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Burn, K. N.
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1 . 4 HOUSE SETTLEMENTS AND TREES K . N . Burn G e o t e c h n i c a l S e c 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 o f Canada, O t t a w a , K I A OR6 ABSTRACT
Many l a r g e c o m m u n i t i e s i n e a s t e r n Quebec and e a s t e r n O n t a r i o a r e s i t u a t e d i n a n ayes t h a t was o n c e i n u n d a t e d by t h e p o s t - g l a c i a l Champlain S e a . I n t o t h i s l a r g e i n l a n d b a s i n was d e p o s i t e d enormous q u a n t i t i e s o f f i n e - g r a i n e d s i l t y c l a y o f t e n c h a r a c t e r i z e d on a m i c r o s c o p i c s c a l e by a n open s t r u c t u r e d s o i l s k e l e t o n and h i g h w a t e r c o n t e n t s . A s a c o n s e q u e n c e t h i s , s o i l may u n d e r g o r e l a t i v e l y l a r g e volume c h a n g e s , c a u s e d e i t h e r by e x c e s s i v e l o a d i n g o r t h e e x t r a c t i o n o f p o r e w a t e r by t h e r o o t s o f r a p i d l y g r o w i n g t r e e s . I n t h i s p a p e r t h e c o n d i t i o n s t h a t l e a d t o t r e e s c a u s i n g s e t t l e m e n t s o f b u i l d i n g s on s h a l l o w f o u n d a t i o n s r e s t i n g on t h e s e d e p o s i t s a r e d e s c r i b e d , and examples o f damage t o h o u s e s i n t h e Ottawa a r e a a r e p r e s e n t e d . P l u s i e u r s g r a n d e s communaut6s d a n s l ' e s t de Qu6bec e t l ' e s t de l t O n t a r i o s o n t s i t u 6 e s d a n s une r 6 g i o n q u i f u t j a d i s i n o n d 6 e p a r l a mer p o s t - g l a c i a i r e d e C h a m p l a l n . Dans c e l a r g e b a s s i n i n t g r i e u r , o n t 6 t 6 d6posBes d 1 6 n o r m e s q u a n t i t 6 s d ' a r g i l e l l m o n e u x
2
g r a i n s f i n s , q u i nc c a r a c t 6 r i s e s o u v e n t , s u r une 6 c h e l l e m i c r o s c o p i q u e , p a r un s q u e l e t t e d e s o l2
s t r u c t u r e o u v e r t e e t p a r une h a u t e t e n e u re n e a u . I1 s ' e n s u i t que l e s o l p e u t s u b i r d e s changements d e volume r e l a t i v e m e n t grand; <?I c a u s e d ' u n c , ; u r c h a r g e e x c e s s l v c ou dc l ' c x t r a c t i o r i de l ' e a u de s e s p o r e s p a r l e s r a c i n c : , d ' a r b r e ; ?i c r o i s s a n c e r a p i d c . Le p r g s e n t a r t i c l e d 6 c r i t l e s c o n d i t i o n s q u i e n t r a f n e n t l e s a r b r e s
2
c a u s e r l e s a f f a i s s e m e n t s de b g t i m e n t s u r l e s f o n d a t i o n s p e u p r o f o n d e s q u i r e p o s e n t s u r c e s d g p e t s , e t i l p r g s e n t e d e s exemples d e dommages f a i t e s 2 c e r t a i n e s m a i s o n s d a n s l a r 6 g i o n d l O t t a w a .Man Is e x i s t e n c e i n t h e u r b a n community i s made more p l e a s a n t by t h e p r e s e n c e o f t r e e s . They p r o v i d e s p l a s h e s o f g r e e n a g a i n s t t h e d r a b h u e s o f b u i l d i n g m a t e r i a l s a n d g r a c e f u l f l o w i n g forms i n c o n t r a s t t o t h e more r i g i d g e o m e t r i c a l s h a p e s imposed by b u i l d i n g t e c h n o l o g y and t h e economics o f s h e l t e r e d s p a c e . They a r e h i g h l y d e s i r a b l e i n t h e s e s e t t i n g s f o r many r e a s o n s y e t , u n d e r c e r t a i n c o n d i t i o n s , t h e y may become t h e i n d l r c c t c a u s e o f c o n s i d e r a b l c s e t t l e m e n t and s e v e r e a n d c o s t l y damage. T h e r e a r e t h r e e c o n d i t i o n s u n d e r which t r e e s may c a u s e b u i l d i n g s t o s e t t l e and a l l t h r e e must o c c u r s i m u l t a n e o u s l y : 1. s u b s o i l c o n d i t i o n s where m o i s t u r e c o n t e n t c h a n g e s l e a d t o a p p r e c i a b l e volume c h a n g e s , 2 . t h e p r e s e n c e o f c e r t a i n s p e c i e s o f t r e e s , and 3 . i n s u f f i c i e n t r a i n f a l l t o s a t i s f y t h e demands o f t r e e s d u r i n g t h e g r o w i n g s e a s o n .
The f i r s t c o n d i t i o n i s a s s o c i a t e d w i t h f i n e - t e x t u r e d s o i l s o r c l a y s which c h a n g e i n volume w i t h c h a n g e i n w a t e r c o n t e n t . They o c c u r e x t e n s i v e l y I n Canada a n d o t h e r p a r t s o f t h e w o r l d (Ward 1 9 4 7 , 1 9 5 3 ; B a r a c o s a n d M o r a n t z , 1 9 5 3 ; J e n n i n g s , 1 9 5 3 ; Skempton, 1 9 5 4 ; C o l l i n s , 1 9 5 7 ; B a r a c o s a n d Bozozuk, 1 9 5 7 ) . Some t y p e s o f s o i l b o t h s w e l l a n d s h r i n k ; e x a m p l e s o f t h e s e a r e commonly f o u n d on t h e P r a i r i e s . O t h e r s o i l s , s u c h a s t h e Leda c l a y w i t h w h i c h t h i s r e p o r t i s c o n c e r n e d , d e c r e a s e i n volume w i t h d e c r e a s e i n w a t e r c o n t e n t , b u t s w e l l l i t t l e o r n o t a t a l l upon r e w e t t i n g . The d i f f e r e n c e l i e s i n t h a t t h o s e i n t h e f i r s t g r o u p c o n t a i n c l a y m i n e r a l s t h a t h a v e a n a f f i n i t y f o r w a t e r w h i c h , when a v a i l a b l e , i s a b s o r b e d w i t h i n t h e c r y s t a l l a t t i c e a n d r e s u l t s i n v o l u m e t r i c e x p a n s i o n . When t h e w a t e r i s u n d e r s u c t i o n i t i s w i t h d r a w n f r o m t h e c r y s t a l l a t t i c e a n d a r e d u c t i o n i n volume o c c u r s . Leda c l a y i s f o u n d e x t e n c i v c l y i n t h o s e p a r t s o f Q u e b e c a n d O n t a r i o t h a t l i e w l t h i n t h e O t t a w a a n d S t . Lawrence R-Lverl l o w l a n d s . It was d e p o s i t e d from g l a c i a l d e b r i s i n t o t h e l a r g e i n l a n d arm o f t h o A t l a n t i c Ocean t h a t e x i s t e d I n t h e c l o s i n g s t a g e s o f t h e W i s c o n s i n e r a a n d known a s t h e C h a m p l a i n S e a ( K a r r o w , 1 9 6 1 ) ( F i g . 1 ) . I t c o n s i s t s l a r g e l y o f m i c r o s c o p i c p l a t e - l i k e p a r t i c l e s t h a t were d e p o s i t e d i n a n e d g e - t o - f a c e a r r a n g e m e n t n o t u n l i k e t h a t o f a " h o u s e o f c a r d s " which i m p a r t s t o t h e s o i l a v e r y open s t r u c t u r e c h a r a c t e r i z e d by h i g h n a t u r a l w a t e r c o n t e n t , h i g h p l a s - t i c i t y , a n d h i g h s h r i n k a g e p o t e n t i a l s . L a r g e r s i l t - s i z e p a r t i c l e s a r e a l s o p r e s e n t i n v a r y i n g d e g r e e s a n d h a v e a m o d i f y i n g e f f e c t on b o t h t h e s t r u c t u r e and t h e s e p r o p e r t i e s ( C r a w f o r d , 1 9 6 8 ) . The s w e l l i n g c l a y m i n e r a l s e n c o u n t e r e d i n t h e c l a y s o f w e s t e r n Canada and e l s e w h e r e a r e e i t h e r a b s e n t f r o m Leda c l a y o r p r e s e n t o n l y i n n e g l i g i b l e a m o u n t s ( B r y d e n a n d P a t r y , 1 9 6 1 )
.
The h i g h s h r i n k a g e p o t e n t i a l i s i l l u s t r a t e d i n F i g . 2 w h i c h shows t h r e e c y l i n d e r s o f t h i s c l a y a l l o f w h i c h w e r e trimmed t o t h e same s i z e f r o m a l a r g e r s a m p l e . C y l i n d e r s 2 a n d 3 w e r e t h e n p e r m i t t e d t o d r y u n t i l t h e i r w a t e r c o n t e n t s had b e e n r e d u c e d a s i n d i c a t e d . T h e s e two s t e p s o f r e d u c t i o n i n w a t e r c o n t e n t e a c h r e p r e - s e n t a v o l u m e t r i c s h r i n k a g e o f 2 0 % . The e n d p o i n t o f d r y i n g i s a g r e a t l y c o l l a p s e d m i c r o s t r u c t u r e i n w h i c h t h e p a r t i c l e s assume a more o r l e s s p a r a l l e l a l i g n m e n t . C l a y s o i l n e a r t h e s u r f a c e h a s b e e n s u b j e c t e d t o many c y c l e s o f d r y i n g a n d r w w e t t i n g , t o o x i d a t i o n , a n d t o t h e e f f e c t o f p l a n t r o o t s s o t h a t i t s o r i g i n a l s t r u c t u r e i s c o m p l e t e l y d e s t r o y e d b u t t h e m a t e r i a l shown i n F i g . 2 i s t y p i c a l o f c l a y t h a t may be e n c o u n t e r e d j u s t b e l o w t h e l e v e l o f f o u n d a t i o n o f s m a l l s t r u c t u r e s . T R E E S The s e c o n d c o n d i t i o n i s t h e p r e s e n c e o f t r e e s w h i c h r e q u i r e m o i s t u r e f o r t h e i r e x i s t e n c e . The s o u r c e o f m o i s t u r e i s n o r m a l l y p r e c i p i t a t i o n w h i c h p e r c o l a t e s i n t o t h e u p p e r l a y e r o f s o i l a n d becomes a v a i l a b l e t o t h e t r e e r o o t s .The movement o f w a t e r o r s a p i n a t r e e i s a n e x t r e m e l y complex p r o c e s s , and i s n o t c o m p l e t e l y u n d e r s t o o d e v e n by p l a n t p h y s i o l o g i s t s . B r i e f l y , i t c o n s i s t s o f two p h a s e s : t h e d r a w i n g o f m o i s t u r e f r o m t h e s o i l v i a t h e r o o t s , t r u n k a n d b r a n c h e s , a n d f i n a l l y t o t h e l e a v e s where a b o u t 9 5 % o f i t i s t r a n s p i r e d i n t o t h e a t m o s p h e r e ; a n d s e c o n d , t h e t r a n s p o r t a t i o n o f t h e p r o d u c t s o f p h o t o s y n t h e s i s f r o m t h e l e a v e s t o v a r i o u s p a r t s o f t h e t r e e f o r t h e b u i l d i n g o f new c e l l s a n d c o n t i n u e d g r o w t h . Thc f i r s t p h a s e i s r e l a t i v e l y u n c o m p l i c a t e d a n d i s t h e o n e most d i r e c t l y i n v o l v e d i n t h e s e o b s e r v a t i o n s . Most p l a n t p h y s i o l o g i s t s a c c e p t t h e ' c o h e s i o n t h e o r y t w h i c h , s i m p l i f i e d , s t a t e s t h a t w a t e r moves p a s s i v e l y a l o n g a p r e s s u r e g r a d i e n t t h r o u g h - o u t t h e w h o l e p l a n t . T h e r e a r e two ' p u m p s ' , o n e a t e i t h e r e n d : t r a n s p i r a t i o n p u l l i n g i n t h e l e a v e s a n d r o o t p r e s s u r e p u s h i n g i n t h e r o o t s (Zirnrnerman, 1 9 6 4 ) . The d o m i n a n t mechanism i s t r a n s p i r a t i o n , a c t i v a t e d by s o l a r e n e r g y , b u t r o o t s u c t i o n i s i m p o r t a n t u n d e r c e r t a i n c i r c u m s t a n c e s , p a r t i c u l a r l y i n t h e s p r i n g b e f o r e t h e t r e e i s i n l e a f . The a c t u a l q u a n t i t i e s o f w a t e r t r a n s p i r e d by t r e e s v a r y w i t h s i z e , s p e c i e s , s o i l c o n d i t i o n s , c o m p e t i t i o n f r o m o t h e r p l a n t s , and c l i m a t e , b u t i n d i v i d u a l t r e e s may
t r a n s p i r e a s much a s 50 t o 100 g a l l o n s / d a y i n mid-summer (Kramer and K o z l o w s k i , 1 9 6 0 ) . E x t e n s i v e r o o t s y s t e m s a r e n e c e s s a r y f o r t h e a b s o r p t i o n o f w a t e r f r o m t h e s o i l , a n d t h e y must b e f l e x i b l e a n d c a p a b l e o f r a p i d e x t e n s i o n i n t i m e o f d r o u g h t i n o r d e r t o m a i n t a i n a f l o w o f m o i s t u r e t o s u s t a i n t h e l i f e o f t h e t r e e . The e x t e n t o f t h e r o o t s y s t e m i s l a r g e l y d e t e r m i n e d by t h e s o i l c o n d i t i o n a n d o n l y p a r t l y by s p e c i e s ,
b u t a s a ~ e n e r a l r u l e t h e r o o t s y s t e m o f a s l n g l e t r e e e x t e n d s o u t w a r d from t h e b a s e o r t h e trunlc a d i s t a n c e a t l e a s t e q u a l t o t h e hei[;ht o f t h e t r e e . I t s e x t e n s i o n downward d e p e n d s upon t h e a v a i l a b i l i t y o f m o i s t u r e . A V A I L A B I L I T Y OF M O I S T U R E C l i m a t e and i t s e f f e c t upon t h e s u p p l y o f m o i s t u r e by p r e c i p i t a t i o n i s t h e t h i r d c o n d i t i o n . A l l t r e e s t h a t grow i n a n a r e a must be c o m p a t i b l e w i t h t h e i r e n v i r o n - ment, i n c l u d i n g b o t h c l i m a t e and s o i l s . T h e i r h a b i t s o f g r o w t h must be s u f f i c i e n t l y a d a p t a b l e t o e n s u r e c o n t i n u e d l i f e w i t h i n t h e wide v a r i a t i o n s o f r a i n f a l l and temper- a t u r e t h a t n o r m a l l y o c c u r w i t h i n t h a t c l i m a t i c zone p e r i o d . Mean m o n t h l y t e m p e r a t u r e s and h o u r s o f b r i g h t s u n s h i n e a r e n o t c o n s t a n t from y e a r t o y e a r b u t f l u c t u a t i o n s i n t h e s e v a l u e s a r e n o t s o c r i t i c a l t o t r e e g r o w t h a s t h o s e o f p r e c i p i t a t i o n .
An e s t i m a t e of m o i s t u r e i n t h e s o i l may be o b t a i n e d from w e a t h e r r e c o r d s by c a l c u l a t i n f : n q u a n t i t y c a l l e d s o l 1 m o i s t u r e d e p l e t i o n (Bozozuk and Burn, 1 9 6 0 ) . Thl:; 1:: u mot11 flc:nt,ion of' n calculation tlevelopetl by 'rhornthwal1,e ( 1 9 4 8 ) f o r t h e c o n t r o l of
Irr~Lyal,lori of' c : e r e , ~ l crop:; I n wtilct~ nio1:;turc' c , t o r e t l I n t h c :;oil I:; c i e p l e t e d by evapotrar1:;p 1r:ltlori , ~ n d r e p 1 cri L:;l~t.tl t ~ y p r c c i p I t a t i o n . C e r e a l s and g r a i n s have r o o t dystem:; ~ u f f ' J c i e r ~ t l y d e e p t o draw r r ~ o l s t u r e from t h e s o l 1 e q u i v a l e n t t o a b o u t
4
i n c h e s o f w a t e r . F o r t r e e s whose r o o t s y s t e m s may go much d e e p e r i t i s assumed t h a t m o i s t u r e w i l l a l w a y s be a v a i l a b l e . The p l o t s i n F i g . 3 show s o i l m o i s t u r e d e p l e t i o n i n Ottawa f o r a number o f s e l e c t e d y e a r s and t h e a v e r a g e v a l u e f o r t h e p e r i o d 1952 t o 1 9 7 0 .MEASUREMENTS OF V E R T I C A L GROUND MOVEMENTS
A t t h e 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 , measurements o f g r o u n d s e t t l e m e n t s a d j a c e n t t o a l i n e o f elm t r e e s g r o w i n g i n Leda c l a y were begun I n 1954 (Bozozuk and Burn, 1 9 6 0 ) .
F i g u r e
4
shows t h e maximum movements t h a t were r e c o r d e d i n t h e y e a r 1 9 5 5 . Very l a r g e movements o c c u r r e d e v e n t h o u g h t h e t r e e s were a l r e a d y a b o u t 40 y e a r s o l d and had e x p e r i e n c e d o t h e r s e a s o n s t h a t were d r i e r t h a n a v e r a g e . Lack o f r a i n f a l l c a u s e d t h e t r e e s t o t a p t h e s u p p l y o f m o i s t u r e a v a i l a b l e i n t h e p o r e s p a c e s o f t h e c l a y r e s u l t i n g i n s o i l s h r i n k a ~ e and s i g n i f i c a n t v e r t i c a l movements.S e t t l e m e n t s i n e x c e s s o f 3 i n c h e s a t t h e s u r f a c e i m m e d i a t e l y a d j a c e n t t o t h e t r e e s were measured and e v e n a t a d i s t a n c e o f 40 f e e t away from t h e t r e e s t h e s e t t l e m e n t was m e a s u r a b l e . It i s i m p o r t a n t t o n o t e t h a t t h e s e t t l e m e n t s t h a t o c c u r r e d i n t h e 4 t o 6 f o o t d e p t h r a n g e i n which most s h a l l o w f o u n d a t i o n s a r e l a i d , t h e v e r t i c a l movements would have r e s u l t e d i n i n t o l e r a b l e s e t t l e m e n t s e v e n 35 f e e t away. T h i s s t u d y a l s o showed t h a t t h e s u b s o i l a t t h e 6 f o o t l e v e l d i d n o t e x p e r i e n c e t h e a c c e l e r a t e d movements a s s o c i a t e d w i t h s h r i n k a g e o f t h e c l a y u n t i l 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 t o t a l l e d 7 i n c h e s .
A r e l a t e d s t u d y o f h o u s e s i n a n o l d e r r e s i d e n t i a l a r e a o f Ottawa was u n d e r - t a k e n and measurements o f d i f f e r e n t i a l s e t t l e m e n t s on many o f t h e b u i l d i n g s r e p o r t e d
(Bozozuk, 1 9 6 2 ) . The s t u d y r e v e a l e d t h a t s m a l l b u i l d i n g s 60 t o 80 y e a r s o l d and founded on Leda c l a y o r i n s a n d d i r e c t l y o v e r l y i n g Leda c l a y h a s s u s t a i n e d d i f f e r e n - t i a l movements o f a s much a s 1 4 i n c h e s and t h a t t h e g r e a t e r s e t t l e m e n t s were a l w a y s o b s e r v e d i n t h o s e p a r t s o f t h e b u i l d i n g s c l o s e s t t o m a t u r e t r e e s . F i g u r e 5 shows a h o u s e on which t h e d i f f e r e n t i a l s e t t l e m e n t s were i n e x c e s s o f 9 i n c h e s . To t h e l e f t o f t h e h o u s e i n t h i s p i c t u r e t h e r e had b e e n a l i n e o f elm t r e e s t h a t had grown t o m a t u r i t y , removed and r e p l a c e d by a s e c o n d g r o w t h . On t h e r i g h t t h e r e had b e e n a g a r d e n w i t h n o t h i n g l a r g e r t h a n s h r u b s g r o w i n g i n i t . T y p i c a l o f o t h e r b u i l d i n g s i n t h e a r e a , t h e f o u n d a t i o n s o f t h e h o u s e were composed o f l i m e s t o n e b l o c k s , which a r e c o n s i d e r a b l y h e a v i e r a n d more f l e x i b l e t h a n f o u n d a t i o n w a l l s n o r m a l l y c o n s t r u c t e d t o d a y . S u p e r s t r u c t u r e s were most o f t e n o f wooden f r a m e and b r i c k v e n e e r , a s y s t e m which m a n i f e s t s d i s t o r t i o n s by t h e a p p e a r a n c e o f d i a g o n a l c r a c k s i n t h e b r i c k w o r k . Water c o n t e n t s o f t h e s o i l and g r o u n d w a t e r l e v e l s were c o r r e l a t e d w i t h t h e o b s e r v e d movements and l o c a t i o n o f t h e t r e e s , l e a v i n g no d o u b t t h a t t h e p r i m e c a u s e o f damage was t h e t r e e s . The l a r g e v e r t i c a l movements, it was c o n c l u d e d , were t h e a c c u m u l a t i o n o f s m a l l e r i n c r e m e n t s t h a t d e v e l o p e d o v e r t h e y e a r s whenever t h e r e was a d r y summer. O t h e r f a c t o r s t h a t a g g r a v a t e d t h e s i t u a t i o n were t h e c o n s t r u c t i o n o f s e w e r l i n e s and p a v i n g of s t r e e t s w i t h t h e i r combined e f f e c t o f d i v e r t i n g l a r g e q u a n t i t i e s o f r a i n - f a l l away from t h e s u b s o i l . It was a l s o g e n e r a l l y c o n c l u d e d from t h e s e s t u d i e s t h a t Leda c l a y , w i t h a w a t e r c o n t e n t e x c e e d i n g 40%, would be s u s c e p t i b l e t o s h r i n k a g e .
F U R T H E R EVIDENCE
T h e r c may be a t e n d e n c y t o c o n c l u d e from t h i s e v i d e n c e t h a t t h e s e r e s u l t s a r e p r o b a b l y no l o n g e r v a l i d b e c a u s e o f improvements i n t h e c o n s t r u c t i o n o f f o o t i n g s and f o u n d a t i o n w a l l s . T h i s i s n o t t h e c a s e , however, a s shown by t h e f o l l o w i n g two c a s e s i n v o l v i n g much newer h o u s e s .
House No. 1
House No. 1 i s l o c a t e d i n what was once a b r o a d s t a n d o f t r e e s s e p a r a t i n g two farm p r o p e r t i e s . The l o t a p p e a l e d t o t h e owners b e c a u s e o f t h e l a r g e number o f t r e e s on i t and t h e y i n s t r u c t e d t h e b u i l d e r n o t t o d e s t r o y more t r e e s t h a n was a b s o l u t e l y n e c e s s a r y d u r i n g c o n s t r u c t i o n . ( F i g u r e 6 , a p l a n o f t h e p r o p e r t y , shows how d i l i g e n t l y he c a r r i e d o u t t h e s e i n s t r u c t i o n s . ) On t h i s p r o p e r t y and a d j a c e n t l o t s t h e r e were more t h a a 30 t r e e s whose t r u n k c i r c u m f e r e n c e s r a n g e d between 1 f o o t and
9;
f e e t : a l l l o c a t e d a t d i s t a n c e from t h e h o u s e l e s s t h a n h e i g h t o f t h e t r e e s .The h o u s e i s a bungalow o f wood-frame c o n s t r u c t i o n and b r i c k v e n e e r r e s t i n g on c o n c r e t e b l o c k f o u n d a t i o n w a l l s . I t i s L-shaped i n p l a n ; e a c h wing m e a s u r e s a b o u t 25 by 50 f e e t . I s o l a t e d f o o t i n g s and s t e e l columns a l o n g t h e c e n t r e l i n e s o f t h e two wings s u p p o r t I beams which c a r r y t h e i n n e r e n d s o f t h e f l o o r j o i s t s and w e i g h t of t h e p a r t i t i o n s . A l l f o o t i n g s a r e a t a d e p t h o f
5;
t o 6 f e e t below e x i s t i n g g r a d e . T h e r e i s no e x c a v a t i o n b e n e a t h t h e a t t a c h e d g a r a g e . The e x i s t i n g e l e v a t i o n s a r o u n d t h e p e r i m e t e r o f t h e h o u s e were e s t a b l i s h e d by t a k i n g r e a d i n g s on t h e f i r s t c o u r s e o f b r i c k s above t h e f o u n d a t i o n w a l l s . D i f f e r - e n t i a l s e t t l e m e n t s were c a l c u l a t e d on t h e a s s u m p t i o n t h a t t h i s c o u r s e was l e v e l a t t h e t i m e o f c o n s t r u c t i o n 1 0 y e a r s e a r l i e r ( F i g . 7 ) . T h i s s u r v e y i n d i c a t e d t h a t t h e h i g h e s t p o i n t o f t h e f o u n d a t i o n w a l l was i n t h e c e n t r e a t t h e f r o n t ( n o r t h s i d e ) . T h r e e s t a t i o n s , 8 ,9
and 1 0 , a r e a t t h e same e l e v a t i o n and i t was assumed t h a t l i t t l e o r no s e t t l e m e n t had o c c u r r e d h e r e . A t e i t h e r e n d o f t h i s w a l l , t o w a r d t h e f r o n t e n t r a n c e and a t t h e g a r a g e , s m a l l amounts o f s e t t l e m e n t were e v i d e n t . Along t h e e a s t s i d e of t h e h o u s e where t h e t r e e s were o f more o r l e s s u n i f o r m s i z e and s p a c i n g and were a p p r o x i m a t e l y t h e same d i s t a n c e away from t h e h o u s e , t h e w a l l a p p e a r e d t o h a v e r o t a t e d a s a u n i t h i n g e d n e a r t h e f r o n t e n t r a n c e . T h e r e was l i t t l e s i g n o f d i s t r e s s i n t h e b r i c k v e n e e r b u t t h e s o u t h e a s t c o r n e r was more t h a n4
i n c h e s l o w e r t h a n t h e f r o n t o f t h e h o u s e ( F i g . 7 ) .A s i m i l a r s i t u a t i o n e x i s t e d on t h e w e s t s i d e where, b e g i n n i n g a t t h e g a r a g e d o o r where t h e r e was v e r y l i t t l e d i s t o r t i o n , t h e amounts o f s e t t l e m e n t i n c r e a s e d r a p i d l y t o w a r d t h e r e a r o r s o u t h s i d e . The s h o r t w a l l ( 2 0 f e e t l o n g ) had s e t t l e d d i f f e r e n t i a l l y by 23 i n c h e s ; a l s o w i t h o u t n o t i c e a b l e d i s t o r t i o n s . On t h e w e s t and s o u t h s i d e s where t h e t r e e s were l a r g e r and more c o n c e n t r a t e d , t h e h o u s e had s e t t l e d between 3 and
4;
i n c h e s . C r a c k i n g o f t h e b r i c k v e n e e r was most o b v i o u s h e r e b e c a u s e t h e two c o r n e r s o f t h e s o u t h w a l l had s e t t l e d more t h a n t h e c e n t r e ( F i g . 8 ) .L e v e l s were a l s o measured on two l i n e s t h r o u g h t h e b a s e m e n t : one a c r o s s t h e s o u t h wing ( S e c t i o n A - A ) and a n o t h e r r u n n i n g r o u g h l y p a r a l l e l w i t h t h e I beam i n t h e s o u t h wing ( S e c t i o n B - B ) . The r e s u l t s o f t h e s e measurements a r e shown i n F i g . 9 t o - g e t h e r w i t h a g r a p h i c a l e x p l a n a t i o n o f t h e i n c r e a s e i n d i s t o r t i o n t h a t r e s u l t e d b e c a u s e t h e s o i l b e n e a t h t h e i n t e r i o r f o o t i n g s was l e s s a f f e c t e d t h a n t h a t b e n e a t h t h e p e r i m e t e r f o o t i n g s .
The p l a s t e r e d w a l l s i n s i d e t h e h o u s e were more s e n s i t i v e t o t h e s e movements t h a n t h e b r i c k v e n e e r and c r a c k i n g was s e v e r e . F i g u r e s
9
and 1 0 show some of t h e damage t h a t o c c u r r e d i n t h e rooms i n t h e s o u t h wing. I n a d d i t i o n , d o o r a n d window f r a m e s were b a d l y d i s t o r t e d a n d f l o o r s s l o p e d n o t i c e a b l y from t h e s u p p o r t o v e r t h e I beams t o t h e p e r i m e t e r w a l l s .S o i l C o n d i t i o n s
-
Two a u g e r b o r i n g s were made t o a d e p t h o f 1 5 f e e t , one a t t h e f r o n t and t h e o t h e r a t t h e back ( F i g . 6 ) . The s a m p l e s o b t a i n e d were a l l c l a y t o a d e p t h o f 1 4 f e e t where some s m a l l s t o n e s w i t h c l a y were e n c o u n t e r e d . F i g u r e l l a shows t h e m o i s t u r e c o n t e n t s p l o t t e d a g a i n s t d e p t h below t h e s u r f a c e . I n t h e u p p e r5
f e e t , w a t e r c o n t e n t s were a l l between 7 and 20 p e r c e n t which a r e v e r y low v a l u e s f o r s u r f a c e l a y e r s . Between 5 and 7; f e e t t h e r e was a r a p i d i n c r e a s e i n w a t e r c o n t e n t t o t h e 60 p e r c e n t r a n g e and t h e r e a f t e r a more g r a d u a l i n c r e a s e t o a l m o s t 80 p e r c e n t a t 13 f o o t v a l u e s t h a t a r e more t y p i c a l o f u n d i s t u r b e d Leda c l a y a t t h e s e d e p t h s .D i s c u s s i o n
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I t i s o b v i o u s from t h e two w a t e r c o n t e n t p r o f i l e s ( F i g . 1 5 a ) t h a t t h e s o i l w a t e r had been s u b j e c t e d t o h i g h t e n s i o n s . To a p o i n t j u s t above t h e f o o t i n g s b o t h a t f r o n t and back t h e w a t e r c o n t e n t s had been r e d u c e d t o ' w i l t i n g p o i n t ' r a n g e i n d i c a t i n g t h a t e v e n where t h e r e were no t r e e s s o i l w a t e r had b e e n l o s t t o lawng r a s s and s m a l l e r p l a n t s and by e v a p o r a t i o n . Between t h e d e p t h s o f 5 and 11 f e e t t h e w a t e r c o n t e n t s a t t h e back o f t h e house a r e c o n t i n u o u s l y l o w e r t h a n t h o s e a t t h e f r o n t i n d i c a t i n g g r e a t e r e x t r a c t i o n o f m o i s t u r e . These d i f f e r e n c e s i n w a t e r c o n t e n t between t h e b a s e o f t h e f o o t i n g s ( 6 f o o t d e p t h and 1 3 f o o t d e p t h ) a r e p l o t t e d i n F i g . l l b . From t h e s e d i f f e r e n c e s , and a s s u m i n g t h a t (1) t h e m o i s t u r e c o n d i t i o n s a t t h e f r o n t were t y p i c a l o f t h e whole s i t e b e f o r e c o n s t r u c t i o n , and ( 2 ) t h e c l a y between t h e s e d e p t h s was a l w a y s s a t u r a t e d , t h e volume change f o r a column o f s o i l a t t h e back o f t h e house was c a l c u l a t e d t o be e q u i v a l e n t t o 8 i n c h e s o f s e t t l e m e n t .
I t i s a l w a y s d i f f i c u l t t o o b t a i n a c l e a r p i c t u r e o f t h e s e q u e n c e o f d e v e l o p - ments o f damage b e c a u s e , i n a new h o u s e , e v e r y l i t t l e c r a c k i s n o t i c e d , many o f which r e s u l t from s h r i n k a g e o f p l a s t e r o r c o n c r e t e a s t h e s e m a t e r i a l s d r y o u t . I t a p p e a r s , however, t h a t no l a r g e movements were n o t i c e d w i t h i n t h e f i r s t 4 o r 5 y e a r s . The d e s t r u c t i v e movements began i n 1963 and i n c r e a s e d e v e r y y e a r t h e r e a f t e r .
T a b l e I i s an a t t e m p t ' t o c o r r e l a t e t h e s e o b s e r v a t i o n s w i t h t h e w e a t h e r d a t a . I t shows t h e maximum v a l u e s o f s o i l m o i s t u r e d e p l e t i o n from 1956 when t h e house was b u i l t t o 1 9 6 6 when t h e f i r s t s e t t l e m e n t s u r v e y was made. U s i n g t h e r e s u l t s o f t h e s t u d y o f s e t t l e m e n t s a d j a c e n t t o t h e l i n e o f elm t r e e s , d e p t h s t o which s h r i n k a g e c o u l d have o c c u r r e d i n e a c h o f t h e s e y e a r s were a l s o c a l c u l a t e d .
The f o u r t h column o f f i g u r e s i n T a b l e I shows v a l u e s o f s o i l m o i s t u r e d e p l e t i o n i n e x c e s s o f 7 i n c h e s i n d i c a t i n g t h o s e y e a r s i n which t h e c l a y b e n e a t h t h e f o o t i n g s was l i k e l y t o have b e e n a f f e c t e d .
I n t h e f i r s t 8 y e a r s t h e r e were o n l y t h r e e i n which s o i l m o i s t u r e d e p l e t i o n e x c e e d e d 7 i n c h e s by s i g n i f i c a n t a m o u n t s . I n 1957 t h e r e was a s m a l l e x c e s s , b u t i n 1959 and 1960 t h e s e e x c e s s e s were l a r g e , i n d i c a t i n g v e r y d r y y e a r s i n which s e v e r e damage would have been e x p e c t e d . The r e a s o n s t h e damage was n o t g r e a t e r i n t h e s e e a r l y y e a r s may be p a r t i a l l y e x p l a i n e d by two f a c t o r s .
The f i r s t was t h e d e s t r u c t i o n o f l a r g e p r o p o r t i o n s o f t h e r o o t s y s t e m s of t h o s e t r e e s c l o s e t o t h e h o u s e d u r i n g e x c a v a t i o n o f t h e b a s e m e n t . T h i s would have c a u s e d a r e d u c t i o n i n t h e r a t e o f growth and demand f o r s o i l m o i s t u r e . It i s p o s s i b l e t h a t e v e n by 1959-60 t h e r o o t s y s t e m s had n o t y e t r e c o v e r e d from t h i s s e t b a c k .
The s e c o n d f a c t o r i s t h e unknown s t i f f n e s s o f t h e f o u n d a t i o n and s u p e r - s t r u c t u r e and t h e i r combined a b i l i t y t o r e d i s t r i b u t e s t r e s s e s . T h i s was c l e a r l y dem- o n s t r a t e d a t a n o t h e r house where a p e r s o n s l e e p i n g i n a c o r n e r room was awakened by what sounded l i k e a r i f l e s h o t . On e x a m i n a t i o n l a r g e c r a c k s were d i s c o v e r e d a c r o s s t h e c e i l i n g and down t h e w a l l s t h a t had n o t been t h e r e p r e v i o u s l y . The n e x t morning c r a c k s i n t h e basement w a l l and t h e b r i c k v e n e e r were a l s o d i s c o v e r e d . The e x p l a n a t i o n f o r t h i s i s t h a t t h e c o n c r e t e f o u n d a t i o n w a l l s a c t e d a s c a n t i l e v e r members s u p p o r t i n g t h e s u p e r s t r u c t u r e w h i l e t h e s o i l s h r a n k from b e n e a t h t h e f o o t i n g s . F a i l u r e o c c u r r e d when t h e p o i n t s of s u p p o r t had r e t r e a t e d s u f f i c i e n t l y f a r from t h e c o r n e r t o o v e r s t r e s s t h e c o n c r e t e , and t h e b r o k e n s e c t i o n d r o p p e d s u d d e n l y t h r o u g h a b o u t i n c h u n t i l t h e f o o t i n g s were a g a i n i n c o n t a c t w i t h t h e s o i l .
I n t h e l a s t t h r e e y e a r s ( 1 9 6 4 - 6 6 ) , t h e s m a l l e r v a l u e s o f e x c e s s i v e s o i l m o i s t u r e d e p l e t i o n p r o b a b l y had f u l l e f f e c t and r e s u l t e d i n r a p i d s e t t l e m e n t and s e v e r e damage.
When i t was p o i n t e d o u t t h a t t h e damage was c a u s e d by t h e t r e e s t h e owners had them removed. One y e a r l a t e r a s e c o n d l e v e l s u r v e y was c o n d u c t e d and t h e r e a d i n g s showed no f u r t h e r s e t t l e m e n t .
C o s t s
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The o r i g i n a l c o s t o f t h e h o u s e was $26,000; 9 y e a r s l a t e r e s t i m a t e s t o r e s t o r e i t t o i t s o r i g i n a l c o n d i t i o n r a n g e d between $12,000 and $30,000. When t h e f i r s t s m a l l damages began t o o c c u r i n 1959-60 t h e owners had a t t e m p t e d t o s u e t h e c o n t r a c t o r f o r f a u l t y workmanship b u t a t t h a t t i m e he was g o i n g i n t o b a n k r u p t c y and t h e o n l y r e s u l t o f l e g a l a c t i o n was a s m a l l r e d u c t i o n i n t h e f i n a l c o s t o f t h e h o u s e . Because o f t h e f u t i l i t y of f u r t h e r l e g a l a c t i o n t h e owners d e c i d e d t h a t t h e y would have t o l i v e w i t h t h e s e s e t t l e m e n t s and r e p a i r e d o n l y t h e c r a c k e d p l a s t e r and b r i c k - work.House No. 2
House No. 2 i s a l s o a bungalow, r e c t a n g u l a r i n p l a n , 25 by 50 f e e t , of wood- frame c o n s t r u c t i o n , and b r i c k v e n e e r , r e s t i n g on c a s t i n p l a c e c o n c r e t e f o u n d a t i o n w a l l s . The ground f l o o r i s s u p p o r t e d i n t h e same manner a s house No. 1 w i t h l o a d s
c a r r i e d t o i s o l a t e d f o o t i n g s on a l i n e down t h e c e n t r e o f t h e b a s e m e n t . F i g u r e 1 2 shows a p l a n view o f t h e house and i t s l o c a t i o n i n r e l a t i o n t o a l i n e of p o p l a r t r e e s on t h e s o u t h e d g e o f t h e p r o p e r t y . The s o u t h w a l l o f t h e h o u s e i s 7 f e e t away from t h e l i n e o f t r e e s which were s p a c e d a b o u t 7 f e e t on c e n t r e s .
A s a t h o u s e No. 1, t h e e l e v a t i o n s on t h e f i r s t c o u r s e o f b r i c k were measured a n d t h e r e s u l t s a r e shown i n F i g . 1 3 . A t t h e n o r t h end o f t h e w e s t w a l l n e x t t o t h e g a r a g e t h e r e d i d n o t a p p e a r t o be any s e t t l e m e n t b u t s o u t h w a r d , t o w a r d t h e l i n e o f p o p l a r t r e e s , t h e s e t t l e m e n t i n c r e a s e d u n t i l a t t h e c o r n e r i t r e a c h e d a magnitude o f 4.7 i n c h e s . Because t h e e x t e r i o r b r i c k f i n i s h was a s e r i e s o f p a n e l s t h e r e i s n o o b v i o u s c r a c k i n g i n t h e b r i c k . The d i s p l a c e m e n t s a p p e a r t o have b e e n accommodated i n t h e d o o r and window o p e n i n g s which were b a d l y d i s t o r t e d .
Along t h e s o u t h w a l l which h a s o n l y one window o p e n i n g t h e w a l l had s e t t l e d f a i r l y u n i f o r m l y b u t a l i t t l e l e s s a t t h e s o u t h e a s t c o r n e r t h a n a t t h e s o u t h w e s t . Northward, on t h e e a s t s i d e , t h e s e t t l e m e n t s d e c r e a s e d u n t i l a g a i n c l o s e t o t h e
g a r a g e t h e r e d i d n o t a p p e a r t o h a v e been any ver3t:i.cal movement. An e x a m i n a t i o n o f t h e basement w a l l s showed t h r e e c r a c k s from b o t t o m t o t o p . Two o f t h e s e o c c u r r e d on
o p p o s i t e w a l l s 30 f e e t away from t h e t r e e s and form a h i n g e l i n e f o r a l l t h e d i s p l a c e - m e n t s . The t h i r d c r a c k was i n t h e chimney f o u n d a t i o n and p r o b a b l y d e v e l o p e d b e c a u s e o f a change i n t h i c k n e s s o f t h e w a l l s e c t i o n and f o u n d a t i o n w i d t h a t t h i s p o i n t . The t e n s i l e s t r e s s e s t h a t d e v e l o p e d h e r e h a v e c a u s e d a c r a c k t h r o u g h t h e b r i c k w o r k above t h e basement w a l l ( F i g . 1 4 ) .
In t h e b a s e m e n t , c r a c k s i n t h e f l o o r were a p p r o x i m a t e l y p a r a l l e l t o t h e s o u t h w a l l i n d i c a t i n g t h a t t h e r o o t s had s p r e a d outward u n i f o r m l y from t h e l i n e o f t r e e s . U n l i k e t h e s i t u a t i o n a t house No. 1, t h i s r e s u l t e d i n t h e i s o l a t e d i n t e r i o r f o o t i n g s s e t t l i n g t h e same amount a s p o i n t s on t h e f o u n d a t i o n w a l l s t h e same d i s t a n c e from t h e t r e e s . T h i s i n t u r n meant t h a t s e r i o u s w r a c k i n g above ground l e v e l was c o n f i n e d t o t h o s e w a l l s a n d p a r t i t i o n s o r i e n t e d normal t o t h e l i n e o f t r e e s .
S o i l C o n d i t i o n s
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The h o u s e was l o c a t e d i n an a r e a i n which t h e r e was Leda c l a y (Gadd, 1 9 6 3 ) . The D r i f t T h i c k n e s s C o n t o u r map o f t h e Ottawa a r e a ( 1 9 5 9 ) i n d i - c a t e d t h a t I t was p r o b a b l y a b o u t55
t o 60 f e e t d c e p . R o r l n g s made by a s o l 1 c o n s u l t a n t conflr'mcd t h l c and showed t h a t t h e w a t e r contcnt:; were l o w c r c l o s e r t o t h e t r e e s a s wa:; found a t house No. 1. The owner a t one ::tage had d e c i d e d t o I n v e s t i g a t e b e n e a t h t h c f o u n d a t i o n s and 1)rokc t h r o u g h t h e c o n c r e t e f l o o r i n t h e basement a t a p o i n t n e a r t h c cf11rnnf:y; he found numerou:; r o o t s a t ~ o u t3
Inche:; In d i a m e t e r i n d r y c l a y .D i s c u s s i o n
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T h i s h o u s e was c o m p l e t e d i n December 1 9 6 3 and by t h e end o f t h e n e x t summer c o n s i d e r a b l e s e t t l e m e n t s had a l r e a d y o c c u r r e d . The f o l l o w i n g summer t h e y were worse and t h e owner i n i t i a t e d l e g a l p r o c e e d i n g s a g a i n s t t h e c o n t r a c t o r . By chance h e c a l l e d i n a s o i l c o n s u l t a n t who had been r e t a i n e d by h i s n e i g h b o u r a number o f y e a r s b e f o r e , f o r p r e c i s e l y t h e same t r o u b l e . U n f o r t u n a t e l y , h i s n e i g h b o u r had c h o s e n n o t t o b e l i e v e t h e c o n s u l t a n t when t o l d t h a t t h e t r e e s were most p r o b a b l y t h e c a u s e o f s e t t l e m e n t . A f t e r t h e t h i r d summer when t h e s e t t l e m e n t s had e x c e e d e d 4i n c h e s a n d h i s own h o u s e had been f u r t h e r damaged, t h e n e i g h b o u r was p e r s u a d e d t h a t t h e t r e e s s h o u l d b e t a k e n down. The maximum s o i l m o i s t u r e d e p l e t i o n s f o r t h e s e y e a r s 1964 t o 1966 were a l l g r e a t e r t h a n 7 i n c h e s . F i g u r e s 1 5 and 1 6 show t h e c o n d i t i o n s t h e h o u s e s were i n a t t h i s t i m e .
C o s t s
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E s t i m a t e s o f r e p a i r s t o r e s t o r e t h e h o u s e t o i t s o r i g i n a l c o n d i t i o n r a n g e d from $6,000 t o $12,000. The owner a t t e m p t e d t o s u e b o t h t h e c o n t r a c t o r and t h e r i e l g h b o u r , a1lerl;ing t h a t t h e Sormer s h o u l d have known when h e s o l d t h e l o t t h a t t h e tree:; were a p o t e n t i a l d a n g e r t o t h e foundation:; and t h e l a t t e r b e c a u s e he had been informed t h a t t h e t r e e r o o t s had been t h e most l i k e l y c a u s e o f damage t o h i s own h o u s e and s h o u l d have r e a l i z e d t h a t h i s n e i g h b o u r ' s new h o u s e would b e a f f e c t e d .However, f o u r y e a r s a f t e r t h e t r e e s had b e e n removed and on t h e e v e o f g o i n g t o c o u r t , t h e l a w y e r s r e p r e s e n t i n g t h e t h r e e p a r t i e s p e r s u a d e d t h e i r c l i e n t s t h a t t h e y s h o u l d e a c h s h o u l d e r a n e q u a l s h a r e of r e s p o n s i b i l i t y f o r t h e damage. The h o u s e was r e p a i r e d by t h e o r i g i n a l c o n t r a c t o r , by c a r e f u l l y j a c k i n g t h e s u p e r s t r u c t u r e i n t o a h o r i z o n t a l p o s i t i o n a n d c a p p i n g t h e f o u n d a t i o n w a l l s s o t h a t t h e t o p s were a g a i n l e v e l . The b r i c k v e n e e r , w e l l a t t a c h e d t o t h e f r a m e , r o s e w i t h t h e w a l l s when t h e s u p e r s t r u c t u r e was l i f t e d . The i n t e r i o r damage t o p l a s t e r a n d t h e f r a m e s o f d o o r s a n d windows were r e p a i r e d and i n 2; y e a r s no f u r t h e r movements h a v e o c c u r r e d .
GENERAL DISCUSSION
T h e r e a r e o t h e r known c a s e s o f d i f f e r e n t i a l s e t t l e m e n t c a u s e d by m o i s t u r e d e p l e t i o n b u t some owners a r e u n d e r s t a n d a b l y r e l u c t a n t t o l e t i t be known t h a t t h e i r h o u s e s h a v e b e e n damaged. One o r two have s u e d c o n t r a c t o r s o r t h r e a t e n e d s u i t on t h e
g r o u n d s t h a t t h e h o u s e was n o t a d e q u a t e l y b u i l t , a n d r e c e i v e d a n a d j u s t m e n t i n c o s t o r h a v e b e e n r e l e a s e d f r o m t h e c o n t r a c t t o buy t h e h o u s e . F o r most o w n e r s , t h e e x p e n s e o f c o m p l e t e r e p a i r a r e p r o h i b i - t i v e , a n d o n l y t h e o b v i o u s s i g n s o f damage a r e p a t c h e d u p . I f t h e y d o n o t r e a l i z e t h a t n e a r b y t r e e s a r e t h e c a u s e o f t h e damage, p a t c h i n g c o n t i n u e s y e a r a f t e r y e a r a n d t h e t r o u b l e i s b l a m e d on some i m a g i n a r y u n d e r - g r o u n d s t r e a m t h a t h a s s o f t e n e d t h e s o i l b e n e a t h t h e f o u n d a t i o n . More t h a n a few o w n e r s a t f i r s t r e f u s e t o b e l i e v e t h a t t r e e s c a n h a v e a n y t h i n g t o d o w i t h t h e i r s e t t l e m e n t p r o b l e m s ; one d e c i d e d , a f t e r u n d e r s t a n d i n g t h e s i t u a t i o n t h o r o u g h l y , t h a t h e would u n d e r n o c i r c u m s t a n c e s d e s t r o y t h e t r e e s a n d t h e h e would l i v e w i t h t h e s e t t l e m e n t s . T h e r e i s a l s o on r e c o r d a c a s e o f a 3 - s t o r e y i n s t i t u t i o n a l b u i l d i n g w i t h f o o t i n g s more t h a n 6 f e e t b e l o w t h e s u r f a c e t h a t h a s u n d e r g o n e s e t t l e m e n t s c a u s e d by t r e e s . E x p e r i e n c e i n d i c a t e s t h a t t h e g r e a t e s t amount o f damage i n t h e s h o r t e s t p e r i o d o f t i m e i s c a u s e d by l i n e s o f p o p l a r t r e e s , p r o b a b l y b e c a u s e t h e y a r e u s u a l l y p l a n t e d c l o s e t o g e t h e r a n d o f t e n q u i t e c l o s e t o t h e f o u n d a t i o n w a l l s . I n d i v i d u a l w i l l o w t r , e e s a r e o f t e n t h e c a u s e o f damage, b u t m a t u r e e l m t r e e s , m a p l e s a n d o t h e r r e l a t i v e l y f a s t - g r o w i n g s p e c i e s h a v e a l s o c a u s e d s e t t l e m e n t s . I n t h o s e m u n i c i p a l i t i e s w h e r e c l a y s w i t h h i g h s h r i n k a g e p o t e n t i a l a r e e n - c o u n t e r e d t h e s e p r o b l e m s w i l l c o n t i n u e . N o r m a l - s i z e b u i l d i n g l o t s , 50 by 1 0 0 f e e t ( i n s u c h a r e a s ) a r e n o t l a r g e enough t o p e r m i t t h e n e c e s s a r y c l e a r a n c e b e t w e e n f a s t - g r o w i n g t r e e s a n d a b u i l d i n g t o a v o i d t h e p r o b l e m o f s h r i n k a g e s e t t l e m e n t s . P e r s o n s may v e r y w e l l b e d e s t r o y i n g t h e i r own p r o p e r t y when t h e y p l a n t s u c h t r e e s i n o r d e r t o p r o v i d e summer s h a d e i n t h e g a r d e n . They m i g h t a l s o b e s u e d by a n e i g h b o u r i f i t c a n b e shown t h a t t h e t r e e r o o t s h a v e a f f e c t e d t h e f o u n d a t i o n o f t h e n e i g h b o u r f s h o u s e .
The c o n s t r u c t i o n o f s e w e r s a n d t h e l o w e r i n g o f t h e w a t e r t a b l e t h a t i t u s u a l l y c a u s e s i s a l s o a c o n t r i b u t i n g f a c t o r i n some a r e a s . T r e e s t h a t w e r e n o t p r e v i o u s l y c a u s i n g p r o b l e m s may now e x t e n d r o o t s y s t e m s a n d damage homes as a r e s u l t .
C O N C L U S I O N S
0 b : i e r ~ v a t i o n : ; rnadc a t t h c D l v i : , i o n of Iju l l d i n p ; Hc::oarct~ i n O t t a w a a n d t h o s e conducted e l s e w h e r e stlow t h a t bui l d i n ~ ; . ; on z h a l Low f o u n d a t 1 o n s s u p p o r t e d by c l a y s w i t h h i g h shrinkage p o t e n t i a l s car1 be : ; e v e r e l y d a n ~ a e e d by t h e p r e s e n c e o f t r e e s whose r o o t s r e a c h i n t o t h e c l a y . T r e e s t h a t c a u s e t h e most damage u n d e r t h e s e c i r c u m s t a n c e s a r e t h o s e o f f a s t - g r o w i n g s p e c i e s t h a t h a v e h i g h demands f o r m o i s t u r e d u r i n g t h e g r o w i n g s e a s o n . A m a j o r c o n t r i b u t i n g f a c t o r t o damage i s t h e l a c k o f r a i n f a l l d u r i n g t h e g r o w i n g s e a s o n . A u s e f u l e s t i m a t e o f t h e a v a i l a b i l i t y o f m o i s t u r e d u r i n g t h e g r o w i n g s e a s o n may b e o b t a i n e d f r o m w e a t h e r r e c o r d s by c a l c u l a t i n g s o i l m o i s t u r e d e p l e t i o n . Damage a p p e a r s t o o c c u r i n t h e O t t a w a a r e a a f t e r t h i s v a l u e e x c e e d s a b o u t
7
i n c h e s w a t e r . M e a s u r e m e n t s o f d i f f e r e n t i a l s e t t l e m e n t s a t two O t t a w a h o n e s w e r e i n e x c e s s o f4;
i n c h e s ; t h e s e h a d o c c u r r e d i n l e s s t h a n 1 0 y e a r s a f t e r c o n s t r u c t i o n a t o n e s i t e a n d i n l e s s t h a n4
y e a r s a t a n o t h e r . E s t i m a t e s o f r e p a i r s t o t h e s e h o u s e s r a n g e d f r o m 25 p e r c e n t t o g r e a t e r t h a n 1 0 0 p e r c e n t o f t h e i n i t i a l c o s t o f t h e h o u s e s . O b s e r v a t i o n s h a v e b e e n c a r r i e d o u t o n l y i n t h e O t t a w a a r e a b u t s i m i l a r s o i l and c l i m a t i c c o n d i t i o n s p r e v a i l i n l a r g e a r e a s o f Q u e b e c a n d O n t a r i o a n d t h e p r o b l e m is p r o b a b l y w i d e s p r e a d . Where t h e s u b s o i l i s Leda c l a y w i t h a h i g h s h r i n k a g e p o t e n t i a l , t h e p r o b l e m c a n b e a v o i d e d by t h e j u d i c i o u s p l a n t i n g o f t r e e s o f s p e c i e s t h a t grow s l o w l y . A C K N O W L E D G E M E N T S The a s s i s t a n c e o f t e c h n i c a l s t a f f a n d t h e e n c o u r a g e m e n t o f c o l l e a g u e s i n t h e G e o t e c h n i c a l S e c t i o n i s g r a t e f u l l y a c k n o w l e d g e d . T h a n k s a r e a l s o e x p r e s s e d t o t h o s e owners o f damaged homes f o r t h e i r w i l l i n g n e s s t o d i s c u s s t h e p r o b l e m s e n c o u n t e r e d , p e r m i t t e d m e a s u r e m e n t s o f s e t t l e m e n t s t o b e made, a n d g a v e p e r m i s s i o n t o u s e t h i si n f o r m a t i o n i n t h e h o p e t h a t s u c h a s s i s t a n c e m i g h t r e s u l t i n a w i d e r u n d e r s t a n d i n g o f t h e p r o b l e m and a r e d u c t i o n i n t h e i n c i d e n c e o f b u i l d i n g damage.
T h i s p a p e r i s a c o n t r i b u t i o n o f t h e 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 o f Canada, a n d i s p u b l i s h e d w i t h t h e a p p r o v a l o f t h e D i r e c t o r .
R E F E R E N C E S
1. Zimmermann, M . H . , 1 9 6 4 . Sap movements i n t r e e s . B i o r h e o l o g y , 2 : 1 5 - 2 7 . 2 . Kramer, P . J . and K o z l o w s k i , T . T . , 1 9 6 0 . P h y s i o l o g y o f T r e e s . McGraw-Hill. 3 . Ward, W . H . , 1 9 4 7 . The e f f e c t s o f f a s t g r o w i n g t r e e s and s h r u b s on s h a l l o w
f o u n d a t i o n s . J . I n s t . L a n d s c a p e A r c h i t e c t s , 1 1 : 7-16.
4 . Ward, W . H . , 1 9 5 3 . S o i l movement and w e a t h e r . P r o c . , T h i r d I n t . C o n f . S o i l Mechs. and F o u n d a t i o n E n g . , 1: 477-482.
5 .
B a r a c o s , A . and M a r a n t z , O . , 1 9 5 3 . V e r t l c a L g r o u n d movements. P r o c . , S i x t h C a n a d l a n S o i l Mechs. C o n f . , N a t . Re:;. C o u n c i l , As:;oc. Com., S o i l and Snow Mechs., T e c h . Memo. No. 2 7 .6 . J e n n i n g s , J . E . , 1 9 5 3 . The h e a v i n g o f b u i l d i n g s on d e s i c c a t e d c l a y . P r o c . , T h i r d I n t . Conf. on S o i l Mechs. 1: 390-396. 7 . Skempton, A.W., 1 9 5 4 . A f o u n d a t i o n f a i l u r e d u e t o c l a y s h r i n k a g e c a u s e d by p o p l a r t r e e s . P r o c . , I n s t . C i v i l E n g r s . 1: 3: 66-83. 8 . C o l l i n s , L . E . , 1 9 5 7 . Some o b s e r v a t i o n s o f t h e movement o f b u i l d i n g s on e x p a n s i v e s o i l s i n V e r e e n i g i n g a n d O d e n d a a l s r u s . Symposium o n E x p a n s i v e C l a y s , P t . 1 . S o u t h A f r i c a n I n s t . C i v i l E n g r s . , 7 : 273-285.
9 . B a r a c o s , A . a n d Bozozuk, M . , 1 9 5 7 . S e a s o n a l movement i n some C a n a d i a n c l a y s . P r o c . , F o u r t h I n t . C o n f . S o i l Mechs. 1: 264-268.
1 0 . Kaprow, P . P . , 1 9 6 1 . The C h a m p l a i n S e a and i t s s e d i m e n t s . S o i l s i n C a n a d a . Roy. : ; o c . Can. S p e c . p u b . 3 : 97-108. 1 1 . Urytlcn, J.ls:. and P a t r y , L.M., 1 3 6 1 . M i n e r a l o g y o f C h a m p l a i n S e a s e d i m e n t s a n d a l j i d e a u c l a y s o i l p r o f i l e . Can. J . S o i l S c i . 4 1 : 1 6 9 - 1 8 1 . 1 2 . E o z o z u k , M . and C u r n , K . N . , 1 9 6 0 . V e r t i c a l g r o u n d movements n e a r e l m t r e e s . G e o t e c h n i q u e , X : l : 1 9 - 3 2 . 1 3 . T h o r n t h w a i t e , C . W . , 1 9 4 8 . An a p p r o a c h t o w a r d a r a t i o n a l c l a s s i f i c a t i o n of c l i m a t e . G e o g r a p h i c a l Review, 3 8 : 1: 55-94. 1 4 . C r a w f o r d , C.B., 1 9 6 8 . Q u i c k c l a y s o f E a s t e r n C a n a d a . E n g i n e e r i n g G e o l o g y , 2 : 4 : 239-265. 1 5 . Gadd, N . R . , 1 9 6 2 . S u r f i c i a l g e o l o g y o f O t t a w a map-area O n t a r i o a n d Q u e b e c . G e o l . S u r v e y o f C a n . , P a p e r 62 ( 1 6 ) .
1 6 . Bozozuk, M . , 1 9 6 2 . S o i l s h r i n k a g e damages f o u n d a t i o n s a t O t t a w a , C a n a d a . Eng. J r . , 45: 7 : 33-37.
TABLE I
Year
SOIL MOISTURE DEPLETION M A X I M A N R C , OTTAWA, 1956 t o 1 9 6 7 t SMD
,
Depth o f s h r i n k a g e , E x c e s s i v e SMD, i. i n c h e s f e e t i n c h e s*
Rased upon NRC s t u d y o f s e t t l e m e n t s a d j a c e n t t o a l i n e o f e l m t r e e s .'
SMD wi.th s h r i n k a g e e f f e c t b e l o w 6 f e e t .F i g u r e
1
-
G l a c i a l M a p o f E a s t e r n C a n a d a s h o w i n g e x t e n t o f C h a m p l a i n S e a d e p o s i t s .F i g u r e
2
-
T h r e e c y l i n d e r s o f L e d a c l a ys h o w i n g e f f e c t o f c h a n g e o f w a t e r c o n t e n t ,
F i g u r e
5
-
8 0
y e a r o l d h o u s e s h o w i n g d i f f e r e n t i a l s e t t l e m e n t s c a u s e d b y s h r i n k a g e o f c l a y .@ L O C A T I O N OF B O R E H O L E S
LEVELS
-
TOP OF BASEMENT WALLI N I T I A L ELEVATION TOP OF BASEM
PARTITION
A
MAX. = 2--3"SECTION A-A
FLOOR JOISTS
SECTION B - B
BASEMENT FLOOR LEVELS
N
-
ONCRETE LOCK WALL
F i g u r e
8
-
V i e w o fS . W .
c o r n e r s h o w i n g e x t e r i o r d a m a g e a n d p r o x i m i t y o f t r e e s , H o u s e N o .1 .
F i g u r e
9
-
V i e w o f i n t e r i o r d a m a g e , H o u s e N o .1 .
F i g u r e
1 0
-
V i e w o f i n t e r i o r d a m a g e , H o u s e N o .1 .
T O T A L W A T E R C O N T E N T C H A N G E E Q U I V A L E N T T O 8 . 3 " S E T T L E M E N T 0 2 0 4 0 6 0 8 0 0 2 0 W A T E R C O N T E N T , % W A T E R C O N T E N T C H A N G E , %
F I G U R E
1 1
W A T E R C O N T E N T P R O F I L E S
-
H O U S E N O . 1
O R 6 0 7 4 - 5/
-
?
+
,
1
C H I M N E Y C R A C K S T 0 5 1 0 2 0 FEET - P R O P E R T Y L I N E-
-F I G U R E
1 2
P L A N
-H O U S E N O .
2
F i g u r e
1 4
-
C r a c k
a t
c h i m n e y ,
H o u s e N o .
2 .
F i g u r e
15
-
H o u s e N o .2
a n d l i n e o f p o p l a r t r e e s .F i g u r e
