Study On Physical And Mechanical Properties And Microscopic Characteristics Of Granite Weathering Crust Under The Influence Of Weathering Degree

Granite and its weathering crust are widely distributed in South China and Southeast China,and the stratum in which it is located is often chosen as the bearing layer of building foundation.The soil in the completely weathering zone and residual soil zone located at the top of the weathering crust of granite is often used in the filling foundation of railway and highway.Due to the weathering can produce weaken the engineering properties of granite weathering crust,understand the impact of the weathering degree of granite weathering crust is very important,however,geotechnical engineering on the properties of granite weathering crust did not form a unified and in-depth understanding,resulting in frequent accidents in the construction of related engineering,threat to people's life and property safety;Or the estimation of the mechanical properties of the granite weathering crust in the design is too conservative,resulting in a significant increase in the cost of the project and a delay in the construction period.Therefore,it is of great significance to study the relationship between weathering degree and various properties of granite weathering crust.In this paper,the basic physical properties,one-dimensional compression,static and dynamic triaxial tests and microscopic tests were carried out on the granite weathering crust soil layer on two slopes in Guangzhou.The main research contents and results of this paper are as follows:(1)One-dimensional compression tests were carried out for completely weathered and highly weathered granite specimens in original condition and remolded condition.The results show that the undisturbed and remolded specimens of completely weathered and highly weathered granite belong to medium compressible soil.Due to the existence of undisturbed specimen structure,the compression coefficient of completely weathered and highly weathered granite undisturbed specimen is smaller than that of remolded specimen,but the compressibility of the two specimens tends to be the same when the load is larger.Highly weathered granites have smaller initial pore ratio and larger pre-consolidation pressure,which result in less compressibility than completely weathered granites.(2)Triaxial consolidation undrained shear tests of completely weathered and highly weathered granite remolded samples were carried out.The results show that the critical state theory is suitable for describing the stress-strain relationship of completely weathered and highly weathered granite remolded samples.The stress-strain relationship of completely weathered and highly weathered granite remolded samples shows strain hardening,and the shear shrinkage trend of the samples in the initial stage changes to the shear dilatancy trend in the later stage.The total stress shear strength index c and ? decrease with the increase of weathering degree,while the effective stress shear strength index cohesive force c' shows a great discretization to the response of weathering degree.(3)Dynamic triaxial tests of completely weathered and highly weathered granite remolded samples were carried out.The results show that the remolded samples of highly weathered granite exhibit higher dynamic elastic modulus E_d and maximum dynamic elastic modulus E_dmax than those of completely weathered granite.Hardin-Drnevich,Romberg-Osgood and Martin-Davidenkov dynamic constitutive models commonly used in soil materials were used to fit the attenuation curves of dynamic elastic modulus of completely weathered and highly weathered granite.It is found that the Romberg-Osgood dynamic constitutive model has a good fitting effect.(4)micro-analysis of completely weathered and highly weathered granite and parent rock.The results show that both completely weathered and highly weathered granite are subjected to strong weathering,and the phenomenon of desilication and aluminium-rich ferritization is obvious.With the increase of weathering degree,the content of primary minerals in granite weathering crust decreases gradually,and the accumulated derived minerals increase.Four chemical weathering indexes are used to quantitatively analyze the weathering degree of granite weathering crust,and it is found that VR is suitable for evaluating the weathering degree of slope granite weathering crust.