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GROUND COMPACTION - URETEK Deep-Injection

EXPLANATION OF URETEK Deep-Injection

URETEK Deep-Injection is a patented procedure, whereby the bearing capacity of foundation soils may be continuously improved down to considerable depths - or just at a specific depth - by injection of expanding resins.

Improvement is achieved by the controlled application of the forces generated by the expansion of unique URETEK resins. The procedure allows densification and compaction of soil directly under a building, without excavation, vibration or mechanical force.

It can be a fast and cost-effective alternative to piling and underpinning.

Following careful, prior evaluation of ground conditions, the procedure is carried out in two distinct and successive phases.

1. Shallow Consolidation
In this first phase, the resins are injected through small holes into the zone immediately and directly below the building's footings, with the intent of confirming or re-establishing building-to-ground contact by filling any voids which may be present. In addition, any loose soil is encapsulated and the immediate ground is improved by an increase in shear resistance.

2. Deep Consolidation
During 'Phase 2', the resin is injected through long, small diameter tubes, to the required depth, directly into the zone most affected by the mass of the building. (Such zone is often depicted by engineers, by a 'pressure bulb' diagram.)

If necessary to provide continuous vertical support, the process of 'Phase 2' may be repeated at successive depths to form a 'column' of densified ground and the entire procedure is repeated at predetermined intervals, in plan, across the area of concern.

Densification/consolidation occurs adjacent to the point of injection, by filling or compacting large and small voids and fissures, the expulsion of water and air and the formation of conglomerates. Consolidation is verified and injection is stopped when the building just begins to lift.

The concept may be explained by the following example:
Imagine a 10 metre long, stiff, reinforced concrete wall evenly supported by a concrete footing set in the ground. The footing distributes a uniform load (of say 2 tonnes per lineal metre) into the ground. Thus, each portion of the ground (the foundation) only has to support a small portion of the mass of the wall.

By Deep-Injecting directly under, say, the middle of the length of the wall and continuing to inject and compact the ground locally, until the entire wall just begins to lift off that single point, one can conclude that the ground at that particular location can now support 20 tonnes. Lifting of the wall has verified that the ground in that location is then some ten times stronger than it needs to be.

This could be repeated along the full length of the wall.

Describing the procedure in more detail:
Once the injected resin enters the ground, it begins to expand in all directions, developing a force of up to 10,000 kPa (1000 tons/m2 or 1400 psi). Naturally expansion is greater in the direction in which the resin encounters the least resistance and so, initially, the resin moves, expands and compacts where the foundation is weakest and has the greatest need of improvement.

All building structures is are somewhat rigid, meaning that to jack-up one part, adjacent parts will have to be lifted as well. The mass of the building provides a concentrated resistance necessary to cause the expansion force to compact the ground horizontally and vertically, with a factor of safety. In fact it controls the amount of compaction achievable.

Finally, when the ground becomes so well compacted in all directions that, despite the weight of the building above, the direction of least resistance is upwards, a laser receiver fixed to the building, indicates that the building has begun to lift.

The beginning of lift indicates that the foundation, at that location, has attained a bearing capacity capable of supporting not only the static load of the building but also the far greater dynamic forces which developed during the lifting process.

The fact that a whole section of the building will have been lifted off one volume of soil, indicates unequivocally that the load bearing capacity, obtained in that volume of soil subjected to the injection, has reached a value appreciably higher than necessary to support the static load.

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