Method to determine frost heave of soil during freezing of seasonally thawing layer

FIELD: construction.

SUBSTANCE: method to determine frost heave of soil during freezing of a seasonally thawing layer includes drilling of a well before start of its thawing, sampling of soil, measurement of depth of seasonal thawing ξ, definition of dry soil density in samples ρd,th. In addition wells are drilled after freezing of the seasonally thawing layer, on the samples they additionally define density of dry soil after freezing of the seasonally thawing layer ρd,f, and the heave value is determined in accordance with the given dependence.

EFFECT: reduced labour intensiveness of works, increased accuracy of determination of heaving value, provision of material intensity reduction.

 

The invention relates to the construction and production is intended for determining the frost heaving of the soil during freezing stenopodidea layer.

There is a method of determining the heaving of the soil, including the drilling of wells, installation of marker to a depth exceeding the depth of seasonal thawing of the soil, filling the sinus between the rapper and the borehole wall with a damp soil, the installation marks on the surface of the earth, monitoring vertical displacements of the brand relative to the frame during the entire period of freezing soil layer [1].

The disadvantages of this method is time consuming due to equipment frames, stamps and conducting long-term observations of swelling soil, as well as the significant cost of metal for the manufacture of frames.

The closest technical solution is the method of determining the frost heaving of the soil during freezing stenopodidea layer including drilling prior to freezing, soil sampling, measurement of the depth of seasonal thawing ξ, determination of the sample density of dry soil ρddensity of mineral particles ρs, soil moisture w, humidity unfrozen water ww(Tfh), humidity limits yield wLand rolling wp, minimum temperature zone pomerani the T fhestimated temperature at the ground surface, equal to the average temperature of the cooling medium during the freezing and calculate the magnitude of the rebound by the formula [2]

where ξ is the thickness of the soil layer before freezing; ρdthe density of the skeleton of the soil, g/cm3; ρwis water density, g/cm3; w - humidity thawed soil; ww(Tfh- the content (by mass) of unfrozen water in frozen soil at a temperature of 0.57 Tfh; Tfh- minimum temperature of the freezing zone, which stops the swelling; ζ=0 if w≤wu.fhand ζ=0,09 when w>wu.fh; wp- humidity limit rolling; T0f- the estimated temperature at the ground surface, equal to the average coolant temperature for the period of freezing.

The other parameters in the formula (1) are determined by the corresponding dependency graph.

The parameter Kbexpressing the vlagoprovodimosti thawed and frozen soils, in practical calculations can be accepted equal to

where wsat- full vaccum thawed soil.

The parameter ψ is determined from the graphs in figure 1 on the ratios of Tfh/T0ffor: (a) sandy loam, (b) loam, clay.

Correlative parameter ηwithexpressing the relationship between the temperature of the fittings and content of unfrozen water in the frozen zone (heave), and temperature Tfhare defined in table 1.

The first initial condition heave the humidity is determined by dependence

where 0,92 density of ice, g/cm3.

Table 1
Parameter values ηwith, kw(T) and temperature termination heave
Type of soilThe number of the plasticity of the soil, the proportion of edTemperature stop heaving, Tfh, °CThe value of the parameter ηwith
Sandy loam0,02<Ip≤0,07of-1.53,55
Sandy loam silt-2,05,00
Loam0,07<Ip≤0,13-2,04,25
Loam silta-2.55,00
Loam0,13<Ipwhat is 0,17 a-2.53,80
Loam silt-3,05,35
ClayIp>0,017-4,02,50

Critical humidity, which determines the second initial condition of rebound, found by the formula

or

where wL- the soil moisture content at the upper limit of plasticity (the border fluidity); Ip=wL-wp- the number of plasticity.

The value of wcrwhen ρs=2.7 g/cm3can be determined according to the schedule in figure 2 (dependence on humidity wcron the border of the fluidity of wLand plasticity Ip).

The disadvantage of this method is the high complexity of the work on the detection of a large number of characteristics of the physical properties and thermal state of the ground.

The purpose of the invention is to reduce the labor intensity, improve the accuracy of determining the amount of rebound, which can reduce the unnecessary expenses associated with the construction of buildings.

The objective is achieved by the fact that according to the method of determining the frost heaving of the soil has frozen the Institute stenopodidea layer, including the drilling of wells with samples before and after freezing Stonetalon layer, measure the depth of seasonal thawing ξ, the density of dry soil to the freezing Stonetalon layer ρd,thand after freezing ρd,fand I hope the swelling by the formula

The amount of rebound is the product of the thickness of the layer of soil to the freezing ξ on the ratio of the increment of the thickness of the layer of soil freezing hf-ξ and the thickness of the layer of thawed soil ξ

Express in the formula (7) hfand ξ through the respective volumes of the ground thawed in Vthand frozen VfStates and arbitrary cross-sectional area of the soil s

In the dependencies (8) the volume of thawed soil in Vthand frozen VfStates Express through the mass of dry soil mdand the density ρd,thand ρd,f

Substituting (8) and (9) in (7), we obtain a computational formula frost heaving frost susceptible soil (6):

An example of the method of determining the frost heaving of the soil during freezing stenopodidea layer

The method is tested on the patient "Tuymaada" Institute of the permafrost SB RAS.

Before the frost melted-through over the summer soil layer at the beginning of October, the special metal probe was determined by its thickness, formed ξ=1,65 m Then coring method was used to drill a well at the depth of the thawed-through layer. Every 30 cm of core cutting ring with a known volume (Vth) was selected samples of thawed soil was Packed them in accordance with the requirements of GOST 5180-2000, delivered in the soil laboratory, dried at 105°C in an oven, weighed the dried samples (md,th) and calculated the density of the skeleton thawed soil by the formula ρd,th=md,th/Vth.

The results of determination of the volume of the samples, the mass of dried soil and calculations of the density of the skeleton thawed soil are presented in the table below.

Table 2
The depth of sampling h, mThe mass of the dried soil sample md,thgThe volume of the cutting ring (wet soil) Vthcm3The density of the dry (skeletal) soil ρd,th, g/cm3
0,369,7350,241,388
0,671,6650,241,426
0,974,815,0,241,489
1,269,4250,241,382

After freezing of the melted-through over the summer soil layer in the month of April was again well was drilled in 1 m from the first well of the same depth. Also every 30 cm core samples were taken of frozen soil to determine the density and moisture of soil, Packed, and delivered to the laboratory with negative temperature.

Samples for determination of moisture content of soil was weighed (mf,1), was dried in a drying Cabinet, the dried samples were again weighed (md,f) and expected moisture content of frozen soil by the formula wf=(mf,1-md,f)/md,f.

The weighings of the samples and determining the moisture content of the soil below the table.

Table 3
Depth selection
samples h, m
The sample mass
mf,1g
The mass of dried
sample md,fg
Douglas wf=(mf,1-md,f)/md,f
0,371,649,140,457
0,663,246,610,356
0,984,762,790,349
1,275,656,840,33

Samples for the determination of density of soil in accordance with GOST 5184-2000 processed to obtain a round shape, weighed in air (mf,2), grabbing a thin thread, dipped in kerosene and weighed in kerosene (mf) and was calculated density of frozen soil by the formula ρfkmf,2/(mf,2-mf), then find the density of the skeleton of frozen soil by the formula ρd,ff/(1+wf).

The weighings of samples of frozen soil on the air and kerosene with a density of pto=0,86 g/cm3and calculations of the density of frozen soil and the density of the skeleton of frozen soil below the table.

Table 4
The depth of sampling h, mThe sample mass in air mf,2gThe result of the weighting of samples in kerosene mf,KgThe density of the frozen ground pf, g/cm3The density of the skeleton frozen ground pd,f, g/cm3
0,3br135.867,901,721,18
0,6120,458,831,761,30
0,9uniforms, 127.661,311,791,33
1,2129,161,681,81,35

For comparison of results of determination of frost heaving of the soil of the proposed method at depths 0,3; 0,6; 0,9 and 1,2 m were established brand, vertical movement was determined by leveling relative to the fixed frame - metal pipes laid in the thickness of frozen ground to a depth of 9.0 m

Calculation data and results of the s definition of rebound method proposed according to the formula h fh=ξ(ρd,thd,f-1)and leveling listed in the following table.

0,3
Table 5
The depth interval, mThe power of the i-th soil layer ξimDensity
skeleton thawed
soil Pd.th, g/cm3
Density
the frozen skeleton
soil pd,f, g/cm3
The magnitude of rebound, cm
the proposed methodon leveling
i-th layer oftotal
0,3-0,60,31,411,253,848,797,4
0,6-0,90,31,461,332,944,954,3
0,9-1,2the 1.441,352,012,013,2

The maximum error in determining the amount of rebound of the proposed method is 18.8%, which is acceptable in terms of density changes of the skeleton of the soil in the horizontal plane.

Industrial applicability. The invention can be applied with success to determine heaving soils on the slopes of linear structures when calculating the depth of the support in the frozen ground.

Sources of information

1. Eagles V.O., Elgin B.B., Zheleznyak I.I. soil Frost heave in foundations of structures. - Novosibirsk: Izd-vo Nauka, 1987. - 136 C.

2. Fundamentals of Geocryology. Part 5. Engineering Geocryology. // edited AT Ershov. - M.: Izd-vo MGU, 1999. - 526 S.

The method of determining the frost heaving of the soil during freezing stenopodidea layer including drilling prior to freezing, soil sampling, measurement of the depth of seasonal thawing ξ, determination of the sample density of dry soil ρd,th, characterized in that it further drilling is performed after freezing stenopodidea layer on the samples additionally determine the density of dry soil after freezing stenopodidea slo is ρ d,fand the amount of rebound is determined by the formula:



 

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