Intrinsic Compression Behavior of Remolded and Reconstituted Clays-Reappraisal

doi:10.4236/ojce.2013.33B002

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Open Journal of Civil Engineering, 2013, 3, 8-12

http://dx.doi.org/10.4236/ojce.2013.33B002 Published Online September 2013 (http://www.scirp.org/journal/ojce)

Intrinsic Compression Behavior of Remolded and

Reconstitu ted Cla ys-Reappraisal

Jie Yin, Yonghong Miao

Department of Civil Engineering, Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang, China

Email: [email protected]

Received June 2013

ABSTRACT

Evaluating the impacts of soil structure on mechanical behavior for natural sedimentary clays is an important issue in

geotechnical engineering. Burland introduced void index for normalizing the compression curves of various remolded

and reconstituted clays to obtain the intrinsic compression line, which provides a reference framework to assess the

in-situ compression behavior. However, it does not quantitatively account for the effects of initial water content on

compressive behavior of remolded and reconstituted clays and the initial water contents of clays are not always limited

to 1.0 - 1.5 times the liquid limits defined by Burland. A modification bas ed on collected tests data was presented on the

expressions of

100

and

defined by Burland. Extensive oedometer test data were also collected on various re-

molded and reconstituted soils with distinct liquid limits and initial water contents to verify the validity of modified

expressions. A normalized compression line deduced by intrinsic compression line is proposed in the e-log p plot,

which can be used to evaluate the effects of soil structure quantitatively on the intact compressive behavior for natural

sedimentary clays.

Keywords: Initial Water Content; Compression Behavior; Remolded and Reconstituted Clays; Oedometer Test

1. Introduction

When encountered in situ, most natural sedimentary

clays show some form of “structure ”. It has been well

accepted that the structure is formed during their deposi-

tional and the post depositional processes, where com-

plicated impacts such as mechanical, chemical and bio-

logical factors are brought into action [1]. The general

term “soil structure” is to mean the arrangement and

bonding of the soil constituents, and for simplicity it

contains all features of a soil that are different from those

of the corresponding reconstituted soil [2-4]. Various

experimental data suggests that the mechanical behavior

in situ state influenced by the soil struc ture is totally dif -

ferent from the remolded and reconstituted state [3]. How

to quantitatively assess the effects of soil structure on

mechanical behavior of natural sedimentary clays is an

important issue in geotechnical engineering [3]. For

solving this problem, the mechanical behavior of the re-

molded and reconstituted clays can be used to establish a

reference framework [3-5]. The most famous normalized

oedometer compression line is the intrinsic compression

line (ICL), which provides an available reference frame

to assess the in-situ compression behavior proposed. He

introduced void index for normalizing the compression

curves of various remolded and reconstituted clays hav-

ing an initial water content being 1.0 - 1.5 times the liq-

uid limit (preferably 1.25 times). However, it does not

quantitatively account for the effects of initial water con -

tent although he presented the existing tests data which

showed reconstituted clays at higher water contents had

higher values of the void ratio at applied stress less than

100 kPa. It is well known that natural water contents of

natural sedimentary soils vary in a wide spectrum of

times liquid limits [5], which are not always limited to

1.0 - 1.5 times the liquid limits.

Based on the existing tests data, th e intrinsic compres-

sion behavior of remolded and reconstituted clays was

briefly investigated and a modification was presented on

the expressions of *

100

e and

defined by Burland for

considering both the effects of liquid limit and initial

water content. A normalized compressive line is deduced

by intrinsic compression line to quantitatively evaluate

the effects of soil structure on the intact compressive

behavior for natural sedimentary clays.

2. Compression Curves of Remolded and

Reconstituted Soft Clays

42 different remolded and reconstituted soft clay samples

obtained from three different places in China were col-

lected for oedometer tests. Basic physical indices are

J. YIN, Y. H. MIAO

shown in Table 1.

It should be noted that some of the soft clay samples in

Label 1 were reconstituted by adjusting its initial water

content (reconstituted clays), the others were just only

remolded (remolded clays). The initial water contents of

the 42 samples range from 0.7 to 2.0 times the liquid

limit. The ratio of initial water content w0 over liquid

limit LL is defined as initial normalized water index

[6], which can be expressed as follow

LLww /

(1)

The typical compressive curves are shown in Figure

1(a), Figure 1(b) and Figure 1(c) for the 42 remolded

and reconstituted clays respectively [7]. The legend in

each figure represented the initial water contents with the

values of

being 0.71 - 1.98, 0.68 - 1.99, 0.70 - 1.99

of each soil corresponding to Table 1. It can be seen that

all the compression curves are similar in shape being

slightly concave upwards when the consolidation pres-

sure is larger than some value respectively, as described

by Burland [3]. Comparing through the three figures,

when the soft clays with about the same initial norma-

lized water index

, at any given value of the consoli-

dation pressure, the larger the liquid limit, the higher the

void ratio is. When concerning any of Figure 1, at any

given value of the consolidation pressure, the larger the

initial water content, the higher the void ratio and higher

compressibility is. However, it is different from that of

Burland. It can be concluded that the compressive beha-

vior of remolded or reconstituted clays is influenced by

both the liquid limit and initial water content.

3. Intrinsic Compression Behavior

Burland stated that the properties of remolded or recons-

tituted clays are termed ‘intrinsic’ properties since they

are inherent to the soil and independent of the natural

state [3]. He presented a useful normalizing index called

void index Iv for normalizing the compressive behavior

of various remolded and reconstituted clays. The void

index is defined as following expression

∗

∗∗

∗−

−

I100

1000100

100

(2)

The quantities *

100

e and

1000

are the void ratios cor-

responding to the app lied stress

= 100k Pa and 1000

kPa of the reconstituted clay at an initial water content w0

of 1.0 - 1.5 times the liquid limit, respectively.

∗

the intrinsic compression index which equals to

100

minus

1000

Then a reasonably unique compression line termed in-

trinsic compression line (ICL) is obtained, expressed as

Iv = 2.45 - 1.285x + 0.015x3 (3)

where

log

in kPa.

When the oedometer tests are not conducted on the

remolded and reconstituted soils, the values of

100

and

1000

can be approximately calculated by the following

equatio ns (Burla nd 1990).

Table 1. Basic physical indices of remolded and reconstituted soft clays.

Soil sample number Sampling site Gs w0 (%) LL (%) PL (%)

1 - 14 Huaian city 2.65 64.4 - 179.7 90.6 38 0.71 - 1.98

15 - 28 Lianyungang city 2.71 50.3 - 146.3 73.6 33 0.68 - 1.99

29 - 42 Fuzhou city 2.67 42.6 - 121.5 61.1 30 0.70 - 1.99

0.11101001000 10000

Consolidation stress (kPa)

Void ratio

64.4% 71.6%

82.5% 90.9%

100.8% 110.9%

118.6% 126.1%

136.9% 143.3%

153.3% 162.5%

173.9% 179.7%

0.11101001000 10000

Consolidation pressre (kPa)

Void ratio

50.3% 58.5%

68.3% 78.0%

84.8% 91.5%

96.0% 104.3%

114.0% 118.5%

126.8% 135.0%

141.8% 146.3%

0.5

1.5

2.5

3.5

0.1110100 1000

Consolidation pressure (kPa)

Void ratio

42.6% 48.3%

57.1% 61.7%

65.8% 72.3%

80.2% 86.9%

91.1% 99.1%

106.3% 110.2%

115.5% 121.5%

(a) (b) (c)

Figure 1. Typical e-logp compression curves of remolded and reconstituted soft clays (a) Lianyungang city clay, (b) Huaian

city clay (c), Fouzhou city clay.

J. YIN, Y. H. MIAO

100

016.0089.0679.0109.0

LLL

eeee +−+=

∗

(4)

04.0256.0 −=

∗Lc

(5)

where eL represents the void ratio at liquid limit.

Burland has pointed out that the above empirical equa-

tions should only be used for values of eL within the

range 0.6 to 4.5 (i.e. wL = 25 to 160%).

According to the test data in Figure 1, the compres-

sion behavior of remolded and reconstituted clays is ob-

viously influenced by both the liquid limit and initial

water content. However, the empirical equation (4) and

(5) only consider the effec t of liquid limit, for eL = Gs*LL

when soil is saturated. That is to say, a modification

should be given on Equation (4) and (5) for considering

the effect of initial water content.

For simplicity, a liner multiple regression based on

tests data in this study is adopted by corresponding com-

puter software. Considering the value of

100

∗

is increased with the LL from Burland and initial

water content or initial normalized water index

Based on the 42 tests data, the best fitted quantitative

equations are given as follows:

084.039.013.1 0100 −+=

∗LL wwwe

(6)

461.025.091.0

−+=

∗LLc

wwwC

(7)

Figure 2 shows the comparison between the measured

values of *

100

e and

∗

from Figure 1 and the calcu-

lated values by Equation (6) and (7). It can be seen that

they are quite consistent, indicating that Equation (6) and

(7) can be used for well predicting the values of

100

and

∗

For further verifying the validity of Equation (6) and

(7), several researchers who published oedometer test

data of some remolded or reconstituted clays were col-

lected as shown in Table 2.

The comparison results are shown in Figure 3. It is

0.5

1.5

0 0.5 1 1.5 2

Measured values of e

*100

Calculated values of e

*100

0.5

1.5

0 0.5 1 1.5 2

Measured values of C

Calculated values of C

(a) (b)

Figure 2. Comparison of the *

100

and

between calculated and measured values (a) for *

100

, (b) for

Table 2. Existing data of remolded or reconstituted soils.

Clays Sample GS LL (%) PL (%) w*0 Reference

Argile Plastique 1 2.58 128.0 31.0 1.00 [3]

London Clay 1 2.71 67.5 26.5 1.00 [3]

Wiener Tegel 1 2.76 46.2 22.0 1.00 [3]

Magnus Clay 1 2.73 35.0 17.2 1.00 [3]

Residual clay 1 2.74 58.0 27.0 1.00 [3]

Red soil 1 2.67 45.3 22.0 1.00 [6]

Black cotton clay 1 2.73 97.3 32.0 1.00 [6]

Red soil 1 2.65 50.0 27.0 1.00 [8]

Brown soil 1 2.65 62.0 31.0 1.00 [8]

Black Cotton Soil 1 2.80 84.0 47.0 1.00 [8]

Ashikari Town clay 6 2.62 80.3 30.9 1.00 - 1.22 [9]

Kawasoe Town clay 2 2.65 50.9 26.6 1.00 - 1.23 [9]

Ariake Town clay 14 2.60 104.8 33.9 1.01 - 1.42 [9]

Kaolinite 4 2.8.0 42.0 26.0 1.00 - 1.75 [10]

Bostion Blue Clay 4 2.68 45.0 23.0 1.00 - 1.75 [10]

J. YIN, Y. H. MIAO

0.5

1.5

2.5

3.5

01 23 4

Measured values of e

*100

Calculated values of e

*100

0.5

1.5

00.5 1 1.5 2

Measured values of C

Calculated values of C

(a) (b)

Figure 3. Comparison of the *

100

and

between calculated and measured values in literatures (a) for *

100

; (b) for

encouraged that most of the independent data have a

close relationship to Equation (6) and (7) although with

some data having a little scatter.

Based on the Equation (2), (3), (6) and (7), A norma-

lized compression line considering both the effects of

initial water content and liquid limit can be obtained in

the e-log p plot written as

( )

∗∗

+⋅

′

⋅+

′

⋅=

100

)(log0.015log1.285-2.45(eCe

σσ

(8)

The values of *

100

e and

∗

can be predicted by Eq-

uation (6) and (7) respectively. Equation (8) can be used

to evaluate the effects of soil structure quantitatively on

the intact compressive behavior for natural sedimentary

clays by enabling the initial water content being equal to

the natural water content.

4. Conclusions

The main conclusions obtained in this study are summa-

rized as follows:

(1) Oedometer tests results for three clays with differ-

ent initial water contents suggest that the compression

behavior of remolded or reconstituted clays is influenced

by both the liquid limit and initial water content.

(2) By correlating with the empirical equations pro-

posed by Burland and oedometer test data in this study, a

simple form of expressions of

100

and

∗

are ob-

tained by the multiple liner regression, which are

084.039.013.1

0100

−+=

∗LL

wwwe

and

461.025.091.0

−+=

∗LLc

wwwC

, respectively.

5. Acknowledgements

This research is sponsored by natural science foundation

of Jiangsu province in China (Grant No. BK2011476),

which is gratefully acknowledged.

REFERENCES

[1] R. J. Chandler, “Clay Sediments in Depositional Basin:

The Geotechnical Cycle,” The Quarterly Journal of En-

gineering Geology and Hydrology, Vol. 33, No. 1, 2000,

pp. 7-39. http://dx.doi.org/10.1144/qjegh.33.1.7

[2] S. Leroueil and P. R. Vaughan, “The General and Con-

gruent Effects of Structure in Natural Soils and Weak

Rocks,” Géotechnique, Vol. 40, 1990, pp. 467-488.

http://dx.doi.org/10.1680/geot.1990.40.3.467

[3] J. B. Burland, “On the Compressibility and Shear Strength

of Natural Clays,” Gé otechnique, Vol. 40, No. 3, 1990,

pp. 329-378.

http://dx.doi.org/10.1680/geot.1990.40.3.329

[4] M. D. Liu, J. P. Carter and C. S. Desai, “Modeling Com-

Pression Behavior of Structured Geomaterials,” Interna-

tional Journal of Geomechanics, ASCE, Vol. 3, No. 2,

2003, pp. 191-204.

[5] S. Buchan and D. T. Smith, “Deep-Sea Sediment Com-

pression Curves: Some Controlling Factors, Spurious

Overconsolidation, Predictions, and Geophysical Repro-

duction,” Marine Georesources and Geotechnology, Vol.

17, No. 1, 1999, pp. 65-81.

http://dx.doi.org/10.1080/106411999274016

[6] T. S. Nagaraj and B. R. Srinivasa Murthy, “A Critical

Reappraisal of Compression Index Equation,” Géotech-

nique, Vol. 36, 1986, pp. 27-32.

http://dx.doi.org/10.1680/geot.1986.36.1.27

[7] Z. Hong, J. Yin and Y. Cui. “Compression Behaviour of

Reconstituted Soils at High Initial Water Contents,” Géo-

technique, Vol. 60, No. 9, 2010, pp. 691-700.

http://dx.doi.org/10.1680/geot.09.P.059

[8] T. S. Nagaraj and B. R. Srinivasa Murthy, “Rationaliza-

tion of Skempton’s Compressibility Equation,” Géotech-

nique, Vol. 33, No. 4, 1983, pp. 433-443.

http://dx.doi.org/10.1680/geot.1983.33.4.433

[9] Z. Hong, “Void Ratio-Suction Behavior of Remolded

Ariake Clays,” Geotechnical Testing Journal, Vol. 30, No.

3, 2007, pp. 234-239.

J. YIN, Y. H. MIAO

[10] A. B. Cerato and A. J. Lutenegger, “Determining Intrinsic

Compressibility of Fine-Grained Soils,” ASCE Journal of Geotechnical and Geoenvironmental Engineering, Vol.

130, No. 8, 2004, pp. 872-877.