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Characteristics Of Ancient Wreathering Crust Of The Cretaceous Redbed Mudstone In Lanzhou Area

Posted on:2016-03-30Degree:MasterType:Thesis
Country:ChinaCandidate:J J ZhouFull Text:PDF
GTID:2180330461475646Subject:Geological Engineering
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Red bed and loess are widely distributed in western China. The ancient weathered red bedrock under the loess frequently form the bottom boundary of the loess landslide, and it is the control boundary condition. Loess landslides related to the frequent occurrence of ancient weathered mudstone in the study area, which caused serious casualties and economic loss, and greatly restricted the local economical development. Therefore, knowing the weathering characteristics and engineering properties of weathered mudstone has important significance for the prevention and treatment of loess landslide in the study area. In this paper, we take cretaceous red weathered mudstone in Lanzhou city and the surrounding areas as research objects, nine rock profiles are selected for the hardness test, resilience test and magnetic susceptibility test based on detailed field geological survey, meanwhile, rock samples are collected in mudstone profile for laboratory integration test, processing weathering degree classification and zoning of red bed mudstone within the scope of 1 m under pebble bed, the interaction for collapsing of ancient weathered mudstone and water-rock interaction has been analyzed, the control function of the ancient weathered mudstone to loess landslides is discussed. Main conclusions are as follows:(1)The results of hardness test, the springback test and susceptibility test showed the same rule. Namely its value in the surface is smaller, with the increase of depth the value is increases. Variation coefficient also presents obvious change law, in argillaceous sandstone profile mutation is about in 10-30cm, in mudstone profile mutation is about in 50cm, and both mutations from 0.6 to 0.7 or so.(2) Magnetic susceptibility test of the nine rock profiles showed that each profile has same tendency which is the magnetic susceptibility is larger on the surface and decreases with the increase of depth; magnetic susceptibility is larger at 10-20cm of 4 sandstone profile surfaces and that of the rest 5 mudstone profile surfaces is also larger at 10-30cm, while the magnetic susceptibility is relatively smaller in the lower part of each profile along with fluctuation phenomenon. The cause of the increased surface susceptibility is mainly weathering and pedogenesis.(3) Disintegration test showed that rock disintegration is very strong at 0-30cm below pebble bed and the disintegration degree is close to 100%, rock disintegration is strong at 30-50cm and weaker at 50-100cm, also the weakest at 90-100cm, of which the disintegration degree is less than 50%.(4) Experimental results show that the depth of strong weathered layer at the surface of cretaceous ancient weathered red mudstone is rather larger which ranges 30-50cm under pebble bed, relatively the depth of strong weathered layer of argillaceous sandstone profile is smaller which ranges 20-30cm under pebble bed. Than the change rule of EC, Total Dissolved Solids (TDS) and pH in the process of the disintegration are synthetically analyzed, which showed that salt in rock loss seriously under the action of groundwater, and the alkaline of groundwater is heightened after the dissolution of soluble salt, which sped up the destruction of the rock cement, meanwhile, the shear strength decrease rapidly. Besides, this also makes the development of strong weathered mudstone at the bottom of loess turned into the slip surface of loess landslide much easier.
Keywords/Search Tags:red bed mudstone, ancient weathered crust, weathering instensity zoning, disintegrating, loess landslide
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