Discuss The Engineering Properties Of Red Rocks In Changsha Region

The engineering properties of red rocks in Changsha region are systmeaticllly discussed for the first time in this dissertation. Through the comparison and statistics analysis of different description and different opinions on engineering tests for red rocks, this dissertation has proposed new mechanical indexes on red rocks in the studied area. The main topics of this dissertation include diagenetic environment of red rocks, its physical properties, its distribution and zonation, and its mechanical indexes.Yanshan movement took place during the Late Jurassic to Early Cretaceous, which makes Cretaceous strata widespread (about22percent) in Hunan Province. Due to hot and dry climate, those sedimentary rocks formed during the Cretaceous-Tertiary are usually red in color, thus, those rocks are usually named as red sandstone, red slate or red rock.The information on engineering geology and rock and soil test in Changsha region is widely collected, and various physical indexes of red rocks in this region including mineral component, color, specific gravity, bulk density and shear wave velocity are systematically summarized and analyzed. As one of clayrock, the complexity of red rocks depend on its mineral composition, lattice structure and diagenesis, and disintegration and argillitization of red rocks usually take place due to soaking, and its weathering and crack will happen because of water loss. However, since red rocks in Changsha region are rich in hydromic/illite, and lack of those unstable clay minerals such as Kaolinite and montmorillonite, its swelling-shrinkage properties are not obvious compared to some mudrock in other regions. The horizontal and vertical distribution of red rocks in Changsha region and its weathering zonation are discussed in this study, and application of weathering red rocks is also proposed. Except for Proterozoic slate occurred in the north of the Martyr Commemorate Park-Hongshan Temple and the south of Laodiao River, red rocks under Quaternary loose soils are widespread along the eastern bank of Xiangjiang River. The lateral changes in lithology and lithofacies are inhomogeneous, but the cyclicity in vertical direction is obvious, which can be ascribed to the differences in stability and resistance against weathering of different red rocks, since there are obvious differences in major rock-forming mineral type, structure, cement and cemented degree in different rocks or different parts in the same rock.The engineering mechanical properties of red rocks are also analyzed in this dissertation, and the undervaluation standard values on bearing capacity of foundation and pile foundation are emphatically discussed, and reasonable value selection is put forth based on the filed test results and engineering examples.The rock mass strength of red rocks in Changsha region is severely weakened during sampling and testing, therefore when the red rocks are used as foundation pile-supported load bed, the foundation bearing capacity f can not be simply calculated according to the result of uniaxial compression strength testing. The long-term practical researches in Changsha region reveals that, it is reasonable the reduction factor ψ is about0.4-0.8when the saturated uniaxial compressive strength is chosen as the fek value.Based on engineering practices and field loading tests in Changsha region, the standard value (qp) of end resistance for various weathering red rocks can be estimated in order to guarantee engineering safety as follows:2000-2400KPa for strongly weathering red rocks,3200-4800 KPa for weathering red rocks, and5400-8000KPa for slight weathering or fresh red rocks.