兰州地区白垩系红层泥岩的古风化壳特征研究

发布时间：2019-01-01 15:48

【摘要】：红层与黄土在中国西部地区广泛分布。黄土下伏的古风化红层基岩往往构成黄土滑坡的底界,是黄土滑坡形成的控制性边界条件。与古风化泥岩相关的滑坡在区内频频发生,造成了严重的人员伤亡和经济损失,极大地制约了当地经济的正常发展。因此,认清泥岩的风化特点和工程属性,对区内滑坡的研究和防治都具有重要意义。本文以兰州及其周边地区白垩系古风化红层泥岩为对象,在详细的野外地质调查基础上,选择了9个阶地卵石层下伏的古风化红层剖面进行了硬度试验、回弹试验和磁化率试验,同时在剖面上取样并进行了室内崩解试验,根据试验结果对卵石层下lm范围内的红层泥岩进行了风化带划分,综合研究了古风化泥岩的崩解性和水岩相互作用,讨论了古风化泥岩对黄土滑坡的控制作用。主要结论如下：(1)硬度试验、回弹试验和磁化率试验结果均显示出相同的规律,即在剖面表层其值较小,随着深度的增加其值增大。变异系数也呈现出明显的变化规律,泥质砂岩剖面上在卵石层下10-30cm处发生突变,泥岩剖面上在卵石层下50cm处发生突变,且均从0.6左右突变至0.7左右。(2)对9个岩石剖面进行磁化率试验,发现各剖面均呈现出表层磁化率较大,随着深度的增加磁化率值有所减小的趋势。其中4个砂岩剖面表层10cm到20cm磁化率值较大,20cm以下磁化率较小；其他5个泥岩剖面为表层10cm到30cm磁化率值较大,其下磁化率值较小,且有上下波动现象。表层磁化率升高的原因主要为风化作用和成壤作用。(3)崩解试验获取的岩石崩解性变化特征为：卵石层以下0-30cm的岩石崩解性很强,崩解度几乎接近100%；30-50cm的岩石崩解性较强；50-100cm崩解性较弱,其中90-100cm崩解性最弱,崩解度还不到50%。(4)对试验结果进行综合分析得到黄土层底部白垩系红层泥岩古风化壳表面强风化层深度较大,达到卵石层下30-50cm范围,相对来说泥质砂岩剖面强风化层深度较小,处于卵石层下20-30cm的范围内。结合泥岩崩解过程中水溶液EC、TDS和pH值的变化规律,认为在地下水作用下强风化岩石中的可溶盐损失严重,其溶解到地下水中后使地下水碱性增强,加快了地下水对岩石胶结物的破坏,导致岩石抗剪强度持续降低,使得黄土底部强风化泥岩容易发育成黄土滑坡滑动面。
[Abstract]:Red beds and loess are widely distributed in western China. The paleo-weathered red bed bedrock under loess often forms the bottom boundary of loess landslide and is the controlling boundary condition for the formation of loess landslide. Landslides associated with paleo-weathered mudstone occur frequently in the area, resulting in serious casualties and economic losses, which greatly restrict the normal development of local economy. Therefore, it is of great significance to recognize the weathering characteristics and engineering properties of mudstone for the study and prevention of landslide in this area. Taking the Cretaceous paleo-weathered red layer mudstone in Lanzhou and its surrounding area as the object, on the basis of detailed field geological investigation, the hardness tests of the paleo-weathered red bed section of 9 terrace pebbles are carried out. The springback test and magnetic susceptibility test were carried out. At the same time, samples were taken from the section and the indoor disintegration test was carried out. According to the test results, the weathering zones of red mudstone in the range of lm under the pebble layer were divided into weathering zones. The disintegration of paleo-weathered mudstone and the interaction of water and rock are studied synthetically, and the control effect of paleo-weathered mudstone on loess landslide is discussed. The main conclusions are as follows: (1) the results of hardness test, springback test and magnetic susceptibility test all show the same rule, that is, the value of the surface layer of the section is smaller, and the value increases with the increase of depth. The coefficient of variation also showed an obvious variation law. In the shaly sandstone section there was a mutation at 10-30cm under the pebble layer, and in the mudstone section there was a mutation at the 50cm under the pebble layer. All of them have mutated from 0.6 to 0.7. (2) the susceptibility tests of 9 rock sections show that the surface susceptibility of each profile is larger, and the value of susceptibility decreases with the increase of depth. The surface 10cm to 20cm susceptibility of four sandstone sections is larger than that below 20cm, while the other five mudstone sections are the surface layer 10cm to 30cm magnetic susceptibility value is larger, its lower magnetic susceptibility value is smaller, and has the phenomenon of fluctuating up and down. The main reasons for the increase of surface magnetic susceptibility are weathering and soil formation. (3) the characteristics of rock disintegration obtained by disintegration test are as follows: the rock disintegrating property of 0-30cm below the pebble layer is very strong, and the disintegration degree is almost close to 100g; The rock disintegration of 30-50cm is strong; 50-100cm disintegration is weak, among which 90-100cm disintegration is the weakest, and the disintegration degree is less than 50%. (4) it is found that the strong weathering layer on the surface of the Cretaceous red mudstone paleo-weathering crust at the bottom of the loess soil layer is deep, and the disintegration degree is less than 50%. To reach the 30-50cm range under pebble, the depth of strongly weathered layer in shaly sandstone profile is relatively small, which is within the range of 20-30cm under pebbles. Combined with the variation of EC,TDS and pH values in aqueous solution during mudstone disintegration, it is considered that the loss of soluble salt in strongly weathered rock under the action of groundwater is serious, and the alkali of groundwater is enhanced when dissolved into groundwater. It accelerates the destruction of rock cement by underground water, which leads to the continuous decrease of shear strength of rock, which makes the strongly weathered mudstone at the bottom of loess easily develop into the sliding surface of loess landslide.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.53;P512.13

【相似文献】