RU2256030C2 - Earth structure built on permafrost ground - Google Patents

Abstract

FIELD: building, particularly for erecting road embankments in areas with high-temperature permafrost ground.

SUBSTANCE: earth structure comprises road bed body and rock layer exposed to air in peripheral zones. Lateral parts of peripheral zones in are water-impermeable from below. Rock layers are connected one to another by underlying rock layer.

EFFECT: increased resistance and operational reliability of earth structure, particularly erected on permafrost ground in summer period.

3 cl, 1 dwg, 1 tbl

Description

The present invention relates to construction and can be mainly used in the construction of road embankments in areas of high-temperature permafrost.

The essence of the problem: Accumulated significant negative experience in the exploitation of road embankments in permafrost (GNPP Tyndinskaya permafrost station, FSUE Omsk Soyuzdorznii, OAO Irkutskgiprodornii, Khabarovsk Institute of Railway Engineers, Central Scientific and Research Institute of Information and Technical and Economic Research of Railway transport / TsNIITEI / et al.) shows that the construction of embankments from thawed soils, especially in the warm period, leads to the formation of a thawed core above the base, inside the embankment, which does not freeze even in winter od. As a result of the unstable, high frost in the ground does not get much-needed her annual "recharging" the cold and is gradually degraded with all its attendant problems.

A known design of the embankment [1], comprising a body made up of a lower part containing waterlogged clay soil, and the upper part of the drainage soil, in which to accelerate consolidation, the peripheral sections of the lower part of the embankment are made in the form of triangular (thrust) prisms from the drainage soil, waterlogged clay soil of this part of the embankment is placed between triangular prisms.

The disadvantages of this embankment design for permafrost distribution areas is that it does not provide “recharging” of the base frozen ground in the central part, especially in high embankments. The latter in the areas of distribution of high-temperature (unstable) permafrost leads to its gradual degradation at the base of the structure. The peripheral parts of the embankment under consideration, made from drainage soils, are also vulnerable to exposure to warm surface water. All this, especially in areas with high-temperature (unstable) permafrost, leads to its general degradation at the base of the embankment, accompanied by long-term settlement and loss of stability.

Closest to the proposed technical solution is an earthen building on thawing permafrost soils [2], containing the body of the subgrade and thrust prisms in peripheral zones, the inner part of which is adjacent to the soils of the supporting part of the body of the subgrade and base, made in the form of a continuous layer of sorted rocky soil in contact with the upper and lower parts of the prisms with air.

However, this technical solution has a number of significant drawbacks. So a layer of sorted rock soil adjacent to the base soil and in contact with the air at the base of the structure during the warm period easily passes warm surface water into the base of the slope parts of the embankment. The latter is capable of starting dangerous thermokarst processes. In addition, the very soaking of the base soil dramatically reduces their strength characteristics. All this together, as a rule, leads to settlement and loss of stability of the structure. Moreover, the sediment of the structure on thawing permafrost soils is able to significantly or completely block contact with the air of the rocky layer in the base. It should be noted that in the winter, significant snow deposits quickly form in the embankment in its lower part. The latter will also hinder the contact of the rock layer at the base of the structure with air during this main period of “recharging” with cold. As a result of additional (increased) convective heat transfer will no longer occur, and the proposed mechanism for the effective freezing of soils of the central part of the body of the subgrade and the base will not be able to work, with all the ensuing consequences.

The aim of the invention is to increase the stability and operational reliability of an earthen structure on permafrost, including being erected in the warm season.

The specified technical result is achieved by the fact that in an earthen structure on permafrost soils containing the body of the subgrade (or layers of pavement) and interlayers of rocky soil in contact with air in the peripheral zones, according to the invention, the peripheral zones in the sloping parts from the bottom are made waterproof and the interlayers from rocky soil are interconnected by the underlying layer of rocky soil. At the same time, the height of the bottom slopes of the peripheral zones waterproof from below is within the limits of:

Sc + Нсв≤Нr≤Нc-No-Nef

where Hr is the waterproofing height from the bottom of the sloping parts of the peripheral zones, m;

Sc and Нсв - precipitation and thickness of snow or surface water at the structure, m;

NEF is the effective thickness of the contact with the air of the layers of rocky soil in the peripheral zones (for example, at least 1.0 m, as in AS No. 1656078), m;

Нc and Нo - the height of the structure and the thickness of the curbs (or pavement) in the peripheral zones, m

The water-proof (waterproofing) bottom slopes of the peripheral zones themselves can be made of non-draining soil or of drainage soil waterproofed with loose side prisms from non-draining soil, and / or anchored with a slope to the slopes of waterproof or draining layers (for example, foam, fiberglass, polyester geomats, etc.), and are closed on top with a layer of heat-permeable materials (for example, from peat, mossy cover, ultraviolet-resistant geotextiles, ysokoporistyh foams, etc.).

The claimed technical solution meets the criterion of "novelty" due to the presence of a combination of new features. Water resistance from the bottom of the sloping parts of the peripheral zones in the summer prevents the filtration of warm surface water (top water) into the base of the structure, which is especially dangerous in high-temperature (unstable) permafrost. Additionally, the proposed interval of changes in their height ensures that cold air flows inside the structure in winter through overlying layers of rocky soil into the underlying rocky layer, despite, as a rule, significant settlement of the bulk structure erected on thawing soils (especially in summer), as well subsequent formation of thick snow deposits (more than 0.5-1 m) at the base of the structure. Thus, conditions are created for reliable winter "recharging" of the base inside the structure.

The claimed technical solution meets the criterion of "inventive step" because the proposed new set of features creates a non-obvious beneficial effect different from the known technical solutions. This effect consists in the temperature shift of the heat balance of the base of the structure under the connecting, underlying layer of rocky soil towards negative temperatures. The latter is ensured both by creating the necessary conditions for the penetration of heavier cold air into the base of the structure in the winter period, and by subsequent retention (stagnation) of it in the lower windproof (watertight) along the edges of the rocky layer inside the structure. As a result, lighter warm air in the summer will not be able to go there. This sharply reduces the annual heat circulation of the base of the structure and lowers its temperature.

Moreover, the air in the upper peripheral rock layers "in contact" with the air, connected by the underlying rock layer, in the summer period provides a preliminary average annual temperature shift of 2.5-4 ° C to the downward direction and thermal insulation (as in "coat") of the underlying cooled rocky layer with heavier cold air in intercomplex voids. As a result, the stability and operational reliability of the structure increases, especially in the conditions of high-temperature (unstable) permafrost. The proposed modifications of the earth structure under consideration also provide it with the necessary seismic stability (see, for example, BCH 61-89, p. 182-183 Mandatory Appendix 10 p.1.2., 1.4z.).

In General, the compliance of the proposed technical solution to the criterion of "inventive step" shows a comparative analysis in the table below.

Table 1.
Comparative analysis of the construction of road bulk structures for the regions of the North. Type of constructive solution of the embankment on permafrost soils Protection of the frozen base of the embankment from the ingress of warm surface water Providing annual “recharge” with cold of the base of the peripheral parts of the embankment Providing annual “recharge” with cold of the base of the central part of the high embankment Suitability of high embankment design for stability in high temperature permafrost 1. Mound (analogue) - + - - 2. Earthworks on thawing permafrost soils (prototype) - + - - 3. The claimed technical solution + + + +

The drawing shows an earthen structure located on permafrost soils 1, containing the body of the subgrade or layers of pavement 2 in contact with the air interlayers of rocky soil, “vents” 3, above the water-tight bottom slope parts of the peripheral zones of the structure 4. Interlayers of rocky soil 3 are connected between themselves the underlying layer of rocky soil 5. In this case, the slope parts of the peripheral zones 4, which are waterproof from below, have the necessary height (in terms of the thermotechnical stability of the structure) and can be waterproof are arranged by arranging powder prisms 6 from non-draining soil and / or anchored with slope to the slopes of waterproof or draining layers 7 made, for example, of foam plastic, carbofol, fiberglass, polyester geomats, etc. The watertight lower sloping parts of the peripheral zones are additionally covered on top with a layer of 8 made of heat-permeable evaporative materials (for example, peat, mossy cover, ultraviolet-resistant geotextiles, highly porous foams, etc.). To increase seismic stability of the structure of the layer of rock 3 can be placed in the gabions of McCaffery.

Earthwork works as follows. In winter, with the onset of negative temperatures, heavy cold air enters the rocky layers of "air" (for the device of which it is desirable to provide for the use of strong, waterproof, frost-resistant rocks 0.2-0.4 m in size) and lowers down to the underlying structure (lower) rocky soil layer (preferably with a fine earth content of not more than 5-6%) in contact with the foundation of the structure in need of an annual “recharge” of cold. The warmer air in this layer, on the contrary, tends to rise upward and is squeezed out through the opposite soil rocky interlayer (on the leeward side), as well as through the upper parts of the rocky interlayers themselves. As a result, the temperature inside the connective underlying rocky soil layer decreases. This contributes to the cooling and “recharging” of cold bearing frozen soils of the base of the central and peripheral parts of the structure on unstable permafrost.

With the onset of positive average daily air temperatures, warm air will also partially (blow out) into the "air". However, as it is lighter than the underlying cold air in the intercomplex voids of the connecting underlying layer of rocky soil, it cannot go down to the frozen base of the structure. In low-wind weather, this air stagnates in the intercomplex voids of the “vents” from the rocky soil and acts as a good heat insulator (since the thermal conductivity of air is lower than that of the foam), which explains the known decrease in temperature in rocky sketches. It is known (see, for example, V. Kudryavtsev, “The effect of summer precipitation infiltration on temperature conditions, seasonal freezing and thawing, and annual soil heat cycles.” In Sat Freezing Studies, Issue VII, Moscow State University Publishing House, 1967), it is observed in summer condensation of water vapor in the air on the stones of rock scree and a sketch, water from which often flows down slopes in nature, with the latter being waterproof. In the proposed technical solution, water vapor in the summer period will mainly condense, as in the rocky draft in the rocky soil of “vents”. At the same time, condensed water flows to non-draining soil or to water-tight or draining layers that are anchored with a slope to the slopes; it enters the layer of heat-permeable evaporation materials (in the form of peat or shaggy cover, etc.) laid on the surface of the lower waterproof parts of the slopes of the embankment. These layers, saturated with drained condensate moisture, will work not only as heat insulators, but also additionally ensure the outflow of solar radiation coming to the slopes due to the active evaporation of the incoming condensate moisture with their developed surface. This ensures that condensate moisture does not get into the frozen base of rock embankments, and its simultaneous use for cooling from radiation heating the lower parts of the embankment slopes due to evaporation (since it takes 2256 kJ of heat to evaporate 1 kg of water, or about 590 calories per 1 g of water). The windproofness of the rock layer between the peripheral zones is ensured by their water tightness, which at the same time prevents the entry of warm surface water (top water) into the base of the structure on permafrost, leading to its degradation. The latter is most dangerous for unstable high-temperature permafrost, for the preservation of which this invention is primarily intended.

Together, the above mechanism allows us to shift the average annual temperature on the surface of the base of the structure from the positive area (as in conventional structures) to negative. The latter significantly improves the conditions for maintaining permafrost at the base of the structure. The result is increased overall stability and operational reliability.

Sources of information

(1) Copyright certificate No. 1081283 A, cl. E 02D 17/18.

(2) Copyright certificate No. 1656078 A1, cl. E 02D 17/18.

Claims (3)

1. Earthworks on permafrost, containing the body of the subgrade and interlayers of rocky soil in contact with the air in the peripheral zones, characterized in that the peripheral zones in the sloping parts below are made waterproof, and interlayers of rocky soil are interconnected by an underlying layer of rocky soil . 2. The earthworks according to claim 1, characterized in that the height of the watertight bottom slopes of the peripheral zones is within Sc + Нсв≤Нr≤Нc-No-Nef where Hr is the waterproofing height from the bottom of the sloping parts of the peripheral zones, m; Sc and Нсв - precipitation and thickness of snow or surface water at the structure, m; Nef - effective thickness of the contact with the air of interlayers from rocky soil in the peripheral zones, m; Hc and But - the height of the structure and the thickness of the shoulders (or pavement) in the peripheral zones, m 3. The earthworks according to claim 1 or 2, characterized in that the lower parts of the peripheral zones that are waterproof from below can be made of non-draining soil or insulated with loose side prisms from non-draining soil and / or anchored to the slopes with waterproof or draining layers (for example, from foams, carbofol, fiberglass, polyester geomats, etc.) and are covered from above with a layer of heat-permeable evaporative materials (for example, peat, moss, UV resistant their geotextiles, highly porous foams, etc.).