Study loess and loess-like rocks primer of the Western Siberia

. Recently, the development problems of the loess subsidence soils as foundations of buildings and structures arise due to climate change on the planet in the consequence to the expansion of human economic activity and other unfavorable factors. For foundations composed of loess subsidence soils, the properties’ prediction is of great importance, taking into account the risks of flooding of territories, modern technologies for setting up foundations in already built-up and newly developed territories. Errors in design can contribute to a significant decrease in the values of strength and deformation characteristics. Also, they can cause subsidence of the soil base, which leads to negative consequences. Therefore, it is important to know the features of the loess subsidence soils formation, their properties, composition, in order to reliably predict their activity under the load during the operational period. This requires modern methods for calculating foundations, taking into account their real properties, such as deformation anisotropy, which is especially important for loess subsidence soils with strongly pronounced anisotropic properties.


Introduction
Loess subsidence soils of the Western Siberia occupy up to 20% of the territory, such large industrial centres as Barnaul, Novosibirsk, Biysk, Omsk, Kemerovo, etc.The operation complexity of the loess soils as the foundations of buildings and structures necessitates their comprehensive study to create rational, new foundations and safe operation of already constructed buildings.In recent years, new problems for the operation of buildings constructed on loess subsidence soils have arisen.The most significant of them is the flooding of urban areas.This is of particular importance for buildings and structures on loess subsidence soils.The process of flooding causes a sharp decrease in strength and deformation characteristics with additional subsidence, destruction of sewer wells, deformation of road surfaces, and etc.Unfortunately, emergency conditions of buildings and structures on loess soils arise not only due to flooding of territories.The existing methods for arranging basements and foundations suffer from certain disadvantages.Compaction of soils with heavy rammers is a seasonal type of work.The performed autumn-winter compaction of loess rocks is often of low quality and leads to unacceptable deformations and often in practice leads to the need to make other decisions.

Methods
Formational Features and Engineering-Geological Characteristics of Loess and Loess-Like Rocks of the West Siberian Plate The West Siberian Plate is considered as one of the major Eurasia structural elements; its outer contours define the natural geological boundaries of the continuous distribution of Mesozoic and Cenozoic sedimentary deposits.It is located in the area between the Kara Sea (north), the Altai-Sayan epiplatform orogen (south), between the Urals (west) and the Siberian ancient platform (east).The most important feature of the West Siberian plate is latitudinal change in the geotechnical setting.In this regard, V.T. Trofimov considers four latitudinal-oriented zones, sharply differing in the modern geotechnical setting: Polar, North, Central and South zones.
In the southern regions of the West Siberian plate, loess and loess-like rocks are on the riverine, drained areas of interfluve valleys and the second-third terraces above the floodplain of the central regions.
In the central part of the plate (according to the research data of V.T. Trofimov and others), loess-like subsidence rocks are mainly widespread.Subsidence properties are manifested their under additional loads and only in rocks adjacent directly to the edge of the slopes, which have a relatively low density and insignificant moisture.Subsidence loess rocks are most widespread in the more southern regions, while subsidence properties are manifested their not only with humidity under additional loads, but also often under the influence of natural pressure.In these areas, non-subsiding loess species are relatively rare.V.T. Trofimov and Ya.E. Shaevich distinguish three following areas within the West Siberian plate: the Ob plateau, which covers an insignificant southeastern part of the West Siberian plate.This area is characterized by the distribution of loess rocks, exhibiting subsidence properties under the load from the soil weight; the southern region is represented by huge spaces of the slab's southern part, the loesslike rocks, which have subsidence properties under additional loads; the northern region, covering the central part of the West Siberian plate, is characterized by the distribution of mainly non-subsiding loess-like rocks with local areas of loess-like strata that have subsidence properties at additional pressures.
A continuation of this work is the map of the engineering-geological conditions of the Novosibirsk region, where five engineering-geological regions and 23 districts are identified.All areas are characterized by the distribution of loess and loess-like rocks, which have subsidence properties with humidity under natural or additional pressure.
As one can find out in the studies, loess and loess-like rocks in the northern part of Tomsk are practically absent, etc. Loess-like rocks of the Omsk Irtysh region are also widespread, but they practically do not have subsidence properties.The same situation is the Kurgan and Tyumen regions, where loess-like rocks have a local character.The study of loess rocks of the Altai Territory is the works' subject of E.V. Trepettsova, G.I. Shvetsova, V.S. Arefieva, T.A. Gorbunova, V.S. Osmushkin and A. Ya.Shvetsov.
Loess and loess-like subsidence soils are widespread in the northern part of Altai, they are alike a cloak in large intermontane spaces and foothill plains, occur in engineeringgeological areas: the Ob and the Ob-Chumyshsky plateaus, the lacustrine-alluvial and Ob-Chumyshskaya plain, Kulunda lowland, valley the Ob River, Tyumen plain, foothill plains of Altai and Salair.The greatest subsidence is observed in loess and loess-like rocks of the southeastern part of the lacustrine-alluvial Ob-Chumysh plain and the Ob plateau in the city of Barnaul.In these areas, the subsidence properties of loess and loess-like rocks are manifested with humidity under natural pressure.Loesslike rocks of the rest of the Altai steppe regions are subsidence, as a rule, under additional pressure.
G.I. Shvetsov identifies the following engineering and geological features of the West Siberian plate: for the southeastern regions of the plate in the basement zone, industrial, civil buildings, land reclamation, road and other structures, deposits of the Late Cenozoic are characteristic, Upper Pliocene-Quaternary and most often Quaternary rocks of various genesis, represented by sandy, clayey, loess and loess-like, as well as gravel-pebble soils.In the Upper Ob region, more ancient deposits of the Jurassic, Cretaceous, Paleocene-Eocene periods prevail; the newest deposits of formations and geological-genetic complexes in the form of interbedded sandy and clayey rocks of various dispersion are widespread in all regions.In the southern regions of the West Siberian Plate, the cover of loess and loess-like rocks is widely developed.There are areas of loess and loess-like deposits in the central regions.These rocks are predominantly weakly lithified, survived only the first stage of lithogenesis, they do not have rigid structural bonds and therefore, most often with weak soils, which physical and mechanical properties intensively change both from the phase state of moisture and from the degree of moisture; the current state of the rocks in the upper part of the West Siberian Plate section is very diverse.Permafrost is widespread in the northern part of the plate, the central part is saturated with highly wetted rocks, and weakly wetted rocks predominate in the southern regions; engineering-geological properties of the West Siberian plate vary in a wide range as a result of their different state.In the regions of the north and center of the plate, highly moistened soils are widespread, which have a relatively low strength, increased or even strong compressibility.Loess and loess-like rocks in the southern plate of the Upper Ob region show subsidence properties in many areas [1][2][3][4][5][6].

Results
Loess-like subsidence rocks of the Upper Ob region are represented by loams and sandy loams with flow rates from solid to semi-solid.Loam is distributed on the territory of the Priobsky plateau, sandy loam-in Kulunda lowland.Within the Novosibirsk Ob region, loess rocks are represented by loam, less often by sandy loam.Analyzing the results of the loam granulometric composition analysis obtained in, we can consider the absence of fractions are larger than 1 mm in the studied volume and the insignificant content of the sand fraction with dimensions of 0.25 ... 1 mm, which is only 1.5 ... 4.1%.The fine sand fraction with the size of 0.05 ... 0.25 mm is 6 ... 34%, the content of the dusty fraction with the size of 0.05 ... 0.005 mm is 50 ... 75%, the content of the clay fraction ranges from 12.1 ... 22%.Loess-like sandy loams, as well as loess-like loams, are characterized by the predominance of dusty particles-60 ... 70%, the content of clay particles there is 5.5 ... 8.5%.The amount of clay particles in loess rocks of the Upper Krasnodubrov sub-formation ranges from 12 ... 22%, the content of the dusty fraction is 54 ... 71%, the content of the sand fraction is uneven in depth: 13% at a depth of 4 m and up to 26% at a depth of 10 ... 11 m.
From the results of granulometric and micro-aggregate analysis given in Table 1, one can see that almost all loess-like rocks have a large dust content of 0.05 ... 0.01 mm in size, which prevails over the content of fine dust (0.01 ... 0.005 m) and dusty sand (0.10 ... 0.05 mm), and that loess-like rocks are strongly aggregated.The content of large grains with a size of E3S Web of Conferences 431, 09006 (2023) ITSE-2023 https://doi.org/10.1051/e3sconf/202343109006more than 0.25 mm in loess-like sandy loams is up to 21%, and in loess-like loams -3 ... 12%, the content of these rocks of fine clay and colloidal particles less than 0.001 mm is 1.5 ... 4.2%.The mineralogical composition of the clay fraction (0.005 mm in size) is represented by hydroslude, mixed-layered formations of hydroslude-montmorillonite composition.Kaolinite and montmorillonite are found as impurities.The mineralogical composition of the fraction with a size of 0.25 ... 0.05 mm is mainly represented by quartz, feldspar, single grains of epidote, hornblende, apatite and other minerals, the presence of iron hydroxide in loesslike loams is not excluded.The gross chemical composition of loess-like rocks of the West Siberian Plate is shown in Fig. 1.
The gross chemical composition of loess -like rocks of the Priobsky plateau is characterized by a high content of SiO2 -59.61 ... 68.36%, Al2O3 -11.02 ...7.82%,FeO3 -3.27 ...7.95%,CaO -1.87 ... 7.11%, and MgO-1.45... 3.67%.V. S. Arefyev, depending on the weathering zones and according to the classification of A. K. Larionov, refers to light loess-like sandy loams and loams characterized by weak bond between the particles (zone of strongly weathered rocks) to the granular-film class of the structure.Light loams are characterized by a stable bond between the particles (the zone of medium-mature rocks), belong to the grain-aggregate class of the structure.Loess-like rocks of the Upper Ob region are slightly saline, the content of carbonates is about 3.5%, and the total amount of soluble salts is 0.1 ... 0.2%.The hydrogen index /pH/ varies in the range of 7.0 ... 7.9 and characterizes the medium as slightly alkaline.The natural moisture content of loess-like rocks increases with depth from 10 ... 11% to 15 ... 17%.In terms of subsidence, loess-like rocks is mainly of the I ground type conditions in terms of subsidence, the value of the relative subsidence of loess-like loams ranges from 0.021 ... 0.079 at a pressure of 0.3 MPa, only in some cases there are loess rocks belonging to the II type.
Considering the physical and mechanical properties of loess-like loams in the vicinity of Barnaul, E. V. Trepettsov states a slight difference in the averaged properties of these rocks from the soils of the Novosibirsk Ob region, given in the work of F. A. Nikitenko.This indicates the comparative uniformity of the granulometric composition and the proximity of the physical and mechanical properties of loess-like loams in the Altai and Novosibirsk Ob region.
The degree and nature of deformation anisotropy in non-rock rocks are very different.This is due both, to the directional effect of gravity during their formation and to the mineral composition, structural and textural features of the rocks, which are determined by numerous geological factors.
Experimental studies to confirm the existence and identify the degree of deformation anisotropy of the soil samples were conducted in the laboratories of "Engineering Geology, Grounds and Foundations" Department in Novosibirsk State University of Architecture and Civil Engineering, named after V. V. Kuibyshev (Novosibirsk) and" Foundations, Grounds, Engineering Geology and Geodesy" Departments in Altai Technical University, named after I. I. Polzunov (Barnaul).
In order to conduct an experiment in different areas of the city, samples of soils with natural humidity and density were taken from Novosibirsk and Barnaul.Samples were taken with metal rings with a height of 0.035 m and a cross-sectional area of 40  10-4 m2.The soil samples were taken at the vertical and lateral positions of the rings (six samples in each case) to determine the deformability of the soil in mutually perpendicular directions.Studies of natural composition soils were carried out in sealers and the device of a single-plane cut of the system" Hydroproject " according to the standard methodology.The deformations' magnitude was recorded by the ICH-10 hour-type indicators with a scale division price of 0.01 mm.The greatest sealing load was created by the pressure p = 0.3 ... 0.4 MPa.Before testing, the devices were graded with steel blocks.The results of the calibration were used in the processing of experimental data.The experimental values of the soil samples' deformations in the vertical and horizontal directions were used to estimate the deformation anisotropy of the soil.The degree of the soil deformation anisotropy was estimated by the anisotropy index  = sx/sz = εx/εz; where sz and sx, εz and εx were absolute and relative deformations in the vertical and horizontal directions, respectively.
The authors obtained the experimental studies' results of solid subsidence loams and loams of Barnaul and Novosibirsk [7,8].As an example, one can see in Table 2 the test results in a compression device of sandy loam of a solid consistency, subsidence (Barnaul) and in Table 3-tests a solid consistency loam of subsidence (Novosibirsk).All the studied loess-like subsidence soils had an index of deformation anisotropy, defined as the ratio of the deformation modules in the vertical and horizontal directions, greater than one.
In addition, the humidity influence on the studies' results of anisotropic samples of loesslike soil under compression conditions was investigated.For ordinary soils, similar studies were carried out by V. S. Arefyev and T. A. Gorbunova.
Samples of loess-like soil of undisturbed structure were taken in two mutually perpendicular directions from three monoliths of soil at a humidity of w1 = 0.13 d.e., w2 = E3S Web of Conferences 431, 09006 (2023) ITSE-2023 https://doi.org/10.1051/e3sconf/2023431090060.23 d.e., and w3 = 0.28 d.e.(d.e. was a fraction of one).The moisture content of the soil samples, taken from each monolith, was determined according to the standard method.The tests were carried out under compression conditions.The load on the samples was transferred in steps of 0.05 MPa (up to 0.3 MPa) with the stabilization of deformations up to 0.01 mm per day.
The anisotropy index of loess-like soil   ЕzЕx depended on the humidity of the tested samples and at a pressure of  = 0,3MPa, it decreased from  = 1,53 for w1 = 0.13 d.e. to  = 1,29 for w3 = 0.28 d.e.

Discussion
We can consider that the structural and textural features of loess-like subsidence soils are caused by the conditions of their accumulation and afforestation.The material and mineralogical composition of the main clay components and sand-dusty particles of loesslike subsidence soils, their formation's conditions can cause a pronounced anisotropy of their anisotropic properties.

Conclusions
Recently, there have been many studies of loess-like subsidence soils, as well as computational, theoretical and practical developments [4][5][6][7][8][9][10][11] that take into account their specifics.This determines the practical significance and emphasizes the relevance of their comprehensive study.The State brief analysis of the issue under the study indicates that a number of its aspects need to be deepened or even primary research.
In the course of the study, the authors revealed that the structural and textural features of loess-like soils were due to the conditions of their accumulation.The chemical composition of the main clay components and sand-dusty particles of loess-like subsidence soil and their mineralogical composition were one of the factors determining the deformation anisotropy of soils.

Fig. 1 .
Fig. 1.Gross composition of loess rocks of the West Siberian plate.

Table 1 .
Results of granulometric and microaggregate analysis.

Table 2 .
Test results of sandy loam of solid consistency, subsidence (Barnaul)