
Министерство образования и науки Российской Федерации
Якутский Государственный Университет им. М.К. Аммосова
Сборник текстов
по специальности «Автомобильные дороги и аэродромы»
на английском языке
Якутск 2004
Утверждено научно-методическим советом университета
Составитель: ст. преподаватель кафедры иностранных языков по ТиЕС Парникова Г.М.
Подготовлено на кафедре иностранных языков по техническим
и естественным специальностям
Настоящий сборник текстов предназначен для студентов автодорожного факультета. Целью сборника является обучение чтению и переводу литературы по специальности на английском языке. Все тексты адаптированы из оригинальной литературы. В сборнике 11 текстов объемом 2500-3000 печатных знаков каждый. Сборник может быть использован для студентов заочного отделения.
Road, Airfield, and Island Embankments. Permafrost
Permafrost exists in a thermal equilibrium between the environmental conditions of the region and the insulating effects of the active layer. Whenever the active layer is altered by a construction project its insulating properties are changed. Usually this results in a loss of protection and increased heat flow into the permafrost. It results in an inevitable melting of the frozen soil and subsidence of the surface if frozen moisture contents for the soil involved are greater than the soil can retain after thawing. If the project is a road or airfield the integrity of the project is jeopardized. When the road or airfield embankment must be built on permafrost, precautions should be taken to avoid degradation of the permafrost, which can cause serious problems to the structure. It should be noted that some permafrost degradation always takes place, and when a structure or facility is constructed at a permafrost site, some degradation is tolerated and even expected. The structure is periodically brought back to its original grade as part of routine maintenance. The amount of tolerance is subject to the structure and its use. Airports tolerate less than roads which tolerate less than dikes etc.
But permafrost is not the only problem facing road and airfield construction in the north. Many sites lack suitable materials for embankment construction and suffer from seasonal freezing and thawing effects. The temperatures of the region have an adverse effect on many commonly used materials such as asphalt. Thaw weakening of embankments inhibits the load carrying capability of the embankment for several weeks of the year during spring breakup. So it will necessary to discuss these problems and some of the current solutions that have been used to address them. Some of the solutions such as insulation are still largely experimental, but are gaining acceptance and becoming more commonly used as more information and experience is gained. Words and expressions:
Permafrost Вечная мерзлота
Thermal equilibrium Термальное равновесие
Heat Тепло
Melting Таяние
Soil Почва
Road (airfield) embankment Дорожная (аэродромная) насыпь,
дамба.
Degradation Размытие
То tolerate Допускать, дозволять.
То freeze Замерзать, покрываться льдом.
То thaw Таять
Insulated roads
The thermal resistance of the original materials in. the active layer at a permafrost location and the evaporative cooling effects of wet soil surfaces reduce the amount of heat that flows into the permafrost during the summer and out of it during the winter. In addition there is the insulating effect of the snow cover in the winter. The depth of the top of the permafrost (the permafrost table) is determined by the balance of winter cooling and summer heating. Whenever the thermal resistance or moisture transport effects of this layer are modified (for example, during a forest fire or clearing for construction), the depth of the permanently frozen layer changes until the balance between winter cooling and summer heating is restored. Likewise during a year with a warmer than average summer or colder than average winter, the permafrost table responds accordingly, moving up or down until the balance is once again restored. Climate changes are usually very gradual and the resulting changes are very small. Larger changes result when the thermal resistance is altered dramatically, by the forest fire mentioned above or by construction activity.
It is difficult to change the climatic influence on an embankment, but the overall thermal resistance of the active layer is within our control. The construction of an embankment over ice-rich permafrost causes several changes to take place.
Often the final result of all of these changes is an increase of thermal resistance above the permafrost table. This causes the level of the frozen layer to rise above its previous depth until once again summer heating and winter cooling approach a balance.
Other factors also enter into play. The reflectivity of the surface, for example, plays an important part in how much energy is absorbed from the sun, and thus what the surface temperature will be. The area available for heat to move in and out of the surface will be different and, like the cooling fins on an air cooled engine, will increase heat flow both in and out. But regardless of the changes, a temporary thermal balance will eventually be reached, and the depth of the permafrost layer will be altered either up or down.
In the far north, the thickness of the gravel embankment often provides enough additional insulation to cause the permafrost to rise into the gravel embankment except at the edges. If the embankment materials are non-frost -susceptible, small changes in the new permafrost table do not involve melting of massive ice forms and the associated detrimental effects.
In general, as the locality of the site moves south, summer heating increases and winter cooling decreases. Therefore, the thickness of the embankment that is needed to establish a thermal resistance that will protect the permafrost becomes larger and larger until it is no longer economically feasible to use gravel alone to protect the underlying permafrost. At this point, thermal insulating materials that have a lower thermal conductivity than gravel must be incorporated into the embankment to achieve the overall thermal resistance needed. It should be recognized that there is no location at which gravel alone is no longer adequate to protect the permafrost. Many secondary factors enter into
consideration such as evaporation, direction of exposure, and other climatic conditions. These factors combine to create a region in which insulation must be added at some sites but not others.
Words and expressions:
Layer Слой
Evaporative Испаряющий, парообразующий
To reduce Сокращать
Insulating Изоляционный
Resistance Сопротивление
To reflect Отражать
Thickness Толщина, слой
Detrimental Приносящий убыток, вредный.
Exposure Местоположение
Climatic conditions Климатические условия