Evaluation of undisturbed sampling techniques for pumiceous soils

Evaluation of undisturbed sampling techniques for pumiceous soils M. Stringer, R. Orense, M. Cubrinovski, M. Pender, M. Asadi

Pumice Soils: a need to know! • Pumice is found in many areas of the North Island • Often encountered as an alluvial deposit, mixed with hard-grained materials. • Pumice grains are: • Lightweight • Highly crushable • Vesicular • Normal rules do not apply! Liu, et al. L. , (2015) Wesley, et al. (1999)

Undisturbed Sampling • Choice of sampler is highly dependent on material type and state • Very difficult to obtain undisturbed samples of sandy (cohesionless) materials due to sidewall friction. • Three soil samplers trialled in Christchurch on silts, silty sands and clean sands. • Can these samplers be used to obtain high quality samples of soils containing pumice? Frozen samples Piston/Core samples Yoshimi et al. (1994)

Finding the right site • To examine performance of samplers requires: • Samples from each device taken at similar depths • Relatively thick deposits of target material • Target soils are within the capability of the sampler • Ideal site for available samplers • • Shallow layers of silty sand material No gravel Modest penetration resistances Very little spatial variation • Logged boreholes used as a screening method to find most promising site for sampling

What comes next • Sampling to take place in next 4 -6 weeks • Limited number of samples will be visually inspected on site for quality • Remaining samples sent to the Auckland Christchurch for closer inspection & testing • Comparison against in-situ shear wave profiles from complimentary Quake. CORE project Silty Sand

Opening Doors • Develop expertise on sampling pumice soils • Understanding which tool is appropriate for use on geotechnical projects to define soil parameters. • Starting point for estimating properties using simple tools • Provide the basis for in-depth studies on similar volcanic materials.