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Lesson 4

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Lesson 4Construction Techniques and Materials

Learning Outcomes

Describe sequence of construction for a micropileIdentify materials used to construct a micropilemicropileDescribe principle function of these materialsDescribe key elements to good grouting

Basic Construction

Sequence InvolvesDrillingPlacing reinforcementGroutingGrouting

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Typical Micropile Construction Sequence with Casing

ADDITIONAL GROUT

COMPRESSIBLESTRATUM

BEGIN DRILLING&/OR INSTALLATION

OF TEMPORARYCASING

COMPLETEDRILLING TO

DEPTH

REMOVE INNERDRILL BIT &

ROD (IF USED)

PLACEREINFORCEMENT &GROUT (BY TREMIE)

REMOVETEMPORARY

CASING, INJECTFURTHER GROUT

UNDERPRESSURE ASAPPLICABLE

COMPLETE PILE(CASING MAY BELEFT IN PLACETHROUGH THE

COMPRESSIBLESTRATUM)

BEARINGSTRATUM

Drilling Method:Principles of Selection

The method selected must:Provide a stable hole of the required dimensions and within stated tolerancesBe compatible with project access and environmental constraints e g noise andenvironmental constraints, e.g., noise and vibration thresholdsAllow completion of each hole within a single dayBe compatible with spoils handling requirementsConsider presence of hazardous materials

Drilling Method: Principles of Selection

The method selected must:Be capable of drilling in all soil and rock conditionsBe able to drill subhorizontal vertical andBe able to drill subhorizontal, vertical, and inclined holesBe able to drill beneath the water tableNot impart damage to ground or existing foundationsBe able to be controlled and monitored

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Traditional Rigs

Excavator-Mounted Drilling Mast

Purpose-Built Low Headroom Drill Rig

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Typical OverburdenCased Drilling Techniques

Single-tube advancementexternal flush (wash boring)drive drilling (lost point)

Rotary duplexRotary percussive duplex (concentric)Rotary percussive duplex (eccentric)Double head duplexHollow stem augerSonic

Single Tube End of Casing Flush

Rotary Duplex Rod and Casing

Nicholson

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Duplex Drilling

Rotary Percussive Concentric Duplex

Rotary Eccentric PercussiveDuplex Drilling

This one is called TubexTubex

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Double Head Duplex

Hollow Stem Auger

Sonic Drilling Rig

4-18Courtesy: Boart Longyear

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Overburden Drilling Methods(FHWA, 1997)

Legend Percussion (Casing)

Percussion (Rod)

Rotation (Casing)

Rotation (Rod)

Flush Casing

CrownShoe

Rod

Bit

1.Single Tube

Advancement(End of Casing

Flush)

2.Rotary Duplex

3.Rotary PercussiveConcentric Duplex

4.Rotary PercussiveEccentric Duplex

5.“Double Head” Duplex 6.

Hollow-StemAuger

Figure 4-9

High Speed, Low Torque Drilling

Low Speed, High Torque Drilling

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Rotary Percussive Drilling(Down-the-Hole Hammer)

Grouting and Grout Function

Transfers loads from reinforcement to surrounding groundMay be load-bearing portion of pileProtects steel reinforcement from corrosionMay be used as drill fluid during initial drillingSecondary/Post grout enhances soil/grout bond further

Typical Grouting Characteristics

Neat cement grouts with water/cement ratios of 0.40 to 0.50Potable water used to reduce corrosion potentialpotentialType I/II cement (ASTM C150/AASHTO M85), in bag or bulk formAdditives to improve pumpability in special casesCompressive strengths of 28 to 35 MPa (4 to 5 ksi)

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Design Guidelines: Neat Cement Grout

Grouting Equipment

MixersHigh-speed, high-shear colloidal mixers recommendedLow-speed, low-energy mixers (paddle mixers) are occasionally still used

PumpsConstant pressure, rotary-screw type pumps (Moyno)Fluctuating pressure piston or ram pumps

Agitation TanksCombined UnitsBatching and Injection Monitoring Equipment (i.e., QA/QC)

Principles of High Speed High Shear Mixers

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Typical Mobile Mixer/Pump Unit

Various Types of Paddle Mixers/Agitators

Pumps

Moyno Pump (Primary grouting) – high volume, low pressure

[50 gpm at up to 300 psi]

Piston Pump (Secondary, post grouting) – low volume, high pressure

[15 gpm at up to 1200 psi]

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Diagram of Progressive Cavity Pump

Piston Pump as used in Post Grouting

Contemporary Bulk-fed Grouting Module

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Keys to Good Grouting

Grout BatchingWater added to mixer using calibrated tank or flowmeterCement is batched by weight either in bagsCement is batched by weight, either in bags or bulk from a siloAdditives are usually proportioned in relation to weight of cement

Keys to Good Grouting

Grout MixingGrout mixing sequence: water, cement, additivesGrout colloidally (high shear) mixed for a

i f 2 i t d th h ld imaximum of 2 minutes and then held in a paddle agitation tank until neededSafe workability time typically not in excess of 1 hour

Grout Monitoring

Principle of Tube à Manchette Method Postgrouting (i.e., Type D)

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Structural Steel

TypesReinforcing steel bars (rebar)Continuous-thread solid steel barsContinuous thread hollow core steel barsContinuous-thread hollow-core steel bars (injection bore)Steel pipe casingComposite reinforcement

Materials - Steel

Courtesy: Contech Systems

Close up of Bit on Injection-bore Threaded Bar

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Reinforcing Core Steel

Placed either before or after initial tremie grouting (but always before the temporary casing is withdrawn)Reinforcement must be clean of surface soilReinforcement must be clean of surface soil and mud Centralizers used to maintain the specified grout cover

Casing/Pipe

TypicalMill Secondary Oil Field CasingFlush threaded joints 80 ksi min Yield Strengthg

Casing

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Casing

Typical Casing Joint

7-inch Steel Casing for Drilling and Reinforcement

4-48

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Grooved Oversized Holein Existing Foundation

Composite Reinforcement

Courtesy: Hayward Baker

Learning Outcomes

Describe a few key drilling methodsIdentify materials used to construct a micropileDescribe principle function of these materialsDescribe principle function of these materialsDescribe key elements to good grouting

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