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1.
中国冻土研究近今进展 总被引：13，自引：4，他引：9
近年来,在南极和青藏高原发现了多种成因的厚层地下冰。冰土的水分迁移、冻胀、成冰机制、强度和蠕变等的研究进一步深化。冻土改造和利用兴起,在寒区砂金矿开采、热桩利用等方面有了良好的开端。 相似文献
2.
Lagoon berms in western Alaska are difficult to design and build due to limited resources, high cost of construction and materials, and warm permafrost conditions. This paper explores methods to treat locally available frozen materials and use them for berm construction. The goal is to find an optimized mix ratio for cement and additives that can be effective in increasing the strength and decreasing the thaw settlement of an ice-rich frozen silty soil. Soil of similar type and ice content to the permafrost found at a project site in Eek, Alaska is prepared in a cold room. The frozen soil is pulverized and cement, additives and fibers are added to the samples for enhancing shear strength and controlling thaw settlement. Thaw settlement and direct shear testsare performed to assess strength and settlement characteristics. This paper presents a sample preparation method, data from thaw settlement and direct shear tests, and analyses of the test results and preliminary conclusions. 相似文献
3.
Experiments about working mechanism and mechanical characteristics of the DX model pile foundation under lateral dynamic and static loading were conducted by using a model system of the dynamic frozen ... 相似文献
4.
Crushed rock subgrade, as one of the roadbed-cooling methods, has been widely used in the Qinghai-Tibet Railway. Much
attention has been paid on the cooling effect of crushed rock; however, the mechanical properties of crushed rock are
somehow neglected. Based on the discrete element method, biaxial compression test condition for crushed rock is compiled
in FISH language in PFC2D, and the natural shape of crushed rock is simulated with super particle "cluster". The effect
of particle size, crushed rock strength and confining pressure level on overall mechanical properties of the crushed
rock aggregate are respectively analyzed. Results show that crushed rock of large particle size plays an essential framework
role, which is mainly responsible for the deformation of crushed rock aggregate. The strength of gravel has a great
influence on overall mechanical properties which means that strength attenuation caused by the freeze thaw cycles cannot
be ignored. The stress-strain curves can be divided into two stages including shear contraction and shear expansion at
different confining pressures. 相似文献
5.
Two major earthquakes in Alaska, namely the 1964 Great Alaska Earthquake and the 2002 Denali Earthquake, occurred in winter
seasons when the ground crust was frozen. None of the then-existing foundation types was able to withstand the force from the
lateral spreading of frozen crust. This paper presents results from the analysis of pile foundations in frozen ground overlying liquefiable
soil utilizing the Beam-on-Nonlinear-Winkler-Foundation (BNWF) (or p-y approach). P-multipliers were applied on traditional
sandy soil p-y curves to simulate soil strength degradation during liquefaction. Frozen soil p-y curves were constructed
based on a model proposed in a recent study and the frozen soil mechanical properties obtained from testing of naturally frozen
soils. Pile response results from the p-y approach were presented along with those from fluid-solid coupled Finite Element (FE)
modeling for comparison purpose. Finally, the sensitivity of pile response to frozen soil parameters was investigated and a brief
discussion is presented. 相似文献
6.
To investigate the mechanical properties of ice-saturated frozen soil, a series of triaxial tests under various confining pressures（0.5 to 9.0 MPa） on ice-saturated frozen loess with ice content of 23.7% were carried out at a temperature-6 °C, and at 1.25 mm/min of loading rate. The triaxial tests include two loading modes, one with monotonic loading（i.e., triaxial compression）, and another with static cycle loading. The test results under triaxial compression show that the strength and deformation behaviors of ice-saturated frozen loess are affected by confining pressure. According to the test results of triaxial loading-unloading cycle test, the elastic modulus evolution with the number of cycles under different confining pressures are analyzed. 相似文献
7.
JAMES BOCKHEIM 《Geografiska Annaler: Series A, Physical Geography》2007,89(3):153-165
Soil‐forming processes and soil development rates are compared and contrasted on glacial deposits in two adjacent and coeval valleys of the Quartermain Mountains, which are important because they display Miocene glacial Stratigraphy and some of the oldest landforms in the McMurdo Dry Valleys. More than 100 soil profiles were examined on seven drift sheets ranging from 115 000 to greater than 11.3 million years in age in Beacon Valley and Arena Valley. Although the two valleys contain drifts of similar age, they differ markedly in ice content of the substrate. Whereas Arena Valley generally has ‘dry‐frozen’ permafrost in the upper 1 m and minimal patterned ground, Beacon Valley contains massive ice buried by glacial drift and ice cored rock glaciers and has ice‐cemented perma‐frost in the upper 1 m and considerable associated patterned ground. Arena Valley soils have twice the rate of profile salt accumulation than Beacon Valley soils, because of lower available soil water and minimal cryoturbation. The following soil properties increase with age in both valleys: weathering stage, morphogenetic salt stage, thickness of the salt pan, the quantity of profile salts, electrical conductivity of the horizon of maximum salt enrichment, and depth of staining. Whereas soils less than 200 000 years and older soils derived from sandstone‐rich ground moraine are Typic Anhyorthels and Anhyturbels, soils of early Quaternary and older age, particularly on dolerite‐rich drifts, are Petronitric Anhyorthels. Arena Valley has the highest pedodiversity recorded in the McMurdo Dry Valleys. The soils of the Quartermain Mountains are the only soils in the McMurdo Dry Valleys known to contain abundant nitrates. 相似文献
8.
Ultrasonic P-wave tests of frozen silt and frozen sand were conducted during uniaxial loading by using an RSM®-SY5(T) nonmetal ultrasonic test meter to study the velocity characteristics of P-waves. The experimental results indicate that the P-wave velocity is affected by soil materials, temperature, and external loads, so the P-wave velocity is different in frozen silt and frozen sand, but all decrease with an increase of temperature and increase at first and then decrease with strain during the loading process. There is an exponential relationship between uniaxial compressive strength and P-wave velocity, and the correlation between them is very good. The characteristic parameters of acoustic waves can, to some extent, reflect the development of internal cracks in frozen soils during loading. 相似文献
9.
Ultrasonic detection technology is of great significance in the detection and evaluation of physical and mechanical properties of frozen soil, but wave propagation characteristics in frozen soil are unclear. Based on the three-phase composition of frozen saturated soil and the mixture theory, considering Bishop's effective stress formula, the wave propagation equations are establish for frozen saturated soil. In wave propagation, an entropy inequality was introduced to describe the coupling of different phases. The analytic expressions of propagation velocity and attenuation law of waves in frozen soil are obtained, and wave propagation characteristics in frozen saturated soil are discussed. Results show that four types of waves(i.e., P1, P2, P3 and S) are found in frozen saturated soil and all four wave types are dissipative waves, in which the attenuation of P3 is the maximum. The velocity of four waves increases sharply at the excitation frequency range of 10~3–10~9 Hz,but the wave velocity at high-frequency and low-frequency is almost constant. When volume ice content increases, the wave propagation velocity of P1 and S decreases dramatically, and the velocity of P2 increases gradually, but P3 velocity increases first and then decreases to zero with increasing saturation. The attenuation coefficients of P1 and S waves begins to increase gradually when the volume ice content is about 0.4, P2 increases first and then decreases with an increase of volume ice content and P3 increases with the volume ice content and decreases rapidly from extreme to zero. 相似文献
10.
Melt shrinkage, salt bulge, and corrosiveness are common problems with saline soils, which damage highway foundations and cause huge financial losses. In order to improve the saline soil subgrade, dyna... 相似文献
11.
The paper presents some methods of numerical modeling and a study of moisture changing in frozen clay soils considering rates of freezing in the base of construction.An impact assessment of moisture changes in clay soils affecting strength characteristics during thawing was carried out in stability tests. 相似文献
12.
Three stages of complex technological monitoring for the increase of high-temperature-permafrost soil bearing capacity are described. The feasibility of process monitoring to improve the targeted strength properties of subgrade bases on frozen soils is demonstrated. The rationale for the necessity of predictive modeling of freeze-thaw actions during the subgrade construction period is provided. 相似文献
13.
The soil-freezing characteristic curve (SFCC), which represents the relationship between unfrozen water content and sub-freezing temperature (or suction at ice-water interface) in a freezing soil, can be used for understanding the transportation of heat, water, and solute in frozen soils. In this paper, the soil freezing process and the similarity between the SFCC of saturated frozen soil and soil-water characteristic curve (SWCC) of unfrozen unsaturated soil are reviewed. Based on similar characteristics between SWCC and SFCC, a conceptual SFCC is drawn for illustrating the main features of soil freezing and thawing processes. Various SFCC expressions from the literature are summarized. Four widely used expressions (i.e., power relationship, exponential relationship, van Genuchten 1980 equation and Fredlund and Xing 1994 equation) are evaluated using published experimental data on four different soils (i.e., sandy loam, silt, clay, and saline silt). Results show that the exponential relationship and van Genuchten (1980) equation are more suitable for sandy soils. The simple power relationship can be used to reasonably best-fit the SFCC for soils with different particle sizes; however, it exhibits limitations when fitting the saline silt data. The Fredlund and Xing (1994) equation is suitable for fitting the SFCCs for all soils studied in this paper. 相似文献
14.
Freezing and thawing during the winter season change soil properties such as density. The density change in the particulate media influences soil stiffness. In addition, freezing of partially or fully saturated soils changes the soil matrix from a particulate media to a continuum. The goal of this study is to investigate the cyclic freezing and thawing effects on elastic waves. Sand-silt mixtures with 10% silt fraction in weight and 40% saturation are prepared. The sand-silt mixtures are placed in a nylon cell, onto which a pair of bender elements and a pair of piezoelectric disk elements are installed for the measurement of shear and compressional waves, respectively. The temperature of the mixtures decreases from 20°C to 10°C to freezing. The frozen sample is gradually thawed at room temperature (20°C). These freezing-thawing processes are repeated three times. The test result shows that the shear and compressional wave velocities significantly increase when the specimen is frozen. When the temperature is greater than 0°C, the elastic wave velocities are lower during thawing than during freezing due to soil structure change. This study demonstrates that soil structure change during the winter season may be effectively estimated from elastic waves. 相似文献
15.
The mechanical property of saline soils varies with moisture and climate in the cold and salt lake region of Qinghai-Tibet Plateau, which influences
project construction. In order to improve foundation reinforcement effect of the Qarhan–Golmud Highway, Qinghai Province,
China, dynamic compaction replacement (DCR) composite foundation was applied in saline soils. A field experiment was conducted in this
area, where strength and working mechanism of pier-soil and deformation modulus of the composite foundation was analyzed after reinforcement.
This paper presents methods for determining the coefficient on the bearing capacity evaluation and deformation modulus of
composite foundation with DCR. Reinforcement case of DCR is highly effective in saline soils of the salt lake regions, which helps the migration
of water and salt in saline soils. 相似文献
16.
The practice of building and operating of railroad beds shows that the greatest at enuation of soils occurs in the spring, during their transition from the frozen to thawed state. The greatest influenc... 相似文献
17.
In order to determine the changing rule of long-term frozen soil strength and elucidate the connection between long-term strength and soil physical properties,frozen loess was subjected to 4,6,8,10,and 50 freeze-thaw cycles,under closed-state conditions in a constant-temperature box.The frozen samples were tested on a spherical template indenter,and the results show that under the effect of repeated freeze-thaw cycles,the long-term strength of frozen loess decreased; changes in the mechanical property indices were highly unstable during the first 10 cycles; the soil strength and density were the greatest at the eighth cycle while the void ratio was the smallest; and after eight cycles all of the indices had less fluctuation and certain rising or falling tendencies.By converting the number of freeze-thaw cycles into elapsed time in the tests,three different forecasting methods of long-term soil strength could be assessed and the soil equivalent cohesive force after 10 years,20 years,or 30 years could be estimated. 相似文献
18.
Dynamic characteristics of heavy-haul railway subgrade under vibratory loading in cold regions are investigated via low-temperature dynamic triaxial tests with multi-stage cyclic loading process. The relationship between dynamic shear stress and dynamic shear strain of frozen soil of subgrade under train loading and the influence of freezing temperatures on dynamic constitutive relation, dynamic shear modulus and damping ratio are observed in this study. Test results show that the dynamic constitutive relations of the frozen soils with different freezing temperatures comply with the hyperbolic model, in which model parameters a and b decrease with increasing freezing temperature. The dynamic shear modulus of the frozen soils decreases with increasing dynamic shear strains initially, followed by a relatively smooth attenuation tendency, whereas increases with decreasing freezing temperatures. The damping ratios decrease with decreasing freezing temperatures. Two linear functions are defined to express the linear relationships between dynamic shear modulus (damping ratio) and freezing temperature, respectively, in which corresponding linear coefficients are obtained through multiple regression analysis of test data. 相似文献
19.
Processes and mechanisms of multi-collapse of loess roads in seasonally frozen ground regions: A review 总被引：1，自引：0，他引：1
Usually, the collapsible loess widely distributed across the world can serve as a type of foundation soil that meets its strength requirement after dense compaction and elimination of collapsibility. However, many problems such as cracks and differential settlement still occur in loess roads in the seasonally frozen ground regions after several years of operation. Many studies have demonstrated that these secondary or multiple collapses primarily result from the repeatedfreezing-thawing, wetting-drying, and salinization-desalinization cycles. Therefore, we conducted a research program to (1) monitor the in-situ ground temperatures and water content in certain loess roads to understand their changes, (2) study the effects of freezing-thawing, wetting-drying, and salinization-desalinization cycles on geotechnical properties and micro-fabrics of compacted loess in the laboratory, and (3) develop mitigative measures and examine their engineered effectiveness, i.e., their thermal insulating and water-proofing effects in field and laboratory tests. Our results and advances are reviewed and some further research needs are proposed. These findings more clearly explain the processes and mechanisms of secondary and multiple collapse of loess roads. We also offer references for furtherstudy of the weakening mechanisms of similar structural soils. 相似文献
20.
《Polar Science》2014,8(2):96-113
Understanding geocryological characteristics of frozen sediment, such as cryostratigraphy, ice content, and stable isotope ratio of ground ice, is essential to predicting consequences of projected permafrost thaw in response to global warming. These characteristics determine thermokarst extent and controls hydrological regime—and hence vegetation growth—especially in areas of high latitude; it also yields knowledge about the history of changes in the hydrological regime. To obtain these fundamental data, we sampled and analyzed unfrozen and frozen surficial sediments from 18 boreholes down to 1–2.3 m depth at five sites near Chokurdakh, Russia. Profiles of volumetric ice content in upper permafrost excluding wedge ice volume showed large variation, ranging from 40 to 96%, with an average of 75%. This large amount of ground ice was in the form of ice lenses or veins forming well-developed cryostructures, mainly due to freezing of frost-susceptible sediment under water-saturated condition. Our analysis of geocryological characteristics in frozen ground including ice content, cryostratigraphy, soil mechanical characteristics, organic matter content and components, and water stable isotope ratio provided information to reconstruct terrestrial paleo-environments and to estimate the influence of recent maximum thaw depth, microtopography, and flooding upon permafrost development in permafrost regions of NE Russia. 相似文献