Geotechnical Investigation Report · OPW26/0149

                                                                                                     PTG/04982 – 0001 – Rev0 – Rev0



Table 4: Summary of Emerson Class Testing

    Borehole No.               Depth (m)                              Material                          Emerson Class No.
          BH01                    0.3 – 1.3                          Silty CLAY                                   6
          BH02                    3.0 – 4.5                          Silty CLAY                                   6
          BH03                     1.0 – 1.5                         Silty CLAY                                   5
 Notes:
      •    Class 1 = Complete Dispersion
      •    Class 2 = Some Dispersion
      •    Class 3 = Dispersion after remoulding
      •    Class 4 = No dispersion (calcite or gypsum present)
      •    Class 5 = Dispersion after soil water suspension
      •    Class 6 = Flocculation
      •    Class 7 = Swelling (not slaking)
      •    Class 8 = Not swelling (not slaking)


Table 5: Summary of CBR Testing

 Borehole        Depth                                                                     MDD
                              Material         FMC (%)     CMC (%)        OMC (%)                      Swell (%)       CBR (%)
   No.            (m)                                                                     (t/m3)
                                   Silty
   BH03          0.5-1.5                        26.0          26.0           25.9           1.55           0.0            4.5
                                  CLAY
 Notes:
      •    FMC = Field Moisture Content
      •    CMC = Compaction Moisture Content
      •    OMC = Optimum Moisture Content
      •    MDD = Maximum Dry Density




8 SLOPE STABILITY ANALYSIS
A global stability analysis has been undertaken in the location of the proposed dam. To undertake the analysis, we
have generated a representative cross section (Section A) as shown on the Test Location Plan presented in Appendix
1. This location was chosen as it both mirrors Section A as per the Bax Engineering drawing set, and also captures the
natural ground profile and proposed cut to fill depths through the location of the dam and associated pond.
In undertaking our analyses, we have assessed both the existing ground profile, and the proposed ground profile. The
existing profile was derived from contour information shown on the drawing sets provided, and cross-checked against
Digital Terrain Model (DTM) information which was obtained from the online Elvis webservice 6 . The proposed
development drawings show the maximum depth of cut will be in the order of 2.5 m, while the maximum thickness of
fill will be approximately 3.0 m. The maximum water level within the pond will be 2 m, which coincides with the crest
of the bund.
To generate the subsurface profile the nearby results from our investigation (BH02 and BH03) were transposed on to
Section A. These boreholes generally suggest two in situ engineering units in this location: stiff to very stiff residual
silty CLAY overlying hard silty CLAY. No denser or higher strength material was encountered within the limit of our
investigation (6 m depth) which would allow the generation of a third, higher strength horizon at depth. Instead, the
slope stability models have been constrained at approximately 12 m depth (double the investigation depth) to provide
a limit to the base of the stability models and limit the formation of improbably deep/long failure surfaces.




6 Geoscience Australia. (n.d.). ELVIS – Elevation and depth (Foundation Spatial Data Framework). https://elevation.fsdf.org.au/


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