The durability of any structure depends largely on the correct laying of the foundation, and not the least role in this is played by a sand pillow. One of the requirements imposed on it is to ensure the stability of the structure during periods of soil movement as a result of changes in the depth of occurrence of water layers( groundwater).This happens, as a rule, in the off-season, when snow melts or heavy rains accompany each autumn period. This can also occur when the soil is heavily frozen.
Sand for pillow
It is to ensure the "cushioning" of the foundation of the building, and make a sand pillow. In addition, the sand well aligns the bottom of the trench. In fact, this is a layer of sand under the base of the basement. Therefore, the pillow is made after the trench is ready for the foundation. Its depth depends, in part, on the composition of the soil on which the structure is erected. When it is prepared, it is deepened by 15 - 30 cm, and sand is poured into the trench.
In some sources it is recommended to use fine and medium-sized sand. However, "connoisseurs" advise not to do this, but to take the sand coarse-grained. Fine sand gives a big "shrinkage", whereas with a large one this does not happen. You can use ordinary river sand( "medium").
Features and tips
If sand is damp, then it does not need to be trampled, it will compact itself. And if the sand is dry, then it must be moistened and tamped. In the latter case, it is poured "in batches" and rammed each of them. The quality of the pillow is easy to check - if a person walks on such a sandy backfill and after it there are no traces, the pillow is compacted well.
It is necessary to take into account the level of occurrence of groundwater. For each locality there is its average value. If it is exceeded in the place of foundation laying, then the thickness of the sand layer should be increased. It is necessary to pay attention not only to the evenness of the entire sandy surface, but also to its "horizontal" nature. Therefore, in the process of ramming the pillow, it is necessary to exercise control by means of a building level.
However, you need to consider what type of foundation will be laid. The article provides general information about the sand cushion. But, depending on the foundation, there are also nuances. For example, what form is better to make a pillow( perhaps, also trapezoidal?).Therefore, in each specific case, it is necessary to study this question in more detail.