ON THE C O E F F I C I E N T OF CHANGE OF THE MODULUS

OF SOIL D E F O R M A T I O N

(UDC 624,131.38)

P. A. K o n o v a l o v and N. Ya. R u d n i t s k i i

Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, Vot. 1, No. 3, pp. 16-17, March, 1964

In the design of the foundations for large panel buildings for case of a lithologically uniform foundation the original characteristics of deformability of the soi l- the modulus of deformation E-obtained from engineering geo- logical surveys are usually assumed to be practically constant under deformation. However, experimental investiga- tions of the magnitude of variation of the modulus of deformation of various foundations in Moscow [1] showed that the compressibility of soils at different points, even a homogeneous foundation, g so much different that it is neces- sary to allow for it in the design of large panel buildings of unequal settlings.

In contemporary methods of design of compartments of large panel buildings of unequal settlings the changes of the modulus of deformation of the foundation soils are calculated according to the length and width of the build- ing by introducing into the calculations the coefficient of change of the modulus of soil deformation [2], which is the ratio of the maximum modulus to the minimmm. In these methods it is assumed that the compressibility of the soils is greatest (or least) under the center of the building, and diminishes (or increases) at the edges; therefore, the variability of the modulus of deformation in the contours of the building follows a linear law (Fig. la) or a parabolic function (Fig. lc, d).

Errors in the determination of the modulus of deformation have both a systematic and a random character and may be partially eliminated; however, random errors do not allow precise calculation.

Therefore, together with the improvement of methods of determining deformation properties of soils, it is nec- essary to determine their probability of variability on the basis of statistical analysis of the results of experhnents[3].

In order to simplify relating standard projects to localities, the Institute of Foundations has worked out tabular vatues of coefficients of variability a of the modulus of deformation E of various forms of soils [4].

For determining the probable value of the coefficient of variability a, a great number of tests were made by stamps of various soils and, in part,results of compression tests of sandy soils were used. The material was analyzed by mathematical statistics methods.

The development of the coefficient of variability a of the modulus of deformation of sandy soils was carried out by the use of values of the modulus of deformation, calculated on the basis of tests by stamps and also on results

mm max

c ~d

mill

m a x

Fig. 1. Diagram of the change of the modulus of deformation of the foundation of a large panel building, a,b) During linear change; c,d) during parabolic change.

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TABLE I

Kinds of sandy soils

3ravelly and coarse Average coarseness Fine Pulverized

Coefficient of porosity

12 460 I 1.25 I 19, 400 I 1.27

0.61-0.7 V % E a

16 330 1.38 18 330 1.44

18 240 1.44

2O I00 1.5

c~ = Emax/Emi n

r , ,

1,0~ f~ 200 ~O# qO0 $#0 E, kg/cm z

Fig. 2. Graph of the dependence of coefficient c~ on the tabular value of the modulus of deformation for sandy soils

c~ = E max/Ernin

7,8

1,4

Fig. :3.

x I

l _

1'00 100 200 300 qO# E, kg/cm z

Graph of the dependence of the coefficient c~ on the tabular value for clayey soils of the Quaternary deposit.

of S. I. Sinel'shchikov's experiments on compression devices with samples of soils from construction areas of European Soviet Union. In age, these soils pertained to the Quaternary, Tertiary, Cretaceous, and Jurassic periods and, in orig- in, to the alluvial, deluvial and fluvioglacial periods. The coefficient of variable of the modulus of deformation of the investigated aggregates of sands varied between 0 and 20%. Table 1 was compiled in order to detect a possible regularity of the change of coefficient of variance V and coefficient of variability a of the modulus of deformation of sandy soils depending on their coefficient of porosity and the granulometrie composition, i.e., according to entries given in Table 13 of SNiP II--B. 1-62 [6].

The coefficient of variability c~ of the modulus of deformation may be presented in the following form:

! 4 - V Emax and hence Ema x Ear(1 + V) and Emin= Ear(1 --V), i.e. Emin 1 - -V

where Ear is the mean arithmetic value of the moduli of deformation of the soils; V is the coefficient of variance in units of one, corresponding to the given Eav.

Table 1 shows that the value of the coefficient of variance V of sands depends slightly on the coefficient of porosity and their coarseness and that the coefficient of variability a of the modulus of deformation is located within the limits of 1.3-1.5.

A graph of the dependence of the coefficient of variability a on the tabular value of the modulus of deforma- tion E 0 for sandy soils is shown in Fig. 2. Each point on this graph corresponds to the results of the numerical ex- periments.

The dependence, designated in the graph, is rectilinear and, therefore, an increase of the modulus of deforma- tion shows an insignificant decrease of the coefficient of variability. The coefficient of variability c~ of the modulus of deformation of sandy soils may, without large error, be assumed to be the average value equal to 1.4, irrespective of the density and coarseness of the sand.

For the determination of the value of the coefficient of variability of clayey soils of Quaternary deposits sec- tions were used according to the coefficient of porosity and the humidity at the limit of roiling [6, Table 13]. From

168

TABLE 2

Soils

m ,

z8 andy Clayey (sandy loams, clayey soil, clay) of the Quaternary

deposit of plastic consistency The same The same ~vlorainic deposits of clayey soils of solid consistency

Coefficient of porosity s

0.6-0.7

1.2-1.5

0.8-I

0.6-0.8

0.4-0.6

Average modulus of deformation E in kg/cm z

380

40

80

120

550

C oefficient of variability

Emax ¢{= Emin

,1.3

1.4 1.8 2.5

I 2.6

TABLE 3

Z Soils Coefficient of variability

!Sandy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . : "1 1.4 iClayey (sandy loams, clayey soil, clay of the Quaternary deposit) . I 1.8 lvlorainic deposit of clayey soik ] 2.5

600 tests conducted on clayey soils of the Quaternary deposit with identical mounting of the stamp and humidity con- tent G _> 0.8, the static loadings of 140 were selected.

In the selection of soil ratings, data from a soil test by deep bores with stamps of 600 cm ~ area were excluded, since these were often located on poorly cleaned soil surfaces, which led to understatement of the values of the mod- ulus of deformation. Statistical analysis of the collected values of E showed that the designated distribution of the values of the coefficient of variability a for clayey soils of the Quaternary deposit (Fig. 3) permit the assumption of a certain allowance a ; 1.8.

Characteristics of certain regional forms of soils, especially morainic soils, were reflected in several regional norms, Tests of morainic soils by stamps, conducted by the GPI Foundation Project on MGU areas and other test areas showed that the modulus of deformation varies from 300 to 800 kg/cm *, within the limits of areas containing homo- geneous soils.

In determining the coefficient of variability of morainic clayey deposits nearIy 80 soil tests were examined from which only soils with a degree of humidity G _> 0.8 and approximately at the same depth of planting the stamp were selected. Soils were tested mainly with circular stamps of 5000 cm ~ area. Morainic soils were found in semi- solid and tight plastic states.

Statistical analysis of the collected data concerning the modulus of deformation showed that for the investi- gated aggregate, the coefficient of variance was 43%; and the coefficient of variability corresponding to it was 2,5. Thus, the obtained coefficients of variability of the modulus of deformation were related to basic forms of soils with- out dividing them into groups according to the coefficient of porosity.

Tables of coefficients of variability of the modulus of deformation were worked out at the same time from sections according to the name of the soil, the coefficient of porosity and the mean modulus of deformation (Table 2) by the Institute of Foundations for massive buildings in Moscow.

After appropriate coordination of the results according to the definition of the coefficients of variability, Tab!e 3 is recommended for designing large panel buildings of nonuniform settlings.

The coefficient of variability a of the modulus of defomlation for clayey and sandy soils of the Quaternary deposits refers only to those forms of soil whose characteristics are presented in Table 13 of SNiP II--B.1-62.

The coefficients of variability of the modulus of deformation of morainic deposits of clayey soils are shown for values E = 3 0 0 - 800 kg/cm z and refers to these groups during filling of the pores with water (degree of humid- i t yG _> 0.8).

169

Tabular data of the coefficient of variability c~ of the modulus of deformation of soil is recommended for use in tying large panel buildings to places where a sufficient quantity of results of soil tests for static loadings, which are necessary for calculations of the specific value of the coefficient of variability of the modulus of deformation for the area's foundation soil, are missing.

LITERATURE CITED

i. D.E. Por shin and N. Ya. Rudnitskii, The Use of Prefabricated Reinforced Concrete for Determination of Com-

pressibility of Soils. "Foundations, Substructures and Mechanics of Soils," No. 2 (1960). 2. V . I . Lishak, The Stressed State and Large Panel Buildings Before the Collection "Problems of Design and Pro-

tection of Buildings and Installations from the Effect of Mining." Works of the Institute Tsentrogiproshakht (1961).

3. N.V. Kolomeiskii, Engineering Geology, Part 2. Moscow, Gosgeoltekhizdat (1956). 4. N. ya. Rudnitskii, Results of Measurement of Settling of Foundations and Deformations of Substructures of Large

Panel Buildings. Works Ts NIISK. Collection "Static Designs of Large Panel Buildings." Gosstroiizdat (1963). 5. S . I . Sinel'shchikov, On Tabular Values of Moduluses of Deformation of Sandy Soils. Works NII Foundations,

Collection No. 42, "Structural Soil Conduct" Gosstroiizdat (1960). 6. Construction Norms and Rules, Part 2, Section B, Chapter I, "Foundations of Buildings and Installations.

Norms of Design" (SNIP II-B.1-62) Gosstroiizdat (1962).

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