1. Case History Evaluation of the Axial Behaviour of Bored Pile from SPT Aung Naing Moe August 2014

2. Outline - Introduction - Axial Capacity of Bored Pile - Case Studies - Conclusions & Discussions

3. Introduction Since 1967, there have been a significant increase in the use of bored piles as foundation in Singapore. Reported by Chang and Broms (1990), approximately 200,000-400,000 m of bored piles is installed each year. The diameter of Bored piles varies from 500 mm to 1800 mm. Until late 1970s, the design procedure for bored piles was essentially empirical and the capacity was very often underestimated.

4. Introduction As a result, the designs were often conservative. One of the most valid reasons for conservative design procedure is the lack of understanding of the behaviour of bored piles in local residual soils and weathered rocks. For the design verification purpose, proof load tests were conducted. Although test piles were occasionally loaded to failure, they were often not instrumented. As a result, only load-displacement behaviour of pile could be determined and test data did not provide the information on the load distribution and the load-transfer characteristics of pile.

5. Introduction To develop the design of bored piles in residual soils and weathered rocks of Singapore, number of studies on instrumented bored piles have been carried out since early 1980s. These studies show that the load transfer is primarily through the shaft resistance and the mobilized point resistance is very small at the working load. The results of these studies were reported by Yong et al (1982), Chin (1982), Chin et al (1982), Buttling (1986) and Buttling & Robinson (1987).

6. Introduction In late 1980s and early 1990s, similar studies were carried out and the results were reported by Chang & Goh (1988) and Chang & Broms (1991). The design recommendations were given on the unit shaft friction, critical displacement and load transfer curve. The more comprehensive study was carried out by Chang & Zhu (2002) and the report was focused on a better understanding of the interaction mechanism between pile shaft and the surrounding soil and the construction effects on the pile performance.

7. Axial Capacity of Bored Pile The function of piles is to transfer the load to the stronger layers of the ground which are capable of supporting the load with an adequate factor of safety and without settling at the working load by an amount detrimental to the structure that they support. At all times, it is important that the stress induced in both pile material and supporting soil is kept within an allowable limit.

8. Axial Capacity of Bored Pile (structural) Structural Capacity For nominally reinforced bored pile, as recommended in BS 8004 and SS CP4 (2003), the allowable structural capacity can be computed as: Q st = 0.25 f cu A c where A c = area of concrete and 0.25 f cu should not exceed 7.5 N/mm 2.

9. Axial Capacity of Bored Pile (structural) For rock socketed reinforced bored piles with full length steel reinforcement, the allowable structural capacity may be determined as axially loaded short columns in accordance with SS CP65 and can be taken as: Q st = where f cu = compressive strength of concrete at 28 days A c = area of concrete f y = yield stress of steel A s = steel area F s = factor of safety (≥ 2)

10. Axial Capacity of Bored Pile Geotechnical Capacity A pile subjected to the axial load will carry the load partly by shear generated along the pile shaft, and partly by normal stress generated at pile base. The ultimate capacity is equal to the sum of ultimate shaft and base resistance.

11. Axial Capacity of Bored Pile (geotechnical) Force Diagram In practice, W p is much Smaller compared to Q u, QuQu WPWP Q u + W p = Q s + Q b QsQs QbQb Q u = ultimate capacity Q s = ultimate shaft resistance Q b = ultimate base resistance W p = self weight of pile Q u = Q s + Q b - W p Q u = Q s + Q b

12. Axial Capacity of Bored Pile (geotechnical) Ultimate Shaft Resistance The ultimate shaft resistance, Q s is generally taken as: Q s = where f s = ultimate unit shaft resistance dA s = local incremental shaft area of pile For layered soil, the above equation can be rewritten as: Q s = where f si = ultimate unit shaft resistance in layer i A si = shaft area of pile in layer i

13. Axial Capacity of Bored Pile (geotechnical) Ultimate Base Resistance The ultimate base resistance, Q b is generally estimated from the relationship: Q b = where f b = ultimate base resistance A p = pile base area

14. Axial Capacity of Bored Pile (geotechnical) Allowable Capacity The allowable capacity is equal to the sum of ultimate shaft and base resistance divided by a suitable factor of safety: Q a = A single global factor of safety (F) of 2.0 to 3.0 is commonly used to evaluate the allowable capacity of single piles. The lower value is often used when the ultimate capacity is determined from load tests and the higher value when the capacity is estimated from a static formula.

15. Axial Capacity of Bored Pile (geotechnical) Another important factor, the settlement of the pile under the working load should not exceed the specified limit. In Singapore, the maximum settlement of bored pile should not exceed 25 mm at 2 times working load (Public Works Department, Housing and Development Board & SS CP4 2003). In the 1 st Phase MRT construction, the Mass Rapid Transit Corporation of Singapore specifies that the maximum settlement should not exceed 6-9 mm at working load and 9-20 mm at 1.5 times working load (Buttling and Robison, 1987).

16. Axial Capacity of Bored Pile (geotechnical) The axial displacement that is required to fully mobilize the shaft resistance for bored piles is usually small, typically 5-6 mm (Whitaker and Cooke 1966, Aurora and Reese 1977, Horvath and Kenney 1979) or 5-10 mm (O’Neill and Reese 1972). Based on the findings by local investigators, 4-9 mm of pile shaft movement is required to fully mobilize the shaft resistance. q s max unit shaft resistance displacement 5 - 6mm t-z curve

17. Axial Capacity of Bored Pile (geotechnical) In contrast a relatively large displacement, approximately 5 % (Aurora and Reese 1977) or 10 % (Woodward et al. 1972) of the pile diameter, is required to fully mobilize base resistance. Thus at the working load, the shaft resistance plays an important role. q b max unit base resistance displacement 5% - 10% of pile diameter q-z curve

18. Axial Capacity of Bored Pile (geotechnical) This difference in the required displacement for fully mobilization of resistance and its effect on pile behaviour are not taken into account in the traditional design approach in Singapore. Since the different displacements are required for fully mobilization of the two resistance components, the use of different partial factor of safety for the shaft resistance and base resistance is recommended in the improved traditional design method. The allowable pile capacity can be expressed as: Q a = where F s is typically 1.5 to 2 and F b is typically 3 to 4.

19. Axial Capacity of Bored Pile (geotechnical) Estimation of Unit Shaft Resistance The load transfer mechanism in the design of bored pile shaft resistance is similar to that used to analyze the resistance to a sliding of a rigid body in contact with soil. Two methods of analysis, one for cohesive soil and the other for non-cohesive soil, can be used to estimate the ultimate shaft resistance of bored pile.

20. Axial Capacity of Bored Pile (geotechnical)  -Method This method is commonly used to estimate the ultimate unit shaft resistance of piles in clay soil subjected to an undrained loading condition (total stress analysis). The skin resistance is evaluated from the undrained shear strength (C u ) as determined by field or laboratory tests. Tomlinson (1957) recommended the  -method to determine the unit shaft resistance as follows: f s =  C u C u = undrained shear strength and  = adhesion factor

21. Axial Capacity of Bored Pile (geotechnical) Evaluation of  Number of studies have been carried out to determine the adhesion factor (  ) for stiff and hard clays and weathered rocks. Generally, the  value decreases with increasing undrained shear strength. The value of a for a given pile at a given site should be determined from a pile load test.

22. Axial Capacity of Bored Pile (geotechnical) However, it is impossible and therefore many attempts have been made to establish the correlation between C u and . Typically, the value of a ranges from 0.25 for very stiff to hard clay to 1.0 soft clay. Some a values suggested by researchers based on the intensive studies in different soils are summarized in following Table.

23. Axial Capacity of Bored Pile (geotechnical) Soil TypeReference Adhesion Factor,  London Clay Golder and Leonard (1954)0.25 - 0.70 Tomlinson (1957) and Skempton (1959)0.30 - 0.60 Tomlinson (1957) and Skempton (1959)0.45 (average) Stiff Clay Woodward et al (1961)0.50 Mohan and Jain (1961)0.66 Whitaker and Cooke (1966)0.44 Reese and O'Neill (1988)0.55 Stiff silty ClayChin (1982)0.80 - 0.85 Beaumont ClayPearce and Brassow (1979)0.60 Kenny Hill Formation, Malaysia Toh, C.T et al (1989)0.50 - 0.54 Silt Stone (highly weathered) Davies et al (1979)0.65 - 0.71

24. Axial Capacity of Bored Pile (geotechnical) Weltman and Healy (1978) studied the ultimate shaft resistance of bored piles in boulder clay and other glacial tills and introduced the  verses C u curve.

25. Axial Capacity of Bored Pile (geotechnical) Kulhawy and Jackson (1984) reported the correlation between a and C u based on the data of over 100 pile load test.  = 0.21 + 0.26 where P a is the atmospheric pressure, 101 kPa. The  value and C u /P a should not exceed 1 and 3, respectively. Based on the comprehensive study, Kulhawy and Phoon (1993) found that both the unit shaft resistance and the adhesion factor vary linearly. (or)  = 0.5

26. Axial Capacity of Bored Pile (geotechnical) Fleming et al (1985) proposed the following relationships. For C u /  ' v <1,  = For C u /  ' v >1,  = where  ' v is the effective vertical stress.

27. Axial Capacity of Bored Pile (geotechnical) Semple and Rigden (1984) proposed the value of a as a function of C u /  ' v and L/d. The a value can be taken as:  = F  p where F is the length factor and  p is peak friction coefficient. The values of F and a p can be obtained from followings:

28. Axial Capacity of Bored Pile (geotechnical) The back calculated a value from results of load tests is subject to soil disturbance, constriction effects and rate of loading. Moreover, the undrained shear strength is not a fundamental soil parameter. It depends on various factors, such as the stress history, the effective overburden stress, the effective friction angle, the water content and the testing method. Therefore the care should be taken when using a method for the estimation of shaft resistance.

29. Axial Capacity of Bored Pile (geotechnical)  -Method The effective stress analysis is commonly used to estimate the ultimate unit shaft resistance of pile in coehionless soil or cohesive soil which is subjected to a drained loading condition (effective stress analysis). In this method, the skin friction resistance is related to the effective overburden pressure  ' v : f s = c' +  ' h tan  ' since  ' h = K s  ' v, tan  ' = tan  ' and the above equation becomes: f s = c' + K s  ' v tan  '

30. Axial Capacity of Bored Pile (geotechnical) In practice, due to the soil disturbance associated with pile installation, the drained shear strength is commonly neglected. f s = K s  ' v tan  ’(or) f s =   ' v Where: c'= drained shear strength  ' h = effective horizontal stress acting on pile shaft  '= effective friction angle between the pile and soil  ' v = effective vertical stress K s = coefficient of horizontal stress  '= effective friction angle  = K s tan  '

31. Axial Capacity of Bored Pile (geotechnical) There is a relationship between the coefficient K s and the coefficient of earth pressure at rest K 0. Kulhawy (1984) recommended K s = 0.7 - 1.0 K 0 and also suggested that  ' = 1.0  ' for cast-in-place piles in sand. For cohesive soil, the value of b ranges typically from 0.25 to about 0.40 depending on the over consolidation ratio (OCR).  = 0.25 (OCR) 0.5 An equivalent can be estimated for residual soils and weathered rocks from the following relationship. OCR = C u /C nu where C nu is the undrained shear strength of the normally consolidated clay which can be estimated from the c/p ratio. If no test data is available, the widely accepted c/p ratio of 0.22 can be used.

32. Axial Capacity of Bored Pile (geotechnical) Number of studies have been carried out to determine the  value. Wong (2005) recommended the following relationship to estimate the .  = (C u /  ' v ) ( C u /  ' v ) Fleming et al (1985) proposed to use the following relationship to estimate the value of b. For C u /  ' v <1:  = (C u /  ' v ) ( C u /  ' v ) and for C u /  ' v > 1.0,  = (C u /  ' v ) ( C u /  ' v )

33. Axial Capacity of Bored Pile (geotechnical) Estimation of Unit Base Resistance The base resistance normally depends upon the shear strength properties of soil within the vicinity of the pile base. Large amount of displacement is required to fully mobilize the base resistance. The mobilized base resistance at the working load is usually small (Chang and Wong 1987).

34. Axial Capacity of Bored Pile (geotechnical) Cohesive Soil The drained end bearing capacity of bored pile in clayey soil is larger than the undrained. However, the displacement required to mobilize the drained capacity would be too large to be tolerate by most of structures. For this reason, the ultimate base resistance of piles in clay is calculated as a function of undrained shear strength (C u ) and bearing capacity factor (N c ). The unit base resistance can be estimated from the following relationship.

35. Axial Capacity of Bored Pile (geotechnical) f b = N c C u The value of N c is usually taken as 9 (Skempton, 1951) if the pile tip penetrates into the bearing stratum by 3 times pile diameter or more. However when the ratio of the embedment depth in the bearing stratum, to the diameter of pile base is less than 3, a linear interpolation is necessary for the adoption of the value of N c (6, Fleming, 1985).

36. Axial Capacity of Bored Pile (geotechnical) Non-Cohesive Soil The bearing pressure beneath a pile in a uniform deposit of non- cohesive soil is directly proportional to the vertical effective stress. From the general bearing capacity equation, the unit base resistance can be express in the terms of the effective vertical stress (  ' v ) and bearing capacity factor (N q ). f b = N q  ' v

37. Axial Capacity of Bored Pile (geotechnical) Berezantzev et al (1961) recommended the value of N q as a function of friction angle  '. The relationship between frictional angle  ' and bearing capacity factor N q is shown in Figure below:

38. Axial Capacity of Bored Pile (geotechnical) Estimation of Pile Capacity from Standard Penetration Test (SPT) The soil parameters derived from laboratory tests are used in traditional method of design for piles. However for stiff cohesive soil, the determination of the undrained shear strength and deformation parameters from laboratory tests is not reliable due to difficulty in “undisturbed” sampling and sample disturbance. Also, obtaining of undisturbed sample in cohesionless soil is very difficult.

39. Axial Capacity of Bored Pile (geotechnical) As a result, in-situ tests are commonly used to calculate the geotechnical capacity of bored piles. The standard penetration test (SPT), developed around 1927, is currently the most widely used in-situ test in many countries around the world. The test method has been standardized as ASTM 1586 since 1958 with periodical revision to date. The reason for preference for SPT test is probably because it is easy to use, inexpensive and the long experience accumulated with interpretation.

40. Axial Capacity of Bored Pile (geotechnical) Estimation of Unit Shaft Resistance As presented earlier, the unit shaft resistance of bored piles is normally estimated by the  method. However it should be highlighted that it is difficult to determine the undrained shear strength from unconfined compression tests or triaxial undrained tests (UU tests) due to sample disturbance. Therefore it is preferable to correlate the C u from penetration tests. For residual soils of Singapore, as recommended by Stroud (1974), the relationship between the standard penetration resistance or N value and the undrained shear strength is: C u = 5 - 6N (kPa)

41. Axial Capacity of Bored Pile (geotechnical) using a value of 0.45, as recommended by Skempton (1959), the relationship between ultimate unit shaft resistance and standard penetration resistance (N) can be taken as: f s = 2.45N (kPa) Meyerhof (1976) suggested that the ultimate unit shaft resistance of bored piles can be estimate directly from the standard penetration resistance (N). f s = N (kPa) A well known relationship f s = 2N (kPa), proposed by Meyerhof (1976) for driven piles in sand, is often used for the design of bored piles in residual soils in Singapore (Broms et al. 1988).

42. Axial Capacity of Bored Pile (geotechnical) Based on the extensive studies of instrumented pile tests in residual soil of Singapore, Chang & Goh (1988) and Chang & Broms (1991) recommended the following relationship to evaluate the ultimate unit shaft resistance of bored piles. f s = 2N (kPa) The Singapore code for foundation, SS CP4 (2003) recommended the following empirical relationship to estimate the ultimate shaft resistance. f s = K s N (kPa) where K s is the skin friction coefficient and value depends very much on the local experience. For soil of Bukit Timah Granite, a value of K s between 1.5 to 2.5 may be adopted. For dense or hard cemented soil in the Old Alluvial, a value of K s between 2 and 3 can be adopted.

43. Axial Capacity of Bored Pile (geotechnical) Estimation of Unit Base Resistance As discussed, the unit base resistance of bored piles is normally estimated from bearing capacity equation, f b = N c C u. Using c u = 5 - 6N based on Stroud (1974) and N c = 9 as recommended by Skempton (1951), the ultimate unit base resistance can be taken as: f b = 45N (kPa)

44. Axial Capacity of Bored Pile (geotechnical) Meyerhof (1976) suggested that the ultimate unit base resistance of bored piles can be estimate directly from the standard penetration resistance (N). f b = 120N corr (kPa) where N corr can be taken as: N corr = C N N 60 where C N is SPT overburden correction factor and N60~N. C N = 10 (1/  ' v ) 0.5

45. Axial Capacity of Bored Pile (geotechnical) Based on the extensive studies of instrumented pile tests in residual soil of Singapore, Chang & Broms (1991) recommended the following relationship to evaluate the ultimate unit base resistance of bored piles. f b = 30 - 45N (kPa) The SS CP4 (2003) recommended that q u may be related to the SPT N-value as: f b = K b 40N (kPa) where K b is coefficient and value depends on the depth of embedment in bearing stratum, effect of loosing of soil at pile base, effect of softening of soil due to ingress of ground water and cleanness of pile base. A K b value of between 1 and 3 may be adopted with limiting value of f b = 10 MPa, unless otherwise verified by load test.

46. Case Studies The main objective is to study the results and performances of load tests conducted on the instrumented bored piles. The piles under this study were located at various sites around Singapore and were installed in different soil conditions and geological formations. The results of 5 instrumented load test data were used in this chapter. The details of the test piles and their locations are summarized in following Table.

47. Case Studies Case Pile Diameter (mm) Penetration (m) Working Load (ton) Test Load (ton) LocationFormation Casting Method 160016.8180558 Senja Road Bukit Timah Tremie 260019.2212742 Balestier Road Old Alluvial Dry 3140019.010003295 Bukit Ho Swee JurongDry 4100028.05801740 Boon Lay Way JurongTremie 590013.0180610 Jalan Kilang JurongDry

48. Case Studies Test Pile Detail Case 1 Test Pile Depth (m)Soil DescriptionSPT 0 - 2.6fill material6 2.6 - 4.0medium stiff silty Clay7 4.0 - 8.0loose clayey Silt with medium coarse sand9 8.0 - 15.0medium dense clayey Silt with coarse sand14-18 15.0 - 15.2Very dense Silt with decomposed Granite100 15.2 - 18.0Hard Granite43-55% RQD

49. Case Studies (test pile detail) Case 1 Test Pile

50. Case Studies (test pile detail) Case 2 Test Pile Depth (m)Soil DescriptionSPT 0 - 1.0fill material 1.0 - 2.7medium stiff silty Clay6 2.7 - 8.0stiff silty Clay13-14 8.0 - 11.5very dense clayey Sand60 11.5 - 14.0hard clayey sandy Silt77 14.0 - 18.4very dense to hard clayey silty Sand>100

51. Case Studies (test pile detail) Case 2 Test Pile

52. Case Studies (test pile detail) Case 3 Test Pile Depth (m)Soil DescriptionSPT 0 - 1.0Firm clayey Silt 1.0 - 2.7medium stiff silty Clay8 2.7 - 8.5stiff silty Clay30-33 8.5 - 12.0very dense sandy Silt56 12.0 - 18.0weathered Siltstone>100 18.0 - 28.0weathered Siltstone>100

53. Case Studies (test pile detail) Case 3 Test Pile

54. Case Studies (test pile detail) Case 4 Test Pile Depth (m)Soil DescriptionSPT 0 - 1.4fill material 1.4 - 6.3loose to medium dense sandy clayey Silt7-11 6.3 - 14.5medium dense to dense sandy Silt25-51 14.5 – 33.5hard sandy Silt>100

55. Case Studies (test pile detail) Case 4 Test Pile

56. Case Studies (test pile detail) Case 5 Test Pile Depth (m)Soil DescriptionSPT 0 - 0.8fill material 0.8 - 3.0Stiff clayey Silt11 3.0 - 5.8hard clayey Silt40-63 5.8 - 7.6hard clayey Silt>100 7.6 -11.2weathered Siltstone>100 11.2 - 17.0weathered Siltstone>100

57. Case Studies (test pile detail) Case 5 Test Pile

58. Case Studies Load Distribution & Pile Capacity The load distribution curves provide the information of axial load variation along pile shaft and at pile tip. The magnitude of load distribution at each soil layer is calculated from the measured strain changes, pile geometry and suitable elastic modulus of pile. The load distribution curves along a pile allow an evaluation of the load transferred to each geological stratum and the corresponding mobilized resistance value at each stage of loading.

59. Case Studies (load distribution & pile capacity) The pile capacity is mobilized by the movement of pile in relation to the surrounding soil. The ultimate capacity, which is the maximum load, is carried by the pile without excessive settlement or failure. For those cases in which the test loads are not high enough to fully mobilize the ultimate capacity, the Chin method of analysis is introduced to estimate the ultimate pile capacities.

60. Case Studies (load distribution & pile capacity) Load Distribution Curves To obtain a greater understanding of the pile-soil interaction behaviour, it is desirable to install further instrumentations in the test piles. The load distribution along the pile shaft and at the pile toe can be measured using vibrating wire strain gauges (VWSGs). The VWSGs measured the axial strain changes in pile shaft and at the pile toe.

61. Case Studies (load distribution & pile capacity)

63. The VWSGs are installed on sister bars (approximately 1.0 m long). Each strain gauge assembly (sister bar) is tied to the pile reinforcement cage at the specified intervals as indicated in test pile detail 1-5. Based on the current construction practice, the maximum interval between two layers of strain gauges is 3.0 m. The signal cable from the VWSG is routed to the readout unit which is stationed near the pile head. The function tests are conducted before the installation of reinforcement cage into the borehole and upon the completion of concreting. The strain changes under each stage of loadings are measured and stored in the readout unit.

64. Case Studies (load distribution & pile capacity) The axial deformation of pile may be measured using a simple rod extensometer. The extensometer consists of a stainless steel rod attached to a fixed anchor point in the pile and placed within a protective pipe. The entire assembly is cast in the bored pile. As the pile undergo compression, the steel rod remains free in the protective pipe which undergoes compression with the pile. A linear transducer is used to measure the axial movement of the steel rod.

65. Case Studies (load distribution & pile capacity) sister bar strain gauge extensometer protective pipe

66. Case Studies (load distribution & pile capacity)

67. Load Distribution Calculations from Instrumentation Data Based on the reading of VWSGs and the extensometers, both the load distribution along the pile shaft and the load-transfer curves can be derived. First a suitable elastic modulus of the pile, E p, is adopted. The suitable elastic modulus value is back-calculated from the axial strain measurement of strain gauges at the first layer. With a proper elastic modulus, the load distribution at each layer of stain gauges can be calculated.

68. Case Studies (load distribution & pile capacity) Adoption of Suitable Elastic Modulus of Pile In general, the elastic modulus is not constant and its value depends on the quality of concrete, amount of axial strain and methods of testing. The results of instrumented load test piles located in NIE site at NTU campus indicate that elastic modulus decreases as axial strain increases (Chang & Zhu, 2002). In this case study, where possible, this modulus degradation was considered in the adoption of suitable modulus value for load distribution calculations.

69. Case Studies (load distribution & pile capacity) The elastic modulus of pile (E p ) was back-calculated from the axial strain measurement of strain gauges at the first layer. Below is the sample of average strain change and back-calculated E p from first layer strain gauges data. Average Strain Change LayerDepthAverage Axial Strain Change Ref(m)(10 -6 ) 1893775667549431131 A2.35148.0307.1487.3692.0948.11268.5 C5.85146.5306.6484.9687.4931.51263.0 E11.85144.5303.8479.7677.3913.21222.2 F14.85139.6295.9464.8641.9854.21091.9 G17.85131.7279.1427.9566.4725.7886.6 H19.85119.7260.5386.6498.4624.3741.2 I21.55104.0232.4331.7426.1534.8612.4

70. Case Studies (load distribution & pile capacity) Test Load1893775667549431131 E p (t/mm 2 )2.542.442.312.171.981.77

71. Case Studies (load distribution & pile capacity) With a proper elastic modulus, the load distribution at each layer of stain gauges can be calculated from the following relationship.  =  p = X =  P =  E p A p  = axial strain  p = axial stress E p = elastic modulus of pile A p = area of pile

72. Case Studies (load distribution & pile capacity) Secondly, the calculated loads at various levels are plotted and load distribution curves at different applied load are obtained. The load distribution curves along a pile allow a calculation of the load transferred to each soil stratum and the corresponding mobilized resistance value at each stage of loading. Based on the pile head movement and the axial strain measured, the relative displacement in the middle of each soil layer between the pile and its surrounding soil or at the pile toe can be computed. A plot of the mobilized shaft resistance verses the relative shaft displacement or the mobilized point resistance versus the tip movement can be obtained for each supporting stratum to reflect the complete load transfer characteristic of the stratum.

73. Case Studies (load distribution & pile capacity) load distribution diagram

74. Case Studies (load distribution & pile capacity) q s max unit shaft resistance displacement 5 - 6mm t-z curve

75. Case Studies (load distribution & pile capacity) q b max unit base resistance displacement 5% - 10% of pile diameter q-z curve

76. Case Studies (load distribution & pile capacity) Test Results Case 1 test pile

77. Case Studies (load distribution & pile capacity)

79. Case 2 Test Pile

80. Case Studies (load distribution & pile capacity)

85. Case 3 Test Pile

86. Case Studies (load distribution & pile capacity)

88. Case 4 Test Pile

89. Case Studies (load distribution & pile capacity)

94. Case 5 Test Pile

95. Case Studies (load distribution & pile capacity)

100. Case Studies Conclusions & Discussions Case No. Depth (m) SPT N Value (blows/300 mm) Shaft Resistance f s, (kPa) f s /N 1 4.3 - 7.39535.9 7.3 - 10.314966.9 10.3 - 13.31819811.0 13.3 - 16.31002982.9 2 0.0 - 10.723522.3 10.7 - 13.7722102.9 13.7 - 16.7981681.7 16.7 - 18.71112602.3 3 3.5 - 6.5561122.0 6.5 - 9.51002472.5 9.5 - 12.51002132.1 12.5 - 15.51503882.6 15.5 - 18.51674292.6 4 0 - 6.511393.5 6.5 - 9.511232.1 9.5 - 12.525241.0 12.5 - 15.525261.0 15.5 - 18.525261.0 18.5 - 21.5421684.0 21.5 - 24.51503132.1 24.5 - 27.51502101.4 5 3.5 - 6.5632083.3 6.5 - 9.51071751.6 9.5 - 12.51504823.2 summary of mobilized shaft resistance

101. Case Studies (conclusions & discussions) Case No. SPT N Value (blows/300 mm) Base Resistance f b, (kPa) f b /N 1 100646864.7 2 1111103399.4 3 167910154.5 4 150579638.6 5 150378225.2 summary of mobilized base resistance

102. Case Studies (conclusions & discussions) Case No. Depth (m) SPT N Value (blows/300 mm) Shaft Resistance f s, (kPa) Critical Displ- acement (mm) 2 7.7 - 10.72352N.A 10.7 - 13.7722103.0 13.7 - 16.7981685.0 16.7 - 18.71112605.0 4 0 - 6.51139N.A 6.5 - 9.51123N.A 9.5 - 12.525245.0 12.5 - 15.525268.6 15.5 - 18.525268.6 18.5 - 21.542168N.A 21.5 - 24.52003137.3 24.5 - 27.520021011.8 5 3.5 - 6.5612085.0 6.5 - 9.51071755.0 9.5 - 12.5150482N.A summary of critical shaft displacement

103. Case Studies (conclusions & discussions) Relationship between unit shaft resistance & SPT (N)

104. Case Studies (conclusions & discussions) Relationship between f s /N & SPT (N)

105. Case Studies (conclusions & discussions) Relationship between unit base resistance & SPT (N)

106. Case Studies (conclusions & discussions) As discussed earlier, the value of elastic modulus decreased with increased in axial strain. The skin resistance increased with increased in standard penetration resistance. As presented, the relationship between the unit skin friction and the standard penetration resistance (N) was 2.4N. The other relationship, the unit end bearing and the respective N, was found to be 46N.

107. Case Studies (conclusions & discussions) Another important parameter, the critical shaft displacement (z s ) to fully mobilize the skin resistance was varied between 3.0 mm and 11.8 mm. In most cases, z s = 3.0 - 8.7 mm which is irrespective of standard penetration resistance, the diameter and the length of piles. Based on the finding from the results of the instrumented test pile reported in this study, the following conclusions can be drawn: a) The adoption of elastic modulus value is very important for the evaluation of load distribution curves which significantly effects the estimation of f s and f b. The modulus degradation and the relationship between E p and value of e should be considered in the calculation of load distribution. A constant E p value should not be adopted especially for the case when the E p value is much lower than the theoretical value.

108. Case Studies (conclusions & discussions) b) For the design of bored pile in residual soil of Singapore, a possible approximate relationship between f s and N is as follows: f s = 2N (kPa) A higher value of f s may be adopted if the soil parameters or the important relationships are available from the load test result. c) For design applications, the unit end bearing value f b can be related to the penetration resistance, N, as follows: f b = 45N (kPa) The higher f b value may be adopted if the debris from the pile bottom is properly removed and pile base is cleaned.

109. Case Studies (conclusions & discussions) d) The test results suggested that the critical shaft displacement, z s = 3.0-9.0 mm for the bored pile in residual soil of Singapore. However, it is expected that similar correlations can be derived for other soil conditions. e) Due to inadequate data, no conclusion could be made on the estimation of the critical tip displacement, z p value. If there is lack of data, it is suggested that the z p value be selected as 5% to 10% of the pile diameter.

110. Thank You.