排序方式： 共有20条查询结果，搜索用时 531 毫秒
1.
The bedrock freeze-thaw and moisture regimes at an actively eroding site on the Niagara Escarpment, Bruce Peninsula, southern Ontario, were monitored between December 1983 and April 1984, and the results compared with amounts of debris collected in an adjacent rock trap. Frost wedging in pre-existing rock fissures is the primary mechanism responsible for the observed rockfall events; hydration effects are negligible. Debris production was more closely related to the duration of the freezing leg of the freeze-thaw cycle than to intensity or to cycle frequency. Release also coincided with periods of high pore saturation (> 60 per cent) and the seepage of water from cracks and fissures. Fewer freeze-thaw cycles were recorded in the air than at 1 and 3.5 cm in the bedrock. The number of cycles that could be declared geomorphologically effective according to established temperature criteria was normally less than half the total number of freeze-thaw cycles recorded in both air and bedrock. Under the current temperature regime at the field site, few effective cycles are capable of penetrating more than 5 cm into the free face. 相似文献
2.
The rate of bedrock weathering by frost action: Field measurements and a predictive model 总被引：1，自引：0，他引：1
Norikazu Matsuoka 《地球表面变化过程与地形》1990,15(1):73-90
Shattering rate, surface temperature, moisture content, and the physical and strength properties of bedrock were measured in four rockwall sites of the Japanese Alps. Five-year observations revealed that the bedrock shattering rate was usually much higher in the freeze-thaw period from October to next May than in the frost-free period from June to September. This indicates that frost action is the most important shattering process, although unusual heavy rainstorms in summer are also responsible for the shattering. A combination of some empirical relationships derived from recent laboratory experiments leads to a predictive model of the frost shattering rate. This model shows that the annual shattering rate is dependent on the annual freeze-thaw frequency on the rock surface, and the degree of saturation and tensile strength of the rock masses. The coefficients involved in the model were determined using the field data. 相似文献
3.
Kevin Hall 《地球表面变化过程与地形》1986,11(2):131-142
Rock moisture content is a major control of mechanical weathering, particularly freeze-thaw, and yet almost no data exist from field situations. This study presents moisture content values for rocks, taken from a variety of positions and conditions, in the maritime Antarctic. Additional information regarding the amount of water the rock could take up, as observed from laboratory experiments, is also presented. The results show that the approaches used in simulation experiments, particularly that of soaking a rock for 24 hours, may produce exaggerated results. It was found that the saturation coefficient (S-value) was a good indicator of frost susceptibility (based on water content) but that the derivation of that value may underestimate the potential of some rocks. The distribution of moisture within rocks is seen as an important, but unkown, factor. The results of these field moisture contents suggest that for simulations of freeze-thaw or hydration to be meaningful then they should have rock water contents based on field observations. 相似文献
4.
Kevin Hall 《地球表面变化过程与地形》1987,12(2):137-149
As part of a study on freeze-thaw weathering in the maritime Antarctic an investigation was made of the physical properties of the local rock. Tests were made of point-load compressive strength, Schmidt hammer in situ rock strength, moisture content, indentor resistance and the size range of weathering products. The resulting data were used to consider the form of freeze-thaw weathering operative in the field and its relationship to laboratory simulations. A distinct difference between ‘massive rock’ and ‘intact rock’ is observed in the field. It is suggested that future studies should generate a greater database pertaining to rock properties as it is an invaluable aid in the study of mechanical weathering. 相似文献
5.
Colin E. Thorn 《地球表面变化过程与地形》1979,4(3):211-228
Reduced major axis analysis is used to describe monthly temperature averages for daily maxima, minima, means and ranges at a sequence of bedrock microenvironments in the alpine zone of the Colorado Front Range. Seven thermistors buried at 1 cm in bedrock provide comparative data on easterly, southerly and westerly aspects, and also upon the impact of snow accumulation (?0.5m to ≥4.0m deep) against an east-facing rock wall. Intersite temperatures commonly differ by less than 5°C and, rarely, by more than 10°C. The freezing intensity of freeze-thaw cycles occurring within the confines of a seasonal snow patch rarely dropped to ?5°C, while at snowfree, vertical faces freezing dropped to ?5°C quite commonly. Comparison with laboratory established criteria for effective freeze-thaw weathering (abundant moisture and freezing to at least ?5°C) suggests that moisture rich microsites lack adequate freezing intensity, while adequately frozen sites lack moisture. Available data suggest that the overlap between freeze-thaw and hydration weathering requires careful re-evaluation. 相似文献
6.
7.
为明确不同含水率古土壤在冻融循环作用下其微观结构特性及古土壤损伤机制,采用核磁共振扫描仪对不同含水率冻融循环后的古土壤试样进行测试,研究冻融循环和含水率共同作用对古土壤微观结构的影响及土体内部损伤变化。结果表明:冻融循环下不同含水率使土体内部产生不同程度的损伤,损伤程度为含水率大的土体大于含水率小的土体。随着冻融循环次数增加,T2谱曲线信号幅度增加,孔隙结构改变,大孔隙、最大孔隙含量增加,中孔隙含量减小; 同时含水率较大的土体孔隙体积增大幅度大于含水率较小的土体,说明在季节冻土区建设工程中含水率越大土体越易发生破坏,因此在工程中应注意防排水问题。依据损伤力学原理,得出土体颗粒连续性与孔隙率关系,进而得出有效应力与孔隙率关系; 根据核磁扫描结果,建立孔隙率与冻融循环次数关系,最终推导出古土壤有效应力与冻融循环次数关系表达式。研究成果为季节冻土区古土壤地层建设工程提供理论指导。 相似文献
8.
A laboratory simulation of rock breakdown due to freeze-thaw in a maritime Antarctic environment 总被引：1，自引：0，他引：1
Kevin Hall 《地球表面变化过程与地形》1988,13(4):369-382
Results of freeze-thaw simulations on three large blocks of quartz-micaschist are presented. Three types of water to ice phase change were identified from temperature and ultrasonic measurements. It is suggested that the type of phase change results from a particular combination of rock moisture content, solute concentration, freeze amplitude, and rate of fall of temperature. The temperature at which ice thawed inside the rock (?0.7 to ?1.9°C) was also found, and this indicates the possibility of freeze-thaw effects without positive temperatures. Approximately 80 per cent of the water that will freeze under natural conditions, in the Maritime Antarctic environment under study, appears to have done so by ?6°. 相似文献
9.
针对西北地区特殊的气候条件和砾质土料源丰富的实际情况,提出采用宽级配砾质土代替黏土作为土工合成材料膨润土垫(GCls)的保护层共同构成垃圾填埋场复合防渗系统的构想。文中选取宁夏银川地区冲-洪积作用形成的天然砾质土料,经人工掺和制配成满足规范对GCls防渗垫保护层渗透系数要求的宽级配砾质土样,在实验室对该土样进行了冻融循环作用下的渗透性能试验研究。结果显示,随着冻融次数的逐渐增加,土样的冻胀率逐渐变大,渗透系数也相应增大,经过12次冻融循环后,渗透系数约增大1～2个数量级;冻融循环初期,冻融作用对土样的影响最为剧烈,随着冻融循环次数的增加以及时间的延续,土样性状逐渐趋于稳定。由于宽级配砾质土对冻融循环作用的敏感性小于粉质黏性土,故采用宽级配砾质土作为Cls/GM的保护层共同组成填埋场复合防渗系统是值得期待的。 相似文献
10.
冻融风化边坡岩体破坏机理研究 总被引：3，自引：0，他引：3
高寒山区岩质边坡冻融风化破坏严重影响公路建设及其运行安全。为了揭示岩体在冻融条件下的破坏机理,本文通过对高寒山区岩质边坡现场调查、编录,结合室内试验及数值模拟等,从不同尺度下综合分析岩体的冻融破坏机理。室内试验显示岩块受冻融后存在强度弱化现象,其受控于岩块的结构构造、胶结程度及初始损伤裂隙发育情况;冻融试验揭示岩体裂隙发育特征对冻胀变形性质起决定作用,裂隙的冻融破坏速率远大于岩块,密闭条件下,裂隙水冻结成冰过程中形成冰劈效应,冻胀力可达33MPa以上;数值分析揭示了边坡温度场受低温、大温差影响最为明显,裂隙带受冻融影响严重,其为边坡冻融风化的通道,裂隙水冻胀形成冰劈是边坡冻融风化破坏的主要模式。 相似文献