GEOSYNTHETICS ENGINEERING: IN THEORY AND PRACTICE Prof. J. N. Mandal Department of Civil Engineering, IIT Bombay, Powai, Mumbai 400076, India. Tel.022-25767328 email: cejnm@civil.iitb.ac.in
Module-13 LECTURE- 62 Designing with Geofoam
Recap of previous lecture.. Design of embankment using geofoam Overturning due to seismic effect Translation due to wind Testing of Geofoam Apparent Density Test Water Absorption Test Compressive Strength Test
Proposed unconfined compression test (PUCT) on EPS geofoam Proposed compressive strength Test on EPS geofoam (a) Schematic diagram (b) Test specimen
Unconfined compression test on EPS geofoam with different densities: (a) ρ = 15 kg/m 3 (b) ρ = 20 kg/m 3 (c) ρ = 22 kg/m 3 (d) ρ = 30 kg/m 3
Compressive Stress (kpa) 180 150 120 90 60 30 0 30 kg/m 3 22 kg/m 3 20 kg/m 3 15 kg/m 3 0 5 10 15 20 Strain (%) Stress-strain relationship for proposed unconfined compression test on EPS geofoam
Density of EPS geofoam (kg/m 3 ) Compressive strength test results: Size of the specimen (mm) Compressive strength (kpa) @ 5% @ 10% @ Yield Initial tangent modulus (kpa) 15 75 φ 150 ht 57.04 62.92 52.89 3395 20 75 φ 150 ht 85.33 93.03 78.85 4074 22 75 φ 150 ht 100.50 106.16 92.67 5213 30 75 φ 150 ht 143.96 150.07 123.56 8149
Compressive strength (kpa) 160 120 80 40 0 Compressive strength @ 10% strain σ c = 5.799ρ - 23.09 R² = 0.998 0 5 10 15 20 25 30 35 Density of EPS geogoam (kg/m 3 ) Relationship between density of EPS geofoam (ρ) and compressive strength @ 10% strain
Compressive strength (kpa) 160 120 80 40 0 Compressive strength @ yield σ c = 4.689ρ - 15.01 R² = 0.988 0 5 10 15 20 25 30 35 Density of EPS geogoam (kg/m 3 ) Relationship between density of EPS geofoam (ρ) and compressive strength @ yield
Compressive strength test results as per different test specifications Density Compressive strength (kpa) (kg/m 3 ) ASTM D1621-10 IS:4671-1984 DIN 53421-1984 PUCT (IITB) @5% @10% @5% @10% @5% @10% @5% @10% 15 54.8 59.6 55.75 63.08 56.89 60.72 57.04 62.92 20 81.6 88.4 82.98 92.56 82.60 90.71 85.33 93.03 22 92.4 108.2 102.07 112.07 98.47 108.31 100.50 106.16 30 128.20 142.7 136.23 151.11 128.50 144.03 143.96 150.07 @5%, @10% represents compressive strength value of EPS geofoam calculated at 5 and 10 percent of axial compression of test specimen. PUCT - Proposed Uniaxial Compression Test.
Tensile Properties of Geofoam (ASTM: D1623 09) Objective To determine the tensile strength properties of geofoam Test Specimen Specimen Type A The recommended Type-A test specimen with its dimensions is shown below Tensile strength test specimen of Geofoam (Density of the geofoam from left to right are 15, 20, 22 and 30 kg/m 3 )
Gripping Assembly Tensile strength test on EPS geofoam Failed specimens in tension
(a) Before (b) After Tensile strength test on EPS geofoam (Density of the geofoam material are from left to right 15, 20, 22 and 30 kg/m 3 ) (a) Before and (b) after failure
Tensile Strength: The tensile strength is calculated by dividing the breaking load by the original minimum cross-sectional area of the specimen. Tensile stress, (σ t ) Calculations t F D 2 F = Tensile force applied to the specimen (kn) D = Minimum diameter of the test specimen (m) Considering Density of EPS geofoam = 20 kg/m 3, 4 Tensile stress Breaking Load Cross sectional area 0.14 0.0287 4 2 216.40 kpa
Stress-strain behavior of EPS geofoam in tension
Test Results of tensile Strength on EPS geofoam Density of EPS ASTM D1623-09 geofoam (kg/m 3 ) Tensile strength (kpa) Strain at failure (%) 15 154.89 2.56 20 216.40 2.71 22 244.54 2.74 30 407.78 2.82
500 Tensile strength (kpa) 400 300 200 100 σ t = 17.14ρ - 116.9 R² = 0.981 0 0 5 10 15 20 25 30 35 Density of EPS geofoam (kg/m 3 ) Correlation between tensile strength and density of EPS geofoam
Proposed Test Specimen for Tensile testing of Geofoam: In the proposed tensile strength test, the test specimen has thickness of 25 mm with a flat section. Figure shows the schematic representation of the test specimen. Schematic representation of tensile strength test specimens
Tensile strength test specimens (Density of the geofoam materials are from left to right as 15, 20, 22 and 30 kg/m 3 ) Tensile strength test gripping assembly
Tensile strength test on EPS geofoam
(a) Before (b) After Tensile strength test on EPS geofoam (Density of the geofoam material are from left to right 15, 20, 22, and 30 kg/m 3 ) (a) Before and (b) after failure
Tensile Stress (kpa) 500 400 300 200 100 0 0 1 2 3 4 Strain (%) 30 kg/m 3 15 kg/m 3 22 kg/m 3 20 kg/m 3 Tensile stress - strain behavior of EPS geofoams
Tensile strength test results and comparison Density of EPS geofoam (kg/m 3 ) ASTM D1623-09 Tensile Strain at strength failure (kpa) (%) PTST (IITB) Tensile strength (kpa) Strain at failure (%) 15 154.89 2.56 154.13 2.23 20 216.40 2.71 216.16 2.62 22 244.54 2.74 246.88 2.63 30 407.78 2.82 411.56 2.74
Shear Properties of Geofoam (ASTM: C273/C273M-07a) Objective: To determine the shear strength parameters of geofoam Test Specimen: The test specimens shall be 300 mm 50 mm 25 mm Schematic representation Shear strength test specimen with different densities (kg/m 3 )
Shear test assembly for Geofoam Plate Shear Specimen of Geofoam and Force Line of Action Shear Strength Test on EPS geofoam
Calculations: Shear Stress (τ) of the geofoam material: P L b τ = core shear stress (kpa), P = instantaneous force on specimen (N), L = length of specimen (m) and b = width of specimen (m). Maximum shear stress (τ max ) max P Lb
Considering Density of EPS geofoam = 20 kg/m 3, P = 1.412 kn, L = 0.3 m and b = 0.05m; max 1.412 0.3 0.05 94.37 kpa Shear Strain (γ) of the geofoam material: u t u = Deformation at peak shear load (mm) t = Thickness of core (mm). 4.67 25 0.1868 mm / mm
Core Shear Modulus (G) of the geofoam material: G P x u L b t P/ u = slope of the force-displacement curve (N/mm) from 0.002 mm/mm to 0.006 mm/mm effective engineering shear strain Now, P/ u = 855.88, t = 0.025 m, L = 0.3 m and b = 0.05 m; G 855.88 0.025 0.3 0.05 1426.467 kpa
Density of EPS geofoam (kg/m 3 ) Maximum load at failure (N) Shear strength test results Shear strength (kpa) Deformat ion at peak load (mm) P/ u (From graph) Core shear modulus (kpa) 15 1255 83.65 5.62 668.18 1113.633 20 1416 94.37 4.67 855.88 1426.467 22 1823 121.57 4.31 902.36 1503.933 30 2089 139.27 2.67 1130.9 1884.833
Breaking Load and Flexural Properties of Geofoam (ASTM: C203-05a) Objective: To determine the breaking load and flexural properties of the geofoam. Methods available Three point method Four point method Flexural strength test methods for EPS geofoam
Test Specimen: The test specimen shall be 300 mm 100 mm 25 mm. Schematic representation Flexural strength test specimen (Density of the geofoam material from left to right are 15, 20, 22 and 30 kg/m 3 )
Flexural Test Assembly for Geofoam Span length = 250 mm
(a) Before (a) After Flexural Strength Test on Geofoam (a) Before and (b) After failure (Density of the geofoam material are from left to right 15, 20, 22 and 30 kg/m 3 )
EPS geofoam specimens after failure Flexural strength test results: Density (kg/m 3 ) ASTM C202-05 Flexural Strength (kpa) Deformation (mm) 15 149.9 25.41 20 211.3 33.13 22 240.6 38.11 30 277.0 46.07
Maximum Fiber Stress (S): S 2 3P L 2 bd S = stress in the outer fibers (kpa) P = load at a given point on the load-deflection curve (N) L = support span (m), b = width of beam tested (m), and d = depth of beam tested, (m)
Considering Density of EPS geofoam = 20 kg/m 3, P = 0.0342 kn, L = 0.25 m, b = 0.1 m and d = 0.025m. Flexural strength 3PL 2 2bd 3 0.03420.25 Flexural strength 2 2 0.10.025 211.3kPa
Maximum Strain (ε): The maximum strain in the outer fibers occurs at mid span. 6Dd 2 L ε = maximum strain in the outer fibers (mm/mm), D = maximum deflection of the center of the beam (mm) L = support span (mm) and d = depth (mm). Here, D = 0.03313 m, d = 0.025 m and L = 0.25 m. 60.03313 0.025 Maximum strain ( ) 2 0.25 0.08mm/ mm
Moment of Inertia: The moment of inertia is calculated as follows: I b d 12 3 I = moment of inertia (mm 4 ) b = specimen width (mm), and d = specimen thickness (mm) Here, b = 0.1m and d = 0.025 m I 0.1 0.025 12 3 1.3x10 7 m 4
Elastic Modulus of geofoam material can be given as, E 1 48 3 P L I D E = elastic modulus (kpa), D = corrected deflection at center of sample (m), I = moment of inertia (m 4 ), L = support span (m), and P = load at a given deformation within the proportional limit of the specimen (kn). P = 0.0342 kn, L = 0.25 m, I = 1.3 10-7 m 4, and D = 0.03313 m. 3 0.0342 0.25 481.310 0.03313 E 7 2584.87 kpa
Flexural strength test results Density of EPS geofoam (kg/m 3 ) Maximu m load at failure (kn) Flexural strength (kpa) Deform ation at center (m) Maxim um strain (mm/m m) Moment of Inertia (m 4 ) Modulus of elasticity (kpa) 15 0.025 149.9 0.02541 0.06 1.3 10-7 2518.69 20 0.0342 211.3 0.03313 0.08 1.3 10-7 2584.87 22 0.0401 240.6 0.03811 0.09 1.3 10-7 2815.95 30 0.0461 277.0 0.04687 0.11 1.3 10-7 3088.52
Please let us hear from you Any question?
Prof. J. N. Mandal Department of civil engineering, IIT Bombay, Powai, Mumbai 400076, India. Tel.022-25767328 email: cejnm@civil.iitb.ac.in