Study On The Characteristics Of Water Strength Change And Disintegration Fracture Type Of Lanzhou Red Sandstone

Lanzhou is located in the west,the upper reaches of the Yellow River,with a high groundwater level.At the same time,a large number of red sandstone layers are distributed in Lanzhou area.Red sandstone is a kind of special rock with very hard texture and high strength in the original state.However,it will soften when encountering water,the particles will fall off and disintegrate,and the strength will be greatly reduced.Because of this,after the construction of Lanzhou Metro test section,the construction process is slow and the construction period is very long.One of the most prominent problems in the construction process is that the high water head difference caused by the high groundwater level in the process of foundation pit excavation causes the groundwater to infiltrate into the red sandstone layer,resulting in its disintegration and softening.In order to explore the special property of red sandstone disintegration and softening when encountering water,this paper takes the red sandstone sampled from the construction site of Lanzhou Metro as the research object,obtains the red sandstone samples with different water content by titration method,carries out uniaxial compression test on them,obtains the stress-strain curve of different water content samples from the initial to the failure,and obtains the peak value of red sandstone with different water content at the same time The influence of water content on the strength,modulus of elasticity and peak strain of red sandstone is analyzed.The data of water content and mechanical properties are fitted.The mathematical model of water content and mechanical properties is summarized,and the influence mechanism is explained.The disintegration characteristics of red sandstone under different soaking time were studied by soaking test.The disintegration morphology of red sandstone under different soaking time is qualitatively described,and the particles after disintegration are collected,screened and statistically processed after drying.The particle size distribution of disintegration particles of red sandstone under different soaking time is analyzed,and the gradual process of disintegration is dynamically described from the perspective of particle transformation.In order to describe the degree of disintegration of red sandstone after immersion in water from a mathematical point of view,it is an urgent need for engineering application to evaluate and quantitatively analyze the disintegration process.According to the analysis,the disintegration process of red sandstone accords with the self similarity of fractal theory,so fractal theory is introduced to describe the phenomenon quantitatively,and the mathematical model of disintegration between particle size and particle size is established by statistics and screening of particles after disintegration,and the self similarity dimension is calculated by means of fractal theory,combining with the macro performance of disintegration When the fractal dimension is about 2.7,the disintegration of red sandstone is basically completed.