Reference Document - Geotechnical Site Classification Repor (As Published)t · MCU25/0022

      The normal structural arrangement is that the inner leaf of brickwork in            Corroded guttering or downpipes can spill water to ground.
      the external walls and at least some of the internal walls (depending on the      • Downpipes not positively connected to a proper stormwater
      roof type) comprise the load-bearing structure on which any upper floors,           collection system will direct a concentration of water to soil that
      ceilings and the roof are supported. In these cases, it is internally visible       is directly adjacent to footings, sometimes causing large-scale
      cracking that should be the main focus of attention, however there are a            problems such as erosion, saturation and migration of water under
      few examples of dwellings whose external leaf of masonry plays some                 the building.
      supporting role, so this should be checked if there is any doubt. In any
      case, externally visible cracking is important as a guide to stresses on the
      structure generally, and it should also be remembered that the external          Seriousness of Cracking
      walls must be capable of supporting themselves.                                   In general, most cracking found in masonry walls is a cosmetic nuisance
                                                                                        only and can be kept in repair or even ignored. The table below is a
     Effects on framed structures                                                       reproduction of Table C1 of AS 2870-2011.
      Timber or steel framed buildings are less likely to exhibit cracking due to       AS 2870-2011 also publishes figures relating to cracking in concrete
      swell/shrink than masonry buildings because of their flexibility.                 floors, however because wall cracking will usually reach the critical point
      Also, the doming/dishing effects tend to be lower because of the lighter          significantly earlier than cracking in slabs, this table is not reproduced
      weight of walls. The main risks to framed buildings are encountered               here.
      because of the isolated pier footings used under walls. Where erosion or
      saturation causes a footing to fall away, this can double the span which a       Prevention/Cure
      wall must bridge. This additional stress can create cracking in wall linings,
      particularly where there is a weak point in the structure caused by a door       Plumbing
      or window opening. It is, however, unlikely that framed structures will be        Where building movement is caused by water service, roof plumbing,
      so stressed as to suffer serious damage without first exhibiting some or all      sewer or stormwater failure, the remedy is to repair the problem. It is
      of the above symptoms for a considerable period. The same warning                 prudent, however, to consider also rerouting pipes away from the
      period should apply in the case of upheaval. It should be noted, however,         building where possible, and relocating taps to positions where any
      that where framed buildings are supported by strip footings there is only         leakage will not direct water to the building vicinity. Even where gully
      one leaf of brickwork and therefore the externally visible walls are the          traps are present, there is sometimes sufficient spill to create erosion or
      supporting structure for the building. In this case, the subfloor masonry         saturation, particularly in modern installations using smaller diameter
      walls can be expected to behave as full brickwork walls.                          PVC fixtures. Indeed, some gully traps are not situated directly under
                                                                                        the taps that are installed to charge them, with the result that water
     Effects on brick veneer structures                                                 from the tap may enter the backfilled trench that houses the sewer
      Because the load-bearing structure of a brick veneer building is the frame        piping. If the trench has been poorly backfilled, the water will either
      that makes up the interior leaf of the external walls plus perhaps the            pond or flow along the bottom of the trench. As these trenches usually
      internal walls, depending on the type of roof, the building can be expected       run alongside the footings and can be at a similar depth, it is not hard
      to behave as a framed structure, except that the external masonry will            to see how any water that is thus directed into a trench can easily affect
      behave in a similar way to the external leaf of a full masonry structure.         the foundation’s ability to support footings or even gain entry to the
                                                                                        subfloor area.
     Water Service and Drainage
      Where a water service pipe, a sewer or stormwater drainage pipe is in the        Ground drainage
      vicinity of a building, a water leak can cause erosion, swelling or saturation    In all soils there is the capacity for water to travel on the surface and
      of susceptible soil. Even a minuscule leak can be enough to saturate a clay       below it. Surface water flows can be established by inspection during and
      foundation. A leaking tap near a building can have the same effect. In            after heavy or prolonged rain. If necessary, a grated drain system
      addition, trenches containing pipes can become watercourses even though           connected to the stormwater collection system is usually an easy solution.
      backfilled, particularly where broken rubble is used as fill. Water that          It is, however, sometimes necessary when attempting to prevent water
      runs along these trenches can be responsible for serious erosion,                 migration that testing be carried out to establish watertable height and
      interstrata seepage into subfloor areas and saturation.                           subsoil water flows. This subject is referred to in BTF 19 and may
      Pipe leakage and trench water flows also encourage tree and shrub roots           properly be regarded as an area for an expert consultant.
      to the source of water, complicating and exacerbating the problem. Poor          Protection of the building perimeter
      roof plumbing can result in large volumes of rainwater being concentrated         It is essential to remember that the soil that affects footings extends
      in a small area of soil:                                                          well beyond the actual building line. Watering of garden plants, shrubs
      • Incorrect falls in roof guttering may result in overflows, as may               and trees causes some of the most serious water problems.
        gutters blocked with leaves etc.                                                For this reason, particularly where problems exist or are likely to occur,
                                                                                        it is recommended that an apron of paving be installed around as much
      •                                                                                 of the building perimeter as necessary. This paving should


                                              CLASSIFICATION OF DAMAGE WITH REFERENCE TO WALLS
                                                                                                           Approximate crack width               Damage
                            Description of typical damage and required repair                                 limit (see Note 3)                 category
             Hairline cracks                                                                                        <0.1 mm                          0
             Fine cracks which do not need repair                                                                    <1 mm                           1
             Cracks noticeable but easily filled. Doors and windows stick slightly.                                  <5 mm                           2
             Cracks can be repaired and possibly a small amount of wall will need to be                 5–15 mm (or a number of cracks               3
             replaced. Doors and windows stick. Service pipes can fracture. Weathertightness              3 mm or more in one group)
             often impaired.

             Extensive repair work involving breaking-out and replacing sections of walls,              15–25 mm but also depends on                 4
             especially over doors and windows. Window and door frames distort. Walls lean                    number of cracks
             or bulge noticeably, some loss of bearing in beams. Service pipes disrupted.




                 8894-193 Sankeys Rd-FEDERAL                                  Page 14 of 15                                                  19/07/2023
Document Set ID: 24390806
                  23591411
Version: 1, Version Date: 18/12/2025
                          28/02/2025