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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