Slope Stability Report 26-5-2019 OPW19-0193

TRUBUILT
SLOPE RISK ASSESSMENT REPORT



      •   In September 1989 Ewarts Road had been formed along with the driveway from Ewarts Road to the
          current residence, the original access along the creek also appeared to be operational. The slope of
          the proposed house was completely clear of vegetation;
      •   By August 1993 the access road along the creek had disappeared between the boundary of the site
          and Upper Pinbarren Creek Road, although the section within the property appeared to still be used;
      •   Vegetation on the slope around the proposed house did not appear until mid-2001, by this time
          vegetation growth on the remainder of the site had grown to about 75% coverage;
      •   Between 2007 and 2011, the slope on the cut to the current residence suffered a minor slumping
          failure;
      •   By 2008 one of the buildings near the creek had been expanded and appears to be used as a
          residence, but this had ceased by mid-2012;
      •   By mid-2015 additional structures had appeared around the current residence;
      •   Between 2015 and the time of the investigation there did not appear to be any changes to the site.


2.4        Subsurface Conditions

The subsurface conditions on the site were found to comprise the following:

      •   Topsoil – Generally 50mm to 100mm thick, comprised pale brown to brown low plasticity clay. The
          soil showed evidence of biological activity but seemed to lack any significant organic content;
      •   Colluvium – This material comprised clay with gravel and gravelly clay. Gravel comprised platy
          fragments of weathered phyllite. This material was about 0.15m thick in HA1 and became thicker
          down the slope to 0.8m thick in HA3. Note that HA3 had a layer of phyllite within the colluvium
          material, this was interpreted as being a boulder deposited within the original material, but which has
          subsequently weathered in-situ;
      •   Residual soil – Comprises low plasticity clay with gravel to clayey gravel. The material had relic
          foliation structures and abundant sericite. Gravelly material comprised pieces and thin layers of
          phyllite with clay seams between, it appears that the contacts of this material may be gradational;
      •   Weathered rock – the weathered rock comprises extremely to highly weathered phyllite. The
          strength was somewhat variable in thin layers between very low to moderate strength. The material
          is distinctly foliated and breaks down to platy material on excavation.

It is noted that although the excavated phyllite part easily and crumble when worked by hand the in-situ
material does not behave in this manner. It is expected that the weathered phyllite can be excavated using
normal machinery for the cut and foundations. It should be noted that the excavated material will be
problematic to compact and if not compacted correctly will be prone to erosion and slumping.

The geological section in Appendix 1 gives the interpretation of the relative position of these geological units
on the site.




LEONTAKIANAKOS-R-001                                Page 4                                             26 May 2019