Is There a Dividing Line Between Non-Frost-Susceptible and Frost-Susceptible Soils?

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PREFACE

The Division of Building Research is currently engaged in studying frost action phenomena, par-ticularly the process involved at the ice-water

interface in a freezing soil. It is hoped these

studies will provide a substantial basis for the development of methods for the preventiol! of de-structive frost action that can be employed under

field conditions. The paper by Dr. Dftckerls

there-fore of particular interest; it presents orie further step toward the better understanding of a most

complex problem.

The frost action criteria for the non-frost-susceptibility of sOils developed by Casagrande have been proven to be qUite successful in numerous

cases. There have been many failures reported,

however, where the requirements of the criteria were

met. The results in this paper show the weakness of

any criteria based on grain size alone. It further

demonstrates the usefulness of clay mineral analyses in the evaluation of sOil behaviour.

The Division of Building Research is indebted to Mr. D.A. Sinclair for translating this paper.

Ottawa

February 1958

Robert F. Legget Director

Title:

NATIONAL RESEARCH COUNCIL OF CANADA

Technical Translation 722

Is there a dividing line between non-frost-susceptible and frost-non-frost-susceptible soils?

(Gibt es eine Grenze zwischen frostsicheren und frostempfindlichen Lockergesteinen?)

Author: Alfred Decker

Reference: Strasse und Autobahn, (3): 78-82, 1956

IS THERE A DIVIDING LINE BETWEEN ｎｏｎＭｆｒｏｓｔＭｓｕｓｾｅｐｔｉｂｌｅ

AND FROST-SUSCEPTIBLE ｓｏｉｌｾ＿

1. _{A. Casagrande's Frost ｃｲｩｴｾｲｩｯｮ}

In 1931, on the basis of many years' observation, A. Casagrande succeeded in establishing a dividing line between

non-frost-susceptible and frost-susceptible soils. From this he

developed a frost criterion for practical road construction.

Ac-cording to Casagrande, a soil can be considered

non-frost-suscept-ible if it has less than 3% grain sizes below 0.02 mm. A'uniform

soil with a non-uniformity index of less than 5 only shows

frost-susceptible ｰｲｯｰ･ｾｴｩ･ｳ if it possesses more than 10% grain sizes

of less than 0.02 mm.

This frost criterion was quiclcly adopted QY German road bUilders (Casagrande 1934), especially for the construction of

the Autobahns.

However, during a discussion on a paper given by the author at a session of the Committee on Road Beds of the Highways

Research Society (Forschungsgesellschaft ffir das Strassenwesen) on 15.9.1953 in Munich, A. Casagrande himself pointed out that in the U.S.A. recently, on the basis of new observations and discoveries, there has been a tendency to consider the grain component below 0.02 mm. as even more critical than had formerly

been thought. Instead of the 3% limit, more and more engineers

there are contending that with a high quality pavement not mOre

than Ｒｾ below 0.02 mm. can be admitted and in some cases even less.

In contrast to this, the view has recently been advocated in

Germany that such a strict ｲｵｬｾ for assessing the

frost-suscept-ibility of a soil is not needed and that the percentages of ｴｾ･

frost-critical grain size should be raised from 3 and 10%,

respectively, to at least 15 and 20%. This demand is based

primarily on investigations of frost damage occurring on West

-4-In this connection, however, it must be emphasized that t.he se conclusions were based entirely on studies of heavy frost damage, i.e., where the pavement had broken up, since this alone was re-garded as being decisive for the durability of the road surface. As the author has already stated emphatically (DUcker, 1955) there are no grounds for such a view until it nas been proved that a road bed containing less than 20% grain sizes below 0.02 mm. actually

does behave in a non-frost-susceptible way. Ho one has as yet

produced such a proof. Apart from the fact that all frost test

results obtained, especially in America, Sweden and Germany, clearly show that the objections made by the oPP?nents of the

frost criterion are now valid, the present author has demonstrated (DUcker 1955) that even a road bed containing a frost-critical grain component of "only" 6 to 17% is entirely capable of causing considerable frost damage to the surface structure, even with a

frost blanket 30 cm. thick. It is true that the damage here is not

of the break-up type but rather consists of longitudinal cracks. Bowever, any unprejudiced person viewing the damage shown in Fig. 1 will have to admit that this cracking, which occurred during the frost period, is not good, nor is it the sort of thing we expect

from a modern road. Without any exaggeration this can be

described as heavy damage, which under the stress of traffic may very quickly lead to a failure of the surface structure.

In view of this controversy over indices and relatively small percentages it appears reasonable to consider seriously whether there actually is in nature any sharp boundary between

ｦｲｯｳｴｾｳｵｳ｣･ｰｴｩ｢ｬ･ and non-frost-susceptible soils as expressed

in the frost criterion. Can the frost-susceptibility of a soil

be expressed solely in terms of its grain composition? As early

as 1939 the author drew attention to the fact that some soils show frost-susceptible properties even when they have no grain

size components below 0.02 mm. At that time he stated

emphatic-ally that "it is qUite impossible to draw a sharp line between frost-susceptible and non-frost-susceptible soils" (DUcker, p. 78, 1939).

-5-2. The Effect of Clay Minerals on the ｾｵ｡ｮｴｩｴ｡ｴｩｶ･ Frost

Behaviour of a Soil

2.1 Earlier Investigations

In the course of his investigations of the effects of frost on cohesive sOlIs the author showed (Decker 1939/40) that their behaviour in the presence of frost is determined not by the grain structure, but by the character of the clay mineral constituting

the "binding" material. Kaolinite, for example, shows extreme

frost susceptibility, whereas montmorillonite exerts a strong inhibiting effect on the water suction caused by the freezing process, so that soils with a more or less high proportion of montmorillonite in the "binding" material are almost entirely

non-freezing. Illite occupies a position midway between kaolinite

and montmorillonite.

2.2 Recent Investigations

The author was able to undertake further investigations

of these problems after the war. Using Casagrande's frost

criterion as a basis, two series of mixtures were made from natural grain fractions, the one being of uniform, the other of

non-uniform composition (Fig. 2). In all the mixtures the content

of frost-critical grain ccmponents below 0.02 mm. was 10%, comprising:

1. pure D6rentruper quartz powder

2. Amberg kaolin

3. Kettig kaolin

4. Geisenheim Ca-bentonite.

The behaviour of these mixtures in the presence of frost was investigated in detail by means of a number of systematic test

series carried out in the freezing cabinet. Regarding the test

methods employed the reader is referred to the author's original

paper describing them (DUcker 1939). The results are summarized

in Fig. 3. This summary shows that all the mixtures exhibit

6

-frost, although they r.ave the same grain content be Low 0.02 mm ,

The gr-eat e st frost-suscepti bili ty is shovm by the mixtures to 'which

10% Amberg kaolin had been added (mixture Ib and lIb). ｾｨ･ water

content of these mixtures in the frozen state is much greater

than in the unfrozen state.. It is noteworthy that the

frost-susceptible properties of the ron-uniform mixture (lIb) are quantitatively greater than those of the uniform mixture (Ib).

The Lovrest frost heave values are obtained for mixtures Id and

lId. These mixtures, made with calclwn bentonite, have the same

water content in the frozen state as in the unfrozen, which means that during freezing no water absorption takes ptace because the clay mineral predominating in the bentonite, namely montmorillonite, owing to its great swelling capacity prevents all flow of water

in the pores. The uniform mixture la, whose 10% grain content

below 0.02 mm .. consists of quartz powder, lies about on the

boundary between frost-susceptible and non-frost-susceptible soils. The non-uniform mixture with 10% quartz powder, on the other

hand, already shows significant frost-susceptibility, reflected both in the frost-susceptibility index (=8) and in the water

content of the frozen SOil. Whereas the water contents of these

mixtures in the unfrozen state were about 12% and 21%, respectively, in the frost zone they showed values of about 16% and 24%,

respectively. The values obtained from the mixtures with 10%

Kettig kaolin lie between these results. The frost-susceptibility

of the uniform mixture (Ic) is about 6%, but for the non-uniform

mixture (IIc) it is already over 10%. The water-content values of

these mixtures show the same pattern. The tmiform mixture (IIc)

increased from 21% to 24% in the frozen state, while for the non-uniform mixture (IIc) the figures were 12% in the unfrozen state and 19% in the frozen.

The tests therefore demonstrate that all eight mixtures with the same 10% component of frost-critical grain size below 0.02 mm. show entirely different quantitative results with respect to their

-7-frost-susceptibility. It can therefore be ｣ｯｾ｣ｬｵ､･､ that it is

not the grain component below 0.02 mm. which is of decisive importance for the quantitative frost behaviour of a cohesive sOil, but rath3r the character of the clay mineral forming the

cohesive grain component. ｾｦｵ･ｲ･｡ｳ the kaolinite in Amberg kaolin

shows the greatest frost-susceptibility properties, these are

completely obscured in the mixtures using montmorillonite. On the

other hand, these results show that, as always, the degree of uni-formity must be taken into account in assessing the

frost-susceptibility of a soil. All the uniform mixture series show

less frost-susceptibility than the non-uniform mixtures.

2.3 American ｉｮｶ･ｾｴｩｧ｡ｴｩｯｮｳ

Agreement with the above results from tests on cohesive sOils

is also shown by the recent American investigations of Haley (1953)

with sandy SOil, silty-gravel sand, silty or Silty-sandy gravel and

similar soils. The frost-critical grain component below 0.02 mm.

varied between 1 and 25%. In Fig. 4 the frost heave values are

plotted a.gainst the percentage of grain sizes below 0.02 mm. The

most important and ｳｴｲｩｾｩｮｧ result noted here is that the various

natural soils of such different grain composition appear to react

qUite haphazardly to frost. In any case, it is clear that the

frost heave value, and hence the frost-susceptibility of the soil, does not depend on the grain size component sizes below 0.02 mm.

For example, a sandy gravel with only 1% frost-critical grain

sizes shows the same frost heave value as a silty sand Or

Silty-gravelly sand with 15% and more of grain sizes below 0.02.

Converseley, sOils with the same proportion of grain sizes below 0.02 mm. show entirely different frost heave values, indicating

both non-freezing and highly frost-susceptible behaviour. Again,

silty sands and silty-gravelly sands with different grain com-ponents below 0.02 nevertheless show entirely similar frost heave

values. It is not difficult to find other examples of

contradic-tory quantitative frost behaviour on the part of soils of similar

-8-Thus, all test results clearly indicate that the decisive factor determining the behaviour of a soil with respect to frost

is not the per-con tage grain content be Low 0.02 mm , but rather the

chemical nature of the "bindlngll material.

The differences in the frost heave values and hence the frost-susceptibility can only be explained by assuming that the kind of clay mineral present in the lIbil1dingll material determines the

cbanges of NateI' content taking place in the frost zone during the

freezing process. The presence of the kaolinite group means that

a SOil will develop considerable frost-susceptibility even wren the clay mineral is still beLow the frost criterion with respect

to grain size. Even a sffiall percentage in the soil is sufficient,

especially in the case of Na-montmorillonite, to prevent absorntion of water due to the freezing process from the water emission

horizon or water table. Between these two types of clay mineral

lie the illites and the micaceous clay minerals which show COr-responding intermediate frost susceptibility values.

3. The Influence of the Metal Hydroxides and Organic Components

in C-Bl Form on tte Q,uantlｴ｡ｾｬ ve Frost ｂｾｨ｡ｶｩｯｵｲ .of a

S01..1-In the winter of 1939-40 the author was called upon to assess

the foundation soil conditions for an airport in Schleswig-Holsteil

and to test the subsoil for frost-susceptibility. My opi.nion was

based on soil samples taken from the B horizon of the heath-podsol

covering a large part of Schleswig-Holstein. From a grain-size

standpoint these consisted of entirely uniform intermediate sands

mixed with a 30 to 40% flne-sand component, as shovm in Fig. 5.

The frost-criticial component below 0.02 mmo varied betw3en 2 and

1%. It would, therefore, have been quite justifiable to assume

that the subsoil of the landing field was non-frost-susceptible. Nevertheless the frost tests carried out with the SOil

samples in the freezing cabinet in accordance \'!i th the normal

ring method (Ducker-, 1939) showed a widely varying frost behav i.our-,

-9-are represented grapbically in Fig. 6. It is evident tllat only

sample 3 shows the characteristic behaviour of a non-frost-susceptible subsoil in the sense that the SOil does not absorb any additional water from the ground-water region during freezing. On the contrary, the water content of the frozen core indicates that during freezing part of the pore water had been expelled downwards, so that the water content in the frost zone was less

than in the unfrozen ground. On the other hand, samples 1 and 2,

although they had the same grain-size composition as No.3, show the ｣ｨ｡ｲ｡｣ｴ･ｲｩｾｴｩ｣ behaviour of a frost-susceptible soil. During freezing, additional quantities of water were conveyed from the unfrozen subsoil to the freezing line, where they crystallized

out to form clean ice lenses. However, continuous ice layers were

not formed. Moreover, the ice lenses were very thin, measuring

only fractions of mil11metres, but they were very nwnerous. The

degree of frost-susceptibility of sample 1 was valued at only about 4%, while that of sample 2, on the other hand, went as high as 8%. Thus, although sample 1 is very close to the boundary between non-freezing and frost-susceptible behaviour, sample 2, despite its possession of an equally "safe" grain composition, shows con-siderable frost-susceptibility.

These test results, which stand in contradiction to the assessment of the samples in terms of the frost criterion, were confirmed during an inspection tour of the bUilding sites during

the winter of 1939-40. It was found- that wherever the B horizon

in typical form and a nearby ground water horizon in the sub-jacent layer were present, this led to the development of typical ice lenses as a result of frost to a maximum thickness of 1 mm. Water content measurements of these soil samples frozen under natural conditions showed values similar to those obtained in the test.

At that time no complete explanation could be given for this behaviour on the part of these intermediate "non-freezing" sands.

-10-The belief was expressed that in the presence of a nearby water hor-Lzon , and ovn.ng to a certain humus and iron colloid content,

these soils of the B horizon tend to show ｦｲｯｳｴｾｳｵｳ｣･ｰｴｩ｢ｬ･

properties.

Subsequently, nowever, this assumption was confirmed by further

investigations of numerous cases of frost damage. In the winter

of 1954-55, for example, in the jurisdiction of the Flensburg Highway Construction Office, stretches of road which showed a typical heath-podsol profile in the subgrade were particularly

subject to frost damage. Both federal highways and first and

second class roads were subject to this damage, ,which ran the whole gamut from light surface cracks to the formation of washboard and even the complete break-up of the surface which is so feared by

motorists. The grain distribution of the subgrade soils was that

of fine-grained intermediate sand without any significant

frost-critical, silt-grain component (about 2 to 5%). On the other

hand, their humus and iron oxide content, clearly recognizable from its characteristic colour, constituted the factor which

actually determined the quantitative frost behaviour of the sands. Because they increased the capillarity of the soil and exerted comparatively high osmotic pressure with a corresponding lowering of the freezing point, a continuous water transport could take place along the surface of the particles and resulted in crystal-lization and concentration of the water in the form of layers of solid ice.

4. Summary

The question stated in the title can be answered tentatively by stating that the frost-susceptibility of a soil is not de-termined by its grain structure, while on the otter hand the

mineralogical and chemical composition of the fine-grain component

plays a very important role. For example, a soil with a

frost-critical grain component of 10% can produce the severest frost break-up if the "binding" material consists primarily of the clay

-11-mineral ｫ｡ｯｬｩｮｩｴ･ｾ On the other hand the SeNle soil may shovr

little or no frost damage when the fine-grain component consists

essentially of montmorillonite or' illite. The metal "hydroxides

such as iron, manganese and a Lurmru.um , as well as organic, i.e.,

humus components, act in a similar way when they occur in gel

form even in completely cohe s ionLes s sands. They sl-'OVJ great

capillarity and. comparatively high osmotic pressures, which

produce a corresponding lowering of the freezing point. Even in

sands which are entirely non-frost-susceptible from the point of view of grain size these factors facilitate the water transport along the surfaces of the particles at temperatureL considerably below the freezing point, so that continuous water absorption into the frost zone is assured, leading to the formation of ice layers and ice lenses.

It is thus apparent that there. is no natural dividing line between the non-frost-susceptible and frost-susceptible sOils, as the author had already pointed out in 1939 (Dftcker, p. 78, 1939). The quantitative frost behaviour of a soil is determined not by the percentage of grain sizes below 0.02 mmo, but by the

mineralo-gical and chemical composition of the "binding" materialo This,

in turn, deterrr.ines the amount of water freed by the freezing

process and conveyed to the frost line, and this water, in its turn, determines the amount of frost heave and hence, when thawing occurs, the extent of damage which will be done to a given road surface

under a given traffic load.

Every attempt to predict kind of frost damage to be expected

-whether heavy, ｭｾ､ｩｵｭ Or light - 1S doomed to failure unless the

mineralogical and chemical composition of the "binding" material

is known. Casagrande's criterion, as adopted by road builders,

therefore, serves merely as a starting point in assessing the frost

behaviour of a soil. In this role it has proved very useful in

road construction wor-k for two decades and there is no need to supplement Or "improve" it.

-12-Blbllography

Casagrande, A. Dlscusslon on frostheavlng. Froc. Hlghway Res.

Board, 11: 168-172, 1931.

Casagrande, A. Bodenuntersuchungen 1m Dlenste des neuzeltllchen

Strassenbaues (SolI lnvestlgatlon In the lnterests of

modern road constructlon). Der Strassenbau, 25 (3), 1934.

Dficker, A. Untersuchungen fiber dle ｦｲｯｳｴｧ･ｦｾｨｲｬｬ｣ｨ･ｮ Elgenschaften

nlchtbindiger BOden (Investigations of the

frost-suscepttble properties of non-cohesive soils).

Forschungs-arbeiten aus dem Strassenwesen, vol. 17, Berlin, 1939.

DUcker, A. Frosteinwirkung auf bindige BOden (Aqtion of frost on

cohesive soils). Strassenjahrbuch 1939-40. Berlin, 1940.

Dficker, A. Ist eine Strassendecke auf einem Untergrund mit einem

frostkritischen Kornanteil unter 20% durch eine 30 cm.

starke Frostschutzschicht frostslcher gegrftndet? (Is a road surface on a bed with a frost-critical grain

com-ponent of less than 20% frost-proof if laid over a frost

blanket 30 cm. thick). Forschungsarbeiten aus dem

Strassenwesen, no. 17, new series, p. 37-43, Bielefeld,

1955.

Haley, J.F. Cold-room studies of frost action in soils, a progress

report. Highway Res. Board Bull. 71, p. 1-18, Washington,

-13-F1g. 1

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Elutriated sizes Siftp,d sizes

CI)

ｾｾ Silt Sand

-,

Gravel ｾ

<Dorl

fine med. fine men. - coarse

.fl

>'H coarse meds coarse fine

J

v

""

c-:

JIl

ＯｉｉＮｾ rJ

ｪｾ

'A

/J

V

VA

I

f

//

f

. -_ｾ 1.-0'_I.oo!:］ＺＺｾ >, ｾ orl ｾ_ｾ

100

as

g.

90

r-i

₈₀

as

ｾ 0

₇₀

ｾ 0

60

ｾ rcJ

50

Q) M M Q)

*0

'H Q) M

₃₀

• ｾ 20 ｾ

10

ｾ

0

aOOl

a006

ao?

a06

-17-QJ

a6

20

6

20

60

F1g. 5

Gra1n compos1t10n of the s011 samples from the Schleswig air f1eld

-18-D1

]0

I

20 JOmm Frozt penetration 11

11

ｾｬｮｻｲＭ

II

;":°.:°. 10 I

1-III

ｾ

20 "<P.-I:: ·rt 15 .p I:: 41 .p I:: 0 ₁₀ 0 J.l (IJ .p d :;: ₅ 0 • E! E'l ｾ Q'c7I---004 ｔＬｏＧｾＭＭＭＭＭＫＭｦＭＭＭＭＫＭｾＭＭＭｴＭＭＭＭｪ 41 ｾ 'O,!t>I---a:l (IJ ,J:I .p,o.,I---I---74---+---+_---I 1Il o ｾ ＰＱｾＭｉＭ｟｟｟Ｏ｟ＧＭＭＭＭ｟ＫＭＭ｟｟｟｟］ｾ［ＮＮＮ［［［Ｒ］ｲＭＭＭＭＭＭｴＭＭＭＭｪ

ｾＥｭ w in frozen

sonD

win unfro::en soil

Fig. 6