Direct push-technologies

Abstract

It is widely accepted that a detailed knowledge of preferential flow and transport paths is essential for site characterization and for a reliable planning of site remediation. Conventional field investigations, however, are invariably hampered by insufficient information about these variations in the subsurface. Commonly, boreholes and geophysical surface measurements are used for such investigation purposes. In case of boreholes, information can be obtained from cores and geophysical logging. Typically, borehole data have high vertical resolutions, but suffer from a lack of information in lateral directions, i.e. between the boreholes. This gap can be filled by the application of geophysical surface measurements which can provide horizontally continuous information. However, due to physical reasons the vertical resolution of surface methods decreases with depth. An alternative approach for the site investigation is the use of Direct Push (DP) technology (also known as "cone penetration testing" or "direct drive technology"). This technology refers to a growing family of tools used to obtain subsurface investigations by pushing and/or hammering small-diameter hollow steel rods into the ground. By attaching gadgets to the end of the steel rods, it is possible to conduct high resolution logging of rock parameters as well as to collect soil, soil gas, and ground water samples. Besides the broad applicability of DP technology, it also allows for a reduction of costs for the installation of monitoring equipment and tomo-graphic surveys. Due to the development of new powerful machines and tools, the application of DP technology increased strongly during the last years and became a viable alternative to conventional methods for site investigation. With the new generation of DP machines several sounding locations can be completed per day. Furthermore, under ideal conditions (e.g. soft, un-consolidated sediments) depths of more than 50 m can be reached. 12.1 Logging tools The most common application of DP technology is the recording of vertical profiles. In contrast to conventional borehole logging, DP methods are mainly set up to record data directly while driving the DP tools into the