DEEP FOUNDATION. Improving Reliability of Foundations for Tall Buildings. By : Ir. Chow Chee Meng Date: th March 2014

Transcription

1 DEEP FOUNDATION Improving Reliability of Foundations for Tall Buildings By : Ir. Chow Chee Meng Date: th March 2014 G&P Geotechnics Sdn Bhd (

2 VIRTUALLY EVERY STRUCTURE IS SUPPORTED BY SOIL OR ROCK. THOSE THAT AREN T EITHER FLY, FLOAT, OR FALLOVER -RICHARD L. HANDY-

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5 REACHING FOR THE SKY

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9 DEEP FOUNDATION

10 WHAT IS A DEEP FOUNDATION It is a foundation system that transfers loads to a deeper and competent soil layer. To support: Axial compression load Uplift/tension Lateral load Traditional function of piles for high-rise Marine structures, slender structures, etc. Reduce overall settlement / differential settlement

11 DEEP FOUNDATION FOR HIGH-RISE Deep foundation for high-rise: Bored piles Barrette piles Caisson piles Driven piles Jack-in spun piles Micropiles, etc. Traditionally used for high-rise

12 DEEP FOUNDATION FOR HIGH-RISE Design aspects for conventional bored piles, caisson, etc. normally covered in various seminar/conferences Focuses on relatively new or innovative design approach for optimum foundation design

13 DESIGN CONSIDERATIONS

14 Allowable Settlement of Building Settlement of high-rise building < 12mm or 25mm? Myth or fact?

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16 Actual Building Settlement Actual recorded settlement of high-rise building 20mm to 125mm Important design considerations NOT total settlement Differential settlement governs

17 Definitions of foundation movement

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20 Not designed by Author or G&P SHIFT??????????? Ground Conditions? Limestone

21 PILED RAFT FOUNDATION Using conventional approach where part of the superstructure load is transferred to the slab/pilecap in contact with the ground At least 25% to 40% reduction of numbers of piles depending on soil conditions

22 DESIGN METHODOLOGY Relatively higher loads imposed onto foundation Piles of varying length Longest piles in the middle and progressively shorter piles towards the edge Strip-raft structural system

23 Strip-raft Piles with varying length SCHEMATIC OF PILED RAFT SYSTEM WITH VARYING PILE LENGTHS

24 ANALYSIS Interaction between pile-soilstructure important Iterative analysis using pile interaction software (e.g. PIGLET, PIGEON) and structural analysis software (e.g. SAFE)

25 ANALYSIS Interaction of piles based on modified solution of Randolph & Wroth (1979) incorporated in the software, PIGEON

26 PILED RAFT FOUNDATION Settlement reducing piles/full piled raft Piles introduced to control settlement Piles required may be as little as 10% of conventional pile design Refer to publications by Randolph, Poulos, Katzenbach, etc.

27 DESIGN METHODOLOGY Settlement reducing piles at concentrated loads (i.e. columns and walls): Condition 1: Moment in structural member Condition 2: Shear in structural member Condition 3: Contact pressure below foundation Condition 4: Local settlement Mainly governed by structural design

28 DESIGN METHODOLOGY Settlement reducing piles To control differential settlement Overall bearing capacity sufficient Smoothened settlement profile Column Loads Settlement reducing piles Large local settlement

29 CASE HISTORIES

30 MEDIUM RISE BUILDINGS 200mm x 200mm reinforced concrete (RC) square piles with pile length varying from 18m to 24m 350mm x 700mm strips and 300mm thick raft

31 Foundation Design for 5-Storey Low Cost Apartment

32 SETTLEMENT MONITORING Total of 14 numbers of precise settlement markers Monitored results up to 313 days CSM02 CSM05 CSM10 CSM1 4 CSM01 CSM04 CSM06 CSM07 CSM09 CSM11 CSM13 CSM03 Legend: CSM Settlement markers (14 Nos.) CSM08 CSM12

33 Settlement (mm) Settlement Profile Across Edge of Building CSM02 = 1/ Distance (m) CSM05 = 1/13950 Centreline = 1/17595 Maximum differential settlement: 27mm CSM10 Maximum local angular distortion: 1/1215 CSM14 = 1/

34 COMPLETED APARTMENT TAN, Y.C., CHOW, C.M. & GUE, S.S. (2005). Piled raft with different pile length for medium-rise buildings on very soft clay, 16 th ICSMGE, September 12-16, 2005, Osaka, Japan.

35 2500 Ton Silo on Very Soft Marine Deposits

36 Foundations for Highrise Bistari Condominiums, KL. Alternative design has reduced the foundation cost by more than 50%, A saving of more than RM5 million An Award of Merit (1998) was given by ACEM

37 Concrete Raft Fill / Alluvium

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39 JACK-IN PILES ONLY FOR LOW- RISE BUILDINGS?

40 HIGH-CAPACITY JACK-IN PILES Myth: Jack-in piles cannot be used for high-rise buildings or in limestone formation Truth: Jack-in piles can be used for high-rise buildings and limestone formation - With proper design and input from experienced geotechnical engineer

41 BEHAVIOUR OF JACK-IN PILES G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

42 BEHAVIOUR OF JACK-IN PILES Rankine Lecture by Prof. Mark Randolph (2003): Bored piles zero residual pressures End-bearing can only be mobilised at relatively large displacement G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

43 BEHAVIOUR OF JACK-IN PILES Driven and jacked in piles - significant residual pressures are locked in at the pile base during installation Higher end-bearing can be mobilised at working load G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

44 BEHAVIOUR OF JACK-IN PILES White & Lehane (2004): Greater number of cycles during pile installation larger reduction in shaft friction G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

45 White & Lehane, 2004 Reduction in shaft resistance!!! G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

46 BEHAVIOUR OF JACK-IN PILES Deeks, White & Bolton (2005): The measured jacking force during installation indicates plunging capacity of the pile G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

47 BEHAVIOUR OF JACK-IN PILES Jacked piles have a high base stiffness Stiffness of jacked piles > 2 times stiffness of driven piles > 10 times stiffness of bored piles G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

48 CASE HISTORIES

49 1 st Site Starting of Jack-In Pile system using large size pile in Malaysia (Year 1999) Installed through municipal dumping site with mine tailings overlying Karstic Kuala Lumpur Limestone bedrock. Use 450mm Spun Pile with Working Load of 1500kN G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

50 1 st Site G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

51 1 st Site G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

52 1 st Site G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

53 Case Histories Four sites in Kuala Lumpur and Selangor, Malaysia : Site A: 31-storey apartment Site B: 45-storey apartment Site C: 40 to 43-storey apartment Site D: 15-storey apartment G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

54 Case Histories (Sites A to D) Pile size: 400mm to 600mm Pile working load: 1520kN to 3000kN All piles generally jacked to 2.0 times working load with holding time of 30- seconds (2 cycles) G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

55 Case Histories (Sites A to D) Silty SAND / sandy SILT overlying Granite Formation (weathered granite) Boulders encountered - Some piles installed after preboring G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

56 Site A Granite Formation G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

57 Site B G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

58 Site B Pile toe at hard weathered granite layer G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

59 Static Load Tests Total of 22 static load tests carried out for the 4 sites All piles selected for testing achieved minimum 2 times working load!!! (No pile failed!) No signs of plunging failure of pile Settlement at working load: mm Settlement at 2*WL: mm G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

60 Static Load Tests Pile as short as 6.5m tested with settlement at working load and 2*WL of 8.32mm and 19.73mm respectively Pile performance are satisfactory for piles where preboring have been carried out Termination criterion adopted adequate G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

61 Preboring through boulders Boulders exposed after preboring G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

62 APPLIED LOAD (kn) Static Load Tests 500mm Spun Pile, Pile length = 6.5m PILE TOP SETTLEMENT (mm) G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd Site B

63 Static Load Tests Site B G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

64 Static Load Tests G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

65 Termination Criteria Termination criterion for jack-in piles in weathered granite: Jack the pile to 2.0 times of the design load for a minimum of two cycles. The corresponding pressure has to be held for minimum 30 seconds with settlement not exceeding 2mm G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

66 Mobilised Resistance Instrumented test piles Site C (3 Nos.) Site D (2 Nos.) Piles instrumented using the Global Strain Extensometer method G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

67 MOBILISED SKIN FRICTION (kn/m 2 ) Mobilised (Shaft) Resistance 600mm Spun Pile, Pile length = 21.4m (Nearest borehole, BH-20) 0.5m to 10.7m 10.7m to 20.9m Site C) DISPLACEMENT (mm) G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

68 MOBILISED END-BEARING RESISTANCE (kn/m 2 ) Mobilised (Base) Resistance mm Spun Pile, Pile length = 21.4m (Nearest borehole, BH-20) End-bearing not fully mobilised DISPLACEMENT (mm) G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

69 SUMMARY Traditional correlations of skin friction based on driven piles (e.g. fs = 2.5*SPT-N) is too conservative for jack-in piles in weathered granite Conservative estimate based on test results: - Ultimate skin friction, f s ~ 5*SPT-N G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

70 SUMMARY Jack-in piles demonstrates higher skin friction possibly due to: - Less disturbance during installation - friction fatigue phenomenon (e.g. White & Lehane, 2004) - Locked-in pressure (residual pressure) effect (e.g. Randolph, 2003) G&P Geotechnics Sdn Bhd ( G&P Geotechnics Sdn Bhd

71 References Tan, Yean-Chin, Chow, Chee-Meng & Gue, See-Sew (2011). Jack-in Pile in Malaysia: A Malaysian Consultant s Perspective, Proceedings of the 2 nd VLA Seminar: New Developments in Jacked Piling, Hong Kong, 18 th March 2011 C.M. CHOW & Y.C. TAN (2010). Performance of Jack-in Pile Foundation in Weathered Granite, 17 th SEAGC, May, Taipei, Taiwan. CHOW, C.M. & TAN, Y.C. (2009). Jack-in Pile Design Malaysian Experience and Design Approach to EC7, IEM Course on Eurocode 7 Geotechnical Design, July 2009, Petaling Jaya, Selangor.

72 HIGH-CAPACITY JACK-IN PILES Myth: Jack-in piles cannot be used for high-rise buildings or in limestone formation Truth: Jack-in piles can be used for high-rise buildings and limestone formation - With proper design and input from experienced geotechnical engineer

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76 SOME UNIQUE PROBLEMS

77 Testing Set-up Using Reaction Piles G&P Geotechnics Sdn Bhd (

78 Testing Set-up Long reaction piles at close spacing used Case histories: Load tests using reaction piles give ERRATIC results Reference: Weele (1993)

79 Ref: A.F. van Weele, 1993 Tested using anchor piles 1100kN 2100kN Tested using kentledge Approx. 2 times smaller using reaction piles!

80 Reaction piles Zone of interaction with test pile Test pile

81 Testing Set-up Latest version of ASTM D1143 Published April 2007

82 Testing Set-up ASTM D1143 Normal kentledge 3 times Clear distance of at least 5 times the maximum diameter Caution on factors influencing results: Possible interaction.from anchor piles..

83 Settlement Criteria for Pile Load Test G&P Geotechnics Sdn Bhd (

84 MALAYSIA S PRACTICE A pile tested shall be deemed to have failed if (JKR, 1988): The residual settlement after removal of the test load exceeds 6.50mm; or The total settlement under the Working Load exceeds 12.50mm; or The total settlement under twice the Working Load exceeds 38.0mm, or 10% of pile diameter/width whichever is the lower value.

85 MALAYSIA S PRACTICE No consideration given to pile length and pile size in setting the settlement criteria Too conservative especially for long piles and big diameter piles

86 Pile shaft shortening (after Ng et al., 2001)

87 SETTLEMENT CRITERIA Settlement criteria for pile testing must take into account Elastic compression of pile which is a function of pile length and pile diameter Movement expected to mobilise shaft friction and end-bearing

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89 SETTLEMENT CRITERIA Proposed settlement criteria for bored piles: For piles founded in soils: M = 12.50mm + ½ PL/AE For piles founded on rocks and/or with short rock sockets and for piles with slip liners: M = 12.50mm + ¾ PL/AE To be adjusted for other specific structural considerations!

90 SETTLEMENT CRITERIA Typically, differential settlement between any two piled foundations unlikely to be greater than 75% of the maximum settlement (Craig, 1998) Typical medium-rise to high-rise building column span = 5.0m to 8.5m Assuming 25m long, 1.2m diameter rock-socketed bored pile with working load = 9800kN Maximum differential settlement = 0.75*18.5mm = 14mm Distortions = 1/350 to 1/600 (Within allowable limits to prevent cracking in walls and partitions and well within the limits for structural damage of 1/150 Skempton & McDonald, 1956) Criteria can be adjusted for specific spans based on fundamental engineering principles!

91 SUMMARY

92 SUMMARY Recent advances and understanding in pile behaviour has improved reliability of foundations for tall buildings Relatively new / innovative design approach: Piled raft/settlement reducing piles High-capacity jack-in spun piles Research findings removed unnecessary conservatism or unsafe design practices, e.g. unrealistic settlement criteria, etc.

93 ON A FINAL NOTE With regard to geotechnical engineering: There are no (insurmountable) weak soils or rocks, there are only weak engineers. Professor Heinz Brandl Vice-President ISSMGE ( )