1983 - Fisher - Modulus of Elasticity of a Very Dense Glacial Till Determined by Plate Load Tests

7/23/2019 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



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.



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



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


53.3 51.0 51.8 0.6 1.5


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.



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



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.

1983 - Fisher - Modulus of Elasticity of a Very Dense Glacial Till Determined by Plate Load Tests

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