Four points, one from Blatz et at. (] 999), one from McRae. (1958), one from Foreman & Daniel (1986) and one from. Daniel & Benson (1990), stand out from the ...
Gurtug, Y. & Sridharan, A. (2002). Geotechnique 52, No. 10, 761-763
TECHNICAL
NOTE
Prediction of compaction characteristics Y. GURTUG*
KEYWORDS: clays; compaction; earthfill; ground improvement; laboratory tests
and A. SRIDHARANt
with a highly plastic clay and kaolinite from Turkey, the authors have obtained the Atterbcrg limits and the compaction characteristics, Ydmax and OMC, through Proctor's test (BSI, 1990). The BS compaction test consists of a mould of volume 944 cm3, internal diameter of 10 cm and height of 11·68 cm in which the soil is compacted in three layers, giving each layer 25 blows from a metal hammer weighing 2·5 kg falling through 30,5 cm. Table I lists the physical properties of the soils used in this study. Apart from their own results, the authors have also used results published in the literature by McRae (1958), Johnson & SaUberg (1960), Foreman & Daniel (1986), Daniel & Benson (1990), Sridharan et al. (1990), Daniel & Wu (1993), Benson & Trast (1995), Boltz et at. (1998) and Sridharan & Nagaraj (2002) for Proctor's Ydmax and OMC.
embankments;
INTRODUCTION The purpose of compacting earth fills is to produce a soil mass that will satisfy the three basic criteria: reduction in settlement, reduction in permeability, and increase in shear strength. Modification of soils at the site to improve their engineering properties is essential in many applications, such as highways, railway subgrades, airfield pavements, and in constructing earth and earth-retaining stmctures. Compaction also plays a vital role in the preparation of a good compacted soil liner waste impoundment site to make it relatively impervious to leachates and thereby reduce the threat of groundwater pollution. Thus mechanical compaction is used as a practical means of achieving the desired strength, compressibility and hydraulic conductivity characteristics of the soils used. Through a laboratory compaction test (such as the Proctor test) the two important compaction characteristics-maximum dry density (Ydmax) and the optimum moisture content (OMC)-are obtained. Over a long period of field experience it has been rea Iised that the Proctor compaction test has become an important means of obtaining Ydmax and OMC. However, it takes considerable time and effort. In view of the large quantities of soils and areas of borrow pits to be tested for their potential use as compacting material. index and other simple tests have been attempted to obtain a preliminary idea of the compaction characteristics of soils (e.g. McRac, 1959; AI-Khafaji, 1987; Sridharan & Nagaraj, 2002). Tn this technical note an attempt is made to obtain compaction characteristics of fine-grained soils through a simple index test, the plastic limit.
RESULTS AND DISCUSSION Figure 1 presents the correlation of OMC with plastic limit as presented by Sridharan & Nagaraj (2002), in which a total of 64 points have been used. It is seen that there is a good correlation between OMC and plastic limit, Wp, given as OMC
Soil
= O·92wp
of soils studied
43,5 21·9 25·0 25·2 7-l 23·5 45,5 75,5 11·0 40,0 Silt: 27·7 4% 98,0 58'0 1·0 index: 2·75 260 % 12·0 48,0 30,0 35,0 42·0 13·0 10·0 37,0 21·1 28·2 27-7 12·0 580 52·0 52·9 2·65 2·78 2·74 Plastic Grain size distribution Clay: limit, % WL: Wp: % % limit, Plasticity Liquid Specific I
I \
I
I
I
I I II Manuscript received August revised manuscript accepted October on this paper closes June for further details see p. ii. I Discussion * Department of Civil Engineering, Eastern MediterraneanUniversity,Gazimagusa,N. Cyprus. I t Department of Civil Engineering, Indian Institute of Science, Bangalore, India. II 761 20
J
2002; 1
30
2003,
(1)
Figure 2 shows the correlation of OMC with Wp with some additional results (86 soils in all). It is seen that the correlation between OMC and Wp remains good, and is the same as in equation (1), despite the use of results from 10 different sources. Two points, one from Blotz et al. (1998) (wp = 8%, OMC = 18%) and one from McRae (1958) (wp = 21%, OMC = 27·5%), stand out from the rest. If it wcrc not for these two points, the correlation would be even better. Figure 3 presents the Ydmax and the dry density of the soil at the plastic limit, Ydwp, assuming it to be saturated. The experiments were done very carefully, with frequent checking of the reproducibility of the results. More than three samples werc taken for determination of moisture content
PRESENT STUDY As part of their experimental study on the compaction characteristics of Cyprus soils (three in number) together
Table 1. Physical properties
of fine-grained soils
2002.
GURTUG
762
AND SRTDHARAN
60 o Sridharan
after the compaction test. The plastic limit test was carried out carefully and strictly following the procedures. Four trials were made for each soil. It is seen that Ydmax and Ydwp are almost the same, In order to further verify the findings of Fig. 3, the dry densities at the plastic limit have been calculated for all the soils shown in Fig, 2. The specific gravities of the soils were used in the calculation wherever they were available. A value of 2·65 was assumed for soils for which the specific gravity was not available. Note that the effect of specific gravity on the dry density calculation is marginal. Fig. 4 is plotted between Ydmax and Ydwp and the line of equality. There is a striking coincidence, in that they are almost the same. Fig. 5 presents the correlation between Ydmax and the dry density at the plastic limit: the equation is
& Nagaraj (2002)
4 McRae (1958) 2ft.
o o
• • o •
50
:;:;;:
Johnson & Sallberg (1960) Foreman & Daniel (1986) Sridharan et at. (1990) Benson & Trast (1995)
o
-E 40
2c o "=
E
wp Ydmax
10
o
=
Ydwp
5
o
10
20
30
40
50
60
o
Plastic limit, wp: %
o
5
10 Ydw,:
Fig. 2. Relationship between plastic limit and optimum moisture content for 86 soils
15
20
25
kNtm3
Fig.4. Comparison of maximum dry density, Ydma" and the density at plastic limit, YdwP
25 25
6, Present study
20
I
20-]
0 4 • • 0 • ••
EZ
~
E
15
15
Z ~
Sridharan & Nagaraj (2002) McRae (1958) Johnson & Sallber9 (1960) Foreman & Daniel (1986) Sridharan et af. (1990) Benson & Trast (1995) Daniel & Wu (1993) Blotz et al. (1998)
iT
6, Present Daniel & stUdy Benson
(1990)
·xrn
rn
E
E
;: 10
;: 10 Ydmax
=
0·98 " .
R = 0'94 -
5
5
o 5
10 Ydw,:
15
20
25
o
5
kNtm3
Fig.3. Relationship between maximum the dry density at plastic limit, Ydwp
dry density, Ydmm and
Fig. 5. Relationship between maximum dry de. dry density at plastic limit, Yd"p, for 86 soil
GURTUG
762
AND SRIDHARAN
60
*'
o • • • o •
50
U
:2
o E 40
Sridharan & Nagaraj (2002) McRae (1958) Johnson & Sallberg (1960) Foreman & Daniel (1986) Sridharan et a/. (1990) Benson & Trast (1995)
after the compaction test. The plastic limit test was carried out carefully and strictly following the procedures. Four trials were made for each soil. It is seen that Y dmax and Y dwp are almost the same. In order to further verify the findings of Fig. 3, the dry densities at the plastic limit have been calculated for all the soils shown in Fig. 2. The specific gravities of the soils were used in the calculation wherever they were available. A value of 2·65 was assumed for soils for which the specific gravity was not available. Note that the effect of specific gravity on the dry density calculation is marginal. Fig, 4 is plotted between Ydmax and Ydwp and the line of equality. There is a striking coincidence, in that they are almost the same. Fig. 5 presents the correlation between Ydmax and the dry density at the plastic limit: the equation is
o
Q)
C o () :!' ::J 1i5
30
'0 E 20 E ::J
OMC R
E
= 0·92 = 0,96
wp
8-10 o
10
o
20
30
50
40
60
Plastic limit, wp: %
Fig. 1. Relationship between plastic limit and optimum moisture content for 64 soils (Sridharan & Nagaraj, 2002)
= 0·98
Ydmax
Ydwp
(2)
Four points, one from Blatz et at. (1999), one from McRae (1958), one from Foreman & Daniel (1986) and one from Daniel & Benson (1990), stand out from the rest. Without these four points Ydmax becomes equal to 0,99 times Ydwp with an increased R = 0·96. Tn view of these data, obtained from 10 different sources, it may not be wrong to assume
60
#-
o • • • o •
Sridharan & Nagaraj (2002) McRae (1958) Johnson & Sallberg (1960) Foreman & Daniel (1986) Sridharan et a/. (1990) Benson & Trast (1995) .I( Daniel & Wu (1993) o Blotz et a/. (1998) .,. Daniel & Benson (1990) '" Present study
50
U
:2
a
..;- 40
c
Q)
Co o :!' ::J 1i5
25 o • • •
Sridharan & Nagaraj (2002) McRae (1958) Johnson & Sallberg (1960) Foreman & Daniel (1986) 20 ~ 0 Sridharan et a/. (1990) • Benson & Trast (1995) .I( Daniel & Wu (1993) o Blotz et a/. (1998) .,. Daniel & Benson (1990) "'E 15 '" Present study
o
30
Z .Y
'0 E 20
~ >"
E
::J
OMC R
.S
g
= =
10
0·92 wp 0·95
Ydmax
10
o
o
=
Ydw,
5
o
10
20
30
50
40
60
Plastic limit, wp: %
o
o
5
10
15
20
25
Ydw,: kN/m3
Fig. 2. Relationship between plastic limit and optimum moisture content for 86 soils
25
Fig. 4. Comparison of maximum dry density, density at plastic limit, YdwP
Ydmax.
and the dry
Q
10 515 25 20
"'E study .~ ~0 '" Present Z
25 " 0 Sridharan & Nagaraj (2002) , • McRae (1958) • Johnson & Sallberg (1960) • Foreman & Daniel (1986) 20-1 0 Sridharan et a/. (1990) • Benson & Trast (1995) .I( Daniel & Wu (1993) o Blotz et al. (1998) T Daniel & Benson (1990) 15-1 '" Present study
;>-'"
0
Ydmax
0 I
=
Ydwp
~
r5j
o
10 Ydmax
R
= 0·98 Ydwe = 0·94
5
o
o
5
10
15
25
20
Ydw,: kN/m3
Fig. 3. Relationship between maximum the dry density at plastic limit, Ydwp
dry density,
Ydmm
and
Fig. 5. Relationship between maximum dry density, dry density at plastic limit, Ydwp, for 86 soils
Ydmm
and
COMPACTIO:\ CH..-\CTERlSTICS OF FINE-GRAINED SOILS that Ydmax is equal to the dry density at plastic limit water content. One can suggest some reasons why the dry density at plastic limit should be equal to the density at optimum moisture content in a Proctor test. In the plastic limit test. the soil is rolled with some pressure. At a water content above the plastic limit, the dry density is less than at the plastic limit: rolling the soil to make it into a thread of 3 mm diameter is possible, and the soil thread will not crumble. If the water content is lower than the plastic limit, cracks will develop at a larger diameter, and it is not possible to make a thread of 3 mm diameter. Here also the dry density will be less than that at the plastic limit. Hence it is the authors' opinion that, at the plastic limit, the dry density is a maximum for that pressure, thread diameter, and method of rolling. It is a coincidence that this dry density at the plastic limit's water content is so close to the Proctor maximum dry density. CONCLUSIONS Standard Proctor test results are extensi\'ely used in earthwork. Any correlation of the compaction characteristics with an index property will be extremely useful for the preliminary design and selection of soils from borrow areas. Such a correlation will not only save considerable time in testing but will also be highly economical. It has been noticed that the OMC is equal to 0,92 times the plastIC limIt. and that Ydmax is equal to 0·98 times the dry density a; the plastic limit water content, YdwP, assuming the degree of saruration at plastic limit to be equal to 100%. Considenng that the test results are from 10 different sources. jt may able to assume that the Ydmax of Proctor's test is dry densiry at plastic limit water content. [","" This srudy highlights the need for careful determination of the plastic limit of soil. Although it is gene~y felt that the plastic limit test is arbitrary, the authors' expenence shows that the test is reliable if it is conducted carefully, and strictly following the procedure. Careful determination reveals good reproducibility even without oersonal errors.
.-\CK.."\JOWLEDGEMENTS The authors wish to thank '--~ful discussion. They thank :ation of the manuscript.
S-j, A simple approach to the estimation soil Q. J Engng Geol. 20, 15-30. Blotz. R- ~_ B=...~ C. H. & Boutwell, P (1998). Estimating ;::;:;;and maximum dry unit weight for optimum Geoiech. Geoenviron. Engng 124, No.9, compacteC ;: 907-91::!. • ~I. (1995). Hydraulic conductivity Benson, C. of thirteen co""'-- Clays Clay Mine!: 43, No.6, 669-681. BSI (1990), British purposes: Compacrio.-British Standards 1n.su==. ~ =cent--density criteria for Daniel, D. & Benson, C. , ':::~g. ..J.SCE 116, No. 12, compacted soil liners. J. 1181-1190. Daniel, D. & Wu, Y. (1993). C=:;.a..""Y...OC arid sites. J. Geotech. Engng, Foreman, E. D. & Daniel, D. E. clay with organic chemicals. J G, No.7, 669-681. Johnson, A. W. & Sailberg, J. R. (19 compaction of soils (compacrion c ment). Highway Research Board Bull McRae, J. L. (1958). Index of compa ings of rhe symposium on applica.. design and construction, ASnl 51? ~Philadelphia: American Society fu~ T=,;: Sridharan, A., Rao, S. M. & Sanj~ expansive soils by sediment \·0 13, No.4, 375-380. ~ compaction Sridharan, A. & Nagaraj, H. B. (2002 characteristics of fine-grain Civ. Engrs Georech. Engng (provisionall. ion).
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Ii
