Geofoam for Swelling Soils
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Transcript of 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: [email protected]
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