Construction work starts from the marking and excavation site for the foundation. Digging takes an important place in estimates of the cost of construction, and a significant amount of money is needed to pay for technologies that produce soil removal. To draw up a budget and estimate the cost, it is not enough to know only the size of the pit - it is also necessary to take into account the characteristics of the soil. One of these characteristics is the rate of loosening of the soil, which allows to determine the increase in volume after removal of the soil.
Illustrative example of calculations
Whatever the construction work, they should all begin with the layout (planning) of the site and the preparation of the foundation. In the estimates provided by the construction company or the owner, the excavation always takes first place. The average consumer is confident that only the excavation and removal of land is included in the evaluation of the preparatory work. However, such work cannot be carried out without taking into account the characteristics of the soil. An important characteristic can be considered the coefficient of loosening of the soil (KRG). Want to figure out what exactly is being discussed and calculate the cost of construction yourself? It is possible. Let's consider a question in more detail.
Why determine the coefficient of loosening of the soil?
Soil volumes before development and after excavation vary significantly. It is the calculations that allow the contractor to understand how much soil will have to be removed. To make an estimate of this part of the work, the following are taken into account: soil density, its moisture level and loosening.
In construction, types of soil are conventionally divided into two main types:
The first view is also called rocky. These are mainly rocks (igneous, sedimentary, etc.). They are waterproof, with high density. For their development (separation), special explosion technologies are used.
The second type is non-cemented rocks. They are dispersed, easier to process. Their density is much lower, therefore, development can be carried out manually, using special equipment (bulldozers, excavators). Uncemented species include sands,
loams, clay, chernozem, mixed soil mixtures.
The most important factors determining the cost of preparatory excavation
What should be considered when calculating? The complexity of the development and, accordingly, the cost of work depends on four indicators:
- humidity (water content in solid particles);
- density (mass of cube of soil before development, in its natural state);
- adhesion (shear strength);
- loosening (ability to increase volumes during development).
The coefficient of loosening of the soil is a table (see below).
We take into account building codes
Soil moisture is fixed in percent. The norm is 6-24%. Accordingly, 5% and below are dry soils, and 25% and above are wet.
The knowledge of adhesion indices 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 regulated by the composition of the earth and its moisture content. In the lightest categories are sandy loam, sand; in the densest - 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 occupy after excavation, in a selected form.
KR on SNIP
Soil loosening coefficient according to SNIP:
- The CD of loose sandy loam, wet sand or loam at a density of 1.5 is 1.15 (category one).
- The CD of dry unconsolidated sand at a density of 1.4 is 1.11 (category one).
- CR of light clay or very fine gravel at a density of 1.75 is 1.25 (third second).
- Raman density of dense loam or ordinary clay at a density of 1.7 is 1.25 (category three).
- Raman shale or heavy clay at a density of 1.9 is 1.35.
We leave the density by default, t / m3.
Residual loosening
This indicator reflects the state of caked soil. It is known that formations loosened during the development of a site coalesce over time. There is their compaction, sediment. The natural process accelerates the action of water (rain, artificial irrigation), high humidity, tamping mechanisms.
In this case, there is no need to calculate this indicator - it is already known and can be found in the table above.
The figures reflecting residual loosening are important both in large (industrial) and private construction. They allow you to calculate the amount of gravel that goes under the foundation. In addition, indicators are important for the storage of selected soil or its disposal.
We calculate on our own
Let's say you want to develop a site. The task is to find out how much soil will be obtained after the preparatory work. The following data are known:
- pit width - 1.1 m;
- type of soil - wet sand;
- pit depth - 1.4 m.
Calculate the volume of the pit (Xk):
Xk = 41 * 1.1 * 1.4 = 64 m3.
Now we look at the initial loosening (coefficient of loosening of the soil in wet sand) according to the table and consider the volume that we will get after work:
Xr = 64 * 1.2 = 77 m3
Thus, 77 cubic meters is the volume of the reservoir that must be removed at the end of the work.