Geotechnical Report

                         SOME GUIDELINES FOR HILLSIDE CONSTRUCTION
                             GOOD ENGINEERING PRACTICE                                                    POOR ENGINEERING PRACTICE
 ADVICE
 GEOTECHNICAL                Obtain advice from a qualified, experienced geotechnical consultant at       Prepare detailed plan and start site works before
 ASSESSMENT                  early stage of planning and before site works.                               geotechnical advice.
 PLANNING
 SITE PLANNING          Having obtained geotechnical advice, plan the development with the risk           Plan development without regard for the Risk.
                        arising from the identified hazards and consequences in mind.
  DESIGN AND CONSTRUCTION
  HOUSE DESIGN          Use flexible structures which incorporate properly designed brickwork,            Floor plans which require extensive cutting and
                        timber or steel frames, timber or panel cladding. Consider use of split           filling. Movement intolerant structures.
                        levels. Use decks for recreational areas where appropriate.
  SITE CLEARING         Retain natural vegetation wherever practicable.                                   Indiscriminately clear the site.
  ACCESS & DRIVEWAYS    Satisfy requirements below for cuts, fills, retaining walls and drainage.         Excavate and fill for site           access   before
                        Council specifications for grades may need to be modified. Driveways and          geotechnical advice.
                        parking areas may need to be fully supported on piers.
  EARTHWORKS            Retain natural contours wherever possible.                                        Indiscriminant bulk earthworks.
                 CUTS Minimise depth.                                                                     Large scale cuts and benching.
                        Support with engineered retaining walls or batter to appropriate slope.           Unsupported cuts.
                        Provide drainage measures and erosion control.                                    Ignore drainage requirements.
                 FILLS Minimise height.                                                                   Loose or poorly compacted fill, which if it fails, may
                        Strip vegetation and topsoil and key into natural slopes prior to filling.        flow a considerable distance (including onto
                        Use clean fill materials and compact to engineering standards.                    properties below).
                        Batter to appropriate slope or support with engineered retaining wall.            Block natural drainage lines.
                        Provide surface drainage and appropriate subsurface drainage.                     Fill over existing vegetation and topsoil.
                                                                                                          Include stumps, trees, vegetation, topsoil,
                                                                                                          boulders, building rubble etc. in fill.
      ROCK OUTCROPS &        Remove or stabilise boulders which may have unacceptable risk. Support       Disturb or undercut detached blocks or boulders.
             BOULDERS        rock faces where necessary.
  RETAINING WALLS            Engineer design to resist applied soil and water forces.                     Construct a structurally inadequate wall such as
                             Found on bedrock where practicable.                                          sandstone flagging, brick or unreinforced
                             Provide subsurface drainage within wall backfill and surface drainage on     blockwork.
                             slope above.                                                                 Lack of subsurface drains and weepholes.
                             Construct wall as soon as possible after cut/fill operation.
  FOOTINGS                   Found within bedrock where practicable.                                      Found on topsoil, loose fill, detached boulders or
                             Use rows of piers or strip footings oriented up and down slope.              undercut cliffs.
                             Design for lateral creep pressures if necessary.
                             Backfill footing excavations to exclude ingress of surface water.
  SWIMMING POOLS             Engineer designed.
                             Support on piers to rock where practicable.
                             Provide with under-drainage and gravity drain outlet where practicable.
                             Design for high soil pressures which may develop on uphill side whilst
                             there may be little or no lateral support on downhill side.
  DRAINAGE
                 SURFACE      Provide at tops of cut and fill slopes.                                      Discharge at top of fills and cuts.
                              Discharge to street drainage or natural water courses.                       Allow water to pond bench areas.
                              Provide generous falls to prevent blockage by siltation and incorporate silt
                              traps.
                              Line to minimise infiltration and make flexible where possible.
                              Special structures to dissipate energy at changes of slope and/or direction.
              SUBSURFACE Provide filter around subsurface drain.                                           Discharge of roof run-off into absorption trenches.
                              Provide drain behind retaining walls.
                              Use flexible pipelines with access for maintenance.
                              Prevent inflow of surface water.
        SEPTIC & SULLAGE Usually requires pump-out or mains sewer systems; absorption trenches Discharge sullage directly onto and into slopes.
                              may be possible in some areas if risk is acceptable.                         Use of absorption trenches without consideration
                              Storage tanks should be water-tight and adequately founded.                  of landslide risk.
  EROSION CONTROL & Control erosion as this may lead to instability.                                       Failure to observe earthworks and drainage
  LANDSCAPING                 Revegetate cleared area.                                                     recommendations when landscaping.
  DRAWINGS AND SITE VISITS DURING CONSTRUCTION
  DRAWINGS                    Building Application drawings should be viewed by a geotechnical
                              consultant.
  SITE VISITS                 Site visits by consultant may be appropriate during construction.
  INSPECTION AND MAINTENANCE BY OWNER
  OWNER’S                     Clean drainage systems; repair broken joints in drains and leaks in supply
  RESPONSIBILITY              pipes.
                              Where structural distress is evident seek advice.
                              If seepage observed, determine cause or seek advice on consequences.
This table is extracted from PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT as presented in Australian Geomechanics, Vol 42, No 1, March
2007 which discusses the matter more fully.

February 2019