For practical purposes the same adfreeze strength values may be applied for the various commonly used foundation materials until more detailed information becomes available. At this stage, and to allow for some factor of safety, an adfreeze strength of 18 psi is used to estimate whether the upward thrust on the foundation will be high enough to lift and distort the structure. These factors are currently under study at the Division of Building Research. Information in the literature indicates that adfreeze strength values for wood and concrete are somewhat less than those for steel, and there is thought to be some dependence on foundation size and geometry. The maximum adfreeze measured on a concrete block wall was about 10 psi at the same site. This was equivalent to an average adfreeze strength in shear of about 12.5 psi and was a little lower than values determined elsewhere under different soil and climatic conditions. The heaving force on 3 ½ -inch diameter steel posts placed in clay had a maximum value of about 6,000 pounds for two consecutive winters for 3 ½ feet of frost penetration. Adfreeze strengths were determined by dividing the heaving force measured in the field by the area of contact between the foundation unit and the frozen soil. The limited number that have been determined are used as a general guide only. concrete, wood, steel) in various soil types.
![placing footing per frost depth placing footing per frost depth](http://www.norsewoodsmith.com/files/image/shop/03-concrete/footing2.gif)
Sufficient adfreeze strength studies have not been carried out to give precise field values for all foundation materials (e.g. With this understanding and a means of identifying frost susceptible soils measures can usually be taken during the planning stage to avoid later trouble. It is necessary, therefore, to consider the probability of adfreezing and frost heaving when designing foundations for structures that are not protected from seasonal frost.Īssessment of the probability of encountering such difficulties with a particular structure and soil requires some appreciation of the frost heaving process ( CBD 26). Thus, the problem may get progressively worse from year to year, increasing the damage to both the foundation and the superstructure.
![placing footing per frost depth placing footing per frost depth](https://cdn-codes.iccsafe.org/bundles/document/new_document_images/1300/FigR403.3_3.jpg)
Frequently, also, soil material drops into the cavities produced by the heaving process so that the structure cannot settle back into its original position. In most cases the amount is not uniform over the whole structure and distortion occurs. Behaviour of concrete block walls and posts in frost heaving soils.Īdfreezing by itself is not undesirable it becomes destructive only when it occurs in frost susceptible (frost heaving) soils and the heaving displacements are transmitted to the structure. This places stresses on such units, and displacements occur unless the dead load of the building or other resisting forces exceed the uplift force (Figure 1).įigure 1. The upward thrust of the growing ice lens is transmitted to the foundation unit to which the frozen soil is bonded by adfreezing. During ice lens growth at the frost line most of the volume change results in an upward displacement of the frozen layer. The change of soil water to ice when the ground freezes greatly increases the strength of soil, but this same strengthening process is also responsible for the strong bond (adfreezing) that may develop between the foundation unit and the soil. This Digest is intended to draw attention to the problem of foundation heave resulting from adfreezing for such structures as attached garages and carports, basement garages, separate garages, unheated warehouses, cottages and mechanical and electrical service units sensitive to differential movements. Movements in the soil resulting from ice lens growth can be transmitted to the structure if soil freezes to the foundation walls or supporting columns. Placing foundation footings below the frost line in frost susceptible soil does not necessarily ensure that a structure will be protected from damage from frost heaving. Adfreezing and Frost Heaving of Foundations Adfreezing and Frost Heaving of Foundations CBD-128. Home > Publications > Canadian Building Digests > CBD-128.