2.11 STRETCHING-DEFORMATION OF SOILS IN THE DESIGN OF FOUNDATIONS

Abstract

В статье представлен анализ напряжений в слоях грунтов при проектировании фундаментов. Выделены стадии деформации, наблюдаемые в процессе повышения давления.

Ключевые слова: фундамент, грунт, напряжение, нормальные напряжения, уплотнение, скольжение.

Abstract. This article presents an analysis of stresses in soil layers in the design of foundations. The stages of deformation observed in the process of pressure increase are highlighted.

Key words: foundation, soil, stress, normal stresses, sealing, sliding.

Introduction. When designing foundations, in addition to indicators of the physico-chemical and mechanical properties of soils in the soil, it is necessary to know the stresses in the soil layers. These stresses arise due to additional external load pressures, both natural and transmitted from the structure, created by the ground's own weight.

The natural pressure and the stresses created by it increase from the surface of the earth to its lower layers. On the other hand, the stresses (pressure) created by the external load tend to decrease (disappear) with increasing depth. In this case, each grounding point is affected by six voltage components (s_x , s_y, s_z, t_xy, t_yz , t_zx).

Methods. Stresses, in turn, cause deformation (change in size and shape) of soils. Normal stresses (s) compress the pieces of soil from all sides, compacting them, which, in turn, leads to chipping of particles with each other and an increase in friction forces between them.

When studying the subsidence of soils in the foundation floor, maximum organizers of normal stresses acting on the vertical axis along steep sections are used (s_z).

Rolling tensioners mutually move parts of the ground relative to each other, trying to disrupt their equilibrium position (t). If the amount of breakdown stresses in any section of the soil is greater than its slip resistance, situations such as displacement of parts of the soil or their displacement from the heel of the foundation may occur.

It is known that the particles of bicr are not connected (blurred), and the structures of mountain soils differ greatly from each other. This also affects their deformation properties under stress. The minerals of the stone soils are interconnected with each other. Therefore, in the existing operating conditions of structures, they are mainly elastically deformed. The deformation properties of mountain soils can be estimated on the basis of the generalized Hooke's law, known for the resistance of materials. Consequently, the modulus of deformation (E), the coefficient of transverse expansion (m) and the shear modulus (G) serve as the main indicators of changes in the shape of mountain soils. In this case, the shear modulus is determined by the expression [1-9]:

G = E / 2 ( 1 + m)                                                (1)

The stress-strain states of alluvial and clay soils with weakly bound particles are somewhat more complicated than those of stone soils. Because these soils, first of all, have a diverse, heterogeneous structure, in addition, the mechanical properties of clay soils also depend on the quantity and quality of the water contained in them.

Results. The modern theory of stress states in sections of eroded soils Prof. N.M. Hersevanov research, according to which the following three types of specific stages are distinguished in soil deformation:

1) Sealing stage;

2) the stage of intensive shear and compaction;

3) the stage of general destruction of the floor.

The first stage of deformation is observed at slightly lower values of stresses transmitted from the foundation to the floor and formed in the soil layers. At the beginning of the first phase, due to elastic deformation of the soil under the action of much lower pressures, the foundation may sag slightly (Fig.1, g, line OA). In this case, precipitation occurs due to elastic deformation of soil particles, bound water and ambient air. The pressure characterizing the limit of elastic deformation of the soil is called its structural strength (р_s).

Figure 1. Stages of soil deformation in the foundation [3]:

a – stage of compaction; b-stage of intense shear and compaction; c-stage of general disturbance; d – deposition graph; 1 – traectory of solid particles; 2 – line of particle arrangement before deformation; 3 – line of particle arrangement after deformation; 4 – local displacement fields; 5 – sliding planes (displacements) ; 6- core.

At values р > р_s of pressure from an external load, due to partial compression of water and air in the soil and a decrease in the adhesion forces, the mutual displacement of soil particles relative to each other occurs. As a result, the soil begins to deform elastically[2].

If the pressure increases even more, in areas close to the edges of the foundation, it is possible to observe a mutual displacement of not only soil particles, but also soil layers (Fig.1, b). That is, the applied stresses on these sections of the soil will be equal to or close to its maximum resistance to displacement A S. This condition indicates that the first stage (compaction) is completed and the second stage begins. The slightly curved connection graph
s = f(p) at the first stage (Fig. 1, g, line OB) is conventionally assumed to be rectilinear in calculations.

Discussion. In the second (intense shear and compaction) phase of deformation, observed in the process of further pressure increase, plastic deformations become more intense. At the same time, local sliding platforms appear along the edges of the heel of the foundation (Fig. 1, b). The second stage ends on the eve of the bulge of the soil on the surface of the Earth, which occurs as a result of the fact that the soil layers begin to shift in all directions. The next load of the soil on the foundation base leads to its sharp subsidence and destruction (loss of bearing capacity). The violation manifests itself in the form of a bulge of the soil in the zone of impact of the foundation on the surface of the Earth (Fig.1, c).

The relationship between the variable external load pressure and the subsidence of the floor is shown in the graph (Fig. 1, d). The limiting the stage of deformation compaction is called the first critical pressure at the p_sr,1 describing the boundary of the stage of strong shear and deformation is called the second critical pressure at p_sr,2 [4].

Conclusion. If the foundation works at the boundary of the first stage of the stress-strain state in the floor (р £ р_cr,1), its bearing capacity is considered sufficient. Because in this case, the immersion obeys the law of linear deformation The soil on the floor of properly designed foundations usually works within the first phase of the shape change. According to building codes and regulations (QMQ 2.02.01-98), based on the results of foundation practice, it is allowed to use floor soil up to a pressure р = R_n slightly exceeding р_cr,1. The R_n pressure is called the normative resistance of the floor soil.

References

1. Rasulov X.Z. Gruntlar mexanikasi, zamin va poydevorlar. T.: O‘qituvchi, 1993.
2. QMQ 2.02.01-98. Binо va inshооtlar zaminlari. ⁄ Davlat Arxitektura qurilish qo‘mitasi. Tо 1998. -144b.
3. Buzrukоv Z.S. Zamin va pоydevоrlar hisоT.:O‘AJBNTM,2004 y.
4. Miralimov, M.Х., & Normurodov, S.U. (2019). CONSTRUCTION FEATURES OF TRANSPORT TUNNELS IN THE MOUNTAIN AREAS OF UZBEKISTAN. Journal of Tashkent Institute of Railway Engineers,15(3), 26-35.
5. Khamitovich, M. M., Ulugbekovich, N. S., & Shomansur o’g’li, T. S. (2021). CALCULATION TECHNIQUE FOR TYPICAL CIRCULAR TUNNEL LININGS WITH TAKING INTO ACCOUNT THE INTERACTION OF THE STRUCTURE WITH THE GROUND. Galaxy International Interdisciplinary Research Journal, 9(6), 362-368.
6. Нормуродов, Ш. У. (2022). ТОННЕЛАРНИ ҚУРИШ БИЛАН БОҒЛИҚ ДЕФОРМАЦИОН ЖАРАЁНЛАРНИ АНИҚЛАШ МАСАЛАЛАРИ. Academic research in educational sciences, 3(10), 447-460.
7. Miralimov, M., Normurodov, S., Akhmadjonov, M., & Karshiboev, A. (2021). Numerical approach for structural analysis of Metro tunnel station. In E3S Web of Conferences (Vol. 264, p. 02054). EDP Sciences.
8. Miralimov, M. (2018). Instructions for the design and construction of antimudflow and anti-landslide structures for engineering protection of highways. Tashkent: Research Institute of Highways, 156.
9. Ulugbekovich, N. S. (2022). STRESS-STRAIN STATE OF THE CONSTRUCTION OF A SUBWAY TUNNEL UNDER SEISMIC IMPACTS. World scientific research journal, 8(1), 3-11.