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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,

silty soil,3m casing 2 piles/day

-ditto- sandstone/granite socket 2m, DTH Hammer 2-3 piles/day

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

Complicated StructuresComplicated StructuresConstricted AccessConstricted AccessConfined SpaceConfined SpaceDifficult sitesDifficult sitesSpecial Foundations…..Special Foundations…..

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But Still – MICROPILES are best when it comes to DIFFICULT Special sites!

I need Capacity but NO Space!

I need 3m rock

socketing!

I also need high lateral capacity piles

by this slope.

TODAY

Eureka! MICROPILE

Boleh!…

Bore pile too BIG – need something

tiny.

1980

1990

Today

Benefits of Benefits of MicropilesMicropiles

When you have When you have problems of problems of low headroom low headroom and restricted and restricted access…access…

No.1 Reason

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Benefits of Benefits of MicropilesMicropiles –– No.1 No.1 ReasonReason

Low Headroom /Low Headroom /Restricted Access Restricted Access

ProblemProblem

Ho Chi Minh City –District 1

Restricted Access?Restricted Access? Proposed 8-storey building….

50’ x 100’ area

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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.

Typical Manpower RequirementTypical Manpower Requirement

14 men14 men3 piles/day/rig3 piles/day/rig

TOTAL TOTAL ProductionProduction

2 @ grout mixer 2 @ grout mixer 1 @ agitator tank1 @ agitator tank1 pump operator1 pump operator1 1 hosemanhoseman

Grouting etcGrouting etc

1 welder1 welder2 general workers2 general workers

FabricationFabrication

1x2 driller1x2 driller2x2 helpers2x2 helpers

Rig (2 No.)Rig (2 No.)

e.g. 100 micropiles, wash bore, φ250mm, 20m, 2 rigs.

Can cut down to only 8-9 men for concurrent activity planning & utilisingready mix or slurry pump mixer, steel pipe & crane.

Production >4piles/day/rig

Overall cost reduction ~ 20-30% by increased production.

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Lessons LearntLessons LearntIn a typical In a typical micropilingmicropiling site,site,

factor in factor in 2020--30%30%time loss due to :time loss due to :

• Breakdowns of rig/pump & other support equipment.

• Traffic Congestion on-site (accessibility)

• Machines Idling (poor planning) btw drilling/installation/grouting.

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…

Crane saves manpower/r

ig time

Steel casing instead of

rebar saves fabrication

Site clean & well-kept makes

maneuvering easy

Small drill rigs (SI rig) with high RPM for

easy soil condition

Concurrent drilling & work close together

saves manpower

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Lessons Learnt 4 Lessons Learnt 4 -- PlanningPlanningMicropiling Stages in Critical Path (Non-concurrent)

1. Setting Out Points + Shifting

2. Drilling, Install casing & ensure hole stability

3. Flushing & Withdrawal of rods

4. Install fabricated rebar

5. Flushing & Grouting

Grouting Plant

Typical Site SetupTypical Site Setup

Air Compressor

Water Tank

Grouting Plant

Fabrication Yard

Current Drilling Location

Preparing to grout pile

here

Clearing of new area for setting

out

Drilling Pump

Access R

d

Entrance/Delivery

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Lessons Learnt 4Lessons Learnt 4Damages to public property/own equipment…

• Make sure you have adequate COVER (+ 3rd party – public injury + property)

• Clear the MESS!

• Check drilling rig / pump regularly

• Check for cracks on drilling rods/joints regularly

• Test the ground before bringing in the rig

Golden Site Rule of Thumb:

Where a man can stand on a ground without sinking, a rig can also enter.Pressure exerted by your feet = Pressure exerted by rig’s track

Lessons Learnt 5 Lessons Learnt 5 ––Avoid relying solely on experience without theory

Use the RIGHT Drilling Equipment/Tools :Drilling Rig (Flexible) – Size, Rotary Torque, RPM, maneuverity

Drilling Type – Wash Bore, Dry Auger, DTH

Drill Bit & Rods – Drag Bit, Roller Bit, DTH (flat/convex), Tubex.

Pump – Recirculating fluid – Diaphragm pump / Piston pump.

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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.

Lessons Learnt 6Lessons Learnt 6Avoid Pile Failures - Avoid Soft Toe

• Clean the TOE – flush well till CLEAR water appears before grouting !

• Tremie tube to be fixed at tip of last casing.

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Lessons Learnt 7Lessons Learnt 7ESTIMATING PILE CAPACITY ON-SITE

Wash Boring;

Rate of Drilling 1m in ½ hrs –eqv- SPT N=100

(Linearly proportional 1m in 15min eqv N=50…)

Skin Friction, fs = 2N kN/m2

End Bearing, fb = 400N/3 or 10000 kN/m2

(whichever is lesser)

Where a man can enter, a micropile can be installed…

Where a micropile can be installed by man, the pile can be tested by man…… by the Micro PDA Hammer Rig. !

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MICROPILES TODAYAre different from their predecessors…

They are now:•Cheap – suits your Budget

•Easy/Fast to Install•High Tech – less labour

•Very High Axial/ Lateral/Bending Capacity

The Future Telescopic The Future Telescopic MicropilingMicropiling RigsRigs

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Solutions for the Difficult Ground