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Rotorua Lakefront In-situ Mass Stabilisation

Rotorua Lakefront In-situ Mass Stabilisation

HEB Construction engaged Geostabilization New Zealand Ltd at the project’s initial stages. During this phase, GeoStabilization provided site sampling, laboratory testing, and physical trial panels. These tasks were required ahead of the main works program to ensure the right mix design and binder applications were applied to Rotorua Lakefront’s sensitive soils.

Being at the heart of the New Zealand Central North Island geothermal fields, the Rotorua region’s soils commonly require stabilisation. Design requirements specified a 2 MPa compressive and 500 kPa shear strength from the mass stabilised block to be developed from a soil profile comprising very soft and sensitive silt materials with a natural bulk density of 1400 kg/m3 and moisture content >100%.

After reviewing the site’s geology, GeoStabilization chose a combination of sulphate resistant cement and lime binders to provide the suitable bearing foundation necessary for a new walkway to the lakefront as part of Rotorua Lakes Council’s Vision to Action.

Working alongside and advising Geotechnical Designer Tonkin & Taylor, GeoStabilization developed the optimum mix design following an exhaustive iterative laboratory testing program using sulphate resistant cement (NZS 3101) and hydrated lime to reduce moisture contents. Test panels were constructed in late 2019 using three variations of the preferred mix design. After curing, they were subsequently cored and UCS tested to verify strength gains from soil stabilisation.

GeoStabilization also has extensive experience in soft soils stabilisation using Allu mixing arms. Working within environmental controls of sheet piled cofferdams and protection screens, 6000 m3 of soils were blended with cement-lime binders to a depth of 4-meters below design level in a 4-month period between February and June 2020; with a 1-month stand-down for COVID-19 lockdown. Binders were prepared as a wet grout and blended into the ground in accordance with strict quality controls including the use of a3D working and As Built models to ensure 100% soil stabilisation.

Daily wet grab samples were UCS tested at 7 & 28 days. Core drilling & 46 No. UCS tests on borehole samples verified soil strengths with all achieving >2MPa. Additionally, wet grab & core samples tri-axial testing verified shear strengths >500 kPa.

Project Photos