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Resettlement of land when cracks appear

When we detect cracks in our home, we must be on our guard, especially when they are structural in nature. These types of cracks usually appear in load-bearing walls, partition walls and even floor slabs. In these cases it is advisable to seek the help of a professional because, fortunately, there are different methods to solve the problem.

In a previous post, we discussed how to distinguish the different types of cracks, giving clues to know how to discern the seriousness of each one. In most cases, structural cracks are caused by the nature of the soil on which the house sits.

The common denominators are usually poor soil compaction or dampness, which can swell the floor, increasing the pressure to the point of lifting the foundations or, in other cases, the generation of voids in the pavement and, therefore, the partial collapse of the foundations. In both cases, what we call “differential settlement” occurs.

Whatever the case may be, we have solutions within our reach with which to overcome this problem. We must not forget that just as important as fixing the cracks in our walls is to remedy the cause that caused them. In this sense, we have two highly recommendable alternatives.

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Expanding resin

On the one hand, we can resort to the injection of expansive resin, which is one of the least invasive methods and reduces the dimensions of the work. After carrying out a study of the problem to locate the points where the greatest pressures are produced on the ground, a series of micro-perforations are made, no more than 3 centimetres in diameter and of the necessary depth to reach the problem.

Once these perforations have been made, the resins are injected. These are two-component polyurethane compounds which, while offering very fast reaction times – reaching up to 30 times their initial volume – have a very high expansion pressure (up to 10,000kPa). The resins penetrate through the soil cavities and compact, helping to settle the soil.

The added advantage of this method is that, once the soil has been compacted, the rest of the resin we inject will serve to increase the pressure upwards, raising the sunken foundations to the point that, with due control, we desire.

Micropiles

Another of the most recommended formulas for resolving differential settlement is pressure driven micropiles. This option is more invasive than the previous one and requires the intervention of machinery with which to make the multiple perforations necessary for the concreting of piles of a much larger diameter than that used in resin injection (up to 15 centimetres).

In this technique, steel pipes are coupled or even welded together and driven into the ground under pressure with the help of hydraulic jacks. The result is very good, as they are perfectly anchored in the original foundation thanks to the high-strength mortar.

The disadvantages of micropiling include the fact that it is a larger project, which also entails a certain complexity due to the large number of ramming operations that may have to be carried out depending on the lack of settlement. In addition, these operations are very difficult to carry out in places with difficult access, such as basements, so perhaps the first method is more suitable in these cases.

Combined technique

In some cases both methods can be combined. In this way, in a first phase, the ground will be settled by injecting resins until the sunken foundations are raised.

Subsequently, this mixed technique uses micropiles of no more than 6.5 centimetres, with the aim of increasing the consolidation achieved with the resin and, at the same time and thanks to its greater depth, relieving the load that the foundation transmits to the ground underneath it.

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