CC BY
8
Section 1. Architecture
Rasulov Khayat Zairovich, doctor of Technical Sciences, professor, Tashkent Institute of Architecture and Construction E-mail: hayat1941@mail.ru
VIBROCREEP LOESSIAL SOILS
Abstract: In article creeping property humidified loess soils is stated results of experimental researches of the author on studying at vibrating influences. It is noticed, that vibrocreep deformation is especially accurately shown in the water sated loess which is exposed to intensive concussion. In such condition of loess, force of an internal friction between particles under the influence of vibration can be destroyed in full or in part, and the soil gets mechanical property of a viscous liquid. Researches on display and course studying vibrocreep in the water sated loess have shown, that it depends on many factors, the main things from which are: density - humidity condition of a soil, its mineralogical and grading structures, durabilities (a friction corner and cohesion), external loading, vibrating influence (acceleration, frequency, amplitude, the period and duration of fluctuations), etc.
Keywords: loess, vibrocreep, fluctuations, long deformation, factor vibroviscosity.
N = 6-n-n-v-r (1)
The consolidation of loessial soils at vibrating influences is carachterized by accumulation of volume deformations in time as a result of accumulation of mutual displacement of particles from each separate period of fluctuations. At increase in frequency of concussion there is an imposing of mutual displacement of particles leading to long deformation of a soil.
Vibrocreep soils are called as the deformation accumulation in time at constant accelerations of fluctuations and pressure [1]. Vibrocreep deformation is especially accurately shown in water sated loess soils, exposed to intensive concussion. As experience show, in such condition of loess, forces of an internal friction between particles under the influence of vibration can be destroyed completely, and the soil gets mechanical property of a viscous liquid. In such conditions, bodies with the density exceeding density of the viscous environment, sink in a soil, and from smaller density - emerge.
The creeping property of a soil shown in the conditions of concussion can be characterized in factor vibrocreep [2]. The factor vibrocreep of humidified loess and the factors influencing this indicator is rather convenient for investigating by means of a method of "ball test" N. A. Tsytovich [3]. In a basis of the given method is put the known formula Stocs establishing dependence the march perform of a ball u in the viscous environment from force N and radius of ball r:
where n - factor vibrocreep.
The carried out researches on display and course studying vibrocreep in the water sated loess have shown that it depends on many factors, particularly: a density - humidity condition of a soil, its mineralogical and grading structures, strengths (angle internal friction and cohesion), external loading, vibrating influence (acceleration, frequency, amplitude, the period and duration of fluctuations), etc. The methods of carrying out of experiences on studying of dependence of factor vibrocreep a soil from acceleration of fluctuations consisted in following.
The soil with natural density and humidity was stirred in a skilled vessel of vibrating installation, and in cases of the broken structure it is kept within the set of particular condition. The vessel was equipped with device recording the mixture of a ball on a soil. Further, the installation of fluctuations at the set acceleration with registration of movement of a ball was carried out. At the end of activity, the cycle repeated at new acceleration of fluctuations, etc.
As a result of such experiences, the schedules of dependence of immersing of a ball from time for loadings different quantity at invariable preservation of value of acceleration of fluctuations is shown. Also, the variable speed of immersing ball in a soil experience and reduction of this speed in process of depth increase has been fixed in the beginning. At the same
time, in process of immersing of a ball of acceleration of immersing to aspire to zero, and speed gets more or less constant
value. This circumstance depended on value of the loading enclosed to a ball and acceleration of oscillatory movement.
M
0,6
0,4
0,2
0,1
0.08
.5 0,06
0,04
0,02
\ / ✓
/
/ /
/ / /
/
/ /
/ 1 ^ -1=
500
1000
1500
2000
2500
3000
Intensity of fluctuation, mm/s2 Figure 1. Dependence of speed of immersing of a ball in a soil from intensity of fluctuation
There is a linear dependence between the established speed of immersing of a ball and acceleration of oscillatory movement (fig. 1). In a considered case the established speed of immersing ball means factor vibrocreep at corresponding fluctuations. On (fig. 2) the schedule of dependence of quantity of factor vibrocreep from acceleration of fluctuations is illustrated. As it is seen from this schedule, that at accelerations of fluctuations, less 1.5 g (g - acceleration a gravity) loess fluctuation practically does not render influence on factor quantity vibrocreep a soil. Only at q > 1.5g start up factor reduction vibrocreep. Between factor vibrocreep q and acceleration of fluctuations and it is approximately possible - to present communication in a kind:
n=p*(a-a0), (2)
where a0 - a threshold vibrocreep a soil; ft - коэ^. balance. Dependence of quantity of forces of cohesion in coherent soils from their condition of humidity allows to assume, that the factor vibrocreep will depend on humidity of loess also. In this direction the researches on the vibrating installation technique is similar to experiences by definition of dependence of factor vibrocreep from acceleration of oscillatory movement have been carried out. Experiences were spent on loess soils with various humidity, however, acceleration of fluctuations and the static loading enclosed to a ball remained invariable.
On (fig. 3) the schedule of dependence of quantity vibrocreep loess from humidity of a soil is illustrated. From drawing it is seen that the factor vibrocreep a soil is not constant in time and depends on quantity of forces of cohesion (connectivity) of loess. At the same time forces of cohesion as the factor of
viscosity of clay breeds, can increase or decrease depending on humidifying degree. Reduction of force of cohesion in addition to sated with water soils influences factor vibrocreep.
We assume that the quantity of forces of cohesion (connectivity) in soils depends on the maintenance of moisture which leads to the fact that the factor vibrocreep will depend also on humidity of a soil. In our experiences the increase in humidity of a soil (for example, to 12-13%) led to increase of value factor vibrocreep (more eightfold).
Results of experiences on research of dependence vibrocreep factor from humidity of a soil allow to assume, that under all other equal conditions immersing of a ball by vibrating (increase the factor vibrocreep) will occur to the greatest speed in that case when the soil is in fool the water sated condition.
In researches with loess soils there are some specific features:
- consolidation of the humidified loess at fluctuation has begun through some time after the appendix of dynamic loading;
- intensity of consolidation during the initial moment was characterized by rather low values and gradually increased yet will not reach a stable condition;
- duration of a finding in a stable condition of deformation depended on humidity of a soil.
It testified the necessity of the account of duration of fluctuation along with its intensity at an estimation vibrocreep of a soil that has given the chance the size of time necessary for tour de creep deformation of a soil to put in dependence first of all from durability of communications (cohesion) of loess.
It is known, that instability of structure loess soils show characteristics of a weak cohesion of their structural elements. Durability of communications depends on structure and water resistance of aggregating substance. Ability of a
softening and dissolution in water of the natural cementing substance creating connectivity between particles of loess defines completely or substantially character of communications.
o -j
V)
u
O
■B. ÙÛ >
>■. ™ s p
u
tn
•C
i
Tpyur № 1
fpyhr It y ht Jfî2 -r /
ys^s rpyHT№12
S -;>
500
.1000
1000 1500 2000 25M
Acceleration fluctuations, inni/sr Figure 2.Dependence 1/n from acceleration of fluctuations for loessial soils
Humidity, 0 a
Figure 3. Character of change of cohesion and viscosity of a soil at humidifying
Character of conhesivity loess soils is expressed by the physical and chemical nature of communications, their water resistance and mechanical durability. We will assume, that the soil has friable addition and possesses forces of cohesion (conhesivity). Loss of stability of structure of such soil is possible at infringement of forces of cohesion between its separate particles under the influence of pressure upon contact particles in the course of fluctuation.
The analysis of results of researches in the light of the aforesaid testifies that following conditions are necessary for infringement of structure coherent soils and transition in a creeping condition:
- friable addition of particles of a soil at which porosity of a soil prior to the beginning of fluctuation nt, causing in-
fringement of its structure, would be more porosity of a soil nK after influence of the specified factor, that is nH y nk ;
- intensity the fluctuations, expressed in the form of acceleration, should be capable to break force of connectivity between soil particles;
- duration of fluctuation should make time demanded for occurrence a stable creeping condition a soil.
As a result it is possible to draw a conclusion that if forces of cohesion (conhesive) between soil particles are not broken by operating fluctuations, the soil is not deformed. Vibrocreep condition of the soil is not shown also when duration of fluctuation is measured only by several seconds (for example, duration of explosive influence).
References:
1. Ivanov P. L. Soils and the bases of hydraulic engineering constructions. TH., "Higher school",- 1985.- P. 65-81.
2. Rasulov H. Z. Seismic stability of the soil bases. - T. "Uzbekistan",- 1984.- 192 c.
