PolyVoid Case Study Gunnedah NSW PolyVoid Slab Under Abnormal - - PowerPoint PPT Presentation

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
• f 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

• ccurred

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 are now connected into 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