Attachment 3 - Geotechnical Report

LANDSLIDE RISK MANAGEMENT                                                                                        AGS SUB-COMMITTEE


                                                                APPENDIX J
                                SOME GUIDELINES FOR HILLSIDE CONSTRUCTION
                      GOOD ENGINEERING PRACTICE                                                            POOR ENGINEERING PRACTICE
ADVICE
GEOTECHNICAL          Obtain advice from a qualified, experienced geotechnical consultant at early         Prepare detailed plan and start site works before
ASSESSMENT            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, timber        Floor plans which require extensive cutting and
                      or steel frames, timber or panel cladding.                                           filling.
                      Consider use of split levels.                                                        Movement intolerant structures.
                      Use decks for recreational areas where appropriate.
SITE CLEARING         Retain natural vegetation wherever practicable.                                      Indiscriminately clear the site.
ACCESS &              Satisfy requirements below for cuts, fills, retaining walls and drainage.            Excavate and fill for site access before
DRIVEWAYS             Council specifications for grades may need to be modified.                           geotechnical advice.
                      Driveways and 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,
                      Strip vegetation and topsoil and key into natural slopes prior to filling.           may flow a considerable distance including
                      Use clean fill materials and compact to engineering standards.                       onto property 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.
   R OCK OUTCROPS     Remove or stabilise boulders which may have unacceptable risk.                       Disturb or undercut detached blocks or
      & BOULDERS      Support rock faces where necessary.                                                  boulders.
RETAINING             Engineer design to resist applied soil and water forces.                             Construct a structurally inadequate wall such as
WALLS                 Found on rock where practicable.                                                     sandstone flagging, brick or unreinforced
                      Provide subsurface drainage within wall backfill and surface drainage on slope       blockwork.
                      above.                                                                               Lack of subsurface drains and weepholes.
                      Construct wall as soon as possible after cut/fill operation.
FOOTINGS              Found within rock where practicable.                                                 Found on topsoil, loose fill, detached boulders
                      Use rows of piers or strip footings oriented up and down slope.                      or 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 on bench areas.
                      Provide general 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 roof runoff into absorption trenches.
                      Provide drain behind retaining walls.
                      Use flexible pipelines with access for maintenance.
                      Prevent inflow of surface water.
           SEPTIC &   Usually requires pump-out or mains sewer systems; absorption trenches may            Discharge sullage directly onto and into slopes.
           SULLAGE    be possible in some areas if risk is acceptable.                                     Use absorption trenches without consideration
                      Storage tanks should be water-tight and adequately founded.                          of landslide risk.
EROSION               Control erosion as this may lead to instability.                                     Failure to observe earthworks and drainage
CONTROL &             Revegetate cleared area.                                                             recommendations when landscaping.
LANDSCAPING
DRAWINGS AND SITE VISITS DURING CONSTRUCTION
DRAWINGS              Building Application drawings should be viewed by 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 see advice.
                      If seepage observed, determine causes or seek advice on consequences.




                                                                                                     Australian Geomechanics – March 2000                    91