Underpinning

To stabilize the Saskatchewan Legislative Building, construction crews installed approximately 1,800 piles under the Dome, North, South and East Wings of the structure. The installation of these piles was carried out using a process known as underpinning. This page outlines the underpinning process and provides photos of the work carried out in this phase of the project.

Consultants advised Saskatchewan Property Management Corporation that new foundation supports were required to prevent the building from further shifting and ensure public safety.

To install the nearly 1,800 piles, construction crews needed to gain access directly below the building. An access ramp was built on the building's south wing to lead crews directly under the building.

Construction crews excavated earth from under the Dome, North, South and East Wings of the building using bobcats to do a majority of the digging. The excavation below the building occurred in stages. Piles were first installed near the access ramp on the east side of the building. From there, crews worked their way towards the Dome and then to the north and south areas of the building.

Pathways excavated under the building provided crews sufficient space to install the new piles.Photos linked below show the excavation and pile installation.

Once underground, construction crews installed the pre-cast concrete piles. The piles were installed by hydraulically jacking one-metre pre-cast concrete pile sections into the underlying subsoil. The building's foundation was used as a reaction point (basically a pressure point), for pushing the piles into the earth below. Additional pre-cast concrete pile sections were then added on to the lower section. Jacking continued until the sufficient number of pile sections required to meet specifications were installed.

Some original piles were removed to make way for new piles while the majority remain. The pre-cast concrete piles were then encased in concrete. The underpinning portion of this project, as well as phase II, followed a strict heritage conservation approach to ensure the historical integrity of the building is retained.

Here you will find photographs of construction crews excavating earth from below the Saskatchewan Legislative Building and installing the new pre-cast concrete piles. You can link to the various work that took place under each wing by clicking on the following links or selecting the correspodning section from the design drawing.

East Wing North Wing Centre Core South Wing

Pile Construction
The pre-cast concrete piles were manufactured under stringent quality control standards and exact specifications to support the weight of the massive structure above.

Approximately 24,300 one metre (three- foot) long pre-cast concrete pile segments were constructed during the course of the underpinning project. Based upon an average pile depth of 13.5 metres ( 41 feet), approximately 80,000 feet of pile segments or 24 kilometers (15 miles) were cast.

Each batch of concrete was tested to ensure that adequate strength was developed. Concrete strength was checked at seven, 14 and 28 days with the first two tests monitoring the strength development. The 28 day test verifies the ultimate strength of the pile. After 28 days, the pile segments were sent to the building and installed.

The series of photographs below illustrate the manufacturing process in greater detail.

How many piles currently exist under the entire building?
There were over 2,700 piles originally installed in 1908. There are approximately 600 in the East Wing, 600 in the West Wing, 490 in the South Wing, 520 in the North Wing and another 525 under the Dome.

How many piles were installed during the restoration project?
Approximately 1,800.

How deep are the old piles?
Approximately 4.5 metres (14 feet).

How deep were the new piles driven into the ground?
The new piles were installed to a minimum depth of approximately 10 metres (33 feet).

Is this the first time since 1908 new piles have been installed?
No. In 1983 construction crews installed new piles under the West Wing of the building to correct structural deficiencies.