After the construction of road works in cold regions, the original geothermal heat exchange conditions have changed, and the result is usually an increase in the amount of heat absorbed in the subgrade. The annual heat accumulation in the subgrade causes the temperature of the lower soil to rise and the permafrost to melt, causing the sinking deformation of the road. In order to ensure the stability of roadbeds, the protection of permafrost in cold regions is the most widely adopted design principle. Various measures are taken to minimize the upper limit of permafrost in the lower subgrade. Insulation technology is one of the more suitable ones. Practice has shown that the design of special embankment structure, the use of ventilation embankments to set up the berms, the embedding of hot rods, the use of schist stone slope protection and the laying of thermal insulation materials are the auxiliary measures to ensure the stability and effectiveness of the roadbed in the cold area. The speed of subgrade changes has a great effect.
2 The principle of thermal insulation treatment method is to add a layer of thermal insulation material in the subgrade, and use the low thermal conductivity (thermal resistance) of the thermal insulation material to prevent the upper heat from entering the lower soil layer, thereby protecting the permafrost. Ways. In order to illustrate the role of the insulation layer, we illustrate the comparative changes in the geothermal profile when there is an insulation layer and no insulation layer. Under the control of the temperature boundary condition of the approximate sinusoidal fluctuation in the upper part of the soil layer, the temperature of the lower soil layer also shows the cyclical fluctuation with the depth amplitude gradually decreasing and the phase gradually lags; therefore, the ground temperature of the permafrost The profile appears as a dynamic curve between the envelopes formed by the lowest and lowest temperatures of the depths of the soil layers. The depth at which the highest temperature envelope is equal to the freezing temperature (usually 0 ft) is the permafrost upper limit. When no insulation layer is placed, the final and lowest temperature envelope usually has a smoother continuous curve. When the insulation layer is placed, if the upper temperature condition remains unchanged, according to the heat conduction principle, the thermal conductivity of the insulation material and the heat conduction of the soil The large difference in coefficient (about 40 times) will cause a large temperature difference (thermal resistance effect) in the upper and lower parts of the insulation layer, which determines the annual amplitude of the soil temperature below the insulation layer, that is, the lowest temperature and the lowest temperature. The range between the envelopes is reduced. In this case, the most temperature envelope intersects the depth axis at a relatively high depth, ie the upper limit of permafrost is raised, which is the basic principle of insulation to protect permafrost.
Based on this principle, the highest temperature envelope under the insulation layer is always inside the last temperature envelope without the insulation layer, that is, the upper limit of the permafrost is always in the absence of the insulation layer when there is insulation layer. The upper limit of frozen soil. For road engineering, the heat accumulation in the subgrade caused by the change of surface heat exchange conditions will lead to the decrease of the upper limit of permafrost. When the insulation layer is laid, it is possible to compensate for the lower limit of the upper limit and keep the upper limit of permafrost stable and even Raise. The smaller the thermal conductivity of the insulation material, the better the effect should be.
3 styrofoam insulation board (EPS) 3.1 physico-mechanical properties of polystyrene foam board The polystyrene foam board is a plate-like material formed by compression of polystyrene foam particles, with light weight and strength. It has the characteristics of low water absorption, good heat insulation performance and convenient transportation. It is a good road engineering thermal insulation material, which can effectively protect the stability of the temperature field of frozen soil roadbed.
3.2 Analysis of thermal insulation effect of polystyrene foam insulation board The field test shows that the ground temperature of the insulation board rises with the rise of surface temperature, and the monthly average ground temperature rises from -14.1T in December to June of the following year. 8, the increase of 22.lt; while the temperature of the insulation board is also rising with the increase of temperature, but the change is small, the monthly average temperature from the -3.3T in December to 1.9T in June of the following year, The increase is 5.2T. It can be seen that the EPS insulation board has a good thermal insulation effect, effectively preventing the influence of atmospheric temperature on the temperature field of the subterranean soil, and ensuring that the temperature of the frozen soil subgrade changes within a small range.
3.3 Applicable conditions of polystyrene foam board When the temperature of the insulation board is the same, the effect of the embankment is more obvious, but the high embankment is not conducive to the loss of summer heat storage in the embankment soil, so it should be determined. The reasonable height of the embankment. In addition, due to the low water absorption rate of the thermal insulation board, the water content is generally high, which will cause the soil layer on the bottom of the thermal insulation board to form a soil-containing ice layer, which will make the road surface freeze more. Therefore, the upper part of the insulation layer cannot be filled with fine-grained soil, and the drainage design of the embankment and the subgrade soil is strengthened to prevent the groundwater from collecting to the middle line of the embankment and storing it on the bottom of the soil on the thermal insulation board.
4 stone ventilation roadbed 4.1 stone ventilation roadbed structure The stone ventilation roadbed is composed of subgrade soil, stone ventilation layer and waterproof layer. The thickness of the stone ventilation layer should be suitable. In addition, in order to ensure a certain porosity and prevent water intrusion, a certain thickness of the filter layer and the waterproof layer are required.
4.2 Working principle of stone-ventilated roadbed The lining stone ventilation roadbed is an engineering measure to actively protect frozen soil. Its working principle is: in the cold season, the cold air has a large density, and the stone gap is made under the action of self-weight and wind. The hot air rises, the cold air descends and enters the foundation; in the warm season, the hot air density is small and it is difficult to enter the foundation, similar to the thermal switching effect.
According to the research results, the embankment of the pebble layer is free to flow or forced to flow in the air due to its large porosity. When the surface of the warm season is heated, the hot air rises and the lower temperature can still be maintained in the schist, and the convection The heat is upward, therefore, the heat in the incoming ground is less; in the cold season, the cold air is infiltrated along the pores, the convective heat transfer is downward, and more cold can be transmitted to the foundation; the heat transfer of the schist in the cold season and warm Seasons may be roughly equal. However, the heat transfer accounts for a small proportion in the whole heat transfer process, so the combined effect of the stone embankment is that the cold input is greater than the heat input. On the other hand, the large pores and strong free convection in the riprap pile make the cold and hot air in winter and summer continue to undergo cold exchange and heat shielding due to differences in air density, etc., and the result is beneficial to protect permafrost.
43 Application conditions The use of appropriately sized riprap as a filler in subgrade engineering in permafrost regions can effectively slow down the melting rate of frozen soil under subgrade in permafrost regions, or promote its artificial upper limit (upper limit of frozen soil) and increase freezing. The stability of the roadbed in the land area. According to the various characteristics of the riprap and the early use effect, and the large slope waterproofing problem is not considered in the general construction, the construction size of the stone is about the left and right.
From the study of the experimental embankment in the Qinghai-Tibet Plateau and the Daxinganling in the northeast and the operation of the Siberian Bayi-A line in the former Soviet Union, coarse-grained materials, especially gravel materials such as stones and large stones, are used as embankment fillers, road rollers for filling and slope protection. There are many advantages to the bead filler. It can make full use of the differential convection characteristics of the cold storage in winter and the proportion of hot and cold air in summer to maintain the thermal equilibrium of the upper limit of the frozen soil, maintain the upper limit of the frozen soil under the subgrade or cause the upper limit to rise. In 1999, it was the national focus of the Northwest Branch of the Institute of Iron and Steel and the frozen soil project. Insulation can be made of insulation materials such as EPS boards. The air duct is an iron pipe provided in the berm or the foot of the slope and communicates with the stone block under the heat insulation layer. They use the one-way convection characteristics of air to reduce the temperature of the base layer in winter to achieve the purpose of protecting the frozen soil.
8 Conclusions (1) The application of subgrade insulation technology measures to protect the frozen soil in the cold area is not yet a mature roadbed melting subsidence prevention and control countermeasures, although in principle the insulation effect of the insulation layer can limit or delay the decline of the permafrost upper limit. However, it is impossible to change the development trend of the frozen land heat budget. The overall effect of the insulation layer should be comprehensively evaluated from the beneficial effects of the warm season to the lower part of the roadbed and the adverse effects of the cold season to prevent heat loss from the permafrost.
In view of the problems of frost heaving, melting and sinking and hot melt sliding of roadbeds in permafrost regions, it is necessary to adopt appropriate insulation technology, and it is necessary to adapt to local conditions to achieve good results.
Among the various methods, it is recommended to compare economic techniques to obtain the best benefits.
(Finish)
Hydroxylamine Sulfate Basic Information
Product Name: Hydroxylamine sulfate
CAS: 10039-54-0
MF: H2O4S.2H3NO
MW: 164.14
EINECS: 233-118-8
Mol File: 10039-54-0.mol
Hydroxylamine Sulfate Chemical Properties
Melting point: 170 °C (dec.)(lit.)
Boiling point: 56.5℃
Density: 1.86
Storage temp.: -20°C
Solubility water: soluble(lit.)
Form: Crystals
Color: White
PH: 3.6 (10g/l, H2O, 20℃)
Water Solubility: 329 g/L (20 ºC)
Sensitive: Hygroscopic
Hydroxylamine Sulphate CAS No.10039-54-0
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