Proceedings of Indian Geotechnical Conference December 15-17, 2011, Kochi (Paper No. H- 224)

INNOVATIVE TECHNIQUE FOR IMPROVEMENT OF FLOOR SYSTEM ON B.C. SOIL

USING HORIZONTAL GEOFOAM LAYER

P.B.Daigavane, Assistant Professor, Govt. College of Engg. Avasari (Pune), email: pdaigava53@rediffmail.com

M.S. Pawar, Research Scholar, Govt. College of Engg. Amravati, email: mspawar. eer@rediffmail.com

ABSTARCT: The expansive soils are well known for their swell – shrink behavior, whenever, the expansive soil

comes into contact with excessive moisture content, swelling pressure is developed in the soil. Expansive soil causes

severe damage to structures wherever no special precautions are taken. The structure built on swelling soils offer great

challenges to civil engineers since, the behavior of soils depends upon the natural conditions.

The paper presents the innovative method for reduction swelling pressure of expansive soils by the use of horizontal

geofoam layer below the flooring. A field study for observing actual reduction in swelling pressure, by constructing

two similar floor systems on black cotton soil of 1350 mm x 2000 mm in plan, one with horizontal geofoam layer and

another without Geofoam layer is carried out.

INTRODUCTION

The expansive soils can be defined as those soils which swell

on absorption of water and shrink on removal of water. Such

soils are found in many parts of the world. In central India so

called black cotton soils are expansive soils. When expansive

soils attract and accumulate water, it exerts a pressure known

as swelling pressure on the overlying materials and

structures.

Many methods have been tried to overcome the severe

problems and difficulties posed by swelling soils. The most

common method is to remove the expansive soil till a hard

stratum is made and replace the expansive soil by more

suitable granular soil.

MATERIALS AND METHODS

Soil

The soil on which the investigation is carried out was from

the premises of Govt. Engg. College Amravati. The soil used

in filling the tank was locally available Black – Cotton Soil.

The Soil was air dried / sun dried in open atmosphere, in lots

of 100 Kgs and a representative sample of 300 Kgs was oven

dried to confirm the result of air drying. The moisture content

prior to the test was 19.4% and at the end of test it was 100%

saturation.

Physical properties of the soil are determined by conventional

laboratory methods in accordance with I.S. -2720. The

properties of soils are mentioned below.

Table 1 Properties of soil

Particulars Value

Specific Gravity 2.67

Liquid Limit 54.32%

Plastic Limit 27.21%

Shrinkage Limit 13.00%

Optimum moisture content 19.40%

Maximum dry density 16.7kN/cum

Void Ratio 59.9%

Swelling pressure 12 kN/ Sq.m.

Free swell Index 72%

Geofoam :

The geofoam used in this investigation is polyethylene foam.

The geofoam sheet of 40 mm thickness is used as horizontal

layer. The properties of Geofoam are mentioned below.

Table 2 Properties of Geofoam

. Particulars Value

Structure Expanded cell

Polymer Polyethylene

Tensile strength 300 – 400 kPa

Modulus of elasticity 10- 40 kPa

Compressive strength @ 10% 19 kPa

Unit weight 0.34kN/cum

FIELD EXPERIMENT FOR SWELLING PRESSURE

TEST ON MODEL FLOOR SYSTEM

The field experimental setup consist of perforated concrete

tank surrounded by masonary saturation tank, loading frame,

LVDTs and load- cells to measure the magnitude of swell

and swelling pressure. The swelling pressures of saturated

soils were measured by constant volume method. The

pressure at which vertical deformation becomes zero was

taken as maximum swelling pressure.

Test Tank:

Two identical R.C.C. Tanks of soils 1000 mm x 1000 mm x

1000 mm depth were constructed. The sides of the tanks were

perforated with holes of 20 mm diameter @ 100 mm center

to center. These tanks were surrounded by outer immersion

tank filled with water for saturation of soil.

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P.B.Daigavane & M.S. Pawar

Fig No. 1 Section

Fig No. 2 Test Set up

Loading Frame:

Two loading frames were fabricated using ISMB 150 mm x

150 mm x 80 mm. compressive load was applied by

mechanical jack attached to the loading frame.

Device For Load And Swell Measurement :

Load cell was used for measuring the load and L.V.D.T.s for

measuring swelling of soil.

Filling The Test Tank:

The soil was filled into the tank, layer by layer with dynamic

compaction method to get the required density. Filling of

tank was done from center to edges and back from edges to

center till the tank was full. Model floor of M.S plate of size

150 mm x 150 mm was kept at center on the compacted soil

and the load cell was kept vertically in contact with the plate.

Placement Of Geofoam:

12 mm thick horizontal compressible sheet (HCS) of

geofoam was placed at three depth ratios, i.e. D/B = 01, D/B

= 02 & D/B = 03 (D - Depth of geofoam, B - Breath of

footing)

The experiment was repeated for different size ratios of

geofoam i.e. L/B = 01, L/B = 02 & L/B = 03 (L - Length of

geofoam,)

FIELD STUDY SETUP

Two similar floor systems of size 1350 mm x 2000 mm on

BC Soil, one with horizontal Geofoam layer and another

without Geofoam layer is constructed for observation of

actual reduction in swelling of expansive soil. The soil below

floor was fully saturated with water by constructing deep

drain around the floor system. The settlement is recorded by

dial gauges.

Fig No. 3 Floor system without Geofoam

Fig No. 4 Floor System in Construction for Horizontal

Geofoam layer

P.B.Daigavane & M.S. Pawar

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Innovative technique for improvement of floor system on B.C. soil using horizontal geofoam layer

Fig No. 5 Floor System with Horizontal Geofoam layer

Fig No. 6 Floor System with Dial Guage

Fig No. 7 Future proposed work with vertical Geofoam layer

OBSERVATIONS

For Tests Tanks

The load applied on footing to maintain the constant volume

was recorded by load cell. L.V.D.T.s were used to measure

the swell of soil. The constant volume tests were conducted

for full saturation condition.

Observations were recorded for horizontal compressible

sheets of geofoam and inferences were plotted as below.

Fig. 8 Reduction in swelling pressure with Geofoam

For Floor Systems :

The Geofoam is placed on B.C.soil below flooring in the

form of horizontal compressible sheet of 40 mm thickness

and of size 1350 mm x 2000 mm. The sheet gets compressed

upon swelling and reduces the swelling pressure to be exerted

on flooring. Observations were recorded for settlement for

floor system with and without Geofoam and results are

plotted as shown in fig No. 9

Fig No. 9 Reduction in settlement with geofoam for floor

INTERPRETATION OF TEST DATA:

For Tests Tanks :

The tests conducted in the tank concluded that the placement

of Geofoam sheet near the footing / flooring i.e. D/B ratio of

one, gives the maximum reduction in swelling pressure.

For Floor System :

Flooring without Geofoam Sheet was deformed in upward

direction upto 8 mm due to swelling of soil. But flooring with

40 mm thick Geofoam sheet below it, the swelling was

absorbed by Geofoam resulting into practically zero

settlement.

Plate size 150 mm x 150 mm

Innovative technique for improvement of floor system on B.C. soil using horizontal geofoam layer

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P.B.Daigavane & M.S. Pawar

CONCLUSIONS

Based on the limited field investigations, following

conclusions can be drawn

1. Reduction in swelling pressure is maxium at D / B ratio of

one and L /B ratio of three

2. Magnitude of swelling pressure decreases with permissible

volumetric expansion.

3. Settlement of flooring decreases by inclusion of

horizontal geofoam layer.

REFERENCES

1. Chen F.Y. (1980) “Foundations on expansive soils”

First edition, Elsiver Applied Science

publisher ltd., U.K.

2. Horvath J.S. (1995) “Geo-foam Geosynthetics”

Horvath Engg P.C. Scarsdale, New York, U.S.A.

3. Daigavane P.B. (1999) “Reduction of swelling

pressures by use of geosynthetics”, Doctoral Thesis,

Nagpur University, Nagpur India.

4. Daigavane P.B., Pawar M.S, Borkar R.P. & Morge

Bagra, (2010) “Improved foundation system

for BC soils using horizontal geofoam layers”

Indian Geotechnical Conference, IIT Mumbai, Vol II

pp 599-600.

5. Shelke A.P. and Murty D.S. (2010) “Reduction of Swelling pressure of expansive soils using EPS

Geofoam.” Indian Geotechnical conference, IIT

Mumbai, Vol II pp 495-498. 6.

6. Daigavane P.B. and Pawar M.S. “Innovative technique

for improvement of foundation system in BC

soil using horizontal geofoam layers.” National

conference on Recent advances in Ground

Improvement Techniques, CBRI Roorkee Vol. No. I

pp 320-328

ACKNOWLEDGEMENTS

The authors wish to acknowledge, Directorate of Technical

Education, Mumbai, Principal Govt. College of Engg.

Amravati, Professor S.V. Joshi, Principal, Government

College of Engineering Avasari and Dr. S.G. Akojwar,

Principal, Dr. Bhausaheb Nandurkar College of Engineering

& Technology, Yavatmal for their valuable guidance, support

and encouragement to write this paper and sponsorship for

conference. Authors are also thankful to AICTE, New Delhi,

for RPS, F.No. 8023/BOR/RPS-34/2006-07.

P.B.Daigavane & M.S. Pawar

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