MCU14/0024 - Response to Information Request - Attachment 3

Using the Qualitive Risk Analysis Matrix (refer appendix) we have established the following
characteristics for the allotment.

Landslip Mechanism : Translational, Rotational or Creep Flow
We consider a potential landslip mechanism will consist of either a Rotational or Translational
Landslide or Creep movement within the sloping profile. Diagramation representation of these
mechanisms are appended to this report. We are of the opinion that this movement could occur
following over excavation or scour.
Likelihood of Landslip ‘ Likely
This is due to the evidence during our site visit which the surface grade within the allotment.
Consequences to Property i Minor
With these factors considered we classify the allotment as:-

MODERATE RISK OF LANDSLIP

Although we consider the allotment has a moderate risk of landslip, building work undertaken on the site
should follow accepted methods which assist in maintaining slope stability.

Such measures are discussed in the following section.

HAZARD MITAGATION — CONSTRUCTION RECOMMENDATIONS

We consider the primary risks for landslip occurring within this allotment is over excavation or,
stormwater scour and vegetation removal.

The construction of any cut/fill platforms within the site will lead to an increased risk of landslip.

Any over excavated (steep) cuts may lead to landslip. Similarly, steep fill batters may be susceptible to
slip or erosion.

Any exposed fill batters are susceptible to weakening from saturating rains and stormwater scour. This
risk is compounded, where poor compaction is achieved when placing the fill. Any fill batter profiles
should be limited to a maximum grade of 1 to 3 (vertical to horizontal). Where possible the fill platform
should be benched into the natural profile after the removal of all organic material i
Surface stormwater runoff should be diverted around fill batters. Vegetating the fill batter can improve
the batters ability to resist slip and or scour. Where these recommendations are unachievable,
benching, shoring or retaining measures should be implemented.

 

Any permanent exposed cut batters should be limited to a maximum slope of 1 to 2.5 (vertical to
horizontal). The face should be protected from stormwater scour with cut off drains above the cut. Catch
drains should also be provided along the base of the cut. The drains must dissipate all stormwater from
above and below the cut. Vegetating the cut batter can improve the batters ability to resist slip and scour.
Steeper batters should be retained with engineer designed retaining walls.

All excavations both temporary and permanent must be adequately battered or retained to prevent
collapse. Temporary excavations for retaining walls can have exposed cut batters of 1 to 1.7 (vertical to
horizontal) taken from the base of the excavation. These earthworks must incorporate shallow surface
spoon drains at the base and along the high side of the cut. Drains must have an efficient outflow down-
slope and clear of the construction area. Any exposed soil face should also be protected against the
potential for stormwater erosion. Saturation of the exposed cut batter from prolonged rainfall will
potentially de-stabilise the cut batter. Programming of the works must consider this possibility.
Temporary backfilling of the slope may be required.Should these recommendations be un-achievable the

 

 

SCG Consulting Engineers 3 SCG Ref: 23277(SL)