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Ice damage to Wilkes Avenue Reservoir, Winnipeg, Manitoba
N A T I O N A L R E S E A R C H COUNCIL CANADA
DIVISION O F BUILDING R E S E A R C H
ICE DAMAGE T O WILKES A V E N U E RESERVOIR, WINNIPEG, MANITOBA L . W. Gold I n t e r n a l R e p o r t N o . 272 o f the 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 O T T A W A M a y
1963
P R E F A C E
T h i s r e p o r t i s a r e c o r d of f u r t h e r c o - o p e r a t i v e w o r k by e n g i n e e r s in the public s e r v i c e of Winnipeg and the Division of Building R e s e a r c h of the National R e s e a r c h Council of Canada. T h e r e p o r t d e a l s with a m o s t unusual c a s e of d a m a g e due to i c e , brought to the attention of DBR/NRC by Mr. N.S. Bubbis, D i r e c t o r of the Waterworks and Waste D i s p o s a l Division of the Metropolitan Corporation of G r e a t e r Winnipeg
.
The m a t t e r w a s c l e a r l y of s u c h i m p o r t a n c e and unusual i n t e r e s t that a r r a n g e m e n t s w e r e m a d e f o r L o r n e W. Gold, Head of the Snow and Ice Section of the Division, to m a k e a s p e c i a l v i s i t to Winnipeg in o r d e r to inspect the r e s e r v o i r in which the d a m a g e had o c c u r r e d . T h i s r e p o r t contains a r e c o r d of h i s o b s e r v a t i o n s and of the deductions he h a s m a d e .
M r . Gold was g r e a t l y a s s i s t e d , by Mr. Bubbis and by M r . W. D. H u r s t , City E n g i n e e r of Winnipeg and m e m b e r s of t h e i r r e s p e c t i v e staffs. Acknowledgement of t h i s a s s i s t a n c e and of the keen d e s i r e of a l l c o n c e r n e d to get to the r o o t of the p r o b l e m i s gratefully acknowledged. T h i s co- o p e r a t i v e attitude, in the public i n t e r e s t , h a s c h a r a c t e r i z e d a l l the Division' s m o s t happy a s s o c i a t i o n s with municipal e n g i n e e r i n g p r o b l e m s in Winnipeg, now extending o v e r m o r e than a decade.
T h e d a m a g e c a u s e d by i c e to the lining of the Wilkes Avenue r e s e r v o i r i s c e r t a i n l y the m o s t unusual of t h e s e p r o b l e m s . No s i m i l a r c a s e of i c e damage i s known to the Division. Accordingly, the Division hopes that i t m a y be p r i v i l e g e d to publish in due c o u r s e a s u m m a r y account of this investigation i n the s c i e n t i f i c p r e s s f o r g e n e r a l benefit. In this way, the p r o b l e m s of one agency c a n be t r a n s l a t e d into c o n s t r u c - tive a s s i s t a n c e to public a g e n c i e s g e n e r a l l y .
M r . Gold's investigation d e m o n s t r a t e s that the unusual t e m p e r a - t u r e r i s e in the Winnipeg a r e a on 5 F e b r u a r y 1963 was a l m o s t c e r t a i n l y the c a u s e of the d a m a g e to the lining of the Wilkes Avenue r e s e r y o i r and s o of the consequent i n c r e a s e d leakage. Although r e l e v a n t m e t e o r o l o g i c a l r e c o r d s have not been studied in any d e t a i l , the sudden r i s e of 40 d e g r e e s
I?.
c a n be d e s c r i b e d a s phenomenal. Coming a s i t did when the i c e cover on the r e s e r v o i r w a s s o thick, the consequences could not have been f o r e s e e n in the light of p r e v i o u s o p e r a t i n g ' e x p e r i e n c e s with Winnipeg's open r e s e r v o i r s .The p o s s i b i l i t y of p r e v e n t i n g a r e c u r r e n c e of . s u c h d a m a g e , should e v e r a s i m i l a r combination of c i r c u m s t a n c e s r e c u r , i s suggested involving the utilization of the h e a t in the w a t e r e n t e r i n g the r e s e r v o i r .
Whether t h i s i s a n economic possibility o r not will r e q u i r e c a r e f u l engineering a s s e s s m e n t , and t h i s i s naturally an inquiry that m u s t be left to the Metropolitan Commis sion authorities. The Division will be glad to a s s i s t , if it can, with any s u c h study, the r e s u l t s of which it will follow with unusual i n t e r e s t .
Ottawa May 1963
R o b e r t F. Legget D i r e c t o r
ICE DAMAGE TO WILKES AVENUE RESERVOIR, WINNIPEG. MANITOBA
L. W. Gold
On 3 F e b r u a r y 1963, a rapid i n c r e a s e was o b s e r v e d in the r a t e of leakage f r o m the Wilkes Avenue r e s e r v o i r in Winnipeg. Inspec- tion of the r e s e r v o i r showed that the upper row of c o n c r e t e s l a b s lining the c e l l s had been pushed upwards p a r a l l e l to the embankment s l o p e s on the n o r t h , west and e a s t s i d e s , a s shown in F i g u r e s 1 and 2.
During the day, the a i r t e m p e r a t u r e had r i s e n rapidly f r o m a low of 5 ° F midnight of 4 F e b r u a r y to a high of 4 5 ° F a t 4:30 in the afternoon of 5 F e b r u a r y . The obvious association of the i n c r e a s e d r a t e of leakage with the r i s e in a i r t e m p e r a t u r e led the Waterworks and Waste Disposal Division of the Metropolitan Corporation of G r e a t e r Winnipeg to consider i c e t h r u s t a s the possible cause of the damage. In r e s p o n s e to a r e q u e s t f r o m The Metropolitan Corporation to the Division of Building R e s e a r c h of the National R e s e a r c h Council, the author visited the r e s e r - voir on 12 and 1 3 F e b r u a r y to study the ice conditions and damage. This r e p o r t contains a r e c o r d of the observations made in t h i s study, and p r e s e n t s the conclusions drawn f r o m these observations. '
D e s c r i p t i o n of R e s e r v o i r
The Wilkes Avenue r e s e r v o i r h a s two c e l l s . The c e l l s a r e r e c t a n g u l a r in shape with dimensions about 800 by 600 by 23 ft. They a r e constructed in Winnipeg clay, the bottom of the c e l l s being about
12 ft below the o r i g i n a l ground s u r f a c e . Embankments, with s l o p e s of 1:3, w e r e constructed around the c e l l s by rolling and compacting s e l e c t e d m a t e r i a l f r o m the excavation.
The c e l l s a r e lined with concrete s l a b s 19 ft 6 in. square and 6 in. thick. Those on the bottom of e a c h c e l l a r e nonreinforced;cthose in the f i r s t two rows up the side a r e reinforced a t 18-in. c e n t r e s . The bottom s l a b s and those of the f i r s t two rows w e r e placed d i r e c t l y on the clay.
The reinforcing in the upper row of s l a b s i s a t 9-in. c e n t r e s . T h e s e s l a b s w e r e placed on top of a 12-in thick fine aggregate f i l t e r blanket with a d r a i n underlying and p a r a l l e l to the lower edge. A sub- g r a d e p a p e r was placed between the s l a b and the f i l t e r blanket. These g e n e r a l d e t a i l s of the r e s e r v o i r s a r e shown in F i g u r e 3.
The joints between the s l a b s w e r e s e a l e d with a 6-in. P.
V.
C. w a t e r s t o p and filled with a sealing compound (thiokol). T h e upper row of s l a b s w a s dowelled to the second row with -in. d i a m e t e r plain s t e e l b a r s 24 in. long on 18-in. c e n t r e s . The portion of the dowels in the upper s l a b w e r e coated with a s p h a l t to d e s t r o y the bond.Water i s brought t o the r e s e r v o i r f r o m Shoal L a k e , a d i s t a n c e of about 90 m i l e s . It e n t e r s the s o u t h c e l l ( # l ) a t the bottom along the south e d g e , through a 54-in. d i a m e t e r h e a d e r . Water p a s s e s out of the h e a d e r through t h r e e 36-in. d i a m e t e r h o l e s located a t the e a s t and w e s t e n d s and c e n t r e of the c e l l . Water flows f r o m the south c e l l to the n o r t h c e l l (#2) through t h r e e 48-in. d i a m e t e r p i p e s located a t the e a s t end, c e n t r e and w e s t end of the dividing embankment. At p r e s e n t , the c e l l s a r e operating in s e r i e s , the w a t e r being withdrawn f r o m the n o r t h c e l l .
The capacity of e a c h c e l l i s about 40 million gallons. The p r e s e n t flow r a t e i s about 10 mgd. T h i s flow r a t e changes slowly s o that i t is n o r m a l f o r the w a t e r elevation to be a t i t s m a x i m u m , about 18. 5 ft a t the beginning of e a c h week and m i n i m u m a t about 17. 5 f t a t the end of e a c h week. The weekly fluctuation in l e v e l is between 8 and 12 in.
P r e v i o u s P e r f o r m a n c e
T h e r e s e r v o i r w a s designed and the c o n s t r u c t i o n s u p e r v i s e d by the E n g i n e e r i n g D e p a r t m e n t of the City of Winnipeg. It w a s completed and filled in the s u m m e r of 1960. During the f i r s t w i n t e r , leakage was o b s e r v e d . T h i s was c o n s i d e r e d t o be due to the opening of a v e r t i c a l joint in the s o u t h e a s t c o r n e r of c e l l #2. T h i s w a s r e p a i r e d in the s u m m e r of 1961. In the f a l l of 1961, the r a t e of leakage was about 10, 000 gal/day. In J a n u a r y 1962 the r a t e of leakage i n c r e a s e d to about 1 mgd. It w a s e s t i m a t e d that the i c e thickness at that t i m e w a s in e x c e s s of 24 in.
In
the s p r i n g of 1962 i t w a s found that d a m a g e had o c c u r r e d at the joint between the f i r s t and second row of s l a b s . Spalling of h e c o n c r e t e was o b s e r v e d above and in the vicinity of the dowel locations. T h e l e a k s between the f i r s t and second row of s l a b s w e r e located by lowering the w a t e r l e v e l in one c e l l to just below the upper joint l e v e l and backing up w a t e r in the u n d e r d r a i n a g e s y s t e m using the head a v a i l - able f r o m the second c e l l , the w a t e r l e v e l of which w a s just above theelevation of the top joint. In the s u m m e r of 1962, the damaged locations w e r e r e p a i r e d and r e s e a l e d with thiokol. The r a t e of leakage in the f a l l of 1962 w a s again about 10,000 gal/day.
ÿ bout 15 D e c e m b e r the r a t e of leakage s t a r t e d to i n c r e a s e again. The i c e t h i c k n e s s a t this t i m e w a s e s t i m a t e d to be about 1 5 in. BY 1 5 J a n u a r y 1963 the r a t e of leakage w a s about 2 mgd. At this t i m e the r a t e of leakage was o b s e r v e d to fluctuate with w a t e r l e v e l , being g r e a t e s t when w a t e r level w a s highest. The initial i n c r e a s e in r a t e of leakage on 17 D e c e m b e r was a s s o c i a t e d with a n i n c r e a s e in w a t e r l e v e l f r o m about 17. 7 ' t o 1 8 . 6 f t . J u s t p r i o r to the d a m a g e done on 5 F e b r u a r y the r a t e of leakage w a s about 2 . 8 mgd. The o b s e r v e d r a t e of leakage and w a t e r l e v e l f r o m 11 D e c e m b e r 1962 to
9
F e b r u a r y 1963, a r e given in F i g u r e 4. Daily m a x i m u m and m i n i m u m a i r t e m p e r a t u r e s f o r the s a m e p e r i o d a r e given in F i g u r e 5.T h e i c e t h i c k n e s s on 5 F e b r u a r y was between 34 and 36 in. T h e r e w a s no snow on the ice. The day w a s v e r y sunny.
Condition of Ice, 12 F e b r u a r y
A v i s i t w a s m a d e to the r e s e r v o i r on the a f t e r n o o n of 12 F e b r u a r y . Snowfall and drifting snow had o c c u r r e d s i n c e 5 F e b r u a r y . T h e i c e was about 50 p e r cent snow c o v e r e d ; about of the p e r i m e t e r w a s sufficiently f r e e of snow for p u r p o s e s of observation,
The i c e w a s o b s e r v e d to be v e r y c l e a r to within about 40 ft of the edge. Around the p e r i m e t e r of e a c h c e l l , t h e r e w a s a band o f ' white i c e a t the s u r f a c e about 40 ft wide. Two l i n e s of c r a c k s p a r a l l e l to the edge w e r e o b s e r v e d in the i c e cover a t exposed locations; one w a s about 40 ft out f r o m the i c e edge and the second about 8 ft. The c r a c k about 40 ft f r o m the edge w a s o b s c u r e d a t many locations by w a t e r that had flooded the s u r f a c e and r e f r o z e n .
O b s e r v a t i o n s m a d e by e n g i n e e r s of the Metropolitan C o r p o r a - tion of G r e a t e r Winnipeg subsequent to 12 F e b r u a r y showed that the i c e f r o m the edge to the 8-ft line of c r a c k s w a s a l m o s t horizontal. It was sloped between the 8-ft and 40-ft line and beyond the 40-ft line w3s a l m o s t h o r i z o n t a l again. Both lines of c r a c k s w e r e in the o r d e r of in. wide at the s u r f a c e .
The top s u r f a c e of the i c e c o v e r was highly c r a c k e d , the c r a c k s f o r m i n g no obvious p a t t e r n within a n a r e a about 10 ft to a n edge. The polygons f o r m e d by the c r a c k s had edges of the o r d e r of
6
in. long.C r a c k s could be s e e n within the i c e and p r e s u m a b l y at the bottom s u r f a c e . T h e c r a c k d e n s i t y a t s o m e s i t e s within the i c e w a s s o g r e a t that f r o m the upper s u r f a c e they a p p e a r e d a s long white bands. The i c e s u r f a c e a p p e a r e d g e n e r a l l y uneven, but the a p p e a r a n c e m a y have been due in p a r t to the p r e s e n c e of i n t e r m i t t e n t shallow snow d r i f t s .
It was r e p o r t e d that on v i s i t s to the r e s e r v o i r p r i o r t o 5 F e b r u a r y w a t e r had been s e e n coming to the s u r f a c e in the vicinity of the 40 - f t c r a c k l i n e , and flooding the s u r f a c e between the c r a c k and the edge. T h i s flooding accounts for the white ice and why the c r a c k 40 ft f r o m the edge was not c l e a r l y visible a t a l l exposed s ~ t e s . An exposed s e c t i o n of the ice cover in c e l l #2 showed 8 l a y e r s of white i c e making up a t o t a l thickness of about 8 in. ( F i g u r e 6 ) . The o b s e r - vations made subsequent to 12 F e b r u a r y showed that along the n o r t h wall the white ice w a s about 5 in. thick in the vicinity of the 8-ft line
c r a c k and about 3 in. adjacent to the 40-ft line.
Locations w e r e o b s e r v e d along the n o r t h wall of r e s e r v o i r #2 w h e r e the ice had pulled away f r o m the c o n c r e t e s l a b . Some fine sand w a s found on the ice s u r f a c e and this was c o n s i d e r e d to be loose sand deposited on the s l a b in the f a l l . The s u r f a c e of the ice showed no s i g n s of having s l i d on the c o n c r e t e . M a r k s on the c o n c r e t e s u r f a c e w e r e t l m i r r o r e d ' l in the ice s u r f a c e . After the damage w a s d i s c o v e r e d on 5 F e b r u a r y the w a t e r l e v e l was lowered about 3 ft o v e r a p e r i o d of two d a y s . It i s c o n s i d e r e d that the i c e pulled away f r o m the s l a b when the w a t e r level w a s lowered.
Damage O b s e r v a t i o n s a f t e r 5 F e b r u a r y
The movement of the upper row of s l a b s w a s p a r a l l e l to the embankment s i d e s . The amount v a r i e d , but a p p e a r e d to be about 6 in. along the n o r t h wall of c e l l #2 ( F i g u r e 1 ) . O b s e r v a t i o n s by a d i v e r between 5 and 12 F e b r u a r y in c e l l #2 showed s e p a r a t i o n s of between
5 and 10 in. a t s o m e points. B e c a u s e of the lowering of the w a t e r l e v e l , the bottom of the ice was so c l o s e to the joint between the s l a b s that v i s u a l inspection w a s difficult. The joint between the second and t h i r d row of s l a b s w a s found to be open 1/16 to 1/8 in. with two locations being found w h e r e i t w a s open between
$
and in.After 12 F e b r u a r y s i x h o l e s w e r e chopped in the i c e c o v e r of
1
c e l l #1, to allow a d i v e r to i n s p e c t the joint between the f i r s t and second row of s l a b s . At e a c h of the holes the joint w a s open; the m i n i m u m opening o b s e r v e d w a s
$
in. and the m a x i m u m 4 in. The m i n i m u m openings w e r e a t the southeast c o r n e r of the c e l l and the m a x i m u m along the n o r t h and w e s t walls.McPhillip S t r e e t R e s e r v o i r
The McPhillip S t r e e t r e s e r v o i r , containing two c e l l s , w a s c o n s t r u c t e d i n 1930. The following comments a r e p r e s e n t e d on the
p e r f o r m a n c e of this r e s e r v o i r b e c a u s e they a r e r e l e v a n t to what o c c u r r e d
The c e l l s of the McPhillip S t r e e t r e s e r v o i r w e r e c o n s t r u c t e d in much the s a m e way a s at Wilkes Avenue except that the s l a b s a r e l a r g e r (about 45 ft by 25 f t by 6 in. ), the r e i a f o r c i n g i s on 18-in. c e n t r e s in a l l s l a b s and t h e r e i s no sand f i l t e r blanket behind the top row. The capacity of e a c h c e l l i s about 20 mg. Water i s brought f r o m a c o v e r e d r e s e r v o i r into one of the c e l l s through a 36-in. pipe and a t one location only. It i s fed f r o m that c e l l into the second through a single 36-in. pipe. The pumping r a t e when f i r s t put into o p e r a t i o n w a s about 10 mgd and i s a t p r e s e n t about 1 5 mgd.
The upper row of s l a b s in both c e l l s i s badly d e t e r i o r a t e d . The s l a b s a r e c r a c k e d horizontally, p a r a l l e l to the 45-ft edge of the s l a b . The c r a c k s a r e located a p p r o x i m a t e l y between the m i n i m u m and m a x i m u m w a t e r depth prevailing in the c e l l s in w i n t e r , and w e r e a t t r i - buted to s o i l movement and f r o s t action.
B e c a u s e the w a t e r flow into the McPhillip S t r e e t r e s e r v o i r i s r e a s o n a b l y l a r g e r e l a t i v e to i t s capacity, and e n t e r s e a c h c e l l a t one place only, t h e r e i s sufficient mixing to bring the w a r m e r w a t e r to the s u r f a c e at the place w h e r e i t e n t e r s the c e l l , and thus to r e d u c e ice f o r m a t i o n . It w a s r e p o r t e d that i c e f o r m s a t t h e s e locations only when the a v e r a g e a i r t e m p e r a t u r e i s below about - 2 0 ° F .
No movement of the s l a b s p a r a l l e l to the s i d e s of the embank- m e n t h a s been o b s e r v e d . A s u r g e tower in one c e l l i s tilted. This could be due to i c e shove o r to s o i l movement. The w a t e r l e v e l in the c e l l s f l u c t u a t e s a s m u c h a s 12 in. in 24 h o u r s . Overthrusting of the ice and i c e r i d g e s have been o b s e r v e d to o c c u r in a s s o c i a t i o n with t h e s e changes i n w a t e r l e v e l .
Water t e m p e r a t u r e s a r e m e a s u r e d a t the McPhillips S t r e e t r e s e r v o i r . In Table I a r e given the w a t e r t e m p e r a t u r e s a t the bottom of the r e s e r v o i r f o r d a t e s in November and D e c e m b e r 1962.
Date 16 November 1962 1 D e c e m b e r 1962 1 5 D e c e m b e r 1962 TABLE I T e m p e r a t u r e " F 3 9 31 D e c e m b e r 1962
During the w i n t e r , i t i s unusual for t h i s t e m p e r a t u r e to be lower than 3 5 ° F . It w a s e s t i m a t e d that ice s t a r t e d to f o r m a t the r e s e r v o i r about 20 November i n 1962. Ice thickness m e a s u r e m e n t s a r e not made.
I n t e r p r e t a t i o n of the Evidence
T h e evidence shows that f o r c e s imposed on the r e i n f o r c e d c o n c r e t e s l a b s by the i c e cover a r e r e s p o n s i b l e f o r the leakage that developed i n the c e l l s a t the Wilkes Avenue r e s e r v o i r i n the w i n t e r s of 1960-61, 1961-62 and 1962-63. It is p o s s i b l e that f o r c e s a s s o c i a t e d with i c e a r e r e s p o n s i b l e for the c r a c k s f o r m e d p a r a l l e l to the embankment .edge in the upper row of s l a b s at t h e McPhillips S t r e e t r e s e r v o i r .
T h e r e a r e two ways by which a n i c e cover c a n apply f o r c e s to t h e c o n c r e t e s l a b s :
( 1 ) A fluctuating w a t e r l e v e l can produce a v e r t i c a l f o r c e combined with a bending m o m e n t (buoyancy f o r c e ) .
(2) T h e r m a l expansion o r contraction of the i c e c a n produce a t h r u s t p a r a l l e l to the i c e s u r f a c e .
Buoyancy F o r c e
Consider the sketch i n F i g u r e 7. If the w a t e r l e v e l in a c e l l is i n c r e a s e d by a n amount H, and t h e whole ice c o v e r m o v e s up with i t , t h e length and width of the i c e s u r f a c e m u s t i n c r e a s e by an amount 6H. F o r H = 8 i n . , the i n c r e a s e i s 48 in. T h e o b s e r v a t i o n s showed that no single c r a c k of t h i s width o r group of c r a c k s with total d i s p l a c e m e n t of t h i s amount f o r m e d in the ice c o v e r . It i s t h e r e f o r e concluded that the
i c e a d h e r e d to the s l a b in the m a n n e r shown i n F i g u r e 7. As a consequence, f o r c e s a r e e x e r t e d 0; the s l a b by the ice. The p r o b l e m to be salved i s that
of a p l a t e of thickness ' h ' totally c o n s t r a i n e d a t the edges and r e s t i n g on a n
1
e l a s t i c foundation of r e a c t i o n ' k t . F o r calculation, r e p l a c e the s l a b by a v e r t i c a l wall a t A-A. It i s r e q u i r e d to find the upward o r downward t h r u s t and the bending m o m e n t a t the wall due to a change i n w a t e r l e v e l H.
The v e r t i c a l deflection of the ice s u r f a c e n e a r the wall i s given approximately by (*)
(::) B. Lofquist in "Lifting F o r c e and Bearing Capacity of an Ice S h e e t t 1 , Technical T r a n s l a t i o n No. 164, National R e s e a r c h Council, gives a solution to this p r o b l e m a s s u m i n g the i c e c o v e r behaves a s a b e a m . The difference between h i s solution and equation 1 i s
w h e r e P i s the v e r t i c a l t h r u s t a t the wall
k i s the subgrade r e a c t i o n which f o r w a t e r = 62. 5 lb/ft 3
E = effective Youngs modulus u = effective Poissons r a t i o .
The bending moment M
T h e bending moment i s a maximum a t the wall and away f r o m the wall
X TI
at
-
- -
...
B - (4)
P B
At the wall M = and at x =
-
rB
W 2
The above calculations show that i f i c e behaved e l a s t i c a l l y , the maximum s u r f a c e s t r e s s , given by
.,
.w h e r e S i s the s t r e s s , would occur a t the wall and would be about five
B t i m e s l a r g e r than the s t r e s s a t x =
-
2 f o r the s a m e change in w a t e r level. Ice c r e e p s under s t r e s s , and the m a x i m u m s t r e s s developed a t the s u r f a c e depends on both the c r e e p r a t e and the t e m p e r a t u r e . If the c r e e p r a t e at a given t e m p e r a t u r e i s g r e a t enough, the ultimate s t r e n g t h of the i c e will be exceeded and c r a c k s will f o r m . C r e e p and c r a c k
f o r m a t i o n w i l l c a u s e the effective value f o r B to d e c r e a s e with t i m e . Although B changes with t i m e , t h e r e i s s o m e evidence f r o m o b s e r
-
vations on the d e f o r m a t i o n of ice cover under load, that the m a t h e m a t i c a l function giving the s h a p e of the deflected s u r f a c e d o e s not change(e. g. equation ( 1 ) ) . In the calculations that follow, this a s s u m p t i o n i s made.
C r a c k s w i l l f o r m a t locations w h e r e the s u r f a c e s t r e s s i s a m a x i m u m , which will be a s s u m e d to be w h e r e the bending moment i s maximum. When the w a t e r l e v e l i s l o w e r e d , a s it w a s a f t e r the
damage to the c e l l s w a s d i s c o v e r e d , the upper s u r f a c e of the i c e c l o s e to the embankment w i l l be put i n tension. B e c a u s e the embankment i s inclined r a t h e r than v e r t i c a l , the m a x i m u m t e n s i l e s t r e s s in the i c e
s u r f a c e will not be w h e r e it m e e t s with the e m b a n k m e n t , but s o m e d i s t a n c e in f r o m that location. The position of the 8-ft c r a c k line indicates that . the m a x i m u m t e n s i l e s t r e s s a t the ice s u r f a c e o c c u r r e d a l m o s t o v e r the point of contact of the lower ice s u r f a c e and the embankment.
If the w a t e r level i s r a i s e d , the ice s u r f a c e a t the location given by x =
f
will be i n tension. Although, a c c o r d i n g to e l a s t i c t h e o r y , the bending moment a t this location i s only about one-fifth of i t s value n e a r the embankment, b e c a u s e the i c e a t t h e s u r f a c e i s colder than the ice i n contact with w a t e r , the s t r e s s that i s developed a tx = - n B , due to the imposed c r e e p r a t e can exceed the s t r e s s developed 2
a t the bottom s i d e of the ice cover at the embankment. It i s t h e r e f o r e p o s s i b l e that a c r a c k will f o r m at the ice s u r f a c e a t x =
-
before one2
f o r m s a t the bottom of the i c e c o v e r adjacent to the embankment. T h i s i s considered to be the cause of the 40-ft c r a c k line.
R e f e r r i n g to F i g u r e 4 , i t c a h be s e e n that the r a t e of leakage began to i n c r e a s e s h o r t l y after 15 D e c e m b e r when the i c e thickness was
18 in. The 40-ft c r a c k line may not have developed a t that t i m e , but would probably have f o r m e d before the i c e w a s 24 in. thick. Again,
b e c a u s e the embankment i s inclined, t h e r e i s s o m e ambiguity a s to w h e r e the d i s t a n c e x i n equation (4) should be m e a s u r e d f r o m . It should
probably be m e a s u r e d f r o m a location between the 8-ft c r a c k l i n e and the i n t e r s e c t i o n of the ice s u r f a c e with the embankment. It was t h e r e f o r e a s s u m e d that a t the t i m e the ice w a s 24 in. thick, t h e d i s t a n c e x i n equation (4) was 3 5 ft. Using this value in equation (4) gives
F o r the i c e to lift the s l a b f r o m the embankment, the v e r t i c a l f o r c e P m u s t exceed a c r i t i c a l value
The bending m o m e n t a t the w a l l corresponding to the v e r t i c a l t h r u s t P o i s given by
2 P o B k Ho B
M o = - -
-
...
2 2
(6)
Consider the situation shown i n F i g u r e 8. A s s u m e that the density of c o n c r e t e = 150 lb/ft3, that t h e r e i s no c o n s t r a i n t along edge B , and no adhesion between s l a b and embankment. The p r o b l e m i s to calculate the
P = 965 lb p e r linear ft. Concluding R e m a r k s on Buoyant F o r c e
The c r i t i c a l f o r c e P o r e q u i r e d to lift t h e s l a b is about 1000 l b p e r l i n e a l ft. F o r B = 22. 3 f t , equation (5) gives f o r t h e change in w a t e r l e v e l r e q u i r e d to produce this v e r t i c a l f o r c e
Ho = 8 . 6 in.
T h e bending moment at the wall i s , f r o m equation ( 6 ) , 11, 150 ft lb p e r l i n e a l ft. The m a x i m u m s t r e s s in the i c e a t the wall w i l l be l e s s than that calculated f r o m e l a s t i c t h e o r y , i . e . about 1 2 5 p s i . T h i s i n d i c a t e s that the ice could have developed the c r i t i c a l v e r t i c a l f o r c e P o without cracking.
T h e s e calculations show that i t w a s p o s s i b l e for the i c e to lift the s l a b s v e r t i c a l l y a t the l e v e l of the joint between t h e f i r s t and second rows. If the w a t e r w e r e to r i s e in the f i l t e r bed to the s a m e height a s t h e w a t e r in the c e l l , the v e r t i c a l f o r c e P o r e q u i r e d to lift the s l a b would be reduced because of the reduction in the effective d e n s i t y of the s u b m e r g e d c o n c r e t e
.
Assuming
B
= 22. 5 f t , the v e r t i c a l f o r c e imposed on the s l a b by t h e i c e p e r inch change in w a t e r level i s , f r o m equation ( 2 ) , about120 l b p e r l i n e a l ft. The bending moment imposed o n the embankment f o r the s a m e change i n water l e v e l i s , f r o m equation ( 3 ) , about 1 , 350
f t lb p e r l i n e a l f t . If the ice i s f r o z e n to the s l a b , the s l a b m u s t be s t r o n g enough to r e s i s t the applied bending moment and heavy enough not to be lifted away f r o m the embankment.
It i s considered that a d r o p in w a t e r level would not c a u s e damage a t the Wilkes Avenue r e s e r v o i r provided that the s l a b i s s t r o n g enough to r e s i s t the bending m o m e n t , because the sand f i l t e r on the clay should be capable of c a r r y i n g the v e r t i c a l load imposed.
The value used for B was obtained f r o m the location of the s u r f a c e c r a c k s . T h e s e c r a c k s probably f o r m e d f i r s t when the i c e was l e s s than 24 in. thick. It i s possible that a s the i c e thickened, the effective value f o r B i n c r e a s e d , but since the ice 40 ft f r o m the edge w a s a l r e a d y weakened by c r a c k i n g , subsequent c r a c k s continued to f o r m a t that location. F o r i c e 36 in. thick, it i s considered that the value f o r B would not exceed 50 f t . The loads given above m a y , t h e r e f o r e , be. on the low s i d e .
F o r c e s Due to T h e r m a l Expansion
A r i s e in a i r t e m p e r a t u r e will cause the i c e cover in e a c h c e l l to expand. If the i c e i s unconstrained a t the edges, the m i n i m u m expan- sion would be that calculated f r o m e l a s t i c t h e o r y
w h e r e AT(y) i s the change in t e m p e r a t u r e of the ice a t depth y.
- 6
cr i s the coefficient of l i n e a r expansion which for i c e i s about 28 x 10
p e r O F .
Combining equations ( 7 ) and ( 8 )
The t e m p e r a t u r e a t the i c e - w a t e r i n t e r f a c e i s 3 2 ° F . It is a s s u m e d that at midnight on 4 F e b r u a r y the ice s u r f a c e t e m p e r a t u r e was 5 " F , and that the t e m p e r a t u r e i n c r e a s e d l i n e a r l y with depth. It i s a l s o a s s u m e d that by 4 o'clock on the a f t e r n o o n of 5 F e b r u a r y the t e m p e r a t u r e of the i c e cover w a s 3 2 ° F throughout. Therefore
and
According to equation ( 9 ) , an unconstrained ice cover 800 ft long would expand a minimum of about 3 . 6 in. and in the 600 -ft d i r e c t i o n , 2. 7 in. In undergoing this expansion, cracking and c r e e p will o c c u r , reducing the i n t e r n a l s t r e s s in the ice and allowing additional expansion. The maximum expansion that could o c c u r f o r a 2 7 ° F t e m p e r a t u r e r i s e , i s l e s s than 7. 2 in. and 5. 4 in. respectively.
The embankments of the c e l l s constrain the ice s o a s not to allow this expansion. According to e l a s tic theory, the f o r c e s imposed on the embankment would be v e r y l a r g e . Field observations have shown that ice c o v e r s 800 ft by 600 ft in s i z e will buckle before this f o r c e could be developed, but with the p r o p e r combination of conditions, i c e c o v e r s 24 in. thick could produce a t h e r m a l t h r u s t of 20, 000 lb p e r lineal ft.
Cause of Damage on 5 F e b r u a r v
It i s significant that the upward movement of the s l a b s o c c u r r e d at the n o r t h , west and e a s t walls but not at the south. The g r e a t e s t move- ment o c c u r r e d a t the north embankment, and this embankment i s the one upon which the sun shines most d i r e c t l y . It i s considered that the upper p a r t of the top row of s l a b s was f r o z e n to the embankment and because of this was capable of withstanding some t h r u s t p a r a l l e l to the s l a b and perpendicular to the embankment edge. The heat received at the s l a b s u r f a c e during the day was sufficient to weaken this bond due to freezing to the point where it failed under the combined action of t h e r m a l t h r u s t and buoyancy.
Buckling would probably develop f i r s t in the long direction of the c e l l , that i s , the waves induced in the i c e would be p a r a l l e l to the 600-ft direction. As a r e s u l t , the ice cover in the 600-ft direction would have a higher r e s i s t a n c e to buckling, and the t h e r m a l f o r c e developed in that direction would be correspondingly g r e a t e r . This i s considered to be the r e a s o n why the g r e a t e s t movement of the s l a b s o c c u r r e d a t the n o r t h embankment. F o r the ice and weather conditions of 5 F e b r u a r y , it i s considered that p r i o r to f a i l u r e the t h r u s t against the 800-ft embankment probably exceeded 20,000 lb p e r lineal ft.
Concluding R e m a r k s
Although the d a m a g e on 5 F e b r u a r y w a s due to a combination of t h e r m a l t h r u s t and buoyancy f o r c e , the i n c r e a s e d r a t e of leakage o b s e r v e d e a r l i e r in the w i n t e r of 1962-63, and in p r e v i o u s y e a r s , i s probably p r i m a r i l y due to the buoyancy f o r c e . R e m e d i a l action w i l l have to take into c o n s i d e r a t i o n both of t h e s e f o r c e s .
T o p r o t e c t the c e l l s a g a i n s t t h e r m a l t h r u s t , e i t h e r the bond between the embankment and the s l a b s w i l l have to be s t r e n g t h e n e d , o r s o m e m e a n s introduced that will allow the ice to expand f r e e l y . It i s of i n t e r e s t that d a m a g e due to t h e r m a l t h r u s t d o e s not a p p e a r to have o c c u r r e d a t the e m b a n k m e n t s of the c e l l s a t the McPhillips S t r e e t
r e s e r v o i r . It i s c o n s i d e r e d that the open w a t e r maintained by the mixing action a t the intake pipes p r e v e n t s the development of damaging s t r e s s due to t h e r m a l expansion of the i c e . The p o s s i b i l i t y of introducing , s i m i l a r action a t the Wilkes Avenue r e s e r v o i r should be investigated.
Assuming the t e m p e r a t u r e of the incoming w a t e r i s 34. 5 " F , and the flow r a t e i s 10 x l o 6 g a l s p e r da;, the heat available f o r p r e - venting ice f o r m a t i o n i s about 2.0 x l o 8 B. t . u . p e r day. The r a t e of heat l o s s f r o m a n open w a t e r s u r f a c e i s given approximately by
120 AT B. t. u. 2 9
ft day
w h e r e AT i s the d i f f e r e n c e between the w a t e r s u r f a c e t e m p e r a t u r e and the a v e r a g e a i r t e m p e r a t u r e . A s s u m i n g that 30,000 ft2 of s u r f a c e a r e to be kept ice f r e e a t O ° F , the r a t e of heat l o s s would be about 7 B. t. u.
f t 2 d a y T h e amount of h e a t s t o r e d in the w a t e r would be m o r e than adequate to s a t i s f y this l o s s .
If the i c e i s f r o z e n to the s l a b s lining the c e l l s , the s l a b s m u s t be heavy enough s o that they a r e not lifted f r o m the embankment by the buoyancy f o r c e and m u s t be s t r o n g enough to r e s i s t the a s s o c i a t e d bending moment. T h e d r a i n at the joint between the f i r s t and second r o w s of s l a b s h a s a volume of about 6 . 6 cu ft p e r l i n e a l ft. If t h i s d r a i n w e r e filled with c o n c r e t e , and the c o n c r e t e attached s e c u r e l y to the bottom of the s l a b s in the top r o w , the added weight would probably be sufficient to p r e v e n t the i c e lifting the s l a b f r o m the embankment with i n c r e a s e i n w a t e r l e v e l l e s s than 12 in. above the level a t t i m e of f r e e z e up. If a g r e a t e r f a c t o r of s a f e t y i s r e q u i r e d , the s l a b could be anchored to the embankment.
It i s c o n s i d e r e d that the buoyancy f o r c e m a y have lifted the s l a b s v e r t i c a l l y a t the McPhillips S t r e e t r e s e r v o i r , but b e c a u s e they w e r e backed by c l a y , no a p p r e c i a b l e w a t e r could l e a k out. The c r a c k s that f o r m e d n e a r the w a t e r l i n e , p a r a l l e l to the embankment edge, could have been due to the bending m o m e n t s induced in the s l a b by the buoyancy f o r c e .
Acknowledgments
The Division of Building R e s e a r c h e x p r e s s e s i t s a p p r e c i a t i o n to Mr. N. S. Bubbis, D i r e c t o r , Waterworks and Waste Disposal Division, Metropolitan C o r p o r a t i o n of G r e a t e r Winnipeg, f o r making available
F i g u r e s 1 , 2 , 4 and 5 of this r e p o r t . The author w i s h e s to a c h o w l e d g e the excellent c o o p e r a t i o n and a s s i s t a n c e r e c e i v e d f r o m the e n g i n e e r s of the W a t e r w o r k s and Waste D i s p o s a l Division of the Metropolitan C o r p o r a t i o n of G r e a t e r Winnipeg, and the E n g i n e e r i n g D e p a r t m e n t of the City of
F i g u r e 1 Evidence of s l a b movement along n o r t h s i d e of c e l l #2. (Photo courtesy Metropolitan Corpora- tion of G r e a t e r Winnipeg. )
F i g u r e 2 Evidence of s l a b movement a t n o r t h w e s t c o r n e r c e l l #2. (Photo c o u r t e s y Metropolitan C o r p o r a - tion of G r e a t e r Winnipeg. )
EL.- 46'
REINFORCED CONCRETE
-
I
NORMAL WATER LEVEL EL.-43'
EL.
-
23'
AND
DRAIN
5
CLAY
FIGURE
3
SKETCH OF SECTION SHOWING GENERAL DETAILS IN CONSTRUCTION OF C E L L
AT WILKES AVENUE RESERVOIR
FIGURE
5
MAXIMUM AND MINIMUM AIR TEMPERATURES AT WINNIPEG
5 0 40 3 0 IL 2 0-
W a 3 l o a W h ZE W I- 0 - - 1 0 - 2 0 -30 I I I I I I I I I I I I I I I I I I I - - --
-
--
- - - - - - I I I I I I I I I I I LJI I I I I I I 15 20 25 30 5 10 15 20 25 30 5 10 15 2 0 ~ 25 30 5 10 15 20 25NOV
1
DECI
JANI
FEEFigure 6 Layers of white ice indicating flooding of ice
