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A Field Assessment of Direct-push Technology for Site Characterization Investigations

by Jim Butler, John Healey, Marcia Schulmeister, and Li Zheng
Kansas Geological Survey, University of Kansas

Presented at the 18th Annual Water and the Future of Kansas Conference

In the last decade, direct-push technology has become a widely used alternative to conventional drilling-based approaches for site investigations in unconsolidated formations. This technology uses hydraulic rams supplemented with vehicle weight and/or high-frequency percussion hammers to rapidly advance small-diameter pipe into the subsurface. The use of this technology for hydrostratigraphic characterization is the subject of a recently initiated research program of the Kansas Geological Survey (KGS).

Information about the stratigraphic framework at a site has traditionally been obtained using drill cuttings supplemented with core samples and/or geophysical well logs. The density of information is thus a function of the number of wells at a site. Direct-push technology provides an alternative to this well-based approach. Various sensors can be incorporated into direct-push equipment to obtain subsurface information at an unprecedented level of detail without the need for permanent wells. The potential of this technology is being assessed at a KGS research site in the Kansas River floodplain using a downhole electrical conductivity (EC) sensor. This work indicates that the EC sensor is an excellent tool for rapid delineation of stratigraphic units. The ability of this sensor to resolve fine-scale stratification is demonstrated by comparison of EC responses to visual descriptions and grain-size data from adjacent continuous cores (>12 m in length). These results indicate that direct-push sensors can be extremely useful for mapping thin, laterally continuous layers that may be difficult to detect with traditional methods.

An understanding of site hydrostratigraphy requires estimation of the hydraulic conductivity (K) of various units. These K estimates are usually obtained by performing various types of hydraulic tests in conventional wells. A series of field experiments were carried out at the KGS research site to investigate the potential of direct-push technology for hydraulic characterization of saturated units. Results of constant-rate pumping tests demonstrated that direct-push pipe strings can serve as very useful temporary observation wells. Direct-push installations were also used as temporary wells for an extensive series of slug tests. Although the small diameter of the direct-push pipe can affect tests in intervals of very high conductivity, slug test K estimates were generally in excellent agreement with those from conventional wells when appropriate well development procedures were used. Ongoing research is focussed on development of a new method (hydraulic profiling) for obtaining near-continuous information about K variations with depth (see

Kansas Geological Survey, Direct Push Methods for Hydrostratigraphic Characterization
Updated March 2001
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