Construction work begins with a marking and excavation site for the foundation. Soil excavation has an important place in construction cost estimates, and a significant amount of money is needed to pay for the technology that does the excavation. To budget and estimate costs, it is not enough to know only the size of the pit - you must also take into account the characteristics of the soil. One of these characteristics is the rate of loosening of the soil, which makes it possible to determine the increase in volume after the removal of the soil.
Illustrative example of calculations
Whatever the construction work, all of them should begin with the marking (layout) of the site and the preparation of the foundation. In the estimates provided to the customer by construction companies or the owner, earthworks always take first place. An ordinary consumer is sure that in the assessmentpreparatory work includes only the excavation of land and its removal. However, such work cannot be carried out without taking into account the characteristics of the soil. An important characteristic can be considered the soil loosening coefficient (KRG). Do you want to understand what exactly is at stake and calculate the construction costs yourself? It's possible. Let's consider the issue in more detail.
Why is soil loosening factor determined?
Soil volumes before and after excavation differ significantly. It is the calculations that allow the contractor to understand how much soil will have to be removed. To draw up an estimate for this part of the work, the following are taken into account: soil density, its moisture level and loosening. In construction, soil types are conditionally divided into two main types:
- cemented;
- uncemented.
The first type is also called rocky. These are predominantly rocks (igneous, sedimentary, etc.). They are waterproof, with a high density. For their development (separation) special explosion technologies are used. The second type is unconsolidated rocks. They differ in dispersion, are easier to process. Their density is much lower, so the development can be carried out manually, using special equipment (bulldozers, excavators). The non-cemented type includes sands, loams, clay, black soil, mixed soil mixtures.
The most important factors determining the cost of preparatory earthworks
Whatshould be included in the calculations? The complexity of development and, accordingly, the cost of work depends on four indicators:
- moisture (water content of solids);
- density (mass of a cube of soil before mining, in its natural state);
- adhesion (shear resistance force);
- looseness (the ability to increase volumes during development).
Coefficient of soil loosening - table (see below).
We take into account building codes
Soil moisture is fixed as a percentage. The norm is 6-24%. Accordingly, 5% and below are dry soils, and 25% and above are wet soils.
Knowing the adhesion parameters helps prevent formation shift during work. The sandy loam index usually does not go beyond 3-50 kPa. For clays, it is much higher and can reach 200 kPa.
Density is controlled by the composition of the earth and its moisture content. In the lightest categories are sandy loam, sand; in the most dense - rocky soils, rocks. Important: the initial loosening data is exactly proportional to the density: the heavier, denser and stronger the soil, the more space it will take after excavation, in a selected form.
KR according to SNIP
Coefficient of soil loosening according to SNIP:
- KR of loose sandy loam, wet sand or loam with a density of 1.5 is 1.15 (category one).
- KP of dry uncompacted sand at a density of 1.4 is 1.11 (category one).
- The CR of light clay or very fine gravel at a density of 1.75 is 1.25 (third second).
- CR of dense loam or ordinary clay at a density of 1.7 is 1.25 (category three).
- KR of shale or heavy clay with a density of 1.9 is 1.35.
We leave the density by default, t/m3.
Residual leavening
This indicator reflects the condition of compacted soil. It is known that the layers loosened during the development of the site, eventually caking. There is their compaction, sediment. The natural process accelerates the action of water (rain, artificial irrigation), high humidity, tamping by mechanisms. In this case, there is no need to calculate this indicator - it is already known and can be viewed in the table above.
The figures reflecting the residual loosening are important both in large (industrial) and private construction. They allow you to calculate the volume of gravel that will go under the foundation. In addition, indicators are important for the storage of the selected soil or its disposal.
We calculate ourselves
Let's say you want to develop a lot. The task is to find out how much soil will be obtained after the preparatory work. The following data is known:
- pit width - 1.1 m;
- type of soil - wet sand;
- Depth of the pit - 1.4 m.
Calculate the volume of the pit (Xk):Xk=411, 11, 4=64 m3.
Now watch the originalloosening (coefficient of soil loosening for wet sand) according to the table and we calculate the volume that we get after work: Xr=641, 2=77 m3
Thus, 77 cubic meters is the volume of the reservoir that is subject to removal upon completion of work.
