Study On Development Law And Engineering Characteristics Of Altered Rocks

The development law and engineering characteristics of altered rocks have important theoretical significance and application value for large-scale engineering construction and mineral resources exploration.In this paper,the altered rocks of Pan'an Pumped Storage Power Station in Zhejiang Province are taken as the research object.The rock and mineral characteristics,physical and mechanical properties,genesis and development law of altered rocks in the study area are systematically studied by means of field investigation,data analysis,laboratory tests and theoretical analysis.The geological analysis and engineering characteristics of altered rock are closely combined to answer the scientific questions of rock alteration degree classification and strength prediction.At present,the study of altered rocks mostly guides mineral resources exploration by identifying and ascertaining the development law of hydrothermal altered rocks.With the development of national economy,more and more large-scale projects have been built in area with altered rocks,and the engineering characteristics of altered rocks have become one of the common engineering geological problems in large-scale projects.Because the development law of altered rocks and engineering characteristics is a cross-disciplinary problem,there are still many key problems that have not been solved very well.At present,the traditional analytical methods such as micro-analysis and geochemistry of altered rocks,which have solved the problems of alteration origin,mineral structure and composition to a certain extent,but their engineering significance is still unclear due to the limitation of scale.Especially in the interdisciplinary field closely related to engineering,there is a lack of rapid identification and classification theory and method of rock alteration which can serve the engineering site.In order to solve this problem,new methods,ideas and means must be introduced to solve the problem.In view of the existing problems in the current research,research in the following four aspects were carried out in this paper:(1)Study on the characteristics of rock and mineral of altered rocks.According to the observation of hand specimens and thin section identification and analysis of altered rocks in the field,the rock types in the engineering area were identified;the analysis of major and trace elements,X-ray diffraction,scanning electron microscopy and energy spectrum of altered rocks showed that five alteration types of rock mass in the engineering area were identified;based on short wave infrared spectroscopy(short for SWIR),seven altered minerals in altered rocks in the engineering area were identified.(2)Study on engineering properties of altered rocks.The physical and mechanical properties of altered rocks are studied through laboratory physical properties tests(rock water content test,rock water absorption test,rock particle density test and rock mass density test)and laboratory uniaxial compression test.(3)Study on the development and distribution of altered rocks.The development law of altered rocks is analyzed on three spatial scales,and the investigation and analysis of altered rocks in five adits,three-dimensional altered geological model analysis of engineering area,and the analysis of altered rocks development characteristics in Jinhua and Xianju areas of Zhejiang Province are completed.The spatiotemporal development and distribution of altered rocks in Pan'an pumped storage power station are studied.(4)Comprehensive analysis.Based on the analysis of the historical background of tectonic evolution in southeastern China,the distribution of altered minerals in some areas of Zhejiang Province and the site investigation of Pan'an pumped storage power station,the viewpoint that rock alteration mainly develops along NE-trending faults in Zhejiang Province is demonstrated from three different spatial scales.The theory that the strength of altered rock is linearly related to the absorption peaks of several different wavelength points in the short-wave infrared region is put forward by introducing short-wave infrared spectroscopy,and which combined with Hoek-Brown strength criterion,a rapid identification system and method for rock alteration degree are established,and a method for estimating mechanical parameters of altered rock in engineering area by alteration geological strength index(short for AGSI)is proposed.Based on the above research,the research progress of this paper can be summarized as the following three aspects:(1)A study method of development law of altered rock based on the tectonic evolution history of the study area is proposed.Based on the deep analysis of regional geological background and geological conditions in engineering area,this method makes a scientific prediction of regional alteration development by studying the causes of rock alteration.In addition,the alteration development period of rock mass can be indirectly measured by this method.(2)A rapid identification and classification method of altered rock based on SWIR is established by introducing the SWIR testing technology.Through analysis,it is found that the intensity of altered rock has a linear relationship with the absorption peaks of several different wavelength points in the short wave infrared region.Based on the analysis of the apparent properties and the SWIR spectrum of the altered rock samples in the project area,a rapid identification and classification method of rock alteration site based on SWIR is established,and the rock alteration grade is divided into five grades.The evaluation index of this method is relatively simple,easy to grasp and operable,and it is convenient for rapid identification,evaluation and classification of alteration degree in site.(3)The geological strength index of rock alteration(AGSI)is proposed.A method for estimating the mechanical parameters of altered rocks is proposed by modifying the Hoek-Brown strength criterion.Based on Hoek-Brown strength criterion,AGSI is introduced into Hoek-Brown strength criterion,and combined with laboratory uniaxial compression test results of altered rocks,mechanical parameters such as cohesion,internal friction angle and deformation modulus of two main types of rock mass in three areas of the project area are estimated.The results can provide technical support for the determination of engineering design and construction scheme of the power station.The method incorporates the alteration factors into Hoek-Brown strength criterion,and expands the application scope of the criterion.The rapid identification and classification method of altered rocks established in this paper takes the altered rock in Pan'an pumped storage power station in Zhejiang Province as the research object.However,the different tectonic evolution history,stratigraphic lithology and other geological conditions in different areas lead to different rock and mineral characteristics,physical and mechanical characteristics of altered rocks and so on.Therefore,it is suggested to select altered rocks from different areas and lithologies to carry out research in order to further improve this method.In addition,remote sensing technology can be used to investigate the development of altered rocks on a larger spatial scale.