Evaluation of the influence of some factors on laboratory test results

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STATEN$ GEOTEKNISKA INSTITUT SGI VARIA ¹⁰⁷

Nguyen Manh Dau

linkoping 1983

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EVALUATION OF THE INFLUENCE OF SOME FACTORS ON LABORATORY TEST RESULTS

NGUYEN MANH DAU

Swedish Geotechnical Institute (SGI) 1983

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1 STATENS GEOTEKNISKA INSTITUT

CONTENTS

1. ACKNOWLEDGEMENTS 2. INTRODUCTION

3. PERFORMED LABORATORY INVESTIGATIONS 3a. Purpose of the investigations

3b. Description of the tests

4. TEST RESULTS

5. LABORATORY TEST METHODS USED IN THE INSTITUTE FOR BUILDING SCIENCE AND TECHNOLOGY (IBST) TO INVESTIGATE THE LIME COLUMN

6. CONCLUSIONS

7. REFERENCES

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STATEN$ GEOTEKNISKA INSTITUT 2

1. ACKNOWLEDGEMENTS

This work was done for 4 weeks at the SGI-laboratory at my four months visit to SGI according to the co

operation between the Swedish Geotechnical Institute (SGI) and the Institute for Building Science and Technology (IBST), Vietnam.

The author specially thanks Mr Goran Holm and Mr Goran Nilson at SGI for support, supervision of the work and

for valuable discussions.

Gratitude is expressed to Mrs Lena Freden for supervision and guiding of the laboratory tests. The author thanks Mrs Eva Dyrenas for her expert typing of the manuscript.

The author also thanks the other members of the laboratory department for their assistance during my time at the SGI

laboratory.

Linkoping, January 18, 1983

Nguyen Manh Dau

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STATENS GEOTEKNISKA INSTITUT 3

2. INTRODCUTION

Up to now, there is no standard method for compaction of soil-lime samples in Sweden. The influence of the com

paction method on the increase of the shear strength has been shown by Ashraf, J.M. and Walker, R.D. 1963 and

found to be negligible. In the Swedish Geotechnical Insti

tute, where the lime column method has been completely investigated, there are two methods for compaction of soil-lime samples, the old method and the new method. In the old method, the equipment shown in Fig. 1 is used and the pressure force cannot be measured or controlled in a detailed manner. In the new method, the compaction equip

ment made at SGI is used and with this new equipment the pressure force is measured and controlled, see Fig. 2.

The relations between these two methods have not been investigated yet, however.

The soil-lime samples are normally stored in a humid room at a temperature of s⁰c. The influence of the temperature during curing on the increase of shear strength of the soil-lime mixture has previously been investigated by Anday, M.C., 1963, Broms, B. and Boman, P. 1979. Anday, M.C. found that the temperature of about 10°c was minimum for the lime to react with the soil. Broms, B, and Boman, P, showed that the shear strength of a stabilized soil stored at 20°c was higher when in a stabilized soil stored at s⁰c. The exact influence of the storage temperature on the strength increase is not fully investigated.

Two different methods, the unconfined compression test and the fall-cone test, are widely used in Sweden as well as in some other countries to determine the shear strength of soil, in general, and of the soil-lime samples, in

particular.

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STATEN$ GEOTEKNISKA INSTITUT

Fig. 1 Old compaction equipment

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Fig. 2 New compaction equipment

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The fall-cone method is a very new one in Vietnam, and has not yet been used for soil-lime samples. So i t is very interesting to use this method on soil-lime samples.

3. PERFORMED LABORATORY INVESTIGATIONS 3a. Purpose of investigations

The purpose of these investigations were:

- To study the influence of compaction methods (such as the old method with a compression force of 75 kg, 100 kg and 125 kg) on the shear strength of the soil-lime samples.

- To study the influence of the test method (for example unconfined compression method and fall-cone method)

on the results of shear strength of the stabilized soils.

- To study the influence of the storage temperature on the increase of shear strength of the stabilized soils.

- To practice on laboratory investigation methods on lime column according to the SGI methods.

3b. Description of the tests

The initial parameters of the soil such as natural water content, liquid limit, plasticity limit etc was determined on undisturbed soil samples. The soil was mixed with un

slaked lime for about 10-15 minutes using the mixing equipment with the bowl and mixing tool shown in Fig. 3, which gave a very homogeneous mixture. The amount of lime was chosen to 13 kg per metre column. This choice was based on Swedish experiences that about 6% of lime is suitable in the actual soil type. With the natural water content of 51% in the actual soil, the percentage of lime will be 5.7% (of dry weight of soil), (normally the per

centage of lime is 5-10%). A special diagram from SGI makes i t easy.

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•

Fig . 3 Mixing equipment

SGI nr 196 Klintland Grali~ko, Linkoping

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The soil-lime samples were compacted in plastic tubes (h=170 mm, ~=50 mm) by old equipment and new ones. At the new equipment, the samples were compacted under different pressure forces= 125 kg, 100 kg and 75 kg.

in which the force of 100 kg normally is used in the SGI-laboratory to compact the stabilized soil. The soil

lime samples, then were stored at +8°c, +20°c and +35°c (+8°c is approximately the ground temperature in Sweden).

The periods of storage chosen were 1, 12, 22 and 51 days after mixing.

Two different methods were used to determine the shear strength of the soil-lime samples, namely the fall-cone tests and unconfined compression tests, see Fig. 4 and Fig. 5. At the fall-cone tests, two different cones were used: the 400 g-cone and the 100 g-cone. When the pen

etration is less than 5 mm with the 100 g-cone, the 400 g-cone should be used instead.

The shear strength of the samples can be calculated using the formula:

T fu = k • 9 • 81. -v-m (kPa)

where k = coefficient. k = 1 for 30°-cone and k = 0.25 for 60°-cone m = weight of the cone

i = penetration depth of the cone

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STATEN$ GEOTEKNISKA INSTITUT ^{t )}

Fig. 4 Fall-cone apparatur

Fig. 5 . Unconfined compression machine

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4. TEST RESULTS

The shear strengths of the soil-lime samples compacted by the old method (with the old equipment) and by the new method (with the new equipment) at the force of 75 kg, 100 kg and 125 kg are shown in Tab. 1 to 2 and Fig.

6 to 7. The results from the unconfined compression tests are shown in Tab. 2 and Fig. 6. It is obvious that the shear strength determined by the unconfined compression tests should be less than from the fall-cone tests since the failure at the fall-cone tests occurs at the point of the cone whereas the failure at the unconfined com

pression tests occurs at the weakest place in the samples in the contact between the relatively stronger aggregates.

Tab. 1 and Fig. 6 show that the values obtained by un

confined compression tests are lower than the values obtained by fall-cone tests. A greater spread in the

values is also obtained by the unconfined compression tests.

To determine the rate of increase in the shear strength of the soil-lime samples, besides the unconfined compression tests the Swedish fall-cone tests can be used (Goran Holm and Lars Hellman, 1978).

Tab. 1 and Fig. 6 to 7 show that the difference in the results obtained by the different compaction methods used in this investigation are small. The densities of all the samples are nearly the same (1.71 t/m3 to 1 .73 t/m ), the 3 shear strengths one day after mixing are nearly the same.

Only the shear strengths 51 days after mixing are a bit different. So, in fact the new method(with the new equip

ment made at SGI) can be used to compact the soil-lime samples. Homogeneous soil-lime samples are obtained by this equipment. Variation in pressure forces from 75 kg to 125 kg has only a small influence on the density and the shear strength of the soil-lime samples.

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1 0 STATENS GEOTEKNISKA INSTITUT

Tab. 1 The shear strength of the soil-lime samples compacted by the different methods.

Method Den- UCD (kPa) Fall-cone (kPa)

sity time (days) time (days)

1 12 22 51 1 12 22 51

Old methoc 1 . 71-

25.6 30.4 45.6 31 . 2 38.45 60.4 63.5 107.5 +8°c 1. 72

New methoc 1. 72- 32.4 42.4 47.6 37.2 33.8 66.5 67.2 11 4. 9 (F=100 kg) 1. 74

+8°c

New methoc 1 . 71- 28.0 37.0 33.6 27.2 43.0 53.3 61. 3 97.7 +25% (F= 1. 73

125 kg) +8°C

New methoc 1. 72- 24.0 28.6 28.0 40.0 40.8 54.1 54.3 91. 8 -25% (·F= 1. 7 3

75 kg) +8°c

Tab. 2. Shear strength of the soil-lime samples stored at the different temperatures.

Storage Den- UCD (kPa) Fall-cone (kPa)

tempera-

sity time (days time (days)

ture

1 12 22 51 1 12 22 51

+8°c 1.72-

(new method) 1. 74 32.4 42.4 37.6 37.2 33.8 66.5 67.2 1 1 4 . 9 +20°c 1 . 7 2-

(new method) 1. 75 35.0 - 52.8 82.4 33.0 81. 5 89.5 189.0 +35°c

1.71-

(new method) 40.8 158.0 226.0 423.0 36.4 347.6 360.3 5 91 . 7 1. 7 3

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1 1 STATEN$ GEOTEKNISKA INSTITUT

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Fig. 6 and 7. Shear strength of the soil-lime samples compacted by the different methods.

SGI nr 196 Klintland Grafiska, Link6ping

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1 2 STATENS GEOTEKNISKA INSTITUT

Tab. 2 and Fig. 8 to 9 show the shear strengths of the soil-lime samples stored at the different temperatures:

+s⁰c, +20°c and +35°c. The highest shear strength was obtained in the samples stored at 35°c even one day after mixing (40.8 kPa with UCD and 36.4 kPa with the Swedish fall-cone test). After 51 days the shear strength obtained was 423.0 kPa with UCD and 591.7 kPa with the fall-cone test.

The increase of the shear stength of the samples stored at s ⁰c and at 20°c is very slow within 22 days and then quicker. In the samples stored at +35°c the increase of the shear strength is very high and very quick compared with the samples stored at +8°c and +20°c (Fig. 8 and Fig. 9).

The increase of the shear strength of the soil-lime samples is assumed to be related to M, where M = f(t⁰,T) (t⁰=storage temperature ⁰c, T = storage curing period - days, f = a

certain function).

Fig. 10 is a diagram showing the increase of the shear strength of the samples stored at +20⁰C and +8°c, plotted with respect to Mand M = (t⁰•T). The curves will be

closer when M = [(t⁰+3) ·T] see Fig. 11. Relatively, the function of Tfu = 0.13 M + 40 or Tfu = 0.13 [(t+3) T]+ 40 can be considered to be an approximate one of the curve of +8°c and the curve of +20°c and then i t is a function in connection with the curve of s ⁰c and the curve of 20°c.

If this principle was right for every curve of different temperature, the increase of shear strength of the samples at a certain temperature would have been found from

another curve where the increase of shear strength has been investigated~ This question should be investigated more in detail to obtain better relations.

Tab. 3 and Fig. 12 show the influence of the storage

temperature on the increase of shear strength of the soil

lime samples. In general, the shear strength increases in

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11 STATEN$ GEOTEKNISKA INSTITUT

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_, ___ j^I _I _' _I _' _' _- _! _' _{: - - __}.i__ . i ' I . i . I • ' - - - - -

Fig. 11 Increase of shear strength of the samples stored at +8°c and +20°c plotted with respect to M=

(t⁰+3) ·T.

lJ7

(18)

Tab. 3. Unconfined compressive strength of the soil

lime samples stored at different temperatures and different periods.

Storage Den- UCD (kPa) Fall-cone (kPa

period (days)

sity

Storace temperature ⁰:c

+8 +20 +35

Storaqe temperature

+8 +20 +35

OC

1 32.4 35.0 40.8 33.8 33.0 36.4

12 42.4 - ^158.0 ^66.5 ^81.⁵ ^347.6

22 37.6 52.8 226.0 67.2 89.5 360.3

51 37.2 82.4 423.0 1 1 4 • 9 189.0 5 91 • 7