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Floor heave due to biochemical weathering of shale
Penner, E.; Eden, W. J.; Gillott, J. E.
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FLOOR HEAVE
DUE
TO BIOCHEMICAL WEATHERING OF SHALESOULEVEMENT DU PLANCHER CAUSE PAR LA DECOMPOSITION 810-CHIMIQUE DE SCHISTE nOA'bEHnOJABPE3YflbTATE6MOXMMM9ECKOrO BMBETPMBAHMRCJAHLlA
E. P E N N E R , W.J. E D E N ond J.E. G I L L O T T , Hotionol Research Council o f Conodo ond Univarsity of Colgory (Conodo)
SYNOPSIS. Heave of a basement f l o o r in a t h r e e - s t o r e y building in Ottawa w a s r e c e n t l y investigated. The building i s founded on black s h a l e of Ordovician a g e known a s t h e Billings f o r m a t i o n . Examination in the heaved zone r e v e a l e d that the s h a l e had been a l t e r e d physically and c h e m i c a l l y t o a depth of 0 . 7 t o 1 m . Below t h i s the u n a l t e r e d shale w a s sound but contained n u m e r o u s p y r i t e v e i n s and a l s o had a g e n e r a l p y r i t i c
s u l f u r content a s high a s 1 . 6 % . The m a i n a l t e r a t i o n p r o d u c t s that w e r e r e s p o n s i b l e f o r the heave, j a r o s i t e and gypsum, w e r e located between shale l a m i n a e and in f i s s u r e s in the a l t e r e d zone. Acidity m e a s u r e m e n t s ranged f r o m pH 2.8 t o 4 . 4 , pointing t o biochemical weathering by autotrophic b a c t e r i a belonging t o t h e
Thiobacillus-Ferrobacillus group. Heaving w a s a r r e s t e d by c r e a t i n g conditions unfavourable f o r b a c t e r i a l growth. T h i s involved neutralizing the heaved a r e a by flooding the shale with a b a s i c solution and keeping the w a t e r t a b l e high a r t i f i c i a l l y t o r e d u c e a i r e n t r y and acid build-up.
Heave of the basement f l o o r of a t h r e e - s t o r e y e x - t e n s i o n t o the B e l l Canada Building in Ottawa, founded on s h a l e , w a s r e c e n t l y investigated. T h e
study was initiated when the d i s p l a c e m e n t of the basement f l o o r i n t e r f e r e d s e r i o u s l y with the align
-
m e n t and operation of power and switching f a c i l i - t i e s located in t h i s a r e a . P r o b l e m s of a s i m i l a r n a t u r e have been d e s c r i b e d by R.M. Quigley and R. W. Vogan (1970) and M . Spanovich and R. B. F e w e l l (1969). A note on the heaving p r o b l e m by t h e a u t h o r s of t h i s p a p e r ( E . P e n n e r et a1 1970) d e s c r i b e s s o m e a s p e c t s of the p r e l i m i n a r y i n v e s t i - gation c a r r i e d out at the p r e s e n t s i t e .
The o r i g i n a l building was c o n s t r u c t e d in 1929 and although a s m a l l amount of heave h a s o c c u r r e d in the ensuing y e a r s i t has not i n t e r f e r e d with the a l i g n - m e n t of t h e equipment located on the b a s e m e n t f l o o r . An extension w a s added t o t h i s building in 1961 with a l l the corresponding f l o o r s located a t the s a m e elevation. Heaving of the b a s e m e n t f l o o r in the e x - tension was noticed about 4 y e a r s a f t e r t h e addition was completed. The affected a r e a i s about 2 2 5 m 2 , which r e p r e s e n t s about one - s i x t h of the total base
-
m e n t space. Heaving was thought t o have s t a r t e ds o m e t i m e in 1964 o r 1965; the d i s p l a c e m e n t of t h e floor w a s sufficiently s e r i o u s by t h e end of 1966 t o initiate an investigation. T h e heaved a r e a a p p e a r e d a s two r o u n d e d d o m e s a s shown by t h e displacement contours in F i g . 1. The influence on equipment
alignment i s shown i n F i g . 2. T h e object of the i n - vestigation w a s t o e s t a b l i s h the c a u s e of heave and t o initiate r e m e d i a l m e a s u r e s f o r controlling the heave until the equipment could be relocated.
GEOLOGY
The B e l l Canada building i s founded on the Billings f o r m a t i o n , a black p y r i t i f e r o u s c a l c a r e o u s and f i s s i l e s h a l e ( A . E . Wilson 1946). The shale f o r m a - tion i s about 6 m thick a t t h i s location and l i e s c o n f o r - m a b l y on interbedded l i m e s t o n e s and s h a l e s of t h e E a s t v i e w formation. T h e s e d e p o s i t s belong t o t h e Ordovician s y s t e m and w e r e f o r m e d s o m e 450 million y e a r s ago. P a l a e o z o i c r o c k s of t h i s age a r e cut by two m a j o r s e t s of f a u l t s in t h e Ottawa a r e a (A. E. Wilson 1946). The B e l l C a n a d a building i s situated about 2.4 lun northwest of the G l o u c e s t e r fault, a m a j o r dislocation which t r e n d s NW-SE. A m i n o r fault which a p p e a r e d t o have a s t r i k e in t h e d i r e c t i o n of t h e heaved a r e a s w a s o b s e r v e d in a n e x - cavation i m m e d i a t e l y south of the B e l l building. T h i s fault was a l s o uncovered during t h e excavation of examination p i t s below t h e floor s l a b of the B e l l C a n a d a building. As will be r e f e r r e d t o l a t e r , the s h a t t e r e d n a t u r e of the s h a l e n e a r the fault
2,
thought t o have contributed t o the s e v e r i t y of the weathering and heaving p r o b l e m .e S U R V E Y P O I N T S
o
P I T S F O R S H A L E S A M P L I N G A N D T R E A T M E N T0 O B S E R V A T I O N W E L L S E! E L E C T . E Q U I P M E N T I COLUMNS I N S P E C T I O N T R E N C H
F I G U R E
I
L O C A T I O N OF I N S T A L L A T I O N S A N D CONTOURS OF M A X I M U M H E A V E , CM
FIG. 2 LEVELLING OF GENERATORS NECESSI- TATED BY FLOOR HEAVE
FLOOR CONSTRUCTION AND LNTERIOR COLUMN FOOTINGS
The 30-cm-thick r e i n f o r c e d c o n c r e t e f l o o r s l a b w a s placed on a 15-cm l a y e r of c r u s h e d l i m e s t o n e . T h i s levelling c o u r s e , which a l s o contained
an
underfloor d r a i n a g e t i l e s y s t e m , had been placed d i r e c t l y on the shale a t about 1. 5 m below the o r i g i n a l s h a l e level. The i n t e r i o r column footings w e r e 2.4 by 2 . 4 by 1 . 2 m thick and placed at about 2.7 m below the o r i g i n a lshale l e v e l , i. e . 1 . 2 m below f l o o r l e v e l .
152
HEAVE AND HEAVING RATES
During t h e o b s e r v e d p e r i o d of heaving beginning i n A p r i l 1967
-
t h e m a x i m u m m e a s u r e d f l o o r d i s p l a c e - m e n t w a s 5 . 6 c m o v e r a p e r i o d of about 32 m o n t h s , a heave r a t e of a p p r o x i m a t e l y 0.18 c m p e r month. B a s e d on t h e e s t i m a t e d f l o o r elevation i m m e d i a t e l y a f t e r c o n s t r u c t i o n , the m a x i m u m t o t a l m o v e m e n t i s 10. 7 c m . A plot of t h e f l o o r movement at v a r i o u s locations i s given i n F i g . 3. The location of t h e points i s noted i n F i g . 1.INVESTIGATION
C o r e r e c o v e r y by d r i l l i n g w a s p o o r in t h e heaved zones s o examination p i t s w e r e excavated a t t h r e e locations within the p r o b l e m a r e a ( F i g . 1 ) . The top 40 t o 50 c m of shale w e r e e x t r e m e l y soft and c r u m b l y and could be r e m o v e d with a hand shovel; below t h i s , excavation w a s c a r r i e d out with the aid of a jack h a m m e r . L a y e r i n g of the shale w a s i n the h o r i z o n t a l plane and the t h i c k n e s s of the l a m i n a e r a n g e d f r o m m i l l i m e t r e s a t the s u r f a c e t o s e v e r a l c e n t i m e t r e s n e a r t h e bottom of t h e 1 . 8 - m excavation. In g e n e r a l t h e s h a l e w a s cut by n e a r - v e r t i c a l joints throughout t h e section.
Joint s u r f a c e s and shale l a m i n a e in the a l t e r e d zone ( t o p 0. 5 t o 1 m ) w e r e c o v e r e d with a yellowish- brown coating and n u m e r o u s c o l o u r l e s s c r y s t a l s .
F I G U R E 3 B E L L B L D G F L O O R M O V E M E N T S
The a l t e r e d zone w a s found t o be a c i d i c and, based MINERALOGY on n u m e r o u s m e a s u r e m e n t s , the r a n g e in pH w a s
established a s 2.8 t o 4.4. Below about 1 m the The m i n e r a l o g i c a l investigation w a s d i r e c t e d a t s h a l e a p p e a r e d to be sound. F i g u r e 4 shows the d e t e r m i n i n g the r e a c t i o n p r o d u c t s of the a l t e r e d difference in the physical a p p e a r a n c e between t h ~ s h a l e . The m i n e r a l o g y of t h e unaltered components a l t e r e d and u n a l t e r e d shale. below t h e weathered c r u s t w a s a l s o studied.
Shale l a m i n a e - a l t e r e d zone (30 t o 60 c m ) .
-
The m o s t i n t e n s e lines i n the X - r a y d i f f r a c t o g r a m s w e r e a t t r i b y t e d t o q u a r t z and gypsum. P e a k s a t t r i b u t a b l e t o 10 A m i c a ( i l l i t e ) and kaolinite o r c h l o r i t e w e r e a l s o f a i r l y strong. J a r o s i t e and p y r i t e w e r e p r e - s e n t but not i n dominant a m o u n t s .Soft m a t e r i a l between l a m i n a e
-
a l t e r e d zone (30 t o 60 c m depth).-
Gypsum and j a r o s i t e w e r e p r e s e n t in dominant quantities. I l l i t e and kaolinite o r chlo- r i t e w e r e a l s o p r e s e n t a s well a s q u a r t z . F u r t h e r X - r a y s t u d i e s suggested t h e p r e s e n c e of some m i x e d - l a y e r swelling c l a y m i n e r a l s .Unaltered s h a l e (120 t o 180 c m ; no visible p y r i t e ) . - D i f f r a c t o g r a m s of t h e s e s a m p l e s differed f r o m t h e a l t e r e d zone i n t h a t l i n e s attributable t o gypsum o r j a r o s i t e w e r e absent. P y r i t e , c a l c i t e , i l l i t e and FIG. 4 PHYSICAL DIFFERENCES
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SHALE IN q u a r t z w e r e a l l p r e s e n t .HAND DUG P I T BETWEEN ALTERED AND UNALTERED SHALE
Veins of p y r i t e
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u n a l t e r e d zone (120 t o 180 c m ) .-
The m a t e r i a l located in joints and p a r t i n g s t h a t w a s visually identified a s p y r i t e w a s v e r i f i e d by X - r a y a n a l y s i s ( F i g . 5). I t w a s u n c e r t a i n , however, whether o t h e r i r o n sulfides w e r e a l s o p r e s e n t . C o l o u r l e s s c r y s t a l s
-
a l t e r e d zone (30 t o 60 c m ) .-
T h e m a j o r phase in t h e abundant c o l o u r l e s s c r y s t a l s visually identified a s gypsum was verified by X - r a y a n a l y s i s .
Yellowish-brown coating on s h a l e laminae
-
a l t e r e d zone (30 t o 60 c m ) .-
The m a j o r p h a s e of the yellowish-brown deposit w a s identified a s j a r o s i t e , K F e 3 ( S 0 4 ) 2 (OH)6.CHEMISTRY
Table I gives the c h e m i c a l a n a l y s i s of the s h a l e
o t h e r s h a l e s . A s would be expected, t h e unaltered s h a l e h a s e s s e n t i a l l y no sulfate sulfur a s might be expected ( s a m p l e s Nos. 2, 3 and 4).
BIOCHEMICAL CONSIDERATIONS
T h e existence of extensive p y r i t e i n t r u s i o n s and a g e n e r a l p y r i t i c content i n the u n a l t e r e d zone, the type of a l t e r a t i o n p r o d u c t s identified in the a l t e r e d
zone and t h e acid conditions in t h e a l t e r e d zone sug- g e s t e d that autotrophic b a c t e r i a w e r e probably i n - volved i n the weathering and heaving p r o c e s s . Auto- t r o p h i c b a c t e r i a l oxidation i s a common phenomenon i n m a n y coal m i n e s (S.I. Kuznetzov et a1 1963) and i s s o m e t i m e s u s e d i n e x t r a c t i n g m e t a l economically f r o m low g r a d e p y r i t i f e r o u s o r e s ( V . F . H a r r i s o n e t a1 1966). The e n e r g y f o r g r o w t h and p r o l i f e r a t i o n of autotrophes i s obtained by the oxidation of i n o r g a n i c compounds in the p r e s e n c e of a t m o s p h e r i c oxygen.
TABLE I. CHEMICAL ANALYSIS, P E R CENT BY WEIGHT
SAMPLE NO. 1 2 3 4 5 6 7 Composite Composite S a m p l e ,Al- Sample, t e r e d Zone, Non-heaved DESCRIP- 0-50 c m . a r e a , Un- TION No visible a l t e r e d , 0 - p y r i t e 15 cm. No visible py- r i t e Sulphate Sulfur P y r i t i c Sulfur Composite S a m p l e , Non-heaved a r e a , Un- a l t e r e d , 2 . 7 m . No visible p y - r i t e T r a c e
Composite Composite Composite Composite
S a m p l e S a m p l e , S a m p l e , Sample, Heaved A l t e r e d Heaved S u r f a c e of A r e a , Un- l a y e r , 0 - A r e a , Un- A l t e r e d a l t e r e d , 4 5 c m . a l t e r e d , Zone 1 . 3 7 m . 1 . 8 m . No visible p y r i t e . Not Not 64 D e t e r m i n e d D e t e r m i n e d Not 1 . 4 5 Not D e t e r m i n e d D e t e r m i n e d
C a r b o n a t e Not Not Not Not Not
( i n o r g a n i c De, D e t e r m i n - D e t e r m i n e d D e t e r m i n e d D e t e r m i n e d 6. 1 2.6 a s C 0 2 ) t e r m i n e d ed
S a m p l e s 1, 2, 3, 4, 6 and 7 analyzed by Division of C h e m i s t r y , National R e s e a r c h Council of Canada.
Sample 5 analyzed by M i n e s B r a n c h , D e p a r t m e n t of E n e r g y , M i n e s and R e s o u r c e s of Canada.
s a m p l e s f r o m both t h e a l t e r e d and u n a l t e r e d zone. P r o t e i n a c e o u s body m a t e r i a l i s produced f r o m a t - T h e s e r e s u l t s show t h a t s o m e p y r i t e s t i l l p e r s i s t e d m o s p h e r i c c a r b o n dioxide and o t h e r n u t r i e n t s s u c h a s in the a l t e r e d zone a s shown by s a m p l e No. 1. T h e nitrogen contained i n the shale.
u n a l t e r e d r o c k h a s a high content of c a r b o n a t e s
( s a m p l e No. 6); a l o w e r content of c a r b o n a t e s w a s T h e m a i n oxidation r e a c t i o n s a r e thought t o be a s found i n the a l t e r e d shale. I n g e n e r a l , t h e s h a l e follows ( H a r r i s o n e t a1 1966, Kuznetzov e t a1 1963): h a s a high o r g a n i c c a r b o n content c o m p a r e d with
p y r i t e f e r r o u s sulfate 2. 4FeSO t O2 t 2H2S04 -' 2 F e 2 ( S 0 ) t 2H20 4 4 3 f e r r i c sulfate 3. 7Fe (SO ) t F e S t 8H 0 -t 1 5 F e S 0 4 t 8H2S04 2 4 3 2 2 f e r r i c sulphate p y r i t e
Reaction No. 1 i s thought by s o m e t o be e n t i r e l y c h e m i c a l although o t h e r s believe the oxidation of sulfide t o be a s s i s t e d by autotrophic b a c t e r i a . R e a c - tion No. 2 i s thought t o be e n t i r e l y due t o the oxi- dation by b a c t e r i a of t h e Ferrobacillus-Thiobacillus
group s i n c e t h i s r e a c t i o n d o e s not p r o c e e d c h e m i - cally i n a n a c i d environment. Oxidation of p y r i t e can p r o c e e d a s given i n r e a c t i o n No. 3 by the r e a c - tion with f e r r i c sulfate, a s t r o n g oxidizing agent produced in No. 2. One of the r e a c t i o n p r o d u c t s i n No. 3 i s f e r r o u s sulfate which the autotrophes o x i - dize again a c c o r d i n g t o No. 2. The m e d i u m b e - c o m e s i n c r e a s i n g l y a c i d i c a s t h e oxidation r e a c t i o n s p r o c e e d s i n c e m o r e acid i s produced than i s utilized. A s t h e shale i s c a l c a r e o u s , t h e f o r m a t i o n of gypsum i s d e r i v e d f r o m t h e n e u t r a l i z a t i o n p r o c e s s between t h e e x c e s s s u l f u r i c acid and c a l c i t e . J a r o s i t e , KFe3(S04)Z(OH)6, a l s o a m a i n r e a c t i o n product in the a l t e r e d zone, f o r m s m o s t r e a d i l y under acid conditions a s found in the a l t e r e d zone. The p o t a s - s i u m content.of j a r o s i t e i s thought t o come f r o m t h e degradation of c l a y m i n e r a l s and/or by base exchange r e a c t i o n s i n the highly acid environment.
T h e s e r e a c t i o n s c a u s e heaving because the m o l a r volumes of the u n a l t e r e d components a r e l e s s t h a n the r e a c t i o n p r o d u c t s . The volume i n c r e a s e f r o m p y r i t e t o j a r o s i t e i s 11 5% and f r o m c a l c i t e t o gypsum
103%. It i s a l s o v e r y a p p a r e n t that the weathered p r o d u c t s f o r m between t h e s h a l e l a m i n a e although in the r o t t e d m a t e r i a l gypsum and j a r o s i t e w e r e found t o e x i s t i n s i d e t h e p o r e s of t h e l a m i n a e .
All f a c e t s of t h e weathering r e a c t i o n s a r e not u n d e r - stood n o r i s t h e exact disposition of the m i n e r a l known before and a f t e r oxidation and how t h i s a f f e c t s volume change. The r e a c t i v e components of the un- a l t e r e d shale, t h e r e a c t i o n p r o d u c t s identified i n the a l t e r e d s h a l e and the a c i d i c condition w e r e s t r o n g evidence, however, that t h e weathering p r o c e s s w a s a s s o c i a t e d with autotrophic b a c t e r i a l oxidation and that i t r e s u l t e d in the heave o b s e r v e d .
M i c r o - o r g a n i s m s of t h e Ferrobacillus-Thiobacillus
g r o u p w e r e i s o l a t e d f r o m the a l t e r e d shale m a t e r i a l s by the Soil R e s e a r c h Institute, Canada D e p a r t m e n t of A g r i c u l t u r e and w e r e subsequently photographed with a scanning e l e c t r o n m i c r o s c o p e ( F i g . 6). T h e s e b a c t e r i a w e r e shown t o have the ability t o oxidize f e r r o u s i r o n t o the f e r r i c f o r m in culture solutions. It was a l s o shown that t h e end product in a n i n o r g a n i c growth m e d i a w a s j a r o s i t e . T h e s e b a c t e r i a a r e known t o r e q u i r e a n acid environment, t h e optimum being around pH 2.2; above pH 4 . 5 d o r m a n c y i s induced.
A i r t o aid b a c t e r i a l growth i s believed t o have gained r e a d y a c c e s s t o the shale v i a t h e empty t i l e d r a i n s y s t e m which had been plaeed in the c r u s h e d l i m e - stone l a y e r below t h e floor. Ln the m i n o r fault zone encountered i n one of t h e examination p i t s , t h e open n a t u r e of t h e f r a c t u r e d s h a l e f u r t h e r facilitated a i r e n t r y and thus heaving and weathering w e r e e x t r e m e l y s e v e r e .
FIG. 5 UNALTERED SHALE WITH PYRITE VEINS IN JOINTS.
FIG. 6 BACTERIA O F THE FERROBACILLUS- THIOBACILLUS GROUP ISOLATED FROM ALTERED SHALE ZONE.
The groundwater table w a s 4 m below floor l e v e l and t h e s h a l e u n d e r t h e f l o o r w a s r e l a t i v e l y d r y . I t h a s been shown m o r e r e c e n t l y t h a t a r e l a t i v e l y d r y e n - vironment i s p r e f e r r e d by t h e s e b a c t e r i a f o r rapid p r o l i f e r a t i o n and t h e f o r m a t i o n of t h e r e a c t i o n p r o - ducts. The b a s e m e n t space w a s a l s o exceptionally w a r m (30°C) due t o the heat l o s s f r o m the power equipment and t h i s too would favour b a c t e r i a l activity.
REMEDIAL TREATMENT
Modifications in t h e power equipment had been m a d e t o allow realignment a s heaving p r o g r e s s e d ; by t h e
s u m m e r of 1969, however, a c r i t i c a l s t a g e had been reached. The choice w a s e i t h e r to m o v e t h e equip- m e n t located on the heaved a r e a o r a r r e s t t h e heaving. The b a s i s f o r the t r e a t m e n t s e l e c t e d w a s t o c r e a t e unfavourable conditions f o r t h e growth of the bactjeria and if t h i s could be achieved, heaving would be stopped.
The t r e a t m e n t technique w a s to n e u t r a l i z e with a b a s e t h e a c i d conditions in the a l t e r e d zone and t o reduce a i r e n t r y by s a t u r a t i o n with w a t e r . The d i - r e c t a i r supply t o t h e s h a l e w a s r e d u c e d by flooding t h e examination p i t s with w a t e r t h e r e b y r a i s i n g t h e w a t e r table into the a c t i v e zone. pH m e a s u r e m e n t s had shown that e x t r e m e l y acid conditions (pH 2.8) existed in r e l a t i v e l y localized pockets of activity. By keeping t h e s h a l e s a t u r a t e d i t w a s hoped t h a t t h e a c i d s in t h e s e pockets would diffuse out and be washed away.
Neutralization with sodium hydroxide w a s thought t o be u n d e s i r a b l e since the sodium ion m i g h t induce s o m e swelling in the c l a y s h a l e s and p o t a s s i u m hy- droxide w a s , t h e r e f o r e , c o n s i d e r e d p r e f e r a b l e . L a b o r a t o r y e x p e r i m e n t s w e r e undertaken t o a s c e r - t a i n if the neutralization p r o c e s s would induce any i m m e d i a t e and u n f o r e s e e n d i m e n s i o n a l changes i n t h e shale. Duplicate s a m p l e s of t h e s h a l e f r o m the a l t e r e d zone, a p p r o x i m a t e l y 0 . 6 c m thick and 20 cm2 in a r e a , w e r e i m m e r s e d in t h r e e concentrations of KOH solution, (0.01, 0.1 and 1 N) under a load of 0.28 kg/cm2. The solutions w e r e changed d a i l y during the e n t i r e period of t h e e x p e r i m e n t . The r e s u l t s a r e shown i n F i g . 7. The 0.01 and 0. 1N solutions induced s m a l l s e t t l e m e n t s of the o r d e r of 0. 1 and 0.2%. The 1 N KOH solutions in- d w e d a swelling of n e a r l y 6%. The d e c i s i o n w a s , t h e r e f o r e , t o keep t h e t r e a t m e n t concentration below 0.1 N KOH although t h e exact n a t u r e of t h e dirnen- sional changes resulting f r o m t r e a t m e n t w e r e not well understood..
X - r a y d i f f r a c t o g r a m s of t h e s e KOH-treated s a m p l e s showed t h e d i s a p p e a r a n c e of gypsum peaks. S e p a r a - t e l y p r e p a r e d s a m p l e s of gypsum and j a r o s i t e f r o m t h e a l t e r e d s h a l e
-
the two m a i n r e a c t i o n p r o d u c t s existing in the a l t e r e d zone-
gave r e s u l t s i n t e r - p r e t e d according t o the following r e a c t i o n s :C
6. F e ( O H ) 3 -t FeOOH t H 2 0
T h e s e r e a c t i o n s s u g g e s t t h a t if KOH w e r e added t o the a l t e r e d s h a l e s o m e of t h e soluble components produced would be washed away i n t h e flooding p r o - c e s s . The r e s u l t m i g h t be t h a t s o m e s e t t l e m e n t would be induced.
NEUTRALIZATION AND FLOODING
T h r e e 5 c m o b s e r v a t i o n w e l l s , 5 c m in d i a m t e r , w e r e d r i l l e d i n t h e heaved a r e a t o a depth of 2.4 m t o m o n i t o r t h e depth t o the w a t e r t a b l e a s t r e a t m e n t p r o c e e d e d ( F i g u r e 1 ) and t o p e r m i t sampling of t h e g r o u n d w a t e r f o r pH m e a s u r e m e n t s .
Examination pit No. 1 ( F i g . 1 ) w a s fitted with an a u t o m a t i c float t o k e e p the pit continuously full of w a t e r . T r e a t m e n t s t a r t e d on 21 J a n u a r y 1970. The p o t a s s i u m hydroxide solution w a s automatically d i s - pensed into t h e pit t o give a concentration l e s s t h a n 0.1 N based on w a t e r consumption. In e a r l y A p r i l 1970 the two o t h e r examination p i t s i n t h e heaved zone w e r e a l s o fitted with a n a u t o m a t i c float and brought into operation f o r t r e a t m e n t and flooding with w a t e r . The KOH solution w a s m a i n t a i n e d i n the s a m e way. During the period f r o m 21 J a n u a r y 1970 t o 13 M a y 1971 o v e r 12 t o n n e s of KOH w e r e d i s - pensed into t h e s h a l e of t h e heaved zone. During t h i s t i m e the pH of the groundwater and t h e depth of
FIGURE 7 DIMENSIONAL CHANGE OF ALTERED SHALE AT THREE CONCENTRATIONS OF KOH
the w a t e r table w a s m o n i t o r e d . T h e s e r e s u l t s a r e given in F i g s . 8 and 9 r e s p e c t i v e l y . The consump- tion of w a t e r w a s about 16000 l i t r e s p e r day. In June 1970, a f t e r about 3 m o n t h s of t r e a t m e n t , an examination t r e n c h w a s excavated between p i t s Nos. 2 and 3 t o m e a s u r e the pH in the s h a l e itself a t v a r i o u s depths. The r e s u l t s a r e shown in F i g s . 10a and l o b . The r e s u l t s w e r e encouraging since the acid conditions in the shale had been g r e a t l y reduced and the f i s s u r e s w e r e well i m p r e g n a t e d with KOH solution although low pH's s t i l l p e r s i s t e d n e a r the s u r f a c e . Observation wells Nos. 1 and 2 a l s o showed that acid conditions p e r s i s t e d and t r e a t m e n t w a s continued. During S e p t e m b e r , October and No- vember 1970 t h e r e w a s a g r e a t i m p r o v e m e n t in t h e pH in the observation w e l l s and the decision w a s m a d e to discontinue the KOH t r e a t m e n t but continue the w a t e r supply t o keep the w a t e r table a s high a s possible and c r e a t e wet conditions beneath t h e slab.
The pH h a s continued to i n c r e a s e and a t p r e s e n t ( D e c e m b e r 1971) i t r a n g e s f r o m pH 6 . 4 to 7 . 1 .
Elevation s u r v e y s have been continued throughout the investigation. A s shown in F i g . 3 f o r the period following the s t a r t of t r e a t m e n t , floor m o v e m e n t s have been controlled s a t i s f a c t o r i l y . Some s e t t l e m e n t h a s o c c u r r e d in the c e n t r e of the heaved zone but t h i s h a s not been sufficiently s e r i o u s t o i n t e r f e r e with the operation of the equipment in t h i s a r e a . The s e t t l e m e n t i s thought t o be the r e s u l t of washing t h e m o r e soluble components out of the heaved shale a s mentioned in r e l a t i o n t o r e a c t i o n s 4 and 5.
Although heaving h a s been a r r e s t e d , i t i s expected that in t i m e the o w n e r s m a y w i s h t o r e p l a c e the heaved floor portion with a s t r u c t u r a l f l o o r . Flood- ing m a y have to be continued t o l i m i t a i r e n t r y and p r e v e n t acid conditions f r o m being r e - e s t a b l i s h e d .
1 9 7 0
1
1 9 7 1FIGURE 8 THE p H IN THE OBSERVATION WELLS
-
FLOODING WITH WATER ONLY
-
Y
, , l l , , , , , l , : , ,
JAN. FEE. MARCH APRIL MAY JUNE JULY AUG SEPT. OCT NOV DEC
/
JAN F E E MARCH APRIL MAY JUNE JULY AUG SEPT OCT NOV, DEC1970
1
1971FIGURE 9 DEPTH TO WATER TABLE AT VARIOUS LOCATIONS IN THE HEAVED ZONE
D I S T A N C E , M STA 0 I 2
CONCRETE FOOTING 2: FIGURE IOo pH MEASUREMENTS O F SHALE I N I N S P E C T I O N TRENCH
>
CONCRETEF O O T I N G
I S A M P L I N G L O C A T I O N 5
FIGURE l o b
PLAN VIEW O F P O S I T I O N O F I N S P E C T I O N TRENCH, PITS N O . 2 A N D 3 A N D CONCRETE F O O T I N G (SEE FIGURE I FOR L O C A T I O N O F TRENCH1
T h e a u t h o r s have been a b l e t o d e m o n s t r a t e t h e p r e - f e r e n c e f o r d r y conditions by the a u t o t r o p h e s f o r r a p i d d e t e r i o r a t i o n of p y r i t i c s h a l e . F i g u r e 11 shows a photograph of a s h a l e s a m p l e of low p y r i t e content (0. 170) t h a t w a s t a k e n a m o n t h a f t e r i t w a s innoculated with t h e s e b a c t e r i a . The s a m p l e w a s k e p t a t 30 "C i n a c o n t a i n e r a b o v e , but not i n c o n t a c t with, w a t e r . T h e light a r e a s i n F i g . 11 a r e a y e l l o w i s h - brown m i n e r a l identified a s j a r o s i t e . S a m p l e s of u n a l t e r e d p y r i t i c s h a l e have been i n f e c t e d in t h i s way f r o m s e v e r a l s h a l e f o r m a t i o n s i n t h e Ottawa r e g i o n and a l l have been shown t o s u p p o r t b a c t e r i a l g r o w t h u n d e r the e n v i r o n m e n t a l conditions d e s c r i b e d .
CONCLUDLNG REMARKS
1. T h e biogenic a l t e r a t i o n of p y r i t e i n s h a l e c a u s e s a n expansion within the a l t e r e d zone and r e s u l t s i n heave of s t r u c t u r e s founded on i t .
2. T h e p r e f e r r e d e n v i r o n m e n t f o r t h e p r o c e s s s e e m s t o be w a r m , r e l a t i v e l y d r y and with a plentiful supply of a i r .
3. T h e p r o c e s s c a n be a r r e s t e d by changing the e n - v i r o n m e n t by s a t u r a t i o n with w a t e r . T h e w a t e r i s believed t o r e s t r i c t t h e supply of a i r and t o p r e v e n t p o c k e t s of high a c i d i t y f r o m developing. 4. L a b o r a t o r y e x p e r i m e n t s i n d i c a t e t h a t v e r y s m a l l q u a n t i t i e s of p y r i t e c a n s u p p o r t t h i s p r o c e s s . ACKNOWLEDGEMENTS T h e a u t h o r s w i s h t o acknowledge t h e c o - o p e r a t i o n of the staff of B e l l C a n a d a f o r t h e i r a s s i s t a n c e w i t h t h e s e s t u d i e s . D r . K. C . I v a r s o n of Soil R e s e a r c h I n s t i t u t e , C a n a d a D e p a r t m e n t of A g r i c u l t u r e , a s s i s t e d
FIG. 11 DEVELOPMENT O F ALTERATION ZONES CONTAINING JAROSITE ON LOW P Y R I T E CONTENT SHALE (0.1qo) ONE MONTH A F T E R INNOCULATION WITH SHALE I N F E C T E D WITH F E R R O - BACILLUS-THIOBACILLUS BACTERLA. with t e s t s and g e n e r o u s a d v i c e c o n c e r n i n g t h e m i c r o - biological a s p e c t s . M r . V . F. H a r r i s o n , M i n e s B r a n c h , D e p a r t m e n t of E n e r g y , M i n e s a n d R e s o u r c e s , and M r . D.S. R u s s e l l , Division of C h e m i s t r y , National R e s e a r c h Council of C a n a d a , a s s i s t e d w i t h c h e m i c a l a n a l y s e s . R E F E R E N C E S Quigley, R.M. a n d R. W. Vogan ( 1 9 7 0 ) , ~ l a c k ' s h a l e heaving a t Ottawa, Canada. C a n . G e o t e c h . J . , 7;
106-112.
Spanovich, M . and R , B . F e w e l l (1969), T h e s u b j e c t i s p y r i t e . C h a r e t t e , P e n n . J . A r c h . , 4 9 , 1 , 15-16. P e n n e r , E .
,
J. E . Gillott and W. J . Eden ( 1970). I n - v e s t i g a t i o n of heave i n B i l l i n g s s h a l e by m i n e r a l o g i - c a l and b i o - c h e m i c a l m e t h o d s . Can. Geotech. J . , 7, 333-338.Wilson, A. E . (1946). Geology of the Ottawa-St. L a w r e n c e lowland. O n t a r i o and Quebec G e o l o g i c a l S u r v e y M e m o i r 241, No. 2474. C a n a d a Dept. of M i n e s and R e s o u r c e s , 6 5 p.
Kuznetzov, S. I.
