Buildings need to sit on a Solid base. In Halifax, that base is bedrock, and bedrock lies close to the surface here. This means construction usually requires blasting out Bedrock. Blasting is a simple process. You drill holes with certain spacing and depth, place explosives at the bottom, set them off, then dig out the Broken Rock, repeating as required. To control Dust and Fragments, Heavy mats made of old tires are laid over the blasting area.
Before excavation can proceed, care must be taken to prevent cave ins. Temporary shoring is installed. This can be seen in the photos above as the steel H Piles, and timber lagging boards.
To install the H Piles, Holes are first drilled down to bedrock with a Large Drill. The H Piles are placed in the hole, and Cemented into place.
The lagging boards are then installed into the H Pile, And fill placed on the backside.
Extra support is required in many cases, and the lagging is secured to the ground behind it via a tieback anchor. Holes are drilled at an angle into the face of the excavation.
And the Anchor inserted into the hole. A crane is often used to help guide the anchor in.
The Cable is then grouted in place with cement
And finally pulled with a Hydraulic Jack, to post-tension it. A cap is then placed on the front to secure the tieback to the lagging and H piles, and the job is complete.
Tiebacks can also be used to anchor anything to bedrock. In the Case of the Roy Building demolition, the foundation of the Vogue Building sits higher then the bottom of the Roy Building. Tieback anchors are being drilled through the bottom of the vogue buildings foundation, to anchor it to the bedrock bellow to ensure the building does not splay out at the base once the rest of the Roy Building is removed.