1MicropilesMicropilesin Constructionin ConstructionChallengesChallenges&&Lessons LearntLessons LearntMicropilesMicropiles -- TimelineTimeline19521952 -- First introduced in Italy for foundationFirst introduced in Italy for foundationrestorationrestoration (underpinning)(underpinning) of WWII damagedof WWII damagedbuildingsbuildings1960’s1960’s –– Widely used in Europe forWidely used in Europe forunderpinning 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
2MicropileMicropile ApplicationsApplicationsSupporting New Loads in Congested AreasSupporting New Loads in Congested AreasSeismicSeismic RetrofitRetrofitArresting Structural SettlementArresting Structural SettlementResisting Uplift/Dynamic LoadsResisting Uplift/Dynamic LoadsUnderpinningUnderpinningExcavation Support in Confined AreasExcavation Support in Confined AreasWhy isWhy is MicropilesMicropiles stillstillunattractive in the South?unattractive in the South?Challenges today…Challenges today…
3ChallengesChallengesNo.1 : High CO$TRM$150–350 /meterPrice Depends on :Reinforcement TypeVolume (φ) of holeGrouting Method (any post grouting)Location - AccessibilityLength/Quantity of pilesChallengesChallengesWhy High CO$T?High Steel (up to 20% As/Ac)High Labour Cost – Low ProdGrout (NS) (+admixture) expensiveFabricate cage in-situ compared tomass production for precast RC pileSpecialist technology expensiveFew players in the market
4ChallengesChallengesNo.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/dayChallengesChallengesWhy 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 bitdifficult – slow down during drillingStart-up check/servicing of rig long
5ChallengesChallengesNo.3a :RisksDamage topublicpropertieswhilemaneuvering/setting-up/drilling.ChallengesChallengesNo.3b : RisksDamage to ownequipment:Rod shears off &drop into hole.Rod/DTH getsstuck in-hole.Rig gets stuck insoft soilWhere’s the other half of mybody???Can thecarwashtake this?
6ChallengesChallengesNo.4 : Prepare for amessy, messy, messy mess…DTH HammerAir-FlushingDad’s favourite “PasarMalam” umbrella…ChallengesChallengesWet, Soggy, Soft ground from washboring makes it difficult to maneuverHelp!!! I’ve lostthe last pile wedrilled – can’tsee a thing!You justcrawled overit!!Whatnow!!!
7ChallengesChallenges -- YESTERDAYYESTERDAYLeading to -ve General PerceptionYou must bejoking.TooExpen$ive!Where aman canenter, Ican installaMicropileI know thePROBLEMS! Idon’t wantto take therisk.But theBENEFITSblah, blah,blah…The Construction Industry TODAYThe Construction Industry TODAYComplicated StructuresComplicated StructuresConstricted AccessConstricted AccessConfined SpaceConfined SpaceDifficult sitesDifficult sitesSpecial Foundations…..Special Foundations…..
8But Still – MICROPILES are bestwhen it comes to DIFFICULTSpecial sites!I need Capacitybut NO Space!I need 3mrocksocketing!I also need highlateral capacity pilesby this slope.TODAYEureka!MICROPILEBoleh!…Bore pile too BIG– need somethingtiny.19801990TodayBenefits ofBenefits of MicropilesMicropilesWhen you haveWhen you haveproblems ofproblems oflow headroomlow headroomand restrictedand restrictedaccess…access…No.1Reason
9Benefits ofBenefits of MicropilesMicropiles –– No.1No.1 ReasonReasonLow Headroom /Low Headroom /Restricted AccessRestricted AccessProblemProblemHo Chi Minh City –District 1Restricted Access?Restricted Access?Proposed 8-storey building….50’ x 100’ area
10Benefits ofBenefits of MicropilesMicropilesNo.2 Reason :High Performance•Loading fr 3 – 500 tons!•Higher As/Ac compared to RC Driven pileAs Micropile 4-8% vs As RC Pile <3%-> Better in Bending, Lateral LoadingShear resistance, Seismic performanceBenefits ofBenefits of MicropilesMicropilesHighAs/AcGood forHigh Lateral/SeismicLoading&Bending
11Benefits ofBenefits 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 ofdrilling…Benefits ofBenefits ofMicropilesMicropilesBy various creativeways of drilling…Wash Boring – Roller (Tricone) BitAugerDown Hole HammerBuriedSteel
12Benefits ofBenefits of MicropilesMicropilesNo.4 Reason :Flexibility(Many Ways) to adjust todifficult soils…• Enhance End Bearing•‘Cross-Breed’ with other Ground Improvementtechnique…Benefits ofBenefits of MicropilesMicropilesFlexibility – Suitsthe soil, Suits yourneeds…
13Benefits ofBenefits of MicropilesMicropilesNo.5 Reason :Almost ZEROVibration/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 - stillgives required As but greatly reducesmanpower 2-3men.•Use Ready Mix grout for large groutingquantity with known grouting time.
14Lessons LearntLessons LearntReducing Manpower;• Use slurry pump mixer instead of gravitymixer into agitator tank. A little moreinvestment goes a long way.•Use a crane to install steel cages/steel pipesinstead of using the rig’s winch/rotary•For large quantities & long term job – install asilo on-site (or get a supplier do so)•With 2 or more rigs, always work close by &cut the manpower for drilling helper & assistantdriller.Typical Manpower RequirementTypical Manpower Requirement14 men14 men3 piles/day/rig3 piles/day/rigTOTALTOTALProductionProduction2 @ grout mixer2 @ grout mixer1 @ agitator tank1 @ agitator tank1 pump operator1 pump operator11 hosemanhosemanGrouting etcGrouting etc1 welder1 welder2 general workers2 general workersFabricationFabrication1x2 driller1x2 driller2x2 helpers2x2 helpersRig (2 No.)Rig (2 No.)e.g. 100 micropiles, wash bore, φ250mm, 20m, 2 rigs.Can cut down toonly 8-9 men forconcurrent activityplanning & utilisingready mix or slurrypump mixer, steelpipe & crane.Production >4piles/day/rigOverall cost reduction ~ 20-30% by increased production.
15Lessons LearntLessons LearntIn a typicalIn a typical micropilingmicropiling site,site,factor infactor in 2020--30%30%time loss due to :time loss due to :• Breakdowns of rig/pump & other supportequipment.• Traffic Congestion on-site (accessibility)• Machines Idling (poor planning) btwdrilling/installation/grouting.Lesson LearntLesson Learnt 22 –– BreakdownsBreakdownsFact : Micropiledrilling rigs canhave up to 30hydraulicswitches & verysusceptible tobreakdown/hydraulicleak/burst.HydraulicHosesIfonebursts…
16Lessons Learnt 2aLessons Learnt 2aFor small sites,use simpler rigswith lowertorque, fasterRPM…(depending on soil type) e.g.SI rigs - fewerbreakdowns.Lessons Learnt 2aLessons Learnt 2aSmall/Constrained sites - SIRig/ Portable Drill frame e.g.‘Jacro’ is the solution!
18Lessons Learnt 4Lessons Learnt 4 -- PlanningPlanningMicropiling Stages in Critical Path (Non-concurrent)1. Setting Out Points + Shifting2. Drilling, Install casing & ensure hole stability3. Flushing & Withdrawal of rods4. Install fabricated rebar5. Flushing & GroutingGroutingPlantTypical Site SetupTypical Site SetupAirCompressorWater TankGroutingPlantFabricationYardCurrentDrillingLocationPreparing togrout pilehereClearing of newarea for settingoutDrillingPumpAccessRdEntrance/Delivery
19Lessons 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 rigGolden Site Rule of Thumb:Where a man can stand on a ground without sinking, arig can also enter.Pressure exerted by your feet = Pressure exerted by rig’s trackLessons Learnt 5Lessons Learnt 5 ––Avoid relying solely on experience without theoryUse the RIGHT Drilling Equipment/Tools :Drilling Rig (Flexible) – Size, Rotary Torque, RPM, maneuverityDrilling Type – Wash Bore, Dry Auger, DTHDrill Bit & Rods – Drag Bit, Roller Bit, DTH (flat/convex), Tubex.Pump – Recirculating fluid – Diaphragm pump / Piston pump.
20Monitor drilling parameters :Thrust Force on Drilling bitDrilling Fluid Flow Rate & PressureRotary/top drive RPMRotary/top drive torqueAir Compressor Output PressureRecirculating Fluid ViscosityWhy?Thrust Force : The thrust force is the force acting along the axis ofthe drill during cutting. The thrust force plays a significant role in thebuckling of the drill.Torque/RPM : The Torque/RPM signifies the power needed by themachine tool to drill the hole. Also, Torque acting on the drill can resultin torsional vibrations affecting hole quality.Lessons Learnt 6Lessons Learnt 6Avoid Pile Failures - Avoid Soft Toe• Clean the TOE – flush well tillCLEAR water appears beforegrouting !• Tremie tube to be fixed at tip oflast casing.
21Lessons Learnt 7Lessons Learnt 7ESTIMATING PILE CAPACITY ON-SITEWash 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/m2End Bearing, fb = 400N/3 or 10000 kN/m2(whichever is lesser)Where a man can enter, amicropile can be installed…Where a micropile can be installed byman, the pile can be tested by man…… by the Micro PDA Hammer Rig. !
22MICROPILES 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 CapacityThe Future TelescopicThe Future Telescopic MicropilingMicropiling RigsRigs