Screw Piles:Screw Piles:Use and DesignUse and Design

Kristen M. TappendenKristen M. Tappenden

November 2006November 2006

ObjectivesObjectives

►► What are screw piles? What are screw piles? ►► geometrygeometry►► fabrication fabrication ►► installationinstallation►► common usescommon uses

►► Why use screw piles? Why use screw piles? ►► advantages over conventional pile typesadvantages over conventional pile types

►► How do we design screw piles? How do we design screw piles? ►► axial failure modelsaxial failure models►► direct pile design approach: LCPC methoddirect pile design approach: LCPC method►► empirical approach: correlates installation effort to axial capaempirical approach: correlates installation effort to axial capacitycity

What are Screw Piles?What are Screw Piles?►► Deep foundations: carry Deep foundations: carry

tensile, compressive, and tensile, compressive, and lateral loadslateral loads

►► Constructed of helical Constructed of helical plates welded to hollow plates welded to hollow steel pipesteel pipe

Emergence of Screw PilesEmergence of Screw Piles►► No related engineering literature exists prior to 1950s/1960sNo related engineering literature exists prior to 1950s/1960s

►► First use of screw piles: First use of screw piles: MaplinMaplin Sands light house in the Thames Sands light house in the Thames estuary in 1838estuary in 1838

Screw Pile GeometriesScrew Pile Geometries

TerminologyTerminology

InterInter--Helix Spacing RatioHelix Spacing Ratio == SS//DD

18 cm diameter shaft18 cm diameter shaft

35 cm diameter helix35 cm diameter helix

5 meter length5 meter length

Shaft diameters: 11 cm to 32 cm (4 ½ to 12 ¾ inches) Shaft diameters: 11 cm to 32 cm (4 ½ to 12 ¾ inches)

Helix diameters: Helix diameters: Commonly 2Commonly 2--3 times the shaft diameter3 times the shaft diameter

30 cm to 91 cm (12 to 36 inches)30 cm to 91 cm (12 to 36 inches)

InstallationInstallation

►► Turning moment applied to the head of screw pile Turning moment applied to the head of screw pile shaft, and pile “twisted” into the groundshaft, and pile “twisted” into the ground

►► Desirable rate of penetration is one helix pitch per Desirable rate of penetration is one helix pitch per revolutionrevolution

►► Video Clip: courtesy of ALMITA ManufacturingVideo Clip: courtesy of ALMITA Manufacturing

Installation EquipmentInstallation Equipment

Screw Pile AdvantagesScrew Pile Advantages

►► Rapid installation (typ. < 30 min per pile)Rapid installation (typ. < 30 min per pile)►► Little installation noise or vibrationLittle installation noise or vibration►► No casing or dewatering requiredNo casing or dewatering required►► Lightweight installation equipment:Lightweight installation equipment:

soft terrainsoft terrain areas of restricted accessareas of restricted access

►► Sustain load immediately after installationSustain load immediately after installation►► May be removed and reMay be removed and re--usedused

temporary structurestemporary structures

►► Resistant to frost heaveResistant to frost heave

Screw Pile LimitationsScrew Pile Limitations

►► Not for use in very hard or rocky soilsNot for use in very hard or rocky soils may sustain damage to the helical platesmay sustain damage to the helical plates piles may be removed and helices checkedpiles may be removed and helices checked

►► Lack of acceptance/understanding in the engineering Lack of acceptance/understanding in the engineering communitycommunity

Typical Screw Pile Uses:Typical Screw Pile Uses:►► Tower foundationsTower foundations

Ft. McMurray, Alberta: 27 cm (10 ¾ in) shaft, one or two 76 cm (30 in) helices, 6 m length

►► Pipeline foundationsPipeline foundations►► Earth retention systemsEarth retention systems►► Guy wire anchorsGuy wire anchors

►► Building Foundations:Building Foundations: WarehousesWarehouses MultiMulti--family Housingfamily Housing Commercial BuildingsCommercial Buildings Modular HomesModular Homes

Hythe, Alberta: 22 cm (8 5/8 in) shaft, single 40 cm (16 in) helix, 8 m length

►►Oil Field FoundationsOil Field Foundations Temporary BuildingsTemporary Buildings Pump JacksPump Jacks CompressorsCompressors TanksTanks

Typically 18 cm (7 in) shaft, single 40 cm (16 in) helix, 7.5 m deep

Screw Pile Failure ModelsScrew Pile Failure Models

►►Cylindrical Shear ModelCylindrical Shear Model

►►Individual PlateIndividual Plate--Bearing ModelBearing Model

Choice of the most representative model depends on Choice of the most representative model depends on the screw pile geometry, in particular the the screw pile geometry, in particular the InterInter--Helix Helix Spacing Ratio (S/D)Spacing Ratio (S/D)

Cylindrical Shear ModelCylindrical Shear Model

After Narasimha Rao et al. (1991)

Effect of InterEffect of Inter--Helix Spacing Ratio Helix Spacing Ratio (S/D)(S/D)

1:1: S/D S/D ≈≈ 1.5 1.5 Cylindrical surface fully formsCylindrical surface fully forms

2: 2: S/D S/D ≈ 2 ≈ 2 Cylindrical surface begins to deteriorateCylindrical surface begins to deteriorate

3: 3: S/D ≈ 4.5 S/D ≈ 4.5 Cylindrical surface nearly nonCylindrical surface nearly non--existentexistent

1 2 3

After Narasimha Rao et al. (1991)

Individual Plate Bearing ModelIndividual Plate Bearing Model

Summary: Failure ModelsSummary: Failure Models

►►Cylindrical Shear Model:Cylindrical Shear Model: MultiMulti--helix screw piles, generally most representative for helix screw piles, generally most representative for

S/D <2S/D <2

►►Individual Plate Bearing Model:Individual Plate Bearing Model: SingleSingle--helix screw pileshelix screw piles MultiMulti--helix screw piles, applicable for S/D>2helix screw piles, applicable for S/D>2

Axial Capacity PredictionAxial Capacity Prediction

►► Theoretical Design MethodsTheoretical Design Methods►►Application of relevant soil strength parameters (Application of relevant soil strength parameters (ssuu ,,αα, , ΦΦ,,γγ,, NNqq, , NNququ))

►► Direct Design Approach: LCPC MethodDirect Design Approach: LCPC Method►►Directly relates results of cone penetration test to ultimate axDirectly relates results of cone penetration test to ultimate axial ial

screw pile capacity, with no intermediate determination of soil screw pile capacity, with no intermediate determination of soil strength parametersstrength parameters

►► Empirical ApproachEmpirical Approach►►Directly correlates measured installation torque to ultimate axiDirectly correlates measured installation torque to ultimate axial al

screw pile capacityscrew pile capacity

Direct Design: LCPC MethodDirect Design: LCPC Method

►► Established design method for predicting the axial capacity Established design method for predicting the axial capacity of conventional piles, based on siteof conventional piles, based on site--specific CPTspecific CPT

►► LCPC method developed in France by the LCPC method developed in France by the LLaboratoireaboratoireCCentral des entral des PPontsonts et et CChauseeshausees, based on results of many , based on results of many fullfull--scale pile load tests (Bustamante and scale pile load tests (Bustamante and GianeselliGianeselli, 1982), 1982)

►► Use of the CPT is advantageous because the test is fast, Use of the CPT is advantageous because the test is fast, repeatable, and provides continuous profile of soil repeatable, and provides continuous profile of soil informationinformation

Direct Design: LCPC MethodDirect Design: LCPC Method

►►Basic premise of LCPC method is to apply Basic premise of LCPC method is to apply scaling (reduction) factors to CPT profile of scaling (reduction) factors to CPT profile of tip resistance to calculate appropriate tip resistance to calculate appropriate components of bearing resistance and components of bearing resistance and friction/adhesionfriction/adhesion

QQtotaltotal = = QQbearingbearing + + QQshaftshaft + + QQcylindercylinder

Direct Design: LCPC MethodDirect Design: LCPC Method

Soil Type Average CPT tip resistance over layer i

Bearing capacity factor

Skin friction factor

Maximum unit skin friction

qc kc α qs

(kPa) (kPa)

Soft clay and mud <1,000 0.50 30 15

Moderately compact clay 1,000 to 5,000 0.45 40 35

Silt and loose sand ≤ 5,000 0.50 60 35

Compact to stiff clay and compact silt > 5,000 0.55 60 35

Soft chalk ≤ 5,000 0.30 100 35

Moderately compact sand and gravel 5,000 to 12,000 0.50 100 80

Weathered to fragmented chalk > 5,000 0.40 60 120

Compact to very compact sand and gravel 12,000 0.40 150 120

LCPC CalculationLCPC Calculation►► Two 36 cm helicesTwo 36 cm helices►► Spacing = 3DSpacing = 3D►► 21 cm shaft21 cm shaft

►► qqss = 35 = 35 kPakPa►► qqb1b1 = 811 = 811 kPakPa►► qqb2b2 = 990 = 990 kPakPa

Calculated Capacity in Compression:Calculated Capacity in Compression:►► Cylindrical Shear: 188 Cylindrical Shear: 188 kNkN►► Individual Plate Bearing: 209 Individual Plate Bearing: 209 kNkN

Calculated Capacity in Tension:Calculated Capacity in Tension:►► Cylindrical Shear: 160 Cylindrical Shear: 160 kNkN►► Individual Plate Bearing: 180 Individual Plate Bearing: 180 kNkN

►► Measured Capacity: 210 Measured Capacity: 210 kNkN in both in both tension and compressiontension and compression

0

1

2

3

4

5

6

7

8

0 1000 2000 3000

qc (kPa)D

epth

(m)

after Zhang (1999)

LCPC MethodLCPC Method——Compression Compression

0.00

1.00

2.00

3.00

4.00

5.00

0 50 100 150 200 250

Axial Capacity (kN)

Dept

h (m

)

QLP, Cylindrical Shear Model QL, Cylindrical Shear Model

QLP, Individual Plate Bearing Model QL, Individual Plate Bearing Model

LCPC MethodLCPC Method

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

C1 C2 C3 T1 T2 T3 C4 C5 C6 T4 T5 T6 C7 C8 C9 C10 C11 C12 T7 T8 T9 C16 C17

Test Pile Designation

Qpr

edic

ted

/ Qm

easu

red

Predicted to Measured Capacity, Cylindrical Shear Predicted to Measured Capacity, Individual Plate Bearing

26 axial load tests, 7 test sites: clay, sand, clay shale, glacial till

LCPC MethodLCPC Method

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

C1 C2 C3 T1 T2 T3 C4 C5 C6 T4 T5 T6 C7 C8 C9 C10 C16 C17

Test Pile Designation

Qpr

edic

ted/

Qm

easu

red

Predicted to Measured Capacity, Cylindrical Shear Predicted to Measured Capacity, Individual Plate Bearing

Empirical Torque CorrelationEmpirical Torque Correlation

►► Direct empirical relationship between torque required to installDirect empirical relationship between torque required to install a given a given screw pile and the pile’s ultimate axial capacityscrew pile and the pile’s ultimate axial capacity

QQultimateultimate = K= Ktt·· T T (after Hoyt and (after Hoyt and ClemenceClemence, 1989), 1989)

►► Analogous to relationship between pile driving effort and pile cAnalogous to relationship between pile driving effort and pile capacity apacity used for driven steel pilesused for driven steel piles

►► Can only predict capacity once pile is installedCan only predict capacity once pile is installed–– best used for fieldbest used for field--level level verification of expected design capacitiesverification of expected design capacities

Torque CorrelationTorque Correlation

0

500

1000

1500

2000

2500

3000

3500

0 50 100 150 200 250 300

Installation Torque (kN-m)

Ultim

ate

Axia

l Pile

Cap

acity

(kN)

Measured Data (11.4 cm shaft piles)Linear Regression, 11.4 cm shaft piles (Kt = 16.9 m-1)Measured Data (14.0 to 40.6 cm shaft piles)Linear Regression, 14.0 to 40.6 cm shaft piles (Kt = 9.19 m-1)

Torque CorrelationTorque Correlation

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

C1 C2 C3 T1 T2 T3 C4 C5 C6 T4 T5 T6 C7 C8 C9 C10 C11 C12 T7 T8 T9 C13 C14 C15 C16 C17 C18 C19 C20

Test Pile Designation

Qpr

edic

ted/

Qm

easu

red

29 screw pile axial load tests, 10 test sites: sand, clay, glacial till, clay shale, sandstone

SummarySummary

►► Screw piles have many advantages, such as ease Screw piles have many advantages, such as ease of installation, immediate loadof installation, immediate load--bearing capacity, bearing capacity, no casing/dewatering requiredno casing/dewatering required

►► LCPC method provides good axial capacity LCPC method provides good axial capacity prediction in clay and sand, but not suitable for prediction in clay and sand, but not suitable for glacial till soilsglacial till soils

►► Torque correlation factors provide good capacity Torque correlation factors provide good capacity prediction for screw piles in a variety of soil typesprediction for screw piles in a variety of soil types

Thank YouThank You

►► Research Partners:Research Partners: Dr. Dave SegoDr. Dave Sego Gerry CyreGerry Cyre Peace Land Piling / Peace Land Power Ltd.Peace Land Piling / Peace Land Power Ltd. ALMITA Manufacturing Ltd.ALMITA Manufacturing Ltd. ATCO ElectricATCO Electric ConeTec Inc.ConeTec Inc.

►► Funding Providers:Funding Providers: Natural Sciences and Engineering Research Council (NSERC)Natural Sciences and Engineering Research Council (NSERC) Alberta Ingenuity FundAlberta Ingenuity Fund University of AlbertaUniversity of Alberta

ReferencesReferencesBustamante, M. and Bustamante, M. and GianeselliGianeselli, L. 1982. Pile bearing capacity prediction by means , L. 1982. Pile bearing capacity prediction by means

of static penetrometer CPT. of static penetrometer CPT. In In Proceedings of the Second European Proceedings of the Second European Symposium on Penetration Testing, ESOPTSymposium on Penetration Testing, ESOPT--II. Amsterdam. II. Amsterdam. BalkemaBalkema Publisher, Publisher, Rotterdam, Vol. 2, pp. 687Rotterdam, Vol. 2, pp. 687--697.697.

NarasimhaNarasimha RaoRao, S., Prasad, Y.V.S.N, and , S., Prasad, Y.V.S.N, and ShettyShetty, M.D. 1991. The behavior of , M.D. 1991. The behavior of model screw piles in cohesive soils. Soils and Foundations, model screw piles in cohesive soils. Soils and Foundations, 3131(2):35(2):35--50.50.

Zhang, D. 1999. Predicting capacity of helical screw piles in AlZhang, D. 1999. Predicting capacity of helical screw piles in Alberta soils. M.Sc. berta soils. M.Sc. Thesis, Department of Civil and Environmental Engineering, UniveThesis, Department of Civil and Environmental Engineering, University of rsity of Alberta, Edmonton, Alberta.Alberta, Edmonton, Alberta.

Questions?Questions?