fees normally associated with a boom pump in the 42-m class. For its first pumping task at Sheppard West, the unit placed concrete for the subway’s elevated platform — a fairly straightforward pour, but one without worry about scheduling around airport flights while reaching long 122-ft, 5-in. (37.3-m) horizontal lengths.

“The 42Z has a compact outrigger footprint as well a short stowed length that is about 7 ft (2 m) shorter than similar model sizes. So we can set up in a really small spot and still have room for ready mix trucks to discharge two at a time,” notes Turney. “The boom can access difficult-to-reach areas as its five-section Z-Fold configuration allows it to maneuver around obstacles within the structure’s highly detailed design.”

Harsh Mix

The majority of the concrete being pumped for Sheppard West consists of a large 1.5-in. (40-mm) crushed stone with a low water-cement ratio, a mix that makes it almost unpumpable —   yet one that is common to Toronto because of the local aggregate. As a result, the tough-to-pump 8,000- to 12,000-psi (55 to 83 MPa) concrete places great demands on concrete pumps.

Turney says, “Our Putzmeister fleet is equipped to pump the extremely abrasive mixes, and we have been able to keep the project on track.”

Due to the complex coordination efforts, harsh concrete mix, and critical nature of every pour, an on-site boom pump is requested as backup; and Amherst, with its expansive fleet of 65 concrete boom pumps, is accommodating.

The Sheppard West Station has an estimated completion date of April 2014, while the entire TYSSE project is targeted for completion in late 2015.