Attachment 2 - Geotechnical Stability Assessment

Attachment F: City Plan policy – Geotechnical stability assessment



Appendix 1: Landslide susceptibility analysis form

LANDSLIDE SUSCEPTIBILITY ANALYSIS                                                                       Analysis No. PG-2096-01
Location:                                      Site No.                 Site Name:
1     Natural Surface Slope                                             9      Material in cutting
Site                                          Level Factor              Site                                             Level Factor
      Less than 5 degrees                       L    0.1                       High strength rock                         L     0.5
0.5   Between 5 and 15 degrees                  M    0.5                       Medium strength rock                       L     1
      Between 15 and 30 degrees                 M    0.8                       Low strength rock                          M     1.2
      Between 30 and 45 degrees                 H    1.2                       Very low strength rock and soil            H     1.5
      More than 45 degrees                      M    0.8                 2     Soil                                       VH    2
2     Slope Shape                                                       10     Cut slope support
Site                                          Level Factor              Site                                             Level Factor
      Crest or ridge                            L    0.7                 0.5 Concrete wall                                L     0.5
 0.9 Planar / Convex                            M    0.9                       Crib wall                                  M     0.9
      Rough / Irregular                         H    1.2                       Gabion wall                                M     1
      Concave                                   H    1.5                       Rock wall                                  H     1.5
3     Site geology                                                             Unsupported                                H     2
Site                                          Level Factor
      Volcanic Extrusive rock                   H    1.1                11     Concentration of surface water
      Sedimentary rock                          M     1                 Site                                             Level Factor
  1   Low grade metamorphic rock                M     1                        Ridge                                      L     0.7
      High grade metamorphic rock               L    0.9                       Crest                                      M     0.8
      Volcanic Intrusive rock                   M     1                  0.9   Upper slope                                M     0.9
4     Soils                                                                    Mid slope                                  H     1.2
Site                                          Level Factor                     Lower slope                                H     1.5
      Rock at surface                          VL    0.1                12     Wastewater Disposal
      Residual soil < 1m deep                   L    0.5                Site                                             Level Factor
      Residual soil 1-3m deep                   M    0.9                 1     Fully Sewered                              M     1
 1.5 Residual soil > 3m deep                    H    1.5                       Onsite disposal – Surface                  M     1.2
      Colluvial soil < 1m deep                  H    1.5                       Onsite disposal – Soak Pit/Trenches        H     1.5
      Colluvial soil 1-3m deep                 VH     2
      Colluvial soil > 3m deep                 VH     4                 13     Stormwater Disposal
5     Fill height                                                       Site                                             Level Factor
Site                                          Level Factor                     All stormwater piped into road drainage    L     0.7
      None                                     L     1.0                  1    Rain water tank with overflows             M     1
 1.1 Less than 1m                              M     1.1                       Stormwater discharge on site               H     1.5
      Between 1 and 3m                         M     1.3
      Between 3 and 6m                         H     1.7                14     Evidence of instability
      More than 6m                             VH    2.5                Site                                             Level Factor
6     Evidence of groundwater                                            0.8   No sign of instability                     L     0.8
Site                                          Level Factor                     Soil Creep                                 H     1.2
 0.7 None apparent                             L     0.7                       Minor irregularity                         VH    2
      Minor moistness                          M     0.9                       Major irregularity                         VH    5
      Generally wet                            H     1.5                       Active instability                         VH    10
      Surface springs                          VH    3
                                                                               Summary
7      Cut height                                                                                                             Factor
Site                                          Level Factor              1      Natural Surface Slope                        M   0.5
       None (Go to section 11)                 L     1.0.               2      Slope Shape                                  M  0.9
       Less than 1m                            M     1.1                3      Site Geology                                M    1
       Between 1 and 3m                        M     1.3                4      Soils                                        H   1.5
 1.7   Between 3 and 6m                        H     1.7                5      Fill Height                                 M    1.1
       More than 6m                            VH    2.5                6      Evidence of Groundwater                     L    0.7
                                                                        7      Cut height                                  H    1.7
8      Slope of cut face                                                8      Slope of Cut Face                           L    0.5
Site                                          Level Factor              9      Material in Cutting                         VH  2
0.5    Less than 30 degrees                    L     0.5                10     Cut Slope Support                           L   0.5
       Between 30 and 45 degrees               M     1                  11     Concentration of Surface Water              M   0.9
       Between 45 and 60 degrees               H     1.5                12     Wastewater Disposal                         M    1
       More than 60 degrees                    VH    3                  13     Stormwater Disposal                         M    1
                                                                        14     Evidence of Instability                    L      0.8
                                                                    Relative Susceptibility (1x2x3x4x5x6x7x8x9x10x11x12x13x14) 0.32

                                                                                                                                  Low




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