Over the years, dams can suffer from leakage from natural weathering and can cause deterioration of the concrete and metals. Common causes of dam failures include sub-standard construction materials, spillway design error, foundation defects such as settlement and slope instability and natural movement that can cause cracks. Water infiltrates into the cracks leaving the dam susceptible to leakage. To prevent this, specialist grout injection is carried out.
Geotechnical Exploration Services a division of Drilcorp, were recently contacted by our client along with other specialist grouting contractors to carry out some ground investigation works on a dam site using Geobore S wireline coring. A recent report of the dam identified that there was further significant leakage and a grouting exercise had been deemed necessary before the reservoir could be returned to normal operating water levels. The site investigation report would provide information to inform the design of the grouting regime.
Ciria who are a construction research group recently published its own guide to good practice in grouting for dams, which covers existing dam sites, new dams and service reservoirs. The guide is available from their website.
Grouting injection methods are a highly specialist area but there is little written evidence on how to carry out the procedures.
Our GES team travelled to a secret location in the UK where they drilled a series of five boreholes one of which was a 45-degree angle hole to a depth of 25 metres and carried out packer testing on site.
Our T44 Beretta and Massenza MI6 Drilling rig was used to obtain high quality samples of both the superficial soils and the bedrock, which could then be used for detailed logging and from which samples could be selected to be sent to the laboratory for testing.
The equipment used was Geobore S core drilling system incorporating triple tube core barrels in which the innermost barrel comprises a one-piece cylindrical semi-rigid plastic liner of minimum 1mm wall thickness. Cores of 102mm diameter were provided, packed and logged.
Once the coring was complete, the holes were backfilled with cement bentonite grout.
Packer testing was also carried out on site. Drilcorp are experienced in this type of testing also known as Lugeon Testing having recently carried out similar works at Saltburn.
Lugeon Testing was developed in 1933 to help understand the water pressure and its application in rock grouting. It was specifically used for dams which were suffering from seepage. More information can be found in our article below.
On successful completion of the job, the dam will be grouted and restored to a safe condition so that the water levels can be restored.