Учебное пособие 2210

Issue № 4 (36), 2017

ISSN 2542-0526

They are all commonly located in the central part of urban construction faced with daunting engineering and geological as well as hydrogeological conditions where pulverescent clayous soil is laid. After comparing existing engineering solutions [3, 4, 6, 7], the authors came up with a new way of laying a drilling injection pile with a controlled widening (Fig. 1) [5].

						1	–– well
						2	–– injection pipe
						3	–– mounting collar
						4	–– rubber membrane-glass
						5	–– rubber cuffs
		3				6 –– pipe supplying a solution
			area
						7	–– packer
						8 –– concrete plug
	2 area
						9	–– consolidated area
1 area

Fig. 1. Scheme of laying a drilling injection pile with a controlled widening:

I — drilling a well; II — assembly of an injection pipe, supply of a packer into the first area of injection holes; III — injection of a solution

The new way combines the advantages of pile and injection methods of strengthening foundations and artificial improvement of construction properties of a soil base by means of a controlled widening, predicted geometric parameters at the end of a pile as well as reinforcement of a soil massive adjacent to a pile using hydrodiscontinuity of a consolidated solution and its consolidation between this discontinuity in the process. A controlled widening was formed during injection of a solution into a membrane-glass insulated on the lower end of the injection pipe [8].

In order to investigate the stress-strain of a foundation massive of the consolidated area for forming a controlled widening series field of studies was carried out to do the following:

1.To determine changes in the initial stress-strain of a foundation massive when a controlled widening is formed with the volume of 30 and 40 liters as well as its partial retention as residual stresses following the injection of a solution;

2.To analyze the results of static tests of the drilling injection piles with a controlled widening andthose without whiledesigning the dependence graphs ofthe pile heaving caused by loading. The field studies were performed in a construction site in the city of Tyumen. The physical and mechanical characteristics of its soil are identified in Table.

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Russian Journal of Building Construction and Architecture

								Таble
			Physical and mechanical properties of a soil base
		Engineering and	Depth	Fluidity	Specific	Angle of inter-	Specific	Deformation
					weight	nal friction	cohesion с,	modulus Е,
	geological element		Н, m	index IL
					γ, kN/m3	φ, degrees	kPa	МPа
1		Semi-solid clay	0.5—1.4	0.15	17.9	18.1	26.0	18.7
2		Soft plastic loam	1.4—6.6	0.62	19.0	16.9	21.0	7.8

1. Determining stresses in the consolidated area at the end of the drill injection pile

The stress-strain of a soil massive of the consolidated area while a controlled widening was formed was read using angular depth stamps and membrane gauge dynamometers [6] (Fig. 2). According to the depth dynamometers, graphs of changes in normal stresses of a soil massive prior and following the injection of a solution into the membrane glass were shown on a computer screen (Fig. 3—4).

Prior to the injection of a solution
		Following the injection of a solution

Fig. 2. Scheme of positioning the depth stamps and dynamometers

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а)		b)
	Lateral normal stresses, kPa	Lateral normal stresses, kPa

	Distance from a widening, cm
							Distance from a widening, cm
			1 Stage
									1 Stage
Injection of a solution:
			2 Stage
						Injection of a solution:			2 Stage
			3 Stage						3 Stage

Fig. 3. Graphs of the distribution of stresses during the injection of a solution into the membrane-glass: а) formation of a controlled widening with the volume of 40 liters; b) 30 liters

All the three graphs almost synchronously show the dynamics of changes in the stresses while a controlled widening is formed in a soil massive. A solution was injected into the membraneglass in three stages with technical breaks of 1 min in order to:

––prevent defects (tear of the membrane wall) during injection of the entire solution volume into the membrane-glass;

––measure the relaxation of momentary stresses of the elastic-plastic state of a soil massive;

––measuretheresidual momentarystressofthe elastic-plasticstate of a soil massive.

Following the formation of a controlled widening at the end of the pile along with a consolidated area of a soil massive, there is a change in the original stress-strain (residual stresses) some of which (the average of up to 43 %) is retained within the consolidated area of a soil massive as residual stresses.

An almost linear character of the graphs of the distribution of stresses at the third stage of injection indicates that residual plastic deformations in the consolidated are selected. Relaxation of stresses in the water-saturated soil massive is due to dissipation of residual pore pressure during filtration consolidation of a pulverescent clayous soil.

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Russian Journal of Building Construction and Architecture

10 cm

20 cm

30 cm

Lateral normal stresses, kPa

Time, h

Controlled widening of 40 liters		Controlled widening of 30 liters

Fig. 4. Graphs of relaxation of stresses following the injection of a solution into the membrane-glass in the consolidated area of a controlled widening:

1 —at the distance of 10 cm from the predicted widening diameter; 2 — of 20 cm; 3 — of 30 сm

2. Results of static tests of the drilling injection pile with a controlled widening

In order to compare the operation of drilling injection piles with a controlled widening with the volume of 30—40 liters and those without, static tests were performed according to the GOST method [1]. As a result, the dependence graphs of the pile heaving on loading were designed with a comparative histogram along the specific bearing capacity (Fig. 5).

Fluent curved lines of the graphs «P3» and «PК4» indicate a slow growth of heaving with two characteristic areas: of the linear operation corresponding with the loading of up to 30—40 kN (VI—VIII) and of the elastic plastic operation corresponding with the loading of up to 50—70 kN (V—VII). For loading that is about half of the bearing capacity of the piles with controlled widenings Fd / 2 up to 30kN (VI), the total heaving was no more than 2 mm, which is particularly important for foundation strengthening through the course of reconstruction.

It should also be noted that curved unloadings of the piles “PK3” and “PK4” (bent lines) are different from the standard form of unloading of a pile [2] with no widening “P1” (a hollow

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line) and are characterized by a maximum bending angle at the initial moment of time, the elastic output is of up to 27 % of the total heaving.

It was also found that the bearing capacity of a pile considering the operation of the tube almost linearly depends on the volume of a widening that is up to two times as large as its value.

Hydro-discontinuity of repeated injection increases the bearing capacity of the pile with a widening by 35—40 %.

S, mm

S, mm

Failure criterion

= 15 mm

Failure criterion

= 15 mm

Specific bearing capacity, kN/m3

mmS,
		Failure criterion = 15 mm

Drilling injection pile with a controlled widening at the end V = 30 liters without the injection of a solution in the hydro-discontinuity mode

Drilling injection pile with a controlled widening at the end V = 40 liters without the injection of a solution in the hydro-discontinuity mode

Drilling injection pile with repeated injection of a solution in the hydro-discontinuity mode and controlled widening at the end V = 30 liters

Drilling injection pile with repeated injection of a solution in the hydro-discontinuity mode and controlled widening at the end V = 40 liters Drilling injection pile with repeated injection of a solution in the hydro-discontinuity mode with no widening at the end

Number of the pile

Fig. 5. Dependence graphs s = f(p)

with a comparative histogram along the specific bearing capacity

In order to determine the geometric parameters of widening, they were excavated (Fig. 6):

––a widening with the volume of 30 liters: d = 340—360 mm, h = 410—430 mm, d/h = 0.8;

––a widening with the volume of 40 liters: d = 370—390 mm, h = 510—530 mm, d/h = 0.7.

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Russian Journal of Building Construction and Architecture

b)

Fig. 6. Geometric parameters of widenings: а) with the volume of 30 liters; b) 40 liters

Conclusions

1.Following the formation of a controlled widening at the end of a pile (unlike other ways of obtaining a widening), there is a consolidated area of a soil massive with an average distribution radius of 0.4—0.6 m from the injection tube and a considerable change in the physical and mechanical characteristics: the density goes up by an average of 25 %; the humidity decreases by 37 %; the deformation modulus increases by 64 %; with the retaining changed initial stress-strain (residual stress) of up to 43 % and linear character of their distribution.

2.The graph of the operation of the piles with a widening under a static compressing load has an initial linear and non-linear (elastic plastic) deformation area. At initial stages of unloading there is an active growth of recurring deformations whose character is fundamentally different from the graph of unloading of regular piles and this is due to the influence of residual stresses in a soil massive while a controlled widening is formed.

3.According to the results of static tests, it was found that a controlled widening at the end of a pile increases its bearing capacity by an average of 2 times due to change in the initial stress-strain of a soil massive in the widening area.

Therefore during loading of a foundation deformation of a base will emerge in the elastic linear stage with a minimum heaving, which is crucial for strengthening foundations as part of reconstruction.

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References

1.GOST 5686-2012. Grunty. Metody polevykh ispytaniy svay [GOST 5686-2012. Soils. Methods of field testing of piles]. Moscow, Minstroy Publ., 1994. 48 p.

2.Konyushkov V. V., Ulitskiy V. M. Otsenka nesushchey sposobnosti buroin"ektsionnykh svay [Evaluation of the bearing capacity of CFA piles]. Vestnik grazhdanskikh inzhenerov, 2007, no. 7, pp. 52—57.

3.Ledenev V. V., Chukanov M. A. Raspredelenie gorizontal'nykh napryazheniy v grunte ot deystviya nagruzki na fundament [Distribution of horizontal stresses in the soil from the action of the load on the Foundation].

Nauchnyy vestnik Voronezhskogo GASU. Stroitel'stvo i arkhitektura, 2011, no. 3, pp. 9—17.

4.Mangushev R. A., Nguen K. Kh. Metodika sostavleniya geotekhnicheskikh kart s uchetom rekomendatsiy po vyboru optimal'nykh tipov fundamentov dlya zdaniy s podzemnym prostranstvom (na primere g. Khoshimina) [Methods of preparing geotechnical maps including recommendations on optimal types of foundations for buildings with underground space (on the example of Ho Chi Minh city)]. Nauchnyy vestnik Voronezhskogo GASU. Stroitel'stvo i arkhitektura, 2008, no. 3, pp. 29—35.

5.Pronozin Ya. A., Zazulya Yu. V., Samokhvalov M. A. Sposob izgotovleniya buroin"ektsionnoy svai s kontroliruemym ushireniem [A method of manufacturing a bored pile with controlled widening]. Patent RF.

6.Petrukhin V. P., Shulyat'ev O. A., Mozgacheva O. A. Novye sposoby geotekhnicheskogo proektirovaniya i stroitel'stva [New methods of geotechnical design and construction]. Moscow, ASV Publ., 2015. 224 p.

7.Pronozin Ya. A., Zazulya Yu. V., Mel'nikov R. V., Stepanov M. A. Opyt sovmestnogo primeneniya in"ektsionnykh svay i kessona pri ustroystve podzemnogo etazha zdaniya istoriko-kul'turnogo naslediya v g. Tobol'ske [Experience of joint use of injection piles and caisson in the device of the underground floor of the building historical-cultural-slide in Tobolsk]. Available at: www.science-education.ru/109-9206

8.Pronozin Ya. A., Samokhvalov M. A., Rachkov D. V. Rezul'taty laboratornykh i polevykh issledovaniy izgotovleniya buroin"ektsionnoy svai s kontroliruemym ushireniem [The results of laboratory and field studies of the manufacture of grout-injected piles controlled broadening]. Promyshlennoe i grazhdanskoe stroitel'stvo, 2014, no. 3, pp. 56—60.

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Russian Journal of Building Construction and Architecture

HEAT AND GAS SUPPLY,VENTILATION,

AIR CONDITIONING,GAS SUPPLY AND ILLUMINATION

UDC536.491

N. Yu. Saprykina1, P. V. Yakovlev2

INVESTIGATION OF THE FORMATION OF THE TEMPERATURE FIELD OF SOIL DURING THE OPERATION GEOTHERMAL HEAT PUMPS UNDER THE INFLUENCE OF GROUNDWATERS

Astraxan' Institute of Civil Engineering

Russia, Astraxan’, tel.: [phone], e-mail: [e-mail] 1PhD student of the Dept. of Heat and Gas Supply and Ventilation Astraxan' State Technical University

Russia, Astraxan', tel.: [phone], e-mail: [e-mail] 2D. Sc. in Engineering, Prof. of the Dept. of Safety and Hydromechanics

Statement of the problem. Developing long-term forecast of energy efficiency of the heat pump, the characteristics of which vary due to changes in the natural distribution of the temperature field of the Earth in the long life of the well is addressed. Given the fact in most cases there are groundwaters that have an impact on the formation temperature, there is an individual study of the influence of seepage flow in the emerging field of temperature.

Results. The description of the prediction of the thermal field soil mass in operation of geothermal heat pumps in the long-term work under the influence of groundwater is presented.

Conclusions. A temperature field regardless of external factors affecting the well operated — flow filtration of the earth has the properties of «compensation cushion». The temperature of the reservoir that is being stabilized does not allow further «displacement» of the field, which may have a positive effect on the overall operation of the system.

Keywords: heat pump, geothermal wells, temperature field, soil mass, filtration flow, groundwater, filtration rate.

Introduction

A soil body is a complex research object that influences the formation of a temperature field around a geothermal well and the parameters of the operation of pumping equipment. A combination of thermophysical and hydrological processes affect the formation of the temperature

© Saprykina N. Yu., Yakovlev P. V., 2017

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of a soil body [1, 5, 9, 13, 14]. Considering the fact that there is mostly groundwater and they affect the bedding temperature, it is necessary that the effect of filtration flows on a forming temperature field of a soil is evaluated for a heat (drain) source, which is a geothermal well. Design of a temperature field will not be complete [2, 3, 10, 15] unless groundwater, which are in motion, form a filtration flow that also transfers heat is taken into account. This effect can be a key factor in studying a temperature pattern of a soil when geothermal heat pumps are used long-term.

1. Моdeling a temperature field of a soil under the influence of a filtration flow

Based on the analysis of the influencing factors and existing research methods for addressing the issue, a mathematical modeling method using a numerical solution was chosen [4]. A motion model of a filtration flow of groundwater is illustrated in Fig. 1.

Fig. 1. Model of calculating a temperature field

H level, G.W. of a soil under the influence of a filtration flow of groundwater:

υ is a filtration rate;

Qbackground is a background flow of the ground; Hlevel. G. W. is a groundwater level;

1 is a geothermal well;

2 is an influence range of a heat flow

Q background

A filtration rate of groundwater near a well is determined with a natural (background) filtration flow that is not influenced by a geothermal well. For most soils Darcy’s law [6] holds true for calculating a filtration rate in a quite wide range of filtration rates:

kФ i ,

(1)

where υ is a filtration rate, m/seс; kф is a filtration coefficient; i is a hydraulic deviation.

A filtration coefficient for different soils varies in wide ranges [7]. For almost water permeable soils (clay, monolith rocky soils) kф <5·10–5 m/day, quite weakly water permeable (loams, heavy sandy loam, uncrumbling sand grains) kф is up to 5·10–3 m/day, for weakly water permeable (heavy sandy loam, weakly crumbling loamy shale, sandstone, limestone) it is up to

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0.5 m/day, for water permeable (thinand fine-grained sands, crumbling rock) –– up to 5 m/day, well water permeable (medium-grained sand, permeable (sand medium-grained, highly crumbling rock) — up to 50 m/day, highly water permeable (pebble, gravelly sand, highly crumbling rock) >50 m/day.

A hydraulic deviation depends on hydrogeological features of a region and is largely due to surface drainage. For each region deviations vary. In the Southern Federal District they are different, e.g., the average deviation of the Volga River is 0.00007, or 0.07 ‰; in the Kuban River below the city of Krasnodar it is 0.01 ‰. Precise coefficients of filtration and hydraulic deviation for a certain geothermal well require more in-depth studies.

Due to the complexity of the problem and influencing factors of groundwater, the solution takes two stages: the first one is obtaining the dependence for a complex heat exchange with no filtration influence; the second one is a modified equation with a correction for filtration. In a cylindrical system of coordinates typical of a vertical well, the equation of non-stationary thermal conductivity holds true [4]. Given a natural background flow of the Earth as a compensating correction as well as a convective component, the equation will take the following form:

	dt	(	dt	x	dt	y dt	z ) a 2t q ,	(2)
	d		dx		dy
						dz

where

dxdt x dydt y dzdt z

–– is a convective component of a change in the temperature; q are sources and drainages of heat that are affected by heat flows of the Earth and heat emission through a surface, Watt/m2; 2 is the Laplacian operator:

2 2t2 y2t2 z2t2 . x

What is particular about the mathematical study is that the initial condition for each new cycle is a temperature field that is retained following the previous cycle. The boundary conditions are divided into three stages. The first stage is when the initial condition is accepted at the moment of the original temperature distribution in the layer prior to the operation of a setup, i.e. this is an even distribution with a background temperature of a layer at all the points. The beginning of the coordinates is at the centre of the well r 0:

t r, t0 ,

(3)

where r0 is a coordinate ranging from r0 r rк , m.

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