Drilled Shaft Design and Construction

Revised 9/2012

14.528 DRILLED DEEP FOUNDATIONSDrilled Shafts Design and Construction

Slide 1 of 51

DRILLED SHAFT CONSTRUCTION

West Tower Arthur Ravenel Jr. Bridge

Photograph courtesy of Marvin Tallent, Palmetto Bridge Constructors

Concrete Mix DesignConsiderations

Dry Construction Method Wet Construction Method Casing ConstructionMethod

Equipment Inspection and Testing

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CONCRETE MIX DESIGN CONSIDERATIONSSCDOT 712.03 - Class 4000DS (see SCDOT 701)

AggregateType

Min. CementContent(lbs/CY)

Min.28 day

f'c(psi)

% Fine toCoarse

AggregateRatio

Max. W/CRatio

Crushed 625 4000 40:60 0.44Stone 625 4000 39:61 0.43

Type G or Type D w/ Type F Admixture Required Slump: 7-9 inches Nominal Coarse Aggregate: inch

Revised 9/2012


Slide 3 of 51

CONCRETE MIX DESIGN CONSIDERATIONSMassDOT LRFD Design Manual (2009)

Section 3.2.3.2 6. The minimum clearance between reinforcing bars shall be 1-

78 and is equal to 5 times the maximum coarse aggregate size (38) for both, the longitudinal bars as well as the spiral confinement reinforcement, to allow for better concrete consolidation during placement. Concrete mix design and workability shall be consistent for tremie or pump placement. In particular, the concrete slump should be 8 inches 1 inch for tremie or slurry construction and 7 inches 1 inch for all other conditions.

Revised 9/2012


Slide 4 of 51

CONCRETE MIX DESIGN CONSIDERATIONS

Figure 1. Concrete Flow Under Tremie Placement (Brown and

Schindler, 2007).

Figure 3. Restriction of Lateral Flow (Brown and Schindler, 2007).

Revised 9/2012


Slide 5 of 51


Figure 9-1. Free Fall Concrete Placement in a Dry Excavation (FHWA NHI-10-016).

Figure 5. Effects of Loss of Workability during Concrete

Placement (Brown and Schindler, 2007).

Revised 9/2012


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Self Consolidating Concrete (SSC) Project for SCDOT (S&ME 2005).

Revised 9/2012


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DRY METHOD (SCDOT 712.07)

Less than 6 inches of water per hour

Sides and Bottom Remain Stable(Engineer can order 4 hours wait period)

Loose material & water can be satisfactorily removed

Temporary casing can be used

Photograph courtesy of GPE Inc.

Revised 9/2012


Slide 8 of 51

UnstableCavingSoils

Water table

CohesiveSoils

Unstable caving soilsprevent maintaining

hole stability

StableNon-CavingSoils

CohesiveSoils

Stable non-cavingsoils maintainhole stability

STABLE vs. UNSTABLE SOILS

Figures courtesy of FHWA NHI-132070 Drilled Shaft Foundation Inspection Course

Revised 9/2012


Slide 9 of 51

WATER TABLE AT OR BELOW THE SHAFT TIP ELEVATION

Generally, soils cave at thewater table preventing

hole stability

Water table

StableNon-Caving

Soils

CohesiveSoils

Water table belowshaft tip does not

impact hole stability

Water table


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DRY METHOD CONSTRUCTION PROCESS

PlacePositionClean &InspectDrill

Drill the shaft excavationClean shaft by removing the cuttings & seepage water

Position the reinforcing cagePlace the concrete

Competent,Non-CavingSoils


Revised 9/2012


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DRILL(SCDOT 712.10)

Continuous Operation. No delays > 12 hrs.

No entering non-cased excavations.

Photographs courtesy of WPC Inc.

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CLEAN & INSPECT



Revised 9/2012


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EXCAVATION CLEANLINESS(SCDOT 712.14D)

INSPECTION OF EXCAVATION (SCDOT 712.14)

50% of Base has < inch of sedimentAND

Maximum depth of sediment < 1 inches

Need SCDOT Qualified Inspectors


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POSITION(SCDOT 712.16)

Spacers needed for 5 inch min. annulus.

Spacer interval < 10 ft.



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PLACE (SCDOT 712.17) ASAP after reinforcement placement. Must be completed in 2 hours (unless

approved). Tremie preferred. Tremie ID > 6 x Max.

Aggregate Size AND > 10 inches. Tremie Embedment > 10 ft. Concrete flow: Positive pressure and

continuous.


Photograph courtesy of WPC Inc.

Revised 9/2012


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PLACE (SCDOT 712.17)

Freefall > 75 ft not permitted.

Freefall Max. Aggregate Size inch, 7-9 inch slump.

Freefall still needs chute. Must have tremie onsite.

SCDOT can always order tremie.



Revised 9/2012


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Less than 6inin one hour = Dry

More than 6inin one hour = Wet

SCDOT 712.08

WET METHOD CONSTRUCTION PROCESSUSE WHEN A DRY EXCAVATION CANNOT BE MAINTAINED

Figure courtesy of FHWA NHI-132070 Drilled Shaft Foundation Inspection Course

Revised 9/2012


Slide 18 of 51

WHEN THE SIDES AND BOTTOM OF THE HOLE CANNOT REMAIN

STABLE

WET METHOD CONSTRUCTION PROCESS

WHEN LOOSE MATERIAL AND WATER CANNOT BE

SATISFACTORILY REMOVEDFigures courtesy of FHWA NHI-132070 Drilled Shaft Foundation Inspection Course

Revised 9/2012


Slide 19 of 51

PlacePositionCleanDrill

Drill the shaft excavation

Clean shaft by removing the cuttings & seepage water

Place the concreteStabilize

Position the reinforcing cage

Stabilize the hole (Plain water, slurry)



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There are two forms of wet shaft construction:

Static Process

Circulation Process


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Drill down to the piezometric level

Slurry introduced

Drilling Completed

Cuttings are lifted from the hole

Piezometric level

Drill down toPiezometriclevel

Temporary surfacecasing installed(optional)

Piezometric level

Slurry addedto hole

Slurry

Hole drilled tocompletiondepth withslurry

Slurry

Piezometric levelPiezometric level

Hole cleanedof slurry &cuttings

Slurry

WET METHOD: STATIC PROCESS


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Slide 22 of 51

Hole is drilled

Slurry level maintained at the ground surface

Cuttings and sand, is circulated to the surface, where it is cleaned and reintroduced down the hole.

Piezometric level

Hole drilled tocompletiondepth withslurry levelmaintained atground level

SlurryProcessor

SlurryProcessor

Temporary surfacecasing install (optional)

Piezometric level

Slurry, with sand& cuttings isre-circulated forprocessing and reintroduced intohole.

SlurryProcessor

SlurryProcessor

Piezometric level

Hole cleaned

SlurryProcessor

SlurryProcessor

WET METHOD: CIRCULATION PROCESS


Revised 9/2012


Slide 23 of 51

SLURRY(SCDOT 712.12)


Photographs courtesy of FHWA NHI-132070 Drilled Shaft Foundation Inspection Course

Revised 9/2012


Slide 24 of 51

Natural mineral clays

Bentonite, attapulgite and sepiolite

Bentonite is the most common

Attapulgite and sepiolite are typically used insaltwater environments

Must be hydrated

WET METHOD CONSTRUCTION PROCESSTYPES OF SLURRY

Revised 9/2012


Slide 25 of 51

Best ApplicationMineral Polymer

Cohesionless Cohesive &Argillaceous Rock

Mixability Difficult - Must be Hydrated Easy

Mix Water Sensitivity SaltwaterSensitive Yes/No

"Caking" Ability Best OK

Suspension Ability Best OK

WET METHOD CONSTRUCTION PROCESSSLURRY COMPARISONS

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Slide 26 of 51

Control tests are used to maintain proper slurrycondition. Tests are conducted for:

Density- the slurry weight

Viscosity- flow: consistency

pH- acidity: alkalinity

Sand Content

WET METHOD CONSTRUCTION PROCESSCONTROLLING SLURRY

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SCDOT 712.12 MINERAL SLURRY ACCEPTABLE RANGES

Property(Units)

ValueRange @Introduction

ValueRange @Concreting

Test Method

Density (pcf) 64.3 69.1* 64.3 75.0 Density BalanceViscosity(sec/qt)

28-45 28-45 Marsh Cone

pH 8-11 8-11pH paperpH meter

* Add 2 pcf in saltwater ** Sand

WET METHOD CONSTRUCTION PROCESSCONTROLLING SLURRY

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Slide 28 of 51

Proper Dosage and Solids Content for Proper Flowability and Cake Properties

Thorough Mixing / Adequate Time for Hydration (Bentonite / Polymers)

Maintenance of Head in Borehole

Maintenance of pH, Hardness, Salts

Minimize Pressures from Tools

WET METHOD CONSTRUCTION PROCESSCONTROLLING SLURRY FOR BOREHOLE STABILITY

Revised 9/2012


Slide 29 of 51

Fails to properly suspend and facilitate theremoval of sediments and cuttings

Does not control caving

Does not control swelling of soils

Hinders slurry displacement during concreteplacement

Leads to a dirty hole

WET METHOD CONSTRUCTION PROCESSIMPROPER SLURRY CONTROL

Revised 9/2012


Slide 30 of 51

WET METHOD CONSTRUCTION PROCESSDIRTY HOLE

Figures courtesy of FHWA IF-99-025 Drilled Shafts: Construction Procedures and Design Methods.

Revised 9/2012


Slide 31 of 51

Poor Slurry Job Excellent Slurry Job

WET METHOD CONSTRUCTION PROCESSSLURRY EXAMPLES


Revised 9/2012


Slide 32 of 51

Where an open hole cannot be maintained.

Where soil or rockdeformation will occur.

Where constructing shafts below the water table or caving overburden.

SCDOT 712.09 & 712.11

SCDOT Types: Construction (712.11B) & Temporary (712.11C)

CASING CONSTRUCTION METHOD

Photograph courtesy of FHWA NHI-132070 Drilled Shaft Foundation Inspection Course

Revised 9/2012


Slide 33 of 51

Smooth, clean, watertight, w/ample strength

Oversized must be approved by SCDOT.

Temporary: Fresh concrete > 5 ft above hydrostatic pressure.

SCDOT 712.11

Construction: Installed as one continuous unit.

Welds are only approved connection.



Revised 9/2012


Slide 34 of 51

1. The Designer shall consider the intended method of construction (temporary or permanent casing, slurry drilling, etc.) and the resulting impact on the stiffness and resistance of the shaft.

4. When a drilled shaft is constructed with a permanent casing, the skin friction along the permanently cased portion of the shaft should be neglected.

MassDOT LRFD Design Manual (2009)Section 3.2.3.2


Revised 9/2012


Slide 35 of 51

Not Permitted by SCDOT

(see 712.11C)

CASING CONSTRUCTION METHODTELESCOPING CASING


Revised 9/2012


Slide 36 of 51

CASING METHOD: CONSTRUCTION PROCESS

PlacePositionCleanDrill

Drill the shaft excavation

Clean shaft by removing the cuttings & seepage water

CasePosition the reinforcing cage

Install casing through caving soils and seal

Caving SoilsFigures courtesy of FHWA NHI-132070 Drilled Shaft Foundation Inspection Course

Revised 9/2012


Slide 37 of 51

CASING CONSTRUCTION METHODCONSTRUCTION (a.k.a. PERMANENT) CASING EXAMPLES


Revised 9/2012


Slide 38 of 51

CASING CONSTRUCTION METHODCONSTRUCTION (a.k.a. PERMANENT) CASING EXAMPLES


Revised 9/2012


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FULL-DEPTH CASING PROCESS

Installation of Casing

Competent Soil

Caving Soil

Competent Soil

Casing

VibratoryDriver

Competent Soil

Caving Soil

Competent Soil

Casing

VibratoryDriver

Water Table

Installation of Casing

Drilling ahead ofcasing

Competent Soil

Caving Soil

Competent Soil

Competent Soil

Caving Soil

Competent Soil

Water Table

Drilling ahead of casing

Remove casing Competent Soil

Caving Soil

Competent Soil

Casing

VibratoryDriver

Water Table

Remove casing


Figure 1. Concrete Flow Under Tremie Placement.

Revised 9/2012


Slide 40 of 51

CASING CONSTRUCTION METHODTEMPORARY CASING REMOVAL

(a) Prior to lifting casingFigure 9-4. Concrete Pressure Head Requirement during Casing Extraction

(FHWA NHI-10-016).

(b) As Casing is Lifted.

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Slide 41 of 51

DRILLED SHAFT EQUIPMENT TERMINOLOGY

Kelly

Table

Crane

Power Unit

Tool


Revised 9/2012


Slide 42 of 51

Single Flight

Double Flight

Double Cut

Triple Cut

Earth augers are generallyused in sands and cohesive

materials.

DRILLED SHAFT EQUIPMENTEARTH AUGERS


Revised 9/2012


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Tapered Geometry

Rock augers are generally used in soft to

hard rock formations.

Conical (Bullet)Carbide Teeth

DRILLED SHAFT EQUIPMENTROCK AUGERS


Revised 9/2012


Slide 44 of 51

This is typical of rock bits designed for drilling in hard to very hard rock.

ReplaceableRoller Bits

Circulating bit

DRILLED SHAFT EQUIPMENTROCK BITS


Revised 9/2012


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GougingTeeth

RippingTeeth

Side Cutting Teeth

DRILLED SHAFT EQUIPMENTDRILLING BUCKET


Revised 9/2012


Slide 46 of 51

This is typical of a cleanout (muck) bucket used to

cleanout the cuttings and sediments from

the bottom of the shaft.

6-51

DRILLED SHAFT EQUIPMENTCLEANOUT (MUCK) BUCKET


Revised 9/2012


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DEEP FOUNDATION DESIGNGEOMATERIAL PROPERTIES NEEDED

Table 13-1. Geomaterial Properties Required for Drained and Undrained Axial Resistances (FHWA NHI-10-016).

Revised 9/2012


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DEEP FOUNDATION DESIGNAXIAL CAPACITY

Where:Qtotal = Ultimate Pile CapacityQskin = Skin Friction (i.e. Side) CapacityQtip = Tip (i.e. Toe) Capacity

Qtotal = Qskin + Qtip

Revised 9/2012


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Qskin = fsAskinWhere:

fs = Unit Skin FrictionAskin = Pile Skin Area

Qtoe = qpAtoeWhere:

qp = Unit End BearingAtoe = Pile Toe (i.e. Tip) Area

DEEP FOUNDATION DESIGNAXIAL CAPACITY

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DEEP FOUNDATION DESIGNGENERALIZED LOAD TRANSFER BEHAVIOR

Figure 13-1(FHWA NHI-10-016).

Qskin = RsQtoe = Rb

Revised 9/2012


Slide 51 of 51

REFERENCES SCDOT Standard Specifications for Highway

Construction (2000). SCDOT Foundation Certification Program Notes. FHWA IF-99-025 Drilled Shafts: Construction

Procedures and Design Methods. FHWA NHI-10-016 Drilled Shafts: Construction

Procedures and LRFD Design Methods NHI Course 132070 - Drilled Shaft Foundation

Inspection.

Drilled Shaft Design and Construction

Documents

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