| SONIC PILE TESTING SYSTEMS |
Commonly known as Echo test, Pulse test, hammer test, Pulse-Echo Method (PEM), Pile Integrity Test (PIT), Impulse Response, etc. In the Sonic test, the top of the pile top is tapped with a lightweight plastic hammer and the reflected wave are recorded by a suitable computerized equipment. From the resulting signal, or reflectogram, one can determine both length and continuity of the pile. In its most basic form, the sonic test measures the time between the hammer trigger, and the reflected wave, to indicate the pile's length. this is very similar to the famous Newton's cradle "executive toy". The PET (Pile Echo Tester) from Piletest.com uses the Pulse-Echo method (PEM) for quick quality control of a large number of piles. The pile top is struck with a lightweight handheld hammer. The reflected wave is captured and analyzed by the PET's digital accelerometer to provide information regarding the length and shape of the pile. The PET is fully compliant to ASTM Sonic standard D5882.
Cross Hole Ultrasonic Monitor Method
The CHUM (Cross Hole Ultrasonic Monitor) uses the Cross-hole Sonic Logging (CSL) method to perform high-resolution quality control of deep foundations. The system uses an ultrasonic wave sent from a transmitter to a receiver pulled through water filled access tubes embedded in the concrete. The measured arrival time and energy are strongly dependent on the concrete quality .
ULTRASONIC PILE TESTING AKA: Cross-hole sonic logging (CSL), "Sonic logging" or "Sonic coring" For the ultrasonic test at lease two tubes (either plastic or steel, minimum diameter of 50 mm or 2"), are cast in the pile and filled with water. A transmitter of ultrasonic pulses is lowered in one of those pipes and a receiver - in another. Both transmitter and receiver are connected by cables to the CHUM which records the first arrival time (FAT) and the energy attenuation as the probes are simultaneously raised to the top. As long as the FAT and the energy attenuation are roughly constant, one may deduct that the concrete quality is also uniform and the pile is therefore acceptable. On the other hand, if at some level there is a noticeable increase in the FAT and/or in the energy attenuation, it means that the concrete at this level is inferior or defective. In such a case, the test may be re-run with the transmitter and receiver at different levels, a technique which enables the determination of both location and extent of the defect (tomography). Installing a larger number of pipes on the perimeter gives an almost complete coverage of the pile cross-section. Because of the character of the ultrasonic method, it can detect defects which may escape detection by other integrity testing methods. It is especially suitable for testing large-diameter piles and slurry-wall elements. If a defect is found, the steel tubes may be pierced at the corresponding depth and the pile repaired by grouting. The piles can be tested after the concrete has gained some strength, usually at an age of five days or more from casting .
1. Concrete pile installed with water-filled PVC/Steel pipes
2. Ultrasonic transmitter
3. Ultrasonic receiver
4. Depth encoders
5. Standard or rugged field computer
6. A defect in the pile and its presentation
Please refer to Piletest.com for more details. Piletest.com Pile testing systems
Impact-Echo is a method for nondestructive
evaluation of concrete and masonry, based on the
use of impactgenerated stress (sound) waves that propagate through the structure
and are
reflected by internal flaws and external surfaces.
Impact-Echo can be used to make accurate,
nondestructive, ASTM approved measurements
of thickness in concrete slabs and plates, (ASTM Standard C 1383 - 98a). It
can also be used
to determine the location and extent of flaws such as cracks, delaminations,
voids, honeycombing and debonding in plain, reinforced and post-tensioned concrete
structures. It can locate voids in the subgrade directly beneath slabs and pavements.
It can be used to determine thickness or in locate cracks, voids and other defects
masonry structures where the brick or block units are bonded together with mortar.
Impact-echo is not adversely affected by the presence of steel reinforcing bars.
A short-duration mechanical impact, produced by tapping a small steel sphere against a concrete or masonry surface, produces low-frequency stress waves (up to about 80 kHz) that propagate into the structure and are reflected by flaws and/or external surfaces.
The wavelengths of these stress waves are typically between 50mm and 2000mm -- longer than the scale of natural inhomogeneous regions in concrete (aggregate, air bubbles, micro-cracks, etc.).
As a result they are only weakly attenuated, and propagate through concrete almost as though it were a homogeneous elastic medium. Multiple reflections of these waves within the structure excite local modes of vibration, and the resulting surface displacements are recorded by a transducer located adjacent to the impact.
The piezoelectric crystal in the transducer produces a voltage proportional to displacement, and the resulting voltage-time signal (called a waveform) is sent to a data acquisition system where it is digitized and transferred to the memory of a computer. In the computer the voltage- time signal is transformed mathematically (by Fast Fourier Transform) into a spectrum of amplitude vs. frequency. Both the waveform and spectrum are plotted on the computer screen. The dominant frequencies, which appear as peaks in the spectrum, are associated with multiple reflections of stress waves within the structure, or with flexural vibrations in thin or delaminated layers.
The fundamental equation of impact-echo
is d = C/(2f), where d is the depth from which the stress waves are reflected
(the depth of a flaw or the thickness of a solid structure), C is the wave speed,
and f is the dominant frequency of the signal. The frequency f is obtained from
the results of a test.
To determine thickness or depth of
a flaw, the wave speed C must be known. It can be measured by observing the
travel time of a stress wave between two transducers held a fixed distance apart
on the concrete surface or by performing a test on a solid slab of known thickness
and observing the dominant frequency. In the latter case the equation is rearranged
to give C = 2df (where d is the known thickness).
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Impact Echo systems can be applied for different usages and in different environments. Tightly confined area such as tunnels, overhead bridges, bended corners, Impact Echo has the proper equipment for you. The following are the different types of tranducers for various applications within the impact echo systems.
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The Cylindrical Transducer The cylindrical transducer is used for impact-echo testing. The cylindrical model is useful for testing in narrow and confined spaces. |
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The Pistol Grip Transducer The pistol grip transducer the pistol grip model is easier to use and is well suited to flat surfaces. |
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The Dualhead Transducer The dualhead transducer on the right is used only for independent measurements of wave speed (required for determining plate or slab thickness in accordance with ASTM Standard C 1381-98a). |
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