Issues with geotechnical investigations, design and construction in remote locations

This paper discusses the complexities of providing geotechnical design parameters for rock anchors and shallow foundations for an access stairwell at the 20 m high, vertical walled, To Sua Ocean Trench in Samoa.

Restricted by an absence of relevant published geotechnical information, local resources and equipment, as well as on-site testing limited to shallow subsurface investigations and visual site observations, the geotechnical design parameters are constrained to conservative estimates.

Hand auger borehole testing with associated in situ strength testing (Scala penetrometer and shear vane testing) was completed in the surficial soils at the top of the trench, rock samples were collected for UCS testing (where accessible) from the vertical walls, and Scala penetrometer testing was completed through the water at the base of the trench. Additionally, geological mapping and detailed evaluation of the rock face was undertaken.

Without cored borehole investigations, rock strength data and evaluation of the presence and prevalence of defects within the rock mass, recommended geotechnical design parameters are conservative assumptions, analogous with published values for weathered, relatively porous, basalt rock from internationally recognized standards. Consequently, geotechnical designs are less cost-effective and assumptions require verification during construction.