Appendix B - Global Stability Assessment Report

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
or steel frames, timber or panel cladding.

Floor plans which require extensive cutting and
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.
Curs 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
RETAINING Found on rock where practicable. sandstone flagging, brick or unreinforced
WALLS 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.
Found within rock where practicable. Found on topsoil, loose fill, detached boulders
FOO Use rows of piers or strip footings oriented up and down slope. or undercut cliffs.
TINGS . A
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.
SUBSURFACE Provide drain behind retaining walls.
Use flexible pipelines with access for maintenance.
Prevent inflow of surface water.
Sepric & 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.