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Meen-Wah Gui, Assistant Professor, Civil Engineering Department,
National Taipei University of Technology, Taipei, Taiwan.
Jean-Pierre Hamelin, Development Director, Soletanche Bachy
4 Rue Henri Sainte-Claire Deville, 92563 Rueil-Malmaison Cedex, France.
Development of an Instrumented Borehole Drilling System for Ground Investigation.
http://www.ejge.com/2004/Ppr0350/Ppr0350.htm
The drilling of holes for grouting tubes creates the potential for obtaining supplementary ground information, which can be valuable to the succeeding tunnel construction.
Based on the offshore exploration technique, an onshore instrumented drilling system that uses a set of pressure transducers placed at various locations of the hydraulic circuits of the machine has been developed and tested on site for ground investigation in order to examine its power to discriminate between ground strata. The method can theoretically be used in nearly every soil type for qualitative interpretation of soil formation changes while grout holes are being drilled. Because of its relatively small sampling interval - at every 5 mm - it can offer to assess local variability of soil formation, which can sometimes be missed by conventional site assessment methods.
In this study, the performance of this system was validated by testing at Kennington Park and Jubilee Line Extension site, in London. The result was then compared with the soil formation obtained from cores samples. Certain components of the drilling system and drilling method have been studied and standardized so that meaningful and globally applicable results can be obtained in the future. The effects of inconsistent drilling system and methods on the quality of data have also been quantified by means of cross-correlation analysis for groups of standardized and non-standardized tests.
Introduction
The concept of instrumented drilling for subsurface investigation has long been applied in the oil and gas industry (Somerton 1959), but it is still a comparatively new concept in on-shore geotechnical engineering. This concept arises from the observation that an experienced driller can actually feel the type of the materials being drilled. If the drilling rig is instrumented and monitored via a computer, these drilled holes can be used to qualify a general view of the soil formations and soil properties through certain drilling parameters prior to a detailed ground investigation. Alternatively, a few conventional ground investigations can first be carried out prior to carrying out further monitored drill holes.
The first on-shore application was via a system called ENPASOL (Hamelin et al. 1982) that was capable of recording various drilling parameters such as bit torque, bit downthrust and drilling speed. It is typically used on rotary destructive drilling rigs and can sometimes be use on coring rigs. In the latter case, the main use is to complete the core description in case of poor recovery.
One motivation for the development of such system is to capitalize on the “fine” data, which is available whenever holes are drilled. In tunneling projects, for example, it has become common to install ‘tube-a-manchettes’ grout tubes during the pre-construction phase of the project, so that grout injections can later be conducted to suppress settlements caused by ground loss. The drilling parameters obtained from the drilling of these grout holes may then be used either to confirm local stratigraphy or to determine the appropriate grout to be used (Guillaud and Hamelin 1992; Chun et al. 1999)
The quality of the data obtained from the drilling system varies depending on the drilling system and drilling method used, and interpretation of the drilling data remains largely qualitative. With the expansion of the drilling data base as a result of its deployment in the underground and grouting works, we hope to improve the understanding of the drilling data quantitatively.
However, in order to obtain a better correlation, certain components of the drilling system and drilling method needed to be standardised so that the correlation derived from different sites can be applied globally without any modification.
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