Research on the phenomenon of increasing borehole diameter at the installation of rod anchors in marl using wet technology compared to dry drilling procedure

Filipović, Satko and Bektašević, Ekrem and Gutić, Kemal and Musa, Namik and Sakić, Noris (2025) Research on the phenomenon of increasing borehole diameter at the installation of rod anchors in marl using wet technology compared to dry drilling procedure. Global Journal of Engineering and Technology Advances, 22 (2). 001-004. ISSN 2582-5003

The excavation of the “Kobilja Glava” tunnel takes place in a complex geological environment and in a highly urbanized zone with an extremely large number of residential buildings located above both tunnel pipes, as well as in the very close distance of them. More exactly, at the entrance and exit tunnel portals there is a decaying crust whose thickness varies from 3.50 to 6.0 meters. It is an extremely incoherent material that is exposed to significant degradation processes under the influence of atmospheric conditions, which significantly create difficulties while prediction of the actual characteristics of material. Also, the excavation job is being carried out in a substrate that is made of marl, dark gray colour with a distinctly layered structure. For the purposes of this work, exploratory drillholes were drilled using two different technologies. The first implies that the drillholes are made using a wet procedure (flushing of the material from drillhole is done using water under pressure), with the measurement of the diameter of the drillhole at three reference locations inside the drillhole. For this technology the reference value of the drillhole diameter would be achieved by statistical processing. The second technology implied that the drilling of exploratory drillhole was carried with the same equipment, using a dry method (the mud of the material is carried out using compressed air), and that the diameter of the drillhole was recorded in the same way, under identical conditions. The aim of research was to establish how the applied wet drilling method affect to the degradation of the physical-mechanical characteristics of the marl, which has a several chain effects on the construction of the tunnel itself (increasing convergence due to the decreasing the physical-mechanical characteristics of the rock mass, the need for by applying additional supporting elements, increased consumption of injection mixture that results in an increase of negative impact on the environment, etc.)