Use of Geofoam for reduction of swelling pressures 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
Physical properties of EPS foam Property
Range
Density kg/cu.m
11.2-28.8
Compressive strength kPa
35 -170
Flexural strength kPa
69-345
Water absorption %
2-4
Functions ØThermal Ølight
insulation,
weight fill,
ØCompressible ØVibration ØFluid
inclusion
damping,
transmission
ØSuper Ø
light weight fill
High strength to density ratio
ØPredictable
material behavior
ØManufacture ØAvailable ØNo
as per ASTM D6817
in various sizes
leachates
ØVolume ØInert
stability
under long term burial conditions
ØTermite ØEasily
resistant
shaped in field and plant
ØAvailable
throughout India
APPLICATION Transportation / Earthworks Embankments, Side-Hill fill, Embankments, fill , Bridge Approach abutments, general fill roads, parking, Median and sound barrier Architecture- landscape, plaza decks, bermed structures, Buildings - Structural fill, foundation walls other Applications - Flood control leaves, dikes/berms, dikes/be rms, vibration isolation
12
10
Expansive soil 8 s s e rt S
Geofoam 6
4
2
0
0
2
4
6
8
Compression or free swell
10
12
Light weight fill
Geofoam between retaining wall and backfill
Ground line
Geofoam over conduits
Basement Geofoam
Drain
Geofoam
Geofoam as thermal insulator
CASE HISTORIES
Geofoam to reduce 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,
• Chem Chemical ical compo compositio sition. n. • Ri Rigi gidi dity ty • Manu Manufactu facturing ring metho method d 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 Serie Series: s: Verti Vertical cal Compr Compressi essible ble Cylin Cylindric drical al Elements (VCCE) in small moulds 3. C Series: Series: Model footin footing g tests in in a large RCC tank using both HCS and VCCE
CONFIGURATION OF MODULDS FOR LABORATORY TESTING Abrv
standard laboratory moulds
Dia mm
Height mm
CR
consolidation rings
65
20
SP
Proctor mould
100
117
CBR
CBR mould
150
150
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.
Table - The properties of these soils Property
Type of Soil BC
Gravel %
BF 6 4
BF55
6 .4 5
0
0
Sa nd %
10.25
0
0
S il t %
67.30
15
15
C la y f r a c t i o n
16.00
85
85
LL %
62
4 72
3 78
PL %
27
3 22
2 57
SL %
15
19
22
DFS %
30
1 40
1 12
LC HC
1 4 .6
1 2 .6
12.30
1 8 .0
1 5 .2
15.00
LC HC
18
3 0 .0
3 0 .0
14
2 2 .5
2 2 .5
Max. D.D kN/cum OMC %
Compaction
The soil was compacted as per light compaction or Heavy compaction procedure (as per I.S. 2720 part 7 and 8 respectively).
TYPE OF GEOFOAM The Geofoam used in these investigations was Polyethylene foam (trademark Profeel).
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
PR OPER TI ES OF O F GEOFOAM GEOFOAM
PROPERTIES
V AL U E S
Structure
Expanded Cell
Polymer
Polyethylene
Tens Te nsiile st stre reng ngth th
300 30 0- 40 400 0 kP kPa a
Modulus of Elasticity
10 -14 kPa
Comp. Strength @ 10%
19 kPa
Unit weight
34 kg /cum
SWELLING PRESSURE TESTS: 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.
SWELLING PRESSURE VS. HEAVE For all soils swelling pressure vs. Heave data was obtained to predict probable swelling pressure of soil with Geofoam.
Lab. Test Results- Series A Soil Compaction mould
HCS Geofoam Thickness (mm)
Measured
Predicted
BC- LC-SP
12
8
14
BCHC-S P
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
14
Swelling pressure (kPa)
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 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
Placement of Geo-foam: A)
Horizon Horiz onta tall la laye yers rs:: The horizon horizontal tal 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.
Test Data from Series B
Test Procedure for C Series Preparation of Soil Filling of test tank Placement of Geofoam Arrangement Arrangeme nt 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-General 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 i n the form of horizontal sheet or vertical cylinder of Geofoam. 4. There is substantial reduction in swelling pressure due to these intrusions.
2- Vertical Swelling 1. Reduction of swelling pressure increases with the thickness of Geofoam sheet. 2. The optimum optimum depth depth ratio of placement 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.
3- Lateral 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
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
For any suggestions
Contact Dr.A.S.Nene M4 Laxmi Nagar, Nagpur (India) 440022 Email: nene_ashok@
[email protected] yahoo.com
