Influence of Deep Foundation Installation Methods Presented by: Morgan NeSmith, PE

Transcription

1 Influence of Deep Foundation Installation Methods Presented by: Morgan NeSmith, PE Director or Engineering To 2⁰ Congresso Internacional de Fundaciones Profundas de Bolivia Santa Cruz, Bolivia May 2015 Scope of Presentation Precast Piles steel, concrete Cast-in-Place Foundations: Drilled Shafts Augered Cast-in-Place Piles / Continuous Flight Auger Piles Drilled Displacement Piles Micropiles 1

2 Factors Influencing Performance Installation Method Foundation Material (concrete, steel, wood) Precast Piles Steel Pipe (open-end or closed-end) H-Pile Tapered Shell (mandrel driven) Concrete Octagonal Square Cylinder Timber 2

3 Driven or Vibrated Piles Driven Piles in Clay 3

4 Driven Piles in Sand Driven Piles in Sand 4

5 Environmental Effects Dynamic loading during installation - Vibrations: good for pile installation, possibly very bad for your neighbors - Noise: not good for anything except upsetting your neighbors - In saturated clay (nearly incompressible in short term) can heave ground and nearby piles Drilled Shafts With casing or slurry, drilled incrementally Typically most useful for: - ultra-high compressive loads (concrete compressive strengths up to 12,000 psi (83 MPa) or greater) - high lateral loads (requiring large amounts of reinforcing steel) - geologies providing little shaft resistance where toe resistance is crucial (e.g. hard, shallow bedrock) - where it would be beneficial to have direct connection from structure column to single foundation element (bridges, structures where pile cap construction is not feasible) In last 15 years, line has blurred between when to use single-pass augered / drilled piles and drilled piers / shafts 5

6 6

7 Drilled Piers Devon Energy - Oklahoma Devon Energy WHQ Drilled Piers 7

8 Drilled Shaft Example Reinforcing Reinforcing installed PRIOR to concrete placement Use concrete, not grout, typically poured from top or tremied to bottom 8

9 Shaft Typically Stabilized by Casing or Slurry Generally Neutral Displacement (if constructed correctly!!!) Casing and slurry can smooth soil surface lowering the friction coefficient between shaft and soil Tremied concrete also has lower bond strength with soil than other cast-in-place methods (grouted or pressure grouted) Not many places in North America where shafts bear in soil only mostly in rock however some in Chicago (hard OC clay locally called hardpan) and Mississippi (large deposits of OC clay) where belled piers are often efficient Many designers neglect shaft and only consider end bearing (possibly very, very conservative) Reinforcing is set after drilling but before concreting so is typically full length whether the shaft needs it or not (lateral loads typically resolved in the upper 6-m to 12-m of shaft) 9

10 Terminology for Cast-in-Place Piles Cast-in-place piles installed by single-pass, rotary drilling processes Continuous Flight Auger European Screw Piles ACIP aka Augercast CFA Displacement Pile Intermediate (Partial) Displacement Auger Pressure Grouted (APG) Pile System Cast-in-place piles grew out of pressuregrouting processes at Intrusion-Prepakt, late 1940s, early 1950s Patent granted to Raymond Patterson for construction of cast-in-place piles by pumping grout through a hollow-stem auger. Licenses granted to Lee Truzillo and Charles Berkel The Evolution of Cast in Place Piles November/December 2013 DFI Magazine 10

11 Augered vs. Screwed or Displacement Gaspar Coelius granted patent for cast-in-place Screw pile in 1960 Analogous to augered.. And to displacement From De Cock and Imbo, Transportation Research Record 1447 Excavated ACIP piles 11

12 Stratigraphy? Stratigraphy? Residual soils from soft to hard to partially weathered rock (PWR = 100+ blows per 30 cm) to bedrock 12

13 APG Pile Example Installation (1) Stem augers hole (2) Grout pumped under pressure (3) Build up grout head prior to withdrawing auger (4) Hollow stem auger retracted while grout pumped into hole APG Pile Installation (2) Grout is injected under pressure (1) Auger drills hole (4) Hollow Stem Auger is retracted while grout is pumped into hole 2007 Berkel & Company Cast-In-Place Pile Seminar (3) Build up grout head prior to withdrawing auger 13

14 Typical APG Pile Rig Hollow Stem Auger Continuous flight auger 75 mm inside diameter pipe Auger diameters: Historical: 300 mm to 460 mm Typical: up to 610 cm = no problem Specialty: 760 cm to 1220 cm Auger section lengths: ~ 1 to 6 m 14

15 JADE SIGNATURE - SUNNY ISLES BEACH, FL 90-cm Diameter (APG) Piles 47-m Deep Over 300 Installed in 20 weeks To resist ~ 1000 metric tons compression Auger Flights attached to Hollow Stem 15

16 Drill Bits Basic Bit - Pengo bit Basic Rock Bit - fitted with carbide teeth Clay Flight Bit - for clay soils Torque Arm Leads 16

17 Gearbox Hydraulically operated top head drive Travels up and down the leads Torques range from about 20 to 120 kn/m Weighs 1 to 5 metric tons Rotational speed ranges from 30 to 60 rpm Grout Pump Hydraulically operated, positive displacement pistonball valve pump Pump pressures typically around 350 psi at pump outlet Stroke vols. typically range from about 0.4 to 1.0 cubic feet per stroke (up to 1.7) Grout hoses typically 2 to 3 inch diameter Can pump grout several hundred feet Grout typically delivered by ready mix trucks 17

18 Typical Limited Headroom (LHR) Rig Used where overhead clearances are at least 2.5 to 3 m Track-mounted or forklift mounted drilling equipment Piles are drilled with auger sections typically 1 to 3 m length Installation time longer than with crane-mounted equipment (thus, more expensive per foot Neutral or Negative Displacement If proper equipment not used, stress release can occur Potential for release is greater in alluvial or marine sands than in residual soils and stiff clay Potential for release is greater in segmental (low-head room) than single auger 18

19 Fresh completed pile Maybe soil wants to displace towards new pile being drilled as horizontal confinement lowers Neutral or Negative Displacement Can suck adjacent piles if drilling too close together Pile to be drilled Fresh pile may collapse into new pile. Typically don t drill adjacent piles (closer than 6 diameters) within 12 hours Pile to be drilled ANCILLARY BENEFITS Minimal Spoils No Vibration Low Noise Easy to vary pile lengths to suit site conditions Grouted bond to soils produces larger shaft resistance than concrete-soil bond or driven pile friction coefficients 19

20 Fixed Mast Platforms Drilled Displacement Piles (full and partial displacement) CFA (APG-FMC) Piles Overview of Drilling Platform and Sensors 20

21 INSTALLATION PLATFORM 200 to 270 kn/m torque 18 to 36 metric tons downward force Fixed mast for stability, inclinometer with display in operator s compartment Grout pressure, measured at top of tools, is displayed in operator s compartment Real-time display of installation parameters (depth, KDK pressure, Installation Effort, grout pressure) pressure CAST-IN-PLACE PILES INSTALLED WITH A FIXED MAST DRILLING PLATFORM (APG-FMC) Wilkins, B., NeSmith, W.M, Tebbenkamp, F., and Duncan, S. (2009) Performance of Cast-in-place Piles Installed with a Fixed Mast Drilling Platform in Claystone Glenrock WY Proceedings of the DFI 34 th Annual Conference on Deep Foundations. Kansas City MO, USA October

22 CFA Example 6 to 9-m of weak, saturated, compressible sand, silt and clay Ground water at m depth Deep foundations for all major units assumed from the outset Initial budget based on 1,600 x 9000-mm dia. drilled piers 3-m into rock with temporary casing. Considered drilled piers, driven piles and auger cast piles Final decision: ** 600-mm dia. CFA pile w/ fixed mast platform** Comments on CFA and Fixed Mast Platforms - Slower penetration and slower rotation with fixed mast than with crane mounted APG piling - Less spoils removed with CFA (maybe ~ 75%) than with APG - Slightly higher shaft values with fixed mast than crane mounted systems - Very economical to replace large pile caps or drilled shafts 22

23 4-0 +/ /- Fixed-Mast Platform Crane-Mounted Platform APG and Displacement Tooling CONVENTIONAL ACIP TOOL INTERMEDIATE (PARTIAL) DISPLACEMENT TOOL DRILLED DISPLACEMENT TOOL Displacement leads to increased horizontal stresses (and densification) for higher shaft resistance in many soils Grout/soil interface is a more effective load transfer interface than pre-cast or steel/soil 23

24 Berkel Displacement Pile Tool Stem, smaller than flighting Reverse flighting Stem becomes progressively larger, terminating in the displacing element Displacing element. Same diameter as the flighting below +- 1-m, regular flighting, 300-mm to 460-mm diameter INSTALLATION METHOD Tool advances as a screw in low to medium consistency soils. In dense soils, material transported up the auger to the displacing element. Material in auger flights is compressed; thus no stress relief in the zone adjacent to the auger. 24

25 INSTALLATION METHOD When the target level has been reached, pumping of grout is begun. Grout pressure is monitored by the operator Lift off and withdrawal rate are varied to maintain pressure where possible. Tool is rotated during withdrawal and material which falls around stem is captured and displaced. Typically get grout return only after tip is at or near ground surface. Soil Improvement Aspects Of Displacement Pile Installation When displacement piles are installed in materials that exhibit granular behavior, there is a significant increase in density in the vicinity of the piles The increase is most pronounced in loose to medium dense materials After a certain density, as the in-situ density of the materials increases, the density percentage change goes down The increase in density is additive-the more piles that are installed, the greater the increase Pressure grouted bond to soils produces larger shaft resistance than concrete-soil bond or driven pile friction coefficients 25

26 DEPTH, ft 13/05/2015 Improvement from Drilled Displacement Tool Installation 1.8 METERS 2.1 METERS 2.1 METERS 46 CM BY 12.2 M EXTRA PILE 1.8 METERS 46 CM BY 12.2 M EXTRA PILE 0.46 M 46 CM BY 7.6 M COMPRESSION TEST PILE 0.46 M 0.46 M 46 CM BY 12.2 M REACTION PILE AMBIENT CONDITION-3D FROM PILE Qc, tsf METERS FINE SAND, TRACE TO SOME SILT, OCCASIONAL THIN SILT/CLAY LAYERS. AVERAGE Qc = 3.1 MPa (32 tsf) METERS

27 DEPTH, FEET DEPTH, FEET 13/05/2015 CPT VALUES COMPARISON AT 1D, OF CPT VALUES, 2D, 1D, 3D 2D, FROM PILE PILE 0 CONE TIP VALUE, TSF METERS FINE SAND, TRACE TO SOME SILT, OCCASIONAL THIN SILT/CLAY LAYERS METERS AVERAGE CONE AVERAGE TIP CONE TIP RESISTANCE 3D OUT 2D OUT 1D OUT RESISTANCE FROM 3.1 M TO 3.1 MPa (32 TSF, 6.5 MPa (68 TSF, 8.1 MPa (84 TSF, 7.6 M (10 FEET TO 25 FEET) N = 8 BPF) N = 17 BPF) N = 21 BPF) CPT VALUES AT 3D and CENTER OF GROUP COMPARISON OF CPT VALUES, 3D FROM PILE AND CENTER OF GROUP 0 CONE TIP VALUE, TSF METERS METERS AVERAGE CONE TIP RESISTANCE FROM 3.1 M TO 7.6 M (10 FEET TO 25 FEET) 3D OUT 3.1 MPa (32 TSF, N = 8 BPF) CENTER OF GROUP 9.6 MPa (100 TSF, N = 25 BPF) 27

28 ANCILLARY BENEFITS Minimal Spoils No Vibration Low Noise Easy to vary pile lengths to suit site conditions DOES THE BENEFIT HOLD UP IN RESIDUAL SOILS? Some empirical indications that shaft resistance in medium to dense sandy residual soils are not as high as expected from marine, alluvial and other younger deposits. 28

29 DESIGN MODELS UNDERESTIMATE GROUP EFFECTS ORDER OF INSTALLATION IN LARGE GROUPS IS CRITICAL Intermediate (Partial) Displacement Pile System 29

30 APG and Displacement Tooling CONVENTIONAL ACIP TOOL INTERMEDIATE (PARTIAL) DISPLACEMENT TOOL DRILLED DISPLACEMENT TOOL Conventional ACIP Auger Stem Partial Displacement Auger Stem 30

31 Equipment/Process Summary Same installation platform as Drilled Displacement Piles-high torque, crowd Large diameter stem, small flight dia. (typically less than 2/3 ratio) Tooling is screwed into ground where possible (displacement), drilled in where necessary (excavation) Improve loose soils, limit stress relief in dense soils Target spoil is less than 75% of neat hole volume May be cast by volume (like APG piles) or by pressure (like Drilled Displacement piles) 31

32 Efficiency Comparison to APG Pile Drilled displacement piles use more expensive equipment Unit capacities from displacement systems can be significantly higher than traditional APG piles Generally: If piles can be shorted and the diameter can be decreased, displacement systems can be more efficient (pending project size) 4-0 +/ /- Fixed-Mast Platform Crane-Mounted Platform 32

33 Screening 1 Insert the Screen Screening 2 Remove Foreign Objects 33

34 Reinforcing Cage Placement Micro Piles (less than 300-mm dia) In general, not as efficient as single-pass drilled or augered systems but: High capacity (particularly for size) Installation in limited access and/or low headroom Minimal disturbance/vibration to adjacent structures Capability to penetrate subsurface obstructions (very useful for rubble in urban fills and boulders in glacial till) Can case through voids (useful in limestone with large cavities) Refer to FHWA Micropile Design and Construction Guidelines and DFI / ADSC Micropile 2010 Seminar (also see local contractors!) 34

35 Example Installations - Micro Piles Copyright 2009 PT. Geonusa Utama Drilling is somewhat neutral displacement. Post grouting and pressure grouting are positive displacement and the pressure grout to soil or rock bond is very high 35

36 Example Pile Top - Micro Piles 2008 Southwest Contracting Ltd Micro Piles at Dulles Airport 36

37 Hollow Bar - Micropiles Hollow Bar - Micropiles Net Neutral Displacement similar unit shaft values as ACIP piles (so far) 37

38 THE END QUESTIONS? 38