While it is true that many parts of Perth are blessed with good quality compatible sand to build upon, there are some sands and related earth working practices which lend themselves to an unacceptable degree of subsidence and or lifting. Also, sand used for foundations which is deemed to contain deleterious materials (such as clay or rock) can have an adverse effect on the structural integrity of a building.
During the leveling of a site, it is not uncommon for earth workers to import sand from another site. This sand should be clean fill, of the correct clay content, and free of vegetation or any un-compressible or decaying material. If such contaminated fill is used, the rotting or un- compactable material can slowly break down leaving voids under the concrete slab and or footings. The concrete now having no or little support can crack and subside to the degree that it affects the structural integrity of the building.
Any surface vegetation and rubbish which exists on site must be dug out and carted away, and not just turned over and buried in the construction zone.
Another cause of subsidence cracking can be from loss of compaction due to washouts. Washouts are more common than they should be with many builders not installing stormwater systems correctly or in some cases not at all, leaving it up to the Client to do it after hand over.
Yet another factor is when incorrectly backfilling to depths. When backfilling to depths it is paramount that this be compacted in layers so that a uniform density is maintained through the entire body of fill.
Sometimes you can be blissfully going about your business, unaware that your neighbour is emptying out his pool just on the other side of your boundary line and causing a loss of compaction of your foundation material without even realising it.
Maybe the neighbour has decided to drop the ground level to a point that undermines your footings. Be vigilant and explore beyond your boundary if you suddenly notice new or changed conditions on your property.
Most builders these days will use Chemical Injection when excavating close to the boundary so as not to adversely affect the neighbouring property.
Alex Morrison has worked with a range of businesses giving him an in depth understanding of many different industries including local locksmiths, financial support and health care. As the owner of Integral Media, he is now utilising his knowledge and experience with his rapidly increasing client portfolio to help them achieve their business goals.