PARAS is a secure and speedy way to assess sub-structure foundations.
Designed to check the depth and integrity of concrete, masonry or steel foundations that are considered to be inaccessible or where other non-destructive methods are of little use; PARAS offers an alternative testing method where conventional pile testing techniques may be inappropriate.
The test requires an access tube to be installed parallel to the pile or sheet piling to be tested. The PARAS system measures the time taken for a signal to travel from a hammer impact point, to a hydrophone transducer as it is lowered down the access tube. A change in the signal arrival time indicates the depth of the foundation.
Housed in a rugged plastic case with high quality waterproof connectors, this lightweight and portable signal acquisition and analysis unit, is designed for testing in all weathers.
Benefits of the PARAS seismic test system:
- Easy to handle and transport between test locations
- Compliant with NFP94-160-3
- Backlit screen for working in dark environments
- Storage for over 700 results
- Can be combined with TDR2 pile testing system
- Operates for up to 8 hours on full charge
- Full equipment training available
- Complete test package available
| All of our equipment is supplied fully calibrated to UK national standards. | |
|---|---|
| PARAS unit | |
| Features | Twin channel hand heldspectrum analyser Daylight viewable screen Tactile large keys for operating with gloves Low power with long battery life Flash memory for instant start up and power down Rugged lightweight unit with waterproof connectors |
| Keypad | Sealed colour coded andfull alphanumeric keypad, tactile and audio feedback |
| Operating temperature | 0 to +50°C |
| Screen | Monochrome LCDtransflective with backlight Contrast keypad adjustable Display area 122mm x 70mm Protective anti-reflective glass |
| Acquisition | 2 channel,16 bitacquisition at 25KHz sample rate Pre-trigger on both channels, auto-ranging gain feature |
| Frequency range | 0Hz to 5000Hz |
| Storage | 700+ results, with fullheader information including site, pile no, operator, transducers anddate/time stamp |
| Depth | Up to 50m |
| Displays | Velocity-time signal: Ateach test depth increment Waterfall plot of all time signals taken on the same test |
| Power | Battery: 1.2V NiMHrechargeable AA cells Auto power off and battery indicator |
| Battery life | 8 hours + on full charge |
| Charge time | Approx 6 hours |
| Charging | External wall plug-incharger for 100/110/250VAC inputs (trickle charge) External cigar plug-in charger for 12VDC inputs (fast charge) |
| Dimensions | L 218mm x W 187mm x D55mm |
| Weight | 1.35Kg |
| Impulse hammer | |
| Type | Constant current loadcell |
| Weight | 1.2Kg with fibre glassshaft |
| Nominal output | 0.15 volts/N |
| Frequency range | 0-1000Hz (black tip) 500-5000Hz (aluminium tip) |
| Range | 0-10,000N |
| Hydrophone | |
| Type | Piezo-ceramic sensor |
| Dimensions | L 300mm x D 25mm |
| Connection | Waterproof hi-pressureJupiter type |
| Cable | 50m reel with 0.5m cablemarkers |
The PARAS analysis software is supplied as standard and incorporates filters for screening data, with the ability to quickly review and analyse each individual test result.
Signals can be analysed in positive, negative or bi-polarity and the threshold for first arrival detection varied. Cursors can be set to follow first arrival times (FAT) over the concrete zone and over the soil zone below the pile. This calculates velocity to compare with normal values and confirm validity of results.
The depth of continuous concrete is determined automatically by the intersection point of the concrete and soil velocity cursors, and marked on the test report. All curves are plotted as a waterfall plot with on screen cursors to define the concrete wave speed, soil wave speed and the intersection corresponding to the foundation depth.
Test results are printed out on a single user definable report sheet.
Before testing, it is necessary to install a plastic tube to within 500mm (maximum), parallel to the pile or sheet piling that is to be tested. This tube should have a closed end and be taken to a depth beyond that which you require, and grouted into place using bentonite or similar.
The tube is generally 50mm in diameter and once installed, is filled with clean water to act as an acoustic coupling with the hydrophone.
To perform the test the hydrophone is lowered down the tube in increments of 500mm. At each step the side of the pile/structure is struck and the hydrophone records the resultant signal from the moment of impact.
As the hydrophone descends the signal will resolve itself, and the arrival time will gradually increase linearly with the depth, as it passes through (providing the tube is parallel with with the pile).
When the hydrophone reaches the base of the pile, the additional signal path is through soil, not steel or concrete, and the first arrival time (FAT) will increase at a greater rate.
The depth of the foundation is determined by the depth at which the rate of first arrival changes.
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