Учебное пособие 2210

а)

Fig. 3. Variants of loading a foundation base

It was found that for the constant deformation modulus Е the curved foundation loaded according to the scheme d (Fig. 3) has a minimum heaving. (The curved foundation loaded according to the scheme e has a maximum heaving (Fig. 3). Heaving caused by the loadin in scheme d in relation to a flat surface (scheme a, Fig. 3) dropped by 19.8 %. In the upper layer of the foundation along the loading axis deformity is almost zero. Loading according to the scheme e with the load concentration in the middle causes heaving to go up by 7.7 % in relation to loading along the surface (Table 1).

In studies by G. G. Boldyrev [2], I. К. Аimbetov [1] the dependencies were found for an increase in the deformation modulus of a foundation base on the lateral pressure for different types of foundations, i.e. E = f(σx). Therefore stress-strain caused by loading along a curved surface in the active zone affects the compression of a foundation base.

41

Russian Journal of Building Construction and Architecture

At E = f(σx) there is not much difference. Due to considering changes in the deformation modulus caused by lateral compression, the loading scheme has more effect. Hence heaving caused by loading according to scheme d in relation to the basic solution (scheme a, Fig. 3) dropped by 20.8 %. Loading according to the scheme e with the loading concentration in the middle caused a 9.9 % increase in heaving in relation to loading on the plane (Table 1). Note that according to the experimental data, the schemes с and d are the most identical to actual ones for loading of a foundation with an upward bulged shell (Fig. 3) [9, 11].

Thus in order to reduce the compression of a foundation and the resulting heaving, such parameters of a shell should be chosen that diagrams of contact pressures have a trapezoidal almost triangle contour with its maximum at the edge.

3. Effect of a relative rising height of a curved loading surface on the deformity of a foundation

Numerical modeling is performed for a curved cylindrical surface with the width with the projection onto the axis Х which is 2.4 m according to the example from [5].

Loading onto a curved surface is applied along the triangle p = 0.5pср+ 2хpср/ В (Fig. 4а) and trapezium p = 3хpср / В where 0 < х < B/2 (Fig. 4b), which is in compliance with the experimental data [8, 12, 15].

Fig. 4. Calculation scheme: а) triangular loading; b) trapezoidal loading

The calculation of heaving was performed with constraints of a compressed massive according to SP (СП) [13]. The original data are В = 6.0 m, pср = 135.7 kPa, q = 30 kPa, ν = 0.499, Нсж = 6.0 m.

A varying parameter is a relative rising height of a surface h h /b . A relative rising height of a shell is considered in the range 0 < h < 0.2, which corresponds to the sloping shells examined in the study.

42

According to the results of numerical modeling, a reduction in the deformity of a foundation base increases as does a relative rising height of the curved part h , which is due to an increase in the compression of a foundation in the active zone by horizontal (lateral) strains (Fig. 5). An increase in the rising height of the curved part non-linearly affects a reduction in the deformity of a foundation. Hence, e.g., an increase in the rising height from 0 to h = 0.1 for a triangular loading reduces the average heaving by 12.9—26.8 % for the examined foundations and an increase in h to 0.2 reduces the average heaving by 16.4—30.2 % respectively (Table 2).

Fig. 5. Diagrams of tangential stresses in a foundation loaded along a flat and curved surface according to numerical modeling in PLAXIS 2D AE

Таble 2

Dependence of the deformity of a foundation base on the type of loading and relative rising height of the curved surface

43

Russian Journal of Building Construction and Architecture

This effect is due to the influence of opposite factors. Hence as the rising height increases, so do horizontal efforts of the compression of a foundation, however the depth of the distribution of extra lateral compression goes down. Therefore a further increase in the rising height and excess of the sloping criterion h = 0.2 are not effective for regulating the deformity of a foundation base (Fig. 6).

Plastic clay sand, triangular loading

Plastic clay sand, trapezoidal loading

Solid clay sand, triangular loading

Solid clay sand, trapezoidal loading

Relative rising height h

Fig. 6. Effect of h on a reduction in the average heaving of a foundation in relation to loading along a flat surface

Another important implication of the numerical calculations is an increase in the efficiency of loading of a foundation along the curved surface as the deformation modulus of the foundation Е drops.

I.e. the deformity of a foundation loaded along a curved surface mostly goes down for weak, strongly compressed foundation bases, which is indicative of the application of the investigated shell foundations.

It should also be noted that while studying the influence of a relative rising height on the stress-strain of a foundation base, the areas of the specific condition of a foundation were evaluated while extra loading exceeded the calculation resistance. For that, the elasticplastic model of a foundation base was applied using the strength criterion by MohrCoulomb.

As seen from the resulting data (Fig. 7), an increase in the rising height of the shell causes a decrease in the area of the points of the specific balance under the edges of the foundation models, which improves the bearing capacity of a foundation respectively. E.g., a change in the relative rising height from h = 0.125 toh = 0.33 decreases the area of the specific balance zone by 30 %.

44

Fig. 7. Distribution of zones of specific balance under the foundation models for the elastic-plastic model of a foundation base: а) h =h 0; b) h = 0.125; c) h = 0.33

4. Influence of changes in the deformation modulus along the depth on the deformity of a foundation

Let us consider the influence of the distribution of the deformation modulus along the depth for a trapezoidal and triangular loadings for the following original data (Fig. 4): = 0.2, b = 6.0 m, p = 135 kPa, q = 30 kPa, ν = 0.499, Нсж = 6.0 m, α = ЕНсж / Е0.

For trapezoidal and triangular loadings the compression effect of a foundation with laterial pressure in the general case is on the rise as the deformation modulus increases from a contact surface to the depth of a compressed massive.

For trapezoidal loading (Fig. 8, Table 3) the effect of decreasing heaving considering *zp and

E = f(σx) at α = 0.25 is 24.4 %, at α = 4 it reaches 37.6 % for this particular task. However, at σzp and E = f(σx) an increase in the deformation modulus with the depth somehow decreases the effect from 13.9 to 11.3 % for α that equals 0.25 and 4 respectively.

Fig. 8. Scheme for determing Е = f(H)

45

Russian Journal of Building Construction and Architecture

Table 3

Dependence of heaving on α for trapezoidal loading

The difference in the change in the effect of decreasing heaving is due to mutual overlapping of the influence of horizontal stresses and changes in the deformation modulus with the depth [10]. Graphically heaving with changes in the deformation modulus with the depth can be fairly accurately described using a power function (Fig. 9).

For triangular loading (Fig. 10, Table 4) the effect of decreasing heaving considering and E = f(σx) at α = 0.25 is 36.9 %, at α = 4 it reaches 47.9 % for this particular task.

46

Therefore loading along a curved surface in the general case is more effective as the deformation modulus increases with the depth.

Fig. 10. Influence of α on heaving of a foundation under triangular loading

Table 4

Dependence of heaving on α for triangular loading

Conclusions

1. In order to reduce the compression of a foundation and heaving of a foundation loaded along a curved surface, such parameters of a foundation should be selected that diagrams of

47

Russian Journal of Building Construction and Architecture

contact pressures have a trapezoidal almost triangular contour with maximum values near the edges.

2.An increase in the hardness of a foundation base loaded along an upward bulging curved surface has been theoretically justified due to an increase in the deformation modulus that is a stress-strain function. An increase in the deformation modulus of a foundation in the active zone of deformity of a foundation base is associated with extra lateral compression, horizontal pressure σх of a foundation in the active zone of a foundation associated with the shape of a contact surface.

3.An increase in the effectiveness of loading a foundation along a curved surface was revealed as the deformation modulus Е drops. I.e. the deformity of a foundation loaded along a curved surface largely decreases for weak, strongly compressed foundation bases, which is in accordance with the application of the investigated band-shell foundations.

4.Loading along a curved surface in the general case is more effective as the deformation modulus increases with the depth.

5.The shape coefficient kф is set forth as a ratio of average heaving: kф = sпл / sоб. The coefficient should be introduced as an increasing multiplier to the deformation modulus in geomechanical models of a foundation base or an increasing multiplier for determining the coefficient of a subbase in contact models. Based on the experimental data, kф can be significantly over one, according to the numerical analysis for a homogeneous foundation kф nonlinearly depends on a relative value of the curved part in the overall width of a foundation.

References

1.Aimbetov I. K. K opredeleniyu modulya deformatsii gruntov metodom trekhosnogo szhatiya dlya raschetov NDS osnovaniya s ispol'zovaniem programmy PLAXIS [The determination of the deformation module of soils by triaxial compression for calculation of the VAT base using the program PLAXIS]. Geotekhnika, 2010, no. 1, pp. 62—67.

2.Boldyrev G. G., Novichkov G. A. O vliyanii metoda opredeleniya modulya deformatsii na ego znachenie [On the influence of the method of determination of the deformation modulus on its value]. Geotekhnika, 2010, no. 3, pp. 36—43.

3.Galerkin B. G. Sobranie sochineniy [Works]. Moscow, Izd-vo AN SSSR, 1952, vol. 1. 391 p.

4.Gorbunov-Posadov M. I., Malikova T. A., Solomin V. I. Metod resheniya smeshannoy zadachi teorii uprugosti i teorii plastichnosti gruntov [The method of solution of the mixed problem of the theory of elasticity and theory of plasticity of soil]. Osnovaniya, fundamenty i mekhanika gruntov, 1971, no. 2, pp. 4—7.

5.Zaruchevnykh, I. Yu., Nevzorov A. L. Mekhanika gruntov v skhemakh i tablitsakh [Soil mechanics in diagrams and tables]. Moscow, ASV Publ., 2007. 136 p.

48

6.Lyav A. Matematicheskaya teoriya uprugosti [The mathematical theory of elasticity]. Moscow –– Leningrad, ONTI NKTP SSSR Publ., 1935. 674 p.

7.Muskhelishvili N. I. Nekotorye osnovnye zadachi matematicheskoy teorii uprugosti [Some basic problems of mathematical theory of elasticity]. Moscow, Nauka Publ., 1966. 708 p.

8.Pronozin Ya. A., Rachkov D. V. Issledovanie vliyaniya formy kontaktnoy poverkhnosti fundamenta na deformiruemost' gruntovogo osnovaniya estestvennogo slozheniya [A study of the influence of the shape of the contact surface of the base on the deformability of the Foundation soil is a natural addition]. Vestnik Tyumenskogo gosudarstvennogo arkhitekturno-stroitel'nogo universiteta, 2015, no. 2, pp. 20—24.

9.Pronozin Ya. A., Zazulya Yu. V., Mel'nikov R. V., Stepanov M. A. Opyt sovmestnogo primeneniya in"ektsionnykh svay i kessona pri ustroystve podzemnogo etazha zdaniya istoriko-kul'turnogo naslediya v g. Tobol'ske [Experience of joint use of injection piles and caisson in the device of the underground floor of a building of historical and cultural heritage in the city of Tobolsk]. Available at: www.science- education.ru/109-9206

10.Pronozin Ya. A., Naumkina Yu. V., Rachkov D. V. Utochnennyy metod posloynogo summirovaniya dlya opredeleniya osadki plitnykh fundamentov [Refined layer-by-layer summation method to determine precipitation slab base]. Akademicheskiy vestnik UralNIIProekt RAASN, 2015, no. 3, pp. 82—86.

11.Pronozin Ya. A., Samokhvalov M. A., Rachkov D. V. Rezul'taty laboratornykh i polevykh issledovaniy izgotovleniya buroin"ektsionnoy svai s kontroliruemym ushireniem [The results of laboratory and field studies of the manufacture of grout-injected piles controlled broadening]. Promyshlennoe i grazhdanskoe stroitel'stvo, 2014, no. 3, pp. 56—60.

12.Pronozin Ya. A., Stepanov M. A. Eksperimental'noe obosnovanie ispol'zovaniya lentochnykh svaynykh fundamentov s predvaritel'no napryazhennym gruntovym osnovaniem [Experimental substantiation of the use of tape of pile foundations with pre-stressed soil ground]. Vestnik Permskogo natsional'nogo issledovatel'skogo politekhnicheskogo universiteta. Stroitel'stvo i arkhitektura, 2014, no. 2, pp. 180—189.

13.SP 22.13330.2011. Osnovaniya zdaniy i sooruzheniy. Aktualizir ovannaya redaktsiya SNiP 2.02.01-83* [SP 22.13330.2011. The base of the buildings. The updated edition of SNiP 2.02.01-83*]. Moscow, 2011. 161 p.

14.Ter-Martirosyan Z. G. Mekhanika gruntov [Soil mechanics]. Moscow, ASV Publ., 2009. 552 p.

15.Chikishev V. M., Pronozin Ya. A., Mal'tsev L. E., Zazulya Yu. V., Stepanov M. A. Raschetno-ekspe- rimental'noe obosnovanie ispol'zovaniya svayno-obolochechnykh fundamentov v vysotnom stroitel'stve [The settlement and experimental substantiation of the use of the pile-shell Foundation in high-rise construction]. Available at: www.vestnik.vgasu.ru/?source=4&articleno=798

49

Russian Journal of Building Construction and Architecture

UDC 624.154

M. A. Samoxvalov1, Yu. V. Zazulya2, M. D. Kajgorodov3

RESULTS OF A STUDY OF STRESS-STRAIN STATE

OF THE SOIL MASSIVE AROUND THE RESULTING BROADENING

AT THE END DRILL-INJECTION PILE

Tyumen' Industrial University

Russia, Tyumen’, tel.: +7-919-943-13-79, e-mail: 89199431379@yandex.ru 1PhD in Engineering, Assoc. Prof. of the Dept. of Geotechnics

2PhD in Engineering, Assoc. Prof. of the Dept. of Construction Industry 3PhD student of the Dept. of Geotechnics

Statement of the problem. The article provides an analysis of the results of full-scale test in actual field conditions of the interaction of piles with the clayous soil foundation associated with the research of the radius of the consolidated zone, vertical deformations of the soil massive around the zone of widening and changes its initial state of stress.

Results. A pile having at its end a broadening in the form of a membrane cup was designed. Static studies showed that a controlled broadening at the end of the pile on average causes a two-fold increase in the load-carrying capacity of the soil massive in the area of the broadening. According to the results of the fieldwork to investigate the interaction of piles with a clayous soil foundation, the radius of the compacted area, vertical displacements of the soil massive in the area of the broadening and changes of its initial stress-strain state were determined.

Conclusions. The fieldwork data have shown the feasibility of a controlled broadening in the form of a membrane cup at the end of drill-injection pile. Studies have shown a significant improvement in the characteristics of the soil after the formation of the broadening at the end of the pile.

Keywords: drill-injection pile, controlled broadening, weak clay soils, static testing, stress-strain state.

Introduction

Currently in the Russian Federation there is a large number of buildings and structures (as well as cultural heritage objects) that are in need of reconstruction, restoration and modernization according to the latest regulations that require that underground spaces of these buildings are utilized for social and engineering infrastructure.

© Samoxvalov М. А., Zazulya Yu. V., Kajgorodov М. D., 2017

50