RU2281995C1 - Method for frost ground heaving determination in dependence of pressure transmitted from foundation to the ground - Google Patents

Abstract

FIELD: building, particularly geological engineering survey for foundation building on seasonally frozen heaving ground bases.

SUBSTANCE: method involves taking at least three ground samples; placing the samples in device, which determines degree of frost ground heaving caused by pressure applied to the ground; installing the device in cooling chamber; freezing the ground samples at predetermined rate; creating pressure p₁ in the first sample, wherein p₁ pressure is equal to average pressure caused by ground gravity at design frost depth; measuring maximal heaving pressure p_f(max) in the second sample with taking into consideration compressibility of ground sample and dynamometer; creating pressure p₂ in the third ground sample, wherein pressure p₂ exceeds that caused by ground gravity at design frost depth determined in particular territory, but is not less than 50 kPa; determining pressure p_f(max), ε'_fp1 and ε'_fp2 from above measurements; defining constant ground parameter m₁; determining m₂ parameter from p₁, p_f(max) and ε'_fp2; calculating average actual value m and actual value ε'_fpi depending on p_i from a given relation.

EFFECT: increased efficiency of frost ground heaving degree determination under any pressure.

1 ex, 2 dwg

Description

The invention relates to the construction, in particular, to the field of engineering and geological surveys for the construction of foundations and structures on seasonally freezing heaving soil bases.

The known method of laboratory determination of the degree of heaving of soils in accordance with GOST 28622-90, M., Gosstandart of the USSR, publishing house of standards, 1990, approved and put into effect on 05/18/90 by the resolution of Gosstroy of the USSR No. 43 [1].

In accordance with this GOST, the test soil sample is placed in a cylindrical cage with an internal diameter of at least 100 mm and a height of 150 mm. In this case, the clip should consist of separate rings 2-5 cm high, interconnected.

Pure fine-grained sand, carborundum and the like can be used as a capillary-porous material for a cartridge pallet. The layer height of the capillary-porous material should be 50 mm.

The holder with the test soil sample is placed in a refrigerator and the samples are frozen in an automated mode at specified temperature and time conditions at a pressure equal to the expected pressure from constant loads at a given depth, but not more than 50 kPa, and the relative value of frost exposure is determined by freezing this sample of soil.

The relative deformation of frost heaving of the soil sample ε _{fh is} calculated with an accuracy of 0.01 according to the formula:

where h _f is the vertical deformation of the soil sample at the end of the test, mm;

d _i - the actual thickness of the frozen layer of the soil sample, mm

The disadvantage of this method of laboratory determination of the degree of heaving of soils is that this method does not allow determining the degree of heaving of soils at pressures greater than 50 kPa.

The practice of designing foundations on seasonally freezing soils shows that the pressure from the foundations, as a rule, reaches from 80 to 300 kPa.

It is known "Device for determining the value of frost heaving of soils from pressure" according to the certificate for utility model No. 25518, IPC class E 02 D 1/00, published in Bull. No. 21 October 10, 2002 [2].

Using this device reduces the time of statistical processing of test results and allows you to determine the ultimate pressure of frost heaving, taking into account the compressibility of the dynamometer and soil in the sample during freezing.

Moreover, in the first group of six samples, the pressure is brought to average pressure from its own weight for the estimated depth of seasonal freezing of the soil for a particular region, in the second group of six samples, the pressure is brought to 50 kPa, and in the third group of three samples, the ultimate pressure is measured heaving taking into account the compressibility of the dynamometer and soil in the sample during its freezing.

This device allows you to determine all the necessary parameters of the known exponential dependence of the degree of frost heaving on pressure, which is described in detail in the abstract of the dissertation for the degree of doctor of technical sciences of the author Golly OR entitled "Integral laws of frost heaving of soils and their use in solving engineering problems in construction" St. Petersburg, VNIIG them. V.B. Vedeneeva, 2000

The exponential dependence of the degree of frost heaving on pressure is described in detail in the article by Ph.D. Abzhalimova R.Sh. under the title “Hypothesis on the distribution of normal frost heave forces over the sole of a hard-frozen soil layer under foundations, see the journal Industrial and Civil Engineering”, No. 12, 2003, pp. 23-26.

A curve of the exponential dependence of the degree of frost heaving of the soil on pressure is shown in figure 2.

However, to date, a more efficient way to determine the degree of frost heaving of the soil, depending on the pressure of the foundation on the soil, has not been created in comparison with the sources known from scientific and technical information [1] and [2].

The aim of the invention is to provide a method for determining the degree of frost heaving depending on the foundation pressure on the soil, not only at pressures up to 50 kPa, but also at any pressures above 50 kPa, which are usually more common when designing foundations in industrial and civil engineering.

The specified technical result is achieved as follows.

The test soil is placed in at least three samples in a device installed in the refrigeration chamber for determining the amount of frost heaving of the soil from pressure. At the same time, in the first sample create a pressure equal to the average pressure of the own weight of the soil with the estimated depth of seasonal freezing for a particular region; in the second soil sample, the maximum heaving pressure is measured with a dynamometer, taking into account the compressibility of the dynamometer and soil in the sample; in the third soil sample create a pressure greater than that of the own weight of the soil at the estimated depth of seasonal freezing for a particular region, but not less than 50 kPa, and the average value of the constant parameter of the soil m at p ₁ and p ₂ and, accordingly, are determined from these measurements , the degree of heaving of the soil according to the formula:

- степень пучинистости грунта при давлении p_i;Where

- the degree of heaving of the soil at a pressure p _i ;

p _i is the changing pressure from the foundation to the heaving soil layer along the freezing depth, kPa, p ₁ <p _i <p _{f (max)} ;

p ₁ - average ground pressure of its own weight for the estimated depth of seasonal freezing for a particular region;

p ₂ - pressure on the test soil sample, with values of at least 50 kPa;

p _{f (max)} is the maximum pressure of frost heaving, taking into account the compressibility of the dynamometer and soil in the sample during freezing, kPa;

exp - exponent, constant value equal to 2.718282;

m is a constant soil parameter, determined experimentally, depending on the physical and thermophysical properties of the soil and freezing conditions.

As the closest analogue to the proposed method, you can take the "Laboratory method for determining the degree of heaving of soils" in accordance with GOST 28622-90 [1].

The list of figures in the drawings.

Figure 1 shows a device for determining the value of frost heaving of soils from pressure, a front view in section.

Figure 2 shows a well-known curve of the exponential dependence of the degree of frost heaving of the soil on pressure.

The proposed method for determining the degree of frost heaving of the soil depending on the pressure of the foundation on the soil is carried out using a device for determining the value of frost heaving of the soil from pressure according to the source of scientific and technical information [2].

This device consists of the following components, devices and tools (figure 1).

In the refrigerating cabinet 1 with thermal insulation 2, a tray 3 with sand is installed, into which water comes from the vessel 4 and a constantly set water level in the tray is maintained. The frame 5 is fixedly mounted on the pallet 3, welded from steel corners, intended for mounting tripods 6 on it, to which are attached the Messura 7, which are affected by the rods 8 when the soil samples 9 are frosty.

The test soil of the undisturbed structure is placed in cylindrical holders and freezing is also carried out in accordance with GOST 28622-90. A thermocouple 10 is installed in each sample.

In the first group of six samples 9 produce frosty heaving at an average pressure of the own weight of the soil at the estimated depth of seasonal freezing for a particular region and determine the value of p ₁ . For the Omsk region, the pressure p ₁ is about 20 kPa, therefore, two weights 11 are installed on the rods 8 of the first six samples, providing a pressure of 20 kPa.

определяют по показаниям мессур 7 по формуле (1).The degree of frost heaving

determined by the testimony of Messur 7 by the formula (1).

. Мессуры 7 обеспечивают точность измерения ±0,01 мм.The following six samples were equipped with five weights 11 each, which respectively provide a pressure p ₂ on the soil in samples 9 of 50 kPa each. And then, according to Messur 7, the degree of frost heaving is similarly determined

. The 7 masses provide a measurement accuracy of ± 0.01 mm.

And on the other three soil samples 9, dynamometers 12 are mounted, fixed to the base of the pallet 3 with bolts 13. Dynamometers 12 show the maximum soil pressure p _{f (max)} from frost heaving, taking into account the compressibility of the dynamometer and soil in the sample.

.An example of determining the degree of frost heaving of the soil by the proposed method and by the formula:

.

As an example, we used the parameters of laboratory tests, with a probability of α = 0.98, of heavy dusty loam from the base of an underground pedestrian crossing in the area of the plant named after P.I. Baranova in Omsk.

, p_f(max)=400 кПа.For soil p _i = p ₁ = 20 kPa,

, p _{f (max)} = 400 kPa.

We substitute these values in the proposed formula:

20 = 400 · exp (-m ₁ · 0.138).

;

; 0,138·m₁=2,966 и m₁=21,71.From this we find:

;

; 0.138 m ₁ = 2.966 and m ₁ = 21.71.

(по показаниям мессур с вероятностью α=0,98).When p ₂ = 50 kPa,

(according to the testimony of the Messurs with a probability of α = 0.98).

According to the proposed method, we determine m ₂ according to the formula (2.2):

;

,50 = 400 · exp (-m ₂ · 0.09);

;

,

.from here

.

.Average value

.

и

, полученные по формуле (2) при среднем значении m=22,405.Find deviations

and

obtained by the formula (2) with an average value of m = 22,405.

;p ₁ = 20 kPa; p _{f (max)} = 400 kPa; m = 22.405;

;

;

.

;

.

The deviation from the actual value was:

;The same with p ₂ = 50 kPa; p _{f (max)} = 400 kPa; m = 22.405;

;

Deviation from the actual

Finally, for the test soil we obtain the dependence formula:

As can be seen from figure 2, the total degree of heaving of the soil from pressure is expressed by the equation:

- степень сжатия динамометра и грунта в образце в процессе его промерзания, определяемая по формуле:Where

- the compression ratio of the dynamometer and soil in the sample during freezing, determined by the formula:

- степень сжатия динамометра, определяемая по показанию мессуры по формуле (1);Where

- the compression ratio of the dynamometer, determined by the indication of the mass on the formula (1);

- степень сжатия талого грунта в образце в процессе его промерзания, определяемая по формуле:

- the degree of compression of thawed soil in the sample during freezing, determined by the formula:

where S is the sediment of thawed soil under compression, determined from the well-known equation, according to SNiP 2.02.1-83 *:

where d is the height of the sample with soil;

p _δ - household pressure on the soil sample in its natural state, equal to p _δ = p · d _i ;

p is the density of the soil, tf / m ³ ;

d _i - the depth of sampling for testing, m

- среднее давление сжатия талого грунта в процессе его промерзания, кПа;

- average compression pressure of thawed soil during its freezing, kPa;

E - soil deformation modulus, determined according to SNiP 2.02.02-83;

β is a dimensionless coefficient equal to 0.8, according to SNiP 2.02.02-83.

от давления с вероятностью α=0,98, кривая 1 и зависимость степени сжатия динамометра и грунта в образце (

) от p_fmax - прямая 2, полученная нами для испытуемого грунта.Figure 2 shows the dependence of the degree of heaving of the soil

pressure with probability α = 0.98, curve 1 and the dependence of the degree of compression of the dynamometer and soil in the sample (

) from p _fmax - line 2 obtained by us for the test soil.

Thus, the implementation of the proposed method became possible thanks to the use of a device for determining the value of frost heaving of soils from pressure according to the certificate for utility model No. 25518.

And the method itself allows the use of seasonally freezing heaving soils as bases for the foundations of low-rise buildings and underground structures, significantly reducing the cost and complexity of construction compared to the current design standards.

Literature:

1. "The method of laboratory determination of the degree of heaving of soils" according to GOST 28622-90, M., Gosstandart of the USSR, publishing house of standards, 1990, approved and put into effect on 05/18/90 by the resolution of the Gosstroy of the USSR No. 43.

2. "Device for determining the value of frost heaving of soils from pressure" according to the certificate for utility model No. 25518, IPC class E 02 D 1/00, published in Bull. No.21 October 10, 2002

Claims (1)

A method for determining the degree of frost heaving of the soil depending on the pressure of the foundation on the soil, characterized in that the test soil, at least three samples are placed in a device for determining the amount of frost heaving from pressure, placed in a refrigerator, where freezing is carried out at a given speed, while in the first soil sample create a pressure p ₁ equal to the average pressure from the own weight of the soil at the estimated depth of seasonal freezing for a particular region, in the second soil sample The maximum heaving pressure p _{f (max) is} taken into account, taking into account the compressibility of the dynamometer and the soil sample; in the third soil sample, a pressure p _{2 is created} that is greater than the dead weight of the soil at the estimated seasonal freezing depth for a particular region, but not less than 50 kPa and according to the results measurements find p _{f (max)} ,

and

and according to the values of p ₁ , p _{f (max)} and

find a constant soil parameter m ₁ , and the values of p ₂ , p _{f (max)} and

- the value of m ₂ , and their average actual value of m, then find the actual value

from p _i according to the formula

Where

- the degree of heaving of the soil at a pressure p _i , kPa; p _i - the changing pressure from the foundation to the heaving soil layer along the freezing depth p ₁ <p _i <p _{f (max)} ; p ₁ - average ground pressure of its own weight for the estimated depth of seasonal freezing for a particular region, kPa; p ₂ - pressure on the test soil sample, with values of at least 50 kPa; p _{f (max)} - the maximum pressure of frost heaving, taking into account the compression of the dynamometer and soil in the sample during freezing, kPa; m is a constant soil parameter, determined experimentally, depending on the physical and thermophysical properties of the soil and freezing conditions.

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