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Depth of the diluted zone in the humidified loess bases under shaking conditions
DOI: http://dx.doi.org/10.20534/ESR-17-3.4-107-108
Rasulov Hayat Zoirovich, Tashkent Institute of Architecture and Construction, Doctor of Technical Sciences, Professor. E-mail: hayat1941@mail.ru Tashhodjaev A. U., Tashkent Institute of Architecture and Construction,
senior teacher
Equality (3) taking into account (4) and (5) will be copied in a kind:
Y
! w
2ng
Tv a = < ,. tgv + c
c c dm o t w w
(6)
Depth of the diluted zone in the humidified loess bases under shaking conditions
Abstract: The article is dedicated to results of researches of authors on a problem of studying of a thickness of a diluted zone in loessial humidified soils in the conditions of influence on them of seismic concussions. From a condition of limiting balance of two counteracting forces (seismic and resistance to shift) the formula is received to define the size of a diluted zone at the moment of influence on the bases of seismic fluctuations. According to the recommended formula, seismic stability of any soil besides size of seismic influence depends onm strong characteristics of a soil, such as: a corner of an internal friction and conhesive, etc.
Keywords: diluted zone; loess soil; concussions; seismic pressure; resistibility to shift; a friction corner; cohesion.
The estimation of stability of the water sated bases of constructions at influence of seismic fluctuations in many respects depends on depth of a diluted zone in the conditions of concussion with value above critical acceleration [4, P. 51].
Thus, initial depth of the diluted zone arising in thickness to fluctuating thickness is defined from a condition:
as > ar (1)
here as - the maximum seismic acceleration arising in soil thickness; a - critical accelerations of fluctuation of a soil.
Kr
The critical acceleration of fluctuationa stands for the maxi-
kP
mum quantity which is resistance expressed strength by properties of the fluctuating soil. According to such concept at the seismic accelerations exceeding critical accelerations, particularly taking into account the given soil there is a destruction of structure of the water sated soil with transformation of it into diluted conditions.
Otherwise a soil fluctuations keeps the static condition without any infringement of durability.
For definition of critical acceleration formulais offered by Rasulov [4, P. 72]:
2ng (atg^w + cv)
For definition of depth of a diluted zone in thickness of a soil we will analysis equalities (6). It is known, that value o in it generalized a dynamic condition of two pressure: from the loading operating on a surface of a soil (oz) and from a body weight of the soil
(Ywz X i.e:
odun = 0z + Y wz (7)
In case of absence of external loading on a soil surface (o = 0), the formula (6) can be copied as:
Y
w
2ng
Tvcac = Y wztg V
(8)
„ T - (2) Yw T • vk
where: g- gravity acceleration; o - normal pressure from construction weight; $ w- a cornerof an internal friction of a soil at humidity w; cv - the general cohesion of a soil; Y w - soil density; T - the fluctuation period; vk - cross speed distributions of seismic waves.
In the course of concussion of the water sated soil special value gets zone definitions dilution when it is observed in following conditions (1).
This zone can be defined from limiting equality:
Ts=s (3)
pw * '
where T - the pressure arising in thicknesses of a soil in process distributions of seismic waves (seismic pressure); spw - resistibility of a soil to shift (durability of a soil).
Seismic pressure can be defined under formula [2]:
Yw-Tv a Yw
Prof. Medvedev S. V. notes, that the Earthquake period ( T ) is distinguished for different soils and depends, basically, from an addition condition. For a case of homogeneous addition of a soil quantity T depends on a thickness of fluctuating layer H and speed of fluctuation of soil particles v in a kind [2, P. 65]:
T = 4H (9)
Including
a
= k
(10)
(4)
2ng 2ng
where z - considered horizon in soil thickness. X - length of wave. Resistibility of a soil to shift is defined in following manner:
Spw = (° + YwZ )tgVw + cw (5)
where o , Yw , , cw - have values as in the formula (1).
where kc - seismicity factor.
Taking into consideration dependences (9) and (10) formula (8) can be written as follows:
0,64 YwkcH = Y wztg (pw + cw (11)
Parametere z in this case represents depth of a diluted zone and it is possible to calculate its value as:
0,64k y H-c , .
L = —-^-w (12)
YwtgVw
Formula (12) in each special case allows to define size of a diluted zone in the water sated soil during the moment (t = 0) appendices of seismic loading.
As follows from it depth of a diluted zone at concussion of the water sated soil depends from quantity of acceleration ofseismic fluctuation (a), or seismic pressure caused by it ( Ts).
Fig. 1 is illustrated dependence Lo = f (o ) as a result of the spent experimental researches on humidified loessial soils. As fol-
v
Section 9. Technical sciences
lows from the schedule, any normal pressure from weight of external loading 7 promotes reduction of a thickness of diluted zone Lo. Such conclusion follows and from the formula (12) also. This cir-
cumstance demands the account of weight of a construction at definition of initial value of a dilution zone in the conditions of concussion of the water sated soil.
160/ 140 »120 g 100
G80 .2 60
3
Q
1 \
\ Loess soils
-
0.5 1.0 1.5 2.0 2.5 3.0 External loading, kg/sm
Figure 1. Dependence between dilution zone and external loading
At the same time, it is necessary to underline a positive role of cohesion of a soil in value of a dilution zone. It is known, that any rise cohesion quantity between soil particles promotes to increase in durability and, from here, bearing ability of the basis. If the general cohesion in the formula (12) to spread out to components, i. e. [1, P. 47]: cv = Cw + c, (13)
where cw - the plastic connectivity having water-kolloid character; cc - rigid structural cohesion.
Depending on a natural condition the soils can be characterised by various cohesions. From here water sated soils in a plastic condition it is possible to express resistibility of the weakest as:
120
Ts=cw (14)
This circumstance testifies the ability to dilute such soils in considerable depth zone. In such condition depth of a diluted zone depends only on plastic cohesion of a soil. And influence of normal pressure from construction weight in considered conditions it is reduced to zero (fig. 2). About extremely instability of water sated soils it is appropriate to notethe seismic relation on consequences oflast strong Earthquakes [3, P. 174-213].In small humidified soils above noted phenomenon proceeds a little differently. Presence at them an internal friction and rigid cohesion making positive impact promote shortening a diluted zone.
100
o 80
N Ö 60
40
20
h0
\
=28 00 r nm/s r
X
»
Cw
0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04
Plasticity lokesion, MPa Figure 2. Dependence between dilution zone and plasticity cohesion
In summary it is necessary to notice, that the established depth of a diluted zone under the formula (12) will correspond to the initial moment ofthe appendix of seismic loading to a soil. At the same
time, the given zone, in certain conditions, can deeps in process of fluctuation of thickness depending on intensity of seismic influence.
References:
1. Maslov H. H. Mechanics soils in building practice, - Moscow, - 1987. - 320 p.
2. Medvedev S. V. Engineering seismology, - Moscow, - 1962. - 284 p.
3. Polyakov S. V. Consequence of strong Earthquakes, - Moskow, - 1978. - 306 p.
4. RasulovH. Z. Seismostability of the soil bases, - Tashkent, - 1984. - 192 p.
