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.

Strength Evolution of Ice Plume Deposit Analogs of Enceladus and Europa

“…Below 1 MPa, the linear increase in resistance with depth (Figure 1a) is consistent with high positive values of the strength‐depth correlation factor. This linear increase has been observed in other cone penetration and micropenetrometer measurements conducted in dry, polar snow, where it was attributed to frictional sliding of unconsolidated ice against the steel rod as the cone‐rod assembly advanced (McCallum, 2012, 2014) and to compaction of the unconsolidated ice ahead of the cone (van Herwijnen, 2013). Above 2 MPa, brittle compressive failure of the cohesive aggregate, in which a rigid network has already developed between grains to the scale of the samples, would explain all findings in that regime: the jerky indentation seen in cone penetration profiles (Figure 1b), the approximately constant relative dispersion, the absence of strength‐depth correlation, and a resistance of overall magnitude comparable to the brittle compressive strength of ice.…”

A brief introduction to cone penetration testing (CPT) in frozen geomaterials

“…Elastic modulus. McCallum (2012) examined the direct determination of an effective elastic modulus for snow directly from CPT data, based on the definition of Young’s modulus as the ratio of uniaxial stress over uniaxial strain. Because snow strength can probably be estimated directly from CPT data and the failure strain for ice undergoing brittle compressive failure is ∼0.003 (Schulson and Duval, 2009) then sufficient information can be obtained to generate a profile of effective elastic modulus from CPT data.…”

“…Additionally, McCallum (2012) conducted a preliminary examination of the relationship between cone tip resistance and ground-penetrating radar (GPR) signal amplitude, and work continues into refining this relationship so spatial extrapolation of CPT data can occur using GPR.…”

“…McCallum (2012) successfully conducted rate-controlled CPT in multi-year fast ice. Testing was conducted to a depth of ∼1.2 m in ice of thickness ∼5 m. However, the test was terminated when the CPT rods started bending at resistances exceeding 40 MPa.…”

“…Bader and others, 1939; Schneebeli and Johnson, 1998; Buteau and others, 2005), they have typically been either manually driven or capable of only limited depth penetration, thereby limiting the attainable data. For this reason, McCallum (2012) modified commercial hydraulically driven CPT equipment to conduct extensive testing in Antarctica, validating the use of commercially available friction-sleeve equipped cone penetrometers in polar snow, terrestrial ice and sea ice.…”