Response to Information Request - MCU12/0184

Geotechnical and Slope Stability Investigation




5.3         Groundwater

No ground water or areas of seepage were observed during the fieldwork.


Notwithstanding the absence of a water table at that time, it is noted that rainfall may partially saturate
the soils and an allowance for such unfavourable circumstances should be made in any proposed

building and retaining wall designs.


6           DESIGN CONSIDERATIONS


6.1         Allowable Bearing Capacities

Based on the outcomes of the geotechnical investigation, and the visual observations of the Coffey field

representatives, it is recommended that footings are founded in the natural material at depths not less
than 0.4 metres. Footings not less than 300mm wide may then be designed using an allowable bearing
capacity of 150kPa.

6.2         Footing Recommendations

Strip and/or pad footings may be adopted for the proposed structures. Footings should be founded in
the residual soil or siltstone and a minimum 0.4 metres into the natural soil profile.


Footing excavations should be assessed before placement of concrete by a suitably qualified and
experienced geotechnical or structural engineer to confirm that founding conditions are consistent with
those assumed above.


During construction, the exposed trenches and footing excavations should not be left exposed to the
weather for extended periods. Water should not be allowed to pond in these areas nor should they be
left unprotected to dry and crack in the sun.


If conditions encountered during foundation excavation differ from those described in this report,

geotechnical advice should be sought prior to footing construction.


7     QUALITATIVE SLOPE STABILITY RISK ASSESSMENT

7.1     Introduction to Qualitative Risk Assessment

Risk assessment is a process where potential hazards are observed and/or assessed, and a judgement
made as to the likelihood of that event occurring and an assessment made as to what the

consequences of such an event might be. The ’risk’ assigned (eg: high, medium or low) is a way of
explaining the combination of likelihood and consequences in a relatively simple form.

7.2     Risk Assessment Methodology

This qualitative risk assessment has been carried out to assess the geological hazards on the site and

attempt to define the likelihood of that hazard becoming an event, and as a consequence the resultant
risk to property. A qualitative assessment ranks risk on a scale as opposed to a quantitative risk
assessment that defines the risk as a numerical probability.




Coffey Geotechnics                                                                                            3
GEOTKPAR01945AA1A
23rd April 2013