observed upon a change in the stress state of the base. This indicates that the character of deformation of foundation beds of swelling soils is determined in many respects by the acting load [i]. We see from Table i that the strength and deformation characteristics change in practically the entire investigated soil stratum. The most appreciable decrease of the deformation characteristics is observed for silts and loams, though they do not have swelling properties. Therefore, when designing foundations of chemical plants with respect to the first and second groups of limit states, it is necessary to take into account the change in the strength and deformation characteristics of the base soil upon its wetting by various liquids. In the meanwhile, there are no instructions in construction specifications and regulations SNiP 11-15-74 concerning consideration of the change in the strength and deformation characteristics of soil as a result of the effect of acid solutions. This is explained mainly by the complexity of the problem and comparatively little degree of knowledge about it. The urgency of this problem is confirmed by observations of the deformations of the buildings and structures in the territory of the BKhZ. LITERATURE CITED i.

E.A.

Sorochan, Construction on Swelling Soils [in Russian], Stroiizdat, Moscow (1974).

DISTURBANCE OF THE STABILITY OF A FOUNDATION BED FROM A LATERAL SURCHARGE G. M. Ulichkin and A. E. Malov

UDC 624.131.531.6

According to Article 3.8 of construction specifications and regulations (SNIP) 11-15-74 [l], foundations should be designed with consideration of the lateral surcharge on the ground surface near the structure. However, in construction practice the effect of this surcharge on the stability of the foundation bed is often ignored, which leads to the occurrence of impermissible displacements of the foundations and even to emergency situations. An example from construction practice in the territory of the Sokolov-Sarbai Beneficiating Plant (city of Rudnyi) is described below, showing to what the arbitrary transposition and stockpiling of cargoes in the immediate vicinity of the foundations of structures can lead. Here, during the construction of an industrial building in the territory of an existing enterprise, there were stockpiles of iron-ore concentrate pellets on the ground surface near the foundations. The load from these stockpiles exceeded the bearing capacity of the foundation bed, as a result of which a considerable volume of soil, within which were the foundations of the structure, moved. At the time of movement, works were completed on the construction of the foundations and on the assembly of the 15.6-m-high metal two-branch columns, roof trusses with a span of 36 m, crane beams, reinforced-concrete hollow roof panels, and lightweight concrete enclosing wall panels. The spacing of the supporting structures was 6 m (see Fig. i). The isolated footings 1 of the building are monolithic, the measurements of the base in plan are 2.8 • 6 m, and the founding depth is 5 m. Along longitudinal axis A there is an ascending slope 2 with a height of 3.2 m, and inside the building there is a 2.3-m-deep pit 3 prepared for the construction of a railroad trestle. The soll conditions of the construction site are given in Table i. In the stratum of the foundation bed there is an interlayer of variegated clay with very thin sand lenses (layer II, see Fig. i and Table i). The loose structure of this layer, high saturation, high compressibility, and low strength characteristics determined the need to use clay layer III, having better construction properties, as the foundation bed of the structure.

Rudnyi Industrial Institute. Sokolov-Sarbai Mine Construction Trust (Sokolovrudstroi). Translated from Osnovaniya, Fundamenty i Mekhanika, Gruntov, No. 5, pp. 7-8, September-October, 1978.

0038-0741/78/1505-0293507.50

9 1979 Plenum Publishing Corporation

293

Fig. I. Diagram of the cross section of the building with an indication of the displaced structures and lateral surcharge. TABLE 1

oo

~

~

Soil layer

1

II

III

Macroporous loam of Quaternary deposits with slump-type settlement l)roperties Opper Paleogene variegated, very soft clay with very thininterlayersand lensesof sand Upper Paleogeneolive-greer~medium and very softclay with thininterlayers and lensesof finesand

0--0,02

3.5

2,75

1.9

O,07--0, I

0,17

0,70

0,69

27

1,5

2,78

1,8

0,23

0,37

! ,03

1,02

6

6--10

0,01--0,02

13,5

2,76

2

0,31--0,42

0,36--0,29

0,87

0,89

8

i2--20

0.04

In November 1971 a large pile IV on fine-grained pellets was placed on the slope along the entire length of the building. The unit weight of the mound was about 3.7-4 tons/m =. When the pile reached a height of 5-6 m displacement of the soil in the form of a slope slide occurred. The foundations of the entire longitudinal row A of the building were in region V of the slide. We note that cases of the displacement of foundations of structures [2, 3] and deformations of overburden dumps owing to loss of stability of their foundation beds were recorded before in regions of the Kustanai Oblast, where there is a layer of clay soils with very thin interlayers of fine sand (layer II), and therefore the inspection service of the plant has some experience in establishing the causes of loss of stability of foundation beds and in eliminating its consequences. In the case under consideration the foundation bed was quickly unloaded by relocating the pile farther from the foundations of the building. Observations of the movement of the foundations by geodetic methods were carried out every 10-12 h. It was established that all foundations of longitudinal row A were displaced by as much as 769 mm in the middle part. Displacements occurred at a rate of about 120-130 mm/h and within 6 h amounted to 98% of the total amount; they diminished gradually toward the ends of the building. A visual inspection of the supporting structures showed the following: For the most part the elements of the roof trusses did not have visible defects and deformations, with the exception of the braces of trusses of axes 17 and 18, which were bent from loss of stability; the columns of longitudinal row A with maximum displacements in the middle of the building (axes 9, i0, and ii) had breaks in the welded joints connecting the base with the branches of the columns; the enclosing wall panels were bent into the building. A check calculation of the frame with the displaced foundation showed the presence of considerable stresses on the lower parts of the columns 4. The tensile stresses in the anchor bolts securing the base of the columns to the foundations of axes 5, 2, and 18 exceeded the yield point of the steel. The Leningrad branch of the Central Scientific-Research and Design Institute of Steelwork (TsNllProektstal'konstruktsiya) worked out a restoration project for the building. It

294

was based on a variant providing comparatively lesser labor intensity and cost of the works. The position of the deformed building was retained and measures were taken to reduce the stresses in the columns and anchor bolts. The enclosing wall panels were disassembled, the nuts and anchor bolts of the crane branches of the columns along axes A and B were loosened, cement mortar was added and steel sheets were placed in the gap under the plate of the column shoe, the crane tracks were straightened, the defects in the welded joints in the base of the columns along axis i0 were eliminated, and the bent braces of the roof trusses and ties of the bottom chords of the girders were replaced. The enclosing panels were hung on assembly platforms, the length of which was established at the site with provision of verticality of the wall. To evaluate the causes of sliding of the bed of the pile and displacement of the foundations, the stability of the foundation bed was calculated on the assumption that the surface of failure of the slide V was a circular arc [4] and the bearing capacity of the weak clay interlayer II in the bed was determined according to [i, 5]. It was also assumed that the interlayer of variegated clay was in an unstabilized state in view of the rapid application of the load from the weight of the pile of pellets. It was found that the circular-arc failure surface with a minimum stability factor intersects the upper layer I of Quaternary deposits and is located mainly in the weak layer II of variegated clay. The stability factor was 0.84. Inverse calculations to determine the average shearing strength for a given stability factor of the bed equal to 0.98 carried out for a failure surface with a minimum stability factor showed that the cohesion was about 0.019 MPa at an angle of internal friction of the weak interlayer equal to 0 ~ as for the unstabilized state. According to the calculations the cohesion at the time of earth movement was close to the values determined in the soll explorations. The bearing capacity of the weak clay interlayer according to [5], by the equation n~=nl§

in an unstabilized

state was determined,

+l--2~+cos2a).

where n2 is the critical normal pressure

on the foundation bed; n~ is the vertical

load:

nl=zy=O,124 MPa; z is the depth of the weak interlayer from the surface of the slope; y is the unit weight of the Quaternary deposits; c I is the calculated specific cohesion; ~ is the angle of slope of the resultant of the external pressure to the vertical:

Ea

6 ---a r c l g -

E a is the total horizontal

pressure

q

;

from the noncohesive

medium on a smooth surface:

hz Ea =

)'1~' 2

sin 2 cpp (1 + I -~2 s i n- q~p~

= 9 tons/rn~

h is the height of the pile, equal to 6 m; yp is the unit weight of the pile; ~ p is the angle of internal friction of the pile of pellets, assumed equal to 45~ q is the linear mass of the pile: b/l

q = yp ~- = 72 tom/m; b is the width of the slope of the pile, assumed equal to 6 m. After calculatlons 0.124 + 4.86c I.

we obtain 6 = 7~

'.

Then n2 = 0 . 1 2 4 + c i ( 3 . 1 4

+ i -- 0.25 + 0.97) =

For the limit state of the bed the external pressure from the pile of pellets is equal to the critical. In this case the necessary cohesion in the soil can be determined from the equality

295

h ~ 0.24 +4,86c

l

Then c I = 0.0239 MPa, which is close to the cohesion of the weak interlayer obtained in the soil explorations. An evaluation of the bearing capacity and stability of the foundation bed showed that the lateral surcharge from the weight of the pile of pellets was the cause of displacement of the foundations. The presence of an open pit for the trestle inside the building after dumping the pile of pellets outside promoted disturbance of the bed. Therefore, any additional loading of the bed should be done with an evaluation of its bearing capacity and analysis of possible consequences. LITERATURE CITED i. 2. 3. 4. 5.

296

SNiP 11-15-74. Design Standards. Bases of Buildings and Structures [in Russian], Strollzdat, Moscow (1975). V. Ya. Putintsev, N. Ya. Rudnitskli, and A. S. Stroganov, "Failure of an industrial buildlng from loss of stability of the foundation bed," Prom. Stroit., No. l0 (1965). G . M . Ulichkln and A. N. Reshetov, "Slip of a slope with bridge piers," Osn. Fundam. Mekh. Gruntov, No. 2 (1975). N . A . Tsytovich, Soil Mechanic [in Russian], Gosstrolizdat, Moscow (1963). V . V . Sokolovskli, Statics of Granular Material [in Russian], Fizmatgiz, Moscow (1960).