1983 - fisher - modulus of elasticity of a very dense glacial till determined by plate load tests
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CAN. GEOTECH.
I. VOL.
20 1983
Modulus of elasticity of a very dense glacial till determined by plate load tests
WILLIAM . FISHER
Jordan Gorrill Associates 562 Co ngress Street
P.O.
Box 7050 Dow ntown Station Portland
M E
04112 U.S.A.
Received April
29, 1982
Accepted September 2, 1982
The modulus of elasticity of a very dense glacial till deposit located in central Maine has been determined by in-situ pla
load tests. The results of these tests are presented and the values of modulus of elasticity evalu ated.
Le modu le d ClasticitC d un dCpBt de moraine g laci aire tr2s dense d ans le centre du Main e a CtC dCterminC partir d essais
chargement de plaques
in situ.
Les rksultats d e ces essais sont prCsentCs et les valeurs du mod ule d Clasticit6 sont ha luC es.
Can
Geotech.
I., 20,
186-191 1983)
ntroduction
Settlements of structures supported by shallow foun-
dations bearing on dense glacial till are gene rally small
and consist mainly of elastic com pression of the till as a
result of the imposed loads. Typically, this elastic
com pression results in settlem ents sufficiently small that
their influence on the performance of most structures is
negligible. However, facilities such as paper m achines
are sensitive to small total and differential settlements,
and settlements related to elastic com pression of even a
dense glacial till can significantly influence their opera-
tion. Th e purpose of this note is to present the results of
three in-situ plate load tests done on a very dense glacial
till deposit located at the site of a prop osed pap er mill in
Skowhegan, Maine. T he
in-situ
modulus of elasticity,
E
of the till determined from these tests was used to
design and evaluate the performance of shallow spread
footings and mat foundations for the proposed paper
machine.
Previous studies
Published values of E for glacial till could only be
located for projects and studies done in Canada. These
values varied widely and were largely dependent on the
apparent denseness of the till and m ethod of determina-
tion. Table 1 presents a sum mary of published values of
E for glacial till, the related degree of stiffness or
denseness, and the method of testing. The data indicate
that higher valu es of E result from in-situ tests such as
plate load and pressuremeter tests than from laboratory
tests. Publish ed values of E determined from plate load
tests on very dense, overconsolidated, glacial tills
ranged from 97 to 69 1 MPa (14- 100 ksi) and, in dense,
apparently normally consolidated, glacial till, from 38
to 69 MPa (5.5-10 ksi). The plate load test was selected
as the most appropriate method of determining E for the
glacial till at the project site.
[Traduit par la revu
Soil conditions
The subsurface conditions encountered at the s
consist of silty clay, glacial till, and phyllitic sch
(bedrock).
A
plan view and an interpretive subsurfa
profile along the alignment of the paper machi
building are shown in Fig. 1. The silty clay, a la
glacio-marine deposit, is brown, stiff to hard, a
contains traces of coarse sand and fine gravel.
The glacial till is an unsorted mixture of clay, si
sand, gravel, cobbles, and boulders. The
surficial l-2
of the till is brown in color and the rem aining underlyi
till is gray. Grain-size analyses of samples of the t
taken at plate load test locations are plotted in Fig.
Values of N, determined by the standard penetrati
test, ranged from 50 to 70 blow s per 30 cm, indicati
that the till is very dense. In view of its very den
condition, the till is considered to be basal, deposit
during the last glacial advance about 10 000 years ag
The paper machine building was designed to be su
ported by shallow foundations bearing on the den
glacial till, as shown in Fig . 1. The groundwater ta
sloped downw ard from el. 53 .0 m at the south end of t
building to el. 49 .5 m at the north end. Generally t
groundwater table was within 3. 5m of the grou
surface.
In situ plate load tests
Testing program
Three plate load tests were done at the locatio
shown in Fig. 1.
A
summary of elevations and so
encountered immediately beneath each test location
presented in Table
2.
The general procedure used for the plate load te
was as follows.
1. The test area was excavated to within about 0.3
(1 ft) of proposed foundation g rade e l. 51.8 m (
168.5 ft) using a Caterpillar D-8 D ozer.
0008-3674183 010181-06 01 .OO/O
01983 National R esearch Council of Canada/Conseil national de recherches du C anada
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TA BLE . Sum mary of published values of m odulus of elasticity of glacial till
Reference
Undrained compressive
strength,
q
MPa ksi) or
Project penetration resistance, Method of
Modulus of elasticity,
E
location NZ lows/30 cm determination
MPa ksi)
Klohn 1965) Northern Sask.
q
1 22) Plate load test 324-697, ave. 497 72)
Excavation rebound
608-1220, ave. 967 140)
Triaxial UU test 31-152, ave 76 11)
Unconfined compr. test
83-283 , ave. 145 21)
DeJong and Edmo nton, Alta. N 1 Foundation settlement 280-490, 41-7 1)
Harris 197 1)
q
0.8 16) Triaxial UU test 10 1.5)
Triaxial CU test 97 14)
Consolidation test 21 3)
Eisenstein and Edmo nton, Alta. 111 Pressure meter 55-245, ave. 173 25)
Morrison 1973)
q
0.8 16)
Radhakrishna and Toronto, Ont.
N
>
200 Plate load test 97-207, ave. 180 26)
Klym 1974) q 1.3-2.9 28-60) Pressure meter 97-290, 14-42)
In situ shear box 138-332, 20-48)
Triaxial CU test 41-242, ave. 138 20)
Soderman et
al.
1968) Southern Ont.
q
0.0 5 1.0) Plate load test 38-69 5.5-10)
NOTE
U
unconsolidated, undrained; CU consolidated, drained.
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CAN. GEOTECH. J. VOL. 20
983
PLATE LOAD TEST
L O C A T I O N
ANCILLARY
FACILITIES
0
2 5 5 0
75
FEET
IIL
L I M I T S O F
6 0 1
k
L I M I TS O F P A P E R MA CHINE B UIL DING WA RE HO USE
A
GROUND SURFACE
SILTY CLAY
A
UL r u u t u u n I ON
EL.
5
WAREHOUSE
P L T- I P L T- 2 P L T- 3
P A P E R MA CHINE B UIL DING
t
FIG.
1.
Plan view of project and interpretive subsurface profile.
'
I
>
FIG.2. Grain size distribution curves, brown and gray glacial till PLT plate load test).
-- - --
-
-
-
5 0 C = - - ~ E L E V A T I O N O F
AVERACC
'An r & nP hY
GRADE
P L A T E L O A D T E S T
'j
4 0 - G L A CI A L T I L L
W
/
=
//A\
P HY L L lT lC S CHIS T B E DRO CK
3 0
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NOTES
TABLE
.
Summary of elevations and shallow subsurface soil at plate load test locations
Elevation (m)
Plate load Ground Test Ground- Depth
test No. surface
level water (m) Soil beneath plate
1 54.9 51.7 53.0 0 0.6
Brown gravelly sandy silt (till)
0.6 1.5
Gray slightly gravelly sand y silt (till)
2
53.5 51.2 51.1 0 1.5
Gray slightly gravelly sand y silt (till)
53.3 51.0 51.8 0.6 1.5
Gray slightly gravelly sand y silt (till)
FIG.
3.
Plate load test setup.
2. A drainage ditch, about 0.6 m (2 ft) in depth, was
excavated around the perimeter of the test area and
back-filled with crushed stone . The ditch w as drained by
use of a sump pump.
3. F inal excavation of the test area, 1.1 m (3.5 ft) in
diameter, was done by hand and the base steel bearing
plate placed over a leveling course of epoxy-type grout.
The 25.4-mm (1-in.) thick steel loading plates were
stacked with decreasing diameter from 8 13 mm (32 in.)
to 305
rnm
(12 in.) in 102 mm (4-in.) increments.
4. The reaction load, consisting of a flat-bed trailer
loaded with 54.5 t (60 sh ort tons) of concrete blocks was
placed over the plates. photo of a typical test setup is
shown in Fig. 3 .
5. Deflections of the plate were measured at three
equidistant points on the perimeter of the bottom plate.
The dial indicators were attached to a reference beam;
they were graduated to the nearest 0.2 5 mm (0.00 1 in.).
The reference beam w as a 3 .7-m (12-ft) long piece of
203-mm (8-in.) W shape steel beam and w as centered
over the bearing plates and supported at each end by a
0.3-m (I-ft) piece of 8-in beam oriented at right angles to
the alignment of the reference beam.
6. The plates were then loaded. Loads were increased
in increm ents producing a contact stress of 95 kPa
(2 ksf from 0 to 38 0 kPa (8 ksf
.
From 38 0 kPa (8 ksf)
to 760 kPa (16 ks f) the bearing pressures were increased
in increments of 190 kPa (4 ksf ). For bearing pressures
from 0 to 380 kPa (8 k sf) the incremental pressures were
maintained for a minim um of 15 min, or until the rate of
settlement was less than 0.13mm/h (0.005in./h),
whichever was longer. Loads applied incrementally,
causing contact stresses from b etween 3 80 kPa (8 ksf)
and 7 60k Pa (16 ksf) were maintained for a minimum
time of 60 min, or until the rate of settlement was less
than about 0.05 mm /h (0.002 in. /h), whichever was
longer. The m aximum contact stress of 760 kPa (6 ksf)
was maintained for about 14 h at location PLT-3 to 18 h
at PLT-1, with rates of settlement of 0.03mm/h
(0.001 in./h) at PLT-3 to 0.01 mm/h (0.0005 in./ h) at
PLT-1. Th e elapsed time for the p late load tests ranged
from 23 h at PLT -1 to 21 h at PL T-3.
7. The plates were unloaded and the test setup
dismantled.
8 .
A
test pit was then dug be neath the location of the
plates to a depth of 1. 6 m (5 ft) below the test level and
representative soil samples obtained for laboratory
testing.
est results
Load-settlem ent curves for the plate load tests are
presented in Fig. 4 . The m odulus of elasticity for each
test was determined by assumin g that the circular plate
was rigid and the till was a semi-infinite elastic solid
The relationship of elastic settlement of a rigid loaded
circular area bearing on a semi-infinite solid is (B owles
1968):
where S settlement (mm ), q contact pressure (kPa)
B
plate diameter (mm),
p
Poisson s ratio, E
modulus of elasticity (kP a), and shape factor.
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CAN.
GEOTECH. J. VOL.
20
1983
V E R G E
P L A T E C O N T A C T P RE S S U R E kPa
P L A T E L O A D T E ST 2
I
FIG.
4. Plate load test results.
For the plate load tests,
B
810m m, 0.4 these tests are:
assumed), and 0.8 8. By rearranging terms and
Test No. Apparent E, MPa ksi)
applying appropriate conversion factors, the expression
in terms of E is:
PLT-1 103 15.0)
6009 PLT-2 112 16.2)
E
kpa)
PLT-3 130 18.8)
The modulus of elasticity was computed using the
above expression and values of q and S from the straight
onclusions
line portion of the load-settlement curve. B ecause a net
The purpose of this note has been to present th
settlement of the plate occurred with each of the tests,
apparent in situ modulus of elasticity of a very dens
the settlements are not entirely elastic. As a result, the
glacial till in the S tate of M aine as determined by pla
use of the term apparent E as proposed by Klohn
load tests.
1965), is recommended to qualify the value of E,
The results of the three tests indicate that the appare
determined. The values of apparent E determined from
E,
of the glacial till at the site ranges from 10 3 15.0 ks
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to
130
M P a
18.8
ksi ) . The se va lues fa l l wi thin the lower
end of the range of publ ished va lues for deposi t s of very
dense glac ia l t il l in Can ada .
NOTES
191
BOWLES, .
E
1968. Foundation analysis and design.
McGraw-Hill, Inc., N ew York, NY.
DEJONG, . , and HARRIS,M. C. 1971. Settlements of two
multistory buildings in Edm onton. Canadian Geotechnical
Journal, 8 pp. 217-235.
EISENSTEIN,. and MORRISON , . A . 1973. Prediction of
foundation deformations in Edmonton using an in situ
pressure probe. Canadian Geotechnical Journal,
10
pp.
193-210.
KLO HN , . J . 1965. The elastic properties of ade nse glacial till
deposit. C anadian Geotechnical Journal,
2
pp. 116-140.
RADHAKRISHNA,. S . , and KLYM,
.
W.
1974. Geotechnical
properties of a very dense glacial till. Canadian Geotech-
nical Journal,
11
pp. 396-408.
SODERMAN,.
G . ,
KIM,Y. D ., and MILLIGAN, . 1968. Field
and laboratory studie s of modulus of elasticity of a clay till.
Sympos ium on Soil Properties from
In itu
Measurements,
Highway Research Board Publication No. 243.