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Some preliminary consolidation tests on peat
NATIONAL RESEARCH COUNCIL CANADA
DIVISION O F BUILDING RESEARCH
SOME PRELIMINARY CONSOLIDATION T E S T S ON P E A T
by
Ivan C
.
Mac F a r laneANALYZED
I n t e r n a l R e p o r t No. 318 of t h e Division of Building Re s e a r c h OTTAWA S e p t e m b e r 1965P R E F A C E
T h i s r e p o r t i s a sequel t o an e a r l i e r I n t e r n a l Report on a review of the l i t e r a t u r e on consolidation of peat. The r e s u l t s a r e outlined h e r e i n of a number of consolidation t e s t s c a r r i e d out a t different i n t e r v a l s over a period of s e v e r a l y e a r s .
The author of t h i s r e p o r t i s a civil engineer in the Soil Mechanics Section, whose work with the Division c o n c e r n s r e s e a r c h on organic t e r r a i n .
Ottawa,
September 1 9 6 5
R . F. Legget, D i r e c t o r .
SOME PRELIMINARY CONSOLIDATION TESTS ON PEAT
by
Ivan C. M a c F a r l a n e
An e a r l i e r p a p e r ( M a c F a r l a n e , 1965) h a s indicated the extent and magnitude of the peat consolidation p r o b l e m and p r e s e n t s a review of the r a t h e r extensive l i t e r a t u r e on s e t t l e m e n t studies of soft foundation s o i l s , p a r t i c u l a r l y peats.
A number of consolidation t e s t s on peats have been c a r r i e d out in the Division of Building R e s e a r c h , National R e s e a r c h Council, in an e f f o r t to d e t e r m i n e some of the unknown p a r a m e t e r s a s s o c i a t e d with s e t t l e m e n t p r o b l e m s of soft foundation soils. T h e s e t e s t s have been p e r f o r m e d a t different i n t e r v a l s over a period of s e v e r a l y e a r s and i n - clude both one -dimensional and t r i a x i a l consolidation te s t s . P e r m e a b i l i t y m e a s u r e m e n t s w e r e made in s o m e of the e a r l i e r t e s t s ; and m o r e recently, m e a s u r e m e n t s have been taken of pore w a t e r p r e s s u r e s . The r e s u l t s a r e
s u m m a r i z e d in t h i s r e p o r t , which h a s been p r e p a r e d f o r information and r e c o r d p u r p o s e s in p r e p a r a t i o n f o r a m o r e detailed t e s t p r o g r a m .
Study h a s r e v e a l e d the difficulties inherent in attempting s t a n d a r d consolidation t e s t s on p e a t s , p a r t i c u l a r y the v e r y fibrous o n e s . The non- homogeneity of the m a t e r i a l a s well a s the unusually l a r g e s e t t l e m e n t s n e c e s s i t a t e d s o m e m i n o r modifications to the usual t e s t p r o c e d u r e s .
ONE -DIMENSIONAL TESTS
T e s t P r o c e d u r e
T e s t p r o c e d u r e s followed f o r the peat s a m p l e s w e r e substantially t h e s a m e a s those f o r inorganic s o i l s , with m i n o r modifications t o allow f o r the e x t r e m e l y high c o m p r e s s i b i l i t y of peat. Samples w e r e obtained in the field with a piston s a m p l e r using 2.80-inch inside d i a m e t e r Shelby t u b e s ; t h e s e w e r e extruded d i r e c t l y into the consolidometer r i n g s . Any obvious woody e r r a t i c s , which would have caused uneven s t r e s s concentrations and differential s e t t l e m e n t , w e r e removed p r i o r t o testing.
A load i n c r e m e n t r a t i o of A ~ = /1 w a s used throughout, and ~
r e m a i n e d on e a c h s a m p l e f o r 24 h o u r s . Following the loading t e s t s , the s a m p l e s w e r e unloaded by i n c r e m e n t s and the rebound c u r v e w a s plotted in the u s u a l m a n n e r .
During t e s t s 63-2-3, 6 3 - 5 - 5 and 63-6-4, p e r m e a b i l i t y t e s t s w e r e r u n on the s a m p l e s a f t e r consolidation under s o m e of the load
i n c r e m e n t s had been completed (although not a f t e r e v e r y load i n c r e m e n t ) . The loading a r m was clamped into a fixed position and w a t e r was p a s s e d through the s a m p l e s u n d e r a constant head. The t i m e r e q u i r e d f o r a given quantity of w a t e r t o p a s s w a s c a r e f u l l y m e a s u r e d , and s e v e r a l t e s t s w e r e run in s u c c e s s i o n a f t e r a p a r t i c u l a r load i n c r e m e n t .
In a few i n s t a n c e s the loading a r m w a s r e l e a s e d during the p e r m e a b i l i t y t e s t t o check f o r swelling of the s a m p l e . T h i s p r o c e d u r e w a s followed, however, only when the s a m p l e w a s subjected t o a heavy load.
A d e p a r t u r e f r o m t h i s g e n e r a l p r o c e d u r e w a s made during t e s t s 98-14-4A and -4B, when p o r e w a t e r p r e s s u r e s w e r e m e a s u r e d . E a c h load i n c r e m e n t w a s added a f t e r the p o r e w a t e r p r e s s u r e f r o m the p r e v i o u s i n c r e m e n t had r e t u r n e d t o z e r o . F o r both t h e s e t e s t s the l o a d - i n c r e m e n t r a t i o w a s v a r i e d , always being l e s s than unity.
T e s t Results
As t h e r e was considerable variation in the t e s t r e s u l t s , it i s difficult t o s e l e c t a typical s e t of c u r v e s . F i g u r e s 1 t o 4, however, i l l u s - t r a t e the r e s u l t s obtained in t e s t 98-14-1 and s e r v e a s an example. They
show the t i m e - s e t t l e m e n t c u r v e s and the p r e s s u r e -void r a t i o c u r v e s
drawn on both s e m i l o g a r i t h m i c and s q u a r e root plots. R e s u l t s of t h i s and o t h e r t e s t s a r e s u m m a r i z e d in Table I.
A g r a p h illust rating p e r m e a b i l i t y v e r s u s volume change due t o consolidation, in s a m p l e 63-2-3, i s shown in F i g u r e 5.
F i g u r e
6
i s the plot of initial void r a t i o v e r s u s c o m p r e s s i o n index. F i g u r e 7 d e p i c t s the c o r r e l a t i o n between initial void r a t i o and the n a t u r a l w a t e r content. F i g u r e s 8A and 8B i l l u s t r a t e the r a t i o of p o r e w a t e r p r e s s u r e dissipation a t v a r i o u s c e l l p r e s s u r e s f o r s a m p l e 98-
14-4B.Discussion of R e s u l t s
The t i m e - s e t t l e m e n t c u r v e s in F i g u r e s 3 and 4 a r e somewhat typical of the r e s u l t s of the other t e s t s , but b e a r little r e s e m b l a n c e t o
t i m e - s e t t l e m e n t c u r v e s f o r clays. In point of fact they r e s e m b l e t i m e
-
s e t t l e m e n t c u r v e s f o r a sand r a t h e r m o r e closely. The peculiar s h a p e s of t h e s e c u r v e s make it impossible to calculate the point of 100 p e r cent p r i m a r y consolidation. They a r e not quite l i n e a r and b e a r a slight r e s e m b l a n c e to the c u r v e s shown by B a r b e r (1961). They would a p p e a r t o indicate, however, that the p r i m a r y consolidation phase w a s completea t a v e r y e a r l y stage.
The s h a p e s of the p r e s s u r e - v o i d r a t i o c u r v e s varied r a t h e r m o r e widely than did the t i m e - s e t t l e m e n t c u r v e s . In some of the t e s t s a much f l a t t e r slope was observed f o r the e-log P curve than i s shown in F i g u r e 2, and in some c a s e s the upward curve i s even slightly concave. T h i s phenomenon i s a l s o noted by Taylor (1942). In such c a s e s , t h e r e f o r e , it i s not possible t o d e t e r m i n e the preconsolidation load, e . g . s a m p l e s 63-5-38x5, 63-6-48x6 and 98-14-4A 8x 4B. P e a t s , however, a r e n o r m a l l y consolidated. All s a m p l e s t e s t e d had v e r y high n a t u r a l w a t e r contents and initial void r a t i o s .
P e r m e a b i l i t y of the peat was initially quite high, but it d e c r e a s e d quite substantially a s the load was i n c r e a s e d . T h i s i s shown graphically i n F i g u r e 5, which i s s i m i l a r to the g r a p h shown by Adams (1 961).
One v e r y i n t e r e s t i n g phenomenon during a s e r i e s of t e s t s was the m a r k e d change in permeability a f t e r consolidation, f r o m any p a r t i c u l a r load i n c r e m e n t , was complete. Under the 5.4 p s i load, f o r example, K v a r i e d f r o m 2.00 x c m / s e c f o r the f i r s t t e s t t o 8 . 1 4 x l o m 7 c m / s e c f o r the fifth. The values shown in F i g u r e 5 a r e the r e s u l t s of the f i r s t t e s t in e a c h s e r i e s .
The plot of initial void r a t i o v e r s u s c o m p r e s s i o n index ( F i g u r e 6) indicates considerable s c a t t e r and no c l e a r l y defined c o r r e l a t i o n is evident. On the other hand, a s t r a i g h t -line relationship is observed between the n a t u r a l w a t e r content and initial void r a t i o ( F i g u r e 7 ) within the range of
values obtained. This l i n e , however, h a s a slightly f l a t t e r slope than that shown by L e a and B r a w n e r (1963). As t h i s relationship i s a function of
the specific gravity of the m a t e r i a l a s well a s of the gas content of the p o r e s , it i s reasonable to expect that the slope of the line will v a r y f o r different peat types. The lack of a c l e a r relationship between initial void r a t i o and c o m p r e s s i o n index i s in a l l probability the r e s u l t of disturbance of the s a m p l e and r a t h e r e r r a t i c t e s t r e s u l t s a r i s i n g f r o m the e a r l y difficulties experienced in c a r r y i n g out consolidation t e s t s on peat.
It m a y be observed f r o m F i g u r e 8 that e x c e s s hydrostatic p r e s s u r e s dissipated in l e s s than 10 minutes f o r m o s t c e l l p r e s s u r e s . As the c e l l p r e s s u r e i n c r e a s e d and the permeability of the peat d e c r e a s e d , however,
t h e t i m e r e q u i r e d f o r p o r e w a t e r p r e s s u r e s t o r e t u r n t o z e r o i n c r e a s e d , although f o r the p a r t i c u l a r s a m p l e indicated it did not e x c e e d about 45 m i n u t e s
.
T h e g e n e r a l difficulty i n d e t e r m i n i n g the boundary between t h e p r i m a r y and s e c o n d a r y p h a s e s of consolidation with the one - d i m e n s i o n a l consolidation t e s t s led to a c o n s i d e r a t i o n of the applicability of t r i a x i a l consolidation t e s t s with p o r e w a t e r p r e s s u r e m e a s u r e m e n t s . A few s u c h t e s t s w e r e c a r r i e d out and a r e d e s c r i b e d in the following pages.
T RIAXIAL CONSOLIDATION TESTS T e s t P r o c e d u r e s
T h e m a i n object of the t r i a x i a l consolidation t e s t s w a s t o study t h e magnitude of the p o r e w a t e r p r e s s u r e s in a peat s a m p l e subjected to a n i n c r e a s e in c e l l p r e s s u r e and t o o b s e r v e the r a t e of d i s s i p a t i o n of t h e s e p r e s s u r e s when consolidation w a s allowed t o t a k e place. F i g u r e 9
i l l u s t r a t e s the a p p a r a t u s used f o r t h e s e t e s t s . T h e p o r e w a t e r p r e s s u r e w a s m e a s u r e d a t the top of t h e s a m p l e s and d r a i n a g e f o r consolidation
o c c u r r e d a t the bottom. T h e w a t e r expelled during c o m p r e s s i o n of the s a m p l e w a s collected in a b u r e t t e a s shown.
F i g u r e 9 a l s o shows t h e p o s i t i o n s of the s a m p l e in the c e l l d u r i n g t h e t e s t . S a m p l e s w e r e e x t r u d e d f r o m 2. 8 0 - i n c h inside - d i a m e t e r Shelby t u b e s . P o r o u s s t o n e s s e p a r a t e d the s a m p l e f r o m t h e p e d e s t a l and the loading c a p , e v e r y component having a d i a m e t e r c l o s e t o that of the s a m p l e s .
T h e t e c h n i c a l p r o c e d u r e s and p r e c a u t i o n s involved in t h e s a m p l e p r e p a r a t i o n s w e r e e s s e n t i a l l y t h e s a m e a s t h o s e u s e d in the p r e p a r a t i o n of a s o i l s a m p l e f o r t r i a x i a l s h e a r t e s t s with p o r e w a t e r p r e s s u r e m e a s u r e - m e n t s . T e s t p r o c e d u r e s w e r e a s follows:
1. With t h e s a m p l e in p l a c e , the c e l l was a s s e m b l e d and filled with w a t e r , t h e p o r e w a t e r p r e s s u r e s y s t e m a d j u s t e d and the b u r e t t e c e n t r e d on z e r o .
2. A light l a t e r a l p r e s s u r e w a s applied t o r i d t h e s a m p l e of any f r e e a i r and w a t e r e n t r a p p e d d u r i n g s a m p l e p r e p a r a t i o n s . T h e no-volume change valve w a s then opened. When e q u i l i b r i u m w a s r e s t o r e d , the no -volume change valve w a s closed.
3 . T h e c e l l p r e s s u r e w a s r a i s e d f r o m 0 t o 8 kg
/
c m 2 using a p r e s s u r e i n c r e m e n t r a t i o in the r a n g e of A ~ = /1 . ~w e r e o b s e r v e d and r e c o r d e d . When they had r e a c h e d a m a x i m u m , the d r a i n a g e valve w a s opened. Consolidation o c c u r r e d and sub sequent
reduction in the p o r e w a t e r p r e s s u r e w a s followed by keeping the m e r c u r y l e g s in the U-tube in balance.
5. P o r e w a t e r p r e s s u r e m e a s u r e m e n t s and volume change w e r e then plotted a g a i n s t log t i m e and s q u a r e r o o t of t i m e
(n).
6 , When the ultimate d e s i r e d c e l l p r e s s u r e had been r e a c h e d , followed by c o m p l e t e consolidation, the no-volume change valve r e m a i n e d c l o s e d and t h e valve t o the p o r e w a t e r p r e s s u r e on the left side of the U-tube w a s closed. T h i s prevented the s a m p l e f r o m a b s o r b i n g w a t e r a s the c e l l p r e s s u r e w a s reduced.
7 . The s a m p l e w a s r e m o v e d f r o m the c e l l , weighed, m e a s u r e d , and o v e n - d r i e d . Specific g r a v i t y and o r g a n i c content values of the oven-dried s a m p l e w e r e d e t e r m i n e d .
T e s t R e s u l t s
As f o r the one-dimensional consolidation t e s t s , v a r i a t i o n in the t e s t r e s u l t s m a k e s i t difficult t o s e l e c t "typical" c u r v e s . T e s t 98-1 5-1 w a s somewhat typical, h o w e v e r , and c u r v e s f o r p o r e w a t e r p r e s s u r e and volume change v e r s u s l o g - t i m e and squaxe r o o t t i m e a r e shown in F i g u r e s 10 and 11. Sample d a t a f o r t h i s and o t h e r t e s t s a r e s u m m a r i z e d in Table 11, and a
s u m m a r y of t e s t r e s u l t s i s given in Table 111. D i s c u s s i o n of R e s u l t s
The few t r i a x i a l consolidation t e s t s c a r r i e d out w e r e explanatory, designed t o develop techniques f o r , and proficiency i n , t e s t i n g peat s a m p l e s . Consequently, i t i s difficult t o d r a w m a n y definite conclusions. I t s e e m s evident t h a t c e r t a i n a s p e c t s of the r e s u l t s r e f l e c t deficiencies in the t e s t a p p a r a t u s and e r r o r s in p r o c e d u r e r a t h e r than the c h a r a c t e r i s t i c s of the m a t e r i a l t e s t e d . N e v e r t h e l e s s , c e r t a i n f a c t o r s w e r e o b s e r v e d t h a t will be of a s s i s t a n c e in planning f u r t h e r t r i a x i a l consolidation t e s t s of a m o r e p r e c i s e n a t u r e .
T e s t r e s u l t s indicated an S - s h a p e d log t i m e - s e t t l e m e n t c u r v e f o r a l l load i n c r e m e n t s . T h i s i s in c o n t r a s t with the o n e - d i m e n s i o n a l c o n s o l i - dation t e s t , which d o e s not always produce an S - s h a p e d c u r v e e x c e p t , p o s s i b l y , f o r the f i r s t load i n c r e m e n t . T e s t s w e r e not c a r r i e d out o v e r a sufficiently long period of t i m e t o produce the c h a r a c t e r i s t i c s e c o n d a r y c o m p r e s s i o n line.
The p o r e w a t e r p r e s s u r e r e s p o n s e t o the c e l l p r e s s u r e w a s o b s e r v e d t o be both e x t r e m e l y slow and quite p o o r , with v a l u e s varying o v e r a wide
range f r o m a s low a s 20 p e r cent t o a s high a s 100 p e r cent of the cell p r e s s u r e . It i s reasonable t o a s s u m e that this may be due both to
inadequacies of the t e s t apparatus and t o unfamiliarity with the m a t e r i a l . F r o m Table 111 it m a y be seen that the dissipation of pore water p r e s s u r e a l s o was e x t r e m e l y slow, in some c a s e s requiring a s long a s 10,000 minutes to dissipate completely. This i s considerably longer than even that r e p o r t e d by Ripley and Leonoff (1 961), who found that in t h e i r t r i a x i a l
consolidation t e s t the dissipation of pore w a t e r p r e s s u r e w a s e s s e n t i a l l y complete a f t e r 1000 minutes for a l m o s t a l l load i n c r e m e n t s for a sample of 1 0 . 1 5 - c m initial height and 5.08 - c m initial d i a m e t e r .
GENERAL DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS
G e n e r a l Discussion
Consolidation of a saturated soil i s a time-dependent volume reduction involving a d e c r e a s e in the water content of the soil. Any soil i s a s y s t e m of two o r t h r e e spatially co-existent phases: a solid phase, a liquid phase and, s o m e t i m e s ( p a r t i c u l a r l y for peat), a g a s phase. When t h e r e i s an i n c r e a s e of p r e s s u r e on such a s y s t e m in equilibrium t h e r e i s a volume change with an escape of fluid f r o m the s y s t e m . T h i s p r o c e s s of volume reduction (consolidation) involves a t i m e lag. Consolidation of inorganic s o i l s i s thought t o be divided into two phases: the p r i m a r y consolidation phase ( d e s c r i b e d by the c l a s s i c a l concept of ~ e r i a ~ h i ) , and the secondary consolidation ( o r c o m p r e s s i o n ) phase. The time lag in the p r i m a r y consolidation phase i s a s s o c i a t e d with the dissipation of e x c e s s pore water p r e s s u r e s and i s due to the r e s i s t a n c e t o volume change offered by the escaping w a t e r . The t i m e lag in the secondary compression phase i s associated with plastic flow o r c r e e p and in effect i s due to r e s i s t a n c e offered by the solid phase t o volume change in the s y s t e m .
In g e n e r a l , the approach t o the consolidation p r o c e s s of peat h a s been s i m i l a r t o that f o r clays exhibiting exceptionally l a r g e secondary c o m p r e s s i o n effects. Most investigators have been preoccupied with the need t o obtain immediate r e s u l t s and have relied on this concept. Exceptions a r e Evgenlev (1961) and Adams (1964), who acknowledged that peat i s a
m a t e r i a l quite different f r o m clay. They considered that the consolidation p r o c e s s involves the expulsion of f r e e water f r o m the m a c r o p o r e s ( or peat m a s s ) and the expulsion of water f r o m the closed p o r e s ( o r solid m a t t e r ) . The l a t t e r is the l o n g - t e r m p r o c e s s and m u s t n e c e s s a r i l y be accompanied by a breakdown of the c e l l s t r u c t u r e within the fossilized plant m a t t e r . It i s this approach that perhaps holds the g r e a t e s t possibility f o r f u r t h e r study. T h i s becomes even m o r e apparent when one c o n s i d e r s the range of peats f r o m the predominantly woody o r non-woody fibrous type to the predominately amorphous-granular type. When the f o r m e r peat type i s subjected to
w a t e r ; f o r the l a t t e r type the p r o c e s s is m o r e colloidal.
L i t e r a t u r e review ( M a c F a r l a n e , 1965) c l e a r l y indicates that the two-phase concept of consolidation, one t e r m i n a t i n g a t a c l e a r l y
defined polnt and the o t h e r continuing f o r a long period of t i m e , l e a v e s something t o be d e s i r e d f o r p e a t s . The point a t which p r i m a r y consoli- dation e n d s and s e c o n d a r y c o m p r e s s i o n begins i s in m o s t c a s e s d i s a p - pointingly o b s c u r e , a f a c t t h a t i s confirmed by the t e s t s d e s c r i b e d in t h i s r e p o r t . It w a s b a s i c a l l y t h i s p r o b l e m that i n s p i r e d the s e r i e s of t e s t s r e p o r t e d h e r e i n .
T h i s i s not a n adequate concept f o r the consolidation p r o c e s s of peat. L e a and B r a w n e r (1963) pointed out t h a t p r i m a r y and s e c o n d a r y consolidation a r e only e m p i r i c a l divisions in a continuous c o m p r e s s i o n p r o c e s s . T h i s was confirmed by Crawford (1964) who s a i d f u r t h e r t h a t (for c l a y s ) t h e r e i s a m p l e evidence t h a t the r e l a t i v e contribution of e a c h phase i s l a r g e l y a function of the l a b o r a t o r y t e s t p r o c e d u r e , especially the r a t e of loading. T h e r e i s no r e a s o n t o doubt that t h i s i s not equally t r u e f o r p e a t s .
T o s u m up, in the investigation of the consolidation p r o c e s s f o r p e a t s t h e r e h a s been a n undue preoccupation with a n extrapolation of the p r i n c i p l e s and p r o c e d u r e s of the consolidation p r o c e s s f o r inorganic s o i l s . An e n t i r e l y f r e s h a p p r o a c h i s indicated. The study of the l i t e r a t u r e did show a l s o t h a t t h e r e a r e s o m e i n t e r e s t i n g and useful s i m i l a r i t i e s in the consolidation c h a r a c t e r i s t i c s of s o m e p e a t s and c l a y s . An examination of t h e s e s i m i l a r i t i e s m a y give s o m e guidance f o r f u t u r e s t u d i e s .
Hamilton and Crawford (1959) d i s c u s s e d v a r i o u s f a c t o r s that a r e known to affect consolidation t e s t r e s u l t s : s a m p l e d i s t u r b a n c e , i n c r e m e n t r a t i o and d u r a t i o n , g a s content, t e m p e r a t u r e , and t e s t i n g techniques. T h e s e will be d i s c u s s e d briefly in relation t o the r e s e a r c h t h a t h a s been c a r r i e d out on p e a t s by the v a r i o u s i n v e s t i g a t o r s a s well' a s the t e s t r e s u l t s p r e s e n t e d in t h i s r e p o r t .
Sample Disturbance
The difficulty of obtaining s a t i s f a c t o r y undisturbed s a m p l e s of peat f o r l a b o r a t o r y a n a l y s i s h a s been mentioned by Anderson (1962), Hillis and B r a w n e r (1961) and o t h e r s . T h i s i s due t o the l o s s of m o i s t u r e during the sampling p r o c e s s , the inability of the s a m p l e t o r e t a i n i t s original
volume with s t r e s s relief due t o the p r e s e n c e of g a s , and the u s u a l d i s t u r b a n c e of a soft s o i l s a m p l e when r e t a i n e d in a tube o r cut out a s a block s a m p l e . Evgen'ev (1961) pointed out that the amount of consolidation in the " p r i m a r y
"
T o e l i m i n a t e v a r i a t i o n s a r i s i n g f r o m t h i s f a c t o r , Wilson (1964) r e s o r t e d t o t h e u s e of r e m o u l d e d s a m p l e s . T a y l o r (1942), h o w e v e r , s t a t e d t h a t l e s s s e c o n d a r y c o m p r e s s i o n o c c u r s in r e m o u l d e d s a m p l e s than in u n d i s t u r b e d s a m p l e s of the s a m e m a t e r i a l . Remoulcling of p e a t s a m p l e s b r e a k s down t h e n a t u r a l f i b r e s t r u c t u r e and c o n s e q u e n t l y
c o m p r e s s i o n c h a r a c t e r i s t i c s a r e not a r e f l e c t i o n of the n a t u r a l condition. L o ( 1 961) noted t h a t f o r c l a y s exhibiting s e c o n d a r y c o m p r e s s i o n , e n t i r e l y d i f f e r e n t and d i s t i n c t b e h a v i o u r s w e r e o b s e r v e d between s a m p l e s in t h e u n d i s t u r b e d and in t h e r e m o u l d e d s t a t e s . F o r the remoulded s a m p l e s t h e s e t t l e m e n t - l o g t i m e c u r v e s d u r i n g t h e s e c o n d a r y r a n g e had a s i m i l a r s h a p e throughout a l l t h e loading i n c r e m e n t s . U n d i s t u r b e d s a m p l e s , h o w e v e r , exhibited pronounced c h a n g e s in t h e s h a p e of t h e s e c o n d a r y c o m p r e s s i o n c u r v e s f o r d i f f e r e n t load r a n g e s . F o r p r e s s u r e i n c r e m e n t s below t h e p r e c o n s o l i d a t i o n load t h e s e c o n d a r y t i m e e f f e c t w a s s m a l l . At p r e s s u r e s n e a r t h e p r e c o n s o l i d a t i o n l o a d t h e r e w a s a n a b r u p t change in t h e s h a p e of t h e c o m p r e s s i o n c u r v e and s e c o n d a r y c o m p r e s s i o n b e c a m e i m p o r t a n t . T h e r e a f t e r s h a p e s of t h e c o m p r e s s i o n c u r v e s r e s e m b l e d t h o s e f o r t h e r e m o u l d e d s a m p l e s .
T h e u s e of r e m o u l d e d p e a t s a m p l e s h a s the advantage of the s a m e i n i t i a l void r a t i o s f o r a l l s a m p l e s , t h e s a m e w a t e r c o n t e n t , and s o m e r e p r o - d u c i b i l i t y of r e s u l t s , but t h e s e m u s t be weighed a g a i n s t t h e f a c t of t h e
e f f e c t of s t r u c t u r a l d i s t u r b a n c e on s e c o n d a r y c o m p r e s s i o n .
T a y l o r ( 1 942) s a i d a l s o t h a t g r e a t e r s e c o n d a r y c o m p r e s s i o n o c c u r s in o n e - d i m e n s i o n a l c o m p r e s s i o n t h a n in t h r e e - d i m e n s i o n a l c o m p r e s s i o n w h e r e t h e d i s t u r b a n c e of t h e s t r u c t u r e i s l e s s . T h i s w a s not too evident f r o m t h e s e r i e s of t e s t s d e s c r i b e d in t h i s r e p o r t , p a r t i c u l a r l y on account of e r r o r s in t h e t r i a x i a l consolidation t e s t .
Load I n c r e m e n t R a t i o and D u r a t i o n
T a y l o r (1942) concluded t h a t consolidation ( of c l a y s ) p r o c e e d s m o r e slowly f o r s m a l l load i n c r e m e n t s t h a n f o r l a r g e , and t h a t p r e d i c t i o n s of r a t e of s e t t l e m e n t m a y be c o n s i d e r a b l y in e r r o r u n l e s s load i n c r e m e n t s in t h e t e s t and in t h e f i e l d a r e e s s e n t i a l l y t h e s a m e . I r r e g u l a r i n c r e m e n t r a t i o s w e r e found t o i n t r o d u c e i r r e g u l a r i t i e s in t h e t e s t r e s u l t s , and it would a p p e a r t h a t t h i s should be s t a n d a r d i z e d f o r a n y p a r t i c u l a r soil.
Hamilton and C r a w f o r d (1959) found t h a t although the s i z e of load i n c r e m e n t s did not affect t h e void r a t i o - p r e s s u r e c u r v e , the i n t e r p r e t a t i o n of t h e m o s t p r o b a b l e p r e c o n s o l i d a t i o n p r e s s u r e b e c o m e s m o r e difficult a s load i n c r e - m e n t s b e c o m e l a r g e r . Newland and Allely (1960) noted t h a t the r a t i o of
i n c r e m e n t r a t i o i n c r e a s e d , becoming close t o z e r o with p r e s s u r e i n c r e m e n t r a t i o s of 10 and above. Leonards and Gireault (1 961) found that, depending on the load increment r a t i o and whether o r not the p r e s s u r e i n c r e m e n t s s t r a d d l e the effective preconsolidation p r e s s u r e , dial reading v e r s u s log t i m e c u r v e s could be c l a s s i f i e d according t o t h r e e typical shapes. L a r g e r a t e s of secondary c o m p r e s s i o n p e r unit of p r i m a r y c o m p r e s s i o n w e r e observed t o be a s s o c i a t e d with s m a l l load i n c r e m e n t ratios. The r a t e of s e c o n d a r y c o m p r e s s i o n p e r unit
height p e r unit p r e s s u r e i n c r e m e n t ( a t a given total p r e s s u r e ) i n c r e a s e d rapidly a s the load i n c r e m e n t r a t i o was reduced.
As h a s a l r e a d y been mentioned, L o (1961) found p r e s s u r e i n c r e - m e n t s in proximity t o the preconsolidation load m o s t significant, p a r t i c u - l a r l y f o r undisturbed s a m p l e s . Wahls (1962) concluded that the t i m e r e q u i r e d f o r the development of the l i n e a r relationship between secondary c o m p r e s s i o n and log t i m e i n c r e a s e d a s the p r e s s u r e i n c r e m e n t r a t i o d e c r e a s e d ; the t i m e r e q u i r e d f o r the completion of p r i m a r y effects a l s o , i n c r e a s e d . F o r a given total p r e s s u r e Wahls a l s o found (in a g r e e m e n t with
L e o n a r d s and Gireault, and Newland and Allely) that the r a t i o of the magni- tude of the p r i m a r y effect t o that of the secondary effect reduced a s the p r e s s u r e i n c r e m e n t (and the p r e s s u r e i n c r e m e n t r a t i o ) is reduced.
Relatively little attention h a s been paid t o the effect of low i n c r e - ment r a t i o on the consolidation p r o c e s s in peat, but t h e r e i s evidence that it i s not too d i s s i m i l a r to that of clays. S c h r o e d e r and Wilson (1962) r e p o r t e d that p r e l i m i n a r y t e s t s indicated that the load i n c r e m e n t r a t i o w a s one of the f a c t o r s governing the consolidation c h a r a c t e r i s t i c s of peat. L e a and B r a w n e r (1963) r e p o r t e d good r e s u l t s using a single i n c r e m e n t load, i. e . a t e s t on which the load sequence on the s a m p l e i s identical with that expected f o r the prototype.
In i n c r e m e n t a l loading t e s t s the duration of e a c h i n c r e m e n t used by m o s t investigators was 24 h o u r s . Hillis and B r a w n e r (1961) suggested that the load i n c r e m e n t be permitted t o r e m a i n on the s a m p l e only 30
minutes t o define the "primary" phase of the consolidation p r o c e s s . In the t e s t s e r i e s d e s c r i b e d in t h i s r e p o r t the load increment r a t i o ( A P / P ) was 1 f o r m o s t t e s t s and the duration, 24 h o u r s . In view of the evidence that the e x c e s s pore w a t e r p r e s s u r e phase in peat i s complete within a few minutes, i t would a p p e a r that the 24-hour duration of loading i s too long f o r s h o r t - t e r m t e s t s and too s h o r t f o r l o n g - t e r m t e s t s t o define the secondary phase
of c o m p r e s s i o n . F u r t h e r r e s e a r c h is needed on t h i s question of load i n c r e - ment r a t i o and duration with r e g a r d t o v a r i o u s peat types.
G a s Content
p o r e s ; indeed, t h i s i s c h a r a c t e r i s t i c of organic s o i l s in which t h e r e i s decomposition of plant residue. Above the w a t e r table the g a s produced i s chiefly carbon dioxide; below, it i s methane, with l e s s e r amounts of nitrogen, carbon dioxide o r hydrogen sulphide. The total amount of g a s in peat consists of the g a s dissolved in the p o r e w a t e r and the gas in bubbles o r void s p a c e s not dissolved in the p o r e w a t e r and known a s "free" gas. The relative proportions of f r e e and dissolved g a s will depend on the p r e s s u r e , t e m p e r a t u r e and type of g a s . I t s
p r e s e n c e will quite certainly have a considerable effect on the c o m p r e s s i o n c h a r a c t e r i s t i c s of peat. Unfortunately, however, this phenomenon h a s , with f e w exceptions, been universally ignored in consideration of cons oli
-
dation of peat.Moran e t a1 (1958) d i s c u s s this m a t t e r a t some length, and f r o m an analysis of consolidation t e s t s show t h a t f r e e g a s m a y amount t o 5 t o
10 p e r cent of the total volume of a typical l a b o r a t o r y sample of highly organic soil. They suggest that the l a r g e secondary compression exhibited in l a b o r a t o r y t e s t s of organic s o i l s may well be due to the influence of t h i s g a s , and t h a t among i t s effects on consolidation a r e : ( 1 ) Upon application of load, compression of the gas m a y cause a delay in the r e s p o n s e of pore p r e s s u r e s to a change in boundary w a t e r p r e s s u r e s . T h i s m a y well account f o r the slow r e s p o n s e noted in the t h r e e dimensional t e s t s d e s c r i b e d in t h i s r e p o r t , a s well a s that r e p o r t e d by Wilson (1963). ( 2 ) When loading h a s been completed, expansion of the g a s will d e c r e a s e the r a t e of consoli- dation.
L e a and Brawner (1963) r e p o r t that a i r ( o r g a s ) content of peat s a m p l e s has been e s t i m a t e d to be a s high a s 7 to 10 p e r cent of total volume, and t h i s i s in close a g r e e m e n t with Moran e t a1 (1958). They suggest that u n l e s s g a s content i s calculated, e r r o r s in void r a t i o ,
assuming full saturation, m a y be a s g r e a t a s 10 p e r cent. It i s advisable that future r e s e a r c h on consolidation of peat should recognize and account f o r the effect of the p r e s e n c e of gas.
T e m p e r a t u r e
Moran
-
e t a1 (19
58) stated in passing that the magnitude of secondary c o m p r e s s i o n v a r i e s with t e m p e r a t u r e (among other f a c t o r s ) . Lo (1961) emphasized that variation in t e m p e r a t u r e has a predominant influence on both the r a t e and magnitude of secondary c o m p r e s s i o n . He suggested that this environmental factor should be controlled in investigations onsecondary compression. Testing techniques
Very little r e f e r e n c e was made by m o s t investigators to consoli- dation testing techniques, with p a r t i c u l a r r e f e r e n c e to t h e i r effect on the
t e s t r e s u l t s . T h e question of undisturbed v e r s u s remoulded t e s t s h a s a l r e a d y been d i s c u s s e d . The paper by S c h r o e d e r and Wilson (1962), however, r a i s e d the question of the effect of woody chunks in the peat, and in the ensuing d i s c u s s i o n of the paper it w a s pointed out that t h e s e woody chunks w e r e removed p r i o r t o consolidation t e s t i n g . T h i s was a l s o the p r a c t i c e f o r the s a m p l e s t e s t e d a t the Division of Building R e s e a r c h . The r e l a t i v e l y i n c o m p r e s s i b l e woody chunks, though s m a l l , c a u s e d s e r i o u s tilting of the top porous plate and the loading cap.
C o m p r e s s i b i l i t y of the a p p a r a t u s w a s not c o n s i d e r e d t o be a n i m p o r t a n t f a c t o r due t o the e x t r e m e l y high c o m p r e s s i b i l i t y of the peat. Ring f r i c t i o n f o r s t a n d a r d consolidation s a m p l e s 0 . 7 5 t o 1 in. thick w a s not taken into account and is not c o n s i d e r e d t o be unduly significant f o r peats. F o r l a r g e s a m p l e s , s u c h a s the 75 c m high s a m p l e s t e s t e d by Wilson (1 964), ring friction undoubtedly b e c o m e s i m p o r t a n t and should be taken into account.
CONCLUSIONS
1. In s t u d i e s of the consolidation of peat some phenomena show a s t r i k i n g r e s e m b l a n c e t o the consolidation c h a r a c t e r i s t i c s of clay and organic clay. Although t h e s e s i m i l a r i t i e s a r e recognized and provide guidance f o r r e s e a r c h , it i s c o n s i d e r e d t h a t the physical p r o c e s s of c o m p r e s s i o n of peat is substantially different f r o m t h a t of clay owing t o i t s e n t i r e l y different n a t u r e .
2. G e n e r a l l y the settlement-log t i m e c u r v e s f o r peat exhibit a n "Sf' shaped c u r v e initially, but t h i s is not a s c l e a r l y pronounced a s f o r inorganic s o i l s . It the r a f t e r a s s u m e s a c h a r a c t e r i s t i c s t r a i g h t - l i n e relationship which continues f o r a long period of t i m e .
3 . P r i m a r y consolidation and s e c o n d a r y c o m p r e s s i o n a r e considered t o be p u r e l y e m p i r i c a l divisions of a continuous c o m p r e s s i o n p r o c e s s , both o c c u r r i n g simultaneously during p a r t o'f the consolidation p r o c e s s .
4. In the l a b o r a t o r y t e s t i n g , the p r i m a r y consolidation phase o c c u r s v e r y rapidly, g e n e r a l l y within a few m i n u t e s with s t a n d a r d s i z e d s a m p l e s . The magnitude of s e t t l e m e n t during t h i s phase is proportional t o thickness (that i s t o length o r d r a i n a g e path). As s o m e c o n t r o v e r s y
s u r r o u n d s the r a t e of consolidation in t h i s p h a s e , f u r t h e r r e s e a r c h n e e d s t o be c a r r i e d out with r e f e r e n c e t o different peat types.
5. Secondary c o m p r e s s i o n of peat can constitute a l a r g e proportion of t o t a l settlement. The magnitude, however
,
is dependent upon many f a c t o r s , s u c h a s low i n c r e m e n t r a t i o , t e m p e r a t u r e , peat type ( d e g r e e of decomposition), load h i s t o r y , but i s independent of d r a i n a g ewith the e s t i m a t e of the magnitude of l o n g - t e r m field s e t t l e m e n t . 6. G a s content (free g a s ) of peat m a y constitute up to 10 p e r cent of
t o t a l volume. The p r e s e n c e of t h i s g a s h a s a substantial effect on' consolidation c h a r a c t e r i s t i c s .
7. The p e r m e a b i l i t y of peat i s initially v e r y high, but it diminishes m a r k e d l y under load. It i s g r e a t e r in the horizontal plane than in the v e r t i c a l plane, logically, owing to the deposition of peat. RECOMMENDATIONS
It i s recommended that future r e s e a r c h into consolidation c h a r a c t e r i s t i c s of peat have a two-pronged approach: field p r o g r a m s c a r r i e d out in conjunction with l a b o r a t o r y p r o g r a m s . The suggested field approach h a s been d e s c r i b e d ( M a c F a r l a n e , 1964) in DBR I n t e r n a l Report No. 304. The l a b o r a t o r y p r o g r a m should be c a r r i e d out under conditions of constant t e m p e r a t u r e . It i s considered that initially a t l e a s t the one -dimensional t e s t offers the b e s t approach to a n a l y s i s . Although it should be kept in mind that the m a t e r i a l being t e s t e d i s quite different f r o m the m a t e r i a l f o r which the consolidation t e s t was designed, it i s believed a t p r e s e n t that the u s e of standard a p p a r a t u s i s valid. F o r l o n g - t e r m t e s t s , however, thought should be given to the effect of the acidity of peats on the consolidation r i n g s ; allowances
should be made for the p r e s e n c e of g a s in the peat; and p o r e w a t e r p r e s s u r e s should be m e a s u r e d f o r a l l t e s t s .
S e r i e s - of t e s t s should be c a r r i e d out using different p r e s s u r e i n c r e m e n t r a t i o s f o r s a m p l e s of the s a m e initial void r a t i o , height, e t c . Samples of different height should be subjected t o s i m i l a r loading
conditions. L a b o r a t o r y predictions f o r magnitude and r a t e of field s e t t l e m e n t f o r a p a r t i c u l a r peat type should be checked by field t e s t s .
Ultimately, however, f o r a p r o p e r a n a l y s i s of peat behaviour a m o r e fundamental approach to the behaviour of peat under load will be n e c e s s a r y , involving a botanical - soil science -engineering examination of the constituent m a t e r i a l s .
LIST O F R E F E R E N C E S
A d a m s , J . I.
,
1961. L a b o r a t o r y c o m p r e s s i o n t e s t s on peat. P r o c . Seventh Muskeg R e s e a r c h C o n f e r e n c e , 18 and 19 A p r i l , 1961, National R e s e a r c h Council, A s s o c . C o m m i t t e e on Soil and Snow M e c h a n i c s , T e c h n i c a l M e m o 71, p. 36-54.A d a m s , J . I.
,
1964. A c o m p a r i s o n of field and l a b o r a t o r y consolidation m e a s u r e m e n t s in p e a t . P r o c . Ninth Muskeg R e s e a r c h Conference 20 and 21 May 1963, National R e s e a r c h Council, A s s o c . C o m m i t t e e on Soil and Snow M e c h a n i c s , T e c h n i c a l Memo 8 1 , p. 117-135.A n d e r s o n , K.
0.
,
1962. Muskeg s t u d i e s in A l b e r t a . Highway R e s e a r c h B o a r d , B u l l e t i n , No. 31 6, p. 23-31, Washington, D. C.A n d e r s o n , K.
0.
and R. A H e m s t o c k . 1959. Relating s o m e e n g i n e e r i n g p r o p e r t i e s of m u s k e g t o s o m e p r o b l e m s of field c o n s t r u c t i o n . P r o c . F i f t h Muskeg R e s e a r c h C o n f e r e n c e , 4 M a r c h 1959. NationalR e s e a r c h Council,Assoc. C o m m i t t e e on Soil and Snow M e c h a n i c s , T e c h n i c a l M e m o 61, p. 16-25.
B a r b e r , E . S .
,
1961. Notes on s e c o n d a r y consolidation. P r o c . Highway R e s e a r c h B o a r d , Vol. 40: p. 663-675, Washington, D. C .C r a w f o r d , C . B .
,
1964. I n t e r p r e t a t i o n of t h e consolidation t e s t . J o u r n a l , Soil M e c h a n i c s and Foundations Division, A. S . C. E.,
Vol. 90:No. SM 5, P t . 1 , p. 87-102.
Evgen'ev, I. E .
,
1961. T h e a c c e l e r a t e d method of obtaining p e a t s o i lc o m p r e s s i o n c h a r a c t e r i s t i c s . (In R u s s i a n ) T o r f y a n a y a P r o m y s h l e n n o s t ( P e a t I n d u s t r y ) No. 1 , p . 2 5 , 2 6 . H a m i l t o n , J . J . and C . B . C r a w f o r d , 1959. I m p r o v e d d e t e r m i n a t i o n s of consolidation p r e s s u r e of a s e n s i t i v e c l a y . ASTM, S p e c i a l T e c h n i c a l P u b . No. 254, p. 254-271. H i l l i s , S . F. and C. 0 . B r a w n e r
,
1961. T h e c o m p r e s s i b i l i t y of p e a t with r e f e r e n c e t o m a j o r highway c o n s t r u c t i o n in B r i t i s h Columbia. P r o c . Seventh Muskeg R e s e a r c h C o n f e r e n c e , 18 and 19 A p r i l 1961. National R e s e a r c h Council, A s s o c . C o m m i t t e e on Soil and Snow M e c h a n i c s , T e c h n i c a l M e m o 7 1 , p . 204-227.L e a , N. D. and C. 0 . B r a w n e r , 1963. Highway d e s i g n and c o n s t r u c t i o n o v e r p e a t d e p o s i t s in the lower mainland region of B r i t i s h Columbia.
L e o n a r d s , G, and P. G i r e a u l t , 1961. A study of t h e one-dimensional consolidation t e s t . P r o c . F i f t h International Conference of Soil Mechanics and Foundation Engineering, Vol. 1: p . 21 3 -2 18.
L o ,
K.Y.,
1961. Secondary c o m p r e s s i o n of c l a y s . J o u r n a l , Soil Mechanics and Foundations Division, P r o c . ASCE, 87, SM 4 , P t . 1 , p . 61-87.M a c F a r l a n e , I. C. , 1965. The consolidation of peat: A l i t e r a t u r e r e v i e w . National R e s e a r c h Council, Division of Building R e s e a r c h . NRC 8 393.
M o r a n , P r o c t o r , M u e s e r and Rutledge, 1958. Study of d e e p s o i l
stabilization by v e r t i c a l sand d r a i n s . No. 88812, B u r e a u of Y a r d s and D o c k s , D e p a r t m e n t of t h e Navy, Washington, D. C.
Newland, P. L. and B. H. Allely, 1960. A study of the consolidation c h a r a c t e r i s t i c s of a clay. Ggotechnique, X:2:62: -74.
Ripley, C. F. and C . E . Leonoff, 1961. Embankment s e t t l e m e n t behaviour on d e e p peat. P r o c . Seventh Muskeg R e s e a r c h C o n f e r e n c e , 18 and 19 A p r i l 1961, National R e s e a r c h Council, A s s o c . C o m m i t t e e on Soil and Snow M e c h a n i c s , Technical M e m o 71, p . 185-204.
S c h r o e d e r , J . and N . E . Wilson, 1962. T h e a n a l y s i s of s e c o n d a r y
consolidation of p e a t . P r o c . Eighth Muskeg R e s e a r c h C o n f e r e n c e , 17 and 18 May 1962, National R e s e a r c h Council, A s s o c i a t e C o m m i t t e e on Soil and Snow M e c h a n i c s , Technical M e m o 74, p . 130-144.
T a y l o r , D. W . , 1942. R e s e a r c h on consolidation of c l a y s . M . I T . , D e p a r t m e n t of Civil S a n i t a r y Engineering
,
S e r i a l 82.Wahls, H . E .
,
1962. Analysis of p r i m a r y and s e c o n d a r y consolidation. P r o cA .
S. C . E . , J o u r n a l of the Soil M e c h a n i c s and Foundations Division, Vol. 88: SM 6 , p . 207-231.Wilson, N. W . , 1964. Consolidation and flow c h a r a c t e r i s t i c s of p e a t . P r o c . Ninth Muskeg R e s e a r c h C o n f e r e n c e , NRC-ACSSM, T e c h n i c a l M e m o 8 1 , p . 150-160.
T A B L E I
SUMMARY O F RESULTS O F T H E ONE-DIMENSIONAL CONSOLIDATION T E S T S
D e p t h Obtained 2'3"-2'4" 2'4" -2'5" 2r4L11 -215111 016~11 -017111 0'9" -0'10" 2r9$1' -2'10$" 3'211 -313" 3'9" -3'1 0" 3'10" -3'11" 4'2'' -4'3" 4'4" -4'5" L o c a t i o n of S a m p l e M e r B l e u e P e a t Bog, Ottawa. M e r Bleue M e r B l e u e M e r B l e u e M e r B l e u e M e r B l e u e M e r B l e u e H e a s l i p , O n t a r i o H e a s l i p H e a s l i p H e a s l i p S a m p l e No. 63- 2 - 2 6 3 - 2 - 3 63- 4 - 3 63- 5 - 3 6 3 - 5 - 5 63- 6-4 63- 6 - 6 9 8 - 1 4 - 1 9 8 - 1 4 - 2 98-14-4A 9 8 - 1 4 - 4 B
-.
C l a s s i f i c a t i o n C o v e r P e a t S p e c i f i c G r a v i t y 1. 38 1. 38 1 . 3 6 1 . 4 4 1 . 4 4 1 . 40 1.40 1 . 6 4 1 . 6 4 1 . 6 4 1 . 64 D a t e T e s t e d 9 . 4 . 57 9 . 4 . 57 1 3 . 6 . 5 7 9 . 7 . 5 7 9 . 7 . 5 7 26.7.57 26.7. 57 1 i . 5. 60 11. 5.60 2 7 . 7 . 6 0 2 9 . 7 . 6 0 E B I E B I E B I E l E l E l E I A1 A1 A1 A1 11 11 11 9 9 9 9 10 10 10 1 0 O r g a n i c Content N a t . W a t e r Cont. 9 68 N a t . e 13. 51
935 13. 29 1 3 . 2 9 1 0 . 2 2 1 1 . 4 2 1 0 . 4 6 6. 58 9. 52 9 . 7 7 9.92 9. 1 5 9 3 . 2 9 3 . 2 8 7 . 7 8 7 . 7 8 7 . 7 87.7 P r e c o n s o l . P r e s s ( P n . ) 0 . 0 8 7 964 704 7 60 7 3 3 494 529 535 570 618 0 . 0 8 6 1 . 0 5 7 C o m p . I n d e x ( C c ) 6 . 0 8 R e m a r k s 6 . 8 5 8 . 5 4 3 . 0 2 2 . 9 2 3. 70 2. 58 Permeability m e a s u r e dI
I I P e r m e a b i l i t y m e a s u r e d1
i P e r m e a b i l i t y m e a s u r e d1
0 . 2 1 5 0. 19 3 . 2 4 . 5 P o r e w a t e r P r e s s u r e s m e a s u r e d . P o r e l v a t e r P r e s s u r e s m e a s u r e d .-
T A B L E II
T A B L E ILI SUMMARY OF RESULTS Sample No. 98-14- 5 98-15- 1 98-15- 2 98-70- 1 98-70- 2 Load I n c r e m e n t ( n o 3 ) 0 9 0 . 5 0 . 5
+
1 . 0 1 . 0 t 2 . 0 2 . 0 i 4 . 0 0 + 0 . 5 0 . 5+
1 . 0 1 . 0 + 2 . 0 2.0 + 4 . 0 4 . 0 9 8 . 0 0 + 0 . 5 0 . 5+
1 . 0 1.0 + 2 . 0 2.0+
4.0 0+
0 . 5 0. 5 3 1.0 0 j 0 . 5 0 . 5 1 . 0 1 . 0 4 2.0 2 . 0+
4.0 T i m e r e q l d . f o r P. W . P. t o r e a c h m a x value ( M i d 4 2 0 68 120 I m m e d i a t e 112 410 1402 1885 I m m e d i a t e 2 1257 1453 1 5 34 I m m e d i a t e 3 2 135 243 T i m e req'd. f o r P. W. P. d i s s i p a t i o n (Min)>
4 59-
-
-
-
-
1005 1457 4605 7 10, 000 330 150 1390 7 4 30 0 > 1 7 , 2 7 1 1290 4280-
-
Volume of p o r e w a t e r expelled ( C C ) P e r load T o t a l i n c r e m e n t Max P o r e W a t e r P r e s s . ( U ) 0.19 0.47 1 . 0 2 2. 1 5 0. 51 0.36 0.57 0 . 6 3 0.79 0 . 5 1 0.29 0 . 3 7 0 . 4 6 0. 36 0 . 6 6 0.47 0.46 0. 66 0 . 9 5 2 8 3 4 . 3 62. 5 4 4 . 7 4 2 . 2 5 1 3 . 2 8 11.8 7. 38 6.47 44.9 16.7 1 2 . 0 9 . 3 70.1 7 0 . 6 43.3 1 5 . 8 1 1 . 1 8 . 1 U m-
3 8 94 102 1 0 7 . 5 102 7 2 57 31.5 1 9 . 7 5 102 58 3 7 2 3 7 2 132 9 4 9 2 66 4 7 . 5 1 6 9 . 5 8 1 . 1 8 8 2 . 9 140.7 78. 3F I G U R E
1
@ -
P
C U R V E , S A M P L E
9 8 - 1 4 - 1
In
* * I n @
O I \ O C V C V C V .
0
10
20
30
40
50
60
7
0
M I N U T E S
F I G U R E
3
T I M E - S E T T L E M E N T C U R V E S , S A M P L E
9 8 - 1 4 - 1
OOOOT
0001
001
0
T
0
'T
T
'0
-
n9t7
'0
081
'I
-
-
-
65P
'T
,560 '1
-
-
-
IF I G U R E 5
P E R M E A B I L I T Y V S V O L U M E C H A N G E DUE TO C O N S O L I D A T I O N , S A M P L E 6 3 - 2 - 3
F I G U R E 6
F I G U R E
7
I N I T I A L
" a "
V S
I N I T I A L W . C .
P
=0.825
P
=1.375
-
-
-
(Unloading)
E L A P S E D T I M E , M I N U T E S
F I G U R E 8 - A
P O R E P R E S S U R E D I S S
I
P A T I O N , S A M P L E 9 8 - 1 4 - 4 B
9 R 3 4 4 1 - 85
10
15
20
25
E L A P S E D T I M E , M I N U T E S
P
=1.375
(Unloading)
F I G U R E 8 - B
P O R E P R E S S U R E D I S S
I
P A T I O N , S A M P L E
98-14-4B
a d 3 4 4 1 - 910 100 L O G - ' T I M E . M I N U T E S
F I G U R E 1 0 - A
/-
I In v
c
a
,
= 8.0) --
- - A U(6
= 8 . 0 ) \-
- --
- - 0 l nterrupted - - 10 100 1m 10,m
LOG-TI ME, M I N . FIGURE 10-B0 10
20
3040
50 60 70 80 TIME M I N .7,
FIGURE 11-A
TIME-SETTLEMENT CURVES, SAMPLE 98-15-1
0 10 20 30 40 50 60 70 80 90 100
d=,
M I N .-
-
-
-
-
Consolidation Interrupted Overnight
-
-
