Limitations

PS 1000 X-Scan Limitations
Due to the scanning principle employed, certain unfavourable circumstances may affect the result:

  • Multiple layers and very inhomogeneous composition of walls or floors. Objects that lie at an angle in the wall.
  • Metal surfaces and damp areas; under certain circumstances, these may be detected as objects in the material bring scanned. The concrete must have dried out fully (at least 4 weeks, depending on the weather, air humidity and temperature).
  • Cavities or voids in the material scanned; these may be detected as objects.
  • Proximity to appliances that emit powerful magnetic or electromagnetic fields, such as mobile phone relay stations or electric generators.
  • Under certain circumstances, objects in a 2nd layer may be difficult to locate. Steeply inclined objects or those lying at a 45° angle to the scanning direction are also difficult to detect.
  • Objects lying perpendicular to the surface scanned cannot be detected correctly.
  • The type or class of material detected or the thickness / diameter of objects found cannot be indicated.
  • Empty plastic pipes / conduits lying alongside steel reinforcing bars cannot always be reliably located as a minimum distance of 40mm (1.6 in) between objects is necessary.
  • Scanning performance limitations must be expected in fibre-reinforced concrete and where layers of insulation, tiles or coatings etc. are present.
  • Objects positioned at greater depth beneath a layer of reinforcing mesh can be detected reliably only if the mesh width is at least approx. 13cm (5.1 in).
  • Objects positioned close to the rear surface of a slab can be located only approximately (or not at all). For reliable detection, objects must be positioned no closer than approx. 40mm (1.6 in) to the rear surface of the slab.
  • Very closely-meshed reinforcing mesh may cause signal interference that looks like objects in the image displayed.
  • Water-filled pipes may appear on the screen as 2 objects, one on top of the other.
  • Over-detection and multiple reflections; Amplification in the signal processing stage is set up in a way that tends to cause too much, rather than too little, to be displayed. Another effect of this is that multiple reflections may appear as objects. Very similar “duplicate” objects then appear behind the real objects in the upper layer.
  • Multiple reflections from the rear surface may result in “ghost objects” that seem to appear behind the slab.
  • Objects positioned behind other metal or metallic objects (foil, sheet metal, etc.) cannot be detected
  • Maximum depth of detection may be reduced by concrete with high signal absorption properties.
  • The detection performance stated in specifications is for concrete of the B35 grade with 16mm (0.6 in) aggregates. Larger aggregate sizes reduce detection performance. Reduced detection performance is also to be expected on the underside of horizontal slabs due to the higher concentration of aggregates present in the concrete in this area.
  • Plates or other wide or extensive objects with a length of more than 20 cm (7.9in) may be detected incorrectly. It is possible that only the edges of the plate are shown in the image.
  • Undesired magnetic fields (such as in the proximity of transformers, motors and other equipment or devices that generate powerful stray magnetic fields may have a decisively negative effect on the detection performance of the EM sensor. In such cases, the results of the scan may be incorrect.

PS 200 Limitations
Reliable Measurements
Base Material

  • Reinforced concrete.
  • Reinforced CMU.
  • (Brick)

Detected Objects
Rebars which comply with one of the following standards:

  • DIN 488
  • ASTM A615/A 615/M-01b
  • CAN/CSA-G30. 18-M92
  • JIS G 3112
  • GB 50012-2002 (China)
  • Metal conduit if sufficient spacing from rebars.

Environment / Working conditions
Smooth and flat surfaces.
Rebar layout Direction

  • Rebars lying orthogonal or within ±5° of 90° to scanning direction.
  • Reinforcement running parallel to the surface.

Rebar layout Diameter

  • Neighbouring bars with a similar diameter.
  • Standard diameters in between 6 – 36mm up to a depth of 60mm, if s:c ≥ 2:1.
  • Calibrated bar sizes: {6,8,10,12,14,16,20,25,28,30,36}
  • Device is calibrated to be accurate to within ± 1 of the above intervals, however this is strongly affected by environmental conditions.

Rebar layout Spacing

  • Minimum bar spacing either 36mm (1.4 in) OR Minimum ratio of spacing : coverage (s:c), whichever value is greater.
  • Minimum ratio of spacing : coverage
  • Depth calculation / bar diameter estimation s:c = min 2:1
  • Bar location s:c = min 1.5:1

Rebar layout Depth calculation

  • Neighbouring bars at similar depth / size.
  • For accurate depths readings minimum depth of 20mm (0.8 in). For readings at all min. 10mm.
  • Maximum depth determination differs with rebar diameter.
  • Typically if diameter is known (DIN) Image Scan / Block Scan:
  • ≤ 10mm: up to 100mm
  • ≤ 14mm: up to 120mm
  • ≤30mm: up to 140mm
  • 36mm: up to 160mm

Linear Scan: up to 100mm

  • Accuracy for unknown bar diameter: ± 10% for depths greater than 20mm.

Pile Integrity Test Limitations

1Test Standards

1.1 PIT is standardised by ASTM D5882 Standard Test Method for Low Strain

Integrity Testing of Deep Foundations

 2 Limitations

2.1 Sufficient access must be allowed to the pile to perform testing. In the absence of any pile cap depth, the client shall provide a minimum excavation of 1m wide x 1m across x 1m below the top of the pile head.

2.1.1 Access to the head of the pile shall be available for testing wherever possible.

2.1.2 If the head of the pile is not accessible, access to at least 1m of the side of the pile shall be provided by the client. Access to more than 1m will be required if there is also no suitable striking location near the head of the pile.

2.2 It is necessary to strike the pile in such a way as to produce a well-defined longitudinal pulse. The blow will be parallel to the axis of the pile and as near as possible to the axis.

2.2.1 Where the head of the pile is available striking will be located in the middle of the head of the pile.

2.2.2 If the head of the pile is inaccessible, it may be possible to strike through structure attached to the pile, or on a fixing or notch attached or cut into the side of the pile. Please note this will greatly decrease the quality of the signal.

2.2.3 The struck surface will be orthogonal to the axis of the pile, clean, firmly attached, not susceptible to oscillation, and should not be damaged by the strike however occasionally some damage may occur. The client shall ensure sufficient exposed area is available for these criteria are not compromised.

2.3 PIT identifies changes in the impedance of a pile, which is determined by the pile’s area, elastic modulus and density. Which of these factors has changed cannot be isolated. As follows;

2.3.1 During the analysis, a change in impedance will be modelled as a change in area.

2.3.2 The detection of severe segregation of the pile can only be performed when the area is known to be constant, such as within an encased pile.

2.4 Accuracy and acceptability of the test is dependent on the quality of the signal, in particular, the level of noise. A high level of noise can render the tests inconclusive.

2.4.1 Structures attached to the top of the pile add a high degree of noise to the signal and may produce inconclusive results.

2.4.2 Some noise can be isolated and filtered, however, this is dependent on the specifics of the test location. Multiple tests are typically required at varying locations to perform most noise reduction.

2.5 Length estimation of the pile requires a toe reflection to be detectable.

2.5.1 To allow detection the strength of the signal reflected from the toe must be significantly greater than the noise level.

2.5.2 Deep reflections within the pile can be attenuated by soil resistance. This may preclude detection of the toe, and is particularly significant in thin slender piles and highly resistive soils.

2.5.3 If a toe reflection cannot be detected, it is not possible to infer the depth of the intact pile.

2.5.4 Belling at the toe of the pile can prevent detection due to interference between the increase and decrease in area.

2.6 Accuracy of length estimation is dependent on the accuracy of the estimated wave speed and therefore subject to other variables identified within these limitations.

2.6.1 This requires testing along the side of the pile, with sufficient separation of the accelerometers to determine the propagation delay. The client shall ensure that approx. 1m separation is available.

2.6.2 If it is not possible to determine the wave speed in a single pile, the average value from neighbouring piles may be used however accuracy will be decreased.

2.6.3. For marine timber piles, wave speed cannot be assumed to be consistent above and below the water-line. Therefore, all testing will be performed between the high tide waterline and the low tide waterline following the change in tides from the water surface.


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