Fill and Substructure Study: East Port Hedland

The purpose of this report is to compare costs of alternative methods for raising the ground floor level of buildings on a low-lying area located within the flood plain of East Port Hedland. The site has been identified by LANDCORP as the most likely next stage of residential subdivision in Port Hedland.

Commonly, in Western Australia, a business as usual (BAU) approach is applied to raising site levels, wherein compacted sand fill is introduced to raise ground levels to the required minimum habitable floor level.

CODA’s role, in conjunction with CAPITAL HOUSE AUSTRALASIA Engineers and DAVIS LANGDON Quantity Surveyors, was to interrogate costs associated with alternative housing typologies and various substructure solutions. From this analysis, costs for a comprehensive range of building types, construction types and site-filling levels have been obtained.

The report considers lots being partially raised by filling to minimum ground levels dictated by 1:20 and 1:50 year flood events. Three common sub-structure types, used to elevate the buildings to the required higher 1:100 year habitable floor level, are examined.

A Cost Calculator and series of Comparative Foundation Studies have been prepared to assist in determining and comparing costs (for filling plus sub-structure only) associated with 135 permutations of House Typology, Building Construction Type, Development Building Footprint and depth of Fill.

Intuitively, break-even costs exist between filling and raising buildings via elevated substructures. The report demonstrates that cost optimization is predominately driven by the cost to supply and place fill material, and the total building footprint intensity (i.e. the sum plan area of all buildings as a percentage of the overall site area being filled).

The report provides an exhaustive basis for analysis of costs associated with raising site levels. Furthermore, the model established is suitable for similar interrogation exercises at any site needing to be raised.

During the course of the investigation an attempt to collate local market views on residential housing typologies and construction methods was made.

Research from established Pilbara Home Builders’ websites revealed that the use of suspended floors is not currently favored and that the preferred house types predominantly comprise of a standard steel roof and wall frame construction with a concrete slab on the ground.

The Queensland floods of 2011 generated an extensive review of the response of Architectural, Civil, Planning and Structural design in relation to development in flood plain areas. Our research has collated some of the findings and identified applicable strategies important for consideration when developing in a flood plain. These included appropriateness of building typology and material selection with regards to resilience to water damage and absorption.

For a full copy of the report please email us at studio@coda-studio.com 

Main Image: Flood prone areas around Port Hedland