Wind farm ground improvement verification.

Testconsult's foundation testing department has been actively involved throughout the ground improvement process at a remote and exposed wind farm site in the east of England. Ground improvements are being made for crane pads to lift giant wind turbines into place. Testconsult were asked to verify ground improvements initially made using vibrated stone columns through a peat stratum. Engineers were concerned when the ground improvement process raised the ground level by approximately 1 meter and had therefore not increased the density of the soils.

Two maintained load tests were set up using 4 metreconcrete bases loaded with steel kentledge blocks. Settlement was logged using our SLT2 static load test monitoring system. Four electronic displacement transducers measured the test base corners. The loading process only reached 50% of the maximum test load before the test was suspended due to excessive differential settlements across the test position.

The monitoring system and accompanying software enabled the test engineer to monitor each individual displacement transducer in real time and track settlement rates. This enabled them to react quickly and prevent potentially dangerous overloading as the foundation began to tip over and fail. The foundation was loaded in incremental stages and within a controlled and monitored environment. Testing the ground in advance averted a potentially dangerous situation before the cranes began their lifts.

Testconsult were invited back to the site in August to verify ground improvement using controlled modulus columns. The new test used a larger 9 metretest pad for a greater zone of influence and a larger factor of safety. A maximum test load of 180 tonnes was applied to the foundation without significant settlement, enabling the new ground improvement method to be rolled out across the site.