Study On Disintegration,Strength And Deformation Characteristics Of Middle Weathered Mudstone In The Red Bed Area Of Southern Sichuan

The Sichuan Basin is the most widely distributed region in my country.The red mudstone in this area has the characteristics of low strength,easy weathering,easy disintegration and softening in water,etc.It is the main cause of engineering geological problems such as engineering landslides,subgrade deformation and foundation instability.The thesis relies on the construction project of the Chongqing-Kunming high-speed railway project,and takes the middle-weathered red bed mudstone from the southern Sichuan area as the research object.Using the methods of data investigation,laboratory experiment and theoretical analysis,the chemical composition,mineral composition and basic physical properties of the red mudstone were obtained.Carried out the submerged disintegration test,free submerged disintegration test and disintegration resistance test of red bed mudstone under lateral conditions,comparatively analyzed the disintegration change rule of red bed mudstone under different conditions,and established the evaluation of the degree of disintegration effective indicators.Through the point load strength test,the strength characteristics of the red bed mudstone are analyzed,and the influence of the water-bearing state,bedding state and the fracture roughness on the strength is discussed.Drawing on the idea of load test and using the geocompression tester to design the red bed mudstone indoor deformation test method,the deformation characteristics of the red bed mudstone were mastered,and the influence of the water-containing state and the structure plane state on the sample deformation was analyzed.The main conclusions are as follows.(1)The red bed mudstone disintegration test under confined conditions found that the red bed mudstone disintegration is controlled by bedding,and cracks are more likely to occur at the bedding and develop along the bedding surface.The samples of different groups have different changes after being immersed in water.The parallel group has a small amount of mudstone on the surface,which is weakly constrained and stripped,but the interior of the samples is intact.The lateral confinement around the vertical group forms a strong constraint on the bedding,preventing cracks from spreading along the bedding plane.The internal constraints of the skewed group samples are weakened after the surface mudstone falls off,so they are greatly affected by the disintegration.(2)The process of red mudstone disintegration during free flooding can be divided into three stages: rapid disintegration,slow disintegration and long-term disintegration.In the rapid disintegration stage,due to the rapid change of the water content of the sample,surface spalling mainly occurs;in the slow disintegration stage,due to weak expansion,the internal stress distribution of the sample is uneven,and the pore fissure expansion is developed,which is mainly manifested as overall fragmentation;long-term disintegration At this stage,the waterrock reaction rate slows down and the disintegration tends to be stable.(3)The results of the red bed mudstone disintegration resistance test show that the aspect ratio is the best to evaluate the red bed mudstone disintegration degree.In the project,the red bed mudstone morphological characteristic index can be compared with the laboratory test results to analyze the degree of red bed mudstone disintegration to prevent damage to the project construction due to the disintegration.(4)Through the red bed mudstone point load strength test,it is found that the physical meaning of the point load intensity index calculated by the three-dimensional area method is clearer,and the influence of the sample shape,size and section roughness on the test results can be avoided.The F test and t test are used to compare the random errors and systematic errors of different calculation methods of point load strength.The results show that compared with the equivalent area method and the loading interval method,the three-dimensional area method has smaller random errors and systematic errors,and is reliable sexuality is higher.(5)The red bed mudstone deformation test found that the elastic modulus of the vertical group is 1.45 times that of the parallel group,and the anisotropy is obvious.After two days of immersion in water,the deformation increased significantly,and the deformation modulus decreased by more than 35%.After 15 days of immersion in water,the deformation modulus of the sample further decreased by 50%.After 30 days of immersion in water,the deformation modulus tended to be stable.