Pile Foundations and Grouting

Pile foundations in permafrost mobilise resistance mainly by side friction rather than end bearing and therefore only side friction is to be accounted for in a design. In consequence, load transfer between the pile and the surrounding ground is therefore crucial and thermal disturbances, as described above, must be minimised. Sego and Biggar (1990) present four ways that grout will cure adequately at sub-zero ground temperatures: 1) grout temperature may be artificially maintained above 0°C using external heat source; 2) use of cement with rapid rates of hydration; 3) use of salts or other additives; 4) grouts with very low water content. A series of different grouts has been tested for their applicability in permafrost in the laboratory as well as in the field (Biggar and Kong, 2001; Biggar and Sego, 1993 a; Biggar and Sego, 1993b; Biggar and Sego, 1993c; Biggar et al., 1993; Biggar et al., 1996). Instead of using a sand slurry backfill, the authors used a cementitious grout (Ciment Fondu), which resulted in greater pile load carrying capacity as the failure surface was transferred into the grout annulus. The high alumina cement-based grout cures by rapidly emitting heat, which maintains it above 0°C until it hydrates and hardens. The hydration heat was minimised so that only minor thermal disturbance of the native ground was observed.

Close cell spray foam, which is easier to transport, may be used as an alternative to create polymer piles (Zaharko and Sego, 2008). As the resin mixture expands, voids are filled creating a bond between the pile and the ground. Because the heat production during the exothermal reaction is very low, very limited thaw occurs around the grout.

Design recommendations have recently been developed for the creep response and bearing capacity of helical piles in Arctic permafrost as foundations for lightweight structures (Zubeck and Liu 2003). While these piles could not be installed through a blocky active layer, there may still be applications within alpine permafrost for such an approach.

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