Construction work begins with the marking of the site and the development of soil under the foundation. Excavation also occupies the first line in the construction budget, and a considerable amount is accounted for by the payment of equipment that produces excavation and removal of soil from the site. To compile an estimate and estimate the cost of work, it is not enough to know the dimensions of the excavation, it is also necessary to take into account the characteristics of the soil. One of such characteristics is the soil loosening factor, which allows to determine the volume increase when excavating it from the excavation
Soil disintegration factor
All soils from the construction point of view can be divided into two groups:
- Concreted or rocky - rock rocks, the development of which is possible only withuse of explosion or fragmentation technologies;
- Uncemented, sampling of which is carried out manually or with the help of excavators, bulldozers, other special equipment. These include sands, clays, mixed types of soils.
The following properties of soils affect the complexity of development and the cost of excavation:
- Moisture is the ratio of the mass of water contained in the soil to the mass of solid particles;
- Clutch - shear resistance;
- Density, that is, the mass of one cubic meter of soil in the natural state;
- Decompositionability - the ability to increase in volume during excavation and development.
Moisture is a measure of its saturation with water, expressed as a percentage. The normal humidity is within 5-25%, and soils with a moisture content of more than 30% are considered wet. At a moisture content of up to 5%, soils are usually called dry.
A wet soil sample
The clutch affects the shear resistance of the soil, in sand and sandy loam this value lies in the range of 3-50 kPa, clay and loam in the range of 5-200 kPa.
The density depends on the qualitative and quantitative composition of the soil, as well as on its moisture content. The most dense, and, accordingly, heavy are rocky soils, the lightest categories of soil are sand and sandy loam. Soil characteristics are given in the table:
Table - Different categories of
Soil As can be seen from the table, the coefficient of initial loosening of soil is directly proportional to soil density, in other words, the denser and heavier the soil in natural conditions, the more volume it occupies in the selected state. This parameter affects the amount of ground removal after its development.
There is also such an indicator as the residual loosening of the soil, it shows how much the soil is susceptible to sediment during caking, when it comes into contact with water, when tamping with mechanisms. For private construction, this indicator is important when ordering gravel to perform a foundation cushion and other works related to the calculation of imported soil. It is also important for the storage and utilization of soils.
Table - name of the soil and its residual loosening%
Example of calculating the soil loosening factor
The application of the coefficients of initial and residual loosening of soils can in practice be considered using the calculation example. Suppose that there is a need to perform the development of soil under the foundation pit of the buried strip foundation with the subsequent piling of the gravel cushion. The soil on the site is wet sand. The width of the foundation pit is 1 meter, the total length of the foundation stone is 40 meters, the depth of the excavation is 1.5 meters, the thickness of the gravel pillow after the ramming is 0.3 meters.
- We find the volume of the excavation, and, consequently, of the ground in the natural state:
- Applying the coefficient of initial loosening of the soil, we determine its volume after development:
where kр = 1,2 is the coefficient of initial loosening of soil for wet sand, taken from the average value( Table 1).
Therefore, the volume of excavation will be 72m3.
- Find the final volume of the gravel cushion after the ramming:
- We find in Table 2 the maximum values of the initial and residual loosening factor for gravel and pebble soils and express them in fractions.
Initial opening ratio kp = 20% or 1.2;residual loosening factor kor = 8% or 1.08.
- Calculate the amount of gravel for a gravel cushion with a final volume of 12 m3.
Therefore, the amount of gravel required for backfilling will be 13.3 m3.
Of course, this calculation is very approximate, but it will give you an idea of what the soil loosening factor is, and what it is used for. When designing a cottage or a house, a more complicated technique is used, but you can use it for preliminary calculation of building materials and labor for building a garage or a cottage.