Pavement Movements Caused by Frost Heaving

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Technical Note (National Research Council of Canada. Division of Building Research), 1959-03-01

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Pavement Movements Caused by Frost Heaving

Burn, K. N.

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'

DIVISION OF BUILDING RESEARCH

NATIONAL RESEARCH COUNCIL OF CANADA

NOT FOR PUBLICATION _USE

No.

271

March

1959

NOTE

O,dZ...,

FOR INTERNAL

ｾ

APPROVED BV NBH

CBC

CHECKED BY

'fE

C

1HIN ][ CAlL

K.N. Burn

PREPARED BY

PREPARED FOR record purposes

SUBJECT Pavement Movements Caused by Frost ｈ･｡ｾＮｲｩｮｧ

During the spring of

1955

large longitudinal cracks appeared in the paved roadway leading down to the rear basement entrance of the Building Research Centre in Ottawa. These oracks, which

appeared primarily in the western side of the roadway, caused

conslderaQle interest, and it was thought ｴｾ｡ｴ they were assooiated with the noticeable heaving of the pavement. To ｩｮｶｾｳｴｩｧ｡ｴ･ the oause of the heaving and to measure its magnitude, the elevation of the pavement at seleoted locations was measured at intervals during the spring thaw. The results of the study appear to support the theory that severe frost heaving occurs when conditions are suitable for the free movement of water to the subgrade where freezing

temperatures prevail.

Although the Euilding Research Centre is founded Qn rock, the rock drops off sharply at the rear of the building and the road-way in question is underlain by a substantial layer of post-glacial marine clay known as Lada clay. The roadway itself is at an

elevation several feet below the original surface and is therefore located within the fissured crust of the clay Which often extends t a depths of 20 feet.

The pavement cracks were first noticed at the beginning of April when the snow cover receded. Observations of the craaks began nnmediately and three cross-sections were established at critical locations and level surveys begun. The location of the craoks and a oross-section through the roadway are shown in Fig. 1.

Level readings and measurements of the widths of cracks were made throughout the month of April, until it appeared that settlement had stopped. Profiles plotted for the three cross-sections A, Band C are shown in Fig. 2. The position of the edge of the snow is shown for the first survey and the widths of the craoks, which were measured to the nearest

1/8

inch with a

oarpenterls tape, are also shown0 A series of photograpns taken

at the site show how rapidly thawing occurred, and indicate the severity of the longitudinal oracks (Figso

3,

4

and

5)

.

'

The ｭ｡ｸｩｾｸｭ measured ohange in elevation was eight inohes, whioh ooourred at the point where the oraok in the pavement surfaoe had been widest (1

3/4

inohes). This, however, may'not represent the maximum amount of frost heave that ooourred during the winter sinoe readings of elevation were begun only after some thawing of the snow oover revealed the presenoe of the oracks and the noticeable heaving of the pavement. Nor may the final profiles measured on 27 April be the same as those that existed before freezing of the sUbgrade started, but these probably would not have differed signifioantly._{. ,}

During the winter, whioh was oomparatively mild but with heavy snowfall, the roadway was plowed off-oontre with the result that the eastern edge was kept partly bare, while snow was piled up on the western side. It is suggested that the snow-oover on the western side permitted the ground beneath it to remain unfrozen and allowed the free passage of water, moving under an hydraulio gradient through fissures toward the oentre of the ｲｯ｡､ｾ to feed the ioe lenses in the subgrade.

...

ｾ

""

ｾ 320-ｾ

315-ｾ

310- t ｾ 50 w SECTION B , I 25 25 DIsTANCE IN FEET

.

rI

f

I 50

SECTIONS

A x o c( IX u '0 ,ex>

STORES ENTRANCE

ｾ

B.R.C.

FIGURE I

PLAN

OF

REAR

OF

BUILDING

RESEARCH

CENTRE

SHOWING

POSITION

OF

CRACKS

IN

ROADWAY

AND

SECTION A

-u-

INDICATES POSITION OF

313' 5 ＮＮＮＮＮＭＭＭＭＭＮＬＭＭＭＭｲＭＺＺＭＭＭＬＮＭＭＭＭＭＭｲＭＭＭＭＭｾ

...

0 <t ILJ ₀ ILJ SECTION B 0:: LL. Z LL.

-

0

z

_312·5 ILJ 0 (,!)

!;;(

0ILJ :>

...

UJ ...J (J) ILJ <t ILJ 312·0 ｴＭＭＭＭＭＭＭＭＭＭＭＭＭｾＭＭＭＭＭｾ

o

5 10 15 DISTANCE IN FEET 20

FIGURE 2

SETTLEMENT

OF

ROAD SURFACE

DURING THAW,

APRIL

1955 , AT

THE

BUILDING

RESEARCH

·

.

Fig.

3 --

1 April

1955

Fig.

4 --

6

April

1955

Fig.

5 --

18

April

1955

Thawing of Snow and Longitudinal Cracks in DBR Roadway