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1.
Quantifying rock fall hazards requires information about their frequency and volumes. Previous studies have focused on quantifying rock fall volume–frequency relationships or the weather conditions antecedent to rock fall occurrences, and their potential use as prediction tools. This paper is focused on quantifying rock fall occurrence probabilities and presents approaches for quantifying rock fall temporal distributions. In particular, von Mises distributions allow direct correlation between seasonal weather variations and rock fall occurrences. The approaches are illustrated using a rock fall database along a railway corridor in the Canadian Cordillera, in which rock fall occurrences were correlated to the morphology and lithology. A Binomial probability distribution applied to the annual rock fall frequency suggests an average daily rock fall probability of 1 × 10?2 across the study area. However, circular (von Mises) distributions associated with weather trends in the area, and fitted to monthly rock fall records, allow estimation of daily rock fall probabilities in different months. This approach allows a direct correlation between rock fall frequencies and seasonal variations in weather conditions. The results suggest daily rock fall probabilities between 4 × 10?3 and 8 × 10?3 for April through July and up to 2.1 × 10?2 in October. Moreover, local peaks in rock fall monthly records are quantitatively explained through the seasonality of weather conditions. Similar values are obtained when applying the Binomial distribution to monthly records. However, this last approach does not show strong distribution fits and does not allow a correlation between rock fall frequencies and seasonal weather variations.  相似文献   

2.
ABSTRACT

In this study, uniaxial compression experiments with seven different bedding angles and six numbers of freeze–thaw cycles were conducted to investigate the influences of freeze–thaw cycles on the elastic parameters and the uniaxial compressive strength of slate. The laws of the elastic parameters, uniaxial compressive strength and failure characteristics were analysed, and a new uniaxial compressive strength prediction model that considers the bedding angle and the number of freeze–thaw cycles as control variables was established and verified using the experimental data. The results showed that the uniaxial compressive strength, elastic modulus and shear modulus decreased exponentially with an increasing number of freeze–thaw cycles. However, the Poisson’s ratio increased linearly with an increasing number of freeze–thaw cycles. The uniaxial compressive strength initially decreased and then increased with increasing bedding angle. There are three forms of failure occurred during the tests: when the bedding angle was 0°≤β ≤ 26.6°, the splitting failure and shear failure occurred at the same time; when the bedding angle was 26.6°≤β ≤ 83.0°, sliding failure occurred along the bedding plane; and when the bedding angle was 83.0°≤β ≤ 90°, splitting failure occurred along the axial direction of sample.  相似文献   

3.
It is important to understand the effect of freeze–thaw cycles on the mechanical properties of rocks. In this paper, the variation of the uniaxial compressive strength, peak strain, elastic modulus and stress–strain curves of granite subjected to freeze–thaw cycles with different heating temperatures were studied experimentally and the relationships were derived. As the number of freeze–thaw cycles increases, the compressive strength and elastic modulus decrease, while the peak strain decreases. In addition, an increased temperature increases the peak strain while decreasing the compressive strength and elastic modulus. An expression for the initial damage for the adopted rock material due to freeze–thaw cycling was proposed based on the Loland model. The current research has established a solid foundation for further experimental studies on the fatigue behavior of granite after freeze–thaw cycling.  相似文献   

4.
Rock falls represent a large percentage of landslide-related hazards reported by Canadian railways in mountainous terrain. A 54.7?km-long section of railway through the Canadian Cordillera is examined that experiences, on average, 18 rock falls each year. An approach for rock fall hazard management is developed based on quantified risk. The approach focuses on defining railway operation procedures (freight train operations and track maintenance) that comply with quantified risks. Weather-based criteria that define periods when rock falls are more likely to occur along the study area are examined. These criteria are used herein to reduce exposure to rock falls and reduce their consequences. Several freight train operation strategies are proposed that comply with a tolerable level of risk adopted in this study for illustrative purposes. The approach provides a simple, flexible and practical strategy for railway operations that can be regularly adopted by the operators, and that is based on a more comprehensive assessment of quantified risk.  相似文献   

5.
Building stone of Anahita Temple seriously suffers from weathering due to long term freezing-thawing and salt crystallization processes. This article investigates possible changes of physical and mechanical characteristics of this stone subjected to freeze–thaw and salt crystallization ageing tests. Fresh samples obtained from the Chelmaran quarry (the main quarry supplying for Anahita Temple stone) were tested under freeze–thaw and salt crystallization experiments. The freeze–thaw and sodium sulfate salt crystallization are suggested to be the most effective factors affecting in apparent deterioration of the stone in compare to the magnesium sulfate salt crystallization test. Significant decreases in mechanical properties of the stone were observed after freeze–thaw and salt crystallization tests. However, more mechanical losses were recorded after the salt crystallization cycles than the freeze–thaw cycles. This is probably due to crystallization pressure of salt crystals in compare to ice wedging force, which promoted more development of micro-fractures in the specimens. Probably, intrinsic factors of the stone such as frequent calcite veins and stylolites, are the main factors that control the durability of Anahita Temple stone. Preferential weakening along these features during freeze–thaw and salt crystallization cycles led to physical destruction and strength loss of the stone. Based on comparison between experimentally induced damages and field observations, reasonably freeze–thaw process is major factor in weathering of Anahita Temple stone. It should be noted that recorded 102 frozen days for the region imply high destruction potential of the stone during freeze–thaw cycles.  相似文献   

6.
Altered and unaltered diabases are commonly deposited on hydrothermally mineralized slopes. To study their damage characteristics during freeze–thaw cycles, they were sampled from Cihai iron ore mine located in an extremely cold region, Xinjiang, China and examined using acoustic and X-ray diffraction experiments to analyze the differences in their main mineral components and explore their damage characteristics under freeze–thaw conditions. Based on the results of these experiments, their damage and degradation patterns were obtained and the evolution of their physical characteristics including the rock mass loss rate (L F), rock strength loss rate (R σ ), P-wave velocity loss rate (V l), and freeze–thaw coefficient (K f) was analyzed. In addition, two groups of equations were established to characterize the relationships of these physical and mechanical properties of the rock specimens with the number and temperature of freeze–thaw cycles. The results show that the mineral composition of diabase changes during its alteration, showing increased clay and calcite, and the degradation and evolution patterns of the physical and mechanical parameters (L F, R σ , V l, and K f) of the altered rocks during freeze–thaw cycles are different from those of diabase, with the altered diabase exhibiting greater damage than the diabase.  相似文献   

7.
This study focused on atmospheric freeze/thaw cycles in Norway and presents the results of processing daily thermal data from 20 Norwegian meteorological stations for the period 1950–2013. Its two major aims were: (i) to provide long‐term time series of atmospheric freeze/thaw cycle data for Norway, and (ii) to analyse their trends over the last six decades. The study highlights the spatial and temporal modalities of the distribution of freeze/thaw cycles in Norway. The differences in the seasonal distributions of cycles and their mean annual number are because of the geographical location of the stations (coastal or inland stations, lowland or mountainous stations) and result from the combined effects of oceanity, continentality, latitude and elevation. The annual average number of freeze/thaw cycles is similar in the north (90) and south of Norway (84) but shows notable differences between coastal stations (27) and inland and/or mountainous stations (114). Since the 1950s, prolonged periods of several years characterized by increasing numbers of cycles have given way to periods of decreasing freeze/thaw frequency. This cyclicity is linked with the Northern Atlantic Oscillation (NAO). Strong positive or negative phases of the NAO since the 1950s have induced marked increases (or decreases) in atmospheric freeze/thaw cycle frequency in Norway.  相似文献   

8.
The Calvert Cliffs, which form much of the western coastline of the Chesapeake Bay in Calvert County, Maryland, are actively eroding and destabilizing, yielding critical situations for many homes in close proximity to the slope’s crest. Past studies have identified that waves directly interacting with the slope toe control cliff recession; however, where waves do not regularly interact with the slope toe, freeze–thaw controls recession. This study investigated the validity of this second claim by analyzing the recession rate and freeze–thaw behavior of six study sites along the Calvert Cliffs that are not directly affected by waves. While waves do remove failed material from the toe in these regions, freeze–thaw is believed to be the dominant factor driving recession at these sites. Past recession rates were calculated using historical aerial photographs and were analyzed together with a number of other variables selected to represent the freeze–thaw behavior of the Calvert Cliffs. The investigation studied sixteen independent variables and found that over 65 % of recession at these study sites can be represented by freeze–thaw through the following variables: (1) slope aspect, (2) soil freeze–thaw susceptibility, (3) the number of freeze–thaw cycles, and (4) the weighted shear strength. Future mitigation techniques at these sites should focus on addressing these variables. Unmitigated, the Calvert Cliffs will continue to recede until a stable slope angle is reached and maintained.  相似文献   

9.
Disintegration of dolostones to dolomite powder (powderization) was a widespread phenomenon in Triassic dolostones of the Buda Hills, where the areal extent of powdered dolostones is large compared to similar occurrences elsewhere in the world. In the Buda Hills, dolostone disintegration proceeded in four stages that correspond to a gradual decrease in particle size, that is, from the parent dolostone to (1) crackle breccia; via (2) mosaic breccia (diameter <2 cm); via (3) mosaic breccia blocks ‘floating’ in dolomite powder; to (4) dolomite powder (diameter 100–300 μm). Stable isotope ratios and trace element compositions of dolomite remained constant throughout these stages, and there are no indications of dissolution in most locations, suggesting that disintegration was predominantly a mechanical process. Combining these findings with the geological history of the region, and supported by a simple freezing/thawing experiment and pertinent experimental studies on weathering of building stones, it appears that powderization in the Buda Hills was caused by repeated freeze–thaw cycles during and/or after the Pleistocene glaciations. Subaerial exposure under cold climate conditions involves multiple freeze–thaw cycles that create mechanical stresses in the rock framework related to the opposing thermal expansion of rock and water that freezes and of ice that liquefies. This process is herewith called ‘cryogenic powderization’. Our data further suggest that the synergy of four factors promoted dolostone powderization in the Buda Hills: (1) tectonics, which created a pervasive fracture network; (2) intercrystalline porosity of the dolostone; (3) relatively high water saturation; and (4) subaerial exposure under cold climate conditions.  相似文献   

10.
With the objective of establishing a distinction between deformation structures caused by freeze/thaw cycles and those resulting from seismic activity, we studied three well–exposed alluvial deposits in a section at Dogai Coring, northern Qiangtang Basin, Tibetan Plateau. Deformation is present in the form of plastic structures(diapirs, folds and clastic dykes), brittle structures(micro–faults) and cryogenic wedges. These soft–sediment deformation features(except the micro–faults) are mainly characterized by meter–scale, non–interlayered, low–speed and low–pressure displacements within soft sediments, most commonly in the form of plastic deformation. Taking into account the geographic setting, lithology and deformation features, we interpret these soft–sediment deformation features as the products of freeze/thaw cycles, rather than of earthquake–induced shock waves, thus reflecting regional temperature changes and fluctuations of hydrothermal conditions in the uppermost sediments. The micro–faults(close to linear hot springs) are ascribed to regional fault activity; however, we were unable to identify the nature of the micro–faults, perhaps due to disturbance by subsequent freeze/thaw cycles. This study may serve as a guide to recognizing the differences between deformation structures attributed to freeze/thaw cycles and seismic processes.  相似文献   

11.
四川雅安市雨城区降雨诱发滑坡临界值初步研究   总被引：6，自引：1，他引：6  
四川省雅安市雨城区位于四川盆地西部,素有"雨城"之称。地质灾害以滑坡为主,且有群发性、浅层、规模小、降雨诱发的特点。作者分析了雨城区大量历史滑坡和降雨量数据,结合雨城区滑坡发育特点,选择3日(72h)内发生2个以上滑坡的点作为统计分析样本,进行不同阶段降雨量耦合关系分析,应用滑坡前3日累计降雨量与3日前15日累计降雨量,建立了滑坡发生与降雨量的统计关系:在雨城区,当前期无降雨、3日累计降雨量达到70mm时,将有滑坡发生;15日累计降雨量达到339mm时,也将可能出现滑坡。  相似文献   

12.
Damages to natural building stones induced by the action of frost are considered to be of great importance. Commonly, the frost resistance of building stones is checked by standardised freeze–thaw tests before using. Corresponding tests normally involve 30–50 freeze–thaw action cycles. In order to verify the significance of such measurements, we performed long-term tests on four selected rocks over 1,400 freeze–thaw action cycles. Additionally, numerous petrophysical parameters were analysed to compare the behaviour of rocks in the weathering tests according to the current explanatory models of stress formation by growing ice crystals in the pore space. The long-term tests yield more information about the real frost sensibility of the rocks. A clear deterioration cannot be determined in most cases until 50 weathering cycles have been completed. In the freeze–thaw tests, the samples are also stressed by changing temperature and moisture, indicating that different decay mechanisms can interfere with each other. Thus, thermohygric and moisture expansion are important damage processes.  相似文献   

13.
Liu  Youneng  Liu  Enlong  Yin  Zhenyu 《Acta Geotechnica》2020,15(9):2433-2450

A constitutive model is proposed for tailing soils subjected to freeze–thaw cycles based on the meso-mechanics and homogenization theory. The evolution of meso-structure upon loading was analyzed within the framework of breakage mechanism. When the new model is formed, tailing soils are idealized as composite materials composed of bonded elements described by an elastic brittle model and frictional elements described by a double hardening model. Based on meso-mechanics and homogenization theory, the nonuniform distributions of stress and strain within the representative volume element are given by introducing a structure parameter of breakage ratio with the derivation of the strain coefficient tensor, which connects the strains of the bonded elements and the representative volume element. The methods for determining model parameters are suggested based on the available tested results. The model proposed here can predict the deformation properties of tailing soils experiencing freeze–thaw cycles with acceptable accuracy. The strain-hardening and post-peak strain-softening behaviors of tailing soils under various confining pressures as well as different numbers of freeze–thaw cycles are well captured, and the dilatancy and contraction features are also adequately represented.

  相似文献   

14.
奎屯河新龙口右岸山体崩塌原因及再次失稳可能性分析   总被引：1，自引：0，他引：1  
奎屯河新龙口段山体历史上多次发生山体塌滑破坏,最近一次山体崩塌较为反常地发生在1月寒冷季节,而不是通 常的7、8月雨季,针对该段山体频繁发生破坏而且还出现反季节崩塌这种特殊情况,从区域地质背景、地震作用、地形地貌、气 候及降水等几个方面分别详细论述了产生崩塌的原因,同时指出这次反季节崩塌产生的触发原因在于气候反常造成雪水入 渗、短时间内发生多次冻融,裂隙中液态水结冰产生膨胀力诱发了此次山体崩塌。采用赤平投影分析论证了潜在崩塌的可能 性问题,指出发生此次崩塌后的右岸山体仍然未达到稳定状态,还可能再次发生破坏,同时应用实体比例投影法圈定了最有 可能破坏的山体位置并对崩塌方量进行了计算,从而对山体潜在崩塌可能性及规模有了一定把握,对该段山体崩塌的防治具 有实际的工程意义。  相似文献   

15.
In order to enhance the detection of prospective rock falls in calcareous cliffs, 25 rock falls have been described in a more detailed way than for an inventory. They are representative of middle size rock falls (10 to 100,000 m3) occurring in the French Subalpine Ranges, at an elevation between 200 m and 2000 m. Structural conditions of the rock masses, morphology of the initial cliff surface and the scar, possible failure mechanisms and processes have been studied. Typical failure configurations have been identified, based on the attitude of the failure surface, in relation to the bedding planes and the cliff surface. Irregular cliff morphology appears to be another important susceptibility factor. In most cases, the classical comparison of the average planes of the main joint sets with the average plane of the slope could not define the potentially unstable masses. Rather, those ones are due to joint planes that deviate from their mean set plane or to irregularities of the cliff surface. The proposed investigation method to detect prospective rock falls mainly consists in observing stereoscopic aerial photographs in order to look for critical configurations. Once a critical mass has been detected, its failure probability for a period of the order of one century must be evaluated (or its life expectancy). The main factor to consider for this purpose appears to be the proportion of rock bridges in the potential failure surface.

The triggering factors of rock falls in our study area have been investigated, by analysing an inventory of 46 rock falls. Statistical tests have been carried out to study the relation between rock falls and daily rainfall, freeze–thaw cycles or earthquakes. A good correlation has been obtained with freeze–thaw cycles, a slight correlation with rainfall and no correlation with earthquakes. This suggests that ice jacking could the main physical process leading to failure by causing microcrack propagation.  相似文献   


16.
Repair mortar and mixture of repair mortar with porous limestone sand aggregate were tested under laboratory conditions. Water absorption properties and micro-fabric analyses with a combination of strength tests were applied to assess the durability and compatibility of repair mortar with porous limestone. Uniaxial compressive strength and flexural strength were measured after 3, 7, 14, 28 and 90 days of casting. Durability was tested by comparing strength test results of samples kept air dry, water saturated, dried in drying chamber, freeze–thaw and non-standardized freeze–thaw cycles. The results indicate that with time various trends in strength were observed. In general, limestone aggregate content decreases more the compressive strength more than the flexural strength of the mortar. Standardized freeze–thaw tests of saturated samples caused a rapid material loss after 25 cycles, while freeze–thaw tests of undersaturated samples demonstrated that even after 100 cycles the test specimens still have a significant strength. Water-saturated samples that contain 50% of limestone aggregate have a 50% loss of strength in comparison with saturated repair mortar, while air-dry and water-saturated repair mortar has a minor strength difference after 90 days. The use of smaller amounts of porous limestone aggregate in repair mortar allow the preparation of repairs that are compatible with the monuments of Central Europe that were constructed from porous limestone.  相似文献   

17.
We evaluate rock fall hazard along the railway corridor to Jerusalem, Israel, in the Soreq and Refaim valleys. For the purpose, we use a combination of historical information on past rock fall events, field surveys aided by the interpretation of aerial photographs, and numerical rock fall modeling. Historical information indicates that on July 11, 1927 an m L 6.2 Dead-Sea transform earthquake caused rock falls in the studied area. The seismically induced rock falls damaged the railway tracks. Field observations revealed that the source area for the 1927 failures was located in the Aminadav formation, at the contact with the Moza formation. At the stratigraphic contact, rock blocks 100–101 m3 in size are formed as a result of tensile stresses and associated fracturing in the dolomite of the Aminadav formation, combined with continuous creep of the blocks on the marl of the underlying Moza formation. We use topographical, geological, and geomorphological information to calibrate a three-dimensional numerical simulation of rock falls in the studied area. We use the results of the numerical modeling, and additional independent information, to assess rock fall hazard and the associated risk in the Soreq and Refaim valleys. Results indicate that in the studied area, rock fall risk to the railway line to Jerusalem is due primarily to Dead-Sea transform earthquakes, with m L  > 6. We identify nine sections of the railway line where rock fall risk exists, for a total length of 2.5 km. We further note that seismically induced rock falls can produce damage to the road network in the studied area, make it difficult or impossible for earthquake casualties to reach hospitals in Jerusalem. We conclude offering recommendations on how to mitigate the risk posed by earthquake-induced rock falls in the studied area.  相似文献   

18.
文章从坡面泥石流的形成条件入手，结合重庆北碚地区地质地貌和气象条件，分析了该地区从1962-2003年发生的坡面泥石流的数据及降雨资料，认为在该区域，降水是诱发坡面泥石流的决定性因素。通过对具体坡面泥石流事例的分析，认为坡面泥石流的发生与前期降雨量和短历时雨强关系密切，前期降雨量对泥石流形成的贡献比较大，短历时雨强主要起到激发作用，当短历时雨强指数〉550时，应发出泥石流危险警报。最后利用发生坡面泥石流前3日累计降雨量和当日前期降雨量，得出了该区域降水诱发坡面泥石流的临界雨量方程。  相似文献   

19.
In cold regions, hydrologic systems possess seasonal and perennial ice-free zones (taliks) within areas of permafrost that control and are enhanced by groundwater flow. Simulation of talik development that follows lake formation in watersheds modeled after those in the Yukon Flats of interior Alaska (USA) provides insight on the coupled interaction between groundwater flow and ice distribution. The SUTRA groundwater simulator with freeze–thaw physics is used to examine the effect of climate, lake size, and lake–groundwater relations on talik formation. Considering a range of these factors, simulated times for a through-going sub-lake talik to form through 90 m of permafrost range from ～200 to >?1,000  years (vertical thaw rates <?0.1–0.5  m?yr?1). Seasonal temperature cycles along lake margins impact supra-permafrost flow and late-stage cryologic processes. Warmer climate accelerates complete permafrost thaw and enhances seasonal flow within the supra-permafrost layer. Prior to open talik formation, sub-lake permafrost thaw is dominated by heat conduction. When hydraulic conditions induce upward or downward flow between the lake and sub-permafrost aquifer, thaw rates are greatly increased. The complexity of ground-ice and water-flow interplay, together with anticipated warming in the arctic, underscores the utility of coupled groundwater-energy transport models in evaluating hydrologic systems impacted by permafrost.  相似文献   

20.
Abstract: Permafrost (perennially frozen ground) appears widely in the Golmud-Lhasa section of the Qinghai-Tibet railway and is characterized by high ground temperature (≥ ?1°C) and massive ground ice. Under the scenarios of global warming and human activity, the permafrost under the railway will gradually thaw and the massive ground ice will slowly melt, resulting in some thaw settlement hazards, which mainly include longitudinal and lateral cracks, and slope failure. The crushed rock layer has a thermal semiconductor effect under the periodic fluctuation of natural air. It can be used to lower the temperature of the underlying permafrost along the Qinghai-Tibet railway, and mitigate the thaw settlement hazards of the subgrade. In the present paper, the daily and annual changes in the thermal characteristics of the embankment with crushed rock side slope (ECRSS) were quantitatively simulated using the numerical method to study the cooling effect of the crushed rock layer and its mitigative ability. The results showed that the ECRSS absorbed some heat in the daytime in summer, but part of it was released at night, which accounted for approximately 20% of that absorbed. Within a year, it removed more heat from the railway subgrade in winter than that absorbed in summer. It can store approximately 20% of the “cold” energy in subgrade. Therefore, ECRSS is a better measure to mitigate thaw settlement hazards to the railway.  相似文献   

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