01 July 1997
(1) Disturbance of the ground surface during the construction season frequently increases the
depth of thaw. This causes the surface to loose trafficability. The ground surface should be covered with a
blanket of gravel or broken stone and work performed from on top of this blanket.
(2) Access to all of the equipment should be limited to the immediate vicinity of the area where
the installation is to occur. This area should be prepared so that access of equipment to the area is
permanent in case work is required later. For example, maintenance work will probably be required at
some later date.
b. Method of Installation. Piles in permafrost areas are not driven to resistance, but rather to some
specified tip elevation. Refreeze of the soil around the pile must occur as quickly as practical to develop the
required pile capacity. This capacity comes from adherence of the soil to the pile and must support the
downward loads and have sufficient resistance to frost heave. Methods of installing piles that can
accomplish adequate pile capacity is by drilling or by steam jetting.
(1) Drilling. This method consists of the dropping of pile sections into a boring hole that is made
dry with an auger or with a rotary drill and slurry.
(a) Truck mounted augers are usually applicable in silts, clays, and some sands. A rotary drill
or local prethawing may be required in coarse sands and in soils containing cobbles.
(b) The excavation after placing the pile sections is backfilled with a soil-water slurry that
bonds to the pile on freezing. The slurry should be placed in the hole at near freezing temperature to
minimize refreezing time.
(2) Steam Jetting. This method consists of thawing a vertical shaft of soil by a steam jet, pressing
or driving the pile into the shaft of thawed soil, and allowing the thawed soil to refreeze.
(a) A 0.75 to 1.25 inch pipe, open or slightly crimped at the point to give better jetting action is
used with steam pressures from 100 to 200 psi. A chisel bit may facilitate penetration in gravel.
(b) Water should be added to the jetted shaft in dry soil to promote thawing.
(c) If the thawed shaft of material is of small diameter, then the steam jets should be worked
alongside the pile as the pile is advanced down the thawed shaft.
(d) The thawed volume of soil should be minimized to reduce refreezing time.
(3) Seating the Pile. The tip of the pile section should be seated firmly on the bottom of the
excavation or thawed shaft of soil to obtain partial capacity and to be able to support the weight of the
construction while the adfreeze is developing between the soil and the pile.