Geotechnical Design

1 Proposed Palisade Wall
An inground palisade wall, with returns to prevent lateral regression and tie-back anchors has been selected to provide protection to the
proposed residential development from the potential cliff-top regression and associated instability. The wall has been designed to protect the land upslope from future slippage for a minimum 100-year period. The palisade wall does not protect the land downslope of the wall. The wall will require ongoing maintenance in the form of shotcreting soil exposed between piles as the cliff regresses.

2 Design Analysis
Rock Science RS2 2D finite element analysis (FEA) software has been utilised to assess the bending moment and shear forces acting on the selected remedial option (elastic-plastic analysis). (i.e. 4.4m above the highest recorded GWL during the monitoring period).


3 Design Loading
The Council Practice Note for Retaining Walls (AC2231, Version 5) recommends a minimum surcharge of 12kPa above walls where there is the potential for future driveways or buildings or 5kPa minimum surcharge for all other cases. An additional surcharge of 20kPa has been applied to account for the building footprint area at the site. This is considered conservative for the analysis as the house foundation are to be founded on pile foundations within the zone of influence of the wall.
A design seismic acceleration of 0.06g for a 1 in 150-year Intermediate Limit State (ILS) event was adopted for the seismic scenario based on the Ministry of Business, Innovation and Employment (MBIE) Earthquake Geotechnical Engineering Manual. Calculations of the
design seismic horizontal acceleration have been appended in this report.

4 Performance Requirements
The target Factor of Safety (FoS) against instability are based on the Auckland Council Code of Practice for Land Development and Subdivision Section 2 – Earthworks and Geotechnicalm Seismic (1 in 150 year) 1.2

5 Elastic-Plastic Analysis
The results of the FEA have been provided to the structural engineer for design of the steel reinforcing and anchor connections.

Retaining Wall Construction

1 Inspections

RILEY would be pleased to provide this service, along with any Council consent mandated construction monitoring, and believes the project would benefit from such continuity.

2 Long-term Slope Maintenance
Vegetation cover should be encouraged to establish on the cliff and the slope below the wall.