Annual Kansas City Specialty Seminar Recent Advances in Design and Construction of Helical Foundations

Transcription

1 Annual Kansas City Specialty Seminar 2014 Recent Advances in Design and Construction of Helical Foundations

2 Helical Foundations History, Applications and Recent Research Dr. Samuel P. Clemence Syracuse University

3 SPECIAL THANKS TO Helical Piles and Tiebacks Committee Deep Foundations Institute Professor Alan Lutenegger University of Massachusetts Amherst

4 OUTLINE I. Helical Foundations Defined II. Historical Development III. Theory & Design IV. Practical Applications V. Recent Advances in Research

5 HELICAL FOUNDATIONS? Screw Piles Screw Anchors Screw Piers Soil Screws Helical Piles Helical Piers Screw Cylinders Helical Anchors Compression = Pile Tension = Anchor

6 System Components Definitions Common Terminology Central Shaft Pier Cap Extensions Coupling Lead Section Helical Blades Pitch Pilot Point

7 EXTENSION SECTIONS 3-0 (91.4 cm), 5-0 (152.4 cm), 7-0 (213.4 cm) & 10-0 (305 cm) Lengths

8 Definitions MACHINE CROWD TORQUE MOTOR TORQUE INDICATOR HELIX LEAD SECTION WITH 4 HELIX BLADES

9 Example Installation Process Installation 1.) Rotate lead section into the ground using a hydraulic torque drive. 2.) Attach one or more extensions and continue rotation. 3.) Halt installation when specified torque is achieved.

10 Vehicle-Mounted Torque Motor Definitions 3,500 FT-LB 6,000 FT-LB 12,000 FT-LB 20,000 FT-LB And beyond

11 Definitions TORQUE MOTOR REACTION BAR FOOT CONTROL

12 Definitions Types of Helical Foundations Helical Pier (Square-Shaft) HELICAL PULLDOWN Micropile LIFT TM Pile Helical Pier (Round-Shaft)

13 PRINCIPAL ADVANTAGES Rapid Installation Immediate Load Capacity Installation in High Groundwater Installation with Traditional Equipment Environmentally Friendly No Soil Cuttings Minimal Site Disturbance Minimal Cleanup Installation in Limited Access & Low Headroom Areas Installation Monitoring as QC

14 HISTORICAL DEVELOPMENT

15 CODE OF HAMMURABI If a builder build a house for a man and do not make its construction firm and the house which he has built collapse and cause the death of the owner of the house - that builder shall be put to death. If it destroy property, he shall restore whatever it destroyed, and because he did not make the house which he built firm and it collapsed, he shall rebuild the house which collapsed at his own expense..

16 Great Pyramid STEP PYRAMID First Pyramid at Sakara Giza, Egypt

17 PYRAMID S THREE MAIN PARTS Step-like central core: innermost section. Only the facing blocks of each sloping band of the core were carefully finished All three parts were constructed simultaneously, one layer at a time. Capstone Casing Blocks Packing Blocks Core blocks Tomb

18 PYRAMID BASE Before construction of the pyramid began, the site was leveled. A network of narrow connecting trenches was cut into the rock over the entire area.

19 PYRAMID FOUNDATION The trenches were filled with water, which acted as a level. When the top of the water was marked on the sides of all the trenches, they were drained. The spaces between the trenches were cut down to the height of the marks. The trenches were then filled with stone.

20 FAILURE!! THE BENT PYRAMID

21 ROMAN ARCH Semicircular with keystone in center

22 CONSTRUCTING ARCHES ROMAN STYLE Wooden centering/scaffolding initially supported stone arch. Support was then burned away to leave the arch system!

23 ROMAN AQUEDUCT Pont du Gard, France

24 MIDDLE AGES ENGINEERING Salisbury Cathedral Gothic structure with its stained glass windows allowed light into the church interior.

25 GOTHIC CATHEDRAL Ribbed Vault: Arrows and dashed lines show how thrusts (forces) from the ribs are carried partly by the flying buttresses.

26 STRESSES DUE TO STRUCTURAL WEIGHT Cathedral at Amiens, France

27 EFFECT OF WIND on taller buildings such as cathedrals

28 STRESS WITH WIND LOADING Cathedral at Amiens, France

29 STRESS CORRECTION! Adding the weight of pinnacles prevented the outer wall from crumbling.

30 COALBROOKDALE BRIDGE, ENGLAND First cast-iron bridge, over the Severn River

31 EARLY DEADMEN ANCHORS Early deadmen anchors were constructed by burying various shaped objects of stone or crude concrete masses. These anchors were installed by hand to depths up to ten feet with load capacities of 500 to 10,000 pounds.

32 SUSPENSION BRIDGES REQUIRE MASSIVE ANCHORAGE SYSTEMS Clifton Bridge of Bristol One of the first iron suspension bridges constructed Designed by Isambard K. Brunel Completed in foot span Required large anchorage system to support suspension cables

33 THE BEGINNINGS 1 st Recorded Use was by Alexander Mitchell ( ) in 1836 for Moorings and was Then Applied by Mitchell to Maplin Sands Lighthouse at the Mouth of the Thames Estuary in England in 1838 Most Engineers Don t Understand or Appreciate That This was THE Major Foundation Technology of the 19 th Century That Dramatically Changed the Globe

34 ALEXANDER MITCHELL ( )

35 ON SUBMARINE FOUNDATIONS; PARTICULARLY SCREW- PILE AND MOORINGS, BY ALEXANDER MITCHELL, CIVIL ENGINEER AND ARCHITECTS JOURNAL, VOL. 12, Whether this broad spiral flange, or Ground Screw, as it may be termed, be applied to support a superincumbent weight, or be employed to resist an upward strain, its holding power entirely depends upon the area of its disc, the nature of the ground into which it is inserted, and the depth to which it is forced beneath the surface.

36 MITCHELL S SCREW PILE SPECIFICATIONS FOR MAPLIN SANDS Material cast iron Shaft diameter 5 in. Screw (helix) diameter 4 ft. Depth below mudline 12 ft. Orientation - vertical

37 Historical Development MITCHELL S SCREW PILE

38 EARLY (PRE-1900) USES OF SCREW PILES Lighthouse foundations Moorings Ocean front piers Railway bridges Underpinning

39 PALACE PIER - BRIGHTON

40 MADRAS (INDIA) JETTY

41 TOWN HALL GREAT YARMOUTH 43

42 HISTORICAL DEVELOPMENT In the 1840 s and 1850 s, More Than 100 Screw Pile Foundation Light Houses were Constructed Along the East Coast, the Florida Coast and the Gulf of Mexico.

43 GEORGE GORDON MEADE DESIGNED LIGHTHOUSES IN THE US

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45 RESTORED LIGHTHOUSE IN MARYLAND Lighthouse on the Chesapeake Bay

46 EXAMPLE OF EARLY SCREW ANCHOR. The original anchors were screwed in the ground like a carpenter s screw. This screw anchor was retrieved from a lighthouse on the Chesapeake Bay in Maryland.

47 49

48 50

49 INSTALLATION A screw pile turned by 8 capstan bars 20 feet long, each manned by four or five men, with a screw 4 feet in diameter passed in less than two hours through a stratum of sand and clay more than 20 feet thick Proceedings of the Institution of Civil Engineers 1877

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51 EARLY INSTALLATION METHODS Capstan and Hand Labor Capstan and Oxen Large Wheel and Hand Labor Mechanical Screw Tower Steam Power Hydraulic Power

52 IMPROVEMENTS IN INSTALLATION METHODS (HYDRAULICS) Large Excavator Backhoe Skid Steer MiniExcavator Hand Installation Special Equipment

53 MIDDLE ERA ( ) Historical Development There was a quiet period that saw the rise of other foundation technologies, and the decrease in use of Screw Piles. During this time other deep foundations such as Raymond, Drilled Foundations, Enlarged Base Foundations, Franki Piles, etc. developed along with major developments in mechanical equipment, e.g., hydraulics.

54 Historical Development MODERN ERA (1950-PRESENT) Advances in installation equipment Advances in geometries Increased need for alternative foundation solutions Increased research into behavior Increased applications through aggressive marketing

55 THEORY AND DESIGN

56 FOUNDATION & ANCHOR CAPACITY Design Considerations: Theory & Design Theoretical Capacity Capacity: Torque Correlations Down Drag Buckling Lateral Resistance Corrosion Group Efficiency

57 DESIGN Theory & Design Design Capacity no better than: Input Data Soil properties Water table location & fluctuation Loads Input Assumptions Estimates Correlations Disturbance/Remolding

58 SCENIC UPSTATE NEW YORK Area of deep, soft soils

59 TRANSMISSION TOWER COLLAPSE DUE TO ICE STORM IN CENTRAL NEW YORK Engineers examining the damage

60 TRANSMISSION TOWER FAILURE SUPPORTED ON DRILLED SHAFT Ice storm caused toppling of tower founded on soft soils

61 EARLY METHOD FOR PREDICTING UPLIFT CAPACITY Uplift Capacity (Kips) Uplift capacity based on empirical charts using torque and soil classification

62 TESTING SITES FOR ANCHORS Physiographic Provinces of New York State (adopted from Fenneman, 1938)

63 FULL SCALE FIELD TESTS

64 TEST RESULTS FOR SHALLOW ANCHOR IN SAND

65 Q u = Ultimate Pullout Capacity W s φ / 2 H 1 PROPOSED FAILURE SURFACE FOR SHALLOW ANCHOR H 3 Q f = Frictional Resistance of Soil on Failure Surface Proposed Failure Surface

66 FULL SCALE FIELD TESTS AT CLAY SITE Specially designed uplift load frame for field tests

67 TYPICAL RESULTS FROM FIELD TESTS Uplift Load (Kips) Short Term Clay Site Test No. Type 3 H/D = 8 Deep Vertical 4 H/D = 8 Deep Vertical 5 H/D = 10 Deep Vertical 6 H/D = 10 Deep Vertical Anchor Deflection (inches) Short-term field results for deep anchors in marine clay Note: 1 Kip = 4.45 kn, 1 in= 25.4 mm

68 LONG TERM TEST IN PROGRESS Danger High Voltage!!

69 RESULTS OF LONG TERM LOADS 0 FOR ANCHORS IN SAND 10.5 K 20 K Anchor Deflection (inches) K Failure 30 K 40 K Long Term Anchor Test Sand Site Test No. 12 Dixie Anchor Vertical H/D= Time (minutes) Anchors sustained applied loads with minimal deflection until failure load was reached

70 RESULTS OF LONG TERM LOADS FOR ANCHORS IN CLAY 4 K 6 K 8 K K 12 K Long Term Anchor Test Clay Site Test No. 10 Vertical H/D=8 14 K Time (minutes) Anchors sustained applied loads with minimal deflection until failure load was reached

71 LABORATORY ONE-QUARTER SCALE ANCHOR TESTS Special, longitudinally split tank used to test anchors in clay After the test is completed, the tank is laid on its side and split open to examine the failure surface

72 A specially adapted grease gun was used to inject lines of white grease into the clay mass before testing the anchor

73 REMOVING HALF OF THE TANK Anchor is retained in place and the tank is split open

74 ANCHOR FAILURE SURFACE IN CLAY Close up of failure wedge above anchor

75 ANCHOR PLACED IN SAND

76 PROPOSED FAILURE MODE FOR ANCHORS IN SAND The failure mode in sands based on the frictional cylinder model Total uplift capacity is the sum of plate bearing capacity and the frictional resistance along the failure surface

77 H 1 Q u Soil Surface INDIVIDUAL PLATE CAPACITY THEORY H 3 H 2 Based on spacing on the helix plates (3 to 4 diameters) the anchor plates behave as individual units Helix Spacing > 3-4 Diameters

78 INDIVIDUAL BEARING PLATE MODEL Theory & Design Total capacity equal to sum of individual helix bearing capacities Capacity due to friction along shaft generally assumed negligible Example: Q H = ΣA(cN C + qn q ) where A = Area of helical bearing plate c = Soil Cohesion q = Overburden Stress γ = Unit Weight of Soil B = Helix Diameter N C, N q, & N γ = Bearing Capacity Factors

79 EFFECT OF DOWN DRAG Theory & Design Grade Q t = Q H - Q f Consolidating Overlying Strata Shaft Section Q f = Σ[πDf s L f ] End Bearing Stratum Helix Plates Q H = ΣΑ(Ν c C + qn q ) Note: Down drag can occur for either grouted or ungrouted shafts. The effect is proportionate with shaft diameter. Down drag is generally due to site grading fill recently placed over soft or loose soils.

80 RELIABILITY OF TORQUE/CAPACITY MODEL Theory & Design Uplift Capacity of Helical Anchors in Soil (Hoyt & Clemence 1989) Analyzed 91 load tests 24 different test sites Sand, silt, and clay soils represented Calculated capacity ratio (Q act /Q calc ) Three different load capacity models Cylindrical shear Individual bearing Torque correlation Torque correlation method yields more consistent results than either of the other two methods and is best suited for on-site production control and termination criteria

81 HISTOGRAM OF RATIOS OF ACTUAL/COMPUTED CAPACITY: INDIVIDUAL PLATE BEARING METHOD Occurrence s Log α Normal = β = 0.82 μ = 1.64 σ = 1.39 R.05 = 0.30 PDF Uplift capacity data was collected from a large number of full scale field tests and compared with theoretical predicted capacity. Note that 1.0 indicates exact agreement between measured and predicted capacity!

82 HISTOGRAM OF RATIOS OF ACTUAL/COMPUTED CAPACITY: CYLINDRICAL SHEAR METHOD 24 Log Normal PDF 20 α β = = 0.72 Occurrences μ = 1.52 σ = 1.20 R.05 = Results from cylindrical shear model

83 HISTOGRAM OF RATIOS OF ACTUAL/COMPUTED CAPACITY: TORQUE CORRELATION METHOD Occurrences Log α Normal = β = 0.51 μ = 1.48 σ = 1.02 R.05 = 0.56 PDF Ratio Q act. /Q calc. Results from Torque Prediction Model: note how close to 1.0 the results are!

84 ISSFME CONFERENCE Presentation on results of analysis of anchor was done at an International Conference on Soil Mechanics and Foundations in Rio de Janeiro, Brazil. Note the hang glider coming off of the mountain (not anyone from the conference!)

85 INSTALLATION TORQUE CORRELATIONS The Torque Required to Install a Helical Foundation or Anchor is Empirically and Theoretically Related to Ultimate Capacity. Theory & Design Q ult = K t T Where: Q ult = Ultimate Capacity [lb (kn)] K t = Empirical Torque Factor [ft-1 (m-1)] Default Value = 10 (33) for 1.5 & 1.75 Square Shaft Default Value = 8 (26) for 3 Round Shaft Default Value = 7 (23) for 3.5 Round Shaft T = Final Installation Torque [ft-lb (kn-m)]

86 INSTALLATION TORQUE VS. ULTIMATE CAPACITY Theory & Design K t is not a constant - may range from 3 to 20 ft.-1 (10 to 66 m - 1 ). Depends on: Soil Conditions Normally consolidated clay K t = 10 Overconsolidated clay K t = Sensitive clay K t < 10 Sands K t = 12+ Central Steel Shaft/Helix Size K t inversely proportional to shaft size Helix Thickness K t inversely proportional to helix thickness Application (Tension or Compression) Compression capacity is generally higher than tension capacity although often assumed equal for simplicity

87 TORQUE ADVANTAGES Theory & Design Provides excellent field control method of installation Monitors soil conditions Torque is a direct measure of soil shear strength Predicts holding capacity of the soil Helical foundations/tiebacks can be installed to specified torque

88 FACTOR OF SAFETY Theory & Design Select an appropriate Factor of Safety (FS) to be applied to the Ultimate Capacity of the anchor/foundation to develop a design, or Working Capacity per anchor/foundation. In general, it is recommended to use a minimum FS =2.0.

89 SLENDERNESS RATIO/BUCKLING Theory & Design Research shows elastic buckling is a practical concern only in the softest soils. Soil provides lateral support to shaft. Practical Guideline: Soil with ASTM D-1586 blow count of 4 or less. Very soft & soft clays Very loose sands Computer programs available for analysis LPILE (ENSOFT. Austin, TX) Finite Element Software - ANSYS

90 FOUNDATION SPACING Theory & Design 5D or 5 ft. Recommended 3 ft. Minimum φ D 5D or 5 ft. Recommended 3 ft. Minimum

91 Theory & Design Lateral Load Capacity Bending Moment Distribution in Pile Enlarged Shaft Section Analysis Methods: 1. Broms 2. Finite Difference (LPILE) 3. Finite Element

92 Theory & Design Lateral Load Capacity Grade Beam & Pile Cap Passive Earth Pressure Resistance Optional Lateral Tieback

93 Theory & Design Lateral Load Capacity Battered Piles Pile Cap

94 CORROSION Theory & Design The data indicate that undisturbed soils are so deficient in oxygen at levels a few feet below ground line or below the water table zone, that steel pilings are not appreciably affected by corrosion, regardless of the soil types or the soil properties. from National Bureau of Standards Monograph 127 by Romanoff Romanoff s monograph pertained primarily to driven steel piling that are traditionally designed using lower allowable stresses. Near surface, the top of helical foundations and anchors should be protected from corrosion by encasement in concrete, proper drainage, and other precautions. Helical piles must be designed for corrosion by taking into account sacrificial thickness lost to corrosion. For permanent structures, corrosion may be accounted for adjusting shaft section properties by the sacrificial thickness per ICC ES AC358.

95 Theory & Design ANCHOR/PILE FOUNDATION SELECTION Specified screw anchor type is based on the required load Mechanical axial load rating must equal or exceed required load plus a factor of safety. Specified screw anchor type is based on the required installation torque. Mechanical torque rating must equal or exceed the anticipated installation torque.

96 PULLDOWN PILES Dense Bearing Stratum Grouted Column Displacement Plate Screw Anchor Recent development involves the combination of helical anchors and grouting. As the helical anchor is installed grout is introduced around the anchor shaft with the use of displacement plates. The result is a helical pile with a grouted shaft that can withstand compressive as well as tensile loads. Compressive capacities of over 100,000 pounds have been measured for PULLDOWN piles.

97 EFFECT OF GROUTED SHAFT Theory & Design Grade Q t = Q H + Q f Stable Overlying Strata Grouted Shaft Section Q f = Σ[πDf s L f ] where: D = Diameter of Grouted Shaft f s = Side Friction and Adhesion L f = Incremental Pile Length End Bearing Stratum Helix Plates Q H = ΣΑ(Ν c c + qn q ) Note: Grouting the shaft of a helical foundation is a proprietary process that can only be done using certain manufacturer s products. Nonetheless, if done, the capacity may be calculated as shown above.

98 PULLDOWN PILE Grout bath

99 PULLDOWN PILE Axial compression test

100 PULLDOWN PILE Displacement plate

101 EXTRACTION OF PULLDOWN PILE Note intact column of grout

102 PULLDOWN PILE Intact grout column

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104 APPLICATIONS

105 EXCAVATION SHORING Application

106 EARTH RETENTION Application

107 Application Electric Transmission Structures

108 TOWER GUY ANCHORS Application

109 PIPELINE BUOYANCY CONTROL Application

110 RECENT APPLICATIONS Construction of large diameter natural gas pipeline in frozen Muskeg in northern Canada in midwinter

111 SECTION OF PIPELINE IN CANADA 5000 pound concrete weights used for buoyancy control to keep pipeline from floating up when swamp thaws out!

112 CANADIAN PIPELINE Thousands of these weights are used on the pipeline.

113 CANADIAN PIPELINE Weights in place

114 CANADIAN PIPELINE Anchoring system for pipelines using helical anchors and a lightweight bracket in place of expensive and bulky concrete weights. The anchors are screwed into the ground below the frost line into more stable, unfrozen soil that holds the pipeline in place throughout the year.

115 CANADIAN PIPELINE Special power torque installation system designed to install anchors in frozen soils

116 RECENT APPLICATIONS SUPERSTORM SANDY DAMAGED HOUSE Hampton Bays, NY Helical piles be used to support the new poured wall foundation

117 Floor Slabs Application

118 Residential Foundations Application

119 Multi Story Structure Foundations Application

120 WALKWAYS FOR WETLANDS Application

121 NATURE WALKS Application

122 Residential Additions Application

123 DECKS & GAZEBOS Application

124 UNDERPINNING Application

125 UNDERGROUND STRUCTURES Application

126 THE OPPORTUNITIES ARE ENDLESS Application Signage Elec Util Government Industrial Soil Control Awnings/Canopies Elec Trans Guys Airports Equipment Fdn Agriculture Outdoor Advertising Elec Trans Fdn Bridges Mines Erosion Control Sound Walls Substation Fdn HUD Housing Nuclear/Chem Sites Slope Retention Roadway Wind Generators Flagpole Aquaculture Military Commercial Amusement Marine Parks Commercial Structure Miscellaneous Parks Bulkheads Metro Rail Constr Equip Fdns Burial Vaults Athletic Fields Moorings Native Amer Reserv Elevator Pits Load Test Anchors Circus Marine Constr Railroad Parking Lots Logging Golf Rural Roadway/DOT PreEngr Metal Buildings Seismic Areas Stadiums TELCOM Tunnel Approach Tiebacks Specialty Lighting Zoos Call Box Urban Roadway Cell Towers Waste Water Facilities Residential Cell Twr Site Equip Fdn Residential Fdn & Walls Tiebacks Oil Oilfield Pipeline

127 RECENT ADVANCES IN RESEARCH

128 PERSPECTIVE 50 to 20 years ago Utility anchors 20 to 10 years ago Underpinning and repair of existing foundations Last 10 years - New foundations for residential and commercial structures

129 NEW GROWTH AREAS

130 INCREASE IN PATENTS AWARDED

131 NEW APPLICATIONS New construction applications as a feasible alternative to traditional foundation methods (drilled shafts or driven piles) Wind turbines, solar panels, transmission towers, oil and gas and telecommunication towers Applications for earthquake resistant foundations and seismic retrofit of existing structures

132 NEW APPLICATIONS CONT. High pressure grouted helical piles can be used to increase the capacity of helical piles. seismic retrofit for structures Higher Capacity, Larger Diameter Helical Piles trend toward higher strength steel Helical piles will be embraced by LEED programs and environmentalists, better technology and more use of sacrificial anodes

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134 FIRST INTERNATIONAL SYMPOSIUM Over forty papers submitted from North America, South America, Europe and Asia Topics Included: Review of Full Scale Field Studies on Screw Piles and Helical Anchors Review of Centrifugal Modeling of Helical Foundations Factors Affecting Torque Correlation Case Histories from USA, China and South America Sponsoring Society : International Society for Helical Foundations

135 Continued Study FINAL INFORMATION INDUSTRY ORGANIZATIONS DFI (Deep Foundations Institute) ASCE (American Society of Civil Engineering) International Society for Helical Foundations helicalfoundations.org HelicalPileWorld.com SOFTWARE HeliCap LPILE (ENSOFT. Austin, TX) Finite Element Software - ANSYS

136 CONCLUSION HELICAL FOUNDATIONS & ANCHORS ARE A VIABLE FOUNDATION SYSTEM

137 ACTUAL CONCLUSION ENGINEERING PHILOSOPHY