geofoam for swelling soils

Use of Geofoam

for reduction of swelling pressures

of expansive soils

By Dr.A.S.Nene

What is Geofoam ?

Geofoam can be defined as any manufactured material created by some expansion process that results in foam with a texture of closed gas filled cells

2-4 Water absorption %

69-345 Flexural strength kPa

35 -170 Compressive strength kPa

11.2-28.8 Density kg/cu.m

Range Property

Physical properties of EPS foam

ØThermal insulation,

Ølight weight fill,

ØCompressible inclusion

ØVibration damping,

ØFluid transmission

Functions

ØSuper light weight fill

Ø High strength to density ratio

ØPredictable material behavior

ØManufacture as per ASTM D6817

ØAvailable in various sizes

ØNo leachates

ØVolume stability

ØInert under long term burial conditions

ØTermite resistant

ØEasily shaped in field and plant

ØAvailable throughout India

APPLICATION

Transportation / Earthworks

Embankments, Side-Hill fill, Bridge Approach abutments,general fill roads, parking, Median and sound barrier

Architecture- landscape, plaza decks, bermedstructures,

Buildings - Structural fill, foundation walls

other Applications - Flood control leaves, dikes/berms, vibration isolation

0 2 4 6 8 10 120

2

4

6

8

10

12

Stre

ss

Compression or free swell

Geofoam

Expansive soil

Light weight fill

Geofoam between retaining wall and backfill

Geofoam over conduits

Ground line

Geofoam

GeofoamDrain

Basement

Geofoam as thermal insulator

CASE HISTORIES

Geofoam to reduce lateral pressures on retaining wall, Caraosel centre, Syracuse New York

Geofoam on infill for plaza Chicago

Project : Hanging Lake Tunnel Light weight fill on ventilation facility

Vehicle emergency escape ramp

Lightweight fill applications Taxiway & Extension ,

New Orleans LA

Slope Stabilization on

route 23A Jewett, NY

GEOFOAM CLASSIFICATION

The most commonly used foams are grouped according to,

• Chemical composition.• Rigidity• Manufacturing method

Geofoam are made from any one of the following material– Polyethylene, – Polyisocyanurate,– Polystyrene / Polystyrol– Polyurethane (product is known as PUF)

LABORATORY INVESTIGATION ON GEOFOAM

Extensive laboratory investigations were

carried out during 1993 to 1999

at VNIT Nagpur.

These investigations can be grouped under three heads;

1. A Series: Compressible horizontal sheets (CHS) in small moulds

2. B Series: Vertical Compressible Cylindrical Elements (VCCE) in small moulds

3. C Series: Model footing tests in a large RCC tank using both HCS and VCCE

CONFIGURATION OF MODULDS FOR LABORATORY TESTING

150150CBR mouldCBR

117100Proctor mouldSP

2065consolidation ringsCR

Heightmm

Diamm

standard laboratory moulds

Abrv

The soils used in these investigations

Ølocally available black cotton soil (BC)

Øbentonite and fly-ash (BF64) in 60:40

Øbentonite and fly-ash (BF55) in 50:50

proportion by dry weight.

Property Type of Soil

BC BF64 BF55

Gravel % 6.45 0 0

Sand % 10.25 0 0

Silt % 67.30 15 15

Clay fraction 16.00 85 85

LL % 62 472 378

PL % 27 322 257

SL % 15 19 22

DFS % 30 140 112

Max. D.D kN/cum LC HC

14.6 12.6 12.30

18.0 15.2 15.00

OMC % LC HC

18 30.0 30.0

14 22.5 22.5

Table - The properties of these soils

The soil was compacted as per light compaction or Heavy compaction procedure (as per I.S. 2720 part 7 and 8 respectively).

Compaction

The Geofoam sheets of thickness 2 to 18 mm were used as HCS

and VCCE element were prepared by rolling 1 mm sheet and sealing the end to form cylindrical elements of 5.12 or 18 mm diameter. The properties of the Geofoam used are shown in a table 2

TYPE OF GEOFOAM

The Geofoam used in these investigations wasPolyethylene foam (trademark Profeel).

PROPERTIES OF GEOFOAM

PROPERTIES VALUES

Structure Expanded Cell

Polymer Polyethylene

Tensile strength 300- 400 kPa

Modulus of Elasticity

10 -14 kPa

Comp. Strength@ 10%

19 kPa

Unit weight 34 kg /cum

The swelling pressures of saturated soils were measured by constant volume method for series A and B. For series C the pressure at which vertical deformation was zero was taken as maximum swelling pressure.

For all soils swelling pressure vs. Heave data was obtained to predict probable swelling pressure of soil with Geofoam.

SWELLING PRESSURE TESTS:

SWELLING PRESSURE VS. HEAVE

14

SoilCompaction

mould

HCS Geofoam Thickness

(mm)

Swelling pressure (kPa)

Measured Predicted

BC-LC-SP 12 8 14

BCHC-SP 12 14 20

BC-LC-CR 4 10 15

BC-HC-CR 2 30 34

BC-HC-CR 4 20 28

BF-LC-SP 12 16 30

BF-HC-SP 12 25 40

BC- Black cotton soil, BF- Bentonite fly-ash, LC- light compaction, HC- Heavy compaction, SP-Standard proctor

mould, CR – Consolidation ring

Lab. Test Results- Series A

Lab. Test Results- Series B

Large scale Test Results- Series C

Soil: The soil used for the final investigations was of Bentonite Fly ash mixture in . 50:50. proportion (BF55) The properties of the soil are already reported in Table 1

Model footing :The model footings were square & circular of 150 mm. size fabricated from 8mm thick M.S. sheet plates. . The depth to width ratios (D/B) selected were, 0.5, 1 & 1.5. In all the tests the model footings were placed at the centre of the loading area and the load was applied at the exact centre of the footing

A) Horizontal layers: The horizontal geo-foam layer, at desired depth was placed during the compaction process i.e. while the tank is being filled. After assuring its proper placement, further layers of soil were placed over it, to give the embedment effect.

B) Vertical cylindrical geo-foam elements. : The placement of VCCE was done, around the footing. To ensure the proper placement, at the desired position, small bores were done with the help of hollow cylindrical tubes of the required external diameters, & then the Geo-foam in the form of VCCE, was placed inside the hole.

Placement of Geo-foam:

Test Data from Series B

Test Procedure for C Series

Preparation of Soil

Filling of test tank

Placement of Geofoam

Arrangement for load applications

Arrangement for heave measurement

Field Test Setup

TANK CONSTRUCTION

Load and heave measurement

Accessories for tank filling

Inner Tank with holes

TANK FILLED WITH SOIL

Instrumentation

Filling of outer tank with water

Periodic Observations

Results of Series C

Conclusions

1. Magnitude of swelling pressure decreases with volumetric permitted expansion.

2. Volumetric expansion can be provided in the form of compressible intrusion.

3. The compressible intrusion can be in the form of horizontal sheet or vertical cylinder of Geofoam.

4. There is substantial reduction in swelling pressure due to these intrusions.

1-General

1. Reduction of swelling pressure increases with the thickness of Geofoam sheet.

2. The optimum depth ratio of placement of sheet is 0.5

3. The optimum size ratio (Bg / Bf) of sheet is 2.0.

4. The probable swelling pressure of soil can be predicted by superimposing stress-strain graph of Geofoam and swell pressure vs. permissible heave.

5. Good co-relation between experimental and predicted values of swell pressures.

2- Vertical Swelling

1. The swelling pressure of soil can be reduced by permitting the soil to expand laterally by providing vertical intrusions.

2. This technique is more suitable for rehabilitation of existing structure on expansive soils.

3. Reduction of swelling pressure increases with size and number of vertical intrusions.

4. For accurate prediction of swelling pressure a more rigorous analysis of stress- strain behavior of swelling soil and Geofoam is necessary

3- Lateral swelling

References

Nene A.S. and Daigavane (1995) " Use of Geosynthetics for Reduction of Swelling Pressures "Fifth International Conference on Geotextiles, Geomembranes and related Products, Singapore, 5-9 September 1994,p 331-334.

Nene, A.S. and Daigavane (1996) "Reduction of Swelling Pressures by Use of Vertical Compressible Geosynthetics Elements" First International Conference on Unsaturated Soil, Paris 6-8 September, Vol. I pp 263-270

Dr.A.S.Nene M4 Laxmi Nagar, Nagpur (India) 440022 Email: nene_ashok@yahoo.com

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