capwap and refined wave equation analyses for driveability predictions and capacity assessment of...

CAPWAP AND

REFINED WAVE EQUATION

ANALYSES

FOR DRIVEABILITY PREDICTIONS AND

CAPACITY ASSESSMENT

OF OFFSHORE PILE INSTALLATIONS

OMAE 2009

Honolulu, HI - May 31 to June 5 2009

Frank Rausche, Matt Nagy, Scott Webster GRL Engineers, Inc.Liqun Liang Pile Dynamics, Inc.

Outline Background

PDA Testing and CAPWAP Bearing Graph and Driveability Variable Soil Setup and Plugging Effects

Problem Statement Procedures and Examples for

Blow Count Depth Matching (BCDM) Refined Wave Equation Analysis

(REWE) Summary

Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

Dynamic pile testing and analysis Using Pile Driving Analyzer®

measure pile top velocity during pile installation; monitoring results include Stresses Integrity Hammer performance Capacity estimate

Perform signal matching with CAPWAP® to calculate capacity plus resistance distribution


CAPWAP (Signal Matching) Result


Wave equation analysis


Based on Smith’s concept Input requirement

Hammer properties Driving system details Pile geometry Soil information

GRLWEAP analysis options include Bearing Graph Driveability

GRLWEAP Bearing Graph

Wave equation analysis


GRLWEAP Driveability Output: Assumption: soil setup gain on shaft is function of log (time)

Problem Statement

We may do PDA/CAPWAP for one pile but need capacity assessment for others

Do Refined wave equation analysis (REWE)

We may have a driving record but no measurements and have to assess bearing capacity

Do Blow Count-Depth Matching (BCDM)


The REWE Procedure



REWE Example – Pile Details

1067 mm dia. OE pipe – 100 m long 3 pile sections Wall thickness: 34 – 44 mm Final penetration: 42 m Final blow count: 17 bl / 0.25 m


REWE Example – Soil Details

Alternate layers of Carbonate clays; Shear strength 100 to 450 kPa Silty, calcareous sands; med. dense to dense

Soils increasing in strength with depth


REWE Example - Hammer

Menck MHU 500T 294 kN ram weight 550 kJ maximum rated energy (1.87 m equiv. stroke) 500 kJ max. applied energy (1.70 m equiv. stroke)


Measurements

PDA Measurements 3.5 m below top of pile with 2 strain transducers and 2 PR accelerometers


REWE ExamplePDA - EOD Results

Transferred Energy (kJ) 473

Max. Top Stress (MPa) 224


REWE Example – EOD CAPWAP Results

Capacity Total/Toe (MN) 10.1/2.0

Damping Shaft/Toe (s/m) 0.5/1.3

Quake Shaft/ Toe (mm) 2.0/15

Blows/0.25 m 17


CAPWAP Analysis

Force and Velocity Measurements plus pile impedance

0 2000 4000 6000 8000 10000 120000.00

20.00

40.00

60.00

80.00

100.00

Load (kN)

Dis

pla

ce

me

nt

(mm

)

Pile Top

Bottom

Ru = 10137.5 kNRs = 8137.1 kNRb = 2000.4 kNDy = 52.4 mmDx = 67.1 mm

10 100

-15000.0

0.0

15000.0

30000.0

ms

kN

4 L/c

Force Msd

Velocity Msd

Pile

Calculated Load-Set Curve

Wave Equation Model

GRLWEAP Hammer Model Driving System as per contractor Pile Model with stabbing guides Soil model from CAPWAP


CAPWAP and GRLWEAP Input/Output Values

Quantity

Default/Measured/Computed

GRLWEAPFirst Trial

Damping Shaft/Toe (s/m) 0.5/1.3 0.5/1.3

Hammer Efficiency 0.95 0.95

Dr. System Stiffness (kN/mm)

N/A N/A

Dr. System CoR N/A N/A

Pile Top Stress (MPa) 224 243

Transferred Energy (kJ) 473 429

Blow Count (Blows/0.25 m) 17 23


CAPWAP and GRLWEAP Input/Output Values

Quantity

Default/Measured/Computed

GRLWEAPFirst Trial

GRLWEAPFinal

Damping Shaft/Toe (s/m) 0.5/1.3 0.5/1.3 0.4/1.0

Hammer Efficiency 0.95 0.95 1.0

Dr. System Stiffness (kN/mm)

N/A N/A 8,000

Dr. System CoR N/A N/A 0.93

Pile Top Stress (MPa) 224 243 225

Transferred Energy (kJ) 473 429 473

Blow Count (Blows/0.25 m) 17 23 17


Comparison of measured with GRLWEAP calculated force and

velocity

10 100

-15000.0

0.0

15000.0

30000.0

ms

kN

4 L/c

Force Msd

Velocity Msd

Pile


Second Procedure: BCDM



BCDM – Example properties as before

1st Step: Obtain driving log Blow count vs depth Hammers and Energy

settings Driving interruption

durations Maybe average of several

pile driving logs


Get fs vs depth from geotechnical report (starting value)

BCDM

BCDM


Get qt vs depth from geotechnical report (starting value)

Determine from driving log match Modified fs

Setup factor Modified qt

Effective toe area


BCDM – Blow Count match

Predict long term capacity from• modified fs,

• modified qt,

• setup factor• effective toe area

Summary

The bearing capacity of offshore piles can be assessed by the following methods: From measurements at EOD and CAPWAP

capacity at EOD Capacity at EOD From monitored restrikes plus CAPWAP

capacity including partial setup Capacity at BOR – may be extrapolated to later times

For similar non-monitored piles using REWE From driving record by BCDM

Extrapolated, estimated capacity from driving interruption information


Summary (continued)

REWE, the REfined Wave Equation analysis requires measurements and helps determine capacity for non-monitored piles driven in similar soils.

REWE requires matching of Transferred energy and top stress from PDA Blow count and CAPWAP capacity


Summary (continued)

BCDM, the blow count-depth matching procedure determines bearing capacity from driving behavior Generally applied to the complete driving log,

including energy and driving interruptions Driving interruption or restrike information

allows for soil setup assessment Without measurements results depend on

hammer performance assumptions


CAPWAP AND REFINED WAVE EQUATION ANALYSES FOR DRIVEABILITY PREDICTIONS AND CAPACITY ASSESSMENT OF OFFSHORE PILE INSTALLATIONS

Thank You, OMAE Conference

Rausche, Nagy, Webster, Liang

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