Site investigations for residential development on the Port Hills, Christchurch.
Thesis DisciplineEngineering Geology
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Three site investigations for residential development on the Port Hills gave a chance to document remedial measures in volcanic bedrock (McCormacks Bay) and cut and fill operations in loess (Westmorland), and to carry out detailed logging and index testing, as well as strength testing in loess (Westmorland and Coleridge Tce). A design-as-you-go approach was adopted for remedial measures in blast-damaged volcanic bedrock at McCormacks Bay Quarry Subdivision because of potential difficulties in obtaining detailed sub-surface information. Remedial measures included: (a) removal of loose blocks, (b) reinforced concrete buttressing, (c) a gabion basket retaining wall, and (d) a vegetation programme. Engineering geological mapping and face logging are important for delineating and subdividing rock and soil units, as well as active and inactive areas of erosion and slope instability. Geotechnical testing programmes, remedial measures and earth works should only proceed after completion and interpretation of engineering geological plans, sections and face logs. Index tests carried out on loess from Westmorland and Coleridge Tce included: (a) grainsize distribution, (b) Atterberg limits, (c) insitu dry density and moisture content, (d) pinhole erosion, and (e) the crumb test for clay dispersion. Grainsize distribution and Atterberg limits are important tests for identifying a material as loess, but show little variation within loess. Dry density, pinhole erosion and detailed field descriptions from a fresh face allow for the division of insitu loess into layers that represent primary airfall and reworked loess, as well as modification by soil/fragipan forming processes. Total strength parameters (c,ø) were obtained for loess by triaxial testing (UU test) of 35mm diameter tube samples. Maximum strength measured was c=178 kPa, ø=30° (W=8.5%), with a minimum of c=0 kPa, ø=30° (W=19%). A comparison of field density tests on loess fill showed that physical tests (tube samples, Balloon densometer, sand replacement) are directly comparable, while results from a nuclear densometer require simple correction factors to be comparable with physical tests.