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LOADTESTDynamic Load Testing (DLT)

INTRODUCTIONDynamic load testing can be an attractive costeffective alternative to traditional full scale static

load testing. Instead of costly, time consumingproof loading using kentledge or anchor piles,the technique uses a heavy falling weight suchas a piling hammer to impart a short durationimpact to the pile head, whilst monitoring thepile response using attached transducers. Thetest generates data required by the foundationdesigner to provide assurance on the relativecapacity of the foundation and can usuallyprovide additional information that can bedifficult to obtain via static load testing.

DESCRIPTIONThe test is performed by striking the pile headwith a piling hammer or other suitable drop

weight whilst monitoring pile soil response interms of pile head force and velocity usingspecially developed bolt-on reusabletransducers. The test may be performed onmany pile types. The equipment used toenergise the transducers and record theiroutput is rugged and portable and easilyaccommodated in the back of a small vehicle.

ADVANTAGES Can provide information difficult to obtain

with static load tests, for example data onskin friction distribution and end bearingcomponents of soil resistance.

Can be used to assess pile integrity. Provides check of operating efficiency of

driving hammer.

Can be used to investigate anomalousdriving behaviour.

Cost effective and rapid to perform.

Up to ten piles may be tested on a day.

Causes minimum disruption to pilingoperations.

No kentledge or anchor piles needed.

Can be performed on piles installed overwater.

Piles do not need to be preselected fortesting prior to installation.

Testing a marine steel tubular pile

Copyright Fugro Loadtest 2011

RESULTSThe measured pile head signals are analysed inreal time to provide:

an estimate of the soil resistancemobilised during the test.

determination of maximum stresses inthe pile and shaft integrity.

measurement of the overall operatingefficiency of the hammer and itscoupling to the pile head.

Additional analysis of each set of dynamic testdata can be performed using the CAPWAP orDLTWAVE pile driving simulation computerprograms. These programs uses an iterativesolution technique to optimise the parametersdefining the soil resistance supporting the pile.

This is done by matching forces at the pile head

computed using stress wave theory with thoseactually measured during the test. Theprograms output many parameters valuable tothe experienced piling engineer.

Typical Measured Signals

CAPWAP Output

Pile Head Load Settlement Curve

The parameters of most value are generally thedistribution of soil resistance down the pile shaftand beneath the pile toe, and the computed pile

head load settlement curve. This analysis isgenerally conducted in the office subsequent tothe field testing but can easily be performed onsite if rapid answers to anomalous behaviourare required, or to optimise driven pile lengths.

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