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8/12/2019 05 Brettman PPT

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Guideline for Interpretation of

Nondestructive Integrity Testing of

Augered Cast-In-Place and Drilled

Displacement Piles

Presented by:

Tracy Brettmann, P.E., D.GEBerkel & Company Contractors, Inc.

Other Key Relevant Publications

Augered Cast-in-Place Pile Manual (DFI, 2003)

Inspectors Guide for Augered Cast-in-Place Piles

(DFI, 2010)

Manual for Nondestructive Testing and Evaluation of

Drilled Shafts (DFI, 2004)

Nondestructive Testing of Deep Foundations,

Textbook by Hertlein and Davis (2006)


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Purpose

The intent of this guideline is to provide practicalguidance for the proper interpretation of NDT results

on ACIP and DD piles.

NDT of deep foundations can generally be divided

into two categories:

(1) low strain or nuclear radiation methods which

evaluate integrity, and

(2) high strain methods which pr imarily evaluate

capacity as well as pile integrity.

This guideline focuses on the evaluation of integrity

using low st rain methods.

NDT Controversy

Many methods and versions available

Experiences with NDT have ranged from very good

to complete failure

Reliability of methods have been questioned

NDT practitioners are unwil ling (or unable) to make

quantitative judgements

NDT can create more questions than answers in

some cases Need Analysis Collateral to properly interpret NDT

results


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ACIP and DD Piles Unique Properties

Large length to diameter ratio (>30)

High component of capacity in skin friction

Pumping grout under pressure through layered soils

produces multip le changes in cross-sectional area

(bulges)

These properties limi t the applicability of certain

types of NDT methods

Impulse Echo (Sonic Echo)

Testing from the pile top with a hammer impact

Generally limited to an L/D ratio


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Impulse Echo (PIT or PET)

Impulse Echo (PIT)

Figure courtesy of

Pile Dynamics Inc


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Records Can Be Difficult to Distinguish

A

B

C

Example test results created using the wave propagation

simulation computer program PileWave

Simulated Response A - Bulge


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Simulated Response B - Bulge

Simulated Response C - Neck


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Sonic Logging

Crosshole for large piles and singlehole for small

(


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Sonic Logging

Interpretation of Results

Gather Analysis Collateral

Evaluation of detailed pile installation records

Evaluation of soil and groundwater conditions

Evaluation of NDT results


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Analysis Collateral

Additional information that makes analysis andinterpretation of nondestructive deep foundation

integrity test data easier and more effective.

(Hert lein 2009 ASCE GSP No. 185)

This step should be done prior to performing any

testing. Geotechnical exploration report s

Foundation design drawings and calculations

Contractors construction records

Field Inspectors notes and detailed pile installation records

Automated mon ito ring equipment (AME) data

Concrete or grout mix design

Reinforcing cage and/or center bar design, as well as centralizing system

Concrete or grout delivery tickets Superintendents daily notes

Grout or concrete strength test results

Pile installation sequencing

Post-grouting installation completion procedures.

Evaluation of Pile Installation Records

Data from AME

Typical systems measure (1) time and depth during drilling, and

(2) time, depth, grout volume, and grout pressure during grouting

AME provides both the operator and inspector (1) a real time

graph of the process to monitor during installation, (2) a hard

copy printout of the data, and (3) a digital record that is stored on

a computer for later review and analysis

Manual Observation Techniques

Monitoring of the grouting phase of the pile installation process is

generally considered to be the most important aspect of the

quality control process. This involves recording the volume of grout pumped to develop

the initial grout head and the volume pumped in discrete

increments along the pile.


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Evaluation of Soil and Groundwater Conditions

Soil conditi ons affect the final shape and therefore the

evaluation of ACIP piles

A change in soil cond it ions may resul t in the change from a

bulge to a return to nominal area

This typically produces a positive reflection at that depth in the

impulse echo test, which can be misinterpreted as a neck when

in fact it is simply a return to the nominal diameter

Understanding which so il layers have the potential for caving

or necking and which do not is essential in evaluating pile head

impact test results.

It is important to understand where (1) the pile section could

not be significantly larger than the nominal pile diameter and

(2) there is a possib ility o f the presence of either a bulge or aneck.

Soil Conditions Potential for Caving

1. Loose sands below the water table have a

significant potential for caving or necking to occur

and therefore should be evaluated carefully.

2. The potential for caving or necking in firm to hard

clays and rock is low.

3. The potential for caving or necking is low in

medium dense to very dense sands above the water

table and dense to very dense sands below the

water table.

4. Medium dense sands below the water table have amoderate potential for caving.

5. Bulging can occur in soft to firm clays and loose to

medium dense sands.


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NDT Results Compared to Soil Condi tions

If the conclusions f rom head impact methods are notconsistent with the soil conditions and groundwater

level, the installation records should be reviewed

carefully to determine if the proper installation

procedures were followed

After a reasonable prof ile analysis is performed, the

calculated pile volume should be compared to the

actual constructed volume of the pile. If the

calculated volume is not in reasonable agreement

with the actual pile volume, then another analysis

should be performed.

Communication

Prompt analysis and reporting are usually cri tical to

a successful project

Unless ful l site information is available immediately

to the tester, the analysis and report may be delayed

or wil l be based upon limited information until the

previously specified analysis collateral information

has been obtained, reviewed and considered

A report that reaches the contractor and/or Owner

mentioning some anomaly orig inally found several

weeks earlier is generally disturbing at least, andhighly problematic if the contractor has de-mobilized

from the site


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Anomaly Evaluation

After all the data have been reviewed and analyzed,any anomalies should be evaluated to determine if

flaws or defects may be present in the pile

The determination of a flaw or defect in a pile should

not be made from the NDT results alone

Since NDT results can be misinterpreted, there

should always be some corroborating evidence that

would produce those results in the pile

Impulse Echo Evaluation Guidelines

Classification of Result Comment

Good pile, clear toe Acceptablepile

No defect apparent, no toe

signal

LongpilepotentiallytoolongforNDTtestcapability,high

pileresistancelimitstestingdepth,and/ormajorbulges

arepresent Maybeanacceptablepilesubjecttoreview

ofinstallationrecords

Probableflawatdepthx,

toeapparent

Seesectionbelowregardingevaluationandremediation

optionsforflaws

Probabledefect

at

depth

x,

notoesignalSee

section

below

regarding

evaluation

and

remediation

optionsfordefects

Inconclusiverecord

FurtherdiscussionwithNDTpractitionerisrequiredas

wellaspotentiallyotherNDTtestingtechniques


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Sonic Logging Evaluation Guidelines

VELOCITY

REDUCTION,

VR(%)

SIGNAL

DISTORTION/STRENGTHCONCRETERATING INDICATEDCONDITIONS

010 None/normal

energyreduction 6dB Good(G)

Acceptablequality

concrete

1020

Minor/lower

energyreduction6.1to9

dB

Questionable(Q)

Minorcontamination,

intrusion,orquestionable

qualityconcrete

>20 Severe/muchlower

energyreduction>9dB Poor/defect(P/D)

Contamination,intrusion

and/orpoorquality

concrete

NoSignal None NoSignal(NS)

Intrusionorseveredefect;

couldalsobecausedby

tubedebonding

~60 Severe/muchlower

energyreduction>12dB Water(W)

Waterintrusionorwater

filledgravelintrusionwith

fewornofines

Summary

When data from integrity tests on deep foundations

indicate the presence of an anomaly, the analyst

should follow a three-step process

1. Confirm that the test was performed in accordance with

applicable standards

2. Once it has been verified that the anomaly is an irregularity in

the foundation, its significance must be evaluated

3. The geotechnical engineer should review the pile design

parameters to assess the likely effect of the irregularity of the

pile

The impact of the anomaly should be evaluated bythe pertinent design-const ruction team members

including the NDT practitioner, the geotechnical

engineer, the structural engineer, and the pi ling

contractor

Documents

05 Brettman PPT