Frost Action and Foundations Penner, E.; Crawford, C

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Frost action and foundations Penner, E.; Crawford, C. B.

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NATIONAL RESEARCH COUNCIL OF CANADA

DIVISION OF BUILDING RESEARCH

FROST ACTION AND FOUNDATIONS

by .

E. Penner and C.B. Crawford

Presented at the 27th Annual University of Minnesota Soil Mechanics and Foundation Engineering Conference February 1979

and published as DBR Paper No. 1090 of the Division of Building Research

Ottawa

March 1983 FROST ACTION AND FOUNDATIONS by E. Penner and C.B. Crawford

ABSTRACT

The relationship between climate, seasonal frost penetration and permafrost is discussed in relation to construction activities. The nature of the ground thermal regime, the mechanism of frost heaving, and the criteria for frost susceptibility of earth materials are outlined.

Practical examples related to the design and construction of building foundations, roads, runways and ice rinks are described and problems of freezing during construction activities and thaw settlement of the ground are reviewed.

Les auteurs 6tudient les relations entre le climat, la p6n6tration du gel saisonnier et le pergglisol en fonction des activitge de construction. 11s examinent la nature du rkgime thermique du sol, la mgcanique du soul2vement di3 au gel et les critsres de giSlivit6 de diffgrents sols.

Les auteurs prgsentent des exemples pratiques relatifs 2 la conception et 3 la construction de fondations, de routes, de pistes d'atterrissage et de patinoires. 11s passent aussi en revue les problsmes du gel en cours de construction et du tassement du sol par le d6gel. In southern Canada and the northern United States the ground freezes every winter and thaws in the spring. Farther north the ground is perennially frozen in a condition called permafrost. The rate and depth of freezing or thawing is of special interest to those involved with the construction of buildings, roads, airports apd other modern structures or service facilities.

There are so many factors influencing the freezing and thawing of the ground that precise computations of the change in phase are difficult if not impossible. Nevertheless, a general appreciation of the factors often permits reaeonable predictability. This paper diecusees the relationship between climate and ground temperatures and the mechanism of frost heaving in relation to a variety of engineering problems.

Although the temperature of the ground tends to reflect the temperature of the air, the Mean Annual Ground Temperature (MAGT) is always higher (at least in northern latitudes) than the Mean Annual Air Temperature (MAAT). The primary reason for this is the influence of snow cover on the surface heat exchange. Summer vegetation has a more complex influence involving both evapotranspiration and shading. Other external factors include sunshine, rainfall, relative humidity, wind speed, precipitation and slope of the surface.

Average ground temperatures are determined by external factors, but variations (daily and seasonal) are controlled by three intrinsic thermal properties: volumetric heat capacity Cv, thermal conductivity K, and the latent heat of water. The water content of the ground obviously has a great influence on these three variables and because water content varies with climate, soil type and drainage conditions, this is further evidence of the difficulties associated with the computation of ground temperatures. Volumetric heat capacity, thermal conductivity, and the latent heat capacity all increase with increasing water content.

The ratio K/Cv, called thermal diffusivity, is a measure of the ease with which unfrozen soil will change temperature. It is usually a maximum at fairly low water contents. As the soil water freezes, the changes in the icelwater ratio and the latent heat of fusion become important factors in ground temperature calculations. In addition, in frost-susceptible soils the amount of water moved to the freezing plane must be estimated; this introduces further errors.

Figure 1 shows monthly average ground temperatures in clay soil with a natural surface cover (grass and undisturbed snow). Note that at a depth of 4.5 m (15 ft) the minimum temperature occurs in July and the maximum in December, in each case about 6 months out of phase with the air temperatures. It may also be noted that there was little if any freezing of the ground under natural snow cover, although frost penetrated about 0.9 m (3 ft) under adjacent snow-cleared conditions (Crawford and Legget, 1957). Figure 2 shows the Mean Annual Ground Temperature profile for sites with natural snow cover (curve A) and snow cleared (curve B) at Ottawa, Ontario and for a snow-cleared area (curve C) at Knob Lake (Schefferville, Quebec). The MAGT varies imperceptibly with depth under natural snow cover (A), but under an adjacent snow- cleared roadway the MAGT near the surface is substantially lower (B). Figure 3 illustrates differences between the MAGT and MAAT for several locations in Canada. These differences vary from about 13"~at Vancouver to 7OC at Kapuskasing in northern Ontario (Williams and Gold, 1976).

FROST PxmTuTIOH

From an engineering point of view, one of the most important interests in ground temperatures concerns the depth of frost penetration. This value is needed for locating water and sewer services and the design of roads, runways, and many types of foundations. The prediction of frost penetration by computation is difficult because of the multitude and complexity of variables. The best way to establish the maximum, minimum and average depth of frost penetration is to ask the people who make excavations the year round, the city water department. An alternative is to refer to a reasonably well-established relationship between air temperatures and frost penetration and modify the result to account for major variations in surface or soil conditions.

The general relationship between air temperatures and frost penetration was established by an extensive investigation of frost penetration through granular base courses under snow-cleared airport pavements in the northern United States (U.S . Corps of Engineers, 1949). The results of these studies showed a general relationship between the maximum depth of freezing and the Freezing Index (F.I.) - the cumulative total of degree days of air temperature below freezing during the entire winter. The F.I. is calculated using the mean daily temperatures with subtractions for days above freezing. The relationship between frost penetration and F.I. is commonly called the "Design Curve."

The Design Curve has, of course, some limitations. It applies to snow-free surfaces and granular soils. It is intended to give an estimate of the maximum frost penetration during the entire winter - its use for estimating penetration some time during the winter is less reliable. It does not take into account the water content of the soil - the most important intrinsic factor.

W.G. Brown (1964) calculated frost penetrations for a variety of soils with a range of water contents and for dry sand and rock using the modified Neumann solution and the Kersten (1949) values for thermal properties. He found that the results varied by a factor of less than 2 to 1, and they bracketed the Design Curve. Although Brown does not recommend calculating frost penetration, he did use his calculations and additional field data to recommend a slight change in slope of the original Design Curve as shown in Figure 4. The average F.I. can be computed from meteorological records or estimated from a Freezing Index map such as is illustrated in Figure 5 (Boyd, 1973; Burn, 1976). Once a value for frost penetration is obtained from the Design Curve, judgment must be applied to account for local conditions. Experience has shown, for example, that 0.3 m (1 ft) of natural snow cover will reduce frost penetration by at least 0.3 m and up to 0.6 m (1-2 ft). Compact snow or ice will reduce penetration by an amount approximately equal to its thickness. Frost will penetrate less into wet clay than into granular soils, but the penetration into almost dry granular soils may be greater than that estimated by the Design Curve.

The difficulties in computing ground temperatures have led to the development of graphical methods for solving field problems dealing with natural or engineering structures lying directly on the ground surface (Brown, W.G., 1963). These include:

1) Shallow lakes and rivers on unfrozen or frozen soil (permafrost);

2) Basementless buildings, either heated or cooled;

3) Ice rinks;

4) Streets and streets bordered by buildings; and

5) Roads and runways.

The method determines the long-term (steady-state) temperature changes in the ground caused by changes imposed on the surface. It is only necessary to know the size and shape of the surface area affected, the new and original surface temperatures, and the geothermal gradient of the region. The example shown in Figure 6 could be applied to a surface discontinuity such as a lake. Temperatures adjacent to a river, road, etc., can be obtained by superposition of isotherms radiating from each side of the temperature discontinuity.

FROST HBhVIMG MECUHISN

Frost heaving results from the freezing of water in fine-grained soils. This process increases the soil volume not only by freezing of in situ pore water (=9 per cent expansion) but also by drawing water to the freezing plane from below. Examination shows that soils that have undergone substantial heaving usually consist of alternate layers of ice- saturated soil and relatively clear ice lenses. This is commonly referred to as rhythmic ice lensing (Martin, 1959). The explanation is that it is caused by a succession of periods of balance and imbalance between heat and moisture flow in the freezing zone. The waterlice phase change that results in ice lens growth (and frost heave) in fine-grained porous media increases the moisture suction at the freezing plane (Penner, 1968). This induces a moisture suction gradient in the unfrozen soil which causes the flow of water to the freezing plane either from a shallow water table or by extracting water from the unfrozen soil below the freezing plane. The flow path of the water is through water-filled pores and the adsorbed water films around the particles.

Ice lenses are formed normal to the direction of heat flow and when freezing penetrates from the ground surface, the lenses form parallel to the surface. Many different heat flow patterns exist, e.g., in ditches, behind retaining walls, and on the sides of road embankments, but the direction of heave and ice lens formation will still be predictable from the direction of heat flow.

There is general agreement on the identification of the important frost action factors, but there is still controversy about the exact nature of their interaction. The school of thought that seems to have greatest support in the literature is based on the size and arrangement of the individual particles that make up the soil fabric. This lends credence to the view that frost action criteria should be based on grain size and grain-size distribution (Penner, 1976(a)). Criteria that are solely based on grain size have been used in soil engineering for many years but not with complete success since this neglects the importance of the available water supply and the imposed freezing conditions. These two factors influence the severity of heaving as much as does grain size but they remain poorly defined in currently used frost action criteria.

The theory that supports grain size and grain-size distribution as basic to the nature of the heaving process was restated by Everett (1961) and by Everett and Haynes (1965). Aspects of the same approach to the thermodynamics of freezing porous systems had been developed in some detail earlier by Penner (1957), Gold (1957) and others. Everett's major contribution was to develop a relatively simple, self-consistent and all- inclusive thermodynamic statement which was lacking in earlier studies. The difficulty with its application is that in nature soils normally have a grain-size distribution while the Everett-Haynes theory deals only with an arrangement of uniform-size spherical particles (Figure 7). It nevertheless is based on a physical model that can be studied experimentally. Penner (1968) using uniform-size glass beads was able to show the Everett-Haynes (1965) model was in fact experimentally correct. Such studies were extended to find the relationship between heaving pressures and particle size by measuring the maximum heaving pressure developed in naturally occurring fragmental particles over a small size range.

The Everett-Haynes equation gives the heaving pressure developed by ice lens growth in a close-packed array of spheres of uniform size of radius r as follows: 6

2uiwcos0 ( 1-B ' ) AP = r when bp = heaving pressure by ice lens growth = icelwater interf ace energy term (0.035 ~*m-~) Oiw O = contact angle B' = ratio of spherelpore radius

Equation 1 is given by the solid line in Figure 8. It was checked by measuring the heaving pressure of ice lens growth at full saturation with compacts of spherical glass beads of uniform size. The measured points (for two different sizes) are given by closed squares. The remainder of the points were obtained using non-uniform fractions of natural soils and Potter's flint, but in each case the radius used for plotting was the smallest for that particular sample.

The conclusions that follow from these results are that the Everett- Haynes model appears valid and that some rather important elements of the ice lensing mechanism are understood. For fragmental particles over a size range the heaving pressure corresponds to that of the smallest particles but the real significance of this finding needs to be further explored.

MOISTIJBE STATUS AMD SOIL TYPg

It should be recalled that the main cause of heaving is the formation of ice lenses from water that has migrated to the freezing zone either from a high water table or from the unfrozen soil by reducing its moisture content. This movement of water is in response to the moisture suction - the driving force - developed in the freezing zone.

Increasing the suction of non-plastic, frost-susceptible soils usually increases the volume of air-filled pores and the state of unsaturation. Clay type soils tend to shrink in response to suction increases; the rate of heaving decreases but does not stop until very high values of suction are reached (Penner, 1963). This explains why simple gravity drainage of frost-susceptible soils does not eliminate heaving although good drainage greatly reduces its severity and is desirable where frost action is anticipated. According to Penner (1957, 1959) suction develops more slowly and to a lower maximum in coarse soils than in finer textured soils as heaving progresses (Fig. 9) and sub- drainage is therefore more effective for coarse-grained soils.

In laboratory experiments with six soils ranging in clay content from 6 to 55 per cent, the induced pF (log of suction in centimetres of water) ranged from 2.6 for a soil containing 6 per cent clay size to 3.7 for 55 per cent clay size (i.e., by a factor of 12). These tests were done by determining the maximum suction induced at different freezing rates. Highly frost-susceptible soils are readily identified, e.g., clays, silty clays and silts, as are completely non-frost susceptible materials e.g., clean sands and gravels. It is difficult to evaluate borderline soils with respect to heaving potential and much research effort has therefore been devoted to the development of criteria for such assessments.

FROST ACTION CRITERIA

Many frost action criteria have been suggested but none is completely satisfactory under all conditions. Criteria available in the literature have recently been listed and divided into two groups according to the type of frost damage that will ensue (Table I) (Anderson et al., 1978). The second of the groups has been subdivided on the basis of whether the evaluation was carried out in the field or in the laboratory.

Because of the unsatisfactory nature of available frost action criteria, numerous studies have been carried out at the Division of Building Research (DBR) in the last two decades to characterize the soil heaving process with respect to freezing rate, overburden pressure and freezing temperature. These factors are particularly important where special emphasis in the criteria is placed on soil type.

EFFECT OF FREEZING RATE AND OVERBURDEM PRESSURE 011 HEAVE

Laboratory experiments designed to predict heaving characteristics in the field are shown to be strongly influenced by the rate of heat removal (Penner, 1972). It can be concluded that, for application in the field, the rate of freezing in laboratory frost heave experiments should be based on rate of heat removal, not frost penetration rate.

The combined influence of freezing rate and overburden pressure can be studied in the one-step freezing test (Ueda and Penner, 1977; Penner and Ueda, 1977, 1978; and Penner and Walton, 1978). The changes in response to increases in overburden pressure in open systems are shown by comparing Figure 10 with Figure 11. At low overburden pressures, water intake is initiated as soon as freezing begins; at higher pressures water intake follows only after a period of water expulsion from the sample. Similarly, changes can also be induced in water flow at constant pressure by the variations in the initial freezing temperature. In such experiments it was observed that the initial heave rate is characteristically maintained for some considerable period. It had also been observed that the heave rate remains constant for a longer period when the overburden pressure is high; in time the heave rate decreases for any overburden pressure used.

The responses in heave rate to overburden pressure agreed with results from others (Line11 and Kaplar, 1959) but, more important, a rather simple relationship emerged also between initial heave rate and freezing temperature at constant overburden pressure. Figure 12 shows these combined effects. The relationship is expressed by the following equation:

where -dh = total heave rate dt P = overburden pressure T = cold side temperature

and

a and b are constants depending on soil type

Further verification of Equation 2 is needed, but if proven correct, it does offer a relatively easy method of reducing laboratory frost heave data and comparing tests that have been carried out at various temperatures and pressures.

The concept of operating a buried gas pipeline in permafrost in a "chilled" mode has greatly stimulated the one-step freezing test to assess the influence of soil type on heaving. One of the main reasons the "chilled" mode was suggested was to preserve the frozen condition of the permafrost and hence avoid serious settlements and pipeline failures in areas of high ice content. On the other hand, failure by heaving is anticipated when crossing unfrozen areas particularly under river crossings or other highly frost-susceptible situations.

The one-step freezing temperature method is a simple simulation of the thermal operating conditions of the pipeline. The interest has been to develop an understanding of the heaving process in response to the magnitude of the freezing temperature and the overburden pressure resulting from pipeline burial. It may be seen, however, that the one- step approach has much wider implications. It forms the basis of a frost susceptibility test to evaluate various soil types for any soil engineering problem.

FBOST HEAVE FORCES

Frost heaving forces that cause damaging displacement to buildings are transmitted from the soil to the structure in two ways. When freezing below footings results in uplift, it is referred to as "basal heaving." In such cases, heaving may be avoided by simply preventing freezing under footings by the use of insulation or placing the footings well below the maximum depth of seasonal frost penetration.

Uplift forces that result when frost-heaving soils are in contact with foundation walls or footing columns are less well known and also more difficult to avoid. In this case the forces due to ice lens growth in the soil adjacent to the foundation are transmitted by "adfreezing" or "frost grip." Such forces depend not only on the contact area between the soil and the structure, but also on the type, size, and geometry of the foundation (walls or columns) and on the heaving characteristics of the soil.

A better understanding of the uplift problem in relation to specific structures was obtained from field studies ranging over several winter periods in an area of seasonal frost. The objective was to confine the origin of the heaving force to one source - either basal or adfreeze - and hence determine by measurement the pattern and magnitude of forces developed as the winter progressed and the thickness of the frozen layer increased.

Basal forces (Penner, 1970) developed against a rock-anchored reaction frame (Fig. 13) by frost heaving in Leda clay under a circular steel plate 0.3 m (12 in.) in diameter and 25.4 mm (1 in.) thick are shown in Figure 14. The magnitude of the forces due to ice lens growth clearly demonstrates that frost penetration cannot be tolerated beneath footings in frost-susceptible soil. Using the Boussinesq elastic theory of stress distribution with values of 1 and 5 for the ratio E /EU (E is the elastic modulus of the frozen layer and E the elastic modulus o unfrozen soil) and 0.5 for Poisson's ratio, t#e maximum vertical stress was calculated to range from 62 to 83 kPa (9 to 12 psi) at the freezing plane when it was at a depth of 0.84 m (2.7 ft). At this point the measured stress at the plate was about 1.8 MPa (270 psi). Stresses at the freezing plane associated with basal uplift of the footing located at the surface were shown to decrease to zero at a radial distance of 1.83 m (6 ft). In normal engineering practice it is not practical to resist such high pressures by loading.

Maximum measured ad£reeze uplift forces (Penner and Irwin, 1969 ; Penner and Gold, 1971; Penner, 1974) of 75 kN (8.5 tons) on a 1.22 m (4 ft) long concrete block wall gave a calculated adfreeze value of about 25 kPa (4 psi). Of special interest was the heave pattern of the ground surface that developed around foundations subjected to adfreezing as shown in Figure 15. It should be noted that at the ends of the wall more soil creep occurred next to the foundation than at right angles to the long dimension of the wall. Such surface patterns are characteristic around piles in the ground and of ice covers in the vicinity of structures subjected to rapid change in water level.

Frost uplift (Penner, 1974) was measured for several consecutive years on 152 and 305 mm (6 in. and 12 in.) diameter steel, concrete and wood piles installed in Leda clay. Individual rock-anchored reaction frames were used for each pile. Typical monthly averages are given in Table 11. The adfreeze values measured in the field were nearly the same for all pile types, although they were a little higher for steel than concrete, followed by wood. Frost Heaving of Foundations

The general lack of appreciation of the magnitude of ground surface movements due to freezing and thawing of the soil often leads to serious building problems.

(a) Cottages and Garages

One of the best examples of frost heaving of foundations occurred at a low-lying cottage site beside the Rideau River near Ottawa, Canada (Crawford, 1968). The small cottage was simply supported on concrete blocks at the corners, at the mid-point of each wall, and under the interior beams. Every year the cottage was distorted so much that doors and windows jammed and occasionally the drains were broken. On the basis of some sketches and a verbal description of the situation, the owner was advised that the problem was caused by frost heaving of the ground and that the simplest solution would be to replace the concrete block footings with vertical steel pipes embedded in concrete below the frost line. Steel pipes were suggested because their small diameter would reduce the possibility of heaving by adfreezing to the adjacent soil.

The owner returned the following spring to complain that the cottage had never been in such bad shape. This disturbing news was followed by a site visit which revealed that the owner had replaced only the perimeter footings, and although the perimeter of the cottage had remained in place the centre had been heaved more than 15 cm (6 in.). Figure 16 shows the level exterior wall; Figure 17 shms the upward deflection of the centre beam still resting on concrete blocks. Since this major oversight was corrected the performance of the building has been satisfactory.

It should be noted that the site is only a few feet above river level and the soil, a silty clay, is extremely frost susceptible. The high water table made excavation so difficult that the owner was not able to embed the pipes in concrete; they were simply rested on small precast concrete slabs at a depth of about 1.1 m (3.5 ft). Although this was only slightly deeper than the depth of frost penetration, the weight of the cottage was sufficient to resist the tendency of the 100 mm (4 in.) diameter pipes to heave by adfreezing to the soil.

Steel pipes or concrete piles are commonly used with success as outer supports for carports where surface frost heaving may occur. Figure 18 illustrates a problem with a garage connected to a house by a breezeway. The garage, founded on a surface slab, has heaved several inches causing distress in the rather inflexible roof. Figure 19 shows an unheated garage built into a house with full depth footings under the garage. In this case freezing was allowed to occur on both sides of the foundation wall causing it to heave relative to the wall around the heated basement. This has resulted in distortion cracks in the brickwork and floor heave that prevents full closure of the door. (b) Entrances

Heaving of entrance steps is common where frost-susceptible soil is used for backfilling. Such damage can occur by adfreezing even when footings are carried to full depth, but it can be avoided by backfilling with crushed stone or clean gravel. Only a thin layer of select material next to the wall and carried down to the footing drains is necessary. A thin surface layer of clay sloping away from the wall will prevent the porous backfill from acting as a drain for surface water.

(c) Cold Storage Warehouses

The failure of cold storage warehouses due to frost action in the underlying soil is not unusual. A number of failures have been investigated (Crawford, 1953; Hamilton et al., 1959). The one described here is one of the worst cases ~f~structuraldamage due to frost heaving ever observed. The damage to the building was so extensive that serious consideration was given to abandoning it. The remedial measures undertaken, however, turned out to be highly successful. The thermal design considerations for structures of this type have been published by Pearce and Hutcheon (1958) and Pearce (1959).

The 15 by 15 m (50 by 50 ft) building was a single-storey reinforced concrete structure founded on shallow spread footings. The slabon-grade floor was of sandwich construction with two 76 mm (3 in.) reinforced concrete layers separated by 150 mm (6 in.) of cork insulation. This was located directly on a subfloor tile ventilating system which was subsequently shown to be ineffective. The operation of the plant proved satisfactory for the first five years, but this was followed by two years of very rapid frost heaving. Figure 20 is an interior view of the refrigerated locker room showing the extent of heave.

Heaving started when the frostline intercepted the frost-susceptible soil located at the footing level. The remedial work involved shuttFng down the plant, opening up the tile eubfloor ventilating system and improving the warm air circulation. Figure 21 shows the depth of frozen soil and floor elevation measurements at one location beneath the floor from the time the structure was instrumented until floor subsidence stopped. Heaving continued for six months after observations started - from January to June 1957 - until thawing was effected by improved air circulation of the duct system below the floor. This study illustrates the serious difficulties that can occur if potential frost action beneath an artificially cooled building is not considered.

FROST ACTIOH DURING COEISTBUGTIOll

The heavy demand for construction following World War I1 encouraged more wintertime building activity. Contractors learned to cope with low temperatures and, today, construction in Canada is a continuous, year- round activity. Some of the most serious winter construction problems are caused by ground freezing but they can be avoided through understanding of the mechanism of frost action and attention to detail. Case 1

Figure 22 shows a small, owner-built house that was left unprotected over the winter. Frost was allowed to penetrate the fine-grain soil under the footings and the resulting frost heaving destroyed the foundation walls (Crawford, 1968). This would not have occurred if the basement had been heated, but it could also have been prevented by protecting the footings with snow, straw or other insulating materials. Similar problems have been observed where frost has penetrated through the basement walls into the backfill causing lateral pressures and cracking of the walls. Once the damage is done, repairs are difficult, costly and often unsatisfactory.

Case 2

A similar problem occurred during construction of a four-storey addition to a major building. It was noticed, when construction resumed after a shutdown caused by especially cold temperatures, that the fomork for the basement walls was 50 mm (2 in.) too high where it joined the existing building (Crawford, 1968). It was quickly established that all of the fornawork was out of position and further investigation revealed that the perimeter footings 2.1 m (7 ft) wide had heaved about 50 mm (2 in.) although they were protected by a layer of straw. The steel formork had extracted so much heat at the centre of the footing that local ice lensing had heaved the entire footing, leaving a void of 50 mm (2 in.) between the concrete and the unfrozen soil along the edge (Fig. 23). The entire aseembly was brought back to its proper position by draping the formork with canvas and applying artificial heat, Construction of the concrete wall was then able to proceed without any detrimental effects.

Case 3

A much more spectacular case of frost heaving occurred during the construction of a seven-storey public building founded on a 380 mm (15 in.) reinforced concrete mat (Crawford, 1968). The basic structure was already in place when the mat foundation began to heave during a particularly cold period. Movement was first noticed where the structure was joined to an underground service tunnel. It was estimated that an average upward movement of about 50 m (2 in.) had occurred and steps were taken immediately to confirm the suspicion that frost heaving was occurring.

Four borings 150 mm (6 in.) in diameter made through the foundation slab revealed 200 to 225 mm (8 to 9 in.) of frozen clay beneath the slab. The clay samples contained numerous ice lenses (Fig. 24) and the average frozen water content was about 91 per cent compared with an initial average natural water content of about 56 per cent. Specimens of frozen clay were machined to fit a special consolidation ring in order to measure the settlement while the material thawed under a vertical pressure equal to the foundation pressure. The average water content of four specimens after thawing and compression was 55 per cent, approximately equal to the natural water content of the clay.

The magnitude of heaving was accounted for by the increase in water content caused by ice lensing and there was no evidence of drying in the natural soil below the frozen zone. As soon as the cause was determined, heaters and fans were installed in the crawlspace above the foundation slab and the building was allowed to settle slowly to its final position, more or less at the original elevation. There was concern that very high water pressures might have developed and caused local erosion of the subsoil, but no evidence of this was observed during the three-week period of thawing.

Case 4

Another example of frost heaving and damage to a building has been described in some detail by Burn and Beach (1978). In this case the construction had fallen behind schedule and the building was still unheated when air temperatures fell to unusually low levels during December. The building, ranging from two storeys to five storeys, has a reinforced concrete frame with deep perimeter footings and shallow interior footings, and the basement floor slab rests on a layer of crushed stone over natural clay. Frost penetrated below the interior footings causing upward movement of several columns. The maximum measured heave of 15 mm (0.6 in.) was not considered to have caused any structural damage, but greater movements of the floor slab caused cracking of the slab (Fig. 25), crushing of some of the non-loadbearing interior partitions, and distortion of steel door frames.

Borings revealed that frost had penetrated about 60 cm (24 in.) below the top of the basement floor slab. The maximum difference in measured elevation from the edge to the middle of a basement room was about 8.5 cm (3.3 in.) and this difference was reduced to half during artificial heating and thaw settlement. Coring revealed that a void remained beneath the slab at the centre of the room after thawing. After several weeks of heating the building reached equilibrium and the necessary repairs were carried out.

Case 5

An interesting frost action problem occurred during the construction of a deep pumping station for a sewage treatment plant in Ottawa (Pappas and Sexsmith, 1968). Excavation was carried out to a depth of 22 m (72 ft) within a temporary sheet pile structure in the shape of two intersecting circles supported by circular ring wales and centre struts at the intersection as shown in Figure 26. The excavation was carried out during December and January and it was quickly realized that the strut loads were higher than would be expected from earth pressures alone. It was also noted that the loads increased during the day and decreased at night, with the total load increasing substantially each day. This was attributed to the lateral penetration of freezing temperatures through the sheet pile walls and the development of lateral heaving pressures. As the struts cooled and contracted at night the soil heaved to fill the void. When the sun warmed the struts during the day they expanded and increased their internal stresses while resisting the heaving pressures.

On one strut the stresses increased from 136 521 kPa (19 800 psi) on 26 December to 165 480 kPa (24 000 psi) on 2 January and to 220 640 kPa (32 000 psi) on 5 January. To reduce these pressures a continuous sheet of polyethylene was hung from top to bottom of the sheet piling and heat . was applied under the sheet beginning 5 January. By 03:OO h on 6 January the stress had decreased to 178 580 kPa (25 900 psi); nine hours later the stress was 109 630 kPa (15 900 psi). Heating and stress monitoring were continued until the weather moderated and finally the clay soil had dried out so much that in many areas there was a void between the soil and the sheet piling.

Most damage to roads is due to frost heaving in the winter followed by thaw-weakening in the spring. The melting ice releases water, usually under conditions of impeded drainage, and the loss of load-bearing capacity (Nordal, 1973) often culminates in excessive surface deflection and sometimes in rutting if traffic restrictions are not imposed (Fig. 27). Criteria now used to prevent heaving of first-class highways and airport runways are so stringent that such catastrophic failures rarely occur.

Even when frost heaving does not occur, there may be a subtle loss of strength during the spring thaw even in so-called first-class highways. Although not catastrophic, it is characterized by surface deflections in the spring that result in more rapid deterioration of the pavement after seasonal freezing. The problem is not well understood and hence the necessary design criteria to prevent it are not known at present. It is becoming more serious, however, as loads increase, and is being given greater attention both in Canada and the United States.

Although major urban streets are designed with select, non-frost- susceptible materials to depths equal to or approaching the normal depth of frost penetration, less important streets are often under-designed and sometimes they fail seriously during the spring thaw. The street shown in Figure 28, for example, had to be rebuilt after only two years (Crawf ord, 1968) .

When a pavement heaves, failure occurs between the surface and structures such as manholes and catch basins that are founded well below the frost line. Figure 29 shows a manhole cover 5 cm (2 in.) below the pavement surface. The discontinuity aggravates surface deterioration and may lead to subsurface erosion and dangerous potholes. This can be avoided by providing a cone of select materials around the structure to stabilize the soil locally and reduce abrupt differences in surface elevation. Observations of frost heave were made at a depressed freight entrance to the Division of Building Research in Ottawa (Burn, 1963) where the upper 30 cm (1 ft) is composed of an asphalt surface over non- frost-susceptible material. This is underlain by natural clay. A ground movement gauge at a depth of 30 cm (1 ft) heaved about 10 cm (4 in.) during the month of December, a further 8 cm (3 in.) during January and February, followed by very slight heave during March. By the end of February a gauge at 60 cm (2 ft) had heaved about 6 cm (2.5 in.) and a 90 cm (3 ft) gauge had not moved. The observed thaw-settlement during April is shown in Fig. 30. The accumulation of snow at the edge of the roadway had a noticeable influence on the surface movements and resulted in a large longitudinal crack in the asphalt. The total maximum heave of about 20 cm (8 in.) is considerably greater than the heave of adjacent roads, probably because the depressed ramp has the groundwater table closer to its surf ace.

THERMAL INSULATION -1ES

Thermal insulation has been successfully used in construction to attenuate freezing and thawing of the ground. In the Far North it has been used to preserve permafrost and prevent thaw settlement; in areas of seasonal frost its main use has been to reduce or prevent frost penetration and frost heaving. Insulation has also been used to mitigate freezing and thawing imposed on the ground by mechanical refrigeration for ice rinks and cold storage buildings. The use of insulation and the introduction of heat into the ground either separately or in combination offers a wide range of possibilities.

(a) Areas of Seasonal Freezing - Roads, Streets, Driveways and Building Foundations

Since base course materials are becoming scarce in many areas the use of insulation offers a viable alternative as it reduces the total pavement thickness required; it may even reduce the total cost of construction. Numerous insulated road test sections have been constructed in Canada and the northern regions of the United States since the early sixties. The use of thermal insulation has a natural advantage in some regions such as in northern Ontario where the winters are long and cold and soil conditions poor for highway construction. There the insulation technique is a fast and efficient method for repairing busy but badly frost-damaged highway sections. This method negates costly detours and deep excavations that would otherwise be required.

Insulated road studies have been carried out at Ottawa and Sudbury, locations with very different freezing indices (Penner, 1967, 1976(b); Penner et al., 1966). The results were used as a basis for developing the information given in Figure 31 which relates the freezing index to the depth of frost penetration below various thicknesses of insulation. The thermal protection this technique provides is considerable. As an example, a 5 cm (2 in.) thickness of expanded polystyrene insulation reduced the frost penetration at Sudbury by 0.9 m (3 ft) during a winter when the frost penetration was 1.6 m (5.3 ft) (freezing index 1450 Celsius degree days).

The construction technique using insulation is not difficult although it involves a good deal of hand labour. Normally the subbase is fine-bladed before hand placing the insulation boards. Crushing of the insulation is to be avoided, hence the base course is usually end dumped and spread by a tracked vehicle (Fig. 32). The boards are pegged with wooden skewers to prevent shifting during the spreading operation. Butting the joints of adjacent boards meets both practical and thermal considerations.

Insulating materials such as foamed-in-place sulphur and polyurethane are also being investigated but the commonly used type is still expanded polystyrene. The apparent advantages of in-place foaming techniques are still on a trial basis in the field.

Insulation has been employed successf ully around footings (Penner , 1969) and has had numerous other applications such as under floors of unheated buildings and under pathways and driveways. Entrances to basement garages (Penner and Burn, 1970) are particularly sensitive to frost action (Fig. 33). When proper designs (Fig. 34) are not used the easiest remedial solution has been to install insulation in critical locations. Today, when heaving is anticipated, the design approach for foundations is the use of a numerical solution to the thermal problem (Rubinsky and Bespflug, 1973). This takes into account the thermal conductivity of the insulation, the placement pattern of the board, the geometry of the footing, the magnitude and duration of freezing and the thermal conductivity of the soil and other materials involved.

(b) Artificial Ice Rinks

The main problems to be anticipated from the freezing of the ground under and adjacent to ice rinks are those caused by heaving. Attention to the possibilities of heaving will always be justified at the design stage for all rinks where there is a requirement for a true ice surface and in rinks that have substantial associated buildings. Rinks that are to be operated throughout the year require special attention.

A practical approach to prevent heaving in a seasonally operated rink is to replace frost-susceptible soils dawn to the predicted depth of frost penetration with coarse-grained material. The depth of replacement under a rink that employs artificial refrigeration provides a ground heat transfer situation that is reasonably amenable to calculation.

The maximum depth of frost will depend on ice temperatures, the duration of the ice season, the average air temperature in the building during the summer off-season and to a lesser extent the thermal properties of the soil (Brown, W.G., 1965) (Fig. 35). Assuming an average arena temperature in the summer of 15.6OC (60°F) the frost depth with an ice temperature of -5.6"C (22°F) is about 2.1 m (7 ft) for a six- month season and about 3.0 m (10 ft) for an eight-month season. At present a numerical finite difference solution is being checked with detailed experimental results from a skating rink on a deep fill. With this approach it is possible to take more of the factors involved into account and with great accuracy.

Two seasonally operated curling rinks in Ottawa which employed a thermal insulating layer below the refrigeration pipes were instrumented. The seasonal frost penetration in an uninsulated curling rink was about 1.8 m (6 ft); in a rink with 2.5 cm (1 in.) of expanded polystyrene it was about 0.91 m (3 ft). There was negligible frost penetration under the rink with 10.2 cm (4 in.) of insulation. Exact comparisons are not justified here but all three rinks were operated for about 63 months at similar ice temperatures.

In cases where heating is to be used, as in a year-round skating rink, some insulation should be interposed between the heat source and the heat sink to reduce both the cooling and heating loads. An example of such a rink design is given in Figure 36. A rink employing this design with heaters operating in the automatic mode was instrumented and assessment of the results will be published later.

(c) Roads Over Permafrost

Roads constructed over ice-rich permafrost terrain can perform satisfactorily if the heat transferred through the road fill is not sufficient to melt the ice and cause severe thaw settlement. The necessary flow resistance to heat transfer can be achieved by simply increasing the thickness of the fill; alternatively, a part of the required thermal resistance can be attained easily by a layer of thermal insulation such as expanded polystyrene. When the required fill depth to prevent thaw is large and good quality fill is scarce - as it is in certain areas of the Mackenzie Valley and the Mackenzie Delta - the use of thermal insulation becomes even more attractive. In order to obtain some experience with insulated roadways in permafrost regions, the thermal response to various thicknesses of insulation and the general behaviour of the insulated road, a test site was constructed and instrumented in the spring of 1972 with a further one in the fall of 1972 along the partly finished Mackenzie Highway (Fig. 37) southeast of Inuvik (Science Dimension, 1973). Data have been collected for about five years but a complete assessment of the results has not yet been made. The reason for two similar test installations was to determine if there was any thermal advantage between a warm or cold ground surface temperature at the time of insulation placement. In the spring the ground surface temperatures would be near a minimum when the insulation was put in place as opposed to the fall installation when the surface temperatures are near a maximum.

Some interim assessments during the first two years gave indications of the behaviour of the various test sections. It was observed that 0.8 m (2.5 ft) of thaw had taken place below 1.2 m (4 ft) of uninsulated fill, which was about the same as in the adjacent undisturbed terrain. Large settlements were observed between insulated and control areas (Fig. 38). Settlements of more than 0.5 m (1.5 ft) had occurred in the control section of the spring installation as opposed to 0.15 to 0.30 m (0.5 to 1 ft) in the fall control section. In the spring installation approximately 0.30 m (1 ft) of thaw had taken place below the 5.1 cm (2 in.) insulated section, about 15.3 cm (0.5 ft) below 8.9 cm (3.5 in.) of insulation and none below the 11.4 cm (4.5 in.) of insulation. Settlement comparisons in the spring site showed that about 0.3 m (1 ft) of settlement had occurred below the 5.1 cm (2 in.) thick insulation and very little below the other insulation thicknesses. Shoulder cracking and slumping in the insulated sections were prominent and thought to be the result of differential thawing effects. The tentative nature of these interim observations is stressed but it does indicate the general pattern of behaviour. Details of the insulation studies on permafrost are to be published after a complete assessment.

PERMAFROST

The northern half of Canada and most of Alaska are underlain by perennially frozen ground, much of it containing alternate layers of ice and soil (Fig. 39). If ice-rich permafrost is allowed to thaw, it will lose strength and compress, often causing extrenne distress or failure of adjacent structures. For this reason it is usually wise to preserve the permafrost in its natural state during and after any construction operations associated with it. When this cannot be done it is equally wise to anticipate the results of thaw settlement on the related construction.

In the Northwest the southern boundary of continuous permafrost (Fig. 5) generally falls between the 7000 and 8000 Freezing Index values. It may also be noted that in this region the boundary follows approximately the -8.3OC (17OF) MAAT contour (Brown, R.J.E., 1978). The southern boundary of discontinuous permafrost, lying considerably to the south of the continuous boundary, ,falls approximately between the 4000 and 5000 Freezing Index values and approximately along the -1°C (30°F) MAAT isotherm. The region between the two boundaries is usually the most difficult from an engineering point of view because the permafrost is less stable and is variable in occurrence.

Figure 40 illustrates a typical ground temperature profile in a permafrost region (Johnston, 1965). The depth of the active layer (annual thaw) varies from a few centimetrea in the Far North to perhaps 3 m (10 ft) near the southern boundary. The MAGT increases uniformly about 2 C deg per 100 m (300 ft) due to geothermal heat flow from the earth's interior and annual variations are barely perceptible below a depth of 10 m (30 ft). Few observations are available, but permafrost is known to occur to depths greater than 300 m (900 ft) in the Arctic islands.

Surface water has a great warming effect on permafrost. Ponding from run-off increases the depth of summer thaw and lakes and rivers will thaw the permafrost to great depths. Johnston and Brown (19641, summarizing observations in the U.S.S.R. and Alaska, noted that the depth of thaw "under lakes that do not freeze to the bottom will be proportional to the local yearly air temperature amplitude regardless of the areal extent of the lake." The location of permafrost and seasonal frost relative to a small lake (300 m (900 ft) diameter) near Inuvik, N.W.T., was determined using borings and ground temperature measurements. A section through the lake in April (Fig. 41) shows the maximum ice thickness of 0.75 m (2.5 ft) a somewhat greater thickness of seasonal frost and a steep boundary between permafrost and unfrozen soil under the lake. Drilling and sampling indicated no frozen ground under the lake to bedrock at a depth of 70 m (230 ft), although permafrost extended to bedrock adjacent to the lake. Temperature measurements indicated permafrost to a depth of about 100 m (300 ft).

The permafrost condition is obviously sensitive to construction operations and other human activities. A review of the literature on the occurrence and character of permafrost and on design and construction considerations is given by Crawford and Johnston (1971).

BUILDING ON PERHAFBOST

The common philosophy of designing foundations on permafrost is to disturb the surface as little as possible and preserve the frozen condition of the ground. In regions where the permafrost is shallow and patchy it may be excavated and replaced by unfrozen non-frost-susceptible material or it may be intentionally thawed and allowed to settle (and consolidate) prior to construction, but these are exceptional circumstances. In cases where the permafrost has been ignored the failures are often catastrophic (Fig. 42). In one major building, provisions were made for jacking and shimming to compensate for foundation settlements, but this was not a satisfactory solution.

A proper engineering site investigation is always the first essential step in designing the foundation. This involves the gathering of background information on local experience if available, studies of air photos and surface features, vegetation and drainage patterns, and a preliminary on-site inspection. Once the best available site is selected, exploratory surveys and detailed investigations are carried out using geophysical techniques, test pits and borings to determine the nature of the frozen ground, particularly the distribution of ice, and, if possible, its temperature (Johnston 1963(a)).

The most extensive early Canadian experience with foundations on permafrost was gained from 1957 to 1960 in the development of the new town of Inuvik on the east side of the Mackenzie River Delta. More than 20 000 piles of local spruce were installed during this period as well as about 1500 steel, reinforced concrete and Douglas Fir piles for special purposes. The design and installation procedures used in the early years at Inuvik have been outlined by Johnston (1963(b)). Most of the original piles at Inuvik were installed in presteamed holes, but since the early 1960's almost all piles have' been placed in slurry-filled drilled holes. Since 1960 there have been about 50 000 piles placed at Inuvik in drilled holes. -

20

At Inuvik the MAGT is about -3OC (26OF), permafrost extends to a depth of about 100 m (300 ft), and the annual thaw (active layer) varies from a few centimetres in areas of peat to 1.2 m (4 ft) in gravel. The approved procedure was to cover a potential building site with 450 to 600 m (13 to 2 ft) of gravel placed directly over the natural moss to prevent surface water accumulation, to protect the natural ground, and to provide a working surface for construction equipment. Holes for piles supporting lightly loaded structures were then steaurthawed to depths of 3 to 6 m (10 to 20 ft) (average 4.3 m (14 ft)) (Fig. 43) and piles were then dropped into the slurry-filled holes and driven to refusal. Piles for heavier loads were placed to depths of from 6 to 9 m (20 to 30 ft). Piles placed in stearthawed holes in the fall (when ground temperatures are warmest) required six months freezeback to ensure adequate anchorage. Those placed in the late winter or spring (when ground temperatures are coldest) could be loaded within a week to a month. Freezeback in slurry- backfilled drilled holes is mch quicker because of less thermal disturbance to the ground. As a rule-of-thumb the depth of embedment in frozen ground should be at least twice the maximum depth of annual thawing (active layer) to resist frost heave forces generated in the active layer.

An alternative design for oil tanks, which can tolerate some differential movement, is to place them on a thick gravel mat containing ventilation ducts, allowing cold air to circulate during winter between the tank and the underlying permafrost (Fig. 44).

Another method of protecting the permafrost is to insulate the surface by covering it with a thick layer of non-frost-susceptible material or insulation. The Inuvik airport runway was protected in this way with a minimum of 2.4 m (8 ft) of rock fill placed over the natural ground. Long-term temperature observations have proven that the underlying permafrost has been preserved, and where thicker layers of stone exist, freezing temperatures are maintained year round within the lower parts of the fill.

Dykes on Permafrost

Water-retaining structures, such as dams and dykes, are easily constructed over permafrost but problems of settlement and stability arise when they are put to use. After flooding, the mean annual surface temperature is suddenly raised above freezing and the underlying ground begins to thaw. Not only must the resulting settlement be compensated for by adding fill to the top of the dyke, but the structure must be stable while the excess water resulting from the thawing of the ice is dissipated. These were the engineering problems faced for the first time in the design of the forebay dykes for the Kelsey Generating Station on the Nelson River in northern Manitoba (MacDonald, 1963). Observations on the performance of the dykes have been reported by Johnston (1969).

The Kelsey station is located west of Hudson Bay at latitude 56ON. The MAAT is about -4.2OC (24.4OF) and the MAGT about -0.5OC (31°F). It is in the middle of the discontinuous zone with extensive areas of permafrost to depths of 10 or 11 m (35 ft). Owing to the wide variation in permafrost occurrences (with ice lenses up to 200 mm (8 in.) thick), large differential settlements were anticipated. Preliminary calculations indicated that all permafrost under the reservoir would thaw within 50 years and that the thaw profile would penetrate well into the dyke foundation. Further, it was estimated from measuring the total thickness of ice lenses in samples that settlements of the order of 1.8 m (6 ft) would occur and that the (thawed) water could escape without causing instability. Sand drains were installed to facilitate subsurface drainage. The relatively small dykes, maximum height of 6 m (20 ft), were constructed of semi-pervious material (sand) that would deform and heal as settlement occurred.

When the reservoir was filled in 1960 the mean annual temperature at the bottom was raised about 6 C deg to 5.5OC (42OF), the winter water temperatures being just above freezing and the summer temperatures rising to about 18OC (65OF). After seven years, thawing under the forebay had reached a depth of 5.2 m (17 ft). In 1962 local dyke settlements as great as 1.5 m (5 ft) had occurred requiring the addition of fill to maintain a safe freeboard. By 1967 maximum settlements had reached about 2.1 m (7 ft) and maintenance was continued. Minor deformations along the crest can be seen in Figure 45.

On the basis of observations from 1960 to 1967 a more refined calculation of rate of thaw and settlement was made by Brown (W.G.) and Johnston ( 1970). The calculations were simplified to a considerable extent because the dykes are relatively pervious and the flow through them creates a fairly uniform temperature at the original ground surface under the dyke. Simple conduction theory was used to compute heat flow and the thermal properties of the ground were estimated from water and ice contents. Volumetric heat capacity, latent heat and the heat removed by percolation of water through the dykes were all taken into account in the calculations. The resulting computed depth of thaw, shown in Figure 46, is in good agreement with the measurements. The authors point out that it is essential to know original moisture contents (ice and water) and mean annual ground and water temperatures. The thermal conductivity of the unfrozen soil can be estimated from a knowledge of soil type and water content. Reliable field data are therefore essential for reliable computations.

Similar problems were encountered at the Kettle and Long Spruce generating stations constructed in later years at sites downstream from Kelsey (Macpherson et al., 1970; Keil et al., 1973). The low head dykes at these sites were successfully constructed using the same design approach as used at the Kelsey station.

Freezing and thawing of the ground can be predicted within reasonable limits but precision is not possible. When fine-grained soils freeze, the phase change of the pore water to ice increases the moisture suction at the freezing plane drawing in water from unfrozen areas. The suction level depends largely on pore size which is in turn related to the size and gradation of soil particles. The resulting frost heaving pressure is similarly related to the soil particle sizes. As the over- burden pressure increases, the rate and amount of frost heave decreases. When frozen ground thaws too quickly for the melt water to escape, a loss of strength occurs and this may lead to serious problems.

It is most important to know in advance if frost action problems will occur either during the construction period or during the expected life of a structure. A proper evaluation takes into account the severity of freezing or thawing expected, groundwater and drainage conditions, soil type and variability as well as the importance of uninterrupted performance of the structure. The cost of mitigative measures and the cost of maintenance must be weighed against the standard of performance and safety required, particularly in the case of airport runways, and also the differential displacement that the structure can accommodate without damage. All such factors should be considered in making an over- all assessment of the degree of frost susceptibility that is acceptable. REFERENCES

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Penner, E., Oosterbaan, M.D. and Rodman, R.W. 1966. Performance of city pavement structure containing foamed plastic insulation. Highway Res. Board, Highway Res. Record 128, p. 1-17.

Penner, E. and Ueda, T. 1977. The dependence of frost heaving on load application - preliminary results. ;roc. International Symposium Frost Action in Soils, Univ. of Lulea, Sweden, Vol. 1, p. 92-101. (Also appeared in Takenaka Technical Res. Rept 18, p. 1-9.)

1#78. A soil frost susceptibility test and a basis for interpreting heaving rates. Proc. Third International Conf. on Permafrost, Vol. 1, p. 721-727.

Penner, E. and Walton, T. 1978. Effects of temperature and pressure on frost heaving. International Symposium on Ground Freezing, Ruhr Univ., Bochum, Germany.

Preus, C.K. and Tomes, L.A. 1959. Frost action and load carrying capacity evaluation by deflection profiles. Highway Res. Board, Bull. 218, NASINRC, Washington, p. 1-10.

Riis, J. 1948. Frost damage to roads in Denmark. Proc. Second Int. Conf. Soil Mech. Found. Eng., Rotterdam, Vol. 2, p. 287-291. Rubinsky, E.I. and Bespflug, K.E. 1973. Design of insulated foundation. Amer. Soc. Civ. Eng., Vol. 99, SM9, p. 649-667.

Sayman, W.C. 1955. Plate-bearing study of loss of pavement supporting capacity due to frost. Highway Res. Board, Bull. 111, NASINRC Washington, p. 99-106.

Science Dimension, 1973. Insulated highways for Canada's North. Nat. Res. Council Canada, Ottawa, Vol. 5, No. 4, p. 16-21.

Townsend, D.L. and Csathy, T.I. 1962. Pore size and field frost performance of soils. Highway Res. Board, Bull. 331, NASINRC, Washington, p. 67-80.

Turner, K.A. 1957. Loss and recovery of bearing capacity of 30 New Jersey soil materials as determined by field CBR tests (1954-55). Highway Res. Board, Bull. 168, NAS~NRC,Washington, p. 9-49. Ueda, T. and Penner, E. 1977. Mechanical analogy of a constant heave rate. Proc. Intergational Symposium Frost Action in Soils, University of Lulea, Sweden, Vol. 2, p. 57-67.

U.S. Corps of Engineers, 1949. Addendum No. 1, 1945-57 to Report on Frost Penetration, 1944-45, Boston.

Williams, G.P. and Gold, L.W. 1976. Ground temperatures. Nat. Res. Council Canada, Div. Bldg. Res., Can. Bldg. Digest 180.

Williams, P.J. 1972. Use of the ice-water surface tension concept in engineering practice. Highway Res. Board, Highway Res. Record 393, NASINRC, Washington, p. 19-29.

Wissa, A.E. and Martin, R.T. 1973. Frost susceptibility of Massachusetts soils: evaluation of rapid frost-susceptibility tests. M.I.T. Soils Publ. 320.

Wissa, A.E., Martin, R.T. and Koutsoftas, D. 1972. Equipment for measuring the water permeability as a function of degree of saturation for frost susceptible soils. M.I.T. Soils Publ. 316. TABLE I. Classification of frost action criteria

GROUP I Frost action criteria based on frost heaving and thaw- weakening

(a) Frost-heave rate (Kaplar, 1971, 1974; Linell and Kaplar, 1959; Jacobs, 1965)

(b) Particle size and particle-size distribution (Casagrande, 1931, 1938; Riis, 1948; Beskow, 1935; U.S. Corps of Engineers, 1953)

(c) Air intrusion (Beskow, 1935; Williams, 1972)

(d) Maximum ice-lens pressure (Hoekstra et al., 1965; Wissa and Martin, 1973)

(e) Pore-size distribution (Townsend and Csathy, 1962) (£1 Permeability (Wissa et al., 1972)

GROUP I1 Frost action criteria based on thaw-weakening only

GROUP IIA Laboratory evaluation

(a) California bearing ratio (Jessberger and Carbee, 1970)

(b) Excess pore pressure (~rownand Yao, 1964)

(c) Resilient strain and resilient modulus (Culley, 1971)

(d) Unconfined compressive strength (modeling study) (Chamberlain, 1973)

GROUP IIB Field evaluation

(a) Combined basis of field California bearing ratio and plate-bearing and traffic tests to establish four soil groups, F1 to F4, as well as the Unified Soil Classification System (Linell, 1953)

(b) Plate bearing (Sayman, 1955)

(c) Benkelman beam (Preus and Tomes, 1959)

(dl Field California bearing ratio (Turner, 1957) TABLE 11. Mean monthly adfreeze values (kPa) for 152 mm (6 in. ) and 305 mm (12 in.) diameter piles in Leda clay

Pile Material Dec. 1971 Jan. 1972 Feb. 1972 Feb. 1973

: S12 '6 12 6 S12 '6 S1 2 Steel 138 105 7 6 6 5 88 63 7 3 7 2

(20.0)** (15.2) (11.0) (9.4) (12.8) (9.1) (10.6) (10.4)

Concrete 136 9 9 7 9 56 67 57 46 4 6

(19.2) (14.3) (11.4) (8.1) (9.7) (8.2) (6.7) (6.7)

Wood 117 105 6 9 58 6 1 5 1 4 3 5 7

* Symbols, S stands for steel pile C stands for concrete W stands for wood The subscript gives the diameter of the pile in inches.

**( 1 adf reeze values, psi FROST ACTION AND FOUNDATIONS by E. Penner and C.B. Crawford

FIGURE WTIOHS

Figure 1. Monthly average ground temperature in a clay soil at Ottawa, Ontario, from May 1954 to April 1955 (under natural surface cover). (Crawford and Legget, 1957).

Figure 2. Relationship between mean annual air temperatures and mean annual ground temperatures. (Crawford and Legget, 1957).

Figure 3. Examples of differences between mean annual ground temperature (0) (MAGT) and mean annual air temperature (*) (MAAT). (Williams and Gold, 1976).

Figure 4. Relationship between freezing index and depth of frost penetration. (Brown, 1964).

Figure 5. Freezing index map of Canada based on the period 1931 to 1960, OF. (Boyd, 1973).

Figure 6. The steady state temperature under a straight line of a large area in the ground surface. (Example: A lake at 3.g°C in a region where the mean annual temperature at the ground surface is -l.l°C). (Johnston and Brown, 1964).

Figure 7. Schematic drawing of ice-water interface before propagating through pore restriction between touching sphere: (a) spheres on close-packed array (b) section A-A. (Anderson et al., 1978).

Figure 8. Relation between experimental heaving pressures in glass bead models and smallest fragmental particles in soil fractions. (Penner, 1973).

Figure 9. Heave and suction development in a closed system. (Penner, 1957).

Figure 10. Frost penetration and heave rate measurements at 0.1 MPa in a f rost-susceptible soil. (Penner and Ueda, 1977).

Figure 11. Frost penetration and heave rate measurements at 0.4 MPa on the same soil shown in Fig. 10. (Penner and Ueda, 1977).

Figure 12. Heaving rate versus the overburden/step temperature ratio. (Penner and Ueda, 1978).

Figure 13. Reaction frame and bearing plate. (Penner, 1970).

Figure 14. Temperature, force and frost depth results on Leda clay. (Penner and Burn, 1978). Figure 15. Ground surface heave at ends of 1.22 m long concrete wall and at right angles to long dimension of wall, 1970-71. (Penner, 1974).

Figure 16. Pipes supported by concrete footing below frost line replace former surf ace footings on this building. (Crawf ord, 1968).

Figure 17. Before foundations were changed (Fig. 17) differential heaving caused this distortion in floor beams. (Crawford, 1968).

Figure 18. When an unheated structure is fastened rigidly to heated one, frost often causes distortions. (Crawford, 1968).

Figure 19. The cracks in the brick wall were caused by differential heaving of ground under unheated building. (Crawford, 1968).

Figure 20. Interior view of refrigerated locker room showing extent of heave. (Hamilton et al., 1959).

Figure 21. Depth of frozen soil and corresponding maximum floor heave conditions. (Hamilton et al. , 1959) . Figure 22. Severe damage to basement when partially completed house was left unprotected during winter. (Crawford, 1968).

Figure 23. Spade demonstrates 5 cm (2 in.) gap that was created under four-storey building by frost during construction. (Crawford, 1968).

Figure 24. Ice lenses in this sample of clay heaved a seven-storey building 5-7.5 cm (2-3 in.) from its original level. (Crawford, 1968).

Figure 25. Frost is more dangerous when building is advanced because distortions Cabove) could be built in. (Crawf ord, 1968).

Figure 26. Heating behind polyethylene curtain to reduce horizontal heave developed in open excavation during winter period.

Figure 27. Relation between frost heave, deflection and 0°C isotherm at the Vormsund test road, Norway. (Andersland and Anderson, 1978).

Figure 28. This is typical damage that can be caused by frost action to heavily travelled road. (Crawford, 1968).

Figure 29. Manhole remained stationary but pavement heaved around it because of discontinuity underground. (Crawf ord, 1968). Figure 30. Measured frost heave of road surface. (Burn, 1963).

Figure 31. Maximum frost penetration beneath an insulating layer placed on wet, frost susceptible soil.

Figure 32. Levelling base course on insulation with a track vehicle.

Figure 33. Frost heave and damage around entrance to basement garage. (Penner and Burn, 1970).

Figure 34. Suggested design for preventing frost damage to basement garage. (Penner and Burn, 1970).

Figure 35. Frost penetration under ice rinks. (~rown,W.G., 1965).

Figure 36. Insulation and heat trace arrangement under year-round skating rink. Figure 37. Panoramic view during the placing of insulation on Mackenzie Highway, 1972. Figure 38. Intersection between 2 in. (5 cm) insulated section and control - large change in elevation.

Figure 39. Large ice lenses in varved clay in permafrost. (Brown, R.J.E., 1968).

Figure 40. Typical ground temperature regime in permafrost. (Johnston, 1965).

Figure 41. Permafrost distribution at a lake in the Mackenzie Delta. (Johnston and Brown, 1964). Figure 42. Thaw-settlement damage to building on permafrost - garage at Hay River. (Brown, R.J.E., 1970).

Figure 43. Pre-steaming holes for pile installation in permafrost. (Brown, R.J .E., 1970). Figure 44. Winter ventilation ducts in thick gravel mat to prevent thaw settlement. (DBR photo).

Figure 45. Crest of dyke on permafrost. (DBR photo). Figure 46. Comparison of calculated and observed thaw rates - Kelsey. (Johnston, 1969). TEMPERATURE, OC

Figure 1. Monthly average ground Figure 2, Relationship between temperature in a clay soil at mean annual air temperatures and Ottawa, May 1954 to A2ril 1955 mean annual ground temperatures (under natural surface cover)

DEGREE DAYS. CELSIUS

VANCOUVER -1 ST. JOHN'S MARITIME SHORT CHARLOTTETOWN DURATION

OTTAWA

GUELPH CQ WINNIPEG - b SASKATOON .-.o

GOOSE BAY - DEEP SNOW. KAPUSKASING - DURATION SCHEFFERVILLE - } FREEZING INDEX. DEGREE DAYS. FAHRENHEIT

Figure 3. Examples of differences Figure 4. Relationship between between mean annual ground temperature freezing index and depth of frost (0) (MAGT) and mean annual air penetration temperature (e) (MAAT) Figure 5. Freezing index map of Canada based on period 1931 to 1960 (OF')

~TLMPER~TURE.T~~T,+I~(IITfTll &TEMPERATURE. TI* lD4. LAKE PT 39'CI 1 (GROUND SURFACE w. -I.IDC)

Figure 6. Steady state temperature under a straight line of a large area in the ground surface

IO.39.C) TI+0.5 IT2-TI) II 39.C)

U - TZ-TI ' The Disturbance

Figure 7. Schematic drawing of ~~H~UESIN CIO~~-~~EI ARI.y ice-water interface before propagating through pore restriction HEAT FLOW -*- . . - .-,. .. .. - '. . ;, . . - .-, - -. ., - 4 between touching sphere: (a) spheres IcE-WATER INTERFACE on close-packed array (b) section A-A OF CRITICAL RADIUS r BETWEEN THREE IOUCHING SPHERES

'~lCllVl

to - -

7 0 0 VOlIELS FLINT - JOII IP F F 4 rftri o $aMr VALUE FOR rorrtts FLINT AND 5011 SFHEPIC41 GLAII BEADS - Figure 8. Relation between 50 - - experimental heaving pressures in glass bead models and smallest V) - fragmental particles in soil fractions t - a

20 -

IV rp,

10 -

lo-bop. 3-Plpr I I I I 1 ' 0 0.02 0. 04 0.06 0.08

HEAVING PRESSURE. MPa

1 I 1 1 I I I I I 35 - -

3n - --I-----* -- \;;:"R; \;;:"R; """T " 2% - CLAY SIZE 55%

- Figure 9. Heave and suction i. :l! I5 - /# development in a closed - system __-..-L- *- T-MOIS;;.R~ CONTENT 25 3 .A - jpr= 2 66 CLAY SlZE 7% I I I I I I I I I I ? 3 I 5 TIM!. DAYS

Figure 10. Frost penetration and heave rate measurements at 0.1 MPa in a frost-susceptible soil

2 I = -77 lonn 2000 3000 UDOO ELAPSED TIME, mln ELAPSED TIMt, mtn

Figure 11. Frost penetration and heave rate measurements at 0.4 MPa on the same soil shown in Fig. 10

Figure 12. Heaving rate versus the overburden/step temperature ratio

Figure 13. Reaction frame and bearing plate (,,...,,.,.. , ....,,,,.,,,, (( (b) FORCE AND AVERAGE STRE55 ON30.5 sm DIA CIRCUIAR SURFACE PIATE 140

Figure 14. Temperature, force and frost depth results on Leda clay

I I I I 1

HC**

la) AT RIGHT ANGLES TO LONG DIMENSION OF LIM ? . WALL (AVERAGE OF LINE NO. 1 AND NO. 2 1 . -

EDGE OF BLOCK WALL Figure 15. Ground surface heave at ends of 1.22 m long concrete wall and at right angles to long dimension of wall , 1070-71

lbl AT WALL ENDS (AVERAGE OF LlNE NO. 1 AND NO. 2 1 LINE 2 r (

W~IW 0 I I 1 2.5 2.0 1.5 1.0 0.5 0 DISTANCE FROM FOUNDATION WALL. m Figure 16. Pipes supported by concrete footing below frost line replace former surface footings on this building Figure 17. Before foundations were ck~anged, differential heaving caused this distortion in floor beams

Figure 18. Fvllen unheated structure is fastened rigidly to heated one, frost of'ten ca.uses distortions Figure 19. Cracks in brick wall were caused by differmtial heaving of grouna under unheated building

Figure 20. Interior view of refrigerated locker room showing extent of heave Figure 21. Depth of frozen soil and corresponding maximum floor heave conditions

Figure 22. Severe damage to basement when partially completed house was left unprotected during winter Figure 23. Spade demonstrates 5 cm (2 in. ) gap created under four-storey building by frost during construction

Figure 24. Ice lenses in this sample of clay heaved a seven- storey building 5-7.5 cm (2-3 in.) from original level Figure 25. Frost is more dangerous when building is advanced because distortions (above) could be built in

Figure 26. Heating behind polyethylene curtain to reduce horizontal heave developed in open excavation during winter period MARCH APRIL MAY JUNE 1020 1020 1020 1020

ASPHALTIC CONC

'HAWED

OIC ISOTHERM

Figure 27. Relation between frost heave, deflection and O°C isotherm at Vormsund test road, Norway

Figure 28. Typical damage that can be caused by frost action to heavily travelled road Figure 29. Manhole remained stationary but pavement heaved around it because of discontinuity underground

DISTANCE, m

Figure 30. Measured frost heave of road surface

312.0 1 ' 1 95.1 0 5 10 IS 20 DISTANCE. FEET t 1 1 1 111111 I I I 11111~ - - - - GROUND SURFACE - -- - - APPROX. 30cm BASECOURSE - - 35ETZZZ INSULATION - WET. FROST SUSCEPTIBLE SOIL -

GROUND SURFACE ------Figure 31, Maximum frost penetration beneath an insulating - - layer placed on wet, frost susceptible soil ------

- -

1 I I I 111111 I 1 1 111111 100 1000 2000

DEGREE DAYS BELOW FREEZING. OC

Figure 32. Levelling base course on insulation with a track vehicle Nl~AlIC'NWAIL. 1610CK 01

(SATURATED SOIL) PERIMETER DRAIN

rnori "SAVE OF PAVEMCN~J' TO SERVICE DRAIN TO INTERNAL SUMP / IJGIENGRrAlrTl UCIC c FOOTING BELOW DEPTH OF MAXIMUM FROST PENETRATION YICAUSC UI ADTOV4II FOOTINGS BELOW DEPTH 01.l MAXIMUM FROST PENETRATION BENEATH GARAGE FLOOR LEVEL

Figure 33. Frost heave and damage Figure 34. Suggested design for around entrance to basement garage preventing frost damage to basement garage

FLEXIBLE PLASTIC TUBING JOINT 7 3. 18 cm

PERIMETER '-

INSULA~~ON I~~,~cm SAND - FILL 0, 21 ~p~

t Ice Temperature = -5.6"C (22°F) I 0-0 0-0 4 5 6 78 910 ICE SEASON, MONTHS

Figure 35. Frost Figure 36. Insulation and heat penetration under ice trace arrangement under year- rinks round skating rink Figure 37. Panoramic view during placing of insulation on Mackenzie Highway, 197 2

Figure 38. Intersection between 2 in. (5 cm) insulated section and control - large change in elevation Figure 39. Large ice lenses in varved clay in permafrost

Temperature. "C -0, 7- Ground Surlace Active Layer, 7 Maximum Mnlhty Mean Temperature Temperature Mlnlmum Mnthty 1 Mean Temperature Lwel ol Negligible Annual Amplilude 1 16.1-15.2m) Figure 40. Typical ground temperature regime in permafrost tltl 1061 (I1 Lahe - ttl .,It, - Figure 41. Permafrost distribution ,1821" at a lake in the Mackenzie Delta GROWD t~

Figure 42. Thaw-settlement damage to building on permafrost - garage at Hay River Figure 43. Pre-steaming holes for pile installation in permafrost

Figure 44. Winter ventilation ducts in thick gravel mat to prevent thaw settlement Figure 45. Crest of dyke on permafrost

KT4 - 01 ke -2 Earl

Figure 46. Comparison of calculated and observed thaw rates, Kelsey