Lyndsell, B.M; Carey, J.M.; Bruce, Z.R. 2019 SLIDE (Wellington): geotechnical laboratory testing of rock and fill materials, factual report. Lower Hutt, N.Z.: GNS Science. GNS Science report 2019/40. 78 p.; doi: 10.21420/YYAV-YQ36
Abstract
The emergence of anthropogenic slopes (modified by cutting and filling) began as soon as people started settling in New Zealand. Many of these early modifications were relatively small in scale – at the individual house scale – and posed limited risk to early infrastructure. Since the 1950's however, earth-moving machinery and technology (bulldozers and scrapers), coupled with the increasing demand for residential and infrastructure development as the population of urban centres has grown, have led to larger scale earthworks at the suburb scale. As a result of this expansion, much infrastructure and many lifelines are now sited on or below modified slopes. The size and scale of slope modification in Wellington is significant and the associated hazards and risks are now emerging given our knowledge of how such slopes in Wellington have performed over the past 70 years, along with results from new research investigating how natural and anthropogenic slopes could perform in future earthquakes. Despite this, the scale of the problem and the level of risk to key infrastructure are not well known in Wellington. To assess the performance of modified ‘anthropogenic’ slopes in central Wellington under strong earthquake shaking and significant rain events, a detailed understanding of the geotechnical properties of their soils and rocks is required. This factual report presents the results of a suite of geotechnical laboratory testing undertaken on samples recovered from five study sites around Wellington. Laboratory testing has been completed on both drill core samples of intact rock and remoulded samples of fill materials. All geotechnical testing reported was completed in the GNS Science Geomechanics Laboratory with the exception of particle size analysis, which was completed by Victoria University of Wellington and WSP Opus Research Laboratories, Lower Hutt. Rock testing comprised of physical properties (e.g. water content, bulk and dry density), potential fracture index, P- and S-wave velocity, unconfined compressive strength and indirect tensile strength testing. Soil testing of the fills comprised physical properties (e.g. water content, Atterberg limits, density) and shear strength testing using both a direct shearbox and dynamic back pressured shearbox. The results of the testing are presented for each investigation site sampled as a series of tables and graphs in Appendices 1 to 5 of this factual report. The strongest rock strengths were from unweathered sandstone which also yielded the highest Brazilian strengths. The P- and S-wave velocities of the Cataclasites varied significantly and showed an increasing trend with increasing unconfined compressive strength. There was also a positive relationship between S-wave velocities and potential fracture index. The fill material densified and strengthened over multiple shearing cycles. The frictional properties increase with increasing grain size suggesting grain locking during shear (auth)
