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CHAPTER II

Migration of moisture in the freezing of soils and the forces of frost heaving

This chapter is devoted to the problem of water migration in freezing soils; the prediction of the magnitude of cryogenic heaving of soils and the heaving forces developed in this process.

On the basis of an analysis of experimental data on the redistribution of moisture in freezing soils (natural soils and those artificially saturated with various cations), the motive forces of migration are established and the seconJ principle of frozen soil mechanics is established. It is called the migration prin-ciple and states that: The migration of water in the freezing of wet soils is a mo- • lecular process of moisture transfer, continuously appearing upon any disturbance of the equilibrium state of the soil phases and upon changes in external actions; (the existence of gradients in temperature, moisture content, pressure, surface energy of the mineral partfcles, velocity of the molecules in the water films, etc.).

Also discussed are the methods of quantitative prediction of moisture accumulation, due to its migration in freezing soils, and the cryogenic heaving of soils caused by this migration. On the basis of experimental data, the order of magnitude is established for the normal and tangential forces of frost heaving in soils that act on the foundations of structures. Methods of frost heaving prevention and control are treated.

CHAPTER III Rheological processes in frozen soils

On the basis of an analysis of the internal bonds in frozen soils, and of a study of the physical causes leading to the development of rheological processes in them, as a result of the initiation and extension of micro- and macrofissures,. three stages of frozen and permafrost soil creep are discussed: transient, steady-state (plasto-viscous flow) and progressive creep.

Equations, based on experimental data, are given for the stressed-strained state of frozen and permafrost soils in the stages of attenuated and undamped creep (including pksto-viscous flow). A procedure is discussed for determining the parameters of these equations. In addition, very simple methods are recommended for the direct investigation of stress relaxation in frozen soils and for determining their long-term strength. This data is absolutely necessary to establish the design strengths of permafrost soils.

As a general conclusion, the special significance of frozen and permafrost soil rheology is established. Without a knowledge of the laws of this rheology, it is improssible to access the deformative and mechanical properties of such soils.

CHAPTER IV

Strength properties of frozen soils, and critical strength values

in this chapter, on the basis of experimental data, obtained mainly from investigations conducted by the author and his colleagues, the instability of the mechanical properties of frozen soils is established. This instability is due to changes in the phase composition, temperature, external pressures and load application times. The magnitudes of the characteristics of the mechanical properties of frozen and permafrost soils are discussed in detail. These characteristics inclu»de the compressive, tensile and shear strengths, adfreezing strength and the resistance to failure by cutting. The quantitative dependence of these values on the above-mentioned factors (changes in phase composition, temperature, etc.) is established.

Extremely simple analytical relationships are given for determining the initial and limiting critical pressure on frozen and permafrost soils regarded as cohesive bodies. These relationships are based on the equivalent cohesion of the soil (determined in a ball test). Calculated values are compared here with the experimental data.

Besides, the determination of the critical pressures for permafrost soils is discussed, as these soils have full shear strength with variable parameters of friction and cohesion.

Examples of strength calculations end the chapter.

CHAPTER V Deformation of frozen soils at subzero temperatures

Three kinds of deformations of frozen soils at subzero temperatures are dealt with: instantaneous (adiabatic and elastic), long-term (compaction, damped creep and steady plasto-viscous flow) and progressive creep (brittle and ductile failure).

Such detailed investigations of elastic deformations of frozen and permafrost soils are given here for the first time. Values obtained by the author are set forth for the elastic constants of such deformations and the dependence of these constants on the composition and the subzero temperature. The laminated stratification of frozen soils is also discussed.

The substantial compressibility of subzero hightemperature permafrost soils is pointed out. Concrete values of the total coefficient of compressibility are given for typical kinds of soils. This coefficient is required in computing the settlement upon the compaction of subzero hightemperature permafrost soils. On the basis of the hereditary creep theory, parameters are established for the exponential and hyperbolic kernels of damped creep.

For plasto-viscous flow, a power equation is adopted on the basis of experimental data for the steady rate of flow. A numerical example is given of the applicatrpn of this equation.

Finally, a detailed discussion is given on the methods for predicting settlements due to compaction and damped creep in the permafrost bases of structures.

CHAPTER VI

Settlement of frozen soils upon thawing

This chapter begins with a discussion of the changes in the properties of dispersive soils upon their freezing and subsequent thawing. Dealt with, in particular, is their increase in porosity which leads, subsequently, to considerable settlement in thawing.

The problem of determining the settlement of frozen soils in thawing was stated by the author as far back as 1933 and, since that time, systematic experiments have been conducted in the compression of thawing soils. It has been established that the change in porosity (and, consequently, settlement) of frozen soils consists of two parts: one independent of the magnitude of external pressure, and the other a direct function of the normal pressure. Next, the history of the problem of prediction of settlement in thawing soils is set forth, and a method devised by the author is given for determining the full stabilized settlement of thawing soils. Also given is the formula used to determine the settlement by summing up settlements, separating out those due to «ice inclusions» and adding the coefficient of closing of thawing cavities». These two factors, however, are very difficult to determine In practice. This is followed by the expanded formula derived by the author for calculating the settlement of foundations on thawing soils according to the equivalent layer method, also developed by the author.

This chapter also deals with the course of settlements in time on thawing soils. Two solutions are given, an engineering and a mathematically strict solution. These solutions are compared and their ranges of application are established. Here settlement is regarded as consisting of three components: thawing settlement, compacting settlement in thawing, and final-compaction settlement of already thawn soil.

The chapter ends with a discussion on the settlement of prethawed soils. The prediction of the settlement is based, in this case, on the nonlinear relationship between compression changes in the porosity and the pressure. Several tables of data and numerical examples are given.

PART TWO

PRACTICAL APPLICATIONS OF FROZEN SOIL MECHANICS

Part Two is devoted to the application of the laws of frozen soil mechanics in construction practice. These laws serve as the basis for establishing the scientific fundamentals of the stable state of various kinds of structures on permafrost soils. Such Structures include apartment houses, industrial buildings, highways and hydrotechnical structures.

CHAPTER VII

Geocryological engineering investigations of permafrost soils

This chapter deals with the main problems and the volume of geocryological investigations required at the constructions site. The concept is given of an integrated geocryological engineering survey of the territories under construction. The programme of field and laboratory investigations of permafrost soils is set forth in great detail. This programme establishes both the minimum necessary investigations (allowing them in some cases to be restricted only to the determination of the total moisture content of the permafrost soils, of their thawing coefficient and temperature), as well as a list of the required design characteristics with references to the procedures used to determine them, set forth in the preceding chapters. The chapter ends with an outline of a programme for stationary observations at geocryological stations. These are highly important in accessing permafrost soils :or the foundation bases of structures.

CHAPTER VIII

Temperature stability of permafrost soils in the built-up territory

This chapter deals briefly with the ways of providing temperature stability of 3ermafrost soils when structures are built on them. After Dr. G. V. Porkhaev, the actors affecting the temperature conditions of the buildings and structures are classified as: general, local and specific factors.

The general temperature stability of the strata of permafrost soils is accessed on the basis of the heat balance according to the meteorological and geocryological data. In investigationg the influence of local factors, first the basic condition determining the formation of thawing range is established (from the Fourier equation for steady heat flow). It is shown that under heated buildings (of a width several times as great as the active layer) a thawing range will be formed in all cases, and the frozen state of the base soil can be conserved only by removing the heat that is continuously liberated by heated buildings.

An approximate solution for the temperature of permafrost soils under heated buildings is set forth. Also given is the more rigorous solution of Dr. G. V. Porkhaev for the extremely complex plane and space problem of the thawing of permafrost soils. This solution is given in the next, chapter in the tabulated and alignment chart forms which are convenient to apply in engineering practice.

The last section of this chapter deals with the temperature stability of dams built of local materials under permafrost conditions. The transient temperature field of such dams was apparently first studied by the Department of Soil Mechanics, Bases and Foundations of the Moscow Civil Engineering Institute. As a result of many years of research, an approximate engineering method of predicting the temperature stability of such dams was developed and checked on physical models by researchers, under the supervision of the author.

The conducted research showed that to conserve the temperature stability of dams, built of local materials on permafrost soils, it is absolutely necessary to provide a waterproof frozen core that can be artificially frozen and thowed as required.

Given at the end of the chapter are data on the calculation of the required freezing time for the cores of dams built of local materials.