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Introduction to Micropile Design 101

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Presentation for

Arizona Ram Jack Seminar

Introduction to micropile analysis,

design, and construction with

TITAN Micropiles

January 15, 2010

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Agenda

• Introduction to Con-Tech Systems Ltd

• TITAN Injection Bore (IBO) Anchor System

• Corrosion Protection

• Micropile Design

• Micropile Geotechnical Capacity

• Micropile Structural Capacity

• Sample Design Calculation for TITAN Micropile

• Micropile Testing

• Installation Equipment

• The ADSC

• References

4Give up?

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Polish!!

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This presentation is made by Con-Tech Systems Ltd

Josef (Joe) Alter

Sales and Engineering ManagerSouthwest Region USACon-Tech Systems Ltd24424 Manzanita DriveDescanso, CA 91916

TEL: 619-659-9931 FAX: 619-659-9932 CELL: 619-894-2616

For a more detailed list of products and systems, please refer to our Web Site:

www.contechsystems.com/cts-cd

7CORPORATE OFFICE & CANADIAN PLANT

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CTS Warehouses and Offices

in North America

Descanso, CANew Port

Richey, FL

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Micropile Definition

• A micropile is a small-diameter (typically less than 300 mm (12 in.)), drilled and grouted non-displacement pile that is typically reinforced.

• A micropile is constructed by drilling a borehole, placing steel reinforcement, and grouting the hole.

• Micropiles can withstand relatively significant axial loads and moderate lateral loads.

• Micropiles are installed by methods that cause minimal disturbance to adjacent structures, soil, and the environment.

• They can be installed where access is restrictive and in all soil types and ground conditions.

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Where to Consider Micropiles

• project has restricted access or is located in a remote area;

• required support system needs to be in close pile proximity to existing structures;

• ground and drilling conditions are difficult (e.g., karstic areas, uncontrolled fills, boulders);

• pile driving would result in soil liquefaction; • vibration or noise needs to be minimized; • hazardous or contaminated spoil material will be

generated during construction; and • adaptation of support system to existing

structure is required.

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Typical Micropile Construction

Sequence Using Casing

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Construction Type Classification

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TITAN Injection Bore Anchor

System and Components

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CTS/TITAN IBO SystemCTS/TITAN IBO System

The Flushing/Stabilizing Grout is injected

through the inside of the hollow Titan bar and

exits through the venturi holes in the Drill-Bit.

Flushing/Stabilizing Grout stabilizes Flushing/Stabilizing Grout stabilizes the

borehole and flushes the cuttings out of the

hole.

The hollow bars with a typical length of 3m

are coupled and drilled to required depth.

After reaching the final depth, the pressure

injection continuous.

With the continuous Injection stage,Injection stage, the

flushing grout will be replaced with a richer

grout.

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Typical cross

section of an

exhumed IBO®

Micro-Pile1

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3

41- Hollow Bar

2- Final Grout W/C 0.45

3- Flushing grout W/C 0.7 Soil Cement mix

4- Ground improvement

Hollow TITAN Bar Ultimate Yield

Dout/Dinin

2kips kips in

mm mm2

kN kN mm

30/16 0.59 49.5 40.5 1.18

382 220 180 30

30/14 0.61 58.5 49.5 1.18

395 260 220 30

30/11 0.69 72.0 58.5 1.18

446 320 260 30

40/20 1.13 121.2 96.7 1.57

726 539 430 40

40/16 1.36 148.4 118.1 1.57

879 660 525 40

52/26 2.07 208.9 164.2 2.05

1337 929 730 52

73/53 2.53 260.9 218.1 2.87

1631 1160 970 73

103/78 4.88 513.2 404.8 4.06

3146 2282 1800 103

103/51 8.53 778.1 618.4 4.06

5501 3460 2750 103

130/60 14.79 1785.5 1180.6 5.12

9540 7940 5250 130

Steel

AreaRod Size

Load Capacity Nominal

Dia.

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Drill Bit

Hollow Titan Bar

Centraliser

Coupling

Bearing Plate

Hex Nut

Pipe Sleeve

CTS/TITAN Hollow Bar System

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Clay Bit: Clay, sand-mixed Ground without Boulders < 50 S.P.T

Carbide-Bit:

For controlled directional drilling (tolerance < 2% of the length)

Button Bit:

Dolomit, Granite, Sandstone; strength 70-150 MPa

Carbide Step Bit:

Weathered Rock, Phylit, Slate, Shale; strength < 70 MPa

Carbide Button Bit: Reinforced Concrete or Rock, strength > 70 MPa

Cross Cut Bit: Dense Sand with Gravel and small Boulders > 50 S.P.T

Drill Bit Selection

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Drill Bit Selection Chart

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Full strength

Couplers, to develop

the ultimate strength

of the bar

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Centralizers

to allow for

grout

passage

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Spherical hex nuts,

2 nuts for tension/compression piles,

(bearing plate with top and bottom nut)

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Double nut and

plate connection

to grade beam

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Corrosion Protection

• Epoxy Coating

• Metalizing

• Sacrificial steel

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Sacrificial Steel Method

TITAN 40/20 hollow bar over 60 years

Allowable Design Load: 72.7 kips

• No Ground Aggression:

6.8% Loss = 72.7 kips * 0.932 = 67.8 kips

• Mild Ground Aggression:

11.2% Loss = 72.7 kips * 0.888 = 64.6 kips

• Aggressive Ground Aggression:

18.4% Loss = 72.7 kips * 0.816 = 59.3 kips

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Sacrificial

Steel

Method

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Soil/Cement mix

Drill Bit

Stabilized and densified Soil

Natural Soil

Hollow Bar

2,0 x d for medium to coarse gravel1,5 x d for sand und sandy gravel1,2 x d for cohesive soil (clay)1,0 x d for weathered sandstone, Phylit, slate

D >

d Drill Bit Diameter

Grout cover

min. 20 mm

TITAN Hollow bar Micro Pile

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Micropile Design

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Micropile Design

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Micropile Design

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Micropile Structural Capacity

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STRUCTURAL DESIGN OF MICROPILE

UNCASED LENGTH

From FHWA Design Guidelines

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Structural Design of Uncased

Pile (IBC)

[ ])4.0()33.0('

barbarygroutgroutcallowablec AFAfP ×+×=−−−

barbaryallowablet AFP ×=−−

6.0

Compression

Tension

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Load Test Structural Capacity

[ ])()85.0('

barbarygroutgroutcncompressioult AfAfP ×+×=−−−

[ ]barbarytensionult AfP ×=−−

Micropile Geotechnical Capacity

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Geotechnical Capacity (ASD)

αbond = grout to ground ultimate bond strength

FS = factor of safety applied to the ultimate

bond strength

Db = diameter of the drill hole

Lb = bond length

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Grout to Ground

Adhesion Strength

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Ultimate Bond Stress for Rock to

Grout as Recommended by PTI

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Ultimate Bond Stress for Cohesionless

Soils to Grout as Recommended by PTI

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Ultimate Bond Stress for Cohesive Soils

to Grout as Recommended by PTI

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Sample Micropile Design

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Bond Stress for TITAN Anchors as

Recommended by ISCHEBECK

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Sample Micropile Design

2

2

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Sample Micropile Design

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The hollow bar, used as both drill rod and

grout conduit, is left in the ground as

reinforcing steel to transmit compressive,

tensile, and lateral forces.

Hollow bars have a larger section

modulus than solid bars.

With the continuous tremi-grout injection,

100% grout cover and therefore excellent

corrosion protection is accomplished,

similar to reinforcing steel in concrete.

Summary

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Micropile Testing Procedures and

Guidelines

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Micropile Load Tests

There are four types of test loading:

•compression test

•uplift or tension test

•lateral-load test

•torsion-load test

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Test Procedures for Ground Anchors

•American Society for Testing and Materials ASTM

D1143/D1143M-07. Standard test methods for deep

foundations under static axial compressive load.

•American Society for Testing and Materials ASTM

D3689-07. Standard test methods for deep foundations

under static axial tensile load.

•PTI. (2004). Recommendations for prestressed rock and

soil anchors. Post-Tensioning Institute, Phoenix, AZ.

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Schematic of Compression Load Test Arrangement

(ASTM D1143/D1143M-07)

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Schematic of Tension Load Test Arrangement (ASTM D3689)

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Schematic of Lateral Load Test Arrangement (ASTM D3966)

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Micropile Tension Test

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Micropile and Anchor Testing

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Exhumed TITAN Anchors

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TITAN

Anchor

Drilled

Through

Boulder

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Injection Bore Strengths - Titan

• Fully supported hole during drilling

• Jetting action to over ream hole –uniformly or in isolated areas

• Penetration of the grout beyond the bit diameter or cut hole limit

• Readily adaptable length and injection process to meet site variability conditions

• Somewhat self adjusting to variable soil conditions

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Equipment For Grouting and Drilling

65VS 100

Water gauge with holding tank

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Neat Water/Cement Grout Mix:

Potable Water

Cement Type I, II or III

Drilling and Flushing - W/C = 0.7-1.0

Final Grout - W/C = 0.45

minimum strength at 28 days = 3,000 PSI.

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Obermann VS-63

High speed high shear-colloidal mixer with two mixers, one for the thinner flushing grout and one for the final grout. Water/cement dosing system and double plunger pump;

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The use of an automatic logging system for

measurement, recording and documentation of grout volume and pressure is also recommended.

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The ADSC

• International Scope;

– headquartered in Dallas, Texas

• 9 Regional US Chapters

• Extensive membership list, significant annual operating budget with a far-reaching agenda

• Representing the Drilled Shaft, Anchored Earth Retention and Micropile construction technologies.

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Work of the ADSC includes

– Establishing standards & specifications for the industries it serves

– Promoting ethical practice– Conducting design, construction and inspection

seminars, worldwide– Developing technical materials– Funding and conducting research– Providing a forum for technology transfer– Stimulating industry growth– Interfacing with corresponding industries and

agencies (FHWA, OSHA, DOTs, etc.)

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Available thru the ADSC

• Network of Experienced and Proven Contractors, Design Professionals and Material Suppliers!

• Training Opportunities– Regional seminars,

– Videos and other media

– Design, Safety, Personnel Training Materials

• Technical Resources– On-Line Technical Library

– Technical Papers

– Design Manuals

– Foundation Drilling Magazine

– Specifications

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References

Standard industry reference with detailed examples of micropile design and

applications

Micropile Design and

Construction Reference Manual, 2005, FHWA NHI-05-039

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FHWA Review and Assessment of Hollow Core Soil Nails for Transportation Projects

Soil Nail Design and

Construction State-of-the-Practice, April, 2006

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Provides guidelines for Buckling calculations of micropiles

ADSC-IAF Document

Buckling of Micropiles

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PTI. (2004). Recommendations

for prestressed

rock and soil

anchors. Post-Tensioning Institute. Phoenix, AZ.

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A History of Micropiles and Early Applications from the Inventor

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Web Resources

• http://www.fhwa.dot.gov/engineering/geotech

/library_listing.cfm

• http://www.dfi.org/

• http://www.adsc-iafd.com

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Questions

Comments

Observations

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Thank You for Your Attention