Shallow foundations on swelling clays in western Canada

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Shallow foundations on swelling clays in western Canada

Hamilton, J. J.

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SHALLO\A/

FOUNDATIONS

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BY

J. J. HAMILTON

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FONDATIONS PEU GONFLANTES

PROFONDES SUR DES ARGILES DANS L'OUEST DU CANADA

SOMMAIRE L e s v a r i a t i o n s d e v o l u m e q u i s e p r o d u i s e n t d a n e l e e s o l 6 e h a u t e t e n e u r e n a r g i l e s o n t 6 t r o i t e m e n t l i 6 e e b l e u r t e n e u r e n h u m i d i t 6 q u i , e I I e , d 6 p e n d d u c l i m a t , d e l a v 6 g 6 t a t i o n e t d e e p r o p r i 6 t 6 e p h y s i c o - c h i m i q u e s d u s y s t l m e n a t u r e l a r g i l e - e a u . L e s b d t i m e n t s q u e l r o n c o n s t r u i t s u r c e s s o l s d 6 r a n g e n t l e s c o n d i t i o n s d t 6 q u i l i b r e d y n a m i q u e q u i existent depuis longtempe e t q u i s e s o n t d 6 v e l o p -p 6 e s dans un milieu ambiant n a t u r e l , L e s f o n d a t i o n s d e s Petits b d t i m e n t s d o i v e n t € t r e c a l c u l 6 e s e n f o n c t i o n d e s - m d u v e m e n t s p o -t e n -t i e l s d u s o l e -t e n v u e d e r 6 d u i r e a u m i n i m u m l e s r i s q u e s d e d o m m a g e s a u x s u p e r s t r u c t u r e s . D a n s l r O u e s t d u C a n a d a , I e s f o n d a t i o n s p e u p r o f o n d e s 5 e c o m -p o r t e n t d i f f 6 r e m m e n t d r u n e r 6 g i o n : I ' a u t r e , p a r e u i t e d e 1 6 g b r e s d i f f 6 r e n c e s d e c l i r n a t . D e s 6 t u d e s o n t 6 t 6 e f f e c t u 6 e s s u r d e s f o n -d a t i o n s b -d a l l e s - s u r - l e - s o l , b s o u b a s s e m e n t p l e i n e t b t e r r e - p l e i n a 6 r 6 , c o m p o r t a n t d e s p i e u x ( p i l i e r s ) e t d e s P o u t r e s ( p i e u x c o u r t s e t r e n f l 6 s , p i e u x l o n g s e t d r o i t s ) , e t d e s s e m e l l e s d i s t r i b u t r i c e s p e u p r o f o n d e s . L e s r 6 s u l t a t s d e c e s e t u d e s m o n t r e n t q u e ' e n g 6 n 6 r a l , l e s d a l l e s - s u r - l e - s o 1 s e s o n t b i e n c o m p o r t 6 e s b W i n n i p e g , d a n s l e M a n i t o b a , e t q u ' e l l e s s e s o n t r 6 v 6 l 6 e s p e u e f f i c a c e s b R e g i n a , d a n s l a S a s k a t c h e w a n . L e s o u l b v e m e n t d e s p l a n c h e r s d e s s o u b a s s e m e n t s c o n s t i t u e u n p r o b l b m e s 6 r i e u x d a n s t o u t e s l e s 1 6 -g i o n s o i r l e s s o u s - s o l s d ' a r -g i l e s e -g o n f l e n t s i l t o n d i m i n u e l a c h a r g e q u t i l s s u p p o r t e n t . I l e s t e s s e n t i e l d e g a r d e r u n e s p a c e v i d e c o n v e n a b l e e o u s l e s p o u t r e s a u n i v e a u d u s o l s i l r o n v e u t q u e I e s f o n -d a t i o n s c o n s t r u i t e s d e p i e u x e n f o n c 6 s p r o f o n d E m e n t e t d e Poutres s o i e n t e f f i c a c e s . S r i l s s o n t p e u p r o f o n d s , l e e p i e u x r e n f l 6 e e t l e e s e m e l l e s d i s t r i b u t r i c e s s u b i s s e n t u n s o u l b v e m e n t b p e u p r b s 6 g a l b c e l u i d e s f o n d a t i o n s e n s u r f a c e . I l e s t f a c i l e d e r e c o n n a i t r e l e s s o l s q u i p e u v e n t c a u s e r d e s d i f -f i c u l t 6 s , m a i s o n p o u r r a s e t r o m P e r d e b e a u c o u p d a n s I a p r 6 v i -s i o n d u t a u x d e -s o u l l v e m e n t e t d e s m o u v e m e n t s t o t a u x e t d i f f € r e n -t i e l s f -t a n -t q u e I ' o n n e c o n n a i -t r a p a s m i e u x I e s e f f e t s d e l a p r e s s i o n d e c 6 n f i n e m e n t d a n s I a s u p p r e s s i o n d u g o n f l e m e n t , l a g r a n d e u r r e l a t i v e d e s v a r i a t i o n s d e d i m e n s i o n s v e r t i c a l e s e t h o r i z o n t a l e s p e n d a n t I a v a r i a t i o n d e v o l u m e , e t l e d e g r 6 d e d 6 p l a c e m e n t d e 1 ' h u m i d i t 6 c a u s 6 p a r l a s u c c i o n e t p a r I e s g r a d i e n t s t h e r m i q u e s .

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SHALLOW FOT'IIDATIONS ON SIIELLING CT.AYS IN

IGSIERN

CAT.IADA

Btr

J. J. llamilton

Research Officer

Prairie

Reglonal Station

Division

of Building

Research

National- Research Council

Saskatoon, Saskatchewan

Ttrls paper rilas presented at the

International

Research and

Engl-neering Conference on ExPanslve

Clay Soils held at Texas A & M

University,

August 3O-SePtember 3,

1965, sponsored by Gormonwealth

Scientific

and Industrial-

Research

Organization-Australia;

Soil

Mechanics Group, Texas Section

ASCE; Texas A&1"1

UniversitY.

This

reprint

is an excerPt from Vol-r:me

IL of the Proceedings of that

Conference.

T e x a s A & U P r e s s

1965

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SHAILOW FOI]NDATIONS ON SWELLING CLAYS IN WESTERN CANA,DA b y J . J . H a m i l t o n R e s e a r c h O f f i c e r , P r a i r i e R e g i o n a l S t a t i o n , D i v i s i o n o f B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l , S a s k a t o o n , S a s k a t c h e w a n ASSTMCT T h e v o l u m e c h a n g e o f s o i l s h i g h i n c l a y c o n t e n t i s c l o s e l y r e l a t e d t o t h e i r m o i s t u r e c o n t e n t , w h i c h i n t u r n i s a f u n c t i o n o f c l i m a t e , v e g e t a t i o n

and physico-chemical properties of the natural clay-water system. Inlan-made

s t r u c t u r e s h a v e a d i s t u r b i n g e f f e c t o n l o n g - e s t a b l i s h e d d y n a n i c e q u i l i b r i u m

condj.tions that have developed under a naLural environment. Foundation

d e s i g n s f o r s m a l l s t r u c t u r e s m u s t t a k e i n t o a c c o u n t a n d a t t e m p t t o m i n i m i z e p o L e n t i a l m o v e m e n t s a n d d a m a g e t o s u p e r s t r u c t u r e s . I n h l e s t e r n C a n a d a d i f f e r e n c e s i n p e r f o r m a n c e o f s h a l l o w f o u n d a t i o n s a r i s e f r o m r a t h e r s m a l l d i f f e r e n c e s i n r e g i - o n a l c l i m a t e . R e s u l t s a r e p r e -s e n t e d o f -s t u d i e -s m a d e o n s l a b - o n - g r o u n d , f u l l b a s e m e n t , a n d c r a w l - s P a c e f o u n d a t i o n s , u t i l i z i n g p i l - e ( p i e r ) a n d b e a m c o n s t r u c t i o n ( b o t h short belled a n d l o n g s t r a i g h t p i l e s ) , a n d s h a l l o w s p r e a d f o o t i n g s . I n g e n e r a l , s l a b s o n

-ground have performed well in Winnipeg, Manitoba, and poorly in Regina'

Saskatcheroan. Ileaving of basement floors is a serious problem in all areas

w h e r e c l a y s u b - s o i l s u n d e r g o a r e b o u n d - s w e l l i n g d u e t o r e d u c e d l o a d i n g .

Maintenance of an adequate void space beneath grade beams is the key to good

p e r f o r m a n c e o f d e e p p i l e a n d b e a m f o u n d a t i o n s . S h a l l o w e r , b e l l e d p i l e s a n d s p r e a d f o o t i n g s h e a v e a p p r o x i m a t e l y t h e s a m e F m o u n t a s s u r f a c e f o u n d a t i o n s .

T h e i d e n t i f i c a t i o n o f p o t e n t i a l l y t r o u b l e s o m e s o i l s i s n o t d i f f i c u l t ,

b u t p r e d i c t i o n s o f r a t e s a n d t o t a l a n d d i f f e r e n t i a l m o v e m e n t s r n a y s t i l l b e i n

error by large amounts until more is knor^rn of the effects of confining

pres-s u r e i n pres-s u p p r e pres-s pres-s i n g s w e l l i n g ; t h e r e l a t i - v e m a g n i t u d e o f v e r t i c a l a n d h o r i

-zontal dimension change during volume change; and the rates of moisture

movement under suction and thernal gradients.

INTRODUCTION

In the three Prairie Provinces, I'l.anitoba, Saskatchewan and Alberta, and

i-n some of the i.ntermountain areas of British Colunbia the semi--arid climate

a n d t h e .deep deposits o f h i g h l y p l a s t i c c l a y c r e a t e s e r i o u s d i f f i c u l t i e s f o r s h a l l o w f o u n d a t i o n s . S o m e o f t h e m a j o r u r b a n c e n t e r s a r e l o c a t e d i n a r e a s o f g r e a g e s t f e r t i l i t y a n d t h e s e c o i n c i d e w i t h t h e p o o r l y - d r a i n e d , f l a t , g e n e r -a l l y t r e e l e s s c l a y p l a i n s . F o u r o f t h e l a r g e s t a n d f a s t e s t g r o w i n g u r b a n c e n t e r s i n t h e P r a i r i e P r o v i n c e s a r e l o c a t e d o n n a j o r g l a c i a l l a k e d e p o s i t s ( F i g u r e 1 A ) . W i n n i p e g , t h e o l d e s t a n d l a r g e s t o f t h e s e , i s c e n t r a l l y J - o c a t e d i n t h e g l a c i a l L a k e A g a s s L z d e p o s i t . W i t h t h e e x c e p t i - o n o f t r e e - l i n e d r i v e r b a n k s , t h e a r e a , p r i o r E o d e v e l o p m e n t , v r a s g t a l l g r a s s p r a i r i - e , s u b j e c t t o p e r i o d i c p r a i r i e f i - r e s a n d f l o o d i n g . E l s o n l , B a r a - o s 2 , M i s h t a k 3 a n d C r a w f o r d 4 h a v e d e s c r i b e d t h e g e o l o g i - c a n d e n g i n e e r l n g c h a r a c t e r i s t i c s o f t h e d e e p c l a y d e p o s i t o f m a i n c o n c e r n t o f o u n d a t i o n d e s i g n e r s .

Another rnajor glacial lake, covering several thousand square miles' was

formed in south central Saskatchewan and left thick deposits of clays of high

p l a s t i c i t y . T h e c i t y o f R e g i n a i s l o c a t e d w i t h i n t h i s v a s t p l a i n s a r e a i n t h e

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M a j o r G l a c i a l L a k e D e p o s i t s i n M a n i t o b a , Saskatchewan and A l b e r t a ' c 5 d _I

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sr'sxr'rcHtvtlt \

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P e d o l o g i c a l i n M a n i t o b a , a n d A l b e r t a S o i l Z o n e s S a s k a t c h e w a n f f A r 0 R s o r L z 0 N t 5 t n l e r i o r P l a i n s E r o s n S o i l Z o n e | ) a r k E r o r n S o i l Z o n e 8 . l c t & o e g r a d e d B a l c k S o l l z o n e C r e t W o o d e d S o i l Z o n ! C . n a d i a n S n i e l d M a i n C l . y A r e a 3 S u b A r c l i c S o i l s H u d 3 0 n B a y t o * l a n d 5 u b A r c t i c S o i l r

Average Annual Preci-p i t a t i o n _{o f M a n i t o b a ,} Saskatchewan and

Alberta

184

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f o r m e r b e d o f g l a c i a l L a k e R e g i n a . C h r i s t i a n s e n ) h a s d e s c r i b e d t h e

p l e i s t o c e r r " g . o l o g y o f t h i s a r e a . T h e c i t i e s o f S a s k a t o o n a n d E d m o n t o n 6 a r e l o c a t e d o n s o m e w h a t s h a l l o w e r g l a c i a l l a k e d e p o s i t s , w h i c h e x h i b i t g r e a t e r h e t e r o g e n e i t y a n d s m a l l e r a r e a l e x t e n t o f t r o u b l e s o m e h e a v y c l a y s .

RELATIONSHIP BETWEEN CLIMATE, SOILS AND VEGETATION

T h e i m p o r t a n c e a n d i n t e r - r e l a t i o n s h i p o f s o i l t y p e , c l i m a t e a n d v e g e t a -t i o n o n f o u n d a t i o n p e r f o r m a n c e o n h e a v y p l a s t i c c l a y s i s r e a s o n a b l y u n d e r s t o o d ' S u b t l e d i f f e r e n c e s i n o n e o r a l l o f t h e s e c o n t r i b u t i n g v a r i a b l e s h a v e b e e n f o u n d r e s p o n s i b l e f o r g r e a t d i f f e r e n c e s i n f o u n d a t i o n p e r f o r m a n c e . , A d e t a i l e d d e s c r i p t i o n o f t h e c l i r n a t e o f c e n t r a l C a n a d a b y K e n d r e w a n d C u r r i e / s h o w s i t t o b e r e m a r k a b l y u n i f o r m f o r s u c h a l a r g e a r e a , w i t h d i s t i n c t i v e r e g i o n a l c l i m a t i c f e a t u r e s w i t h i n t h e g e n e r a l a r e a u n d e r c o n s i d e r a t i o n i n t h i . s p a p e r . T h e g r e a t v e g e t a t i - o n r e g i o n s a n d t h e m a j o 5 s o i l z o n e s ( F i g u r e 1 8 ) c o i n c i d e g e n e r a l l y w i t h t h e m a j o r c l i m a t i c r e g i o n s o a l t h o u g h , i n r e a l i t y , t h e r e a r e n o s h a r p b o u n d a r y l i n e s b u t r a t h e r b r o a d t r a n s i t i o n b e l t s . I n a d d i t i o n t o t h e f o u r m a j o r c i t i e s , t w o s m a l l e r u r b a n c e n t e r s a r e s h o w n o n t h i s f i g u r e , E s t o n a n d T i s d a l e , S a s k a t c h e w a n . E s t o n i s w i t h i n t h e b r o w n s o i l z o n e , i - n a n a r e a o f a v e r a g e a n n u a l p r e c i p i t a t i o n o f a p p r o x i m a t e l y 1 2 i n . ( F i g u r e lC). R e g i n a a n d S a s k a t o o n f a l l w i t h i n t h e d a r k b r o w n s o i l

zorre, in which the average annual precipi-tation varies betv/een 14 in. in the

n o r t h e r n l a t i t u d e s a n d 1 8 i - n . i n t h e s o u t h e r n l a t i t u d e s . E d m o n t o n , T i s d a l e a n d W i n n i p e g f a l l w i t h i n t h e b l a c k a n d d e g r a d e d b l a c k s o i l z o n e , w h i c h h a s c h a r a c t e r i s t i c r a i n f a l l r a n g i n g b e t w e e n 1 6 i n . i n t h e n o r t h e r n l a t i t u d e s a n d 2 0 i n . i n t h e s o u t h e r n l a t i t u d e s . N a t u r a l v e g e t a t i o n i n t h e b r o w n s o i l z o n e i s c h a r a c t e r i s t i c a l l y s h o r t g r a s s p r a i r i e o r m i x e d p r a i r i e c o m p r i s i n g s h o r E g r a s s a n d s m a l l a s p e n o r w i l l o w i n t h e d e p r e s s i o n a l a r e a s . V e g e t a t i o n o f t h e d a r k b r o w n s o i l z o n e i s m j - x e d p r a i r i e a n d t h e s o i - l c o n t a i n s h i g h e r o r g a n i c c o n t e n t . I n a r e a s o f h i g h e r a n n u a l p r e c i p i t a t i o n t h e b l a c k o r d e g r a d e d b l a c k s o i l z o n e s a r e f o u n d . T h e s e a r e c h a r a c t e r i s t i c a l l y t a l l g r a s s p r a i r i e o r p a r k l a n d p r a i r i e i n w h i c h a s p e n a n d b l a c k p o p l a r h a v e i n v a d e d f o r m e r t a l 1 g r a s s p r a i r i e . U n l i k e m a n y a r e a s o f t h e w o r l d w h e r e s w e l l i n g a n d s h r i n k i n g s u b - s o i l c o n d i t i o n s a r e r e p o r t e d , t h e m e a n a n n u a l g r o u n d t e m p e r a t u r e t h r o u g h o u t t h e C a n a d i a n p r a i r i e s i s m a n y d e g r e e s b e l o w t h e t e m p e r a t u r e m a i n t a i n e d i n b u i l d -i n g s f o r h u m a n c o m f o r t . T h e m e a n m o n t h l y a i r t e m p e r a t u r e i s b e l o w 3 2 " F f o r a l m o s t s i x m o n t h s o f e a c h y e a r t h r o u g h o u t m o s t o f t h e p o p u l a t e d a r e a o f M a n i t o b a , S a s k a t c h e w a n a n d A l b e r t a . A l t h o u g h t h e f o w w i n t e r t e m P e r a t u r e s a r e h e l p f u l i n r e d u c i n g t h e p o t e n t i a l e v a p o r a t i o n a n d t r a n s p i r a t i - o n l o s s e s f r o m t h e s o i l , a n d t h e r e f o r e i n r e d u c i n g t h e a r i d i t y o f t h e a r e a , t h e y c o n t r i b u t e t o v o l u m e c h a n g e d u e t o i c e s e g r e g a t i o n a n d m o i s t u r e m i g r a t i o n i n d u c e d b y t h e r m a l g r a d i e n t s . P r e c i p i t a t i o n o n t h e p r a i r i e s i s c h a r a c t e r i s t i c o f a r n i d d l e - l a t i t u d e ' c o n t i n e n t a l c l i m a t e . M o s t a i r m a s s e s m o v i n g i n t o t h e p r a i r i e s a r e p o o r l y s u p p l i e d w i t h v a p o u r , h a v i n g b e e n f o r c e d t o p a s s o v e r m o u n t a i n r a n g e s o r f r o z e n a r c t i c s e a s . T h e g r e a t e s t p r e c i p i t a t i o n i s r e c e i v e d f r o m m a r i t i m e t r o p i c a l a i r m a s s e s m o v i n g i n f r o m t h e G u l f o f M e x i c o o r f r o m t h e A t l a n t i c t o t h e s o u t h o r e a s t . A d d i t i o n a l m o i s t u r e i s c o n t r i b u t e d b y t h e f o r m a t i o n o f d e w , b y c y c l o n i c a c t i v i t y a n d b y s c a t t e r e d t h u n d e r s t o r m s . G r e a t v a r i a t i o n f r o m l o n g - t e r m a v e r a g e a m o u n t s i s t h e r u l e f o r p r a i r i e p r e c i p i t a t i o n . I n s o m e a r e a s t h e s e d e v i . a t i . o n s f r o m a v e r a g e c o n d i t i o n s m a y p e r s i s t f o r m o n t h s o r e v e n y e a r s , a n d g i v e r i s e t o p r o t r a c t e d d r o u g h t o r h u m i d c o n d i t i o n s .

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THE NATURE OF GROT]ND MOVEMENTS

As an early part of an over-all study of the performance of building f o u n d a t i o n s i n W e s t e r n C a n a d a , t h e Divisi-on of Building R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l , C a n a d a , e s t a b l i s h e d s e v e r a l g r a s s - c o v e r e d t e s t p l o t s a t s i t e s r e p r e s e n t a t i v e o f d i f f e r e n t s u b - s o i l a n d c l i m a t i c c o n d i t i o n s . F i g u r e 2 s h o w s t h e r e s u l t s o f v e r t i c a l g r o u n d m o v e m e n t s a t t h r e e sites o n n a t u r a l

c l a y e y s u b - s o i l s . F i g u r e 2 A i l l u s t r a t e s t h e d y n a m i c b a l a n c e b e t w e e n soil moisture budget and vertical ground movements at vari-ous depths, as well as

t h e e f f e c t s o f g r o u n d freezing o n v e r t i c a l g r o u n d m o v e m e n t s . S o m e o f t h e results presented i-n this figure have been reported and the phenomena involved i n t h e d y n a m i c e q u i l i b r i u m m o r e fu1ly d.iscussed in a previous p a p e r g . S u r f a c e movements due to swelling and shrinking in excess of 3 in. have been measured i n u n d i s t u r b e d c l a y h a v i n g n a t i v e g r a s s c o v e r . I n a d d i t i o n , i t h a s b e e n f o u n d that movements large enough to affect buried watermains or shallow founda-t i o n s h a v e b e e n m e a s u r e d at depths exceeding 8 ft. E m p i r i c a l r e l a t i o n s d e r i v e d f r o m T h o r n t h w a i t e t s e v a p o t r a n s p i r a t i o n c a l c u -l a t i o n s h a v e b e e n found useful i n e v a l u a t i n g t h e c l i m a t e f a c t o r i n n a t u r a l g r o u n d m o v e m e n t s . T h e d e p t h o f frost p e n e t r a t i - o n i n u n d i s t u r b e d c l a y i s a f f e c t e d b y t h e s o i l m o i s t u r e c o n d i t i o n s b e f o r e f r e e z e - u p , € n d t h e s o i l m o i s -t u r e d e p l e -t i o n c a l c u l a t i o n i s a l s o u s e f u l i n p r e d i c t i n g w h e t h e r o r n o t f r o s t h e a v i n g o r s h r i n k a g e will o c c u r . A p p l i c a t i o n o f t h e s o i l m o i s t u r e d e p l e t i o n c a l c u l a t i o n i s a l s o u s e f u l i n p r e d i c t i n g w h e t h e r o r n o t frost h e a v i n g o r s h r i n k a g e w i l l o c c u r . A p p l i c a t i o n o f t h e s o i l m o i s t u r e d e p l e t i o n c a l c u l a t i o n i n a r e a s d r i e r t h a n s u b - h u m i d h a s n o t p r o v e d fruitful, b u t c a l c u l a t i o n s o f such conditions as cumulative departure from long-term averages give indica-t i o n s o f t h e l e n g t h a n d s e v e r i t y o f d r o u g h t o r w e t t e r t h a n a v e r a g e p e r i o d s .

T y p i c a l s o i l m o i s t u r e p r o f i l e s a n d p l a s t i c i t y v a l u e s m e a s u r e d a t t h e v a r i o u s t e s t p l o t s a r e g i v e n o n F i g u r e 3 . A l t h o u g h t r e n d s i n s o i l m o i s t u r e c o n d i t i o n s a r e c o n s i s t e n t _{w i t h t r e n d s i n g r o u n d m o v e m e n t , attempts to} calcu-late _{ground movement from change in moi-sture content have not been entirely} s u c c e s s f u l . T h i s m a y b e p a r t l y d u e t o t h e l a r g e h y s t e r e s i s e f f e c t i n t h e m o i s t u r e c o n t e n t / v o l u m e r e l a t i o n s . L i m i t e d u s e o f s o i l m o i s t u r e t e n s i o m e t e r s

i n t h e s e t e s t p l o t s h a s s h o w n t h a t , w i t h t h e e x c e p t i o n o f w e t p e r i - o d s i n W i n n i p e g , s o i l m o i s t u r e s u c t i o n s a r e i n e x c e s s o f t h e n o r m a l r a n g e o f field t e n s i o m e t e r s . U n d e r n a t u r a l g r a s s c o v e r , s u c t i o n s i n t h e t o p 4 f t i n

W i n n i p e g s e l d o m r i s e a b o v e p F 3, but in Regina and Eston suctions i n t h e t o p 4 f t o f s o i l w o u l d n o r m a l l y b e i n t h e r a n g e o f p F 3 t o p F 4.2, I n s o i l p r o -f i l e s w h e r e t h e r e i s c o m p e t i t i o n b e t w e e n d e e p r o o t e d s h r u b s o r t r e e s and g r a s s e s , s u c t i o n s m a y r e a c h o r a p p r o a c h t h e w i l t i n g p o i n t t h r o u g h o u t t h e depth of the rooting zorte.

T y p i c a l c l a s s i f i c a t i o n t e s t r e s u l t s f o r s o i l s i n s e v e r a l u r b a n a r e a s having swelling and shrinking soil problems are shown on the plasticity chart a n d a c t i v i t y c h a r t ( F i g u r e s 4 A a n d 4 8 ) . l J i l l i a m s t r u c r i t e r i a f o r c l a s s i f y i n g s o i l s i n t o g r o u p s o f very high, high, medium and low potential e x p a n s i v e n e s s have been drawn on the activity chart and i-ndicate that most of the soils e n c o u n t e r e d i n t h e g l a c i a l l a k e d e p o s i t s o f W e s t e r n C a n a d a f a l l w i t h i n t h e v e r y h i g h p o t e n t i a l e x p a n s i v e n e s s c a t e B o r y , a l t h o u g h t h e a c t i v i t y r a t i o i s g e n e r a l l y b e l o w 0 . 7 5 .

The problem of foundation movement on heavy clay soils has been recog-n i z e d f o r a r e l a t i v e l y l o n g t i m e a n d v a r i o u s s a t i s f a c t o r y e n g i n e e r i n g s o l u -t i o n s h a v e b e e n f o u n d for larger b u i l d i n g s . I n p r o j e c t s f o r w h i c h f o u n d a t i o n i n v e s t i g a t i o n s a r e c a r r i e d o u t a n d d e s i g n s a r e n a d e b y q u a l i f i e d e n g i n e e r s ,

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e c o n o m i c a l a n d s a t i s f a c t o r y f o u n d a t i o n s a r e t h e r u l e . T h e r e a r e s t i l l , h o w e v e r , a l a r g e n u m b e r o f s t r u c t u r e s f o r w h i c h i n d i v i d u a l f o u n d a t i o n d e s i g n s a r e n o t m a d e . I n t h e h o u s e b u i l d i n g i n d u s t r y t r a d j - t i o n a l f o u n d a t i o n d e s i g n m e t h o d s h a v e n o t c h a n g e d g r e a t l y i n h a l f a c e n t u r y . R o a d w a y s , s i d e w a l k s , a n d s u r f a c e f o u n d a t i o n s f o r s m a 1 l s t r u c t u r e s m u s t b e p l a c e d d i r e c t l y o n t h e s o i 1 . S e r v i c e p i p e l i n e s b u r i e d b e l o w d e e p e s t f r o s L p e n e t r a t i o n a r e s t i l l s u b j e c t t o s h r i n k a g e a n d / o r s w e l l i n g m o v e m e n t s i n t h e v i c i n i t y o f d e e p - r o o t e d p l a n t s .

T h e f o l l o w i n g e x a m p l e s i l l u s t r a t e t h e t y p e a n d degree of problems en-c o u n t e r e d b y s h a l l o w foundati-ons in Western Canada.

SLAB-ON-GROUND CONSTRUCTION I n t h e l a t e 1 9 4 0 ' s a n e r ^ r d e s i g n , w h i c h g r e w q u i c k l y i n p o p u l a r i t y , u t i l i z e d t h e s l a b - o n - g r o u n d t e c h n i - q u e f o r h o u s e s . A s t h i - s w a s a n u n t r i e d a n d u n p r o v e d f o u n d a t i o n s c h e m e , e x p e r i m e n t a l t e s t s l a b s w e r e - c o n s t r u c t e d i n O t t a w a a n d W i n n i p e g b y t h e Division o f B u i l d i n g R e s e a r c h l l . T h e h l i n n i p e g s l a b , p l a c e d o n a typical u n d i s t u r b e d s o i l p r o f i l e , u n d e r w e n t o n l y m i n o r d i f f e r e n t i a l m o v e m e n t s t h r o u g h o u t i t s t e s t l i f e o f t h r e e y e a r s a n d i n d i c a t e d t h a t l i g h t r e i n f o r c i n g t o s t r e n g t h e n t h e s l a b a g a i n s t s e a s o n a l f l e x u r e a t t h e e d g e s w o u l d b e s a t i s f a c t o r y . A c c o r d i n g l y , a l a r g e n u m b e r o f s l a b s - o n - g r o u n d h a v e s i n c e b e e n b u i l t a n d h a v e g i v e n v e r y s a t i s f a c t o r y p e r f o r m a n c e i n t h e W i n n i p e g a r e a . E x c e p t i o n s i n c l u d e d i f f i c u l t i e s e n c o u n t e r e d a s a r e s u 1 - t o f f r o s t a c t i o n b e n e a t h u n h e a t e d p o r t i o n s o f t h e s l a b s , a t t a c h e d g a r a g e s , c a r -p o r t s , b r e e z e - w a y s o r w h e r e l a r g e t r e e s o r shrubs had been planted in close p r o x i r n i t y , a l l a s m i g h t b e e x p e c t e d . I n t h e r n i d - 1 9 5 0 t s , a l a r g e n u m b e r o f s l a b - o n - g r o u n d h o u s e s h r e r e c o n -s t r u c t e d i n t h e c i t y o f R e g i n a , S a s k a t c h e w a n . S u c c e s s f u l e x p e r i e n c e i n L l i n n i p e g e n c o u r a g e d b u i l d e r s t o u s e a s i m i l a r m i n i m u m o f r e i n f o r c i n g s t e e l . T h e p e r f o r m a n c e o f t h e s e s l a b s w a s q u i t e d i f f e r e n t . l ' I i t h i n t h e f i r s t w i n t e r a f t e r c o r n p l e t i o n s e v e r a l o f t h e s l a b s w e r e s h o w i n g s i g n s o f d i s t r e s s . B e c a u s e t h e r e s e e m e d t o b e a s e a s o n a l cycle, with some improvement and re-level1ing o f t h e s l a b s d u r i n g t h e s p r i n g , i t w a s h o p e d t h a t t h e m o v e m e n t s w o u l d r e m a i n w i t h i n t o l e r a b l e l i m i t s . W i t h i n t w o t o f i v e y e a r s , h o w e v e r , a l a r g e n u m b e r o f s l a b s h a d e x p e r i e n c e d s e v e r e d i f f e r e n t i a l m o v e m e n t s . A l t h o u g h t h e s e w e r e l a r g e , t h e d a m a g e t o t h e e x t e r i o r a n d i n t e r i o r o f t h e h o u s e s w a s s u r p r i s i n g l y s m a l l , d u e t o t h e i r f r a m e c o n s t r u c t i o n , o p e n f l o o r p l a n , a n d t r u s s r o o f d e -s i g n . N o n - l o a d b e a r i n g p a r t i t i - o n s w e r e o f t e n f o u n d t o b e s u s p e n d e d a n i n c h o r m o r e a b o v e t h e f l o o r s l a b , h a n g i n g f r o m t h e r o o f t r u s s e s . T h e m a g n i t u d e o t d i f f e r e n t i a l m o v e m e n t s w a s e a s i l y d e t e r m i n e d , b u t i t w a s n o t p o s s i b l e t o determine to what extent the edges had gone up or the center had gone down. SLAB MOVEMENTS RELATED TO WEATHER

Surveys of damage in a number of the Regina houses were begun in 1960. C h a n g e s i n e l e v a t i o n o f t h r e e p o i n t s o n o n e o f t h e f l o o r s l a b s a n d o n a n o u t -s i d e d o o r -s t o o p ( F i g u r e 54) are compared with vertical g r o u n d m o v e m e n t s a t v a r i o u s d e p t h s i n an open field w i t h u n d i s t u r b e d s o i l c o n d i t i o n i n t h e v i c i n -i t y o f t h e d a m a g e d h o u s e s ( F i g u r e 58). T h e s e p l o t s s h o w t h a t t h e n o r t h e a s t corner of the floor slab had risen more than 3-l/2 in. and that the annual rate of movement had been approximately the same from the time of construc-t i o n . T h e c e n t e r o f t h e floor s l a b a p p a r e n t l y s e t t l e d a p p r o x i m a x e t y I - L / 2 i n . b e f o r e h e a v i n g b e g a n i n 1960, and since that time heaving has continued at an e q u a l o r s l i g h t l y g r e a t e r r a t e t h a n t h a t a t t h e n o r t h e a s t c o r n e r o f t h e f l o o r

(13)

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slab. The point at the mid-length along the west side has shorrn a seasonal i n c r e a s e i n t h e r a t e o f h e a v i n g d u r i n g t h e e a r l y s p r i n g and sunmer period, w h e n s n o w n e l t a n d r a i n c o n t r i b u t e t o i n c r e a s e d s o i l m o i s t u r e a r o u n d t h e s l a b ,

a n d a r e d u c e d r a t e o f h e a v i n g t h r o u g h t h e s u m n e r - f a l l - w i n t e r p e r i o d . T h e c o n -c r e t e d o o r s t o o p o n t h e o u t s i d e o f t h e w e s t w a l l h a s u n d e r g o n e l e s s h e a v i n g and experienced more seasonal effects on the rate of heavi-ng than has the f l o o r s l a b n e a r b y .

Comparing the slab movements with open-field ground movements (see F i g u r e 5 8 ) s h o w s t h a t d u r i n g p e r i o d s o f r a i n f a l l o r i n c r e a s e s i n s o i l m o i s -t u r e -t h e s l a b m o v e s u p and is less affec-ted t h a n t h e n a t u r a l s o i l p r o f i l e b y t h e d e m a n d s o f v e g e t a t i o n o n s o i l m o i s t u r e . T h e n e t r e s u l t i s a c o n t i n u i n g r i s e , w h i l e o p e n - f i e l d a r e a s g o u p a n d d o r r n s e a s o n a l l y a s m o i s t u r e g o e s i n a n d o u t o f s o i l s t o r a g e .

The maximum amplitude of ground movement measured in the natural soil p r o f i l e a t a d e p t h o f 1 f t w a s o f t h e o r d e r o f 2 L n . , w i t h s o m e e v i d e n c e o f t h e r m a l s h r i n k a g e o f t h e o r d e r o f 3 / 4 L n . d u r i n g t h e w i n t e r o f L 9 6 2 - 6 3 . M o v e m e n t s a t a d e p t h o f 1 0 ft or greater proved to be insignificant d u r i n g

t h i s p e r i o d , b u t v e r t i c a l g r o u n d m o v e m e n t i n e x c e s s o f L / 2 j - n . d e v e l o p e d a t t h e 5 - f t d e p t h f o l l o w i n g t h e s u u m e r o f 1 9 6 3 .

A s a v e r a g e s o i l m o i s t u r e c o n d i t i o n s a t d e p t h s a r e r e l a t e d t o l o n g - t e r m p r e c i p i - t a t i o n t r e n d s , i t h a s b e e n f o u n d u s e f u l t o u s e p l o t s o f c u m u l a t i v e departure from average annual precipitat.ion when examining change in vertical g r o u n d m o v e m e n t s w i t h t i r n e . F i g u r e 6 s h o w s a p l o t o f c u m u l a t i v e d e p a r t u r e f r o m a v e r a g e a n n u a l p r e c i p i t a t j . o n f o r R e g i n a , p r e p a r e d f r o m i n f o r m a t i o n p u b -l i s h e d b y t h e M e t e o r o l o g i c a l B r a n c h , D e p a r t m e n t o f T r a n s p o r t , d a t i n g b a c k t o t h e y e a r 1 8 8 9 . A s i l l u s t r a t e d b y t h i s f i g u r e , t h e s r - u n m e r o f L 9 6 O w a s h o t a n d dry, and the annr.ral precipitation 6.6 in. below the long-term average. Dur-ing the early sunrner of. 1962 heavier than average rainfall occurred and soil m o i s t u r e s t o r a g e w a s i n c r e a s e d , a s i s i n d i c a t e d b y h e a v i n g o f t h e l - f t g a u g e

( F i g u r e 5 8 ) . D u r i n g t h e m o n t h s of May, June and July 1963, precipitation w a s a g a i n m u c h a b o v e n o r m a l , w i t h further h e a v i n g o f t h e 1 - , 3 - , a n d 5 - f t g a u g e s m e a s u r e d . I n t h e l a t e s r r m m e r and fall o f 1 9 6 3 h e a v i n g b e c a n e s i g n i f i c a n t a t

t h e 5 - f t d e p t h , a l t h o u g h t h e d e m a n d s o f v e g e t a t i o n h a d d e p l e t e d s o i l m o i s -t u r e f r o m -t h e -t o p 2 f-t of soil. A g a i n , f o r t h e s p r i n g a n d e a r l y s u u n e r

p e r i o d o f L 9 6 4 , t h e e f f e c t s o f s p r i n g s n o w m e l t a n d a b o v e - a v e r a g e r a i n f a l l i n the summer months on vertical ground movements can be seen in the open-field ground movements.

INFLUENCE OF PRE-CONSTRUCTION WEATHER

C o m p a r i s o n o f f l o o r s l a b c o n t o u r s f o r a f l a t s l a b c o n s t r u c t e d i n 1 9 5 5 ( F i g u r e 7 4 ) w i t h t h o s e f o r a f l a t s l a b c o n s t r u c t e d i n 1 9 6 0 ( F i g u r e 7 8 ) i n -d i c a t e s s o m e i n t e r e s t i n g d i f f e r e n c e s . F o r t h e s l a b b u i l t i n 1 9 5 5 t h e r e w a s apparently a combination of settlement at the center and heaving at the e d g e s , w h e r e a s f o r t h e s l a b b u l l t i n 1 9 6 0 , a l l a r e a s o f t h e f l o o r s l a b h a v e e x p e r J - e n c e d h e a v i n g t o a g r e a t e r o r l e s s e r e x t e n t . A s s o i l m o i s t u r e c o n -d i t i o n s w e r e n o t m e a s u r e d a t t h e f i r s t s i t e , p r i o r t o c o n s t r u c t i o n , t h e y m u s t b e i n f e r r e d f r o m e x a m i n a t i . o n o f m e t e o r o l o g i c a l i n f o r m a t i o n f o r t h e p e r i o d p r i o r t o c o n s t r u c t i o n . F i g u r e 6 s h o w s t h a t t h e r e w a s a p e r i o d o f m u c h a b o v e -a v e r -a g e r -a i n f -a l l l a s t i n g f r o u r 1 9 4 9 u n t i l t h e t i m e o f c o n s t r u c t i o n . T h i s amounted to a cumulative departure from long-term average annual precipitati-on o f s o m e 3 0 i n . o f p r e c i p i t a t i o n .

I t i - s p o s t u l a t e d t h a t a s a r e s u l t o f t h i s l o n g w e t p e r i o d t h e s o i l s i n

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t h e t o p 5 o r 6 f t o f t h e o p e n - f i e l d s o i l p r o f i l e w e r e a t m o i s t u r e c o n t e n t s h i g h e r t h a n E h e l o n g - t e r m a v e r a g e m o i s t u r e c o n t e n t . B e c a u s e o f c o n s t r u c t i o n a n d c h a n g e o f s o i l t e m p e r a t u r e c o n d i t i o n s i n t h e v i c i n i t y o f t h e n e w c o n s t r u c

-tion it is reasoned that thermal gradients could induce moisture movement

h o r i z o n t a l l y f r o m w a r m e r t o c o o l e r a r e a s i n t h e v i c i n i t y o f t h e b u i l d i n g p e r -i m e t e r . M o i s t u r e m o v e n e n t f r o m t h e s u b - s o i l s l o c a t e d c e n t r a l l y b e l o w t h e s l a b

towards its perimeter might take place until a new dynanic equilibrium was

e s t a b l i s h e d f o r t h e n e w e n v i r o n m e n t a l c o n d i t i o n s . A t t h e s a m e t i m e , t h e e d g e s o f t h e s l a b w o u l d b e r i s i n g u n d e r t h e i n f l u e n c e o f t h e g a i n o f m o i s t u r e f r o m t h e i n t e r i o r a r e a s o f t h e s l a b s u b - s o i l a n d t o t h e p e r i m e t e r e f f e c t s o f n a t u -r a l p -r e c i p i t a t i o n a n d i r r i g a t i o n w a t e r a d d e d f o r l a n d s c a p i n g i m p r o v e m e n t s . I t i s s u g g e s t e d t h a t s o i l m o i s t u r e c o n t e n t d u r i n g t h e s u r n m e r o f 1 9 6 0 w o u l d b e r e p r e s e n t a t i v e o f l o n g - t e r m a v e r a g e c o n d i t i o n s , b e c a u s e F i g u r e 6

shows no cumulative departure from the long-term average. Although the summer

o f 1 9 6 1 w a s d r y , t h e r e w a s a p p r e c i a b t e a n d f a i r l y u n i f o r m h e a v i n g o v e r t h e e n t i r e a r e a o f b o t h t h e 1 9 5 5 a n d 1 9 6 0 s l a b s . I t i s b e l i e v e d t h a t m o i s t u r e

movement away from the center of the slab built in 1955 would cease when the

m o i s t u r e c o n t e n t o f t h e s o i l i n t h e p e r i m e t e r a r e a s r e a c h e d h i g h e n o u g h l e v e l s t o r e v e r s e t h e m o i s t u r e m o v e m e n t p o t e n t i a l t o w a r d s t h e d r i e r c e n t r a l a r e a s .

T h e m o i s t u r e s t r e s s g r a d i e n t f o r t h e s l a b b u i l t i n t h e s u n m e r o f 1 9 6 0

would be towards the center of the slab area from the beginning, and any

mois-t u r e a d d e d a r o u n d mois-t h e p e r i m e mois-t e r w o u l d t h e r e f o r e t e n d t o m i g r a t e t o w a r d s t h e c e n t e r a n d p r o d u c e a g e n e r a l h e a v i n g c o n d i t i o n o v e r t h e s l a b a r e a . F i g u r e s 3 8 a n d 8 s h o w , r e s p e e t i v e l y , t h e c h a n g e i n m o i s t u r e c o n t e n t w i t h t i m e i n t h e o p e n - f i e l d c o n d i t i o n a n d t h e d i f f e r e n c e i n m o i s t u r e c o n t e n t d i s t r i b u t i o n

a r o u n d t h e 1 9 5 5 s l a b d u r i n g A u g u s t , 1 9 6 0 , w h e n t h i s f l o o r s l a b w a s u n d e r

-going maxi-mum differential displacement. Figure 9 shows the change in

mois-t u r e c o n mois-t e n mois-t a mois-t mois-t h e p e r i m e mois-t e r o f t h e 1 9 6 0 s l a b f r o m L h e t i m e o f c o n s t r u c t i o n u n t i l J u l y 1 9 6 4 .

HEAVE RESIJLTING FROM PLI.JMBING LEAKS

S o m e e s p e c i a l l y s e r i o u s c a s e s o f h e a v i n g h a v e b e e n a t t r i b u t e d t o l e a k a g e

f r o m s u b s u r f a c e p l u m b i n g l i n e s . D i f f e r e n t i a l m o v e m e n t s o f 3 o r 4 i n . a r e

c o n r m o n in t h e s e s i t u a t i o n s , a n d t h e p a t t e r n o f h e a v i n g i s o f t e n m o r e d e s t r u c

-tive and difficult to correct than that from normal heaving. An example of

this type of movement in a light industrial building in Regina, Saskatchewan,

h a s b e e n r e c o r d e d . T h e s u p e r s t r u c t u r e f o r t h e b u i l d i n g w a s s u p p o r t e d o n p i l e a n d g r a d e b e a m f o u n d a t i o n s a n d a 4 - i n . c o n c r e t e f l o o r s l a b p l a c e d o n a 6 - i n . g r a v e l f i l l . O n s p e c u l a t i o n t h a t i n t e r e s t i n g m o v e m e n t s r n i g h t t a k e p l a c e i n

this building vertical ground movement gauges at different depths in the

sub-s o i l , b u i l d i n g m o v e m e n t p o i n t s , a d e e p b e n c h m a r k , a n d a n e u t r o n m o i s t u r e m e E e r a c c e s s t u b e w e r e i n s t a l l e d d u r i n g t h e c o n s t r u c t i o n p e r i o d i n t h e l a t e s u n m e r o f 1 9 6 1 .

R e a d i n g s w e r e t a k e n p e r i o d i c a l l y a f t e r i n s t a l l a t i o n . B y t h e m i d d l e o f

A u g u s t , 1 9 6 2 , a m a x i m u m h e a v e o t 3 - I / 2 i n . h a d d e v e l o p e d i n t h e e e n t r a l p o r

-ti"on of the slab directly above the centerline of a sub-floor plumbing trench

( F i g u r e 1 0 ) . T h i s h e a v e c a u s e d a m a x i m u m a n g u l a r d i s t o r t i o n o f 1 / 3 0 ( 1 i n .

L n 2 - L / 2 f t ) a n d s e r i o u s l y d a m a g e d i n t e r i o r p a r t i t i o n s . I t w a s a l s o f e a r e d t h a t d a m a g e t o t h e s u p e r s t r u c t u r e w o u l d r e s u l t i f i n t e r i o r l o a d - b e a r i n g p a r

-titions continued to heave, and eepecially if the reinforced concrete grade

b e a u s w e r e l i f t e d o f f t h e c a s t - i n - p l a c e c o n c r e t e p i l e f o u n d a t i o n .

At the point of maximum heave a leak was discovered in the hot water

(18)

WATER

CONTENT,

%

n30

Center

of west

wall

Near

north east

c0rner

tr

I

t

F lr F CL

u.r

a

c)-

o Open

field

a - a

o - E

soIL MOISTI'RE

CONDITIONS

rN AUGUST,

1960, AT SI"A,B-ON-GROIJND

ITOUSE

BUILT rN Lg55;

COMPARING

OPEN FIEID UOISTI'FE CONDITIONS

WIIII 1IIOSE IN

FIGI]RE 8

1,96

I

tr

(19)

50

0 W A T E R

C O N T E N T ,

7 O

nn

o-o

July 7, 1964

o-o

Sept

& 1960

CHANGE

IN SOIL MOISTURE

CONDITIONS

AT

SI,AB-ON-GROI]ND

EOUSE BUILT IN 1960 FROM

TIME OF CONSTRUCTION

I]NTIL JULY ]-964

FIGURE 9

L97

0 LJ

-CL

l.rl

o

10 l5

(20)

4 . 0

3 . 0

ttl lrl c ) ^ ^ - / t l C9

z

- 1 . 0

l+l I

0 196r

1962

1963

HEAVING OF FLOOR SURFACE AND AT THREE DEPTHS IN THE SUB-SOIL

M O I S T U R E

C O N T E N T ,

% ( D R Y W E I G H T

B A S I S )

0 1 0 n n 4 0 5 0

Concrete

floor

Gravel

subf

loor

H i g h l y

plastic

Regi

na

clay

MOISTURE

CONTENT

PROFILES BEFORE

AND AFTER

HEAVING

FIGURE 10

1 9 8

Floor

slab surface

\

\J

{{

. { _

i"-s

i S

3 S

S s

6 i

_--37" below

floor surface

/

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original

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{r-

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_\

_{49" below}

_{floor surface}

-=

32"

below

original

grade

I09" below

floor surface

= 92" below

original

grade

o Aug 23,

o Aug 21,

(21)

l i n e f r o m w h i c h i - t w a s e s t i m a t e d t h a t s o m e 7 , 5 0 0 g a l o f w a t e r h a d e s c a p e d , s a t u r a t e d t h e g r a v e l f i l l u n d e r t h e f l o o r s l a b , a n d m i g r a L e d f o r a c o n s i d e r -a b l e d i s t -a n c e a l o n g t h e l e n g t h o f t h e b a c k - f i l l e d p l u r n b i n g t r e n c h . T h e t o t a l l e a k a g e r e p r e s e n t e d t h e e q u i v a l e n t o f a p p r o x i m a t e l y 6 i n . o f w a t e r o v e r t h e e n t i r e f l o o r a r e a o f t h e b u i l d i n g . T h e s u b g r a d e h a d b e c o m e f u l l y s a t u r a t e d a n d t h e n e u t r o n m o i s t u r e m e t e r i n d i c a t e d a n a v e r a g e i n c r e a s e i n s o i l m o i s t u r e c o n t e n t ( F i g u r e _{1 0 B ) , a b o v e t h a t a t t h e t i m e o f c o n s t r u c t i o n ,} o f 1 0 p e r c e n t i n t h e E o p 2 f t o f h e a v y c l a y s o i l u n d e r l y i n g t h e g r a v e l f i l l , 5 p e r c e n t i n t h e n e x t f o o t , a n d a n a v e r a g e o f 2 p e r e e n t i n c r e a s e o v e r t h e n e x t 5 f t o f d e p t h . T h e f l o o r s l a b s u r f a c e a n d t h e r e b o u n d g a u g e s , i n s t a l l e d a t v a r i o u s depths below the slab, indicated a vertical dimension change in the soil

( F i g u r e 10A) of 5 percent in the top 2 ft, 3 - I l 3 p e r c e n t i n t h e n e x t f o o t , a r r d L - L / 4 p e r c e n t o v e r t h e n e x t 5 f t .

The observed heaving correlates well with uovements expected from the i n t e r p r e t a t i - o n o f l a b o r a t o r y s w e l l i n g t e s t s o n u n d i s t u r b e d s a m p l e s w h e n c o n -s i d e r a t i o n i s t a k e n o f t h e e f f e c t s o f o v e r b u r d e n , r e s t r a i n t , a n d u n e q u a l h o r i z o n t a l a n d v e r t i c a l s w e l l i n g . O b s e r v a t i o n s h a v e b e e n c o n t i n u e d a t t h e si-te for several months to study final equilibrium conditions of volume and moisture distrj-bution. Figure 10 shows the amount and rate of heaving and

t h e c h a n g e i n m o i s t u r e c o n t e n t i n t h e s u b - s o i l a t t h i s s i t e . FOUNDATIONS I,ilITH CMWL SPACE

O b s e r v a t i o n s h a v e b e e n m a d e o n f o u r d i f f e r e n t t y p e s o f s h a l l o w f o u n d a -t i o n s f o r b a s e m e n t l e s s h o u s e s b u i l t i n R e g i n a d u r i n g t h e s u n m e r o f 1 9 6 0 . E a c h w a s c o n s t r u c t e d d u r i n g t h e s a m e p e r i o d , o n s i m i l a r s o i l s , a n d h a d v e r y s i m i l a r s u p e r s t r u c t u r e s . A s l a b - o n - g r o u n d w a s c o n s t r u c t e d t o a d e s i g n v e r y s i m i l a r t o t h e o n e r e p o r t e d e a r l i e r i n t h i s p a p e r . T h e o t h e r s a r e f r o m a l a r g e n u m b e r o f l o w c o s t h o u s e s b u i l t o v e r c r a w l s p a c e s . O n e d e s i g n u t i l i z e d 6 f t - d e e p , u n d e r - r e a m e d ( b e l l e d ) p i l e s , a n d 2 - f t d e e p r e i n f o r c e d c o n c r e t e beams spanning approximateLy L2 ft between the piles. Another used a shallow s p r e a d f o o t i n g a n d a 4 - f t r e i n f o r c e d c o n c r e t e f o u n d a t i o n w a l l . T h e s p r e a d f o o t i n g s w e r e p l a c e d a p p r o x i r n a t e l y 2 f t b e l o w o r i g i n a l g r a d e . T h e t h i r d d e -s i g n u -s e d 1 6 - f t d e e p , r e i n f o r c e d , c a s t - i - n - p l a c e c o n c r e t e p i l e s a n d 2 - f t d e e p g r a d e b e a m s s p a n n i n g a p p r o x i m a t e l y 1 3 f t . I n t h i s c a s e t h e c o n t r a c t o r p r o -v i d e d a -v o i d s p a c e o f a p p r o x i m a t e l y 2 L n . b e l o w t h e g r a d e b e a m s t o a c c o m o d a t e s o i l s w e l l i n g . C h a n g e s i n e l e v a t i o n a n d d i f f e r e n t i a l m o v e m e n t s a r e s h o w n i n F i g u r e 5 C . I t i s i n t e r e s t i n g t o n o t e t h a t t h e m a x i m u m h e a v i n g o f t h e f l a t s 1 a b , t h e s h o r t , b e l l e d p i l e a n d b e a m , a n d t h e s h a l l o w s p r e a d f o o t i n g h o u s e s w e r e a l l essentially the s€rme, and that very similar movements have occurred at these h o u s e s a n d a t t h e p r e v i o u s l y r e p o r t e d f l a t s l a b d u r i n g a s i m i l a r p e r i o d . M a x i -m u -m d i f f e r e n t i a l h e a v i n g o f t h e f l a t s l a b i - s o f t h e o r d e r o f L - L / 4 i ' n . , t h a t

f o r t h e s h o r t - p i l e c o n s t r u c t i o n 3 / 4 L n . , a n d t h a t f o r t h e s h a l l o w s p r e a d f o o t -i r g , a p p r o x i m a t e L y 3 / 4 j - n . T h e r e a r e s o m e i - n d i c a t i o n s t h a t t h e d i f f e r e n t i a l movement rate of the slab-on-ground remai-ns higher than that for the other

t w o h o u s e s . A s w o u l d b e e x p e c L e d , t h e l o n g e r p i l e s a r e p e r f o r m i n g m u c h b e t t e r , b u t t h e r e i s r e a s o n t o b e l i e v e t h a t t h e v o i d s p a c e b e n e a t h t h e b e a m s is now filling, and that in the future heaving of the grade beams may become s i g n i f i c a n t .

(22)

MOISTURE LOSS FROM HEATED CRAWL SPACES

In foundations r4tith a crawl space below a structural floor system it is

e s s e n t i a l t h a t a : r e f f e c t i v e v a p o u r b a r r i e r b e p l a c e d o v e r t h e e n t i r e s o i l s u r -f a c e t o p r e v e n t m o i s t u r e l o s s . A c a s e o f s e v e r e d e s i c c a t i - o n o f t h e s u b - s o i l , w h i c h r e s u l t e d i n s e t t l e m e n t o f s h a l l o w f o u n d a t i o n s o f a l a r g e c h u r c h h a l l i n

Regina, illustrated the importance of this detail. During a l0-year period

of exposure of the natural soil in the crawl space to the low relative

hunid-i t y o f t h e b u i l d i n g , t h e s o i l m o i s t u r e p r o f i l e a s s u m e d t h e c o n d i t i o n s s h o w n i n F i g u r e 1 1 .

T h e s o i l s u r f a c e i n t h e v i c i n i t y o f t h e b o r i n g i n d i c a t e d a l i n e a l s h r i n k

-a g e o f -a t l e -a s t 3 . 3 p e r c e n t ( f o u n d by summation of the width of the cracks of

1 / 8 i n . o r g r e a t e r ) . A m e a s u r e m e n t o f t h e s e t t l e m e n t o f t h e b u i l d i n g i n t h e

a r e a i n d i c a t e d a t o t a l o f 2 . 2 L n . a t t h e t i m e o f m o i s t u r e m e a s u r e n e n t . A

c o m p a r i s o n o f m e a s u r e d a n d p r e d i c t e d s e t t l e m e n t , b a s e d o n a s s u m e d i n i t i a l a n d m e a s u r e d f i n a l w a t e r c o n t e n t s , f u r t h e r i l l u s t r a t e d t h e n e e d f o r m o r e i n f o r

-mation on the relative magnitude of vertical and horizontal dinension changes

a s s o c i a t e d w i t h m o i s t u r e c h a n g e . HOUSES WITII BASEMENTS

Although slabs-on-ground have been popular under certain conditions in

the low cost housing market, and some. of the more expensive custom built

h o u s e s a r e f o u n d e d o n d e e p p i l e f o u n d a t i o n s , t h e m a j o r i t y o f h o u s e s c o n

-structed in Western Canada are bui.lt over full basements. Conventional

con-struction for a house basement includes excavation of approximately 6 ft of

s o i l o v e r t h e e n t i r e p l a n a r e a o f t h e h o u s e ; p l a c i n g c o n c r e t e s t r i p f o o t i n g s ( o f t e n 8 t o 1 0 i n . d e e p a n d 2 4 t o 3 0 i n . s q u a r e ) ; a n d c o n s t r u c t i n g a l i g h t l y

r e i n f o r c e d c o n c r e t e w a l l ( 8 to 10 in. thick and 8 ft high). F r o n 8 t o 1 0 i n .

o f g r a v e l i s p l a c e d u n d e r a 3 t o 4 i n . t h i c k , u n r e i n f o r c e d c o n c r e t e f l o o r

s l a b . A t i l e d r a i n a g e s y s t e m i s u s u a l l y p l a c e d a r o u n d t h e o u t s i d e o f t h e

perimeter footings and is connected to a sump or ser^rer.

The weight of soil excavated is usually much greater than the weight of

t h e f i n i s h e d s u p e r s t r u c t u r e a n d f o u n d a t i o n s . T h e u n i t b e a r i n g p r e s s u r e s e x e r t e d b y t h e p e r i n e t e r f o o t i n g s a r e o f t h e o r d e r o f 0 . 3 t o n p e r s q f t f o r s i n g l e - s t o r e y w o o d f r a m e c o n s t r u c t i o n ; 0 . 3 5 t o n p e r s q f t f o r s i n g l e - s t o r e y

masonry veneer; and 0.45 ton per sq ft for two-storey uasonr)r veneer

con-s t r u c t i o n . T h e s e b e a r i n g p r e s s u r e s a r e c o n s i d e r a b l y b e l o w t h e u s u a l s w e l l

-ing pressures measured for clay soils from the 6-ft depth at naturally

occurring water contents, and are very much below the swelling pressure of

clays from this depth if they have previously been desiccated by tree growth

o n t h e s i t e . U n d e r f l o o r a r e a s c o v e r e d b y t h e u s u a l t h i n c o n c r e t e f l o o r s l a b

and gravel sub-base, the unit pressures on the soil are from one third to one

quarter the previous overburden pressure before excavation. The incidence of

heaving of these floor slabs is very high. Heaves in excess of 1 ft have

occurred in areas of Winnipeg where deep-rooted trees rrere removed prior to

construcLion, and in more arid areas such as Eston, Saskatchewan, basenent

f l o o r h e a v i n g i n e x c e s s o f 2 f t h a s b e e n o b s e r v e d . O n t h e o t h e r h a n d , i n

older buildings where tree growth has been encouraged near shallow

founda-tions in areas that have not previously supported the growth of trees,

settlement of foundation walls due to soil shrinkage has resulted.

In order to document the performance of trdo conventional basement-type

(23)

MOISTURE

010 CONTENT,

n

% (DRY WEIGHT

nrm50

BASIS)

o

a

\

_o

\

a

\

a

,

o

I

a

,

o

F LL

-F CL IJ

o

I

a

I

o

I

'\-1

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?

a

t

o

\

/

(

a

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FIGURE 11

20L

(24)

m e a s u r e m e n t o f f o o t i n g , w a 1 l a n d f l o o r m o v e m e n t s , a n d t o m e a s u r e t h e

rebound of the soil underlying the excavation during and following

construc-t i o n . B o t h o f t h e s e s i t e s w e r e formerly c o v e r e d w i t h s c r u b b r u s h v e g e t a t i o n , a n d t h e s u b - s o i l s h a d b e e n s u b j e c t e d t o s e v e r e d e s i - c c a t i o n b e f o r e e x c a v a t i o n . F i g u r e 1 2 g i v e s t h e r e s u l t s o f l e v e l s u r v e y s r u n o n f o u n d a t i o n w a l l s , i n -t e r i o r f o o t i n g s , f l o o r s l a b , a n d t h e s u b - s o i l s t r a t a a t o n e o f t h e s e h o u s e s . A b r i e f r e v i e w o f t h e c o n s t r u c t j - o n s c h e d u l i n g i s o f i n t e r e s t i n i n t e r -p r e t i n g t h e s e m o v e m e n t s . J u s t p r i o r t o e x c a v a t i o n o f t h e b a s e m e n t , o n 6 O c t o b e r L 9 6 L , t h r e e r e b o u n d g a u g e s w e r e i n s t a l l e d a t d e p t h s o f 2 . 3 f t , 4 . 2 f t , a n d 7 . 2 f t b e l o w t h e f i n a l b a s e m e n t f l o o r e l e v a t i o n . A f r o n t - e n d l o a d e r t h e n e x c a v a t e d s o m e 6 ft of soil o v e r t h e e n t i r e f l o o r p l a n a r e a o f t h e h o u s e , w h i c h v r a s 4 7 f t l o n g b y 3 7 ft wide. A p p r o x i m a t e l y 1 i n . o f r a i n f e l 1 i n t o t h e o p e n e x c a v a t i o n o n 1 0 O c t o b e r a n d f o o t i n g s w e r e p l a c e d o n 1 8 O c t o b e r . S e t t l e m e n t s u r v e y p o i n t s w e r e i n s t a l l e d i n t h e c o n c r e t e b a s e m e n t r a a l l o n 3 l

October. The framing was roughed in by the end of December and a furnace was

i n s t a l l e d t o a l 1 o w c o n s t r u c t i o n t h r o u g h t h e s e v e r e l y c o l d w i n t e r . A s m a y b e s e e n i n F i g u r e 1 2 , t h e r e b o u n d g a u g e s i n d i c a t e d h e a v i n g a t t h e 2 . 3 - a n d 4 . 2

-ft depths innnediately after excavation and rainfall. A11 gauges have shown a

c o n t i n u e d m o v e m e n t s i n c e t h a t d a t e . T h e 2 . 3 - f t g a u g e h a s s h o w n a s e a s o n a l

ehange in the rate of heavi-ng. The heaving rate during the summer is

a p p r o x i m a t e l y t w i c e t h a t d u r i n g t h e w i n t e r . T h i s c a n b e r e l a t e d t o t h e i n -c r e a s e d a v a i l a b i l i t y o f w a t e r i n t h e g r a v e l s u b - f l o o r d u r i n g s u r f f n e r m o n t h s , a n d m a y p o s s i b l y a l s o b e i n f l u e n c e d t o s o m e e x t e n t b y h i g h e r s u b - s o i l t e m -p e r a t u r e s d u r i n g t h e h e a t i n g s e a s o n .

Plots of wall movements are shovm at the top of Figure 12. The gauge

showing the maximum upward displacenent is located near a corner of the

base-m e n t w h e r e base-m a x i base-m u base-m i n c r e a s e o f s u b - s o i l m o i s t u r e w o u l d b e e x p e c t e d . A l s o p l o t t e d i s t h e t o t a l m o v e m e n t o f a p o i n t t h a t u n d e r w e n t i n i t i a l s e t t l e n e n t

and has since shovrn heaving. Maximum differential movement measured to date

has been approximately 3 in. The dotted line, giving the mean change of

e l e v a t i o n f o r t h e t e n s e t t l e m e n t p o i n t s i - n s t a l l e d i n t . h e b a s e m e n t w a l l , i n -d i c a t e s t h e g e n e r a l t r e n d o f u p w a r d m o v e m e n t .

Shown also in Figure 12 are measurements of change of elevation of two

p o i n t s o n t h e f l o o r s l a b , o n e o v e r l y i n g t h e r e b o u n d g a u g e i n s E a l l a t i o n s , t h e o t h e r a t a n o u t s i d e e d g e o f t h e f l o o r s l a b n e a r t h e w a l l s e c t i o n s h o w i n g m a x i -m u n r i - s e . T h e t h i r d p o i - n t p l o t t e d i s t h e c h a n g e i n e l e v a t i o n o f a n i n t e r i o r c o l u m n f o o t i n g i n t h e v i c i - n i t y o f t h e r e b o u n d g a u g e s . T h e c h a n g e i n f l o o r s l a b e l e v a t i o n s i n c e i t s c o n s t r u c t i o n h a s c l o s e l y p a r a l l e l e d t h e w a l l a n d s u b - s o i l m o v e m e n t i n t h e s a m e v i c i - n i t y d u r i n g s i m i l a r p e r i o d s . T h e i n t e r i o r f o o t i n g m o v e m e n t s h a v e b e e n s l i g h t l y s m a l l e r t h a n t h o s e o f t h e f l o o r s l a b , a s r n i g h t b e e x p e c t e d f o r t h e i n c r e a s e d l o a d i n g c o n d i t i o n . A n e i g h b o r i n g h o u s e , b u i l t i n 1 9 6 0 , h a s u n d e r g o n e d i f f e r e n t i a l f l o o r h e a v i n g o f a p p r o x i n a t e l y 4 i n . t o d a t e . H e a v i n g o f t h e w a l l s a n d f l o o r s t i l l

continues at a rapid rate, and measurements of movements and change in

mois-t u r e c o n mois-t e n mois-t a r e b e i n g c o n mois-t i n u e d .

DISCUSSION OF VARIOUS METHODS OF PREDICTING VOLUME CHANGE

A t t e m p t s h a v e b e e n m a d e f o r e a c h o f t h e a b o v e - c i t e d c a s e s t o a p p l y s e v -e r a l o f t h -e p o p u l a r l y a d v a n c e d m e t h o d s o f p r e d i c t i n g t h e v o l u m e e h a n g e a r i s -i n g o u t o f t h e n e w e n v -i r o n m e n t a f t e r c o n s t r u c t i o n . P r e d i c t i o n m e t h o d s s u c h a s t h o s e p r o p o s e d b y C r o n e y e t a L L 2 ( b a s e d o n s u c t i o n p r o f i l e s d e s c r i b i n g d y n a m i c e q u i l i b r i u m m o i s t u r e c o n d i t i o n s b e f o r e a n d a f t e r c o n s t r u c t i o n ) h a v e