| Carbonaceous mudstone(CM)is widely distributed in Southwest China,where the annual precipitation is usually 1200-2000mm or even higher.The carbonaceous mudstone disintegrates when experiencing dry-wet cycles and temperature changes.After disintegration,its strength decreases sharply,wetting deformation is large,and there is continuous disintegration phenomenon,which resulting in layered disintegration of carbonaceous mudstone from the outside to the inside.Therefore,it is urgent to carry out improvement research on carbonaceous mudstone to improve its application in engineering.This paper takes disintegrated carbonaceous mudstone(DCM)as the research object,mainly relying on the key project of the National Natural Science Foundation of China " The catastrophic mechanism,evaluation method and control measures of artificial mudstone slope under thermo-hydro-mechanical coupling action".Carried out the research on the improved DCM solidification effect and embankment slope stability,and selected polyvinylidene fluoride two kinds of polyurea hydrophobic materials were used to modify DCM.Compared with the traditional improved material cement,the changes of mechanical strength,hydraulic properties and water stability before and after improvement were studied.The changes of microscopic morphology,pores,composition,fabric and reinforcement mechanism of DCM before and after improvement were analyzed by various microscopic tests.Based on the tensile shear composite failure criterion and the obtained mechanical strength test data,the relationship between the mechanical strength of modified pre disintegrated carbonaceous mudstone is analyzed;Based on the strength reduction method considering tensile strength,the stability of embankment slope is calculated by FLAC3D.They have certain theoretical significance and engineering application value.The main research contents and relevant conclusions are as follows:(1)The mechanical strength of modified DCM is improved obviously,but the process of improving DCM by polyvinylidene fluoride is complicated.Multiple linear regression was used to analyze the factors affecting the strength of modified DCM.The results showed that the main factors affecting the strength of DCM modified by cement were curing days,cement content and water content.The main factors affecting the strength of DCM modified by polyurea are dosage,component A:B and water content.(2)The dry-wet cycle has a great negative effect on DCM modified by cement,and the compressive capacity of the samples drops sharply after 10 drying-wetting cycles.The uniaxial tensile strength of DCM modified by polyurea does not change obviously with temperature and is almost not affected by high humidity.The uniaxial tensile strength decreases with the increase of the number of dry-wet cycle,but the decreasing range is gradually weakened.The shear strength of specimens decreases gradually with the increase of the number of dry-wet cycle,which is similar to the uniaxial tensile strength and unconfined compressive strength.(3)The saturation osmotic coefficient of DCM modified by cement decreases with the increase of compaction degree and water content,with the increase of curing days,it first decreases and then stabilizes,and increases with the increase of dry-wet cycle.The saturation osmotic coefficient of DCM modified by polyurea is negatively correlated with compaction degree,polyurea content,water content and curing days,and is basically in the same order of magnitude as the DCM modified by cement.(4)The soil-water characteristic curve of modified DCM was obtained by combining pressure plate instrument and filter paper method,the corresponding volumetric water content of the two methods was highly consistent in the range of<200kPa matric suction.When the cement content is higher,more water is needed,and the water holding property of the sample is worse.The degree of influence on water holding capacity of DCM modified by polyurea is as follows:dosage,component A:B,compactness.The more times of dry-wet cycle,the residual water content becomes smaller.Based on Childs&Collis-Geroge(CCG)model,the permeability coefficient curve of DCM modified by polyurea(5 wt%)was predicted.The permeability coefficient increases from unsaturated state to saturated state.The permeability coefficient decreases with the increase of matric suction.The relationship between permeability coefficient and matric suction or volumetric water content can be expressed by exponential function.(5)With the increase of dry-wet cycle,the graded CM blocks disintegrated rapidly,the content of fine particles increases,and the disintegrated particles undergone a process from uniform to uneven,and then to uniform.With the increase of vertical load,the particle disintegration is more sufficient.The addition of polyurea can effectively slow down the disintegration of graded CM,and the effect of polyurea content of 5 wt%is better than that of 10 wt%,but it is also affected by the destruction of polyurea layer by mechanical sieve.There is an obvious linear positive correlation between the disintegration ratio Dr and the standard basic entropy A.The smaller the standard basic entropy,the smaller the disintegration ratio,and the greater the degree of particle disintegration.The standard basic entropy A of CM first decreases rapidly with the increase of dry wet cycles,and then tends to be stable.With the increase of vertical load,the standard basic entropy A decreases as a power function.(6)The cement hydration product hydrated calcium silicate can fill the pores between the DCM particles,and agglomerate DCM particles into aggregates.The soil particles are wrapped by cement hydrate to form large particles,the inter-particle cementation exhibits a cemented particle-pore-cemented particle structure.The fluorinated chain segment can shield the polarity of polar groups,so that the surface of polyvinylidene fluoride has hydrophobicity.Polyvinylidene fluoride has good cementation,which can fill the pores in DCM,effectively increase the bonding strength of DCM particles,and solidify the particles into a new whole.Polyurea modified DCM into hydrophobic composites with cementation through polymerization,the three-dimensional bond is formed in DCM,which makes the modified sample become a four phase material,reduces the porosity and improves the mechanical strength and crack resistance of the composite.(7)The composite failure criterion of tension and shear is more suitable for engineering practice.There is a good linear relationship between unconfined compressive strength and uniaxial tensile strength of modified DCM,and the relationship between uniaxial tensile strength and shear strength can be fitted by a hyperbola.Taking an embankment section of Liuzhou Heshan Nanning expressway as the research object,the stability of DCM and modified DCM are analyzed.The safety factor of the DCM slope after 10 dry-wet cycles is 1.21,which no longer meets the specification requirements of no less than 1.25.And the safety factor of the improved DCM slope does not change much after 10 dry-wet cycles.By analyzing the horizontal displacement and the vertical deformation,the slope of DCM with 10 dry-wet cycles is the maximum value,which is 0.10 and 0.43mm respectively,while the horizontal displacement and the vertical deformation of the modified DCM is very small,which is about 1/104～1/102 of the embankment slope of DCM with 0 dry-wet cycle. |
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