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Integrated surveying system overcomes dam challenges

The Hinze Dam supplies water to one of southeast Queensland?s fastest growing areas. The Hinze Dam Stage 3 project was the dam?s second major upgrade. It involved raising the dam?s height by 15 metres, almost doubling its capacity to 309,000 million litres.

The work was performed by the Hinze Dam Alliance, a consortium of private sector companies ? Thiess, URS Corporation and SKM ? working in conjunction with Seqwater, the water service provider for the South East Queensland (SEQ) region.

Site conditions meant that the surveyors needed as much assistance as possible and they turned to the Trimble VX Spatial Station for answers.

When the work was completed, around two million cubic metres of material had been added to the earth and rockfill dam structure. The clays were obtained from new foundation excavations and from borrow areas on-site. In addition, an old quarry utilised in the construction of the original dam in the early 1970s was reopened to meet the requirements for more rock. The rock was drilled, blasted and crushed on-site.

During the initial construction of the dam, the old quarry was excavated into the side of a steep hill, with five or six benches built into a nearly vertical 70m face. The benches were re-formed during the new quarrying process.

To monitor both the volumes of rock being placed into the dam wall and the rate of use of the finite reserves of good rock in the quarry, surveyors from the Hinze Dam Alliance team measured monthly changes in volume at the quarry face.
Before they could start, however, they needed to define the old quarry face?s shape.


The surveyors made good use of the Trimble VX?s robotic function and the unit?s ability to integrate position data collected by 3D scanning and a GNSS receiver. These features allow data to be collected and set out to be performed through a combination of the technologies and a single software interface, the Trimble Survey Controller software.

The Hinze Dam Alliance team had a Trimble GPS base station at the site that operated 24 hours a day, seven days a week, broadcasting satellite signal corrections to all the Trimble GNSS positioning equipment on the site.

Todd Foster was the Alliance surveyor responsible for the quarry. In using the Trimble VX Spatial Station, he set it up in a spot about 150m to 300m away from the quarry face and relocated the Trimble GNSS rover with the Trimble TSC2 controller a reasonable distance away from the Spatial Station to perform a resection. With the Trimble VX prism fitted on the vertical rover pole under the GNSS antenna, he used the survey controller to start an integrated survey, which allowed collection of GNSS and optical survey data. The Spatial Station tracked the prism from an unknown position at this stage.

Through the Trimble Survey Controller software, Todd initially instructed the Trimble GNSS rover to store a position. The software then automatically switched to the Spatial Station technology and stored the raw vector between the Trimble VX and the prism. This procedure was repeated and, in a seamless interaction between GNSS, the Spatial Station and the controller, the station co-ordinates of the Trimble VX were calculated. In effect, integrated surveying allows the Trimble VX to determine a resected position if the Spatial Station can sight to two or three points where GNSS satellite lock is available.

With the station co-ordinates established remotely and combining Trimble VISION technology within the Spatial Station, Todd was able to click several points from a video image on the TSC2 running survey controller. This defined a polygon and subsequently established the required boundaries for the 3D scan. He could then specify the density of points to be collected either as a density or as a function of time. Once the scan was complete, the point cloud could be downloaded to Trimble?s RealWorks Survey Software for processing.


At Hinze Dam, the scan time function was particularly useful because the continuous movement of machinery afforded surveyors few opportunities to capture what they needed. The machines were always operating adjacent to the face that required scanning, and at times four benches were being worked simultaneously.

Quite often survey work must be conducted from the benches because the benching and the height of the quarry face above the quarry floor do not allow a full sighting of the face from the floor. In these instances, Todd had to work during the quarrymen?s breaks. Even then, time was tight and the capability of selecting a scan time was an advantage.

When the Trimble VX Spatial Station was not in use at the quarry, Todd could utilise it over at the new ?saddle dam?, monitoring material placement, or one of the other surveyors could use it working on the main dam construction or concreting works. The Hinze Dam Alliance also found the one-second Trimble VX ideal for stability monitoring around site and for survey control that required high accuracy.

Ultimately, the instrument was used for ?as-constructed surveys? of dam embankments and the concrete spillway.

For Todd Foster and the other surveyors at Hinze Dam, the Trimble VX Spatial Station fulfilled their needs. ?When you consider that the VX reduces our surveying time and allows quarrying to carry on uninterrupted, you really couldn?t ask for a better survey technique for this job,? he said.

Trimble 3D machine control and guidance systems featured prominently on the Hinze Dam?s construction site. Three dozers, three hydraulic excavators, a grader and a roller were equipped with Trimble technology.

Source: Trimble

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