Plate Load Testing on wind farms made efficient – Case Study

The Plate Load Test is an excellent insitu site investigation field test used to determine the ultimate bearing capacity of the ground and the likely settlement under a given load. It is designing for measuring static loads on spread footings (e.g. to determine whether the ground has sufficient bearing capacity to support structures like wind farm towers, temporary cranes pads or piling rigs), and for repetitive plate loading tests of soils and flexible pavement sub grades.

However, using the traditional Plate Load Test with dial gauges has some issues including:

• the setup is time consuming
• results are not immediately available as all settlements are manually recorded and have to be tabulated and plotted later, adding further delay
• safety as the operator is constantly ducking under the counter weight to record the dial gauge readings

One of our clients, Pearce Geotech, was looking for a solution for these problems because they were tendering for the Mount Gellibrand Wind Farm project being developed by Acciona Energy 25km northeast of the regional centre of Colac in western Victoria.

A Joint Venture between WBHO and Civilex were to deliver the civil Balance of Plant for the Mount Gellibrand Wind Farm, which include construction of foundations for 44 turbines, construction of 27km internal roads, hardstands and 5km of local road upgrades.

Proof rolling wasn’t acceptable on this wind farm project, because it is not quantifiable and didn’t conform to the specification.

The project required over 200 Plate Load Tests to be carried out. On the internal roads, testing was every 500m and on 90 degrees curves and every hardstand for the turbine towers was tested at 4 different points.

The following outputs were required:

• Strain modulus of the second loading cycle, Ev2 (an indicator for the bearing capacity of the soil under the loading plate)
• Modulus of subgrade reaction, ks (a measure of the stiffness)

Pearce Geotech selected the AX01 Plate Load Test specifically because it provided the following:

• Short operation time (approx 25-30 mins per test including setup, test & results graphing), rather than 2-4 hours just to setup and do the test (with manual data analysis adding significant extra time)
• No further data analysis or calculations required – data is analysed electronically on the spot, saving significant time
• No manual recording of data – results date/time stamped and GPS located so data recording / transposition errors eliminated)
• Safe operation as operator away from the counterweight and does not read dial gauges and record results whilst under the counterweight

Pearce Geotech Principal, Daniel Pearce, commented:

“I would hate to go back to doing the Plate Load Test using the old method using dial gauges. It would be so time consuming, not to mention manually recording and then processing all the results.”

Having successfully completed the Mount Gellibrand Wind Farm project and with NATA accreditation in the pipeline, they are now bidding other projects including the Pacific Hydro 80MW Crowlands Wind Farm near Ararat, a landmark 39-turbine wind farm, with a consortium of 14 organisations purchasing half its power output.