Cone Penetration Testing in Polar Snow

Abstract Rate-controlled Cone Penetration Testing (CPT) using unique portable equipment was recently conducted in Antarctica. This testing was undertaken in an attempt to investigate the strength and thence bearing capacity of polar snow via insitu means. The application of this technique may prove useful in assessing numerous physical parameters of snow and other geomaterials found within the Polar Regions including stratigraphy, density, strength and bearing capacity. This paper explores some of the data found within this preliminary investigation and highlights the possibilities for future employment of the method, including the possibility of introducing Laser Induced Florescence tools (LIF) as additional sensors for the insitu detection and speciation of hydrocarbon contaminants. Further, the measuring of sleeve friction in addition to tip-resistance may provide insight into material microstructure, significantly enhancing any strength estimate. The use of this easily deployable equipment in polar environs can provide significant site investigation data that may not otherwise be obtainable. Introduction Investigation of snow pack physical properties has long been of interest to researchers, both as a means of assessing avalanche potential, and for estimating the load bearing capacity of snow pavements. Abele (1990) outlines three methods of strength assessment; surface load tests, sample testing and probing, however only probing provides a time and cost effective insitu means of assessment. The Swiss rammsonde is a portable impact penetrometer that has been used since the 1930's to assess snow stratigraphy and the relative resistance of snow layers, however it is of limited value in calculating reliable empirical or physical relationships due to the rate-dependency of snow. Schaap and Fohn (1987) have used a manually inserted modified electric cone penetrometer with a cone diameter of 11.3mm, however the manual insertion method and restricted capacity limit the usefulness of a similar device in polar snow. Numerous other instruments have been developed for assessing snow strength and stratigraphy (Bradley, 1968; Dowd & Brown, 1986; Mackenzie & Payten, 2002; Schneebeli & Johnson, 1997) however they are all limited in depth and capacity, and are not suited for assessing dense polar snow packs where strength in uniaxial compression may approach 3 MPa (Mellor, 1975). Adaption of existing commercial CPT equipment was therefore necessary. Equipment A set of 10kN ‘basement’ rams with a stroke of 50cm was connected to a proprietary steel A-frame and mounted within a fabricated steel box. This innovative CPT rig was constructed to mount directly onto the standard three-point hitch of an agricultural tractor (Fig. 1). The standard three-point hitch cannot counter substantial upward reaction forces, hence an additional heavy steel bar was used to connect the base of the A-frame with the upper tractor-link as necessary. This link could be easily removed to allow lifting of the ‘box’ for conduct of additional tests, and additional screw anchors can be used should additional reaction force be necessary. This arrangement can be mounted on any suitable tractor and allowed rapid testing over large areas.