Formation Mechanism Of Red-strata Landslide Based On Water-rock(soil)interaction

Red-strata landslides are widespread in the Sichuan Basin and have the characteristics of group occurrence,which poses a great threat to people's lives,property,and engineering construction.Water is one of the main factors in the formation of red-strata landslides.From the perspective of water-rock(soil)interaction,the formation mechanism of red-strata landslides can be revealed more systematically and in-depth.In this paper,the internal mechanism and influence of water-rock(soil)interaction on the formation of red-strata landslides were studied through mineral composition analysis,microstructure analysis,geotechnical experiments,and simulation experiments and using the mineral composition as the starting point.The results are as follows:(1)Based on the analysis of the mineral composition,microstructure,strength,and deformation characteristics of the slip zone soil,the characteristic minerals that control the physical and chemical properties of the slip zone soil are clay minerals(mainly illite).Clay mineral(mainly illite)accounts for a large proportion of all mineral components in slip zone soil.Clastic minerals such as quartz and feldspar are wrapped by the clay matrix and do not assume the framework role in the soil.The strain-softening characteristics of slip zone soil are related to the tensile disintegration and particle rearrangement of clay minerals.The high cohesion and low internal friction angle of slip zone soil are caused by the characteristics of small particle size,large specific surface area,and surface charging of clay minerals.Studies have shown that clay minerals(mainly illite)are characteristic minerals in the landslide zone of red strata.Based on the above characteristics,it is concluded that clay minerals(mainly illite)are the characteristic minerals in the soil of the red-strata landslide.(2)Through the simulation experiment conducted in the high-pressure,open,and flowing system,the influence of different factors(pressure,p H,flow rate,and chemical component)on the chemical water-rock(soil)interaction was determined.The reaction rules of chemical water-rock(soil)interaction under different environmental conditions were determined through high-pressure open flow system simulation experiments.Montmorillonite and calcite,which are the representatives of clay minerals and clastic minerals respectively,were selected as the experimental materials,and the dissolution of minerals was selected as the research object.Results show that the dissolution rate of minerals increases with the increase of pressure,but the pressure has a certain limit to the increase of dissolution;(2)Different minerals have different responses to pressure,and the response of montmorillonite is far stronger than calcite;(3)The rate of mineral dissolution is negatively correlated with p H in the acidic conditions;(4)The flow rate effect of mineral dissolution is very complicated,which is affected by pressure,p H and mineral type;(5)Mineral dissolution does not satisfy the stoichiometric relationship.The phenomenon that different factors have different effects mainly related to the reaction position of mineral crystals,the H~+activity of the reaction solution,the reaction equilibrium state,etc.(3)Through the strength experiment,disintegration experiment,theoretical analysis,and other methods,combined with the characteristics of mineral crystals,the influence rule of water-rock(soil)interaction on the formation of the red-strata landslide were qualitatively and quantitatively determined.The clay mineral content in the slip zone soil continues to increase during the formation of the landslide due to the hydrolysis of feldspar minerals at the slip zone and the migration of the secondary clay minerals at other locations,resulting in the increase of cohesion and the decrease of the internal friction angle of the slip zone soil.The original minerals dissolve strongly in the acidic water environment,which causes the microstructure of the soil to change from dense to loose and broken,resulting in a significant decrease in the strength of the slip zone soil.The existence of expansive minerals such as illite and montmorillonite makes the soil possess the characteristic of disintegration,leading to the disintegration of the soil under the conditions of seasonal climate changes and changes in the reservoir water Table.A large number of fissures are developed in the slope,which not only provides seepage channels for groundwater but also enhances the sensitivity of slope safety factor to rain intensity.Before the rapid slide of the landslide,the infiltration of a lot of rainwater significantly increased the weight of the slope body.Simultaneously,it produced a higher hydrostatic pressure in the slope body,which promoted the occurrence of the landslide.