PolyVoid Case Study

Gunnedah NSW

PolyVoid Slab Under“Abnormal Moisture”

Conditions

The Customer’s Concern

• Client contacted Builder claiming the slab had sunk under his en-suite

• 3 hairline cracks were around the doorway from bedroom to en-suite, and en-suite to wardrobe

• The fall of the non-screened shower had changed and water was falling away from the waste slightly

It Started With This

‘Pooling’ Capability

Created with Paving Edge

Drains All Covered Up

Half of the Pot Plants had been

removed at this stage

A Tap Was Leaking

Continuously next to a

lightweight Section of the

House

En-Suite

No drainage behind DIY retaining

wall

What We Knew About the Soil

• The site tested as having a Ys of 100-120mm• It had rained for a month prior to construction of the slab and the soil was considered to be at 40-50% saturated• This was one of the first PolyVoid Slabs in NSW and therefore the practice of connecting the edge piles was not carried out• Only the soil around this particular wall was wet. In all other areas of the house perimeter, the soil was dry

The Soil’s Reaction

The Soil’s Reaction

Edge-Beam Voids

Compressing under Heave

Force

Soil had not swollen as much at the perimeter. There was still space under the edge-voids

The Soil’s Reaction

Plastic Membrane

225mm PolyVoid

‘Heaved’ Soil

The Soil’s Reaction

An estimated total of

200-210mm of heave has occurred

Root Cause Determination

• After many inspections and assessment by structural and geotechnical engineers, it was determined that there had been a two-stage effect on the slab• Stage 1 was that the daily watering of the many pot plants, leaking tap, and lack of proper drainage had created the initial stages of heave• The Stage 1 level of movement caused the plumbing to fail under the en-suite as the proper expandable joiners were not used• Stage 2 was the excessive moisture forced under the slab from the shower waste as the plumbing was not working

The Soil’s Reaction

The fully suspended slab allowed the plumber to get in and replace the pipes and joiners

The Soil’s Reaction

The fully suspended slab allowed the plumber to get in and replace the pipes and joiners

The End Result• The plumbing was repaired using the appropriate joiners etc• The soil was removed from the underside of the slab and left to dry for a period of time• The slab settled back down the 50mm onto the piers• All of the cracks closed up and the shower is now falling properly directly into the waste• Further investigation has revealed an unidentified source of subsoil water, and a storm water run-off issue at the back of the property. The council is now involved

Key design changes

PolyVoid Slabs for Reactive Soils

Screw Piles arenow connectedinto the slab

Key Design Changes• After years of research, testing and number crunching, The Katana Void Slab Manual has been published• The concrete member calculations in this design manual has been given third party certification by a leading Australian engineering firm• Extensive testing on the new slab design proved the slab’s capability in soils with a Ys of up to 140mm• All Katana documentation is available for structural engineers on a specifically issued USB stick