Aleshin A.S.
Aleshin A.S.

Алешин Александр Степанович Aleshin A.S.
д-р физ.-мат. наук, зав. лаб. ИФЗ РАН


Publications

The advantages and disadvantages of the NEHRP soil classification
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The influence of local ground conditions on the parameters of seismic vibrations is the subject of study in seismic microzonation. This section of engineering seismology underwent radical changes at the end of the last century. The Commission on Seismic Safety of the National Institute of Building Sciences of the United States, as part of the implementation of the National Earthquake Damage Reduction Program, developed new NEHRP Recommendations, which are significantly different from all that has been used in the world practice of anti-seismic construction. The main provisions of this NEHRP classification have been adopted in many national building codes, including Eurocode 8 and Kazakhstan's seismic regulations. One of the essential features of the classification is the use of the average values of the velocities of transverse waves and the densities of the ground thickness with a thickness of 30 meters. In Russia, the provisions of the NEHRP norms have not yet been properly developed. Currently, the issue of extending the norms of Kazakhstan to the entire territory of the CIS countries is being considered. For this reason, the article examines in detail both the advantages and disadvantages of the NEHRP Recommendations in order to extract useful experience and adapt to the realities of Russian anti-seismic construction. In particular, the error in the representation of the parameters of the soil mass by average values is shown. The ways of overcoming the identified shortcomings of the description of the soil mass with the help of model representations are outlined


Issue: №5 2018
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“Difficult” Questions of Development of Seismic Microzoning
Issue: №6 2019
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The regulatory framework for earthquake-resistant construction in Russia has recently been supplemented by a number of new long-awaited documents. This seemingly positive phenomenon gave rise to a situation that in one article was not without reason called «normative chaos». This situation is largely due to the difference between the basic concepts and relations of new and familiar old normative documents, which generates a state in the mind, defined by psychologists as cognitive dissonance. Of course, this phenomenon is temporary and understandable, but for the case of examination and passage of working documentation, it is certainly harmful. This work aims, at least in part, to provide answers to questions.
The most important contradictions are briefly considered and reasoned answers to the questions are given. A complete analysis of the problems involved requires much more than the allowable size of the article.

About Dynamic Range of SMZ
Issue: №3 2019
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In this paper, the system of seismic microzoning (SMZ) is considered from an information point of view in the form of a seismic channel, one of the most important characteristics of which is the concept of dynamic range. The question of the value of the dynamic range for each of the applied SMZ techniques is studied in detail. In addition to purely academic interest, the solution of this problem will allow to correctly assess the contribution of various factors (seismic stiffness, spectral features, nonlinearity, etc.) to the total value of seismic intensity and thus contribute to improving the efficiency of SMZ.

Apology of Seismic Rigidity Method
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The seismic rigidity method, which is one of the first instrumental methods of assessing the influence of soil properties on the parameters of seismic impacts, is currently experiencing contradictory to his attitude. On the one hand, this is the most commonly used method of seismic microzoning (SMZ), on the other hand it is hardly possible to find in SMZ another method that invokes such hard and various criticism. It should to note that these criticisms are not captured in the form of printed articles, but it is constantly occurs in various discussions, private views, etc. that only complicates public discussion. What here is true and must be take into account, and that should to reject? This article is the attempt to understand these interesting and practically important issues. 

Fundamentals of Continuum Theory of Seismic Microzonation
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Basic concepts of seismic microzoning in Russia are the degree of intensity and ground categories that correspond to discrete structure in the ratio «seismic impact ? reaction of the ground». Meanwhile, the parameters of seismic effects, and the parameters of ground properties are continuous in the space. The article expounds the basic theory, adequately representing the above mentioned space continuity. Thus, many the concepts of seismic microzoning, used now, become either more correct, or unnecessary.

The Basic Definitions of the Seismic Microzonation: Category, Intensity Value, Model
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It is fulfilled a content analysis of the basic concepts of microseismic zoning: categories, macroseismic degrees and models. It made the conclusion about necessity of refusal of macroseismic degrees and categories and using of continuous models of seismic effects and ground massif. 

Fundamental aspects of seismic microzonation
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Seismic microzonation (SMZ), as generally accepted, is an essential part of engineering survey regulated by numerous normative documents. At the same time, the scientific component of the SMZ work falls back into the shadow, if at all is considered. Meanwhile, the SMZ touch upon the bases of many fundamental problems of seismology, building physics, soil mechanics, seismic wave, etc. The paper concerns a brief consideration of the SMZ aspects, which traditionally belong to the field of fundamental science.

On site coefficients
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Introduction into practice of engineering-seismological researches of the description of seismic impacts by instrumental characteristics demands use of site coefficients for the account of influence of structure features and characteristics of the top part of a geological section. The article shows that the site coefficients, at least in the field of linear representations, can be uniquely describe through a single parameter of the soils – the average seismic rigidity of the 30-meter thickness composing the upper part of the cut. Simple relations allowing determining the response spectrum of soil by parameters of the soil model are deriving. By means of site coefficients, it is possible to construct a response spectrum of a soil model and to calculate necessary characteristics of seismic impacts. In the field of nonlinear coupling of soil model properties and seismic effects parameters, it is proposing to use reduction coefficients.

On the Spectral Characteristics of the Soil Massif

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The regulatory framework for seismic microzoning in Russia has recently been supplemented by a number of new generation documents. In particular, the document SP 283.1325800.2016 was adopted. In it for the description of spectral characteristics of a soil thickness the value of a maximum of coefficient of dynamism b was used. The scope of the normative document did not allow to describe in detail the method of obtaining and features of the use of this parameter, which is why it turned out to be an unusual innovation for prospectors. The article describes in detail how this value is obtained and how to use it. The ways of setting the standard values of the dynamic coefficient are analyzed. It is shown that the standard values do not cover the range of possible variations in both the properties of seismic effects and the reactions of the soil mass to these effects. The values of the maximum coefficient of dynamism can be significantly higher than the current normative values of 2.5. The importance of taking into account the internal structure of the soil mass is shown. Instead of soil categories the basic concept of construction, the defining features of engineering-seismological investigations in the study area, it is proposed to use the notion of model ground conditions. Special attention is paid to the consideration of nonlinear phenomena under strong seismic impacts. The effect of the nonlinearity of the stress-strain relationship on the spectral characteristics of the soil layer under strong seismic impacts is studied. It is shown that the nonlinearity significantly reduces the intensity of resonance processes in the soil massif. 

The antiresonance phenomena in seismic microzonation
Issue: #3 2021
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The
interference of incident and reflected seismic waves in the ground massif near
the day surface is the cause of resonant effects. In the practice of seismic
microzonation (SMZ), a resonant increase in the total seismic intensity is of
particular importance. At the same time, the presence of inverse layers in the
ground layers interference leads to a decrease in the intensity of the total
seismic impact, what is naturally named antiresonance. The article considers
the conditions for the occurrence of antiresonance and evaluates the limits of
its effectiveness. The natural and man-made causes of antiresonance and the
possibility of using it to reduce the intensity of seismic impacts are
particularly noted.

Solving a direct problem as a new method of seismic microzonation
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The article describes a new type of seismic microzonation, called the method of solving a direct problem. The main methodological technique in this case is the formation of  models of the soil layer on the basis of complex engineering-geological and geophysical studies. An original computer simulation technique based on the use of a short acceleration pulse as theinitial seismic impact is proposed. In the calculations of the increment of seismic intensity, a new formula is used that takes into account all the factors of the influence of soil properties on the parameters of seismic impacts – seismic rigidity, water saturation, resonant effects and the nonlinearity of the reaction of soils to strong seismic impacts. Based on the obtained data, the models of ground layers at the construction site are mapped and the parameters of seismic impacts that correspond to the properties of each model of ground massif are determined. The proposals presented in the article are reflected in the regulatory documents devoted to the SMZ of objects of increased responsibility and territorial planning