Assessment of compressible soils and differential settlement for a proposed cooling tower at Te Mihi Power Station, Taupo

This paper presents the challenges faced during a geotechnical assessment to support the design of a new Cooling Tower within the Steam Turbine Generator (STG) Platform at Te Mihi Power Sation, Taupo, New Zealand. Along with a variable ground model as a result of extensive historical cuts and fills undertaken within potentially compressible soils across the platform, a previously constructed surcharge in the form of an earthfill embankment also extends across a portion of the future Cooling Tower footprint and has remained in place for the past 12 years. The extents of these soils and historical loading sequence were modelled using Settle3 software to predict potential future total and differential settlement associated with the construction of the proposed Cooling Tower spanning across these various zones.

Analysis showed that total settlements including elastic, primary consolidation and creep for a 50-year period in response to the Cooling Towers’ unfactored widespread loads were up to 164mm. Maximum angular distortions of 1:40 were predicted to occur across the transition zone into the previously surcharged area.

An initial option to address the predicted settlements was to extend the existing preload embankment to encompass the remainder of the Cooling Tower footprint that extends over these compressible soils. The intent of this is to over-consolidate the compressible soil in the remainder of the platform to reduce post-construction settlements and differential settlements to within tolerable levels.