Abstract:

A new sampling method using thick water-soluble polymer was developed to obtain high quality drillcores from more difficult grounds like fractured zones or heavily weathered rocks. Yanagisawa et al. (2004) suggested some mechanisms for this sampling technique like Weissenberg effect and/or film coating effect of the polymer solutions. The Weissenberg effect is one of the characteristic behaviors of non-Newtonian viscous fluids and represents an increase of normal stress due to revolutionary movements (Masuda, 1987). As one of its typical phenomenon, some polymer solutions tend to move inward and climb along the revolving axis when stirred by a rotator. The increase of normal stresses, thus confining stresses on drill-cores, certainly contributes to increase shear strengths during rotary drilling. In addition, Sato (2009) proposed an introduction of high water-absorption polymer as an additive to the water-soluble polymer solutions for a better performance of the polymer sampling method. However, it is not known the relationship between the Weissenberg effect and concentration of high watersoluble polymer, or concentration of water-absorption polymer. Furthermore, a couple of cases were reported where quality samplings were not achieved using this polymer sampling method in coastal sandy grounds within a site of power station and close vicinity of railway tracks. The influences of salinity of groundwater and the earth currents were considered as possible reasons for these problems. Therefore Ishizaki et al. (2010) demonstrated that, marked Weissenberg effect was observed for the concentrations 4–10% for water-soluble polymer, practically no effect was found for the concentrations 0.00–0.15% for super-absorbent polymer. Therefore, to understand the mechanism of the polymer sampling, the film forming effect of both water-soluble polymer and super-absorbent polymer. In the meantime, there was a case where undisturbed samples could not be obtained from sandy ground by this polymer sampling. Since the site was in a polymer station located close to the sea side, the salinity of groundwater and the telluric currents were considered as possible reasons for the failure. Therefore, investigation was also made to examine the influences of salinities and electrical currents on the film forming effect of both water-soluble polymer and superabsorbent polymer.

Background

A new sampling method using thick water-soluble polymer was developed to obtain high quality drill-cores form the most difficult grounds such as fractured zones or heavily weathered rocks. Yanagisawa et al. (2004) suggested some mechanisms for this sampling technique like Weissenberg effect and/or film coating effect of the polymer solutions. The Weissenberg effect is one of the characteristic behaviors of non-Newtonian viscous fluids and represents an increase of normal stress due to revolutionary movements (Masuda, 1987). As one of its typical phenomenon, some polymer solutions tend to move inward and climb along the revolving axis when stirred by a rotator. The increase of normal stresses, thus confining stresses on drill-cores, certainly contributes to increase shear strengths during rotary drilling. In addition, Sato (2009) proposed an introduction of high water-absorption polymer as an additive to the water-soluble polymer solutions for a better performance of the polymer sampling method.

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