aayvat
Structural
- Oct 10, 2008
- 11
Hi everyone,
I'm working on a project in a remote region of continuous permafrost in northern Canada. The average permafrost temperature is -8deg C, active layer is approx. 3ft. My client has an existing structure in place; a steel structure on concrete foundation walls, columns on pilasters and footings. The building size is about 30ft x 75ft. The foundation walls are 5ft high, with about 3ft in the earth. The exterior of the foundation walls are covered with 4in rigid insulation. There is also 4in of horizontal insulation underneath the building (T.O. insulation is B.O. foundation wall). Above this layer of insulation is 1.5ft crushed stone, followed by 8in sand w/ PVC membrance, and the top layer is 8in crushed stone. The floor finish is currently crushed stone.
My client has asked for the design of a permanent steel floor and proposed to have the floors supported on piles. A concrete slab is not preferred. My understanding is that the building has been designed to retain heat inside the building and the insulation prevents the heat from transferring to the frozen earth below the building, and so, the permafrost remains frozen and settlement is minimized.
By installing piles, as proposed by the client, the permafrost below the structure will be disturbed during installation. I also believe the pile will act as a break in the thermal gap formed by the insulation. The heat transferred from the inside of the building through the pile can thaw the surrounding permafrost, resulting in annual settlement. Is it correct to assume this?
There are options to keep the piles from transferring heat to the surrounding soil, like artificial refrigiration and insulating the piles. These may be costly solutions for such a remote site.
Another idea is to provide intermediate pilaster/footings at 15ft and support the floor beams on the existing and new intermediate pilasters, but I'd like to keep the floor seperate from the existing structure. Is building a floor directly on the crushed stone a reasonable solution?
Are there any permafrost specialists out there that can inspire me with their two cents? I've attached a sketch showing a section of the current building and my concern with installing piles.
I'm working on a project in a remote region of continuous permafrost in northern Canada. The average permafrost temperature is -8deg C, active layer is approx. 3ft. My client has an existing structure in place; a steel structure on concrete foundation walls, columns on pilasters and footings. The building size is about 30ft x 75ft. The foundation walls are 5ft high, with about 3ft in the earth. The exterior of the foundation walls are covered with 4in rigid insulation. There is also 4in of horizontal insulation underneath the building (T.O. insulation is B.O. foundation wall). Above this layer of insulation is 1.5ft crushed stone, followed by 8in sand w/ PVC membrance, and the top layer is 8in crushed stone. The floor finish is currently crushed stone.
My client has asked for the design of a permanent steel floor and proposed to have the floors supported on piles. A concrete slab is not preferred. My understanding is that the building has been designed to retain heat inside the building and the insulation prevents the heat from transferring to the frozen earth below the building, and so, the permafrost remains frozen and settlement is minimized.
By installing piles, as proposed by the client, the permafrost below the structure will be disturbed during installation. I also believe the pile will act as a break in the thermal gap formed by the insulation. The heat transferred from the inside of the building through the pile can thaw the surrounding permafrost, resulting in annual settlement. Is it correct to assume this?
There are options to keep the piles from transferring heat to the surrounding soil, like artificial refrigiration and insulating the piles. These may be costly solutions for such a remote site.
Another idea is to provide intermediate pilaster/footings at 15ft and support the floor beams on the existing and new intermediate pilasters, but I'd like to keep the floor seperate from the existing structure. Is building a floor directly on the crushed stone a reasonable solution?
Are there any permafrost specialists out there that can inspire me with their two cents? I've attached a sketch showing a section of the current building and my concern with installing piles.
