Installation of cables for monitoring purposes in the ground by using Horizontal Directional Drilling

Abstract: The median age for Swedish earth embankment dams is about 60 years. Due to its longevity, one of the major concerns is the internal erosion causing increased seepage through the dam, which ultimately may increases the risk for dam failure. To meet this challenge, there is a need for improved monitoring methods. This in turn requires sensors to be installed inside the earth embankment dams in order to achieve sufficient coverage and resolution, which is currently being investigated in an experimental dam at Vattenfall's laboratory in Älvkarleby. Horizontal Directional Drilling (HDD) has been proposed as a method for installing sensors in the filter zone of earth embankment dams, but it needs to be investigated if this can be done without damaging sensor cables or the dam itself. To approach the aim of the thesis, it was considered to carry out a field-test to install an Electrical Resistivity Tomography (ERT) cable with HDD, not in a dam but on a suitable test site, with similar material properties as parts of the dam, and finally to locate the installed cable with independent methods. Several key questions are listed to track the degree of success of the experiment. Based on the answers to the key questions, it can be concluded that the field test to install the ERT cable with HDD was not successful. About locating the installed cable with independent methods, an idea for positioning of the cable through resistivity measurements was theoretically tried but, because the system of equations developed was analytically unsolvable, it was concluded that it was not feasible. Unfortunately, based on the technologies used, it was not possible to make an accurate judgment on whether HDD is a suitable tool for installing sensors in hydropower earth embankment dams for monitoring purposes. Anyhow, certain recommendations can be drawn from it, such as to carry out an adequate preliminary study in advance to choose the optimal excavation site and to study the technical specification of the drill rig to find out if it is suitable for the drilling and subsequent cable installation. From this project, it is recommended to make a second drilling test in the future considering everything learned in this master thesis.