In France as abroad, property, industrial, logistical or development projects are born every day in spite of continuously reduced availability of suitable land.

To meet the problems of unsuitable land, the construction professionals often use soil consolidation techniques. One of them, pre-loading, consists of using the weight of a fill to compact the soil.

		A simple principle
		One of the major problems in a construction project is the prevention of possible damage to the structure of a building due to settling of the ground. Building land is made up of numerous materials that behave differently depending on their nature or the weather conditions to which they are subjected. The soil’s compressibility, particularly that of the layers it is made of, is one of the criteria that should be studied before construction starts. Pre-loading of land, before starting work, is a technique whose aim is to consolidate the lower compressible layers and to ensure settling to stabilise the surface before construction of the final structure.

		How is it done?
		Quite simply, by putting in place the equivalent weight in fill material of the future building. Thus the ground is compressed under the weight of the fill. When the ground is stabilised (when it has settled), the fill is removed and construction work may start. The pre-loading time depends on the nature of the ground and the thickness and depth of the compressible layer. It can vary between 2 months and a year, even longer. The soil is compressed by removing its contained water. This phenomenon may be speeded up by the installation of vertical drains that drain the water to other parts of the soil or to the surface. This technique is simple to use but very uncertain regarding the pre-loading times; a real challenge for constructors who must ensure quality work in optimum times.