1640
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
When carrying out static tests No. 2 there was a natural
earthquake intensity of 7 points and lasting about 2 minutes at
which average pressure on a sole of stamps made р = 87 kPa ≈
0,9R, i.e. 90% from the size of calculation resistance (bearing
ability) the bases. The measured sizes of additional increments
of deformations of stamps and deep brands made 27% from the
total value, recorded at static tests (Usmanov R.A. 2009).. In
this case, as well as at static tests, increments of additional
deformations of soil also were recorded at a depth equal to
diameter of a stamp and more than 80% of their size occurred at
a depth to an equal half of diameter of a stamp.
Before tests of weak water-saturated soil for explosive
influences, by analogy to static tests, load of stamps was
finished to 80 kPa (0,8R), i.e. made 80% from bearing ability of
the basis. Imitation of seismic influence it was carried out by
means of camouflage explosions of charges of the explosives
located at a certain distance and depth from a tested site (fig. 2a,
b). as the settlement parameter of intensity of explosive
influence the speed of fluctuation of the soil, well correlating
with a mass of a charge and epicenter distance was accepted.
For installation of charges of explosive in thickness of weak soil
the special explosive columns, consisting of the metal container
for installation of a charge of explosive by diameter of d = 0,22
m and height h = 1,0…1,2 m, and also the upsetting metal pipe
welded on it d = 0,05 m (fig. 3) which immersion on necessary
depth was made by means of the drilling rig.
Figure 5. Scheme of an explosive column:
1 – pipe d = 0,05 m; 2 – borehole d = 0,22 m;
3- charge of explosive; 4- pipe d = 0,2 m
At explosive impacts of deformation of stamps continuously
increased and there was a loss of their stability. In the course of
tests of underground water rose above a sole of stamps by 0,3 -
0,4 m that is connected with increase of steam pressure in the
thickness of soil when passing seismic waves.
As a whole, results of numerous pilot studies and operating
experience of various constructions in the conditions of weak
water-saturated loess soil show that seismic influences by
intensity of 7, 8 and 9 points promote decrease in bearing ability
of soil of the basis of stamps and the foundations for 10, 20 and
30% respectively.
13 THE CONDENSED SOIL PILLOWS
In the conditions of the republic one of most widely applied
artificial methods of preparation of the bases is the device of the
condensed sandy and gravel pillows that is explained by
existence of a large number of a natural standard material, its
low cost and efficiency of their application in practice of
construction. The corresponding researches and experience of
design specify that 1,0 diameters of a stamp or base width are
recommended to appoint thickness of the condensed soil
pillows not less than 0,75d. In this direction the great interest is
represented by researches of features of the device and work of
the high-condensed gravel and sandy pillows (at the density of
dry soil
ρ
d
≥ 2,2 t/m
3
and coefficient of consolidation of k
com
>
1,0) on weak water-saturated loess soil with consistence I
L
= 0,8
(Usmanov R.A. 2009). The specified pillows were arranged on
weak soil with thickness h = 0,5; 0,75 and 1,0 m. By results of
tests the calculation resistance (bearing ability) all artificial
bases made more R = 500 kPa that more than by 5 times
exceeds value of calculation resistance of weak soil of natural
addition (R = 90 kPa).
Researches of work of the high-condensed pillows at
explosive influences by intensity of 9 points were conducted on
a site where on a mark of underground water it was arranged
high-condensed (
ρ
d
> 2,2 t/m
3
, k
com
> 1,1) a gravel pillow with
thickness h = 0,75 m on water-saturated loams with consistence
I
L
= 0,8. On a skilled site stamps by the area A = 1,0 sq. m (d =
1,13 m) were established and loaded by a technique of static
tests up to the average pressure on a sole р = 480 kPa (fig. 4).
For comparison results of test of stamps are given in the same
schedule in the conditions of weak soil at the size of average
pressure р = 80 kPa (Usmanov R.A. 2009). Imitation of seismic
forces was carried out by means of explosive influences, similar
to a technique given in fig. 2 and 3.
The maximum gain of deformations of stamps at seismic
fluctuations made all S
eq
= 7% from the general a precipitation
recorded at static tests. As a whole, the obtained experimental
data and the subsequent experiment of construction showed on
high efficiency of application of the high-condensed pillows
from sandy and gravel materials in the conditions of weak
water-saturated soil and high seismicity of the region.
Figure 4. Scheme of carrying out tests by explosive influences:
a) the scheme of an arrangement of skilled stamps and explosive wells
(1 - 40 numbers and an order of detonation of wells); b) section of an experimental site
