Deep piles and bore holes project examples

• Sonar surveying of cooling water intakes during
  construction
• Sonar profiling of bridge pile bore hole

Sonar surveying of cooling water intakes during construction

Detailed underwater “as is” drawings of an underwater cliff face were needed to enable new cooling water intakes for a pump station to be drilled through rock into a man-made lake. The intakes were to be approximately 500 feet in length. The area to be surveyed was approximately 25 metres (80 feet) high and 49 metres (160 feet) wide, centered on a cliff wall approximately 200 feet below water level.

The objective was to determine an accurate portrayal of the shape of the cliff face and the existing intake lines. The survey had to be tied in to the existing inlets, benchmarks and pump house at the top of the cliff.

The deliverables included:

• recorded profiles of an area along the cliff face adjacent to the existing fresh water inlets
• X, Y, and Z data suitable for detailed DTM generation and contouring
• an AutoCAD drawing of the area, including grids and contours
• a hard copy report and CD of the area.

AquaCoustic ascertained that a single rotating beam sonar survey would produce the best results and be the most cost effective method. Using a rotating beam sonar head ensures that each data point obtained is directly related to the location of the head; each data point is obtained individually by the submerged rotating head and the profiles obtained are the exact raw data profiles, rather than the computed grid data obtained from a multibeam profiler.

An RTK-GPS, profiling sonar and Robotic Total Station were used, along with a suite of computer programs. Surveying was conducted from a 30 ft pontoon boat.

Separately, AquaCoustic were also contracted to perform a profiling sonar survey of the new intake boreholes themselves in order to obtain a detailed 3D image. These boreholes consisted of five 44” diameter incline shafts through the rock within which 36” casings were to be inserted.

An accurate profile of each shaft was also acquired to indicate suitable locations for packers, and video was also used to determine the location of cracks and other irregularities which would affect the fitting of the liner and grouting material.

Underwater ROV inspection was also performed to observe and record the cliff face at ‘break through’, during initial placement of annular grout backfill around the liner to ensure that no cement entered the lake, and to document the exact as-built location (elevation and coordinates) of each inclined intake. A profiling sonar, digital video, attitude sensor, and a Robotic Total Station were all used. The underwater inspection was conducted from a 30 ft pontoon boat.

Sonar profiling of bridge pile bore hole

A new six lane suspension bridge was being built across a navigable river. Each of the four suspension towers rested on 12 deep piles. The piles were excavated to a depth of 100 meters below river bottom and care had to be taken to keep the holes vertical. It was also important to know the finished volume of the excavation and the finished shape before the rebar was installed and the concrete was poured.

AquaCoustic were contracted to do a sonar profiling survey in two stages. The first stage, at 50 metre depth, was to ascertain whether the hole was vertical and if not, which way the shaft was drifting. The second part of the survey was at the full depth. This gave drift from vertical, shape and volume. 12 piles for each of the four towers was inspected.