1 Lesson 4 schnabel-eng.com Lesson 4 Construction Techniques and Materials Learning Outcomes Describe sequence of construction for a micropile Identify materials used to construct a micropile micropile Describe principle function of these materials Describe key elements to good grouting Basic Construction Sequence Involves Drilling Placing reinforcement Grouting Grouting
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004 Lesson Construction Techniques & Materials 3-12
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1
Lesson 4
schnabel-eng.com
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
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
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)
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