NDT Investigation of Timber Structural Elements at Campbell’s Stores

Campbell’s Stores was established in 1839 and remains one of the most important heritage-listed building in Sydney. Included in its remediation, GBG Australia (GBG) was commissioned by Taylor Thompson and Whitting to conduct Non-Destructive Testing (NDT) of the timber structural elements. Ground Penetrating Radar (GPR) and Ultrasonic Pulse Velocity (UPV) testing were utilised as the technique to provide information on the building.

The purpose of the investigation was to provide a structural assessment of the current condition of the support and bearers of the heritage-listed building. The results provided were to allow the client to assess any repair and maintenance costs as well as the structural integrity of the building. Visual and tap testing were already completed and provided target areas for NDT testing.

GPR data was collected with a 1.5 Hz surface-couple antenna connected to a GSSI SIR3000. The technique was able to locate evidence of internal rot, soft timber, termite damage, pipes and large splits or shakes. Bearers were images from south to north along the beam where profiles were scanned on either side of the beam as well as the underside. Columns were then scanned from their highest point to the ground on all accessible sides to ensure detection of anomalies in the corners of the beams.

The UPV measurements were recorded to find the material strength of the timber, that any timber loss, moisture content and defects (such as air-filled cracks and voids) will be detected. However, as the natural growth of the timber changes the density of the material and its directional elements, a fixed elastic modulus could not be calculated accurately.

Geophysical Investigation to Map Areas of Archeological Significance, Victoria

GBG Australia undertook a geophysical investigation to map areas of archeological significance at the site of an old Inn near Melbourne, Victoria. For this investigation Frequency Domain EM (FDEM), Ground Penetrating Radar (GPR) and Magnetic Gradiometry were utilised to gain information on any possible archeological remains within the area of investigation.

MASW data was collected using the GSSI EMP-400 Profiler. A frequency range of between 15 kHz and 10 kHz was used for this investigation which equated to a depth of investigation of approximately 0.5 m to 1.5 m.

The GPR investigation was undertaken using a SIR-3000 acquisition system and 400 MHz ground coupled antenna. The system was mounted in a cart for ease of investigation.

The Magnetic Gradiometry survey was undertaken with the GEM GSPM-35G Potassium gradiometer. The investigation was performed at 1 m centres with readings being undertaken every 15 ms.

Non-Destructive Investigation of a Dam Spillway, Queensland

GBG Australia undertook a non-destuctive investigation to map areas of abnormal concrete along a Dam spillway, Queensland. For this investigation Ground Penetrating Radar (GPR) and Ultrasonic Tomography were utilised to gain information on the condition of the concrete.

GPR data was collected using a SIR3000 control and acquisition System by GSSI. A range of antennas were used including a 1.5GHz, 900MHz and 200Mhz ground coupled antennas.

The Ultrasonic Tomography was collected using the Acoustic Control Systems A1040 MIRA Ultrasonic tomography system.

Geophysical Investigation to Determine the Subsurface Conditions Beneath a Roadway, ACT

GBG Australia undertook a geophysical investigation to map the subsurface conditions and structures beneath a multilane roadway, ACT. For this investigation MASW and Electrical Resistivity Tomography (ERT) was utilised to gain information on the depth of bedrock in addition to other subsurface structures.

MASW data was collected using the Gemetrics Geode seismic recorder. An array of 24 4.5Hz geophones was utilised. A sledgehammer striking a rubber plate was used to generate the low seismic energy.

The Resistivity Tomography was undertaken using a Syscal Pro 72 Switch Resistivity System. A Dipole-Dipole array was used with 3m electrode spacings. This setup resulted a maximium depth of penetration of beyond 30m.

All geophones/electrodes and shot locations were taken using a high accuracy DGPS and levels along the lines were taken using a laser level.

Geophysical Investigation to Locate Graves Within Rookwood General Cemetery, Sydney, NSW

GBG Australia undertook a geophysical investigation to map location of burials within the grounds of the Rookwood General Cemetery, Sydney, NSW. For this investigation Ground Penetrating Radar was used to identify the location and depth of burials onsite.

The Geophysical data was collected using a GSSI SIR-3000 and 400MHz surface coupled antenna. An effect depth of approximately 1.8m was achieved in this investigation.

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