Drought damage to Winnipeg house foundations in 1977

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Drought damage to Winnipeg house foundations in 1977

NATIONAL RESEARCH COUNCIL OF CANADA DIVISION OF BUILDING RESEARCH

DBR INTERNAL REPORT NO. 441

DROUGHT DAMAGE TD WINNIPEG HOUSE FOUNDATIONS IN 1977 by J . J . Hamilton

Checked by: Approved by: C

.

.

.

Prepared for: r e c o r d p u r p o s e s

Date: J u l y 1977

A prolonged drought i s t h r e a t e n i n g t o cause s e v e r e damage i n Winnipeg t o thousands o f small s t r u c t u r e s , such a s h o u s e s , and municipal s e r v i c e s and s t r e e t s . Many i n q u i r i e s have come t o t h e P r a i r i e Regional 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 Research i n

Saskatoon, and t o Winnipeg c o n s u l t i n g e n g i n e e r s and c o n t r a c t o r s , from homeowners wondering what t o do a b o u t d i s t o r t e d and c r a c k e d f o u n d a t i o n s . ?he p u b l i c media ( r a d i o , t e l e v i s i o n and newspaper) have made s e v e r a l r e q u e s t s f o r s t a t e m e n t s t o h e l p t h e p u b l i c under- s t a n d t h e problem and t h e a l t e r n a t i v e s a v a i l a b l e f o r r e h a b i l i t a t i n g e x i s t i n g s t r u c t u r e s o r , i n c o n s t r u c t i o n o f new s t r u c t u r e s , t o

minimize f u t u r e problems

.

On 2 3 _{March 1977, t h e w r i t e r h o s t e d a n i n f o r m a l m e e t i n g a t t h e} S h e r a t o n Carl t o n Hotel i n Winnipeg t o d i s c u s s c u r r e n t concerns a b o u t t h i s s u b j e c t . An i n v i t a t i o n was s e n t t o many who had p r e v i o u s l y a t t e n d e d t h e two-day s e m i n a r on Shallow F o u n d a t i o n s

-

C o n s t r u c t i o n a n d Performance J a n u a r y 9 and 1 0 , 1975, a t t h e Univer- s i t y o f Manitoba and co-sponsored by t h e P r a i r i e Regional 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 Research. The l i s t o f t h o s e who a t t e n d e d

i s g i v e n i n Appendix A . The l a r g e s t r e p r e s e n t a t i o n came from c o n s u l t i n g f i r m s and t h e s t a f f o f t h e U n i v e r s i t y of Manitoba. W o r e p r e s e n t a t i v e s o f t h e Canadian P o r t l a n d Cement A s s o c i a t i o n , and one each from CWC and a l a r g e g e n e r a l c o n t r a c t o r a l s o p a r t i c i p a t e d . O t h e r s made t e l e p h o n e c o n t r i b u t i o n s o r met s e p a r a t e l y w i t h t h e w r i t e r t o e x p r e s s t h e i r thoughts on t h e s u b j e c t .

?here was l e n g t h y d i s c u s s i o n o f s e v e r a l f a c e t s o f t h e c u r r e n t s i t u a - t i o n , such a s t h e s e v e r i t y o f t h e problem t o d a t e , t h e p r o b a b l e conse- quences o f c o n t i n u e d drought, and a d v i c e t h a t could b e g i v e n t o home- owners t o minimize expense and inconvenience. Some s u g g e s t i o n s were a l s o made on d e s i r a b l e d e t a i l s o f new c o n s t r u c t i o n t o minimize f u t u r e conse- quences o f b u i l d i n g on e x c e p t i o n a l l y d r y s u b s o i l s . There seemed t o b e g e n e r a l agreement on t h e f o l l o w i n g p o i n t s .

Winnipeg s u b s o i l s a r e now e x p e r i e n c i n g t h e l o n g e s t d r o u g h t c o n d i t i o n i n many y e a r s . Where d e e p - r o o t e d v e g e t a t i o n i s growing i n heavy c l a y s , s e v e r e s h r i n k a g e i s t a k i n g p l a c e t o t h e depth of r o o t i n g . Foundations l o c a t e d a t l e s s e r d e p t h s and t h e ground s u r f a c e a r e s u b j e c t t o s e t t l e - ments r a n g i n g up t o s e v e r a l i n c h e s . I f t h e drought c o n t i n u e s w e l l i n t o t h e summer o f 1977, t h e magnitude and p r e v a l e n c e o f damage t o b u i l d i n g s w i l l

i n c r e a s e g r e a t l y . Many homeowners a r e now contemplating remedial and r e p a i r measures which can r a n g e i n c o s t from a few hundred t o s e v e r a l thousand d o l l a r s . U n f o r t u n a t e l y , g u a r a n t e e s can seldom, i f e v e r , b e g i v e n t h a t no f u r t h e r damaging movements w i l l t a k e p l a c e w i t h prolonged drought o r when c l i m a t i c and s u b s o i l m o i s t u r e c o n d i t i o n s r e t u r n t o more normal a v e r a g e s . I n s p i t e o f much accumulated i n f o r m a t i o n on t h e c y c l i c and l o n g - t e r m b e h a v i o u r o f Winnipeg s u b s o i l s and shallow f o u n d a t i o n s , t h e p u b l i c has l i t t l e u n d e r s t a n d i n g o f t h e complex problem and many homeowners a r e i n d i f f e r e n t o r a r e i n c a p a b l e o f i n t e r p r e t i n g and c a r r y i n g o u t t h e n e c e s s a r y o p e r a t i n g and maintenance p r o c e d u r e s t o minimize damage and expense. The p u b l i c o f t e n h a s d i f f i c u l t y i d e n t i f y i n g whose s e r v i c e s t o o b t a i n t o a s s i s t them i n a n a l y z i n g t h e i r problem and s e l e c t i n g t h e most a p p r o p r i a t e c o u r s e o f a c t i o n . Various t r a d e s , r a n g i n g from handyman-home- r e p a i r tradesmen t o l a r g e c o n t r a c t o r s s p e c i a l i z i n g i n f o u n d a t i o n i n s t a l - l a t i o n and r e p a i r s , o f f e r s e r v i c e s r a n g i n g from minor patch-ups t o major underpinning o r r e b u i l d i n g f o u n d a t i o n s . I t i s u s u a l l y d i f f i c u l t f o r t h e p u b l i c t o l o c a t e and engage a r e p u t a b l e tradesman, c a p a b l e o f f u l l com- p r e h e n s i o n o f t h e n a t u r e o f t h e problem and o f c a r r y i n g o u t t h e most economic r e h a b i l i t a t i o n .

Even t h e most e x p e n s i v e r e p a i r jobs have o f t e n g i v e n l e s s than s a t i s f a c t o r y long- term performance. O f t e n p e r i o d i c , minor a d j u s t m e n t s t o basement columns and j u d i c i o u s 1 ands cape d r a i n a g e and i r r i g a t i o n a r e more s a t i s f a c t o r y than expensive "one-sho t" remedial measures. There a r e few c o n s u l t i n g e n g i n e e r i n g firms i n Winnipeg c a p a b l e of g i v i n g s a t i s - f a c t o r y a d v i c e o n t h e d e s i g n o f r e p a i r and maintenance work. The p u b l i c i s o f t e n n o t p r e p a r e d t o pay a d e q u a t e l y f o r such p r o f e s s i o n a l s e r v i c e s and t h e firms a r e n o t s t a f f e d t o h a n d l e l a r g e nwnbers o f such i n q u i r i e s d u r i n g t h e s e i n f r e q u e n t c l i m a t i c extremes. There i s a p p a r e n t l y no

p u b l i c agency t o g i v e i n f o r m a t i o n and a d v i c e t o t h e p u b l i c , a l t h o u g h t h e magnitude o f damage may r e a c h d i s a s t r o u s p r o p o r t i o n s i n coming months.

A l l who a t t e n d e d t h e meeting, and o t h e r s who phoned i n t h e i r

comments, a g r e e d t h a t a n o n - s e n s a t i o n a l s t a t e m e n t , aimed a t t h e a v e r a g e householder, should b e i s s u e d t o t h e media. The i n t e n t o f t h e s t a t e m e n t should b e t o a l l a y undue f e a r s , t o g i v e a f a c t u a l d e s c r i p t i o n o f t h e problem i n laymanls terms, and t o d e s c r i b e a l t e r n a t e s a v a i l b l e t o t h e average c i t i zen. P r o f e s s o r Andrew Baracos had b e e n approached r e c e n t l y by one o f t h e c o l u m n i s t s o f t h e d a i l y Winnipeg Tribune t o p r e p a r e such a

s t a t e m e n t . P r o f e s s o r Baracos o f f e r e d t o p r e p a r e t h i s , b a s e d on t h e consensus o f t h i s d i s c u s s i o n and on h i s many y e a r s o f e x p e r i e n c e w i t h such problems i n Winnipeg. H i s e x c e l l e n t l e t t e r t o M r . Val Werier o f t h e Winnipeg Tribune i s i n c l u d e d i n t h i s r e p o r t , w i t h h i s p e r m i s s i o n , a s Appendix B .

I n h i s f i n a l paragraph, P r o f e s s o r Baracos mentions pamphlets a v a i l - a b l e from t h e D i v i s i o n o f B u i l d i n g Research; The p u b l i c a t i o n s S e c t i o n of t h e D i v i s i o n o f B u i l d i n g Research have b e e n a s k e d t o s e n d t h e

f o l l o w i n g DBR p u b l i c a t i o n s t o anyone from t h e Winnipeg a r e a r e q u e s t i n g i n f o r m a t i o n on "house f o u n d a t i o n s on s w e l l i n g clays1' _: Canadian B u i l d i n g D i g e s t s 12, 62, 80, 84, 148 and 184 and B u i l d i n g Research Note 100. Names and a d d r e s s e s o f t h o s e a s k i n g f o r t h e s e p u b l i c a t i o n s w i l l b e s e n t t o t h e D i v i s i o n s P r a i r i e Regional S t a t i o n f o r follow-up.

I f t h e d r o u g h t p e r s i s t s w e l l i n t o t h i s summer, and i f proposed w a t e r r a t i o n i n g f u r t h e r r e s t r i c t s t h e amount of i r r i g a t i o n t h a t h o u s e h o l d e r s can c a r r y o u t , t h e s i t u a t i o n could become very s e r i o u s f o r thousands o f houses i n t h e Lake Agassiz Basin. More formal o r g a n i z a t i o n o f and more

c o n c e r t e d a c t i o n by p r o f e s s i o n a l s i n t h e b u i l d i n g i n d u s t r y , l e g i s l a t i v e and r e g u l a t o r y a g e n c i e s , and municipal a u t h o r i t i e s w i l l b e n e c e s s a r y . The r e t u r n t o more normal p r e c i p i t a t i o n c o u l d l i m i t t h e magnitude o f t h i s d i s a s t e r - i n - the-making, b u t would n o t e l i m i n a t e a s e r i o u s c h a i n o f e v e n t s which h a s a l r e a d y s t a r t e d .

APPENDIX A LIST OF ATTENDEES Baracos, P r o f . A . , Burgess, N e i l C r o s i e r , A . , Dyregrov, A . O . , F r a s e r , A . , Graham, P r o f . J . , G u l a h u s s e i n , M . E . , Hamilton, J . J . Hodgins, J a c k Rogowsky, D . , Rooke, W . G . , Wodell, R . , Zwarich, D r . M.A., U n i v e r s i t y o f Manitoba R.M. Hardy _E A s s o c i a t e s C r o s i e r K i l g o u r

6

C e n t r a l Mortgage and Housing C o r p o r a t i o n U n i v e r s i t y o f Manitoba. Norenco A s s o c i a t e s L t d . N a t i o n a l Research Counci 1 Poole C o n s t r u c t i o n L t d . U n i v e r s i t y o f Manitoba Canadian P o r t l a n d Cement A s s o c i a t i o n Canadian P o r t l a n d Cement A s s o c i a t i o n U n i v e r i s t y o f Manitoba

HAD DISCUSSION WITH J . J . HAMILTON SEPARATELY

D a l k i e , H . A .

Domaschuk, P r o f . L .

APPENDIX B

?HE UNIVERSITY O F MANITOBA DEPARTMENT OF CIVIL ENGINEERING

LIUNIVERSITE DE MANITOBA DEPARTEMENT DE GENIE CIVIL

WINNIPEG, CANADA R3T 2N2 March 25, 1977 M r . Val W e r i e r , Winnipeg T r i b u n e , Winnipeg, Manitoba. Dear M r . W e r i e r :

You had a s k e d me t o comment on p o s s i b l e problems Winnipeg home owners may f a c e from t h e e f f e c t s of a l e n g t h y d r y p e r i o d , on house f o u n d a t i o n s . I t h i n k most o f y o u r r e a d e r s a r e aware t h a t s o i l s o v e r much o f t h e Winnipeg a r e a s w e l l when t h e y become wet a n d s h r i n k on d r y i n g . The w e t t i n g o c c u r s from r a i n f a l l , snow-melt a n d lawn w a t e r i n g . During d r y p e r i o d s , e v a p o r a - t i o n and t h e w a t e r demand o f t r e e s and o t h e r v e g e t a t i o n , c a u s e d r y i n g .

S t u d i e s have shown t h a t t h e t o p 10 t o 12 f e e t o f s o i l below ground s u r f a c e can b e a f f e c t e d . House f o u n d a t i o n s w i l l move upwards (heave) when t h e s o i l underneath s w e l l s , and move downwards ( s e t t l e ) , when t h e s o i l s h r i n k s . Most l o c a l h o u s e s w i t h basements a l s o undergo h e a v i n g f o r

s e v e r a l y e a r s a f t e r t h e basement h a s been e x c a v a t e d . T h i s o c c u r s b e c a u s e t h e w e i g h t o f t h e house i s c o n s i d e r a b l y l e s s than t h e weight o f t h e s o i l s removed f o r t h e basement. C a r e f u l measurements on my own house b u i l t i n 1961, show t h a t t h e basement w a l l s have heaved a b o u t 7 i n c h e s , and t h e basement f l o o r a b o u t 4 i n c h e s more. Winnipeg g e o t e c h n i c a l ( s o i l s )

e n g i n e e r s have r e p o r t e d many s i m i l a r examples o f t h i s g e n e r a l l y common s i t u a t i o n . The movements can t a k e p l a c e p r a c t i c a l l y u n d e t e c t e d w i t h no harm t o t h e house, a s l o n g a s t h e basement w a l l s and t h e basement

i n t e r i o r p o s t s , a l l move up by t h e same amount, o r down by t h e same amount. Houses b u i l t t o C . M . H . C . o r C i t y o f Winnipeg code r e q u i r e m e n t s

i n t h e l a s t 2 5 y e a r s o r so, have b e e n d e s i g n e d t o t a k e i n t o a c c o u n t t h e e f f e c t s o f p o s s i b l e heave o r s e t t l e m e n t . Some o l d e r houses a s a r e s u l t o f p r e v i o u s damage, may have had a l t e r a t i o n s t o make them l e s s p r o n e t o damage

.

The s e c r e t o f s u c c e s s i s t o make s u r e a l l p a r t s o f t h e house move up, o r down by t h e same amount. The o n l y e x c e p t i o n is w i t h t h e basement f l o o r which i s u s u a l l y d e s i g n e d t o move up and down independently. T h i s i t w i l l u s u a l l y do, and i n t h e p r o c e s s i t may unavoidably c r a c k , and "hwrrp-~p'~ i n t h e middle. T h i s h a s t o b e a c c e p t e d a s p a r t o f t h e c o s t o f

The following a r e some simple s t e p s a home owner s h o u l d t a k e t o avoid s e r i o u s damage:

1. Be aware o f t h e symptoms t h a t t h e house i s s e t t l i n g o r heaving unevenly.

These i n c l u d e :

*

* Formation o f new c r a c k s , o r i n c r e a s e i n t h e s i z e o f o l d c r a c k s i n p l a s t e r w a l l s , c e i l i n g s , stucco, and basement w a l l s .

*

I f you n o t i c e t h e s e symptoms, check t h e main beams i n t h e basement. These a r e u s u a l l y o f t i m b e r (sometimes o f s t e e l ) , t h a t a r e

supported on p o s t s , and i n t u r n s u p p o r t t h e upper p a r t o f t h e house. The underside o f t h e beam should b e s t r a i g h t ( n o t neces- s a r i l y l e v e l ) , f o r t h e e n t i r e l e n g t h of t h e beam. I f t h e beam has a hump o r d i p , t h e p o s t s s u p p o r t i n g t h e beam w i l l r e q u i r e a d j u s t - ment. I n most houses, t h e s e p o s t s have a screw- jack top which

w i l l r a i s e o r lower t h e beam. I n some o t h e r houses t h a t have wooden p o s t s , i t may b e a d v i s a b l e t o r e p l a c e t h e wooden p o s t s w i t h

a d j u s t a b l e p o s t s , i f adjustment i s n e c e s s a r y .

The job o f a d j u s t i n g t h e p o s t s i s f o r a c a r p e n t e r o r a handiman who i s f a m i l i a r w i t h t h e jacks and t h e i r o p e r a t i o n . Unless t h e a m u n t o f adjustment r e q u i r e d i s small, say less than 1/4 inch, t h e adjustment should b e made i n s t a g e s o v e r a p e r i o d o f a few weeks t o a v o i d sudden damaging s t r a i n s t o t h e b u i l d i n g frame. 3 . _{I f you have p a r t i t i o n s i n t h e basement, t h e s e should n o t extend}

t i g h t between basement f l o o r and c e i l i n g . I n some c a s e s , even where s p a c e had been provided between t h e t o p o f t h e p a r t i t i o n and

t h e c e i l i n g , e x c e s s i v e basement f l o o r heave may have c l o s e d t h i s space. With no s p a c e , t h e p a r t i t i o n pushes up a g a i n s t t h e c e i l i n g and w i l l g i v e t h e "symptoms" of t r o u b l e a l r e a d y mentioned. Such troublesome p a r t i t i o n s should b e removed o r s h o r t e n e d i n h e i g h t . 4 . You should check t h e s i z e and proximity of t r e e s c l o s e t o t h e

house. What was once a small shrub can now b e a g i a n t w i t h r o o t s e x t e n d i n g t o , and below t h e f o u n d a t i o n s . During dry p e r i o d s , t h e r o o t s w i l l e x t r a c t l a r g e q u a n t i t i e s o f w a t e r f r o m t h e s o i l , and l i t e r a l l y cause s e v e r a l i n c h e s of s e t t l e m e n t . That p a r t of t h e house n e a r e s t t h e t r e e s e t t l e s m o r e , with r e s u l t i n g c r a c k s i n t h e basement w a l l s , s t u c c o , p l a s t e r , e t c . Research h a s shown t h a t t r e e s can a f f e c t b u i l d i n g s t o a d i s t a n c e from t h e t r e e equal t o t h e h e i g h t o f t h e t r e e . F a s t growing t r e e s a r e t h e w o r s t o f f e n - d e r s . I would be i n c l i n e d t o remove any t r e e t h a t i s c l o s e r t h a n a b o u t 10 t o 1 2 f e e t from t h e house, and even f u r t h e r if i t

appears t o b e damaging t h e house. I t i s a l s o p o s s i b l e by deep- w a t e r i n g t o p r e v e n t t h e t r e e r e m v i n g w a t e r from t h e s o i l . Deep w a t e r i n g r e q u i r e s t h a t h o l e s b e d r i l l e d t o depths o f 10 t o 1 2

r o o t s . The h o l e s can b e d r i l l e d w i t h a 4 t o 6 _{i n c h a u g e r , and}

f i l l e d w i t h c l e a n g r a v e l . The g r a v e l i s k e p t s a t u r a t e d by w a t e r i n g . A l o t o f work i s e n t a i l e d .

5 . Ille ground around t h e house s h o u l d b e examined. You may f i n d t h a t an o p e n i n g h a s formed i n t h e ground where t h e s o i l h a s shrunk away from, and exposed t o c o n s i d e r a b l e d e p t h , t h e s i d e o f t h e basement w a l l . I t i s a wise p r e c a u t i o n t o a v o i d h a v i n g s o i l f a l l i n t o t h e opening and on no a c c o u n t s h o u l d s a n d o r o t h e r s o i l b e used t o f i l l t h e o p e n i n g . A damaging push a g a i n s t t h e basement w a l l can develop i f t h e c r a c k h a s been f i l l e d and t h e s o i l becomes wet and t r i e s t o s w e l l . P i e c e s o f f i b r e g l a s s i n s u l a t i o n s t u f f e d i n t o t h e t o p o f t h e c r a c k w i l l keep t h e s o i l from f a l l i n g i n . The i n s u l a - t i o n w i l l a l s o h e l p t o keep t h e basement warm. There can b e a g r e a t d e a l o f h e a t l o s s through a basement w a l l . A slow lawn s p r i n k l i n g , o r r a i n can s u p p l y enough m o i s t u r e t o c l o s e t h e c r a c k . The lawn s p r i n k l i n g s h o u l d b e done f o r a s t r i p s e v e r a l f e e t wide a l o n g t h e s i d e s o f t h e h o u s e .

6 . _{I t i s good p r a c t i c e t o have sod, f l o w e r b e d s , e t c . around t h e}

house s l o p i n g upwards towards t h e house. A s l o p e r i s i n g 4 i n c h e s i n about 4 f e e t w i l l keep r a i n w a t e r and snow-melt from f l o w i n g towards t h e basement w a l l . Water from r a i n s p o u t s s h o u l d n o t p o u r towards t h e h o u s e . You may have t o i n s t a l l h o r i z o n t a l e x t e n s i o n s t o t h e down s p o u t s t o c a r r y t h e w a t e r away. These measures w i l l

h e l p a v o i d l o c a l wet s p o t s which w i l l c a u s e some p a r t s o f t h e house t o heave unevenly. I t a l s o h e l p s p r e v e n t basement f l o o d i n g

from e x c e s s i v e w a t e r e n t e r i n g t h e weeping t i l e d r a i n s around t h e house d u r i n g heavy r a i n s .

7 . A word o f c a u t i o n i f you a r e c o n t e m p l a t i n g u n d e r - p i n n i n g w i t h p i l e s , mud-jacking, o r o t h e r s i m i l a r t e c h n i q u e s . These c o n s t i t u t e "major s u r g e r y " which s h o u l d b e u n d e r t a k e n only w i t h competent e n g i n e e r i n g o r a r c h i t e c t u r a l a d v i c e . The n a t u r e o f such work r e q u i r e s t h e p r e p a r a t i o n o f drawings showing t h e number o f p i l e s , s i z e a n d l e n g t h , l o c a t i o n , and amount o f s t e e l r e i n f o r c e m e n t r e q u i r e d , e t c . I t i s a l s o n e c e s s a r y t o e v a l u a t e whether such measures w i l l p r o v e e f f e c t i v e . Wrongly used, t h e measures can even b e t h e c a u s e o f f u t u r e damage when e x c e s s i v e l y wet c l i m a t i c c o n d i t i o n s r e t u r n . I t s h o u l d b e n o t e d t h a t u n d e r - p i n n i n g , mud- j a c k i n g , e t c . a r e n o t u s u a l l y r e q u i r e d .

I hope t h e above i n f o r m a t i o n w i l l b e o f some h e l p t o your r e a d e r s . S e v e r a l pamphlets a r e a v a i l a b l e from t h e D i v i s i o n o f B u i l d i n g Research, N a t i o n a l Research C o u n c i l , Ottawa, KIA O R 6 . They can b e o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n and r e q u e s t i n g i n f o r m a t i o n on

"House foundations on swell i n g clays". We do r e s e a r c h a t t h e U n i v e r s i t y on t h i s problem b u t u n f o r t u n a t e l y o u r commitments do n o t normally permit

u s t o g i v e advice t o i n d i v i d u a l home owners.

S i n c e r e l y yours,

(signed) A . Baracos, P r o f e s s o r ,