Micropiles Micropiles in Construction in Construction Challenges Challenges & & Lessons Learnt Lessons Learnt Micropiles Micropiles - - Timeline Timeline 1952 1952 - First introduced in Italy for foundation First introduced in Italy for foundation restoration restoration (underpinning) (underpinning) of WWII damaged of WWII damaged buildings buildings 1960’s 1960’s – Widely used in Europe for Widely used in Europe for underpinning old sensitive structures underpinning old sensitive structures mid 70’s mid 70’s – First introduced in USA (New York & First introduced in USA (New York & Boston) Boston) 1980’s 1980’s – Being introduced in East Asia Being introduced in East Asia Today Today – ‘Micro ‘Micro- mini Revolution’ worldwide mini Revolution’ worldwide
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MicropilesMicropilesin Constructionin Construction
Challenges Challenges & &
Lessons LearntLessons Learnt
MicropilesMicropiles -- TimelineTimeline19521952 -- First introduced in Italy for foundation First introduced in Italy for foundation restoration restoration (underpinning)(underpinning) of WWII damaged of WWII damaged buildingsbuildings1960’s1960’s –– Widely used in Europe for Widely used in Europe for underpinning old sensitive structuresunderpinning old sensitive structuresmid 70’smid 70’s –– First introduced in USA (New York & First introduced in USA (New York & Boston)Boston)1980’s1980’s –– Being introduced in East AsiaBeing introduced in East AsiaTodayToday –– ‘Micro‘Micro--mini Revolution’ worldwidemini Revolution’ worldwide
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MicropileMicropile ApplicationsApplicationsSupporting New Loads in Congested Areas Supporting New Loads in Congested Areas SeismicSeismic Retrofit Retrofit Arresting Structural Settlement Arresting Structural Settlement Resisting Uplift/Dynamic Loads Resisting Uplift/Dynamic Loads Underpinning Underpinning Excavation Support in Confined Areas Excavation Support in Confined Areas
Why is Why is MicropilesMicropiles still still unattractive in the South?unattractive in the South?
Challenges today…Challenges today…
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ChallengesChallengesNo.1 : High CO$TRM$150–350 /meter
Price Depends on :Reinforcement Type
Volume (φ) of holeGrouting Method (any post grouting)Location - AccessibilityLength/Quantity of piles
ChallengesChallengesWhy High CO$T?
High Steel (up to 20% As/Ac)High Labour Cost – Low ProdGrout (NS) (+admixture) expensiveFabricate cage in-situ compared to mass production for precast RC pileSpecialist technology expensiveFew players in the market
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ChallengesChallengesNo.2 : SLOWWash Boring Φ250mm x 25m,Drag/roller bit, 4T25 cage,
ChallengesChallengesWhy SlowAlthough Drilling rate alone is high(e.g. up to 1’/min DTH thru granite)
Adding/Dismantling of Rods manuallyInstallation/Extract of casing time-consumingManual in-situ fabrication of cage on-siteFixing of couplers, spacers, welding take timeManual mixing of cement groutSame machine used for cage installationHigh rig breakdown (mostly hydraulic)Estimation of soil / selection of drill bit difficult – slow down during drillingStart-up check/servicing of rig long
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ChallengesChallengesNo.3a : Risks
Damage to public propertieswhile maneuvering/setting-
up/drilling.
ChallengesChallengesNo.3b : RisksDamage to own
equipment:Rod shears off & drop into hole.Rod/DTH gets stuck in-hole.Rig gets stuck in soft soil
Where’s the other half of my body???
Can the carwash
take this?
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ChallengesChallengesNo.4 : Prepare for a messy, messy, messy mess…
DTH Hammer Air-Flushing
Dad’s favourite “PasarMalam” umbrella…
ChallengesChallengesWet, Soggy, Soft ground from wash
boring makes it difficult to maneuver
Help!!! I’ve lost the last pile we drilled – can’t see a thing!
You just crawled over
it!!
What now!!!
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Challenges Challenges -- YESTERDAYYESTERDAYLeading to -ve General Perception
You must be joking.
Too Expen$ive!
Where a man can enter, I
can install a
Micropile
I know the PROBLEMS! I don’t want to take the
risk.
But the BENEFITS blah, blah,
blah…
The Construction Industry TODAYThe Construction Industry TODAY
Benefits of Benefits of MicropilesMicropilesNo.2 Reason :High Performance•Loading fr 3 – 500 tons!
•Higher As/Ac compared to RC Driven pile
As Micropile 4-8% vs As RC Pile <3%
-> Better in Bending, Lateral Loading
Shear resistance, Seismic performance
Benefits of Benefits of MicropilesMicropilesHigh
As/Ac
Good for
High Lateral/
SeismicLoading
&
Bending
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Benefits of Benefits of MicropilesMicropilesNo.3 Reason :Can Penetrate Anything• Drilling thru stiff clay, sandstone, timber, granite (except buried steel). •Easier penetration in rock compared to bored pile.
By various creative ways of drilling…
Benefits of Benefits of MicropilesMicropiles By various creative
ways of drilling…
Wash Boring – Roller (Tricone) Bit
Auger
Down Hole Hammer
Buried Steel
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Benefits of Benefits of MicropilesMicropilesNo.4 Reason :
Flexibility
(Many Ways) to adjust to difficult soils…• Enhance End Bearing
•‘Cross-Breed’ with other Ground Improvement technique…
Benefits of Benefits of MicropilesMicropiles
Flexibility – Suits the soil, Suits your needs…
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Benefits of Benefits of MicropilesMicropilesNo.5 Reason :
Almost ZERO Vibration/Noise.NO Complains!
Lessons LearntLessons LearntLesson 1 :
Micropiles are LABOUR INTENSIVE!Cost $ can be reduced by :
Reducing Manpower;•Using Steel Pipes as alternative to rebars - still gives required As but greatly reduces manpower 2-3men.
•Use Ready Mix grout for large grouting quantity with known grouting time.
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Lessons LearntLessons LearntReducing Manpower;• Use slurry pump mixer instead of gravity mixer into agitator tank. A little more investment goes a long way.
•Use a crane to install steel cages/steel pipes instead of using the rig’s winch/rotary
•For large quantities & long term job – install a silo on-site (or get a supplier do so)
•With 2 or more rigs, always work close by & cut the manpower for drilling helper & assistant driller.
Lesson Learnt Lesson Learnt 2 2 –– BreakdownsBreakdownsFact : Micropiledrilling rigs can have up to 30 hydraulic switches & very susceptible to breakdown/ hydraulic leak/burst. H
yd
rau
lic
Ho
ses
If o
ne b
urs
ts …
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Lessons Learnt 2aLessons Learnt 2aFor small sites,use simpler rigswith lower torque, faster RPM…(depending on soil type) e.g.
SI rigs - fewer breakdowns.
Lessons Learnt 2aLessons Learnt 2aSmall/Constrained sites - SI Rig/ Portable Drill frame e.g. ‘Jacro’ is the solution!
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Lessons Learnt 2aLessons Learnt 2aSmall/Constrained sites using SI Rig / Drill Frame
Yangon, Myanmar
SI Rig thru Yangon Soil :
Alluvial soil – Stiff silty CLAY, Drag bit, φ500mm, 20m deep, SI Machine – 1-2 piles per day!
In Johor, M’sia:
φ250mm, 20m deep, Drag/Roller bit, soft – medium clay/marine clay; > 1-1.5 piles per day!
Lessons Learnt 3Lessons Learnt 3Plan Well – Accessibility & Maneuverity very important…
Monitor drilling parameters :Thrust Force on Drilling bit Drilling Fluid Flow Rate & PressureRotary/top drive RPMRotary/top drive torqueAir Compressor Output PressureRecirculating Fluid Viscosity
Why?Thrust Force : The thrust force is the force acting along the axis of the drill during cutting. The thrust force plays a significant role in the buckling of the drill.
Torque/RPM : The Torque/RPM signifies the power needed by the machine tool to drill the hole. Also, Torque acting on the drill can result in torsional vibrations affecting hole quality.