Publisher’s version / Version de l'éditeur:
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la
première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
Research Paper (National Research Council of Canada. Division of Building
Research), 1962-10
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.
https://nrc-publications.canada.ca/eng/copyright
NRC Publications Archive Record / Notice des Archives des publications du CNRC :
https://nrc-publications.canada.ca/eng/view/object/?id=96f36d3a-868f-46a4-8aaa-02ea4539153e
https://publications-cnrc.canada.ca/fra/voir/objet/?id=96f36d3a-868f-46a4-8aaa-02ea4539153e
NRC Publications Archive
Archives des publications du CNRC
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.
For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.
https://doi.org/10.4224/40001223
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
An evaluation of pavement performance over muskeg in Northern
Ontario
S e r
TH1
N2lr 2
no.
171
c . 2
BLDG
NATIONAL
RESEARCH
CANADACOUNCIL
ANALYZED
DIVISION OF BUILDING RESEARCH
AN EVALUATION OF PAVEMENT PERFORMANCE OVER
MUSKEG IN NORTHERN ONTARIO
BY
I. C. MACFARLANE AND A. RUTKA
REPRINTED FROM
H I G H W A Y RESEARCH BOARD B U L L E T I N NO. 316. 1962
P. 32 - 4 3
RESEARCH P A P E R N O . 1 7 1 O F T H E
DIVISION OF BUILDING RESEARCH
PRICE 25 C E N T S OTTAWA OCTOBER 1962 r- v;-,i*:#> P. 9 < - > a = e NRC 6 9 9 2
T h i s publication i s being d i s t r i b u t e d - by the D i v i s i o n of Building R e s e a r c h of t h e National R e s e a r c h Council. It should not be r e p r o d u c e d in whole o r in p a r t , without p e r m i s
-
s i o n of the o r i g i n a l publisher. T h e Division would be glad t o be of a s s i s t a n c e in obtaining s u c h p e r m i s s i o n .P u b l i c a t i o n s of the Division of Building R e s e a r c h m a y be obtained by m a i l i n g the a p p r o p r i a t e r e m i t t a n c e , ( a B a n k , E x p r e s s , o r - P o s t Office Maney O r d e r o r a cheque m a d e p a y - able a t p a r in Ottzwa, to the R e c e i v e r G e n e r a l of Canada, c r e d i t National R e s e a r c h Coupcil) to the National R e s e a r c h Council, Ottawa. S t a m p s a r e not acceptable.
A coupon s y s t e m h a s been introduced to m a k e pay-
m e n t s for publications r e l a t i v e l y s i m p l e . Coupons a r e a v a i l - able i n denominations of 5, 2 5 a n d 50 c e n t s , and m a y be ob- tained by m a k i n g a r e m i t t a n c e a s indicated above. T h e s e coupons m a y be u s e d for the p u r c h a s e of a l l National R e s e a r c h Council publications including s p e c i f i c a t i o n s of the Canadian Government Specifications B o a r d .
R c g r i ~ i t c d Irom B u l l c t i ~ ~ 316
tIi~ll\v;~y R c s c a r c l ~ Board, Waslii~igton, D. C . . U. S. A
An Evaluation of Pavement Perf ormanee over
Muskeg in Northern Ontario
I. C. MACFARLANE, Associate Research Officer, Division of Building Research, National Research Council, Ottawa, and A. RUTKA, Acting Materials and Research Engineer, Ontario Department of Highways, Toronto
This paper is a r e p o r t of a cooperative r e s e a r c h program c a r r i e d
out in 1958 and 1959 by the National Research Council, Canada, and the Ontario Department of Highways t o study the performance of s o m e existing r o a d s over muskeg in northern Ontario. Investigation of close to 50 different muskeg a r e a s included classification of the muskeg, determination of the depth and type of fill, depth of t h e o r - ganic deposit, and type of mineral s o i l substratum. Roads over the muskeg a r e a s w e r e a s s e s s e d on the b a s i s of performance and s u r - face condition relative t o adjacent sections of road on mineral soil terrain. Many peat samples w e r e obtained for laboratory analyses, which included water content, specific gravity, acidity, and a s h content.
During the second stage of the project an extensive s e r i e s of field vane t e s t s was c a r r i e d out in c e r t a i n selected muskeg a r e a s
that w e r e typical f o r a certain region. Three different s i z e s of vanes
w e r e used. It is shown that r o a d performance is better in muskeg
a r e a s with tall t r e e growth than in a r e a s with little o r no t r e e growth, other factors being equal. No correlation was evident between r o a d condition and type of f i r m m i n e r a l s o i l substratum. However, an
intermediate unstable layer of soft m i n e r a l s o i l is shown to be an
important factor in r o a d performance and condition. Although vane
testing appears t o be a feasible method for determining the s h e a r
strength of peat and excellent duplication of r e s u l t s w a s possible f o r
any particular s i z e of vane, these t e s t s revealed a marked variation
in the s h e a r r e s u l t s depending on the vane size. Laboratory t e s t r e - s u l t s indicate correlations between moisture content and depth, specific gravity and moisture content, and acidity and carbon content.
@A LARGE PART of the total a r e a of Canada is covered with an organic mantle
known a s muskeg, much of i t occurring north of the main population centers. Its ex- tent is not known precisely but i t has been estimated that t h e r e a r e s o m e 500,000 sq m i of muskeg in Canada, o r approximately 12 percent of the total land a r e a .
The word "muskeg" is distinctive to Canada and the northern United States and is
derived f r o m the Chippewa Indian work "maskeg" meaning "grassy bog.
"
F o r engineer-ing purposes, muskeg (or organic t e r r a i n ) may be defined a s "terrain composed of a living organic mat of mosses, sedges o r g r a s s e s , with o r without t r e e and shrub growth, underlain by a usually highly compressible mixture of partially decomposed
and disintegrated organic m a t e r i a l commonly known a s 'peat' o r 'muck"'
(1).
Mus-keg is associated with a very high water table and is characterized by i t s low bearing
capacity. The depth of t h e s e organic deposits varies f r o m a few inches to many feet
and they may be underlain by either marl, clay, silt, sand, gravel, o r bedrock. The whole of Ontario-in common with most of the r e s t of Canada-has been glaci-
ated. As is typical of glaciated regions, muskeg a r e a s a r e encountered t o a greater
o r l e s s e r degree depending on the physiographic formation. One of the many com-
plex problems in Ontario highway engineering, therefore, is the satisfactory construc-
32
tion of r o a d s over muskeg. In s o m e r e g i o n s , a s much a s 80 percent of the length of a p a r t i c u l a r r o a d p r o j e c t is over inuskeg of v a r i a b l e depth and con~position. It is not unusual f o r t h i s muskeg t o be underlain by deposits of v e r y s o f t m a r l , silt, o r clay, thereby greatly i n c r e a s i n g t h e t o t a l depth of unstable m a t e r i a l .
It is s o m e t i m e s possible t o circumvent muskeg a r e a s , but due to the high geometric s t a n d a r d s f o r modern highways and a l s o due t o economic considerations, i t is often n e c e s s a r y t o construct r o a d s d i r e c t l y a c r o s s muskeg. The height of t h e embankments may v a r y between 4 and 40 f t . T h e r e f o r e , if a s a t i s f a c t o r y r o a d s u r f a c e is t o be p r o - vided, it is evident that detailed investigations and analyses of r e s u l t s m u s t be made t o e n s u r e that the p r o p e r t r e a t m e n t s a r e c a r r i e d out.
Generally, the tendency h a s been t o r e m o v e o r to d i s p l a c e the peaty m a t e r i a l and t o
construct the roadbed on a m o r e stable foundation. Because the w a t e r t a b l e is very
c l o s e t o the s u r f a c e , backfill m a t e r i a l m u s t r e m a i n s t a b l e when saturated. Granular s o i l s a r e the m o s t suitable f o r t h i s purpose, but in many p a r t s of Ontario they a r e s c a r c e o r nonexistent. In s o m e c a s e s cohesive s o i l s have had t o be u s e d f o r backfill because of t h e prohibitive c o s t of t r a n s p o r t i n g m o r e s u i t a b l e m a t e r i a l s .
The expanded construction p r o g r a m of the Department of Highways of Ontario in the
northern p a r t of the province, w h e r e muskeg is extensive and costs a r e high, has
necessitated a p a r t i c u l a r l y careful consideration of t h e construction of a satisfactory
and economical r o a d over muskeg. It is t h e s e northern a r e a s that a r e usually associated
with a s c a r c i t y of suitable g r a n u l a r m a t e r i a l f o r u s e in t h e t r e a t m e n t of muskeg a r e a s . It is t h e r e f o r e d e s i r a b l e t o know something of t h e engineering c h a r a c t e r i s t i c s of the muskeg encountered in o r d e r to a s s i s t in the economic design of roads.
I BACKGROUND O F PROJECT
Some r o a d s constructed o v e r muskeg have p e r f o r m e d quite satisfactorily while
I
o t h e r s have not. It was thought that a c o m p a r i s o n of t h e s e existing s u c c e s s f u l and un- successful r o a d s would be a u s e f u l and significant study to a s s i s t in determining s o m e
I of the engineering p r o p e r t i e s of muskeg. T h e difficulty of establishing the s u c c e s s of
I a p a r t i c u l a r r o a d w a s r e a l i z e d but it w a s thought that t h i s could be clone by r e f e r e n c e
I t o settleme11J and to qualitative s t a n d a r d s of p e r f o r m a n c e .
A joint r e s e a r c h p r o g r a m w a s consequently undertaken by t h e Department of High- ways of Ontario and the Division of Building R e s e a r c h of the Natlonal R e s e a r c h Council, Canada. T h e main object w a s t o study t h e p e r f o r m a n c e of e x i s t i n g r o a d s o v e r muskeg, t o obtain pertinent construction details and then t o attempt t o group muskeg a r e a s ac- cording t o t h e i r bearing p r o p e r t i e s . A f u r t h e r objective was t o attempt to c o r r e l a t e r o a d p e r f o r m a n c e with the Radforth Classification System f o r muskeg
(2).
T h e g r e a t extent of muskeg in n o r t h e r n Ontario and t h e many p r o b l e m s associated with i t made t h i s a r e a the obvious choice f o r t h e r e s e a r c h p r o g r a m . Only those r o a d s w e r e investi- gated that had been built d i r e c t l y on the muskeg s u r f a c e , and where no s p e c i a l t r e a t - ment of the muskeg had been undertaken.GEOLOGY O F THE AREA
The g e n e r a l a r e a covered in t h e investigations extended f r o m North Bay along Highway 11 t o Nipigon and t o P o r t Arthur and F o r t William, u p Highway 17 t o Kenora,
then Highway 71 t o Emo and along Highway 11 t o Rainy R i v e r ( ~ i g . 1). Basically,
t h e r e a r e two different t y p e s of t e r r a i n in the a r e a investigated, bothlocated within the P r e - C a m b r i a n shield. T h e topographic f e a t u r e of the rocky t e r r a i n ( c h a r a c t e r i s t i c of the Kenora region) is i t s ruggedness ancl the countless number of lakes ancl d e p r e s s i o n a l a r e a s , the latter being filled in with soft clay o r m a r l and peat. The o t h e r type of topo- graphy i s t h e extensive f l a t a r e a s of clay plain with d e p r e s s i o n a l a r e a s containing very soft clays and peat, located p r i m a r i l y between Kirlrland Lake and Longlac. Figure 2 , which denotes the geomorphic subprovinces of northern O n t a r i o , shows t h e s e features i.n Inore detail.
VARIABLES
The condition of a particular section of road constructed over muskeg will depend on a large number of variables which include:
1. Traffic loads and volume; 2. Age of road;
3. Depth and type of roadway fill;
--
I?@:
\
::',
F:sw r{:: R I D G E S[]l[~~ll~n
T H E C O C H R A N E C L A Y P L A I NEm
W E S T E R N S A N D Y U P L A N D S o E o R G I A N B A Y R O C K Y P L A I N~ 4 3
;;ESKEsAGAMI R I D G E S n n o1r-qij-a
R A I N Y R I V E R C L A Y P L A I N M U S K O K A R I D G E S er P O C K E T SF
m
T H E H U D S O N B A Y B O O S K E N O R A S A N D C L A Y U P L A N Dt-md
N O R T H S H O R E - S U D B U R Ym]
T H E L O N G L A K E R O C K Y A N D P A T R I C I A B O G S A N D L O A M Y R I O G E S A N D P O C K E T S L I M Y D R I F T U P L A N D S T I L L R I D G E S [r@-I T H E E A S T E R N S A N D Y N l P l G O N R I D G E S A N D P O C K E T U P L A N D S4. Type of road s u r f a c e (gravel, prime, hard surface, etc. );
5. Extent of maintenance; 6. Muskeg type;
7. Muskeg depth;
8. Depth of unstable m i n e r a l soil layer (if any) beneath the organic material; 9. Type of f i r m m i n e r a l s o i l substratum;
10. Drainage r e g i m e of the muskeg, both natural and man-made.
The p r o c e d u r e s followed in t h i s investigation were established in a n effort to evalu-
a t e a s many of t h e s e variables a s possible.
INVESTIGATIONAL PROCEDURES General
The r e s e a r c h program was undertaken in two stages, each taking one s u m m e r . Stage I (Summer 1958) provided the m o r e general information and covered a s large an a r e a a s possible. The muskeg was classified, the depth t o f i r m substratum de- termined, and the type of m i n e r a l subsoil w a s established. Samples of t h e peat in each a r e a w e r e obtained, classified, and retained for routine laboratory analysis. The type and depth of t h e roadway fill w a s a l s o determined. Finally, the performance and condition of the road in a particular a r e a was a s s e s s e d on a qualitative basis and relative to the condition of adjacent sections of the r o a d o v e r mineral soil. Evaluation of the r o a d s ranged f r o m excellent through v e r y good, good, fair, poor, bad (repre-
senting s e v e r e settlement o r deterioration of t h e s u r f a c e ) t o very bad (representing a
s h e a r failure a t s o m e t i m e in t h e road's history a s evidenced by the p r e s e n c e of "mud
waves"). Some 44 different muskeg a r e a s w e r e investigated in the first s t a g e and
r e s u l t s r e p o r t e d (3).
In the second stage (summer 1959) muskeg a r e a s were selected that w e r e typical
for a c e r t a i n region ( a s determined f r o m an analysis of r e s u l t s of s t a g e I) and a m o r e
exhaustive s e r i e s of t e s t s w e r e c a r r i e d out. These included extensive vane testing,
together with t h e procuring of a number of "undisturbed" tube samples of p e a t for
laboratory testing. For purposes of comparison, a r e a s w e r e chosen that had s i m i l a r
t e r r a i n conditions (such as muskeg type and depth) but that had a wide variation in the
a s s e s s m e n t of r o a d performance. T h r e e p a i r s of such a r e a s were compared, in a n
attempt to l e a r n why the r o a d was unsatisfactory in one location and satisfactory in
another. An additional t h r e e s i t e s , where a s h e a r failure had occurred, w e r e inves-
tigated with r e g a r d to determining the profile of the peat-soft clay interface. Vane Testing
T h r e e different s i z e s of vanes w e r e used; e a c h had conical ends and sharpened edges and w e r e of the recommended H/D r a t i o of 2. Table 1 shows their dimensions.
TABLE 1
Vane Diameter (in. ) Height (in. ) "K" Factor
S 2.0 4.0 5 6
M 2 . 8 5.6 2 0
The vanes w e r e attached to aluminum "E" d r i l l r o d s and manually pushed into the ground. To maintain reasonable portability, no casing w a s used. Torque w a s applied through a specially designed head attached t o t h e end of the d r i l l rod. Torque was
measured by means of a torque wrench with a maximum capacity of 150 ft -1b. Every
effort was made t o r o t a t e the vane a t a constant speed in e a c h test, the r a t e of s t r a i n
being about 3 deg p e r s e c . Following s h e a r failure, a remoulded t e s t was r u n in the
usual manner (four complete revolutions, a 1-min wait, then a repeat of t e s t ) . At
the complete peat profile and into the soft m i n e r a l soil sublayer, when t h i s w a s present. Undrained s h e a r strength w a s computed f r o m the relationship
S = K x torque
RESULTS Road Assessment
Those r o a d s r a t e d a s f a i r o r better w e r e considered to be satisfactory; t h o s e rated
as poor o r w o r s e w e r e considered to be unsatisfactory. Of the 44 a r e a s investigated
in s t a g e I, 27 w e r e classed as satisfactory, 17 as unsatisfactory. In t h e flat plain
type of topography c h a r a c t e r i s t i c of the Kapuskasing region, 75 percent of the over-
muskeg road sections investigated were c l a s s e d as satisfactory (compared to adja-
cent sections of the road on m i n e r a l soil t e r r a i n ) . In c o n t r a s t , in the type of topo-
graphy c h a r a c t e r i z e d by a rugged rocky t e r r a i n , with the depressions between rock
outcrops being either lakes o r muskeg (typical of the Kenora region), only 38 percent
of the road sections investigated w e r e classed as satisfactory. It is in this type of
topography that a deep layer of s o f t clay beneath the organic cover was observed most
frequently.
A s u m m a r y of t h e general information obtained in s t a g e I is given in Table 2, which shows the relation between road performance, muskeg coverage c l a s s , depth of
f i l l , depth of the organic m a t e r i a l and of the soft mineral s o i l sublayer (if any), as
well a s the type of f i r m mineral s o i l substratum. All sections of road a s s e s s e d a s
very bad w e r e underlain by a soft mineral soil layer. The range of total unstable
depth for t h e s e s h e a r f a i l u r e s w a s 25 to 50 ft. No shear failure was observed for a depth of unstable m a t e r i a l of l e s s than 25 ft.
Table 3 p r e s e n t s a s u m m a r y of the relationships observed between t h e t h r e e p a i r s
of muskeg a r e a s investigated during stage 11. An analysis of t h e r e s u l t s indicates that
the main f a c t o r s contributing to t h e unsatisfactory condition of the road a t s i t e 2 as
compared to s i t e 1 w e r e t h e inadequate depth of fill and poor drainage conditions. At
s i t e 4, the unsatisfactory condition of the r o a d w a s indicated by excessive and differen-
t i a l settlement, giving it a "roller-coaster" effect. Poor drainage and a l e s s satis-
factory muskeg type than a t s i t e 3 a r e the possible r e a s o n s f o r this condition.
Road and muskeg features a t s i t e s 5 and 6 w e r e so s i m i l a r that i t was difficult to s e e the r e a s o n for the difference in road performance. P a r t of the answer, however,
may be the location of the r o a d a t s i t e 6, which is constructed quite close to a sharply
sloping r o c k outcrop. The manner of the r o a d f a i l u r e would indicate that t h e fill may be slipping along the plane of t h e rock face.
At t h r e e different s i t e s where a s h e a r f a i l u r e had r e s u l t e d i n mud waves being
pushed up on one o r both s i d e s of the road, hand borings w e r e made through the center
of the mud waves, as well as through the natural muskeg, to determine the depth to
the soft intermediate zone. Levels were made of the ground surface and f r o m this in- formation the elevation of the soft clay-peat interface w a s plotted. It was found that this soft clay-peat interface followed the g e n e r a l contour of t h e surface mud wave, in- dicating that the failure zone extended down into the soft m i n e r a l soil layer.
Vane T e s t s
In peat, high deformations accompany the development of s h e a r . The t o t a l s t r a i n
in the vane s h e a r t e s t s was frequently as much as 50 deg, and occasionally reached
90 deg. It was g r e a t e s t f o r the s m a l l vane, l e a s t for the l a r g e s t vane. P a r t of this angular rotation was due to twist in the r o d although t h i s was observed to b e generally l e s s than about 5 deg. It was possible t o obtain an excellent reproducibility of results f o r each vane in a s e r i e s of t e s t s a t any p a r t i c u l a r site. A p a r t from an occasional
exceptionally high value due to t h e vane s t r i k i n g a root, the s h e a r values f o r any one
vane a t a given depth did not deviate markedly f r o m the mean value. Sensitivity val-
T A B L E 2
S U R F A C E A N D S U B S U R F A C E C H A R A C T E R I S T I C S O F A R E A S I N V E S T I G A T E D
R o a d No. of P r e d o m i n a t i n g D e p t h of D e p t h o f P e a t D e p t h of S o f t T o t a l U n s t a b l e T y p e of P e r f o r m a n c e R o a d s C o v e r C l a s s F i l l (in.) (it) S u b s o i l (ft) D e p t h (it) S u b s t r a t u m
E x c e l l e n t 1 A E I R o c k 17 10 2 7 Sand ( d e p t h uninotvn) V e r y good 3 AE 60-66 9 - 2 0 0 - 12 9-32 Clay, s a n d , r o c k G o o d 11 A E I 12-24 4 - 1 1 0-30 4 - 4 1 Clay, s i l t , s a n d , r o c k F a i r 12 A-BE1 12-45 5-11% 0-6 5-17% Clay, s a n d B-DFI P o o r 9 A-BE1 12-60 5%-14 0 - 1 8 5%-32 Clay B-DFI B a d 2 I n c o n c l u - 24 ( 1 only) 2 - 1 0 0 2 - 1 0 Clay, s a n d s i v e
V e r y bad 6 B-DFI R o c k 13-19 6-34 25-47 Clay, s i l t
(depth
TABLE 3
Muskeg Features Average
MXY. Depth Shear
Road F e a t u r e s Depth Under Value
Depth o i F i l l Type Classiii- 01 Peat Road S u b s o i l (Vane M)
Site Topography Drainace PerIormallce SurIace (It) 01 Fill cation (It) (it) T y p e (psi)
1 Flat plain Well Good to Paved 5-6 Sand, A-BE1 12% 8 Sandy 844
drained very good clay + s i l t
sand
2 Long Ilat Very wet, Poor to Paved 2% Sand A-BE1 12 7 % Sand 534
a r e a be- poorly fair B-DEI
tween r o c k d r a ~ n e d outcrops
3 Flat plain Well Very good Paved 5 S u ~ d A-BE1 9 7 Silty 626
drained and c l a y
rrrnvel
4 Flat plain F a i r l y Poor to Paved 5 ~ k d y B-DEI 8 4 Sandy 455
wet f a i r gravel 11 s i l t
5 Depres- Quite \vet Good Paved Not ob- Rock B-AEI 11 to Not Silty 484
sional taul- 4l(soft ob- c l a y (Peat)
a r e a a b l e clay) tain- 467
41 (Re- able (Clay)
fusal)
6 Delxcs- Very wet Very bad Paved Not ob- Rock B-DF 12 Not Sandy 543
s ~ o n a l t a b AEI 12 to ob- s i l t ( P e a t )
a r e a able 33 (Soft tail,- 456
clay) able ( c l a y )
33 (Re- fusal)
T h e r e w a s a m a r k e d variation in t h e s h e a r r e s u l t s between the t h r e e v a n e s . When
t h e a v e r a g e s h e a r value f o r e a c h vane is plotted against depth, all t h r e e c u r v e s have
a s i m i l a r shape and c l e a r l y r e f l e c t any l a y e r s of higher o r lower strength. The s m a l l
vane, however, gave r e s u l t s about double t h o s e of the medium s i z e vane a n d from
f o u r to f i v e t i m e s those of the l a r g e vane. T h i s w a s consistent for a l l s i t e s investi-
gated. T h e r e w a s no s t r o n g evidence of a c o r r e l a t i o n of s h e a r strength with muskeg classification type, although t h e upper range of s h e a r values obtained w e r e generally
in muskeg types having t a l l t r e e growth ( c l a s s e s A and B).
In those muskeg a r e a s not underlain by a s o f t m i n e r a l s o i l layer, the v a n e t e s t s
did not consistently indicate a n i n c r e a s e in s h e a r s t r e n g t h with depth. In fact, the
s h e a r s t r e n g t h r e m a i n e d f a i r l y constant throughout the depth of the deposit. In those
muskegs underlain by a s o f t m i n e r a l s o i l l a y e r , however, t h e r e tended t o b e a slight
i n c r e a s e in s h e a r strength with depth, r e a c h i n g i t s maximum value at, o r j u s t above, the transition zone. T h i s w a s followed consistently by a d r o p in the s h e a r strength of t h e soft m i n e r a l s o i l l a y e r . On the average, t h e s h e a r s t r e n g t h of t h i s soft m i n e r a l s o i l layer w a s found t o be 77 p e r c e n t of t h e s h e a r s t r e n g t h of the peat. F i g u r e 3 gives vane t e s t r e s u l t s f r o m one s i t e and s h o w s the consistent relationship that obtains between the t h r e e vanes throughout depth. T h e s e c u r v e s a r e generally indicative of t h e t r e n d a t the other s i t e s investigated. When a l l values of vane s h e a r w e r e plotted against water content, n o c l e a r c o r r e l a t i o n w a s evident.
3 9
VANE S H E A R , P S F Laboratory Results
The water content of peat v a r i e s over a wide range and may even exceed 1,000 percent of the dry weight. When water content w a s plotted against depth for each s i t e , a c u r v e was produced s i m i l a r in shape to the vane s h e a r curves ( s e e Fig.
3 f o r a sample curve). Peat generally
exhibits a n acidic quality, the acidity (as measured by pH) being proportional to the organic content (or ignition loss) a s shown in Figure 4.
Figures 5, 6, and 7 show an apparent critical zone f o r the peat s a m p l e s studied. T h i s zone is indicated for organic con- tents g r e a t e r than 75 percent, specific gravity values of soil solids l e s s than
about 1.6, and water contents g r e a t e r than
,,
approximately 600 percent. Higher values of organic content represent the "pure"
36 peats, with comparatively little admixed
mineral matter. Therefore, beyond
t h i s critical zone (i. e . , in the "pure" F i g u r e 3. Vane s h e a r and w a t e r content v s
peats) t h e r e is no evidence of c o r r e l a - depth.
tion between the organic content, speci- fic gravity of soil solids, and water con- tent. Up t o t h i s zone, however, it is s e e n that a s organic content increases, specific gravity values d e c r e a s e and water content increases. The void r a t i o will correspondingly increase with in- creased organic content and consequently the compressibility of the peat will also increase.
In Figure 5, that p a r t of the curve be-
low the c r i t i c a l zone a g r e e s closely with
the r e s u l t s of Cook
(4)
regarding the r e -lationship between water content and specific gravity.
$
A consolidation test p r o g r a m has been 60 -
s t a r t e d at the Division of Building Re- i Z
W
s e a r c h on the tube samples of peat in an I-
Z 50-
effort to determine when the p r i m a r y phase o u
of peat consolidation is completed and
a l s o to determine how much of the settle-
$
4 4 0 -ment is due t o secondary consolidation. '3
6z
0
30 -
DISCUSSION O F RESULTS The problem of evaluating objectively the many variables involved in a s s e s s i n g
road performance c r e a t e s s o m e difficulty 10
in correlating the road performance with
.\
muskeg type. It is evident that factors
0
\.:
other than muskeg type a r e influential in
0
2.0 3.0 4.0 5.0 6.0 7.0 8.0determining the performance of a road P H
constructed over muskeg. Consequently,
SPECIFIC GRAVITY
F i g u r e 5. Water c o n t e n t v s s p e c i f i c g r a v i t y .
beginning of the r e s e a r c h project did not e m e r g e . Nevertheless, it can be s e e n f r o m
Table 2 that, although t h e r e is considerable overlap in muskeg type in the different
road a s s e s s m e n t categories, a trend is observed f r o m tall t r e e s to dwarfed trees and s h r u b growth a s the road a s s e s s m e n t drops from excellent to very bad. This i s especially t r u e f o r those muskeg a r e a s directly underlain by a f i r m m i n e r a l soil sub-
s t r a t u m (i. e.
,
no intermediate soft layer). It may be concluded, therefore, that r o a d sconstructed over muskeg types containing t a l l t r e e growth ( c l a s s e s A o r B in the cover- age formula) performed m o r e satisfactorily than those on muskeg types with little o r no t r e e growth. No correlation was evident between road performance and t h e type of f i r m mineral s o i l substratum.
Traffic loads and volume a r e important t o t h e performance of any road. In this in- vestigation, where performance of roads over muskeg was compared to the perform- ance of adjacent roads over m i n e r a l s o i l t e r r a i n , traffic loads could safely b e assumed to be the s a m e f o r both sections of road and w e r e not t h e r e f o r e considered further.
The cause of s h e a r f a i l u r e s in muskeg a r e a s underlain by a soft m i n e r a l s o i l layer i s due largely to this layer r a t h e r than to the peat itself. T h e shear s t r e n g t h of this layer was generally l e s s than that of the peat overlying it and it would s e e m the zone of failure i s in this soft subsoil. Consequently, from the point of view of both consoli- dation movements and embankment stability, the greatest difficulties in road construc- tion over muskeg can be expected in these depressional-type muskegs.
Table 3 indicates that an inadequate depth of fill and a high water level (acting to-
gether o r separately) contribute to the poor performance of a road on muskeg. In
s o m e c a s e s , peat was observed to be "pumping" through a v e r y shallow fill subjected
to heavy t r u c k traffic. In a t l e a s t one instance, stumps w e r e noted to be puncturing
through the asphalt surface of a road. Lea and Brawner
(2)
have recommended aminimum depth of f i l l on preconsolidated peat of 3 % ft. T h e s e investigations confirmed
1.2 1.4 1.6 1.8 2.0 2.2 2.4 SPECIFIC G R A V I T Y
F i g u r e 6. S p e c i f i c g r a v i t y vs o r g a n i c c o n t e n t .
The vane a p p a r a t u s , although initially developed f o r u s e i n clay s o i l s , h a s been u s e d extensively r e c e n t l y f o r d e t e r m i n i n g t h e s h e a r s t r e n g t h of peat. T h e r e i s s t i l l s o m e question, however, r e g a r d i n g t h e validity of t h i s a p p a r a t u s f o r s u c h a complex s o i l a s p e a t . In t h e i r c o m p r e h e n s i v e r e p o r t , Cadling and Odenstad (6) concluded ( a f t e r investigating t h r e e s i z e s of v a n e s ) that t h e influence of t h e v a n e dimensions does not a p p r e c i a b l y affect t h e s h e a r r e s u l t s f o r c l a y s . When t h e a v e r a g e s h e a r s t r e n g t h for t h e different vanes w a s plotted against depth, they showed v e r y good c o r r e l a t i o n . T h e a u t h o r s point out, however, that design c o n s i d e r a t i o n s p l a c e c e r t a i n l i m i t s on t h e p r a c t i c a l s i z e s of vanes that can be used.
It is r e a s o n a b l e t o a s s u m e that f o r a f i b r o u s m a t e r i a l s u c h a s peat, the particle s i z e r e l a t i v e t o t h e vane s i z e is significant. T h i s might account for s o m e of the v a r i a - tion betweenthe r e s u l t s f o r t h e t h r e e s i z e s of vanes u s e d in t h i s investigation. An- o t h e r factor-the effect of which h a s not y e t b e e n fully a s s e s s e d - i s r o d f r i c t i o n . I t w a s thought that t h e e x t r e m e l y wet condition of peat t o g e t h e r with the d i s t u r b a n c e caused by p e r i o d i c vane r o t a t i o n r e d u c e s r o d f r i c t i o n t o a negligible value.
Since t h e conclusion of t h i s p r o j e c t , a few f u r t h e r vane t e s t s have been c a r r i e d out in o r d e r to evaluate t h e effect of rod f r i c t i o n . Although not extensive enough to
of i n c r e a s e in s h e a r s t r e n g t h of the peat
P i g w e 7. Organic c o n t e n t vs > r a t e r c o n t e n t . W i t h depth.
on
the average, t h e shear1800 1600 1400 1200 s c- Z w t 1000 z 0 u IL 8 0 0 - 3 600 400 200 o s t r e n g t h r e m a i n e d fairly c o n s t a n t through- out depth.
5. In general, no significant relationship w a s evident between vane s h e a r strength
and w a t e r content of peat.
6. S h e a r s t r e n g t h of p e a t d o e s not a p p e a r t o be a p r o b l e m in the s t a b i l i t y of high-
way embankments on m u s k e g not underlain by a soft s u b l a y e r . E x c e s s i v e and dif-
f e r e n t i a l s e t t l e m e n t s a r e the m o r e s e r i o u s problem.
7. Unsatisfactory r o a d p e r f o r m a n c e is s o m e t i m e s due t o a n inadequate depth of
subgrade. T h e r e c o m m e n d e d minimum of 3 % f t a p p e a r s t o be a r e a s o n a b l e figure. 8. A low-lying r o a d and a high water level in the muskeg were important contribu- ting f a c t o r s in s o m e a r e a s t o t h e d e t e r i o r a t i o n of the r o a d s u r f a c e .
9. T h e vane s h e a r s t r e n g t h of t h e s o f t m i n e r a l s o i l s u b l a y e r was found t o be
generally l e s s than the s h e a r s t r e n g t h of t h e overlying p e a t .
10. Shear f a i l u r e s in a r e a s underlain by a soft m i n e r a l s o i l layer (clay, silt, o r m a r l ) a r e due chiefly t o t h i s l a y e r and not n e c e s s a r i l y t o t h e peat.
11. P e a t becomes m o r e a c i d i c with a n i n c r e a s e in o r g a n i c content.
O R G A N I C CONTENT. % 4. T h e r e w a s no consistent evidence
I I I I I I I I :
I.
-1
- -.I'
- -I .
- . J - I -.
iy
- I -..I
-..I'
-
-..
i'.
-. .
-I.
.
- -.
-*I-.
.
I .
-.:I
.
_
. .-
.
zp: - -!. -F:
.
-:.
.
..':<. - 7 -.
,
/.'
..
.
-. .
.-
.
-,
.
#..
7. /' ..$.
-. /.
.-
'I.
.
.- .
- *..
:./
.
- • . p ;- ". :.
d'.-
./'a -:::
/-./.
.
- t.2...
o ! I . I I I I I I 2 o 40 60do
12. A s t h e organic content of peat i n c r e a s e s , t h e r e is a corresponding i n c r e a s e
in the w a t e r content and a d e c r e a s e in t h e s p e c i f i c gravity of s o i l s o l i d s , u p to a c e r -
t a i n c r i t i c a l zone beyond which t h e s e t h r e e c h a r a c t e r i s t i c s have no c l e a r relationship. justify definite conclusions, t h e t e s t s in- dicated that f o r t h e initial 5 o r 6 ft of depth, r o d f r i c t i o n i s a f a i r l y negligible f a c t o r . F o r g r e a t e r depths, however, i t a p p e a r s t o have s o m e effect on t h e vane s h e a r r e s u l t s , p a r t i c u l a r l y in t h e c a s e of t h e s m a l l s i z e vane. A f u r t h e r s e r i e s of t e s t s is planned.
SUMMARY
1. Sections of road built o v e r types of m u s k e g t h a t s u p p o r t t a l l t r e e growth ex- hibit b e t t e r p e r f o r m a n c e than t h o s e over a r e a s with l i t t l e o r no t r e e growth, if m o s t of the o t h e r f a c t o r s a r e equal o r s i m i l a r . However, r o a d p e r f o r m a n c e cannot be generally c o r r e l a t e d with m u s k e g classifi- cation t y p e alone.
2. T h e r e w a s no evident c o r r e l a t i o n of vane s h e a r s t r e n g t h with m u s k e g type, ex- c e p t that t h e u p p e r range of s h e a r values w a s generally i n inuskeg t y p e s with c l a s s e s A o r B in the c o v e r a g e f o r m u l a .
3 . S e r i e s of vane s h e a r t e s t s show good reproducibility of r e s u l t s . Vane s i z e is apparently a factor to b e considered a n d f u r t h e r r e s e a r c h to d e t e r m i n e the optimum s i z e s e e m s justified.
ACKNOWLEDGMENTS
T h i s p a p e r , a joint contribution of t h e O n t a r i o D e p a r t m e n t of Highways a n d the
Division of Building R e s e a r c h , National R e s e a r c h Council, Canada, is published with
t h e approval of M r . W. A. C l a r k e , Chief Engineer of t h e Department of Highways of
REFERENCES
1. MacFarlane, I. C.
,
"Muskeg Research: A Canadian Approach."
HRB P r o c .,
38:638-650 (1959).
2 . Radforth, N. W., "A Suggested Classification of Muskeg f o r the Engineer.
"
Eng. J o u r n . , 35: 1199-1210 (1952).
3. MacFarlane, I. C., and Rutka, A., "Evaluation of Road Performance o v e r Muskeg
in Ontario.
"
P r o c . , 40th Convention, Canadian Good Roads Association, p.396-405 (1959).
4. Cook, P. M.
,
"Consolidation C h a r a c t e r i s t i c s of Organic Soils."
P r o c .,
9thCanadian Soil Mechanics Conference, National R e s e a r c h Council, Associate Committee on Soil and Snow Mechanics, Technical Memorandum 41, p. 82-87 (1956).
5. Lea, N. D.
,
and Brawner, C. 0.,
"Foundation and Pavement Design f o r Highwayson Peat.
"
P r o c . , 40th Convention, Canadian Good Roads Association, p.406-424 (1959).
6. Cadling, L . , and Odenstad, S . , "The Vane Borer." P r o c . , No. 2, Royal Swedish Geotechnical I n s t . , Stockholm (1950).
Discussion
PHILIP KEENE, Engineer of Soils and Foundations, Connecticut Highway Depart- ment-The authors a r e to be congratulated on t h e i r excellent paper, containing a l a r g e
-
amount of factual data on the ~ r o i e c t s involved and well-founded conclusions where
they felt t h e s e w e r e justified.-
heir
efforts r e p r e s e n t another example of t h e skilledand competent work being done by engineers and other s c i e n t i s t s of Canada on the problems involving muskeg.
The authors have noted that when s l i d e s o c c u r r e d , r e s u l t i n g in the f a m i l i a r rapid subsidence of the embankment and the formation of mud waves beyond t h e t o e of em- bankment slope, the zone of r u p t u r e always went through a soft m i n e r a l s t r a t u m lo- cated below the peat. The m i n e r a l layer is d e s c r i b e d a s clay o r silt o r both.
The authors s t a t e that high deformations accompany t h e development of shearing in peat. In contrast, deformations due to s h e a r s t r e s s e s in soft mineral s o i l a r e r e l a - tively much s m a l l e r . Hence, i t is probable t h a t a s an embankment w a s being placed and s h e a r s t r e s s e s w e r e being developed in t h e underground, t h e peat furnished very s m a l l s h e a r i n g r e s i s t a n c e while the deformations w e r e s m a l l , and consequently a l a r g e s h a r e of t h e shearing r e s i s t a n c e w a s borne by t h e silt-clay. J u s t before the
t i m e of r u p t u r e , the silt-clay w a s s t r e s s e d to i t s ultimate s h e a r i n g s t r e n g t h , with a
s h e a r i n g s t r a i n of perhaps 2 o r 3 i n . , while t h e peat w a s r e s i s t i n g , a t that s t r a i n , a t
perhaps 50 percent of i t s maximum ultimate s h e a r i n g s t r e n g t h . After the silt-clay
failed, t h e peat then must r e s i s t nearly a l l t h e shearing f o r c e and because it was un-
able to do s o , it then failed. Hence, this progressive failure explanation would be
based on l a r g e differences in s t r e s s - s t r a i n c h a r a c t e r i s t i c s between peat and soft m i n e r a l s o i l r a t h e r than on ultimate s h e a r i n g strengths of both materials.
