QuakeCoRE Project Update 17 January7 2017 Liquefaction characteristics of pumiceous deposits from high-quality sampling RP Orense & M Stringer

Background In two previous QuakeCoRE research projects, the focus was on sites where liquefaction had been observed following the 1987 Edgecumbe earthquake. Using field-obtained parameters (CPT, shear wave velocity, screw driving sounding data), assessment of the occurrence/non-occurrence of liquefaction at these sites following the earthquake was done using available empirical chart-based approaches. Conventional push-tube sampling and more advanced sampling techniques, such as the gel-push sampler and Dames-Moore sampler, were used to obtain samples at a site to evaluate the most appropriate sampling technique that can obtain high-quality undisturbed pumice deposits. More field tests and soil sampling, as well as laboratory testing, are required at other pumiceous sites in the North Island to supplement current findings.

Previous Research (1) Dilatometer tests Cyclic resistance ratio, CRR Dilatometer Modulus, ED (MPa) Horizontal stress index, kD (after Orense et al. 2012) 7

Previous Research (2) Cone Penetration Test Shear wave velocity Cyclic resistance ratio, CRR Cyclic resistance ratio, CRR (after Orense et al. 2012) Tip resistance, Qtn,cs Shear wave velocity, VS (m/s) Penetration-based methods do not correlate well with the laboratory-obtained CRR. Reason: The shear stresses during penetration were so severe that particle breakage formed new finer grained materials, the mechanical properties of which were very different from the original pumice sand. 8

Research objectives Characterise various pumiceous sites in the Waikato Region by performing field testing at designated sites (e.g. cone penetration tests, shear wave velocity profiling) and high-quality undisturbed soil sampling. Identify appropriate approach(es) for evaluation of liquefaction triggering in pumiceous deposits. It is envisioned that the results of this project will aid in the development of industry guidelines for evaluating liquefaction potential of pumiceous soils.

Research Methodology Identify target sites in the Waikato Region where field testing and sampling will be performed. Perform field testing at the designated sites. If possible, CPT and Vs-profiling and undisturbed sampling would be conducted as close to each other as possible (ideally <2m between investigations). Obtain undisturbed pumiceous samples from the target sites using advanced (e.g. Gel-push or Dames & Moore samplers) sampling techniques. Note: The choice of sampler for each site will be guided by the results from the 2016 QuakeCORE project. Conduct stress-controlled undrained cyclic triaxial tests on the undisturbed soil samples obtained (from previous project as well as this project) and determine the liquefaction resistance of the samples, as well as the development of strain and excess pore water pressure with the applied cycles. Compare the cyclic resistance obtained in the laboratory with the field-based cyclic resistance estimated from field-based parameters. Also, attempt to perform energy-based and/or strain-based approach to best explain the liquefaction resistance of pumiceous soils.

Expected impacts In the short-term, the research output will assist the local profession through guidelines on obtaining high-quality undisturbed soils for use in geotechnical investigation and appropriate field testing at pumiceous sites. Careful examination of the material behaviour under different loading conditions in the laboratory are expected to advance our understanding of the similarities and differences in the behaviour of natural pumiceous deposits relative to purely hard grained material. In the long-term, the research outputs will be combined with previous, on-going and planned future work to develop design guidelines in evaluating liquefaction potential of pumiceous deposits. In addition, the planned journal publications and conference presentations detailing the research outputs will inform the end-users on how to deal with these soils.