Direct Shear Interface Test for Shaft Capacity Of

E. Saibaba Reddy,1 D. N. Chapman,2 and V. V. R. N.Sastry3 Direct Shear Interface Test for Shaft Capacity of Piles in Sand ␦r ⌬r ␾ ␾p ␾r ␥ ␥max ␥min ␥test ␴n ␴r ␴rc ␴rf ␴v ␶f REFERENCE: Reddy, E. S., Chapman, D. N., and Sastry, V. V. R. N., “Direct Shear Interface Test for Shaft Capacity of Piles in Sand,” Geotechnical Testing Journal, GTJODJ, Vol. 23, No. 2, June 2000, pp. 199–205. ABSTRACT: For precise estimation of shaft capacity of a pile, it is essential to determine accurately the soil-pile interface friction angle (␦). The apparatus available to measure the value of ␦, the miniature pile test apparatus and the soil-pile-slip test apparatus are only available for research purposes. This paper presents the details of an investigation carried out using the conventional direct shear test apparatus to measure the value of ␦ for soil-pile interface. The direct shear interface tests were conducted using four types of surfaces and two types of sands. The values of ␦ obtained from these tests are compared with the internal friction angle (␾) of the sand and with the results obtained from soil-pile-slip tests. The interface test results are also used to estimate the shaft capacity of a few model piles embedded in sand. The shaft capacity, Qs in kN of a pile in sand is estimated as KEYWORDS: direct shear test, interface friction, internal friction, pile foundation, sand, shaft capacity Qs ⫽ ␴rf Tan␦ As (1) where ␴rf ⫽ average radial stress on pile surface at failure, (kPa) ␦ ⫽ soil-pile interface friction angle, (degrees) As ⫽ surface area of pile, (m2) Nomenclature As B C CLA Cu D Dr D10 D50 D60 e emax emin etest ƒs k Qs Qt ␦ ␦p ⫽ residual interface friction angle ⫽ relative displacement between the soil and pile surface ⫽ angle of internal friction ⫽ peak angle of internal friction ⫽ residual angle of internal friction ⫽ unit weight (density) ⫽ maximum density ⫽ minimum density ⫽ density at test ⫽ normal stress ⫽ radial stress ⫽ confining stress ⫽ average radial stress at failure ⫽ average effective vertical pressure ⫽ shear stress at failure ⫽ surface area of pile ⫽ diameter of pile ⫽ undrained shear strength ⫽ centre line average ⫽ uniformity coefficient (D60 /D10) ⫽ embedded depth of pile ⫽ relative density (density index) ⫽ diameter of particles corresponding to 10% finer ⫽ diameter of particles corresponding to 50% finer ⫽ diameter of particles corresponding to 60% finer ⫽ void ratio ⫽ maximum void ratio ⫽ minimum void ratio ⫽ void ratio at test ⫽ average unit shear stress ⫽ coefficient of lateral earth pressure ⫽ shaft capacity of pile ⫽ ultimate tensile capacity ⫽ interface friction angle ⫽ peak interface friction angle There are two basic parameters in Eq 1, that need to be precisely estimated to calculate the shaft capacity of a pile. The first one is the radial stress on the pile surface at failure (␴rf) and the second is the soil-pile interface friction angle (␦). It has been a practice [1, 2] to estimate ␴rf from ␴rf ⫽ k ␴v (2) where k ⫽ coefficient of lateral earth pressure, and ␴v ⫽ average effective vertical pressure (kPa). Based on experience it is realized that ␴rf is not only a function of ␴v, but also depends on the volume of soil displaced due to the pile installation and method of installation (i.e. bored or driven or jacked) (Vesic et al. 1980; Kraft 1991; McClelland 1974; Meyerhof 1976; Polous 1989). Some researchers have suggested a limiting shear stress on the pile surface (Meyerhof 1976; Bustamonte et al. 1987; Tomlinson 1977). With the development of instrumentation of model and prototype piles, attempts are now being made to measure the radial stress along the length of the pile shaft (Bond et al. 1991; Jardine et al. 1992; Lehane et al. 1993; Reddy 1996; Reddy et al. 1997; Reddy et al. 1998). The second aspect of the problem is to estimate the soil-pile interface friction angle (␦). Some research has been reported on the 1 Department of Civil Engineering, JNTU College of Engineering, Kukatpally, Hyderbad, A. P. India. 2 School of Civil Engineering, University of Birmingham, Birmingham B15 2TT, U. K. 3 Division of Engineering, Saint Mary’s University, Halifax, Nova Scotia, CANADA, B3H 3C3. © 2000 by the American Society for Testing and Materials 199 so that they fit into the mold of conventional direct shear test apparatus (Reddy 1996).2 45. Kraft and Lyons 1974). these apparatus are available at research level and are inaccessible for a conventional geotechnical engineering laboratory. For each interface.656 2. Properties of Materials Two types of silica sand and two materials. However.35 0. Miniature pile test apparatus (Coyle and Reese 1966. The equipment also provides a hard copy of roughness details in the form of a graph. This paper presents a simple means of measuring the interface friction angle (␦) between a soil and a pile surface using conventional direct shear test apparatus with a few modifications. Direct Shear Test Results Triaxial Test Results Normal Stress (kPa) ␾p ␾r ␾p ␾r 50 100 150 41. A 10% increase of ␾p in the plain strain TABLE 1a—Soil properties (classification tests).9 40. Then. namely steel and aluminium alloy. and 150 kPa).8 43.74 2. were used for making interfaces. From Table 1c. the top surfaces of two plates.40 1.9 40.530 1. The relative displacement.8 40. However.221 0.20 17.30–0. Grain Size Distribution Soil Type – D10 (mm) – D50 (mm) – D60 (mm) Cü Specific Gravity Sand–1 Sand–2 0.75 17.4 44. Each pile surface was prepared with two roughness values. tests were conducted under three normal stress values (50. smooth and rough. The interface test results are also used to estimate the shaft capacity of a few model piles.3 46. of pile material (Potyondy 1960). ␥test (Table 1b).659 0.452 0.3 44. This is because the triaxial test represents a 3-D case. density.4 Sand–1 Sand–2 Sand–1 Sand–2 ␾p ␾r 38. Reddy et al. 1(a). The upper half of the shear box was filled with sand at the test density.417 0.5 46. During the tests. The average variation in undulations is reported as the CLA. 1998) are available to measure the soil-pile interface friction angle (␦).59 16.01 14. Sand–1 was a locally available sand and Sand–2 was a dust-free Leighton Buzzard sand.769 0.507 0. respectively. The test results are analyzed to compare with the internal friction angle (␾) of the soil. the roughness that developed on the aluminium alloy was observed to be more than that on the steel surface.0 TABLE 2a—Properties of pile material (strength and hardness).6 41. Surfcom equipment measures the surface roughness in terms of surface undulations measured in micron units (Reddy 1996).0 46.3 46.98 17. Kraft and Lyons 1974. All the plates were initially fabricated with smooth surfaces at the top. It has been a practice to approximate ␦ as a fraction of internal friction angle (␾) of the soil (Meyerhoff 1976.0 39.527 48% 93% . Density ␥ in (kN/m3) Void Ratios (e) Soil Type ␥max ␥min ␥test emin emax etest Relative Density (Dr) Sand–1 Sand–2 18.34 245 42 case of direct shear test over the ␾p of the axis-symmetrical case of the triaxial test is considered reasonable (Cornforth 1967). Coyle and Sulaiman 1967) and soilpile-slip test apparatus (Reddy 1996. b and c.574 0. However.924 0.544 0. it can be observed that the peak internal friction angle ␾p of soil obtained from direct shear test is about 10% more than that obtained from a triaxial test. More details on the measurement of properties were presented elsewhere (Reddy 1996). The strength and hardness values of the pile materials are presented in Table 2a. the shear load and the relative displacement between the sand and the metal surface were measured. were made rough with equal effort.200 GEOTECHNICAL TESTING JOURNAL study of ␦ (Meyerhoff 1976. 100. Direct Shear Interface Test The conventional direct shear test apparatus was used for the interface test. due to its lower hardness value (see Table 2b). ⌬r versus the shear stress curves obtained from the tests on smooth steel surface and Sand–2 under the three normal stresses are shown in Fig. it is known that ␦ is not only a function of soil properties but also a function of surface roughness and hardness. From the curves TABLE 1b—Soil properties (density tests). whereas the direct shear test is a plain strain (2-D) problem. The classification.3 40. The test plate was positioned into the lower half of the direct shear box.32–0. The whole assembly was placed and loaded in a conventional direct shear apparatus. Potyondy 1960). The design of plates was made. and strength properties of sands used in the investigation are presented in Tables 1a.0 40.1 Average 40. four pieces of square plates (two of aluminium alloy and two of mild steel) were fabricated.36 0. one of each material. These interface test results are also compared with the soil-pile-slip test results obtained from more sophisticated testing performed with the same materials. In order to perform these tests.00 2.650 TABLE 1c—Soil properties (shear strength parameters) (all angles are in degrees). The roughness of pile surface (measured as Center Line Average CLA values) obtained using Surfcom 20C/30C equipment are presented in Table 2b. Pile Material Young’s Modulus (GPa) Tensile Strength (N/mm2) Poison’s Ratio Vickers Hardness Number Mild Steel Aluminium alloy 210 70 250 310 0. 1(a) the peak and the residual interface shear stress values were obtained. 1998). with a pile element embedded in the soil (Reddy et al.80 1. the peak interface friction angle (␦p) between Sand–2 and the metal surfaces is varying between 18. The relationship between the normal stress and the shear stress (peak and residual) from the curves in Fig.44 0. These values are about 43% to 56% of the peak friction angle (␾p ⫽ 40. Qt in kN is given by Qt ⫽ Qs ⫹ Wp (3) where Qs ⫽ shaft capacity. It can be ob- . 1b—Observed peak and residual interface friction angle between smooth steel surface and Sand-2. The ultimate load required to pull-out the pile element gives the ultimate tensile capacity (Qt) of the pile element. with an average CLA ⫽ 0. ␮m) Smooth Surface Rough Surface Trials Trials Pile Material 1 2 3 Average 1 2 3 Average Mild steel Aluminium alloy 0. 1998).17 2.1-mm diameter and 150-mm long.38 0. These values are about 41% to 64% of ␾p (46.14 1. Analysis and Discussion of Test Results Comparison Between ␦ and ␾ FIG. kN Wp ⫽ self weight of pile.9°) of Sand–1 (Table 1c).09 0. which is utilized in computing the shear stress on the surface of pile element at failure (Reddy et al.0 ␮m) embedded in Sand–2 are presented in Table 4 (Reddy et al. and 38. and needs to be analyzed for each case. 1(a) are shown in Fig. and that it is dependent on the soil-pile interface properties and relative density of sand.01 shown in Fig.53 0.63 0. 25. kN FIG. The above observations indicate that the interface friction angle ␦p value changes with roughness of metal surface.3°) of Sand–2 (Table 1c).69 0.4° and 23°. From Table 3a it can be observed that the peak interface friction angle (␦p) between Sand–1 and different metal surfaces is varying between 17.87 2. This indicates that ␦ value cannot be generalized as a constant percentage of ␾.5 to 1. In all.8° (Table 3).REDDY ET AL. aluminium alloy pile elements (12.7. The peak and the residual interface friction angles ␦p and ␦r respectively are obtained.66 0.8 and 29. 1(b). The complete set of interface test results are presented in Tables 3a and b. Comparison with Soil-Pile-Slip Test Results Soil-pile-slip test apparatus is similar to a triaxial test apparatus. Roughness of the Pile Surface (CLA.4. For the same variation of roughness of metal surfaces the ␦p variation is 13% (56 ⫺ 43%) for Sand–1 at a relative density of 48% and is 23% (64 ⫺ 41%) for Sand–2 at a relative density of 93%.28 2. 24 tests were performed with eight combinations of interfaces. 1998).37 1. Similarly. The soil with a pile element is subjected to the required confining pressure. and the pile element is then gradually pulled out of the soil sample.60 0. The test results obtained from the three smooth surfaces. ON SHAFT CAPACITY 201 TABLE 2b—Properties of pile material (roughness).47 1. 1a—Relative displacement-Shear stress variation between smooth steel surface and Sand-2. 1 Confining Pressure.9 16.9 23.3 82. Here. 2 is based on limited data. 2 shows the apparent variation of interface friction angle (␦p) obtained from the soil-pile-slip test with the diameter of the pile el- Average ␦p degrees 26.3 17. This indicates that the interface slip dilation is predominant in small diameter piles and will reduce with an increase in the pile diameter.2 17.4 22.6 Average 17. This value is more than the corresponding interface friction angle ␦p ⫽ 23. it is seen that the ␦p obtained from the soil-pile-slip test approaches the direct shear interface results for large pile diameters.405 0.8 22.5 27. varies very marginally with pile diameter.6 22.3 28. it may be noted that the extrapolation shown in Fig.5 served from Table 4 that the interface friction angle ␦p is independent of confining pressure. 1993.7 m.3 22. Further.2 ement.756 0.8 21.5 18.6 21.4 26.4 21. Fig.3 24.4 38.9 26.1 22.8 23. TABLE 3b—Direct shear interface test results with sand–2*. because of the interface slip dilation.7 25.8 17.°.6°. obtained from the direct shear interface test (Table 3b).1 33.3 31.7 23. From Fig.4 33. the apparent variation in ␦p is due to interface slip dilation.998 0.7 20.204 0. ␶f kPa ␦p degrees 70 120 170 70 120 170 70 120 170 0.0 21. Steel Surface Aluminium Alloy Surface Smooth Rough Smooth Rough Normal Stress ␦p ␦r ␦p ␦r ␦p ␦r ␦p ␦r 50 100 150 18.2 23.7 18.0 27. 2 it can be observed that the ␦p is decreasing with increasing pile diameter and the relationship can be extrapolated to 23.8 20. for Sand–2 for smooth surface of aluminium alloy.3 25.2 83.1 63.1 25.4 28.8 63.7 * All angles are in degrees. Hence. obtained from direct shear interface tests for a pile diameter of about 1. Steel Surface Aluminium Alloy Surface Smooth Rough Smooth Rough Normal Stress ␦p ␦r ␦p ␦r ␦p ␦r ␦p ␦r 50 100 150 17.503 0.8 18.3 23.3 21.9 26.202 GEOTECHNICAL TESTING JOURNAL TABLE 3a—Direct shear interface test results with sand–1*.4 16. and has an average value of 26.4 61. Qt (kN) Shear Stress at Failure.4 * All angles are in degrees.6 23. the direct shear interface test results can be used to obtain reliable values of ␦ to estimate the shaft capacity for field piles.6 26.4 18. The objective of the plot is to obtain the possible diameter of pile element .6 22.1 17.9 18. TABLE 4—Soil-pile-slip test results (sand–2 and smooth aluminium alloy).9 32.7 Overall Average (␦p) 26.1 27.6 20.2 21. The interface slip dilation is the mechanism associated with the particle movement and change in the volume of soil adjacent to a pile surface during pile loading.8 23. Since there is no installation stresses in soil-pile-slip test (Reddy et al.9 18.6 18.8 14.1 25.0 22.4 18. 1998).1 20. More details on this aspect are available in the literature (Lehane et al. Werching 1987).8 15.8 26.4 22.5 19.3 22.3 18.0 27.7 18.0 Average 18.8 18.480 34.8 28. ␴rc (kPa) Ultimate Tensile Capacity. This apparent increase in the friction angle is expected for small diameter pile elements.100 1. This is due to an increase in ␴r at failure.600 1.0 29.8 21.2 20.5 84. Diameter of Pile Element (mm) 12.7 25. Reddy 1996.0 22.8 27.380 0.5 18.6°. degrees.REDDY ET AL.7. a unit weight of 17. and 38. kN/m3. All model piles were tested with an embedded depth of 40 mm. ON SHAFT CAPACITY that gives ␦p equal to that obtained from the direct shear interface test. FIG. in a long compressible field pile the relative displacement between the pile surface and the soil varies with depth. which was the density at which the direct shear interface tests were conducted.1 mm) made of steel and aluminium alloy with roughness values similar to those of test plates presented in Table 2b.5).4. One model pile was placed at the center of the tank and jacked slowly through the pile access unit. assuming a linear variation of radial stresses (Das 1990). As the load on the pile is increased. and adopting the corresponding ␦p value from the Tables 3a and 3b in the following equation fs ⫽ (␴rc ⫹ 0. D ⫽ embedded depth of pile. since the model pile is short (D/B ⫽ 10. 3. ␥ ⫽ unit weight of sand. The 203 sand (Sand–2) was placed in the test tank in four layers. However. The effective stress in the sand was increased by applying vacuum in the tank. In the above analysis. . Each layer was compacted with a plate vibrator for about four min.5␥Dk) Tan␦p (4) where ␴rc ⫽ confining pressure in sand due to vacuum. The tests were conducted in a test tank of cross section 975 mm ⫻ 695 mm having a depth of 680 mm. The tests were conducted on different diameter piles (12. a few monotonic tensile tests were conducted. obtained from direct shear interface test. m ␦p ⫽ peak interface friction angle. After filling with sand. Estimation of Shaft Capacity of Model Piles As a part of an investigation into the behavior of model piles under cyclic tensile load (Reddy 1996). k ⫽ coefficient of lateral earth pressure (k ⫽ 1. in a period of 15 min (Reddy 1996). 1997. 3—Model pile test apparatus. After ensuring that constant vacuum pressure was achieved. Using this method. The ƒs value is calculated. the shaft capacity is estimated based on the peak interface friction angle ␦p (Eq 4). Reddy et al. as shown in Fig. kPa. the pile was subjected to monotonic pullout force using a compressed air driven piston system. 2—The apparent variation of ␦p with the diameter of pile element due to interface slip dilation. the test tank was made airtight by covering it with a polythene sheet as shown in Fig. 25. Reddy et al.36 kN/m3 at a relative density of 93% was achieved. The tensile (shaft) capacity of different model piles (Qt) and the average shear stresses (ƒs) on the pile surface at failure are presented in Table 5. The model pile test apparatus was specially designed to increase confining pressure in the test tank by the application of the vacuum pressure. 3.28 for ␾ ⫽ 40° [6]) FIG. Maximum displacement occurs near the head and it reduces gradually to a minimum towards the pile tip. the surface friction reaches a maximum value initially near the pile head and the load gets transferred to the lower portions of the pile (Reddy et al. 1998. 08 ⫹10.1 (Steel-Smooth) 25. the effect of jacking will be maximum for the largest diameter pile.1 (aluminium alloy-rough) a b ␴rc (kPa) Shaft Capacity (kN) Observed Estimateda % Error b Sand–1 20 0.9 Sand–2 70 0.736 23. Conclusions Direct shear interface tests were conducted using two sands and four metal surfaces.0 Sand–1 55 0. M.830 17. S. Bowles.720 56. • The direct shear interface test results are comparable with those obtained from the soil-pile-slip tests. estimated from the direct shear peak interface friction angle ␦p.” John Wiley and Sons. Canada.” Journal of Geotechnical Engineering. 1998). Canada. • The interface friction angle ␦ can not be expressed as a constant percentage of the internal friction angle ␾ of the soil. A. H. Mike O’Reilly of Kingston University.. It is stated (Jardine et al. Vol. L.” McGrawHill Book Company. 117. • The shaft capacity of model piles.345 7. Pennsylvania. Siva Kumar. the observed shear stress is more than the estimated value so that the estimates are conservative and safe. 47–73. the ultimate shaft capacity of a compressible field pile can safely be estimated using the residual friction angle ␦r instead of ␦p.9 Sand–1 45 0. Further. due to large displacements. and Saint Mary’s University. 2. is conservative and safe.46 15.. Prof. DalTech.F. if the average radial stress on the pile surface is known.06 22. Therefore. The reasons for the above two observations can be explained as follows: It is reported (Jardine 1992. during the preparation of the manuscript is also appreciated. Jardine of Imperial College of Science and Technology. 1991. Surrey. Dalhousie University. “Pile Foundations Analysis and Design. in most cases. pp. Though the direct shear interface test results presented in this paper are encouraging. From the test results the following conclusions are drawn: • Soil-pile interface friction angle ␦ is a function of interface properties. Vesic. the shaft capacity can be computed using the direct shear interface peak friction angle (␦p). G. ASCE. Halifax. “Performance of Axially Loaded Pipe Piles in Sand. Hence. (formerly at University of Nottingham) Professor S. “Load Transfer in Pile-Soil System.2 Sand–2 70 2. G. J. 1980.1 mm. India. the increase in the radial stress in the case of larger diameter displacement piles in the field would be mainly due to the soil densification during the pile installation. Test results from a wide range of pile diameters will provide a better understanding interface friction angle. London.740 46. Rama Samy of University of Roorkee.K. and Davis. These two factors cause an increase in ␴r value and hence the increase in the observed ƒs values. Cornforth 1967) that the effect of interface slip dilation will be small for large diameter piles. Average Unit Shaft Friction. 1970. Brown of University of Nottingham. due to the phenomena of interface slip dilation.35 ⫺1. From Table 5 it can be observed that. H. (kPa) Pile Diameter (mm) (Pile Material) Sand Type Confining Pressure 38. Useful suggestions from Dr. The support given by Mr. • The extrapolation presented for the effect of pile diameter is based on a limited test data. Considering the effect of interface slip dilation to be almost equal for all model piles. Kraft.204 GEOTECHNICAL TESTING JOURNAL TABLE 5—Observed shaft capacity of model piles.2 ⫹3. R. Leigh University. the difference between the observed and the estimated values are maximum for the largest diameter pile (38. U. .08 ⫹35. but it can be assumed from each individual case. and Prof. 1982.18 ⫹15. The Commonwealth Universities of London and Natural Sciences and Engineering Research Council of Canada provided the financial support. Halifax. Further.81 42... U. E.37 42.1 (Steel-Smooth) 38.7 (Aluminium alloy-rough) 38. it would be useful to obtain the values of ␦ from larger areas of interface (150 or 200 mm square) to simulate closely the interface properties of prototype piles. Acknowledgments The research presented in this paper was carried out at University of Nottingham.K. The estimated average unit shear stresses together with the observed values are presented in Table 5. From the above analysis it can be stated that for large diameter piles in sand. New York. are greatly appreciated. E. Conference on Design and Installation of Pile Foundations and Cellular Structures. References Polous. by the time the soil next to the lower portion of the compressible pile reaches its peak shear stress. 272–296.1 mm) out of the three diameters used in the model tests.21 7. the soil around the upper portion of the pile experiences residual shear stress.0 from Eq 3 % Difference between the observed and the estimated value based on the estimated value of fs. Werching 1987) that the radial stress (␴rƒ) along the pile surface can be higher than the initial radial stress (␴rc) used in the computations. pp. New York. J. Hence. the jacking of the pile increases both the densities of the sand and the radial stress on the pile surface. fs.” Proceedings.. Hence. the maximum difference between the observed and estimated shear stress values is noticed for the pile with the largest diameter of 38. M. “Foundation Analysis and Design.4 (Steel-Rough) 12. No. E. and Frank. R. Dordecht. “Design and Performance of the Imperial College Instrumented Pile. Reddy. “Pile Behaviour—Theory and Application. University of Nottingham. E.. 1997. M. “Design and Performance of Soil-Pile-Slip Test Apparatus for Tension Piles. M.. D. G. N.. ASCE. 4. Kluwer. OTC 2 081. 4. 1998. 1998.. and Lahane. 1987. pp. ON SHAFT CAPACITY McClelland. “Pile Design and Construction Practice. Vol. J. “Mechanism of Shaft Friction in Sand from Instrumented Pile Tests. S. Das. Potyondy.. 1992.REDDY ET AL. 68. and Lyons.” PhD thesis. 1990. 1977. No. J.. Houston. pp.” Computers and Structures. Vol. “Bearing Capacity and Settlement of Pile Foundations. UK.” Geotechnique. 13–22. L. 1993. P. Cornforth. “An Investigation into the Response of Piles in Sand under Vertical Cyclic Tensile Loads. “Modified T-Z Model—A Software for Tension Piles. J. J. Vol. 1991. and Gianeselli. 143–167. 2. pp. Mike O’Reilly and Chapman. O’Reilly.. Meyerhof. N. E. M. et. G. Werching. B. 1966.. N. H. pp. Chapman. “Design of Deep Penetration Piles for Ocean Structures. ASTM. 3.. “The Development of Shaft Friction and End Bearing for Piles in Homogeneous and Layered Soils. 1967. and Reese.” Journal Soil Mechanics and Foundation Engineering. I. Vol. M. 261–278..D. “Skin Friction Between Cohesive Granular Soils and Construction Materials. Ch. International Conference... pp. 149. Tomlinson.. Polous. “Le Dimensionnement des Foundations Profondes. Jardine. M. Paper No. D. D. Reddy. Bustamante. Vol. Polytechnic of South Wales. Nova Scotia Technical College. pp. B. “Friction Coefficients for Piles in Cohesionless Material. Jardine. 1998.. and Dalton. Liaison Laboratory P.. J. E... J. Coyle. 1989. “Skin Friction for Steel Piles in Sand. Jardine. 1974. 102.. Vol. Vol. 93.” Masters of Engineering Thesis. Amsterdam.. M.. ASCE. the Netherlands. Reddy..” Journal of Geotechnical Engineering. No. 487–503. GT1. 653–658.” Computers and Structures.” Geotechnical Testing Journal. 1996. pp. H.” Geotechnique 39. 69. 365–415. 100. No.. 14. R..” Journal of Geotechnical Engineering. No. 92. No. 1960. SUT. Halifax. pp. 413–424.. Vol. pp.. “Load Transfer for Axially Loaded Piles in Clay. and O’Reilly. pp. S.” London: Cement and Concrete Association. 6th Offshore Technology Conference. pp. 197–228. 1974. SM2. H. C.” Geotechnical Testing Journal. Canada. M. SM6. S. J. Nova Scotia. June. Vol. Proceedings. GT3.” Ph.. G. H. and Chapman.. 1976. ASCE. M. Kraft. No.” Proceedings.. 4. J. L. R. and Chapman. M. Elsevier Science Publishers. Coyle.” Offshore Site Investigations and Foundation Behaviour. Earth Anchors.. Vol.. H.. . Lehane. G. S. No. and Sulaiman. L.. pp.. GT7. A. R. thesis. 1–26.. 709–747. 1967. 19–35. R. M. 119. Reddy. C. No. O’Reilly. S. Frank. B. Vol.. S.. 205 Reddy. P. J.” Computers and structures. S.. N. 613–625. Bond. UK. M. ASCE. Bond. 1987. P.... No. B. 62. pp. Everton. E. 21. A. 661–680. “State-of-the art: Ultimate Axial Capacity of Grouted Piles. No. C. May-June pp.” Bull. pp. P. “Some Experiments on the Influence of Strain Conditions on the Strength of Sand. Vol.” Journal of Geotechnical Engineering. 2.” Journal Soil Mechanics and Foundation Engineering. 132–139. “A Software to Predict the Behaviour of Tension Piles. “A Computer Package for the Design of Piles Under Cyclic Tensile Load. D. ASCE. 149–158.