Method for evaluation of extent of clay soils repacking in natural deposit

FIELD: construction.

SUBSTANCE: in method samples of soil are picked, density and humidity are determined in natural condition, as well as density of soil particles, overburden pressure at the depth of sample picking and preconsolidation pressure. Additionally humidity is determined at liquid limit, as well as size composition, content and density of particles of fine, with size of less than 2 mm, and coarse, with size of more than 2 mm, fractions, steady-state density of sample. Balance pressure for overburden density of picked soil sample is defined according to the formula: coefficient of repacking is determined by ratio of picked sample density and balance density for overburden pressure: coefficient of tension by ratio of balance and overburden pressures: and then, having obtained values of these coefficients, extent of sample repacking is defined.

EFFECT: increased efficiency and accuracy, reduced labour intensiveness and duration of balance pressure determination, wider interval of pressure values and preconsolidation properties.

3 cl, 4 dwg, 2 tbl, 2 ex

 

The invention relates to the field of design and construction of civil, industrial, hydrotechnical facilities, including oil and gas platforms, and is used to characterize the physical and stress-strain state of shale, assessment of conduct under load dense cohesive soils with a natural structure, when the device of the pits and the choice of measures to ensure slope stability and the pit bottom, to create the initial stress state during testing of soil samples under conditions of uniaxial compression, the determination of strength parameters.

For the assessment of novelty and inventive step of the claimed solution consider a number of known technical devices of similar purpose.

There is a method of determining the rate of compaction of argillaceous rocks [1] on the relative expression of porosity

where Kd- an indicator of compaction, Douglas;

εf- the porosity corresponding to the transition of water-saturated sediment from flowing in a plastic condition;

εp- the porosity in the transition of sediment from the plastic to the solid state.

The values of efand εpare determined from the following relations:

where Wfand Wp- weight humidity, corresponding to values of εfand εp;

γ is the specific weight of the rock.

On the obtained values of Kdthere are the following status species: nedouplotneniya, the initial degree of compaction, plastic, switching to semi-solid, semi-crowded.

The main disadvantage of the method-analogue is conditional, allowing roughly approximated to characterize the status and properties of rocks, because the definition of the natural porosity of young sediments in the laboratory can give a large deviation from the initial porosity of the same sediment being laid on the bottom of the reservoir under natural conditions. A conditional is a quantity that characterizes the transition compactible water-saturated sediment from flowing into the plastic and plastic in a semi-solid state.

Known methods of determining the degree of overstocking clay rocks on a difference of porosity in their natural state and made from pastes them at a pressure equal to the natural [2], and the ratio of the porosity of the paste (with initial moisture content equal to the moisture on the border of flow and pressure, equal natural) and in its natural state [3].

The disadvantage of the way of analog is the need for time-consuming sample preparation and the performance of the long-term experiments on compression the compression of the clay soil at different stages of loading. How counterparts do not provide a definition of pressure predoplatnoy, under which the formed clay rock.

Known methods of determining factor overstocking clay soils the ratio of the difference between the value of the previous pressure (pressure predoplatnoy) and natural (social pressure) to the natural pressure [4 and 5]

where Fnyfactor overstocking;

Py- previous pressure (pressure predoplatnoy);

Pnpnatural pressure.

Determining the value of the previously existing pressure is based on the results of compression tests of clay soils with a natural structure.

The disadvantage of this method is similar assessment is overstocking on the shape of the curve of compression, different from that usually observed for normally compacted formations. Soil can be normally consolidated despite the fact that the nature of its compression curve can differ from normal. For this reason, the prediction of the nature of the compression curve, based on the geological history can sometimes be very wrong.

Closest to the claimed combination of essential characteristics is that we have adopted for the prototype way Casagrande [6, 7], including the selection of the sample grancanariano patterns, determination of density and moisture in a natural state, the density of the soil particles, household pressure at the depth of selection of the sample, seal the compression device with the unloading and re-loading, determine the pressure predoplatnoy and coefficient of overstocking.

Prototype method consists in the following. For the selected soil sample to determine the density and moisture in a natural state, the density of soil particles. The soil sample is placed in a compression device, and a stepped load up to a certain pressure, and then unload and re-load (recompression) to a pressure exceeding the pressure predoplatnoy, fixing the value of precipitation for each pressure stage. According to the obtained results is based compression curve in semi-logarithmic scale e=f·lnσ. The graph is determined by the point corresponding to the maximum curvature of the curve re-loading, is a horizontal line through this point and tangent to it, then is the bisector of the angle between them. Is determined by the intersection point of the bisectors with a continuation of the straight part of the compression curve, the projection of which on the axis of the pressure p and give pressure value predoplatnoy. The coefficient of overstocking is determined by the formula

where OCR coefficient perempat is to be placed, cu;

- pressure predoplatnoy, MPa;

domestic pressure, MPa.

Consumer pressure is calculated by the formula

where ρ is the density of the soil, g/cm3;

h - depth of sampling soil sample, m

This method is included in the current British (BS) and American (ASTM) standards.

The disadvantages of the prototype method in addition to the large labor costs and low productivity is the low accuracy of determination of the pressure predoplatnoy, because it is in some area surrounding the point of inflection of the laboratory curve compression. The method is applicable for moderately crowded soils, because the capacity of the laboratory equipment in some cases do not allow you to create large vertical pressure (>10 MPa).

The technical result, which is aimed invention is to improve performance, accuracy, reduce labor intensity and duration determine the equilibrium pressure, the expansion of the ranges of pressures and characteristics of predoplatnoy.

To achieve the mentioned technical result in the proposed method, including the selection of the sample of soil, determination of density and moisture in a natural state, the density of the soil particles, domestic pressure on globenewswire sample, pressure predoplatnoy, additionally determine the humidity at the boundary point, granulometric composition, the content and the density of particles is small, smaller than 2 mm, and large, larger than 2 mm fractions, the equilibrium density of the sample and determine:

- the equilibrium pressure for residential density of selected soil sample

where- the equilibrium pressure, MPa;

ρdo- the density of the dry soil of the selected sample, g/cm3;

WLthe humidity at the boundary point, D.S.,

determine the coefficient of overstocking on the ratio of densities of the selected sample and the equilibrium domestic pressure

where ρdc- equilibrium density for domestic pressure, g/cm3and the stress ratio on the ratio of pressure equilibrium and household

wheredomestic pressure, MPa,

and then on the obtained values of these coefficients determine the degree of overstocking sample.

In addition, the present invention has optional features that characterize its special cases, namely:

- when developing pits when determining the equilibrium density domestic pressure to reduce the pressure removed from SL which I ground while the coefficients overstocking and voltage is determined taking into account the obtained values of the equilibrium density and household pressure;

- during the construction of constructions, such as buildings or embankments, in the determination of equilibrium density into account in addition to household passed on the basis of the pressure from the weight of the structure, and determine the coefficients overstocking and stress.

Distinctive features of the proposed method are the determination of moisture on the border of the yield, particle size distribution, content and density of the particles of the fine and coarse fractions, the equilibrium density of the sample, the equilibrium pressure for residential density of selected soil sample, the coefficient overstocking on the ratio of densities of the selected sample and the equilibrium for household pressure.

This saves working time by eliminating the need to seal the sample in a compression device, to extend the pressure range of predoplatnoy compared with the possibilities of laboratory equipment, as well as accurate assessment of the degree of predoplatnoy clay soils is improved by determining the equilibrium pressure, formed the natural (household) density of soil in the natural occurrence and the equilibrium density for the existing household (natural) pressure.

<> The proposed method is illustrated by drawings, figure 1-4.

Figure 1 shows the dependence of the porosity coefficient of the vertical pressure of the sample Cambrian clay selected from the wells with depth to 21.0 to 21.1 m

Figure 2 - dependence of the coefficient of porosity from the vertical pressure of the sample Vendian clay horizon, selected from a well with a depth of 74.9-75,15 m

Figure 3 - change of the coefficient of overstocking in the depths of the Cambrian and Vendian clays of the power unit and high-rise buildings.

Figure 4 - change of stress ratio on the depth of the Cambrian and Vendian clays of the power unit and high-rise buildings.

The method is as follows.

A sample is taken of the clay soil of the undisturbed structure, determine its moisture content and dry density of soil ρdo. Determine the soil moisture content at the boundary fluidity WL, granulometric composition and the content of small (smaller than 2 mm) and large (larger than 2 mm) fractions, the density of particles ρsmsmall and large ρskfractions, the equilibrium density ρdcfor household pressure. The magnitude of the current domestic pressureat the depth of sampling soil sample is calculated by the formula

,

where ρ is the density improvement is ü selected soil sample, g/cm3;

h - depth of sampling soil sample, m

The equilibrium density of the fine earth (d<2 mm),for current household pressure is determined in accordance with [8], taking

whereis the equilibrium density of the fine fraction (d<2 mm), g/cm3;

WL- the soil moisture content at the boundary fluidity, cu;

- the pressure is equal to the current domestic pressure, MPa.

The influence of the content of the coarse fraction on the value oftake into account the known methods [9, 10]

,

where- the equilibrium density for the applicable household pressure with regard to the content of the coarse fraction, g/cm3;

ρsk- the density of the particles of the coarse fraction (d>2 mm), g/cm3;

is the density of dry soil fine-grained deposits (d<2 mm), defined by the formula (4);

Pm- the content of the fine earth (d<2 mm) in the sample by mass, cu;

Pk- the content of the coarse fraction (d>2 mm) in the sample by mass, cu

The degree of overstocking judged by the values of the coefficients overstocking kρvoltage and kσdefined by the formulas (2) and (3).

Depending on the magnitude of the resulting coefficient is to distinguish the following States clay soils:

- ratio of overstocking the degree of overstocking

kρ=1 - normal concentration,

kρ<1 - nedouplotneniya,

kρ>1 - perepletenie;

- kσthe degree of stress state

kσ=1 - normal stress or stable state characterized by the absence of sediment and excess pore pressure,

kσ>1 - overstrained, unstabilized, in contact with water is possible deformation of the swelling, the presence of negative pore pressure,

kσ<1 - neonarrative, unstabilized for saturated soils, accompanied by precipitation, the presence of excess pore pressure.

This is a set of essential features that provide technical result for all cases covered by the present invention.

During the development of deep excavations are often observed increases mark the bottom of the pit as a result of decompression and swelling. Precipitation structures on such soils are often very significant. In the excavation of the pit decreases the magnitude of the current domestic pressureand by [8] to determine the equilibrium density ρdcfor domestic load, reduced by the amount of pressure in the other layer of soil, and taking into account the obtained values of the equilibrium density and domestic pressure by the formulas (2) and (3) determine the coefficients of overstocking and voltage. Based on these coefficients specify the deformation and strength characteristics of soil determine the amount of precipitation and stability of structures.

During the construction of constructions (buildings, embankments) on crowded clayey soil on the basis of the additionally transmitted pressure from the weight of the structure, increasing domestic pressure. Determined by [8] the equilibrium density ρdcfor domestic pressure, increased taking into account the pressure from the construction and obtained values of the equilibrium density and domestic pressure by the formulas (2) and (3) determine the coefficients of overstocking and voltage. Based on these coefficients specify the deformation and strength characteristics of soil Foundation, determine the amount of precipitation and stability of structures.

Examples of assessing the degree of overstocking Cambrian clay from the base of a power facility in the Leningrad region and Vendian clay horizon from the base of a tall building in St. Petersburg.

Example 1.

The task is to determine the equilibrium pressure for residential density and the degree of overstocking Cambrian clays at the base energy of the object in lening the infernal region.

The calculation is made for two wells drilled on the construction site to a depth of 16.5 to 41.9 m with a sampling of undisturbed soil structure. For selected samples to determine the wet density ρ and dry soil ρdmoisture in a natural state W and on the border of the fluidity of WLhousehold (natural) pressure σabout, granulometric composition, the results of which determine that all of the samples do not contain coarse particles (larger than 2 mm) smfbl, the density of the soil particles, the average component ρs=2,74 g/cm3. The equilibrium pressure for household density is determined by the formula (1).

For example, for a sample taken from a well with a depth of 21.7-of 21.9 m, the equilibrium pressure equals

The equilibrium density for household pressure equal todetermined by the formula [8],

The coefficient of overstocking is determined by the formula (2):

The stress ratio is determined by the formula (3):

Thus, the soil sample at a depth of 21.7-21,9 m is crowded condition under pressure less than that which formed the natural density. Figure 1 shows that in the investigated interval Yes the lines of 0.01-5,50 MPa failed to get the greatest curvature of the graph, i.e. to go on a straight line filtration consolidation of the sample. In this regard, there is no possibility to determine the value of pressure predoplatnoy and coefficient of overstocking OCR according to the method described in the prototype.

The equilibrium pressure for residential density of the proposed method obtainedi.e more pressure that can be created in the device.

Example 2.

The task is to determine the equilibrium pressure for residential density, the equilibrium density and the degree of overstocking for Vendian clay horizon from the base of a tall building in Saint-Petersburg.

The calculations were carried out for 13 samples of clay from wells with different depths from 47,0 up to 100.3 m

Physical characteristics of Cambrian and Vendian clays and calculated pressures of household and equilibrium, and coefficients of overstocking and voltages are given in table 2.

The graph (figure 2) does not show a drastic change curve for a sample taken from a depth of 74.9-75,15 m in the investigated pressure range from 0 to 4.6 MPa, which does not allow to determine the pressure predoplatnoy and the ratio predoplatnoy OCR on the prototype method.

The proposed method corresponding values obtained as follows: the equilibrium pressure for household densityi.e. more pressure, PR is which were tested sample, the coefficient overstocking kρ=1,08, the stress ratio kσ=9,27.

According to the results of calculations based on the proposed method and are given in table 2, build charts the changes in depth ratios overstocking kρvoltage and kσCambrian and Vendian clays shown in figure 3 and 4. From the above graphs it follows that all the studied soils are overstocked. The coefficient overstocking kρCambrian clays from the base energy of the object when the depth is increased from 16.5 to 41.9 m is reduced from 1.21 to 1.13, the stress factor kσdecreases from 40,80 to 14,60. The soil in the investigated layer is in the crowded condition, so when the pit excavation possible rise bottom that will require the development of measures to eliminate or strengthening of the Foundation.

For Vendian clays at the base of a tall building by increasing the depth from 47,0 to 100,30 m ratio overstocking varies from 1.04 to 1.12, the stress factor kσfrom 3,20 to 14.75. All the samples studied are overstocked condition. When the device deep excavation under high-rise building in the seizure of significant soil layer decreases the amount of domestic pressure, resulting in an increase in the coefficient of overstocking soil, what can aswat significant elevation of bottom of the pit and will require the development of measures to strengthen the Foundation.

The use of the invention reduces the cost, complexity and duration of the assessment of the degree of predoplatnoy clay soils, to expand the designated pressure range of predoplatnoy and to improve the accuracy due to the fact that the humidity at the boundary fluidity and equilibrium density estimate the degree of predoplatnoy clay soils, determining the equilibrium pressure for residential density and coefficient of overstocking and voltage.

Table 1
№ p/pDepth selection, mParticle size, mm
Granulometric composition of the soil, %
2-1,01-0,50,5-0,25of 0.25-0.10,1-0,050,05-0,01from 0.01 to 0.005Less than 0,005
1to 21.0 to 21.1-3,44,34,33,3of 21.9 19,143,7
221,7-of 21.9-1,00,82,310,015,715,954,3
374,9-75,15-0,10,30,26,530,312,849,8

The list of references

1. Priklonski VA the Soil. - M.: Gosgeolizdat, 1949, s-316.

2. Denisov NA ABOUT the nature of the deformation of clay rocks. - M.: Minisplit of the USSR, 1951, s-29.

3. Meschan S.R. Long resistance crowded clays shift. // Proceedings of the Academy of Sciences of the Armenian SSR. Mechanics, 1966, t, No. 5, p.48-52.

4. Methodological manual on engineering-geological study of rocks. - M.: 1968, t, s-240.

5. Leonhard D.A. and foundations. - M.: stroiizdat, 1968, pp.93-94.

6. Casagrande A. The Determination of the Preconsolidation Load and Its Practical Influence. Pro, Ist International Conf. on Soil Mech. and Found. Eng., Boston, Discussion D-34, Vol. 3, 1936, p.60.

7. Goldstein MN. The mechanical properties of the soil the century - M.: stroiizdat, 1979, s, 162, .IV.30.

8. Ermolaeva A.N. The construction of cut-off devices of clay soils taking into account technological characteristics. - SPb., News VNIIG, 1996, t, s-381.

9. Bortkevich S. C., Vocal VI, Cornilov A.G., royko NF quality Control compaction of soil materials in the construction of high dams.// Hydraulic engineering, 1981, No. 5, p.9-12.

10. Recommendations for laboratory determination of maximum density for cohesive soils in relation to compaction rollers: P 50-90/VNIIG them. Beaudreau. - L.

1. The method of assessing the degree of overstocking clay soils in the natural occurrence, including the selection of the sample of soil, determination of density and moisture in a natural state, the density of the soil particles, household pressure at the depth of selection of the sample, pressure predoplatnoy, characterized in that it further determine the humidity at the boundary point, granulometric composition, the content and the density of particles is small, smaller than 2 mm, and large, larger than 2 mm fractions, the equilibrium density of the sample and determine:
the equilibrium pressure for residential density of selected soil sample:

where- the equilibrium pressure, MPa;
ρdo- the density of the dry soil of the selected sample, g/cm3;
WLthe humidity at the boundary fluidity, cu, and determine the coefficient of overstocking on the ratio of densities of the selected sample and the equilibrium domestic pressure:

where ρdc- equilibrium density for domestic pressure, g/cm3and the stress ratio on the ratio of pressure equilibrium and household:

wheredomestic pressure, MPa, and then the obtained values of these coefficients determine the degree of overstocking sample.

2. The method according to claim 1, characterized in that during the development of pits in the determination of equilibrium density domestic pressure to reduce the pressure from the excavated soil layer, and the coefficients of overstocking and voltage is determined taking into account the obtained values of the equilibrium density and domestic pressure.

3. The method according to claim 1, characterized in that during the construction of constructions, such as buildings or embankments, in the determination of equilibrium density into account in addition to household passed on the basis of the pressure from the weight of the structure and determine the coefficients overstocking and stress.



 

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2 cl, 1 dwg, 2 tbl, 1 ex

FIELD: agriculture, agronomic chemistry, agronomic ecology, soil biology, and chemical analysis of soil.

SUBSTANCE: method involves determining content of mineral nitrogen and potentially mineralizable nitrogen provided by soil incubation at temperature of 34-36°C for 7-8 days; converting mineral and potentially mineralizable soil nitrogen to solution by boiling incubated soil suspension in water in the ratio of 1:5 during 20 min for sandy, sandy loam and medium loamy soil and during 30 min for heavily loamy soil; subjecting aqueous extraction of soil sample to analysis by means of Kieldal apparatus for determining nitrogen content actually available to plants under light alkaline hydrolysis conditions; determining nitrogen content potentially available to plants under drastic alkaline hydrolysis conditions; forecasting fertilizer nitrogen dose on the basis of nitrogen content actually available to plants for predetermined yield of specific crop with the use of coefficient of assimilation by plants of soil nitrogen and fertilizers, and amount of nitrogen needed for production of 1 centner/hectare of product from formula: ,

where D is forecast fertilizer nitrogen dose; N is kg/hectare; Yc is crop yield for which fertilizer nitrogen dose is calculated, centner/hectare; C is amount of nitrogen needed for production of 1 centner/hectare of product of designed crop, kg/hectare; Naa is amount of nitrogen in soil actually available to plants, kg/hectare; 0.4 is coefficient of usage by plants of available nitrogen from fertilizer, %. Method may be used for evaluation of humic podzol soil with regard to its nitrogenous state, forecasting of need for nitrogenous fertilizer by plants, determining stock of nitrogen available to plants and forecasting of crop yields. Method does not require prolonged observations and controlling of soil temperature during plant growing periods.

EFFECT: increased efficiency, elimination of employment of expensive bulky equipment for performing forecasting process.

5 dwg, 4 tbl

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