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Interfacial friction between soils and solid surfaces Dr. R. G. Robinson Assistant Professor Department of Civil Engineering IIT Madras

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Shallow foundation Deep foundation Tip resistance Typical field situations

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Retaining walls Typical field situations

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Reinforced earth walls Typical field situations

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Geosynthetic reinforced earth slopes Typical field situations

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Geotextiles Typical field situations

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Definition of coefficient of friction and friction angle Soil Solid material P T P Normal Force T Shear Force Coefficient of friction, =tan = T/P where, is the friction angle T P Normal stress=P/A Shear stress = T/A

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Potyondy (1961)Rowe (1962)Silberman (1961) Ingold (1984) Apparatus used for evaluating friction angle

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Jewell and Wroth (1987) Murthy et al. (1993) Coyle and Sulaiman (1967) Apparatus used for evaluating friction angle

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Brumund and Leonards (1973)Ingold (1984) Heerema (1979)Yoshimi and Kishida (1981) Apparatus used for evaluating friction angle

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Desai et al. (1985)Uesugi and Kishida (1986) Paikowsky et al. (1995)Abderrahim and Tisot (1993) Apparatus used for evaluating friction angle

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Some Terminologies

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Three Phases in Soils S : Solid Soil particle W: Liquid Water A: Air Air Void ratio, e = V v /V s Water content, w = M w /M s

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Relative Density (D r ) Loosest Densest e max = 0.92 e min = 0.35 (Lambe and Whitman, 1979)

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Particle shapes-- Sand Rounded Subrounded Subangular Angular Coarse- grained soils (Holtz and Kovacs, 1981)

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ASTM D 4253; ASTM D 4254 Maximum and minimum void ratio Maximum void ratio Minimum void ratio

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Direct shear test f shear strength of soil n Normal stress ccohesion intercept angle of internal friction

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n1 n2 n3 Displacement Typical direct shear test results n1 n2 n3 Angle of repose cv cv ~ Angle of repose Dense sand Loose sand

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Interface friction in sands

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Factors influencing interfacial friction angle of Sand Surface Roughness Surface Roughness Density of sand Density of sand Normal stress Normal stress Rate of deformation Rate of deformation Size of apparatus Size of apparatus Grain size and shape Grain size and shape Type of apparatus Type of apparatus

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Influence of sand density and surface Roughness Toyoura sand Soma sand

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Soil TypeSoil Condition Silica sandloose dense Calcareous sand from Guam loose dense loose, crushed loose, ground dense, crushed Calcareous sand from Florida loose medium dense medium, crushed medium, ground dense, crushed Results of triaxial and soil-steel friction tests (after Noorany, 1985) Influence of sand density……

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Acar et al Levacher and Sieffert 1984

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Limiting values of I Maximum Values: Potyondy (1961), Panchanathan and Ramaswamy (1964), Uesugi and co-workers reported the limiting maximum value of is the peak angle of internal friction p Yoshimi and Kishida (1981) report that the maximum limiting value is the critical state friction angle cv

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Interface Source Sand-material Sand-smooth surface Sand-smooth material Sand-normal glass Sand-pyrex glass Sand-stainless steel Sand-steel Glass beads-steel Material-Material Diamond-diamond Sapphire-sapphire Metal-diamond Steel-sapphire – 6 7 tan -1 (0.07/R i ) § Lambe and Whitman (1969) Yoshimi and Kishida (1981) Tatsuoka and Haibara (1985) Uesugi and kishida (1986b) Tejchman and Wu (1995) Paikowsky et al. (1995) Bowden and tabor (1986) Notes: Particle-to particle friction angle §R i Modified roundness Minimum Values of Reported by Various Authors

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Influence of normal stress Potyondy (1961); Acar (1982): Both δ and Φ decreases with normal stress but the ratio (δ/ ) remains constant Heerema (1979), Uesugi and Kishida (1986), ORourke et al. (1990) is independent of normal stress For soft materials: increases with normal stress due to indentation of sand into the material (Panchanathan and Ramaswamy, 1964; Valsangkar and Holm (1997)

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Heerema (1979) Heerema (1979) –Rate of deformation from 0.7 to 600 mm/s –No influence Lemos (1986) Lemos (1986) –Rate of deformation to 133 mm/min –No influence Influence of Rate of deformation

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Brumund and Leonards (1973) Brumund and Leonards (1973) –Rods with interface area of 225 cm 2 and 400 cm 2 –No appreciable difference Uesugi and kishida (1986) Uesugi and kishida (1986) –Simple shear apparatus, 40 cm2 and 400 cm 2 –No influence ORourke et al (1990) ORourke et al (1990) –Direct shear apparatus of size equal to 6cm x 6 cm, 10 cm x10 cm, 28 cm x28 cm and 30.5x30.5 cm –No significant influence Influence of Size of apparatus

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Influence of grain size and shape Particle diameter (mm) Friction angle (degrees) Rowe (1962) Rowe (1962), Uesugi and Kishida (1986), Jardine and Lahane (1994): decreases with increase in grain size Angular particles give higher friction angle (Uesugi and Kishida 1986; ORourke et al. 1990; Paikowski et al. 1995)

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Kishida and Uesugi (1987) Kishida and Uesugi (1987) –Simple shear versus direct shear –No difference Thandavamurthy (1990) Thandavamurthy (1990) –Direct shear versus model pile tests –Direct shear gives 20% higher Abderrahim and Tisot (1993) Abderrahim and Tisot (1993) –Direct shear- Ring torsion-Pressuremeter probe –Direct shear > Pressuremeter probe >Ring shear Influence of type of apparatus

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QUANTIFICATION OF INTERFACE ROUGHNESS

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versus Roughness (Bosscher and Ortiz 1987)

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Normalized Roughness (Kishida and Uesugi 1987)

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Correlation with Normalized Roughness (Kishida &Uesugi 1987)

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Modified roundness of a particle Definition of modified roundness (Uesugi and Kishida 1986)

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Correlation between, R n and R (0.27) (0.19) (0.17)

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Author(s) Type of testing apparatus Results of investigation Potyondy (1961) Direct shear apparatus with the sand on the top of test material increases with density and = p increases with density and lim = p Broms (1963) Direct shear mode by sliding the material over the sand A value of 23 o was obtained irrespective of sand density Yoshimi and Kishida (1981) Ring shear with the test material on top of sand Density has no influence and lim = cv Acar et al. (1982) Similar to Potyondy increases with density increases with density Noorany (1985) Similar to Broms Influence of density is negligible Uesugi et al. (1990) Simple shear with the sand on top of the test material increases with density lim = p increases with density lim = p Summary of some published interface friction tests

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Analysis of past studies From the review the following three conclusions can be drawn: increases with surface roughness and reaches a maximum limiting value (2) For very rough surfaces, tends to a limiting maximum value which could be either the peak angle of internal friction p or the critical state friction angle cv. can either increase or remain constant with the increase in sand density.

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Author(s) Type of testing apparatus Results of investigation Potyondy (1961) Direct shear apparatus with the sand on the top of test material increases with density and = p increases with density and lim = p Broms (1963) Direct shear mode by sliding the material over the sand A value of 23 o was obtained irrespective of sand density Yoshimi and Kishida (1981) Ring shear with the test material on top of sand Density has no influence and lim = cv Acar et al. (1982) Similar to Potyondy increases with density increases with density Noorany (1985) Similar to Broms Influence of density is negligible Uesugi et al. (1990) Simple shear with the sand on top of the test material increases with density lim = p increases with density lim = p Summary of some published interface friction tests

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Type A apparatusType B apparatus SAND Material Loading cap Schematic of Type A and Type B apparatus

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Sl.No.FeaturesType AType B I Apparatus configuration Relative position of solid material and sand and sample preparation. Application of normal stress to the interface. Apparatus type in literature Soild material is on the top of sand. The sand specimen is prepared first and the solid surface is placed over the prepared leveled surface. Normal stress is applied through the material to the interface. Ring torsion apparatus, direct shear apparatus by sliding solid material over sand. The sand specimen is on the top of solid material surface. The sand is prepared directly on the solid surface. Normal stress is applied through the sand the interface. Direct shear apparatus by sliding soil over solid material, simple shear apparatus, translational test box etc. Features of Type A and Type B apparatus

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Sl.No.FeaturesType AType B II Influence of type of apparatus on the results obtained Influence of roughness Influence of density of sand. Maximum limiting value of increases with roughness Negligible. The maximum limiting value for very rough interface is critical state of angle of internal friction of sand increases with roughness. increases with the increase of density. The limiting maximum value is the peak angle of internal friction of sand. ….. Features of Type A and Type B apparatus

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Experiments in Direct shear apparatus

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Solid materials used Material 1– Stainless steel

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Material 2– Mild steel Material 3– Mild steel

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Material 4– Ferrocement Material 5– Ferrocement

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Surface profiles of the materials Stainless steel Mild steel Concrete surface Mild steel Concrete surface

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Grain size distribution curves of the sands used

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Sand No. GsGs D 50 mm CuCu D av mm ( d ) max kN/m 3 ( d ) min kN/m Note: G s Specific gravity of soil grains ( d ) max Maximum dry density ( d ) min Minimum dry density Properties of sands used

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Raining Technique--Calibration curves

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Schematic of Type A apparatus

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Type A apparatus

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Schematic of Type B apparatus

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Type B apparatus

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Typical shear stress-movement curves Type A Type B Sand 6, n = 140 kPa

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Sand 4 Material 5 n = 70 kPa

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Typical failure envelopes (Type B) Peak Critical state

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( pB / ) versus Relative density (Type B) Thandavamurthy (1990)

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Variation of ( pB / ) with D av (Type B)

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Proposed Roughness index Relative Roughness (R) R a Average Roughness D av Average particle size

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Variation of ( pB / ) with R

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Variation of cvB with R

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Comparison of cvA with cvB

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Drained shear strength of fine- grained soil-solid surface interfaces

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Clays are sheet like and possess plasticity characteristics

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Grain size distribution curves of the soils used

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PropertySoil Red Earth KaoliniteIllite Atterberg Limits Liquid limit (%) Plastic Limit (%) Plasticity index (%) Grain Size Sand (%) Silt size (%) Clay size (%) Average particle size ( m) Coefficient of consolidation, C v (cm 2 /sec) x x x Properties of cohesive soils used

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Variation of shear stress with deformation rate of illite

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Soil Deformation rate (mm/min.) CalculatedAdopted Red Earth Kaolinite Illite Deformation rates calculated and adopted for tests under drained condition

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c nc pcpc OCNC Normal stress Shear stress Failure envelope of a soil at constant preconsolidation pressure

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OCR=1 n =100, 200 and 300 kPa OCR=5 p =500 kPa n = 100 kPa p =1000 kPa n = 200 kPa p =1500 kPa n = 300 kPa OCR=10 p = 500 kPa n = 50 kPa p =1000 kPa n = 100 kPa p =1500 kPa n = 150 kPa FAILURE ENVELOPE WITH CONSTANT OCR Red earth Illite

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Shear movement, mm Typical shear stress-movement curves

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Typical failure envelopes Normal stress

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Variation of B and ( B / ) with OCR B o B /

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Variation of ( B / ) with R a

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Variation of ( B / ) with R

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Comparison of values from Type A and Type B

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SUMMARY Interfacial friction depends on mode of shear for sands and the maximum value of friction angle is controlled by the type of apparatus used to evaluate the friction angle Interfacial friction depends on mode of shear for sands and the maximum value of friction angle is controlled by the type of apparatus used to evaluate the friction angle For clays, mode of shear has no influence For clays, mode of shear has no influence

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Research Issues Modeling of interface behaviour : shear stress-movement curves Modeling of interface behaviour : shear stress-movement curves Roughness Roughness Hardness of solid material Hardness of solid material Rigidity of materials Rigidity of materials Mode of shear Mode of shear Particle size and shape Particle size and shape

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Acknowledgements CSIR for funding 1.Prof. K. S. SUBBA RAO Department of Civil Engineering IISc, Bangalore 2. Prof. M. M. Allam Department of Civil Engineering IISc, Bangalore

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Thank you

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