Pleasant. For the underground stations, a considerable amount of specialty foun- dation works was needed, including: secant pile walls, soldier piles and wooden lagging, ground anchors, utility support structures, micropiles for underpinning, working platforms, guidewalls, and struts/ steel bracing. The general scope and time constraints resulted in the following work being performed: • Total of 2,157 piles installed • 2,760 Lm (9,055 LF) of wall installed • 48,519 linear m or Lm (159,183 LF) of drilling • Pile lengths ranging from 10 to 42 m (33 to 138 ft) • Up to 8 drilling rigs operating at the same time • Up to 6 tie back machines operating at the same time Design Management and Project Concerns Because of the numerous stakeholders involved, design management was one of the most challenging parts for this project. Aecon Foundations subcontracted the needed design work to Pedelta Engi- neering. The utilities required a significant Working in tight spaces Typical plot of verification of drilling verticality amount of attention and coordination, as it was not intended to relocate them per the design concept. Another challenge was working around and not causing dis- turbance to the tunnels already installed under a separate contract prior to the installation of the shoring work for the new segments. The available right of way didn’t allow enlarging the station. In several areas, the piles for the shoring wall were as close as 12 cm (5 in) from the existing tunnel segments. The project requirement for the drilling of the secant piles around and adjacent to the existing tunnel segments was a verticality tolerance of less than 0.5%. The level of accuracy could be achieved using the support provided by the equipment suppliers and the Jean Lutz system. During drilling, the verticality was measured at three different levels, at the minimum. If the required tolerance was achieved at a depth of 15 m (49 ft), only then could drilling be continued. Sequence of Work/Staging Forest Hill Station The general layout of each station is very similar. With an entrance/egress near each end, the station box itself is around 120 m (394 ft) long to accommodate four wagon trains. At the Forest Hill station, the 100 • DEEP FOUNDATIONS • NOV/DEC 2018 arrangement of the station box is a little different — both entrances/egresses are on one side of the box. The existing grade was about 4% in this area, which required the contractor to stage traffic and utility work in addition to creating a safe condition for the drilling rigs on this steep slope. Along both sides of the 120 m (394 ft) long box, the contractor established essentially five different elevations for the construction work. In the very narrow areas, there was no space for a service crane. Therefore, the BG 39 rig needed to drill the holes, offload rebar cages from the trucks, support the cages during splicing and lowering into the hole, and support the tremie pipes during concrete placement. The length of the secant piles along the box alignment (long direction) ranged from 35 to 40 m (115 to 131 ft). Due to the project constraints and circumstances, the pro- duction rate was slow, with only one pile being completed per work day. Sequencing The client had to pay considerable rent for the use of the roads and for diverting traffic. For the four stations of Segment No. 2, the goal was to develop a workable solution to reduce the disruption of traffic along Eglington Avenue to a minimum. There- fore, the top-down construction method seemed to be the best approach.
