Study On Energy Evolution And Mechanical Properties Of Red Bed Soft Rocks In South China Under Acidic Environment

Water-rock interaction is the most extensive and common problem in geotechnical engineering construction.Groundwater causes damage to rock mass through physical,chemical and mechanical aspects,which degrades its mechanical parameters and reduces its bearing capacity.With the use and discharge of oil and coal and human production activities,acid rain and groundwater pollution are increasingly serious,which makes rock mass unstable under the effect of time,inducing geological disasters such as collapse and landslide.Red beds are widely distributed in South China and have poor mechanical properties,which seriously affect the construction and long-term stability of geotechnical engineering.In view of the above problems,this paper has carried out an experimental study on South China red bed soft rock under acidic environment,and analyzed the deterioration law and mechanism of its mechanical properties.The main research results are as follows:(1)The physical properties of red-bed soft rock under acidic environment were analyzed.The results showed that the lower the acidic PH and the longer the curing time,the greater the mass loss rate of red-bed soft rock,and the faster the mass loss rate in the early curing period,and the white crystalline material was precipitated on the surface.(2)Mechanical properties of red bed soft rock under acidic environment are analyzed.The results show that: Under the double accumulation of acidic environment and time effect,the increase of acidity and curing time will increase the peak strain,decrease the peak strength,decrease the elastic modulus,and enhance the plastic deformation ability of red layer soft rock.In the triaxial compression test curve,the proportion of compaction stage gradually increases and the starting point of elastic stage shifts back.(3)The damage and deterioration of red-bed soft rock under acidic environment were analyzed.The results showed that with the increase of curing time and the enhancement of solution acidity,the damage of red-bed soft rock gradually increased,and the macroscopic failure mode of the specimen showed a trend from single inclined plane shear failure to conjugate shear failure and then to tens-shear composite failure.The microscopic failure modes of specimens tend to change from flake and scale structure to through-crack and then to dislocation in space.A mixture of calcium sulfate,kaolinite,orthosilicate and other substances was formed when the specimen was dissolved and hydrolyzed with the acid solution and attached to the surface of the specimen.(4)The constitutive model of red bed soft rock under acidic environment is derived.The results show that the statistical damage constitutive model derived by using Lemaitre equivalent strain principle and Weibull distribution is in good agreement with the experimental results,and can better describe the influence of PH change and time effect on the mechanical properties of red bed soft rock.(5)The energy evolution analysis of red-bed soft rock under acidic environment is carried out.The research results show that: the stronger the acidity and the longer the curing time,the greater the damage degree of red-bed soft rock,the lower the energy storage capacity and the total input energy.At the same time,the greater the initial damage degree,the more micro-cracks are formed,resulting in lower dissipation under load.