Geological description
Soils created directly by man without technical control. Modern or ancient rubble, dried mud fill placed, and soil from nearby cuttings. They are completely heterogeneous, containing enormous boulders of concrete mixed with plastics, rotting roots and industrial ash. Ubiquitous on vacant plots in the centres of metropolitan areas or in recent extensions such as districts gained from hillside slopes.
Foundation ?
Absolute prohibition on providing structural support on them. Option A: Excavate it entirely and found on undisturbed ground. Option B: Drill through it completely with piles down to the intact substrate.
Excavatability ?
Totally random. You can knock the old foundation pad of the demolished 18th-century building, losing the teeth on the bucket, or you can sink.
Settlements ?
Unpredictably large and uncontrollable (> 10 cm). They never stop settling.
Water table ?
Frequently contaminated if it is an area with a factory history or a classic uncontrolled dumping ground.
Seismic risk ?
Artificial backfills are soils with the worst seismic performance. Their heterogeneity and low compaction cause irregular amplification of the waves and a high risk of differential settlement. In areas with any level of seismic activity, it is essential to remove the backfill or carry out deep piling down to competent natural ground.
Construction advantages
- Typically plans, the result of discharges or prior site clearings.
Site limitations
- It is completely prohibited to support the house here under the regulations. They are made of rubble.
- They require drilling them using piles until the true ground is reached, or emptying them completely and filling them with concrete/clean gravel (very high additional cost).
- Risk of contamination, sulphates that attack the concrete, or even gases if it was a refuse tip.
Where this soil is found
Alerts
Hazard- To carry over the backfill is an unmovable rule of civil construction and always requires a mandatory minimum geotechnical study to verify the thickness of the artificial layer.
- Abrasion for foundation concrete due to the sulphate content (rotten foliage, gypsum from older partitioning walls). It may require antibacterial admixtures or sulpho-resistant concretes.
- Pay attention to the presence of enclosed, flammable organic gases; it is compulsory to check with gas detectors during drilling in areas of former landfill.