the need for specs - Amplus Ltd

1 pile INTEGRITY EVALUATIONS: THE NEED FOR SPECIFICATIONSPile integrity tests are now required on most piling contracts. The test methodsand procedures are, however, rarely specified. Consequently, integrity surveys can(and frequently are) undertaken using inappropriate testing systems which providelittle, or in some cases, no information regarding the integrity of the piles. Reportingcan also be misleading. Facts, arising directly from the test data, and inferencesare often indistinguishable and reports rarely provide the Specifier with anyindication of the limitations of its conclusions or the level of assurance afforded bythe pile integrity 1 & 2 show test data from inadequate systems which routinely measurethe response of the test system and not that of the pile .

2 Surveys using thesesystems provide negligible assurance of pile integrity. Despite this, and as a resultof market pressures, these systems remain in widespread 3 & 4 show sonic echo results from a sound and a defective pile ,respectively. The defective pile has the samenominal dimensions as the sound pile butcontains a serious neck at 2m depth - seephoto. The two test results are practicallyidentical and the major defect is thus notdetectable. The sonic echo method, althoughwidely used, was developed for checking precast piles for cracks incurred during echo tests are not generally suitable forevaluating cast in place piles, particularlythose formed in variable 5 - 8 show the more sophisticatedFrequency Response and Relative ImpulseResponse (RIR) data for the sound anddefective pile above.

3 The affect of the defect isclear. The Frequency Response and RIR methods were developed specifically forthe evaluation of cast in situ response to requests from several Local Authorities and leading ConsultingEngineers, N D Technology has developed a model specification for theevaluation of cast in situ piles. The Specification is generic and is designed toensure that integrity evaluation works are undertaken to a worthwhile House, Upper New Road, West End, Southampton SO30 3 BATel: 023 8046 5992 Fax: 023 8047 3931 Web: Registration No.

4 5071025 Specification for the non destructive integrity evaluation of pilesSpecification NDT/PIESpec - 198 Purpose of WorksThe survey is to serve as a screening process to identify acoustically anomalous piles which canthen be then be subject to further engineering survey data will be used as a factor in assessing the constructed quality of each pile and not asfinal proof of the serviceability of each Test OrganizationThe Works shall be carried out an approved and independent Specialist must supply all necessary personnel and plant to undertake the MethodAll piles shall be evaluated by the Relative Impulse Response (RIR) method as specified in detail inthe following sections.

5 The following methods shall not be used: Sonic Echo, TNO, PIT, Pulse Echo,Transient Dynamic test organization may be requested for the following to demonstrate compliance with thespecification:1)Calibration certificates for the impulse hammer, vibration transducer and digital signalprocessing unit, or a whole system )An example test )Computer simulations of the pile responses at the site to be surveyed:a) The Frequency Response (FR) of an infinitely long pile at the given siteb) The FR and Relative Impulse Response (RIR) of pile of the design )

6 The FR and RIR of a pile containing a 30% reduction in impedance at a depth 3m whichextends to a depth of EquipmentThe test equipment shall comprise a vibration transducer, an impulse hammer and a digital vibration transducer shall measure the pile head impulse hammer shall impart and measure an impulsive force to the pile digital signal processor shall simultaneously acquire both the force and velocity signals andfacilitate storage of the digital data for post processing and measuring system and both transducers shall have dynamic ranges of at least 60 dB and flatfrequency responses over the minimum bandwidth of 20 - 2500 Measurements and ComputationsAt

7 Least the following shall be computed on line and on site for each axial frequency response of the pile expressed as Mobility M (kg. s-1) versus frequency (Hz).The pile head dynamic stiffness K ( )The pile head characteristic impedance Z ( ) as computed from the geometric mean of themobility spectrum from 100 Hz to 1000 House, Upper New Road, West End, Southampton SO30 3 BATel: 023 8046 5992 Fax: 023 8047 3931 Web: Registration No. 5071025 The frequency response shall be measured over the following minimum bandwidths.

8 Piles with diameters <= 900mm , 0-2000 Hz bandwidthPiles with diameters > 900mm, 0- 1000 Hz bandwidthAdditional computationsThe Relative Impulse Response (RIR) of each pile shall be computed from the measured RIR is defined as the reflection coefficient between the actual pile and a nominal pile of infinitelength embedded in the same shall be processed to produce graphs of Reflection Coefficient versus depth and rootImpedance versus depth. The latter shall be used to produce a visualization of the in-situ pile Reporting RequirementsAn initial evaluation of the piles shall be undertaken frequency response or (if available) the RIR pile shall be assigned an initial classification.

9 The classification signifies the acoustic status ofeach pile and what further actions are required (if any) on completion of the site survey. Theclassifications and their meanings are defined in the table ClassificationSelect whenRequired Actions by Main ContractorOKNo impedance anomalies are presentNone, proceed as normalREVIEWA ssessment of pile is pending receipt of further information or data requires further processingObtain final assessment of pile before proceeding to incorporate pile in the worksTRIM & RETESTA nomaly is present at pile head which precludes evaluation of the underlying pile shaftRetrim pile to sound concrete and schedule a retestANOMALOUSA reduction of impedance below that appropriate for the nominal pile shaft has been detectedObtain Engineer's instruction before proceeding

10 To incorporate pileA list shall be prepared which shows for each pile surveyed the pile number and its initial acousticalclassification. The list shall be presented to the Main Contractor by the test engineer before leavingsiteDetailed Analysis of test dataThe nominal characteristic impedance value for the pile shaft shall be estimated from considerationof the pile diameter, the concrete mix and the pile age at the time of the test. The RIR shall becomputed between the test data and a pile of infinite length and nominal characteristic impedance,founded in the prevailing strata.