5 th international workshop on micropiles seattle, wa, september 24-27, 2003 a little reminder on...

5th International Workshop on MicropilesSeattle, WA, September 24-27, 2003 GEOSYSTEMS, L.P.

A little reminder on the proper A little reminder on the proper selection of micropile drilling selection of micropile drilling techniquetechniqueDr. Donald A. BruceDr. Donald A. Bruce

““Primum, non nocere” (Lizzi, 1982)Primum, non nocere” (Lizzi, 1982)


Micropiles installed as new Micropiles installed as new foundation system for existing foundation system for existing major line railway bridgemajor line railway bridge

On Abutment No. 2, micropiles On Abutment No. 2, micropiles installed through loose to installed through loose to medium fine sands, below water medium fine sands, below water table into rocktable into rock

On Abutment No. 1, micropiles On Abutment No. 1, micropiles installed through existing installed through existing masonry buttress wall overlying masonry buttress wall overlying dense clay till.dense clay till.

Micropiles installed as new Micropiles installed as new foundation system for existing foundation system for existing major line railway bridgemajor line railway bridge

On Abutment No. 2, micropiles On Abutment No. 2, micropiles installed through loose to installed through loose to medium fine sands, below water medium fine sands, below water table into rocktable into rock

On Abutment No. 1, micropiles On Abutment No. 1, micropiles installed through existing installed through existing masonry buttress wall overlying masonry buttress wall overlying dense clay till.dense clay till.

Recent Case HistoryRecent Case History


Contractor used air Contractor used air flush rotary (and flush rotary (and occasional percussive) occasional percussive) in sands, and air flush in sands, and air flush TUBEX (ODEX) in the TUBEX (ODEX) in the wallwall

Results?Results?


Abutment No. 2, major Abutment No. 2, major sinkholes and loosened sinkholes and loosened zones extending up to zones extending up to surface and under trackssurface and under tracks

Abutment No. 1, severe Abutment No. 1, severe structural damage to wall, structural damage to wall, settlement, and sinkholes settlement, and sinkholes under track and under under track and under roadroad

Consequence?Consequence?

Abutment No. 2, major Abutment No. 2, major sinkholes and loosened sinkholes and loosened zones extending up to zones extending up to surface and under trackssurface and under tracks

Abutment No. 1, severe Abutment No. 1, severe structural damage to wall, structural damage to wall, settlement, and sinkholes settlement, and sinkholes under track and under under track and under roadroad

Consequence?Consequence?


Project completely suspended since April 2003.Project completely suspended since April 2003. This bridge upgrading itself is a This bridge upgrading itself is a relativelyrelatively

inexpensive project, BUT…inexpensive project, BUT… This bridge upgrading is on the critical path This bridge upgrading is on the critical path

(literally) of the whole North Eastern U.S. high (literally) of the whole North Eastern U.S. high speed rail program.speed rail program.

ConclusionsConclusions: Knowledge of overburden : Knowledge of overburden drilling systems as used in drilling systems as used in urban/transportation applications is not urban/transportation applications is not universally at a high level AND/OR universally at a high level AND/OR complacency has set in locally.complacency has set in locally.


1. Introduction1. Introduction

ScopeScope Typically 75 to 300 mm diameterTypically 75 to 300 mm diameter Typically ≤ 60 m depthTypically ≤ 60 m depth Typically within 30° of vertical or horizontalTypically within 30° of vertical or horizontal

RestrictionsRestrictions DeviationDeviation Damage to soil and/or structureDamage to soil and/or structure Federal Regulations (e.g., USACOE 1997 for Federal Regulations (e.g., USACOE 1997 for

embankment drilling)embankment drilling)

Generally contractor-drivenGenerally contractor-driven

(“performance” specification)(“performance” specification)


2.12.1 CommonalitiesCommonalities

Continuous, straight penetrationContinuous, straight penetration Constant diameter, stable and clean Constant diameter, stable and clean

borebore Consistent with the purpose of the drill Consistent with the purpose of the drill

hole (e.g., grout hole vs. anchor hole)hole (e.g., grout hole vs. anchor hole) Appropriate combinations of thrust, Appropriate combinations of thrust,

torque, rotation, percussion, flushtorque, rotation, percussion, flush Cost effectiveCost effective Dictated by ground, not historical biasDictated by ground, not historical bias Environmentally compatibleEnvironmentally compatible


2.2 Rock Drilling Methods2.2 Rock Drilling Methods

2.2.12.2.1 RotaryRotary High rpm, low torque, low thrust (blind or core)High rpm, low torque, low thrust (blind or core) Low rpm, high torque, high thrustLow rpm, high torque, high thrust

2.2.22.2.2 Rotary PercussiveRotary Percussive Top HammerTop Hammer Down-the-hole Hammer Down-the-hole Hammer

– Direct circulationDirect circulation– Reverse circulationReverse circulation– Dual fluid drillingDual fluid drilling– Water hammersWater hammers

2.2.32.2.3 Rotary Vibratory (Sonic)Rotary Vibratory (Sonic)


2.2.3 Sonic Drilling: Advantages

Can provide continuous, relatively Can provide continuous, relatively undisturbed cores in soil (75-250 mm undisturbed cores in soil (75-250 mm diameter) and rockdiameter) and rock

Very high penetration ratesVery high penetration rates Readily penetrates obstructionsReadily penetrates obstructions Depths to 150 mDepths to 150 m Can easily convert to other types of Can easily convert to other types of

drillingdrilling No flush in overburden, minor amounts No flush in overburden, minor amounts

in rockin rock


2.3 Overburden Drilling2.3 Overburden Drilling

2.3.12.3.1 For stable soils (i.e., “open-holing”)For stable soils (i.e., “open-holing”) SSCFASSCFA Rock drilling methodsRock drilling methods

2.3.22.3.2 For unstable soilsFor unstable soils HSCFAHSCFA Combination methodsCombination methods Slurry supportedSlurry supported CasedCased

GEOSYSTEMS, L.P.


Cased Methods for Unstable Soils SonicSonic Single tubeSingle tube

– RotaryRotary– PercussedPercussed

Rotary duplexRotary duplex Rotary percussive duplex, concentricRotary percussive duplex, concentric Rotary percussive duplex, eccentricRotary percussive duplex, eccentric Double head duplexDouble head duplex

– RotaryRotary– Rotary percussiveRotary percussive


OVERBURDENDRILLING METHODS

Overburden isSTABLE*

Overburden isUNSTABLE*

SolidStemAuger

Open Hole(with Rock

DrillingMethods)

HollowStemAuger

“Combination”Methods

SlurrySupportedMethods

CasedMethods

VERY HIGH ------------------------------------------------------------------------------------ Instantaneous Penetration Rate Potential ---------------------------------------------------------------------------------- LOWER

LOW ------------------------------------------------------------------------- Technological Sophistication ----------------------------------------------------------------------- HIGH

LOW --------------------------------------------------------------------------- Presence of Obstructions --------------------------------------------------------------------- SEVERE

LOW ----- Presence of -- SEVEREObstructions

HIGH --– Environmental ---- LOWConcerns

SonicSingleTube

RotaryDuplex

RotaryPercussive

Duplex(Eccentric)

DoubleHead

Duplex

*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.

Bentonite PolymerSelf

HardeningRotary

PercussiveDuplex

(Concentric)


3.3. Drilling EquipmentDrilling Equipment

Key factors in drill rig selectionKey factors in drill rig selection PowerPower Thrust/pull backThrust/pull back ManeuverabilityManeuverability StabilityStability AccessibilityAccessibility Noise emissionNoise emission User friendlinessUser friendliness


4. Circulation Type and 4. Circulation Type and ApplicationApplication

Up-hole velocity (UHV) > “sinking velocity”Up-hole velocity (UHV) > “sinking velocity” UHV (m/min) =UHV (m/min) = 1274 x Flush Pump Rate 1274 x Flush Pump Rate

(Liters/min)(Liters/min)

DD22 – d – d22 (mm) (mm)

wherewhere D =D = drill hole diameter (in mm)drill hole diameter (in mm)

dd == drill string diameter (in mm)drill string diameter (in mm) Typical UHVTypical UHV

• Air, or air/water “mist”:Air, or air/water “mist”: 1500 m/s (max 1500 m/s (max 2100 m/s2100 m/s

• Water:Water: 36 m/s (max 120 m/s)36 m/s (max 120 m/s)• Low to medium viscosity mud:Low to medium viscosity mud: 30 m/s30 m/s• Very thick mud:Very thick mud: 18 m/s18 m/s• Foam:Foam: 12 m/s12 m/s


Air vs. Water – Rotary vs. Rotary Air vs. Water – Rotary vs. Rotary PercussionPercussion

Guideline for selectionGuideline for selection– Provide clean holeProvide clean hole– Enhance penetration rateEnhance penetration rate– Minimize tool wearMinimize tool wear– Consistent with purpose of holeConsistent with purpose of hole– Minimal damage to formation and/or Minimal damage to formation and/or

structuresstructures– Environmentally compatibleEnvironmentally compatible– Reconsider options if “lost flush” occursReconsider options if “lost flush” occurs


5.5. Recording of Drilling Recording of Drilling Progress Progress and Parametersand Parameters

Value of real time continuous Value of real time continuous monitoring for design purposes monitoring for design purposes (manual vs. automatic)(manual vs. automatic)

Look for “exceptions and Look for “exceptions and unexpecteds” [Weaver, 1991]unexpecteds” [Weaver, 1991]

Indication of progressive Indication of progressive improvement (e.g., denser, less improvement (e.g., denser, less permeable conditions)permeable conditions)

Concept of Concept of specific energyspecific energy Several generations/evolutionsSeveral generations/evolutions


Calculation of Specific EnergyCalculation of Specific Energy

e = F + 2 π N TA AR

wheree = 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)


6. Specifications6. Specifications

Must be tailored to project at hand and to Must be tailored to project at hand and to the objectives to be accomplished” [Weaver, the objectives to be accomplished” [Weaver, 1991]1991]

Generally “Performance”Generally “Performance” Flexibility needed as project unfoldsFlexibility needed as project unfolds Items which should be specifiedItems which should be specified

– Hole location, length, orientation, and inclinationHole location, length, orientation, and inclination– Minimum hole diameterMinimum hole diameter– What is What is notnot permissible permissible– Deviation and straightness (measurement and Deviation and straightness (measurement and

tolerances)tolerances)– Actions required in “extreme conditions”Actions required in “extreme conditions”– Recording and presentation of dataRecording and presentation of data

Specifications must contain Specifications must contain all available dataall available data


7. Final Comments7. Final Comments

““Profile of a Driller”Profile of a Driller”

““Drillers are as diverse a group of Drillers are as diverse a group of people as the industry in which people as the industry in which they work. Every drilling they work. Every drilling operation is different and requires operation is different and requires a highly skilled person to ensure a highly skilled person to ensure that the drilling process is that the drilling process is successful.” successful.”

Australian Drilling IndustryAustralian Drilling IndustryTechnical Training Committee Ltd. (1997)Technical Training Committee Ltd. (1997)

5 th international workshop on micropiles seattle, wa, september 24-27, 2003 a little reminder on...

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