Pile top drill rigs from Aker Wirth on the home straight

Dam reinforcement with an innovative drilling technique on Lake Cumberland, USA

 

Lake Cumberland in Kentucky is one of the largest lakes in the USA. Its hinterland is a nature reserve and a popular recreation area. In addition to this, it is also used with the adjacent Wolf Creek Dam to generate power. Over the years, massive erosion at the base of the dam has led to ever greater leaks which now threaten the stability of the dam. Attempts to stop seepage through injections were unsuccessful, so another solution needed to be found to safeguard this critical structure.

 

The dam has been sealed since 2010 using a drilling technique which Aker Wirth developed specially for this project together with its customer Treviicos (Trevi), lead of the Joint Venture (JV) responsible for the Wolf Creek Dam Rehabilitation Project. The client is the US Army Corps of Engineers which is responsible for all dams in the USA.

 

The dam is a combined earth fill and concrete structure. It is 1,7 km long and up to 79 m high. More than 1000 boreholes are necessary for sealing, and these are drilled vertically up to a depth of 95 m in the dam wall, right into the bedrock. The boreholes are realised with up to five Aker Wirth pile top drill rigs, each with a drilling diameter of 1,25 m.

 

Innovative high-precision boring technique 

The boreholes are realised in a special order, with holes 1, 3, and 5 being drilled first and then filled with concrete. Following setting, holes 2 and 4 are realised. A continuous concrete wall is created in the dam wall in this manner after filling with concrete. 

 

The boreholes must overlap adequately for the entire length to ensure the watertightness of the dam in the long-term. To achieve this, the client specified extremely close tolerances for the straightness of boreholes. In order to achieve this to date unique level of precision, Aker Wirth, in close cooperation with Treviicos, developed a special drill string with triple stabilized drill collars and a drill bit with stringer (centre point). This system was supplemented by a measuring device provided by the client, which enables control of verticality at any drilling depth. With this, the requirement for quality documentation of straightness of the borehole specified by the client was met.

 

”We worked with Aker Wirth for the procurement and customization of the RCD rigs as required by the specific conditions of the project site and continued the developments of this specialized equipment throughout the process” noted Fabio Santillan Project Manager for the JV.

 

“We drew on experience from previous projects and developed our pile top drill rigs further to meet specific project requirements”, explained Willi Schmitz, Product Sales Manager Drilling & Area Sales Manager North America at Aker Wirth. “The fact that our rigs, which have been in continuous operation for over three years, are consistently reliable and drill with enormous precision underscores our high standards as a provider of highly efficient drilling technology.”

 

The reverse circulation drilling method is employed for drilling itself. Accordingly compressed air is injected directly above the drill bit into the drill string. The resultant air-water mixture has a specific lighter density. The pressure difference between the surrounding pressure and low pressure in the drill string starts the transport process. This energy-efficient and robust procedure is realised with clean water free of chemical additives, making it very suitable for use in ecologically sensitive areas.

 

The Aker Wirth pile top drill rigs have already successfully mastered more than 90 % of the total of 1000 boreholes in the Wolf Creek Dam. Boring should be completed in spring 2013.