RU2317367C1 - Culvert for motor road built on heaving base - Google Patents

Abstract

FIELD: motor road constriction, water control structures of irrigation systems to be erected in heaving ground, particularly culverts.

SUBSTANCE: structure comprises water supply conduit composed of reinforced concrete links, heat-protective screen arranged at culvert base, embankment and race consolidation means. Heat-protective screen is made of artificial material having increased thermal resistance and load-bearing capacity, for instance of foamed polystyrene. The heat-protective screen is arranged directly under culvert of culvert foundation or under protective layer arranged over it. The screen has thickness of not less than that of ground freezing area about culvert at culvert location area. Heat-protective screen has thickness determined by equivalent layer method. Thickness of design ground freezing layer at culvert base is defined by preset mathematical condition.

EFFECT: reduced thickness of heat-protective screen in comparison with stricture created of peat-and-mineral mixture and other natural heat insulation materials or compositions thereof.

4 cl, 4 dwg, 1 ex

Description

The claimed technical solution relates to the field of construction of roads, namely, designs of culverts on roads with a seasonally frozen heaving base, and can be used in other similar cases, in particular in the design and construction of network tubular culverts and waterworks on reclamation systems in heaving soil.

A known method of erecting a network of hydraulic structures on heaving soils, including extracting a foundation pit, creating an artificial foundation from non-clay soils with a thickness of at least 2/3 of the estimated freezing depth, installing a water supply path, backfilling and material fastening of the input and output parts (Hydrotechnical structures / G. V.Zheleznyakov, Yu.A. Ibad-zade, P.L. Ivanov and others; Under the general editorship of V.P. Nedrigi. - M.: Stroyizdat, 1983.- 543 p. (P. 417-419 ), ill. - Designer Handbook).

The disadvantage of this method is that due to the lack of measures to prevent mudding of the artificial base soil by clay particles transported by the water stream, the structure is characterized by insufficient reliability and durability. In the short term of its operation (4-6 years), the flowing artificial base is intensively clogged and acquires the properties of medium and even heavily downy rocks, as close as possible to frosts to soils of a natural base. The effectiveness of the event is sharply reduced.

Also known is a culvert on a motorway with a heaving base, including a water path from prefabricated bell-reinforced concrete links, artificial gravel and sand cushions 1.5 m thick at the base of the inlet and outlet sections of the water supply path, a vertical screen from prefabricated reinforced concrete elements in the alignment of the pipe inlet , an embankment from local soil, a roadway and reinforcing the input and output parts of the stone outline structure (Typical project: Round culverts concrete prefabricated from long links Series 3.503.1-112.97. Issue O: Materials for designing. - M.: Transmost OJSC, 1997).

As for the above technical solution, the low efficiency of this design of the culvert is in the predisposition of artificial pillows to mudding and intense frost heaving, as well as in the annually accumulating residual bulging of the impervious screen with all the ensuing negative engineering (structural) and operational consequences.

In terms of technical nature and the achieved result, the closest to the claimed technical solution is a culvert pipe on a heaving base, including a water supply path made of prefabricated reinforced concrete links, a heat shield made of peat-mineral mixture in the pipe base, an embankment and reinforcing pools (Svyazhenin A.N. Network interaction of hydraulic structures of drainage and humidification systems with a heaving base: Abstract of dissertation for the degree of candidate of technical sciences / VNIIGiM named after ANKostyakov. - M., 1989 - 20 p.).

The disadvantages of this technical solution are significant labor costs for the device in difficult geothermal conditions, for example, the Khabarovsk Territory heat-insulating screen with relatively low heat-insulating properties of the peat-mineral mixture with a thickness of 1.4-1.8 m, the complexity of the preparation of the mixture, reducing the bearing capacity formed thus artificial base compared to a base of natural mineral soil, as well as the predisposition of artificial base to moro Nome heave, causing a reduction of operational reliability and durability of the structure.

The objective of the invention is to increase the stability of the culvert on the road with a heaving base by protecting it from freezing and heaving with the use of advanced technologies and materials that increase the effectiveness of anti-infestation measures and reduce labor costs by 4 ... 5 and more times during its practical implementation in construction .

The problem is solved due to the fact that according to the claimed technical solution, at the base of the culvert there is a heat shield, which is made of a high-temperature resistance and bearing capacity artificial material, for example polystyrene foam (λ = 0.028 ... 0.030 W / (m · ° C) , R = 0.25 ... 0.50 MPa, with low water absorption in 30 days, not more than 0.4% by volume);

the screen is located directly below the pipe or the pipe foundation, or under the protective layer arranged between it and the pipe (foundation) and has a width not less than the width of the halo of freezing of soil around the pipe at the screen laying level;

the thickness of the heat shield is determined by the equivalent layer method, while the thickness of the calculated layer of freezing soil of the natural base of the pipe is determined by the condition:

d _foi ≥d _fi -d _ufi ,

where d _foi is the thickness of the calculated layer of freezing of the soil of the base of the pipe in the i-th section along its length, subject to equivalent replacement (compensation) with a heat shield, m;

d _fi is the estimated depth of seasonal freezing of the soil of the pipe base in the i-th section along its length in the absence of a heat shield, m;

d _ufi - the maximum freezing depth of the foundation soil under the condition of pipe stability under the heat shield in the i-th section along the pipe length (m), which is determined by the dependence:

here q _ri is the calculated force of the vertical pressure of the soil of the embankment above the pipe, acting for 1 linear meter. m pipe length (determined taking into account the reliability coefficient for the load γ _f = 0.9), KN / m;

q _Ti - the estimated weight of 1 linear. m of pipe (taking into account the weight of the foundation, KN / m), determined with a load factor of reliability γ _f = 0.9;

σ _fi is the calculated value of the specific normal to the sole of the pipe (foundation) force of frost heaving of the soil of the pipe base, kPa / m (kN / m ³ );

b _Ti is the calculated width (outer diameter) of the pipe or the sole of its foundation, m;

γ _c is the coefficient of working conditions (0.9);

γ _n is the reliability coefficient (1,1).

The culvert may also differ in that in the case of calculation according to the maximum permissible deformations (for example, for pipes on ameliorative systems in heaving soils, for which the stability requirements are somewhat reduced), the maximum freezing depth of the base soil under the heat shield d ' _ufi (m) may be defined by the condition:

where d _ufi is the maximum freezing depth of the soil under the pipe stability condition (corresponds to the beginning of the construction upward movement) under the heat shield in the i-th section along the pipe length, m;

h _usi is the maximum permissible value of the joint deformation (elevation) of the base and the most pliable pipe element (link) under the influence of frost heaving forces, m;

m _oi is the weighted average heaving modulus (fractions of units) in the zone of formation of the maximum allowable deformation h _usi , which is determined by the dependence:

here m _i , h _i are, respectively, the heaving modulus (fractions of units) and the thickness (m) of the i-th soil layer in the freezing zone of the pipe base, which causes the maximum permissible deformation (elevation) h _{usi of the} most pliable element (link) of the structure.

The culvert may also differ in that, depending on the position of the calculated freezing front along its length, the heat shield can be made continuous along the length of the pipe or consisting of two parts with their placement on the inlet and outlet sections of the water supply path of the structure.

In addition, in all cases, the device heat shield of a permeable (hydrophilic) material, it can be coated with a hydrophobic composition, such as epoxy resin, or enclosed in a shell of a waterproofing material, such as a plastic film.

The technical result provided by the above set of essential features of the claimed invention consists in a 5 ... 7-fold decrease in the thickness of the proposed heat shield compared to its design from peat-mineral mixture and other natural heat-insulating materials or their compositions, reducing labor costs for the construction of the screen, improving the quality (culture) of construction and installation works, operational reliability and durability of the structure as a whole.

In addition to the heat-shielding function, the claimed screen introduces at least two more important properties into the pipe construction, which beneficially affect the reliable and durable operation of the structure:

- prevents (screens) the migration of water from the underlying soil layers of the natural base into the embankment, protecting it from frost heaving;

- increases the bearing capacity of soft soils of a natural base: water-saturated sandy loam, loam, sand, etc.

The dependencies given in the application materials are obtained mainly from the condition of limiting equilibrium of the acting forces, i.e. based on the impossibility under normal conditions of moving the pipe (link, element) upward under the influence of the forces of frost heaving of the base soil. The exception is culverts on reclamation systems in heaving soils that allow known deformations (linear, angular) in the absence of significant violations of operational properties. These pipes represent a special class of structures, the technical requirements for them are slightly reduced and therefore are not considered here intently (Svyazhenin A.N. Interaction of network hydraulic structures of drainage and humidification systems with a heaving base: Abstract of dissertation for an academic degree. Candidate of Technical Sciences / VNIIGiM named after A.N. Kostikov. - M., 1989 - 20 s .; Gavrilenko VI. Improving the reliability of tubular culverts in heaving soils (on the example of land reclamation systems of the Khabarovsk Territory). - Manuscript, Dep. NI ITEgroprom Ministry of Agriculture of the Russian Federation, 1995. - No. 107 BC-95. - 147 p. And others).

From a practical point of view, the proposed technical solution is applicable not only to the culverts indicated here from round long prefabricated bell-shaped reinforced concrete pipes, but also to other culverts constructed on roads and railways: rectangular reinforced concrete, steel, corrugated metal, and other solutions thereof.

Figure 1 shows a plan (top view) of the inventive culvert (W) with the outline of the location of expanded polystyrene in plan, for example, from PENOPLEX plates;

figure 2 is given a longitudinal profile (section) of VT with a possible laying of expanded polystyrene into profiles along the length of the structure;

figure 3 shows a cross section of the VT in the area of the axis of the roadway;

figure 4 presents graphs of the maximum, under the condition of stability of the pipe, the depth of freezing of the soil of the base under the screen d _uf depending on the height of the embankment above the pipe h _n for the middle part of VT from reinforced concrete pipes with a diameter of 1.5 m for natural soils of heavily-grained (1) and medium-grained (2).

The construction includes: a water supply path from bell-shaped reinforced concrete long pipe links 1; input (output) head links 2; precast reinforced concrete mold blocks 3 at the base of the links of the water supply path; a protective layer 4 above the heat shield; heat shield 5 from extruded expanded polystyrene, for example, PENOPLEX boards; waterproofing 6 polystyrene foam (screen 5), for example, from a plastic film, epoxy resin, etc .; the leveling layer 7 under the screen of expanded polystyrene, for example from cement sand (a dry mix is possible), etc .; embankment 8; strengthening of the ups 9; a halo of frozen soil in the zone of the pipe 10; the lower boundary of frozen soil in its natural state (without heat shield) 11; the lower limit of the maximum freezing under the heat shield of the middle part of the pipe 12.

The construction works as follows. At the beginning of the winter period, the soil freezes primarily in the zone of open elements: on top of the embankment 8, at the base of the reinforcements of the pools 9 and in the area of the input and output head-ends of the pipe 2. Moreover, if the reinforcements of 9 inlet and outlet channel channels are already in the initial stage of freezing under the influence of forces of frost heaving of the soil, they undergo displacements upward, then directly at the structure such deformations of the reinforcements 9 and head units 2 are uncharacteristic. Firstly, this is due to the presence of a powerful strengthening of the bed bottom, for example, a stone sketch under which there is a pillow made of gravel or sand gravel, and secondly, by preventing the migration of moisture (water) from the base of the structure to the freezing front due to the screening function developed in plan heat shield 5 having a waterproofing 6, for example, from a plastic film. Having a calculated thermal resistance, the heat shield 5 does not allow freezing of the base soil under the head links 2, providing them with sufficient stability.

In the future, as the winter period develops, a halo of frozen soil 10 is actively formed from the links 1 in the zone of the reinforced concrete pipe. During the calculated freezing, the block 3, the protective layer fall into the cooling zone at the inlet and outlet sections of the water supply path of the structure 4 above the heat shield 5 (under the swab block 3) and the heat shield itself 5. In the middle part of the water supply path with calculated freezing (maximum by the condition of stability of the pipe link 1) in the cooling and freezing zone, besides the above elements, there is a leveling layer 7 under the heat shield 5 and partially the soil of the natural base. At the same time, the forces of frost heaving formed in the latter are insufficient to violate the stability of the system of elements of the structure located above it.

Under all conditions of freezing, the lower boundary 11 of the halo of frozen soil 10 does not extend beyond the lateral boundaries of the heat shield at the level of its location along the entire length of the culvert. As a result of this, its heat engineering effect is optimized as much as possible and the stability of the structure is reliably ensured.

With the onset of stable positive air temperatures and thawing of the soil, the strengthening of the headwater 9 gradually returns to its original (winter) position. Soil of the base of the middle part after complete thawing is consolidated up to its natural state. Links 1 and 2 of the pipe remain motionless both during freezing and thawing of soils.

An example of calculating a heat shield in relation to the conditions of freezing and heaving of soils in the zone of Khabarovsk.

The calculation is performed in three stages:

1. Calculate the standard and estimated depth of seasonal freezing of soil at the base of the pipe according to SNIP II-18-76: Foundations and foundations on permafrost soils / NIIOSP im. N.M. Gersevanova. - M.: Stroyizdat, 1977 .-- 45 p. (p.37) and Recommendations on improving the designs and design standards of artificial structures built on heaving soils, taking into account the natural conditions of the BAM zone. - M.: VNIIT, 1981. - 55 p. (KhabIIZhT).

2. At the second stage, we set the width of the heat shield according to the method of B.A. Elizarov: Calculation of the parameters of the heat shield // Reclamation construction in the winter. - L .: SevNIIIGiM, 1980 - p. 38-47.

3. At the third stage, we determine the thickness of the heat insulator at the input (output) section of the structure and in its middle part.

1. When solving the first stage of the problem for the city of Khabarovsk, we proceed from the general formula:

Where

where t ₂ is the average air temperature for the period of negative temperatures, ° C (the value of t ₂ in the calculations is taken with a plus sign);

τ ₂ - the duration of the period with negative air temperatures, h;

W _n - weight content of unfrozen moisture in the soil in fractions of a unit, determined according to A.2.12 for a temperature equal to 0.5 · (t ₂ + t _nz );

ρ is the specific heat of melting of the ice, assuming equal to 80,000 kcal / tf;

W _c - total humidity in fractions of a unit;

γ _sc.m — volumetric weight of the skeleton of frozen soil, tf / m ³ ;

C _m - volumetric heat capacity of frozen soil, kcal / m ³ deg;

The missing data are taken from the USSR Climate Guide, issue 25: Air and soil temperature. - L .: Gidrometizdat, 1966 .-- 312 p. The remaining information is shown in example 3 (step 3):

W _c = 0.30; λ _m = 1.55 W / m · ° C; With _m = 590 kcal / m ³

t ₂ = -14.9 ° C; t _ns = -1.1 ° C; W _n = 0.126; τ ₂ = 24 · 30 · 5 = 3600 h

k _ω = 0.46 (Table 1 SNiP)

(концентрация порового раствора, табл.3 СниП при t_нз=-1,1°C); k_p=0,135.

(the concentration of the pore solution, table 3 SNiP at t _NC = -1.1 ° C); k _p = 0.135.

Then we have:

q ₂ = 80,000 (0,300-0,126) · 1.6-0.5 · 590 · (14.9-1.1) = 18201 kcal / m ³ .

As a result, the standard depth of seasonal freezing of soil is:

The estimated depth of soil freezing at the input (output) section of the structure is determined by the condition:

where m _m is the coefficient of thermal influence of the foundation (for a foundationless pipe m _m = 1,1);

m _x - coefficient taking into account the effect of the embankment (1.0 - for heads and end sections; 0.3 - for the middle part of the pipe 28.0 m long, 1.5 m in diameter, the length of the middle part is 28.0-12.0 = 16 m).

For the middle part of the pipe we get:

2. At the second stage of the calculation, we set the screen width according to the pipe zones according to the formulas:

where a - lateral freezing, m;

l = b _t - the width of the pipe at the bottom of the mold block (foundation), m

Then for the input (output) section we have:

and for the middle part we get:

3. And finally, at the third stage of the calculation, we determine the thickness of the screen at the end sections of the pipe and on its middle part.

The calculation of these parameters of the heat shield made of extruded foam polystyrene, for example, from PENOPLEX boards, is carried out according to the method of N. Tsukanov. and Granovsky M.Yu. (Tsukanov N.A., Granovsky M.Yu. Calculation of thermal insulation to limit the depth of soil freezing // Thermophysical studies in transport construction. -M.: Transport, 1985. - p. 67-73).

Initial data: thermal conductivity coefficient of the screen material λ _e = 0.03 W (m · ° С); the length of the culvert (water path) l _T = 28.0 m; pipe diameter d = 1.5 m; pipe wall thickness h _article = 0.16 m; the thermal conductivity of the concrete λ _δ = 1.8 W / (m · ° C), the thickness of the mold block down h _bl = 0.16 m (λ _δ = 1.8 W / (m · ° C)). Strong-loamy loams γ _oδ = 18 kN / m ³ , W = 30% with a coefficient of thermal conductivity in the frozen state λ _m = 1.55 W / (m · ° С) lie at the base. It is known that the area of the plot of negative temperatures during the winter is Ω _t = 74.6 ° С · month. The average temperature of the base soil at the beginning of the winter period at the end sections of the pipe is T _ok = 4.0 ° C, the heat transfer coefficient from the surface is α = 0.10.

3.1. We carry out the calculation for the end sections of the pipe.

3.1.1. We find the stock of latent heat:

Ω = 34.2 · γ _ck · W · i, kJ / m ³ with relative ice content of loam i = 0.6

According to the precondition of the problem for the input and output sections of the structure d _fo = 0 (there is no freezing).

3.1.2. We find δ _R , and in:

δ _R = 0.086-0.430 · d _fo = 0.086-0.430 · 0 = 0.086 (m ² ° C) / W

a = (0.350 · 10 ^-4 · Ω-0.06) · (d _fo +0.161) + 1.51 = (0.350 · 10 ^-4 · 8.50 · 10 ⁴ -0.06) · (0 + 0.161 ) + 1.51 = 1.979 W month / (m ² ° C)

c = (3.99 · 10 ^-4 · Ω + 3.72) · (d _fo +0.035) + 3.14 = (3.99 · 10 ^-4 · 850 · 10 ⁴ +3.72) · (0 +0.035) + 3.14 = 4.457 W · month / m ² .

3.1.3. Define the coefficient K:

3.1.4. We calculate the necessary (calculated) thermal resistance R:

correction ΔR - taken equal to zero.

So, the calculated thermal resistance is R = 8.963 (m ² ° C) / W.

Then the thickness of the heat shield at the inlet and outlet sections of the structure will be equal to:

So, to prevent freezing at the inlet and outlet sections of the pipe, polystyrene foam with a thickness of at least 0.26 m from PENOPLEX boards of grade 45 is required. This is without the influence of a possible external load: the weight of the pipe (inlet link), the embankment above it, etc.

3.2. We perform the calculation for the middle section of the pipe (using the previous data, except T _OS = 4.2 ° C and the thermal effect of the embankment due to its height equal to h _n = 8.0 m).

The presence of a significant embankment makes it possible to admit the maximum freezing depth of the foundation soil under the condition of pipe stability under the heat shield equal to d _ufi = 0.15 m.

Having retained the previous initial data (except for d _fic = 0.96 m), we perform similar calculations, assuming Ω = 8.50 · 10 ⁴ kJ / m ³ .

According to the precondition of the problem, for the middle part of the pipe, d _ufc = 0.15 m is permissible, see Fig. 4 - for strongly-soiled soils of the natural base of the pipe in the middle part along the length of the screen, freezing of the soil under the screen by 15 cm is possible with an embankment height above the pipe h _n = 8.0 m without loss of stability of the structure.

3.2.1. We find the corresponding δ _R , and in

δ _R = 0.086-0.430 · d _ufc = 0.086-0.430 · 0.15 = 0.0215 (m ² · ° C) / W;

a = (0.045 · 10 ^-4 · 8.5 · 10 ⁴ +0.52) · (0.15 + 1.933) + 0.44 = 2.370 W · month / (m ² · ° C)

c = (4.02 · 10 ^-4 · 8.5 · 10 ⁴ +0.95) · (0.15 + 0.035) + 3.49 = 9.987 W · month / m ² .

3.2.2. Define the coefficient K:

3.2.3. We find the necessary (calculated) thermal resistance R:

Then the thickness of the heat shield on the middle part of the pipe will be:

Thus, in the circumstances, in the presence of an embankment above the pipe h _n = 8 m, it is enough to lay a heat-protective layer of expanded polystyrene with a thickness of not more than 35 mm under the central (middle) part of the pipe

Summarizing the above, it can be argued that there are real opportunities for the successful design and construction of culverts on heaving grounds using the recipe described here. This will significantly reduce labor costs for pipe construction, improve the culture and quality of construction and installation works and, most importantly, increase the reliability and durability of structures in general.

Claims (4)

1. A culvert on a motorway with a heaving base, including a water supply path made of prefabricated reinforced concrete units, a heat shield at the base of the pipe, an embankment and reinforcement for downholes, characterized in that the heat shield is made of a high thermal resistance and load-bearing capacity of artificial material, for example, polystyrene foam, located directly below the pipe or pipe foundation or under a protective layer arranged above it and has a width of not less than the width of the halo freezing the soil around the pipe at the level of its location, and the thickness of the heat shield is set equivalent method layer, the layer thickness calculation freezing pipe foundation soil condition determined d _foi ≥d _fi -d _ufi , where d _foi is the thickness of the calculated layer of freezing of the soil of the base of the pipe in the i-th section along its length, subject to equivalent replacement (compensation) with a heat shield, m; d _fi is the estimated depth of seasonal freezing of the soil of the pipe base in the i-th section in the absence of a heat shield, m; d _ufi - the maximum freezing depth of the foundation soil under the condition of pipe stability under the heat shield in the i-th section along the length of the pipe (m), which is determined by the dependence

, where q _ri is the design force of the vertical pressure of the soil of the embankment, acting on 1 linear m pipe length (determined taking into account the coefficient of reliability of the load γ _f = 0.9), kN / m; q _Ti - the estimated weight of 1 linear. m of pipe (taking into account the weight of the foundation, kN / m), determined with a load safety factor γ _f = 0.9; σ _fi is the calculated value of the specific normal force of frost heaving of the soil of the base of the pipe, kPa / m (kN / m ³ ); b _Ti is the calculated width (outer diameter) of the pipe or the sole of its foundation, m; γ _s - coefficient of working conditions (0.9); γ _n is the reliability coefficient (1,1). 2. The culvert according to claim 1, characterized in that in the case of calculating the maximum permissible deformations, the maximum depth of freezing of the base soil under the heat shield d ′ _ufi (m) is determined by the condition

, where d _ufi is the maximum freezing depth of the foundation soil under the pipe stability condition (corresponds to the beginning of the construction upward movement) under the heat shield in the i-th section along the pipe length, m; h _usi is the maximum permissible value of the joint deformation (elevation) of the base and the most pliable pipe element (link) under the influence of frost heaving forces, m; m _oi is the weighted average heaving modulus (fractions of units) in the zone of formation of the maximum allowable deformation h _usi , which is determined by the dependence

, here m _i , h _i are, respectively, the heaving modulus (fractions of units) and the thickness (m) of the i-th soil layer in the freezing zone of the pipe base, which causes the maximum permissible deformation (elevation) h _{usi of the} most pliable element (link) of the structure. 3. The culvert according to claim 1, characterized in that in the case of a heat shield made of a permeable (hydrophilic) material, it is coated with a hydrophobic composition, for example, epoxy resin, or enclosed in a sheath of a waterproofing material, for example, of a plastic film. 4. A culvert according to any one of claims 1 and 2, characterized in that, depending on the position of the calculated freezing front, the heat shield can be made continuous along the length of the pipe or consisting of two parts with their placement on the inlet and outlet sections of the water supply path of the structure .

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