Parramatta Square (PS) is a mega three-hectare precinct development, located in the heart of Sydney’s second central business district (CBD), Parramatta, and consisting of a myriad of residential, commercial and retail elements.

BG&E provided structural and civil engineering, and flooding and drainage services for the precinct.

6-8 PS were the sixth and eighth stages of the $2 billion precinct and comprised a 63-storey commercial tower, with ground floor retail and five floors of basement parking. The retention system for the 6-8 PS site formed part of the overall site retention system for 3, 4 and 6 PS, which had diaphragm walls constructed along the boundary adjacent to 1PS. BG&E’s design avoided the use of D-wall anchors, specifically by creating temporary pad footings within the site to provide temporary support.

Our highly-skilled engineers deployed a shoring methodology for the existing D-wall, foundations/hydrostatic slabs, and the inclined composite concrete-filled (CFT) composite columns between the lower ground and level one. Jump floors were adopted for lower ground, podium three and level three, which represented the first typical floors. Reinforced concrete core walls, suspended slabs and a concrete roof were also included.

The following constraints were implemented:

• a retention system for 6-8 PS, which formed part of the overall site retention system at 3 and 4 PS. The 6-8 PS columns were relatively close to the boundary at Parramatta Railway Station, and subject to design for impact loads, due to potential train derailment;
• the extent of the podium three level is smaller than the first floor and the majority of podium three is spread across a three-storey void, hence hanging columns were used to eliminate the need a very high scaffolding system;
• as column restraint was only available for some columns on the lower ground and first floor, column restraint was significant on these levels to ensure we achieved the intended design parameters for the CFTs. A temporary steel platform on the first floor was also built, which enabled adequate space for the formwork system used on the typical floors; and
• the jump structure allowed the builder to deliver an ambitious construction programme and BG&E was heavily involved in the construction phase of the steel jump structure, to ensure any challenges were quickly addressed. Working through alternative arrangements and construction sequencing early with the respective parties and design team, allowed the project to proceed despite some site constraints.

Situated on nearby the river, Parramatta is growing quickly and with limited land space, densification is taking the form of high-rise developments.

BG&E undertook a flood assessment of the site, to consider local overland and mainstream flooding from the Parramatta River, including:

• developing a 2D-hydraulic model for the Parramatta CBD to better understand the local overland flood and to provide the flood protection measures;
• developing baseline model scenarios to set critical flood levels and flood pattern for the existing scenario;
• developing scenarios to determine the new building floor levels, basement car-park entries, and the redeveloped pedestrian walkway entry to the Parramatta Station (the results have been used to inform automatic, manual flood barrier and flood door designs to provide the most effective flood mitigation strategies);
• preparing flood maps and reports and working with the respective architects to determine the design levels throughout the site, based on the design criteria provided by Council.

BG&E also delivered the associated civil design works, including an upgrade of two intersections and reconstruction of 350 metres of Darcy Street, to provide the frontage for 4 and 6-8 PS, a public domain, a 4,8000 square metre paved area including an outdoor dining facility and seating area, and a major pedestrian thoroughfare to Parramatta Station. The design works included road design, pavement grading, stormwater drainage, subsoil drainage design, utility co-ordination, water sensitive urban design and erosion and sediment control.