| Climate change in the northwest has received widespread attention in the last three or four decades,showing a trend of increasing temperatures and precipitation,with significant increases in precipitation in autumn and winter.In the low temperature environment from October to March each year,the freeze-thaw cycle affects the slopes of the red layer with crumbling and cracking,posing a threat to the construction and operation of buildings and transport projects in the deposit area.The red-bed mudstone absorbs water and then undergoes an uninterrupted water-ice phase change internally under the action of freeze-thaw cycles,the volume increment of pore ice squeezes the rock and destroys the overall structure of the rock.The infiltration of ice melt water along the pore space makes the internal structure of the rock more loose,and the development of rock fracture expansion causes slope instability,uneven settlement and other diseases.Studies of the effects of freeze-thaw cycles on red-bed mudstones under regional climatic conditions have mainly focused on the composition,structure and mechanical properties of red mudstones,and have mostly focused on the differences brought about by regional climatic differences.In this paper,a series of indoor tests on red-bedded mudstones under different numbers of freeze-thaw cycles were carried out in the Hui Cheng basin in the northwest region as the study area.To study the effect of the number of freeze-thaw cycles on the fracture development pattern in terms of both disintegration and cracking.Six machine learning models were used to predict the fracture rates of seven sets of tests based on the test data,and the machine learning model with the best prediction was proposed.The results of the study can provide experimental and theoretical references for the design of red-layered slopes affected by freeze-thaw cycles,early identification and prevention of slope diseases.The main work and conclusions are as follows:(1)Disintegration is the rock behaviour that occurs when cracks develop to penetration and can laterally reflect the development pattern of cracks.The disintegration characteristics under freeze-thaw cycles were analysed by indoor rock disintegration tests,in terms of particle size gradation curves,disintegration rates and logistic regression models of disintegrating particles.The results show that freeze-thaw cycles increase the proportion of small particle disintegrates,promoting the development of fine fractures and increasing the disintegration rate.As the number of freeze-thaw cycles increased,the disintegration rate increased from 80.16% to 94.55%,higher than the 55.42% of the non-freeze-thaw group.(2)Crack characteristics and mechanisms of red-bedded mudstone under different freeze-thaw cycles.A discussion of the stages of fracture development,the changes in each feature and the cracking mechanisms under freeze-thaw cycling is summarised based on water absorption fracture tests on circular pie-shaped specimens.Noting that freeze-thaw cycles mainly affect the stage of block development.There is a coupling between fracture length and even-width development,and crack development lags behind water absorption.As the number of freeze-thaw cycles increases,fracture rate in the stable phase increases from 13.41% to 19.30%.Explain the cracking mechanism in relation to penetration mechanics and stress.(3)Fractality prediction for red-bed mudstones based on six machine learning methods.Analyse the accuracy of each forecasting model against the forecasting data and compare the forecasting data index of the models cross-sectionally.35 predictions from the seven datasets had a validity rate of 88.6%.The preferred best prediction model is a radial basis function neural network and convolutional neural network,with accurate prediction of fracture rates and high model applicability. |
