1 - GEOTECHNICAL INVESTIGATION REPORT - 150320 LAR Road Investigation Ridgewood Geotech 23042015_Rev1-Combined

     Ground conditions comprise a layer of residual soil overlying weathered argillite. Tree roots
     are assisting stability within the residual soil layer (see Plates 33 and 34). Undercutting and
     minor slumping has occurred in places (see Plates 27 and 37).

     6.0 Laboratory Testing
     Selected samples collected from the field were delivered to a local NATA accredited
     laboratory (Geotech (SC) Pty Ltd) for testing. Table 2 below provides a summary of
     laboratory test results. Detailed test certificates are present in Appendix C.

     Table 2: Summary of Laboratory Test Results

Auger          Depth       Material       PI       LS      Particle Size Distribution           4 Day Soaked CBR
Hole No.        (m)         Type         (%)       (%)                                          Compacted CBR




                                                                                  (silt/clay)
                                                                                                Dry Density Value


                                                            Gravel




                                                                                    Fines
                                                                           Sand
                                                                                                   Ratio     (%)
                                                              %



                                                                            %



                                                                                       %
AH15-02     0.0-      B-C         14     7.5       52         29        19        100% Std                          20.0
            0.125
Combined* 0.0-0.07 B-C             -      -        50         30        20        100% Std                          19.0
            /0.13
AH15-02     0.2-0.9   S/G          -      -        23         20        57        100% Std                          13.0
AH15-06     0.03-0.7 S/G          22     9.5       19         19        62        100% Std                          11.0
     Notes: B-C = Base-Course; S/G = Subgrade, PI = Plasticity Index, LS = Linear Shrinkage
            * Combined sample – AH15-01 0-0.065 m; AH15-03 0-0.11 m; AH15-04 0.0-0.1 m;
                                AH15-05 0-0.13 m

     7.0 Engineering Comments and Recommendations
     7. 1 Pavement Design
     Results of the auger hole investigation indicate that the base-course/running surface is
     typically similar in composition along the length of the proposed upgrade section. Materials
     typically comprise a mixture of gravel and sand (~80%) and clay/silt fines (~20%) and
     produced 4 day soaked CBR values of 19% and 20%. This layer appears to be well
     compacted however the thickness is variable and extremely thin at some locations (i.e. <100
     mm in 3 of 7 locations). Rock fragments within the layer generally appear to be strong. The
     percentage of fines in the tested samples exceeds that which would usually be considered
     acceptable for a base-course material (typically limited to a maximum of 5-10% fines).
     Although details regarding design axle loads and number of repetitions are unknown, it is
     suggested that due to the variability in thickness of this layer, it should be neglected in the
     design considerations for the pavement and the CBR value of the underlying soil (residual
     and/or fill) should be used in design of the new pavement subgrade.

     Subgrade materials underlying the base-course typically comprise gravelly sandy clays of
     either fill or residual soil origin. The fill appears to have originated from on-site cut-to-fill
     being generally similar to the residual soils on-site. Investigation results suggest similar
     composition of subgrade materials along the length of the pavement section to be upgraded.
     Laboratory results for two samples tested produced 4 day soaked CBR values of 11% and
     13%. Based on these results and the consistency of the subgrade materials encountered it
     is suggested that a maximum design CBR value of 11% be used for design purposes.



     File: 150320 LAR Road Investigation Ridgewood Geotech 23042015_Rev1                              Page 5 of 7