The upper layer of soil with a thickness of several tens of centimeters, containing humus and roots of plants, has a low strength, so the house on this layer cannot be built — it must be removed. Of course, you can use it in the garden for beds and hotbeds, flower beds and flower beds. Further, it is necessary to pay special attention to the opened layer of a ground — durability of the future construction depends on its properties. The best soil is homogeneous, and the foundation on such soil will be deposited evenly, without distortions and cracks.
Let's consider the most common types of soils and peculiarities of foundation erection.
The most durable is rocky ground. Rock soils are cemented and soldered, lying in the form of a solid mass or fractured rock layer, they are the most difficult for engineering and geological research and in the Moscow region are usually found at great depths. Rocky soils are characterized by high compressive strength in a water-saturated state. These may be erupted rock arrays with a crystalline structure characterized by significant density and low moisture content, or layered structures consisting of sedimentary rocks composed of sandstone, limestone, dolomite and clay shale. It does not deform, dilute, or freeze, but it is also very heavy for construction work. Therefore, trenches in such soil can be avoided by laying the foundation directly on the surface of the pre-leveled site.
The next strongest is gravel and cartilage. Gravel is a natural or artificial material, which is pelletized grains of 5-70 mm in size and a smooth surface. They as well as the rocky ground, do not deform and do not erode, slightly freeze. In these soils, the depth of the foundation should be at least 0.5 meters. The design resistance of such soils is 6.0 kg/cm2 (for dense soils) and 5.0 kg/cm2 (for medium-density soils).
The clay is even less firm it is widely spread throughout the Moscow region and is one of the main soils to be studied in engineering and geological surveys. Clayey soils consist of very fine (less than 0.005 mm in size) particles, which are mainly flaky in shape. Clayey soils are divided into clays (with clay particles content exceeding 30%), loams (10...30%) and sandy loam (3...10%). Clay is deformed (compressed), during freezing it expands significantly, squeezing the foundation, and the ground pressure can reach 10 t/m2. Clays have many thin capillaries and a large specific contact surface between the particles. Through the capillaries, the water fills all the pores of the clay, forming thin water-colloid films that envelop the particles of the ground skeleton. The mutual attraction created ensures the viscosity of the clay soil. Since the clay pores are mostly filled with water, the freezing of the clay increases the volume and starts the blowing process. Clayey soils are subject to more compression than sandy soils, but under the influence of loads, the compaction speed of clay is much lower than that of sand. As a result, the clay-based buildings continue to precipitate for a long time. The bearing capacity of a clay base is mainly dependent on its moisture content. Thus, the bearing capacity of clay in plastic and liquefied state is very low, while dry clay is able to withstand a significant load. In places with high ground humidity, the depth of the foundation should correspond to the calculated depth of freezing. This also applies to other damp soils. The design resistance of such soils is 3.0 kg/cm2 (for dense soils) and 1.0 kg/cm2 (for medium-density soils). Therefore, it is very important to know the physical and mechanical parameters of the clay deposits during construction in the Moscow region.
Sandy soils consist of particles of 0, 1... 2 mm. As well as clays they are very common in the Moscow region. Depending on the ratio of particles of different sizes, sands are divided into gravel, large, medium size, fine and dusty sands. Sandy soils are very easy to work with. The coarser and cleaner the sand, the greater the load it can absorb. Due to the high permeability of water, moisture of gravel, large and medium-size sands practically does not affect their mechanical properties, and fine and dusty sands saturated with water, acquire mobility (floats). This leads to a significant decrease in the bearing capacity of the base. Coarse and clean sands are not swollen during freezing, give a quick and final settlement under load and are a good base. The depth of foundation laying on such soils will be determined by the calculated depth of freezing.