Dawn Tattle, president of Anchor Shoring & Caissons says, “not only is the site in a densely populated area adjacent to homes and businesses, the crews worked adjacent to active rail lines with numerous trains passing daily. During the 7-hour working day, approximately 60 trains passed through the site in very close proximity to working crews.” Safety was paramount. While trains were passing through the site, it was a railroad requirement that all equipment and men stop working. In addition, at those times, all personnel were required to stay 6 m (20 ft) from the tracks and were required to face the tracks. For the faster commuter trains, this work interruption could last as little as 2-3 minutes, while interruptions caused by the slower freight trains could last as long as 25 minutes. The most disruption to the site occurred during the morning commute between 7 to 9 a.m., so work did not really get underway until after that time. Once work finally commenced the race was on to finish as much as possible before the afternoon commute – hence the shortened work day. The amount of disruption caused by the trains was a big unknown faced by the JV going into the project, but crews adapted quickly to the very unusual work environment. The project’s main task involved the installation of 2.7 km (1.7 mi) of interlocking pipe pile wall. The pipe was 914 mm (36 in) diameter x 16 mm (5/8 in) wall, with lengths ranging from 11 m to 24 m (37 ft to 80 ft). The interlocks were a so-called “P-T” connection consisting of a small slotted pipe (the ‘P’) and a mating I-beam that was cut along its web (the ‘T’). Both of these special members were welded to opposing sides of the 914 mm (36 in) pipe to create ‘interlocks.’ These interlocks would later be cleaned and grouted. These connections were needed to provide a water- tight barrier as the excavation for the lower-level rail would be below the water table. “We were building both a foundation wall and cofferdam,” says Patrick Bermingham, CEO of Bermingham Foundation Solutions. In fact, in some areas of the project, we installed sheetpile cross-walls to help facilitate the future excavation of the site, to be conducted in phases. The total number of installed 914 mm (36 in) piles was 2,440, with the largest portion of piles being installed along the center line of the new underpass (about 1 km or 0.6-mi), and 0.8-km (0.5-mi) of wall installed on either side of the underpass. The primary method of installing the interlocking pipe piles was to use large, diesel impact hammers (Berminghammer B-6505s) and Bermingham L-23 Vertical Travel Leads. The piles were all installed in one piece with no splicing (up to 24 m [80 ft] lengths). The hammers were all equipped with hydraulic trip cylinders for starting the hammers, as well as direct-drive helmets and Bermingham’s variable throttle control. These leads and hammers were installed on three 160 ton cranes. “The hammers have 200,000 ft-lbs (271 kJ) of rated energy and drive the piles to depths ranging from 30 to 80 ft (9 to 24 m),” says Bermingham. The soil conditions on the site made the pile driving difficult at times. The upper soil layers consisted mainly of silt and clay with SPT blow counts in the range of 20-30, however, beneath the silt and clay was a very dense sand layer with blow counts in range of 100. This sand layer was typically encountered at a depth of about 9 m (30 ft) and was 2-3 m (6.5-10 ft) thick. Once the piles penetrated this very dense sand layer, the difficult driving continued since the layer beneath the sand consisted of a Glacial Till (silt-clay) with blow counts that ranged from 30-90. This Glacial Till is common to the Toronto area. Bermingham performed the initial test-pile program for the job in 2008. The test piles were slightly smaller in diameter (762 mm/30 in) than the final-design production piles and they were driven with a reinforced toe in anticipation of the difficult driving conditions. Vibratory hammer being positioned at the site PDA testing of these test-piles showed that the toe reinforcement was warranted. When the production piling began using the larger 914 mm (36 in) piles, the toe reinforcing was omitted and some of the early production piles experienced some deformation of the toe. Later in the contract, the toe reinforcement was put back into the design. In addition to reinforcing the pile toes, the JV thought it necessary to protect the ‘P’ and ‘T’ connections welded to either side of the piles. After some experimentation, we found that bevelling the leading edge of the ‘P’ connection helped the small pipe to cut into the harder layers. The ‘T’ connection seemed to stand up well to the driving without any need for reinforcement or modification. Some piles that were suspected to have deformations of either the toe or the “P-T” interlocks were extracted using a very large HPSI 1600 vibratory hammer and a 275 ton (249 tonne) crane which proved very effective in extracting the piles. Any deformed piles were later replaced. DEEP FOUNDATIONS • JULY/AUG 2012 • 9
