Technical Measures for Limitation of Frost Depth in Soil

Renovation processes of existing buildings, including historically protected ones, are most of the time focused on energy saving. Nonetheless these processes might affect the function of existing shallow foundations. This paper deals with the influence of soils moisture content onto the depth of freezing. The depth of freezing depends on the type of soil as well, not just the moisture content. The influence of water and soils composition are generally perceived to be substantial for depth of freezing. Sub-zero temperatures do significantly change the soils characteristics, which has an effect to the building structure. The purpose of the research done by the personnel of Brno University of Technology was to determine the effects of special measures against frost penetration of soil. These measures included the application of various materials and solutions over the terrain in winter to monitor frost depth of soil.

Performance Evaluation of Different Insulating Materials using Field Temperature and Moisture Data

Including insulation layers in pavement structures has become a common strategy to minimize frost penetration in cold regions. This study investigated the performance of two different insulation materials, extruded polystyrene board and bottom ash, in a test road in Edmonton, Alberta, Canada, eight years after construction. The two insulation materials were used in a fully instrumented test road, including three insulated sections 20 m in length. The insulated sections are as follows: the first section has 1 m of bottom ash (B. Ash), the second section has a 10 cm polystyrene layer (Poly-10), and the third section has a 5 cm polystyrene layer (Poly-5). Both B. Ash and polystyrene layers were placed on top of the subgrade layer, at a depth of 70 cm from the surface. A conventional section next to these three sections was used as the control section. Volumetric water content data and temperature variation were used to analyze the influence of the insulation materials on the subgrade. It was concluded that both B. Ash and Poly-10 layers protected the subgrade from freezing. The Poly-10 section showed the lowest rate of change in subgrade temperature during the monitoring period. B. Ash and Poly-10 reduced the frost depth by 23% and 70% compared with the control section, respectively. It was concluded that Poly-10 protected the subgrade soil from freezing and excessive moisture more effectively than B. Ash; however, the temperature in the layer above the insulation layers (pavement base layer) was significantly lower during winter for the Poly-10 section.

Temperature Flows in Railway Tunnels: Field Measurements of Frost Penetration

Even though extensive pre-grouting is carried out during the construction of tunnels, certain leakages and drips remain. These remaining leakages are remedied by a combination of post-injection and drainage measures with, for example, frost insulated drain mats, whose function is to prevent the cold tunnel air from reaching a leakage spot and causing water to freeze. Despite these measures, some water may still enter the tunnels and cause problems during winter with ice formations and frost shattering. Icicles, ice pillars and ice-covered roads and railway tracks require constant maintenance. If ice occurs in the fracture network close to the tunnel contour or in the interface between the rock and shotcrete, it can cause degradation of the load-bearing capacity of the tunnel and fall-outs of both materials. In tunnel sections with water leakage problems it is common to protect the load-bearing structure from freezing with insulated drainage systems. To determine where along the tunnel efforts must be made to prevent ice formation, the temperature conditions of tunnels must be investigated. This article presents parts of the results from field measurements in two Swedish railway tunnels. The measurements involves monitoring of air and rock temperatures, air pressure and air velocity. Keywords: Frost penetration, ice formation, frost shattering, temperature measurement, maintenance, railway tunnel.

Influence of Compaction Level on the Water-Heat-Vapor Characteristics of Unsaturated Coarse-Grained Fillings Exposed to Freezing and Thawing

Compaction level is an important control index to guarantee subgrade stability. Under freezing-thawing cycles, water-heat-vapor characteristics due to different compaction levels of unsaturated coarse-grained fillings of high-speed railway (HSR) subgrade are key factors in understanding the mechanism of freezing-thawing deformations. Experiments have been performed to study the characteristics of water-heat-vapor of coarse-grained fillings with different compaction levels exposed to freezing and thawing. Fluorescein was used to trace the variations of liquid water in external moisture supply. Test results indicated that compaction level affected the water-heat-vapor characteristics of coarse-grained fillings to some extent. The increase of compaction level increased frost penetration and freezing rate; however, initial water replenishment time delayed during freezing process; liquid water migration height and external liquid migration increased, but total moisture migration, the amount of vapor migration, and vapor of the soil sample moving up to the top pedestal simultaneously reduced. Repeated freezing-thawing cycles improve the compaction of coarse-grained fillings. Variation of the amount of moisture caused by the increase of compaction level may decrease the frost heaving of coarse-grained fillings. Therefore, proper selection and uniformity of compaction level is of critical importance in HSR engineering.

Establishment of Intrinsic Permeability of Coarse Open-Graded Materials: Review and Analysis of Existing Data from Natural Air Convection Tests

This paper presents a review and analysis of large-scale air convection tests and the establishment of intrinsic permeability in coarse open-graded materials. Natural air convection can make a significant contribution to heat transfer during cooling periods. In seasonally freezing environments this can result in excessive frost penetration and subsequent frost-related problems. Intrinsic permeability largely defines the onset of convective heat transfer in granular materials. Conventional methods for measuring intrinsic permeability cannot be applied to very coarse materials. Large-scale laboratory experiments on natural air convection can serve as an alternative method for determining this crucial parameter. This paper gives an overview of four different experimental test setups for measuring natural air convection, all differing in physical shape, boundary conditions and heat flux/temperature measurement devices. Comparison between these is difficult because the air convection pattern can differ and in some cases the shape and number of convection cells cannot be validated. Most of the studies available in the literature use theoretical equations to approximate intrinsic permeability. A method based on the analytical Nu-Ra number relationship is employed to establish the values of intrinsic permeability. Tests that provide enough data to enable the use of the Nu-Ra relationship are very limited. The overall results show a reasonable correlation between experiment-based intrinsic permeability and theoretical approximation. However, several issues must be addressed: first, differences may exist between the intrinsic permeability of natural and of crushed materials due to the shape effect. Second, the method used is in theory valid only for two-dimensional air convection within a square enclosure heated from below. Yet the results show that this method could be extended to other conditions with a certain degree of confidence. Third, a good estimate of intrinsic permeability is possible only with accurate experimental measurement.

INFLUENCE OF FROST PENETRATION AND CRYOGENESIS ON SOIL PROPERTIES

Изучено влияние низких температур на изменение процессов ионного обмена в исследуемых почвах, изменение растворимости малорастворимых и труднорастворимых соединений. В качестве объекта были выбраны мерзлотно-таежные почвы, характерные для Якутии. Замораживание почвенных растворов сопровождается увеличением концентрации ионов в незамерзшей части, разрушением алюмосиликатов, изменением прочности связи воды с почвенно-поглощающим комплексом. Это проявляется в инфракрасных спектрах, дериватограммах, а эффект был зависим от продолжительности и кратности промораживания. Замерзание верхней части почвенного профиля при наличии многолетней мерзлоты приводит к развитию тиксотропии. Установлено, что интенсивность развития этих процессов отличается для почв разного гранулометрического и минералогического состава, гумусированности, для органических и минеральных горизонтов. Содержание катионов водорастворимых солей в замерзших и незамерзших почвенных растворах мерзлотно-таежных почв составляло соответственно К – 4,7±2,5 и 42,8±28,5 мг/л; Са – 0,2±0,1 и 3,2±1,4; Fе – 0,04±0,01 и 0,38±0,03 мг/л. Эти отличия были характерны для отдельных горизонтов почв. Замерзшая часть раствора менее минерализована, незамерзшая часть содержит большие концентрации элементов. Обсуждается роль многолетней мерзлоты в процессах почвообразования. Низкие температуры профиля и сниженная биологическая активность обуславливают специфику протекания реакций ионного обмена, изменение растворимости осадков, создание водоупора. Эти процессы способствуют аккумуляции веществ в надмерзлотном слое, возникновению новых градиентов и геохимических барьеров в почвенном профиле. Наблюдается локальное развитие почвообразования в слое, образующемся над вечной мерзлотой, при отсутствии промывного водного режима. Low temperatures lead to alterations of ion exchange processes in the soil, fallout solubility. As an object, permafrost-taiga soils characteristic of Yakutia were chosen. The soil solution freezing is provided with ion densification in unfrozen parts, alumosilicate damage, change of bond strengths between water and the soil adsorption complex, infrared spectra, thermograms. Freeze-up of the upper soil profile in the presence of permafrost causes tixotropy development. However, the rate of these processes development differs for the soils of different granulometric and mineralogical content, high humus content, for organic and mineral horizons. At this rate, the water-soluble cation content in frozen and unfrozen soil solutions of cryomorphic-taiga soils was К – 4,7±2,5 and 42,8±28,5 mg/l; Са – 0,2±0,1 and 3,2±1,4; Fе – 0,04±0,01 and 0,38±0,03 mg/l accordingly. These distinctions were typical for certain soil horizons. Frost penetration of the soils modified their thermograms and infrared spectra. The effect depended on the persistency and frequency of the frost penetration. The frozen part of the solution is less mineralized, the unfrozen part contains large concentrations of elements. The role of permafrost in soil formation is discussed. Low profile temperatures and reduced biological activity determine the specifics of the ion exchange reactions, changes in the solubility of precipitation, the creation of a water seal. These processes contribute to the accumulation of substances in the permafrost layer, the emergence of new gradients and geochemical barriers in the soil profile. There is a local development of soil formation in the layer formed over permafrost, in the absence of washing type of water regime.