Influence of soils on ground underground pipes during earthquake

The most important characteristics for soil evaluation are bulk density, porosity versus pressure, angle of internal friction and adhesion. As you know, these characteristics can not be considered "constants", but depend on the state of the rock.

The aim of the paper is to study the effect of water saturation on the strength of sandy soil. In the following chapters, some analysis will be carried out of experimental materials on the resistance of sandy soil to shear in an air-dry and completely water-saturated state obtained by the author in a laboratory studying the physical and mechanical properties of soils. On a concrete example, the inconstancy of the coefficient of friction for the same rock will be considered, depending on its state. And also curves of changes of this characteristic are constructed in connection with the change of the ground state from air-dry to completely water-saturated state.

Also, the magnitude of the angles of internal friction of sandy soil will be considered, depending on its granulometric composition and density.

The strength of soils in a broad sense is their ability to resist destruction. In engineering-geological purposes, first of all, it is important to know the mechanical strength of soils, i.e. their ability to resist destruction under the influence of mechanical stresses. Moreover, if the deformation characteristics of soils are determined at stresses that do not lead to destruction, the strength parameters of the soils correspond to critical destructive stresses and are determined under extreme loads that cause either division of the body into parts (for elastic soils) or irreversible change in the shape of the body as a result of deformations of the plastic flow (for plastic soils).

The physical nature of the strength of soils is determined by the forces of interaction between their structural elements - crystals, grains, debris, aggregates, particles, etc., i.e. depends on the type and features of the structural links. The greater the force of interaction between the structural elements of the soil, the higher its strength is in general [3].

The modern scientific thought of many scientists gives a definite indication that the stability and strength of the soil in the structure is strongly influenced by the water present in its pores, therefore the water resistance of soils, along with other physical characteristics, occupies a significant place in soil science.

To sandy soils it is customary to refer to soils that have a granular structure and between grains of which, due to the absence of this or that cementing substance, there is not any significant coherence. The maximum amount of water that can be absorbed by sandy soils does not exceed the volume of their pores in the dry state. Absorbing water, these soils do not expand (do not swell), and when dried - do not shrink (do not shrink). In addition, the distinctive properties of sandy soils is the lack of plasticity and some ability to suck water through the capillaries.

Based on the results of investigations of sandy soil, the dependence of the angles of internal friction on the granulometric composition and porosity, and on the degree of water saturation was established.

The size of the angle of internal friction in sandy soils is affected by dispersity. With an increase in dispersion, the angle of internal friction naturally decreases due to a decrease in the cohesive forces of the particles: for sand of medium size, φ = 300, for fine sand, φ = 270. The porosity has a significant effect on the magnitude of the shear resistance, while increasing the initial shear resistance. Indeed, for dusty sand having a porosity value of 39%, the greatest internal friction angle in the dry state was found to be φ = 310. For the fine sand, having a porosity value of 41%, the smallest angle φ = 270 was detected. Determination of the shear resistance must be made taking into account the porosity, since otherwise the results turn out to be distorted.

A specific example has revealed and confirmed the assumption of the inconstancy of the coefficient of friction for one and the same rock, depending on its state. The effect of water saturation on the shear resistance of sands of small and medium size is manifested through a slight change in the angle of internal friction. The effect of water saturation is found to a large extent only for dusty sands through a change in the stress state under shear and through a change in the angle of internal friction by 70 compared to the air-dry state.

Used sources:

• 1.    Булычев В.Г. Механика дисперсных грунтов. М.: Стройиздат, 1974.

• 2.    Грунтоведение / Под ред. Е.М. Сергеева. М.: Изд-во МГУ, 1974. с. 198199.

• 3.    Грунтоведение / Под ред. В.Т. Трофимова. М.: Изд-во МГУ, Наука, 2005. 1024 с.

• 4.    Гольдштейн М.Н. Механические свойства грунтов. М.: Стройиздат, 1979. 252 с.

"Экономика и социум" №2 (45) 2018