CYCLIC SWELLING BEHAVIOUR OF CLAYS

Presented By Vinay S D

II Sem, Geotechnical Engineering

EWIT

CONTENTS

Introduction  Scope of Presentation Materials and methods Case study Conclusions References

INTRODUCTION Expansion of clays is caused due to wetting of

soil,which results in volume increase.

It causes serious damage to civil engineering structures.

Cyclic expansion and shrinkage of clays and the associated movements of foundations may result in cracking and fatigue to structures.

By cyclic swelling it is meant that a soil specimen is wetted and allowed to swell then dried to its initial water content at room temperature , then wetted again to swell, dried once more, and so on.

 SCOPE OF PRESENTATION

The basic objective of this study was to investigate the effect of cyclic swelling on the expansive characteristics of clays.

When clay specimens are repeatedly subjected to full swell than allowed to desiccate to their initial water content show sign of fatigue after each cycle ,thus exhibiting less expansion.

The swelling potential increases with the number of wetting and drying cycles.

Expansion reaches an equilibrium state after about 3 to 5 cycles.

MATERIALS AND METHODS

Clay Soil

CONSOLIDATION TEST

CASE STUDY

Project : Cyclic Swelling Behavior of Clays.

Location : Irbid a city in Northern Jordan.

Objective: Determining swell-shrink behavior of clay.

PROJECT BACKGROUND To study the effect of cyclic swelling on the

expansive characteristics of clays six expansive soils were obtained from various locations in Irbid (a city in northern Jordan).

Previous investigations of Irbid soil (Masoud 1988) indicated that it consists of

Properties Percentage

Clay 50-80

Silt 10-45

Sand 2-15

Liquid limit 65-90

Plastic limit 15-40

Shrinkage limit 10-20

All of these properties. along with Irbid city being in a semiarid region. serve only to indicate that the soil in this area is expansive in nature.

Additionally, clays in this area are generally classified as highly to very highly expansive in nature (Basma 1993).

To accomplish the desired objectives and as was stated earlier, six soils from various locations were utilized in this study.

PROPERTIES OF TEST SOILSProperty

A B C D E F

Depth of sampling (m)

4.0 6.0 6.0 3.5 3.0 2.5

Initial watercontent, W(%)

12.0 21.0 20.3 20.0 15.0 20.0

Initial dry unit weight(kN/m')

16.0 l7.0 16.0 l7.0 16.8 17.2

LL 35 79 57 75 62 81

PI 22 27 15 37 34 38

Property

A B C D E F

Grain size distribution

Sand (%)

32.0 8.0 38.0 3.0 20.0 5.0

Silt (%) 32.1 33.2 29.8 20.0 28.9 23.3

Clay (%)

37.9 58.8 32.2 77.0 51.1 71.7

TESTING PROCEDURE Remoulded specimens were prepared by

compacting the soil at its natural water content and dry unit weight directly into the consolidation ring.

The compacted soil sample was placed in a consolidation cell between air-dry porous stones and subjected to a vertical confining pressure of 6.9 kPa (I psi).

It should be noted that for each soil considered, two identical samples were prepared, as was just mentioned. The first specimen was used to determine the swell percent and the second was utilized to assess the swell pressure.

To determine the percent swell the sample was inundated with distilled water. allowing it to fully swell for at least 40 hr.

At this stage, the water was removed and the consolidation cell was dismantled.

The test sample (still within the consolidation ring) was then allowed to air-dry to its initial water content within the laboratory environment.

Measurements of water loss for each sample were recorded at intervals of approximately 15 min for the first 3 hr, then every 100 min thereafter to 500 min, then at I day.

Cycles after at least 48 hr of wetting followed by the air drying period required to revert the samples to their initial water contents were repeated for the six soils.

For brevity and space limitation, a plot of the vertical swell and shrinkage for only two soils, namely, A and F, as function of time are presented below.

The change in swell pressure with the number of wetting and drying cycles was also determined by the constant volume swell test.

In this test. the samples were air dried to their corresponding initial water contents then fully inundated with distilled water.

As swelling commences, vertical deformation was prevented and the samples were kept at their initial void ratio by continuously adding loads at every vertical expansion.

The loads were continually added until no expansion was observed.

At this stage the swell pressure was calculated as the load required to retain zero swell divided by the specimen area.

CHANGE OF SWELL POTENTIAL AND SWELL PRESSURE WITH CYCLENUMBER FOR TEST SOILS

SUMMARY AND CONCLUSION

Swelling and swell pressure decrease with increasing number of cycles.

The most reduction in swelling and swell pressure was recorded after the first cycle.

Even though both properties decrease, they seem to level off after about 4 to 5 cycles.

REFERENCES

Effect of Micro fabric on Undrained Static and Cyclic Behavior of Kaolin Clay.

Cyclic Triaxial Tests on remoulded clays. Rate effects and cyclic loading of sensitive

clays.

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