Geotechnical Investigation Report

     PRACTICE NOTE GUIDELINES FOR LANDSLIDE RISK MANAGEMENT 2007



          APPENDIX G - SOME GUIDELINES FOR HILLSIDE CONSTRUCTION

                 GOOD ENGINEERING PRACTICE                                                            POOR ENGINEERING PRACTICE
ADVICE
GEOTECHNICAL     Obtain advice from a qualified, experienced geotechnical practitioner 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
                 Use flexible structures which incorporate properly designed brickwork, timber        Floor plans which require extensive cutting and
                 or steel frames, timber or panel cladding.                                           filling.
 HOUSE DESIGN
                 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.                                           Indiscriminatory bulk earthworks.
                 Minimise depth.                                                                      Large scale cuts and benching.
      CUTS       Support with engineered retaining walls or batter to appropriate slope.              Unsupported cuts.
                 Provide drainage measures and erosion control.                                       Ignore drainage requirements
                 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.
      FILLS      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.                       Disturb or undercut detached blocks or
  & BOULDERS     Support rock faces where necessary.                                                  boulders.
                 Engineer design to resist applied soil and water forces.                             Construct a structurally inadequate wall such as
                 Found on rock where practicable.                                                     sandstone flagging, brick or unreinforced
   RETAINING
                 Provide subsurface drainage within wall backfill and surface drainage on slope       blockwork.
     WALLS
                 above.                                                                               Lack of subsurface drains and weepholes.
                 Construct wall as soon as possible after cut/fill operation.
                 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.
   FOOTINGS
                 Design for lateral creep pressures if necessary.
                 Backfill footing excavations to exclude ingress of surface water.
                 Engineer designed.
                 Support on piers to rock where practicable.
SWIMMING POOLS   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
                 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.
    SURFACE      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.
                 Provide filter around subsurface drain.                                              Discharge roof runoff into absorption trenches.
                 Provide drain behind retaining walls.
   SUBSURFACE
                 Use flexible pipelines with access for maintenance.
                 Prevent inflow of surface water.
                 Usually requires pump-out or mains sewer systems; absorption trenches may            Discharge sullage directly onto and into slopes.
    SEPTIC &
                 be possible in some areas if risk is acceptable.                                     Use absorption trenches without consideration
    SULLAGE
                 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 Vol 42 No 1 March 2007                                                                 113