in layers in the soil. The latter formation, referred to by Tsytovich as ‘recurrent vein ice’,
frequently occupies some 50% of the top 20 m of the soil in the northern parts of Russia and
is responsible for the severe foundation problems in the region. The recurrent vein ice can
contain layers of unfrozen water within the permanently frozen soil and foundation pressure
applied to such ground can result in substantial settlement. Because of the variation in thick-
ness of the active layer the upper zone of the permafrost can undergo considerable changes
such as major heaving, the collapse of ice caverns, and the migration of unfrozen water.
9.4.2 The effects of adfreezing on piled foundations
Penner and Irwin(9.12)measured the uplift forces caused by adfreezing on 89 mm steel pipe
anchored into unfrozen soil. The measurements were made in the Leda clay of Ontario in a
region where a deep penetration of frost occurs below the ground surface. The Leda clay
consists of a 70% clay fraction and a 30% silt fraction. The formation of ice lenses in the
soil caused a surface heave of 75 to 100 mm where the frost penetrated to a depth of 1.2 m.
The adfreezing force on the steel pipe was 96 kN/m^2.
Further measurements in the Leda clay have been reported by Penner and Gold(9.13).
When the frost penetrated to a depth of 1.09 m, causing a surface heave of 100 mm, the
measured peak adfreezing forces on anchored columns were as follows:
Steel: 113 kN/m^2
Concrete: 134 kN/m^2
Timber: 86 kN/m^2
Penner and Irwin(9.12)quote similar measurements by Kinoshita and Ono(9.14)as follows:
Iron pipe: 204 kN/m^2
Vinyl pipe: 193 kN/m^2
Concrete pipe: 134 kN/m^2
Epoxy-resin coated concrete pipe: 600 kN/m^2
Grain size can affect adfreeze strength, with clays and coarse soils, particularly those with
low moisture content, being lower than sandy soils.
Dalmatov(9.15)(as quoted by Andersland and Ladanyi(9.10)) expressed adfreezing forces by
the equation:
FLha(c0.5b Tm) (9.1)where Fis the total upward force due to frost heave (kgf ), Lis the perimeter of the foundation
in contact with the soil in centimetres, hais the thickness of the frozen zone in centimetres,
Tmis the surface temperature ( C), and band care constants determined experimentally.
Dalmatov’s values of band cfor timber piles in a silty sandy clay were 0.1 and 0.4
respectively. The measured forces on the steel pipe in Leda clay when expressed by Dalmatov’s
equation gave the same values of band cbut Penner and Irwin(9.12)regard this as somewhat
coincidental.
Measurements of the magnitude of frost heave forces on steel plates restrained from uplift
in Leda clay were made by Penner(9.16), the plates being placed at various depths in the
450 Miscellaneous piling problems