Micropile Installation Methods And Selection.ppt
Micropile InstallationMethods and SelectionDr. Donald A. BruceAgenda1. Drilling in Rock and Overburden1 1 Methods1.11.2 Flushing Characteristics1.3 Monitoring While Drilling2. Grouting2.1 Classification of Micropiles Based on Grouting Method2.2 Means, Methods and Materials2.3 QA/QC3. Storage Handling and Placement of Reinforcement4. Growth of the Micropile Market in the U.S.5. Final Remarks1
1. Drilling in Rock and Overburden1.1 MethodsScope and Commonalities Scope Typically 3 to 12‐inch diameter.Typically 200‐foot depth.Typically within 30 of vertical or horizontal.Mostly beneath the water table.Required in all types of ground, natural or placed, unconsolidatedor lithified, and will often encounter obstructions.May face Federal regulations, e.g., USACE 1997.Must cause minimal damage to the ground or existing structures.Must allow completion of the hole in one day.Must be consistent and able to be controlled and monitored.Generally contractor‐driven (“performance specification).Scope and Commonalities (continued) Continuous, straight penetrationConstant diameter, stable and clean boreConsistent with the purpose of the drillhole (e.g., grout hole vs. anchor hole)Appropriate combinations of thrust,torque, rotation, percussion, flushCost effectiveDictated by ground, not historical biasEnvironmentally compatible2
Evolution of Rock Drilling MethodsDawn of the ADSC AgeBasic drilling method selection guide for rock using noncoring methods,Littlejohn and Bruce, 1977 (adapted from McGregor 1967).Rock Drilling Methods (Disco Era) Rotary High rpm, low torque, low thrust (blind or core) Low rpm, high torque, high thrust Rotary Percussive Top Hammer Down‐the‐Hole Hammer Direct circulation Reverse circulation Dual fluid drilling Water hammers Rotary Vibratory (Sonic)3
Overburden Drilling MethodsOVERBURDENDRILLING METHODSOverburden isUNSTABLE*Overburden isSTABLE*SolidStemAugerOpen Hole(with RockDrillingMethods)HollowStemAugerHIGH --– Environmental ---- LOWConcernsLOW ----- Presence of -- oubleHeadDuplexLOW ------------------------- Presence of Obstructions ------------------- SEVERELOW ----------------------- Technological Sophistication --------------------- HIGHVERY HIGH ---------------------------------- Instantaneous Penetration Rate Potential -------------------------------- LOWER*Stability refers to the overburden’s ability to maintain the shape and size of the drilled hole without detriment to thesurrounding ground after withdrawal of the drilling system.Basic drill method selection guide foroverburden (Bruce, 2003).Notes on the 2003 Classification Basic subdivision is stable vs.unstable. Stable overburden can bedrilled with SSCFA or rock drillingmethods (e.g., rotary with air).Most overburden is unstable – especially when holes are longand in “difficult” urban settings.Unstable methods are subdivided into 4 categories:1. HSA – but be careful.2. “Combination” methods – can offer original and effectiveproject solutions.3. Slurry‐supported methods – organic polymers offerconsiderable advantages over bentonite.4. Cased methods – now 5.4
Some Evolutionary Notes DTH usually superior to Top Drive or Rotary in Rock penetration ratesper foot costsd i i controlldeviationlarge diameter ( 40 inches) to greater depths ( 300 feet)Very sophisticated computer programs/simulationsoptimize design for speed, durability, reliability andfor special applications (e.g. “short” hammers andhigh frequency hammers)hammers).PISTON(34 LBS)BIT(33 LBS)New Piston‐Bit Combination (Equal Mass)New Simple, High Frequency RX HammerSome Evolutionary Notes(continued) Air pressures have increased from 160‐250 psi in 1970’s, to up to 500 psit dtoday.Better understanding of metallurgy of components and bits.More widespread use of reverse circulation.More widespread use of water powered DTH’s – efficiency, lowerflushing velocities, straighter holes.Use of rotary vibratory methods (Sonic) but mainly for overburden,“thethe only true innovation to come to the drilling industry since theChinese invented cable tool drilling some 3,000 years ago” (Roussy,2002).5
More Recent DevelopmentsThese include: Numa “Superjaws” – featuring 2‐4“wings” which open by pressure onthe face of the hole.hole Directdescendent of old Acker CasingUnderreamer System.Atlas Copco “Elemex” system – a ring on the casing redirects theair flush away from the DTH bit face and so makes it easier tocontrol.Center Rock “Rotoloc”Rotoloc system – features a patented method ofextending, locking and retracting cutting wings on the centralpilot bit, in a very simple and reliable fashion. Does not rely ondownwards pressure on the face and leaves nothing behind inthe ground.Roto‐Lock (retracted)Roto‐Lock (extended)6
1.2 Flushing Characteristics Up‐hole velocity (UHV) “sinking velocity”In water, sinking velocity (Vz) is Vz 106 x d2 m/s where d isthe diameter of the particles.Ability of flush to carry or suspend cuttings dependent on: rate of flow of fluid Viscosity of fluid size and shape of cuttings s.g. of fluid and cuttingsUHV (m/min) 1274 x Flushl h Pump Rate (Liters/min)(/)D2 – d2 (mm)where D drill hole diameter (in mm)d drill string diameter (in mm)Acceptable Up‐hole Velocities.7
Drilling FlushCharacteristics Air vs. Water – Rotary vs.Rotary PercussionGuideline for selection: Provide clean holeEnhance penetration rateMinimize tool wearConsistent with purpose of holeMinimal damage to formation and/or structures Environmentally compatible Reconsider options if “lost flush” occurs1.3 Monitoring While Drilling Fundamental Concept Manual Monitoring Automated Monitoring BenefitsBfi to OwnerOandd ContractorC(not(coveredd ini thishipresentation)8
Basic Principles of Monitoring While Drilling (MWD)Fundamental ConceptEvery hole that is drilled in the ground is a potential source ofinformation on the properties and response of the ground. Thisobviously applies to designated site investigation holes, but isequally true of every production hole, such as drilledfor anchors, micropiles, nails or groutholes. Such information can becollected byy two basic methods:manual and automatic. The data mustbe studied in real time to be useful.Examples:1. Helps determine or verifyappropriate bond zone horizons foranchors and micropiles.2 Secondary and higher order holes2.will demonstrate progressivedensification of ground incompaction grouting projects.3. Helps select appropriate jet groutingparameters.4. Will provide a mechanical andhydraulic “picture” of the rock massat each phase of a grout curtainproject.9
Basic Principles of Monitoring While Drilling (MWD)Manual Monitoring The value of routine drillers’ logs can begreatly enhanced by periodic recordingof:––––––––penetration ratethrusttorqueflush return characteristics (cuttings,volume)drill “action”interconnections between holeshole stabilityygroundwater observations These data can easily be recorded by a good driller who has been briefed aboutthe overall purpose of the project andso understands what to look for.These data should be recorded at 5 ft maximum intervals.Basic Principles of Monitoring While Drilling (MWD)Automated Recording of Drilling Progress and Parameters Value of real time continuousmonitoringg for designg ppurposesp(manual vs. automatic)Look for “exceptions andunexpecteds” [Weaver, 1991]Indication of progressiveimprovement (e.g., denser, lesspermeable conditions)CConceptt off specificifi energySeveral generations/evolutions as software and hardwareevolve10
Automated MonitoringCalculation of Specific Energye F 2πNTAARwheree specific energy (kJ/m3)F thrust (kN)A cross sectional area of hole (m2)N rotational speed(revolutions/second)T torque (kN‐m)R penetration rate (m/sec)2. Grouting2.1 Classification of Micropiles Based on GroutingMethodGrouting and Grout Function Transfers loads from reinforcement to surroundingground May be load-bearing portion of pile Protects steel reinforcement from corrosion May be used as drill fluid during initial drilling Secondary/Post grout enhances soil/grout bond further Basis for Micropile Classification11
Classification Based on Grouting Method Type A: Gravity Type B: Pressuregrouting throughcasing Type C: Single, globalpost grout Type D: Multiple,Multiplerepeatable post grout Type E: Injection borebarsGravity Filling Techniques (Type A) Grout introduced into the drill hole through a tremie pipeexiting at the bottom of the hole No excess pressure is applied This type and phase of grouting is referred to as theprimary treatment Typically only used when pile is founded in rock, or whenlow-capacity piles are being installed in stiff or hardcohesive soils12
Pressure Grouting Through the Casing(Type B) Grout injected under controlled pressure throughpressure cap on top of drill casing (often the drillinghead itself) Additional grout injected under pressure after primarygrout has been tremied (as temporary casing iswithdrawn) Enhances grout/soil bond characteristics Can be limited to the load transfer length within thedesign-bearing stratum, or extended to the full length ofthe pilePost-Grouting (Types C and D) Additional ggrout injectedjvia ggrout tubes after pplacinggof primary grout Higher water content grout used(w/c ratio 0.5 to 0.75) High pressures used ( 1 MPa) Type C only used in France to date13
Type E MicropilesClose up of Bit (Injection-Bore Threaded Bar)2.2 Means, Methods and MaterialsTypical Grouting Characteristics Neat cement grouts with water/cement ratios of 0.40 to0.50 Potable water used to reduce corrosion potential Type I/II cement (ASTM C150/AASHTO M85), in bag orbulk form Additives to improve pumpability in special cases Compressive strengths of 28 to 35 MPa (4 to 5 ksi)14
Basics: Design of Neat Cement GroutRelationship of Geotechnical Bond Valueto Grouting Pressure450420390Ultimate Capacity of Anchor .83.5Grouting Pressure [N/mm2]Influence of GroutingPressure on Ultimate LoadHolding Capacity15
Grouting Equipment Mixers– High-speed, high-shear colloidal mixers essential– Low-speed, low-energy mixers (paddle mixers) areoccasionally still used, but should not be Pumps– Constant pressure, rotary-screw type pumps (Moyno)– Fluctuating pressure piston or ram pumps Agitation Tanks Combined Units Batching and Injection Monitoring EquipmentKeys to Good GroutingGrout Batching Water added to mixer using calibrated tank or flowmeter Cement is batched by weight, either in bags or bulk froma silo Additives are proportioned in relation to weight of cement16
Keys to Good GroutingGrout Mixing GroutG t mixingi i sequence: water,t cement,t additivesdditi Grout colloidally mixed for a maximum of 2 minutes andthen held in a paddle agitation tank until needed Safe workability time typically not in excess of 1 hourGrout MonitoringElectronic Pressure and Flow Recorder17
Limiting Excessive Takes of Primary Grout Injecting excessive quantities may be dangerous as wellas wasteful Remedies include:– changing the rheology of the primary grout (e.g. addsand; reduce water/cement ratio; use appropriateadditives)– changing the hydration characteristics of the primarygrout (e.g. use accelerator)– in extreme conditions consider pretreatment of theentire area with an economic controllable grout (e.g.low mobility grout/concrete)2.3 Grouting Quality Assurance and Quality Control(QA/QC) Critical importance Plans and specification development stage through finalconstruction–Implementation of all requirements–Enforcement of qualifications–S b itt l reviewsSubmittali–Installation18
Site Organization and Leadership“Mission Control”19
Preproduction TestingMaintaining Good Photographic Records inReal Time20
Construction MonitoringGrouting – Mixing and Pumping Ensure continuous grout placement Ensure cement is colloidally mixed and grout iscontinuously agitated Prevent presence of air in the grout lines Do not draw down the level of grout in the agitation tankbelow the crown of the exit pipe Ensure exclusion of foreign matter during groutplacementConstruction MonitoringGrouting – Placement Prevent heaving or ground distress Prevent soil in bottom of hole from blowing in Grout as soon as possible after drilling the bond zone Use tremie to ensure complete filling of hole Tie tremie tube loose enough for removal during/or aftertremie grouting21
Construction MonitoringGrouting – Placement (continued) Observe suitable grout return Maintain a positive head at the grout holding tank Measure grout pressures close to the point of injectionto account for line losses Monitor grout pressures and volumes throughout bothtremie grouting and pressure grouting (if used)processes Typical post-grouting pressures are typically 200-600 psi- safety issueGrout TestingCubes – practically useless as a routineQA/QC tool22
Real time testingg of fluid ggroutproperties is far superior– Baroid Mud Balance (SG)– Marsh Cone (Fluidity)3. Storage, Handling and Placement ofReinforcementTypes Reinforcing steel bars (rebar) Continuous-thread solid steel bars Continuous-thread hollow-coresteel bars (injection bore) Steel pipe casing Composite reinforcement23
Placed either before or after initialtremie grouting (but always beforethe temporary casing is withdrawn) Reinforcement must be clean ofsurface soil and mud Centralizers used to maintain thespecified grout coverHandling and Storage Store in a protected location Inspect steel when delivered tosite Reject steel that exhibits flakycorrosion or pitting Extra care with corrugatedprotected/epoxy-coatedt t d/t d barsb24
Installation Install either before or afterinitial grout placement butbefore temporary casing(if used) is withdrawn Record the total pile lengthand bond zone length Insert to the prescribedlength without the use offorce Do not damage corrosionprotection or centralizersduring installationInstallation (continued) Ensure reinforcement is clean of any surface soil, oil, mudetc. Check attachment and intervals (typically 2.5 to 3 meters)of centralizers and spacers Center reinforcement in borehole Ensure full engagement of successive bar or pipesections25
HugeAnnual MarketDegrree of InfluenceNone 210TradeAssociationsContractors/Suppliers 180FederalGovernmentISM 150 120StateGovernments 90ProfessionalEngineering 60SocietiesAnnual Estimmated Market ( millions)4. Growth of the Micropile Market in the U.S.Universities 30197019751980198519901995200020055. Final Comments“Profile of a Driller”Drillers are as diverse a group of“Drillerspeople as the industry in whichthey work. Every drillingoperation is different and requiresa highly skilled person to ensurethat the drilling process issuccessful.”Australian Drilling IndustryTechnical Training Committee Ltd.(1997)26
Areas of Concern–Micropiles in karst. (Owners must recognize needfor pregrouting and/or remedial grouting.)–Decline in standards (“familiarity( familiarity breeds contempt”)contempt ).–Continued support for DFI, ADSC and ISMmicropile activities.Dedicated to the Vision ofDr. Fernando Lizzi(1914-2003)The Godfather of Micropiles27
Sonic Single Tube Rotary Duplex Rotary Percussive Duplex (Eccentric) Double Head Duplex Bentonite Polymer Self Hardening Rotary Percussive Duplex (Concentric) Stem Auger . Type I/II cement (ASTM C150/AASHTO M85), in bag or bulk
Initial Design Considerations A. Micropile spacing B. Micropile length C. Micropile cross section D. Micropile type (i.e., Type A, B, C, or D) Step 5. Final Design A. Geotechnical strength limit states 1) Bond length design 2) End bearing 3) Group effects for axially loaded micropiles 4) Uplift resistance of single micropiles and micropile .
DESIGN OF MICROPILE SYSTEM Design of micropile soil stabilization was carried out by the design procedure proposed by FHWA manual FHWA SA-05-039 by Sabatini et. al. (2005). Turner and Halvorson (2013) proposed a simpler method of design, in which the structure is designed for resolved axial loads acting on the micropile. Turner and
and determine/economize weld sizes. Sunrise was the first lattice tower project for which steel micropile caps were comprehensively tested and ultimately installed. Two prototype pile caps were constructed and installed on micropile foundations at a test site Figure 5: Stress Predictions From Finite Element Modeling
The Green Micropile The Design and Analysis of a Geothermal Micropile System A Major Qualifying Project submitted to the faculty of Worcester Polytechnic Institute in partial fulfillment of the requirements for the degree of Bachelor of Science in Civil Engineering by _ Ashley Perry Approved:
into the finite element guardrail-micropile-reinforced soil-wall analysis. From the analysis, the hybrid micropile-truncated GRS wall design was found to be capable of supporting the guardrail system under MASH TL-4 collision impact condition and a lateral design impact load of 88 kips for a 40" guardrail was recommended.
also necessitated micropile design flexibility. In some cases, surficial talus deposits can hide buried finer grained soils and debris- or mudflow deposits. In other areas, nearby bedrock - outcrops or geologic map indications of bedrock were misleading, and deep soils would necessitate longer, specialized micropile bonds.
Micropile foundations were constructed utilizing primarily helicopter access for seven 500 kV double-circuit tubular steel pole structures with in the protected habitat. The successful implementation of a design-build strategy between the overhead design team and the contractor led to significant refinements in the foundation design.
The results of the preliminary micropile design for 9 5/8-inch-diameter micropiles and 7-inch-diameter micropiles are presented in Tables 2 and 3, respectively. The preliminary design assumes that lateral loads on the piles will be relatively low. We will consi der lateral loads on the piles in our final design. General Micropile Recommendations
