Volume 25, Issue 2 (June 2002)
A Multisleeve Friction Attachment for the Cone Penetrometer
Accurate knowledge of the strength of soil-geomaterial interfaces is becoming of increasing importance in geotechnical engineering. Systems whose performance is heavily dependent on soil-geomaterial interfaces include deep foundations, synthetic impervious liners, trenchless technologies, and an assortment of earth retaining structures. The strength of the interface is typically estimated by applying adjustment factors to values of soil or interface strength measured in laboratory tests. These adjustment factors are intended to correct for differences between the test and anticipated operating conditions such as variations in soil type and density, strain rate, surface roughness, or confining stress and are often empirically based with little theoretical underpinnings. Of these adjustment factors, the surface roughness is considered to be of utmost importance in that it has the potential to alter the interface strength by 100% or more.
This paper describes the development of a new multisleeve Friction attachment for the cone penetrometer that allows for direct in situ measurement of the relationship between interface strength and surface ronghness. As discussed herein, the ability of the attachment to quantify this relationship, in conjunction with additional ongoing research, provides the opportunity to improve the design of friction dependent systems, as well as site characterization. A key characteristic of the penetrometer attachment is the ability to obtain four individual sleeve friction (fs) measurements at each elevation within a sounding, in addition to the conventional Cone Penetration Test (CPT) fs measurement. This allows for direct in situ analysis of the effects of sleeve roughness on the fs measurement. Considerations pertinent to the development of the device including assessments of the conventional CPT fs measurement and soil geomaterial interface mechanisms are first presented. A description of the new penetrometer attachment including key characteristics and capabilities follows. Finally, validation of the operation of the device through laboratory and field tests is described, and future applications of the attachment are discussed.