Research On The Mechanical Characteristics And Creep Properties Of Calcareous Mudstone In The Humidity Field

Three directions free swelling tests of calcareous mudstone specimens were conducted under laboratory conditions in this paper. By using YAW series microcomputer controlled electro-hydraulic servo compression testing machine control system combining with CTA-1 coal rock acoustic-electric data acquisition system supplied by American Physical Acoustics company, the uniaxial compression experiments on calcareous mudstone with different water content were carried out and the influence of humidity field on mechanical properties of the specimens was also analyzed. The constitutive model of the calcareous mudstone under humidity conditions was studied based on coupling equation of humidity stress field theory, elastic-plastic constitutive theory, damage mechanics and viscoelastic theory. The research results could provide helpful information for hydropower project, mining, construction, environmental and petroleum engineering on the rock hydraulics issues. The main achievements and innovative points are as follows:Based on theory humidity stress field and combined with elastic-plastic theory, elastic-plastic constitutive model of incremental type which had taken the humidity into account was found. The elastic-plastic constitutive relations and the loading-unloading criterion were derived from isotropic hardening model and kinematic hardening model.The time-effect law of full free swelling was studied through the tests of three directions free swelling. The concept of time threshold value was presented and the variation law of swelling strain versus time under laterally constrained condition was deduced hereby. By connecting with porous media theory, dynamic porosity model of unsaturated geotechnical medias which had considered humidity swelling effect was derived.By researching the effect of water content on mechanics and acoustic emission features, it was found that the elastic modulus and the compressive strength decreased with the increasing water content when peak strain showed the reverse trend. The damage evolution law of water-bearing rocks under uniaxial compression was also studied which had combined with the damage mechanics theory, and then the damage constitutive model of calcareous mudstone which had taken the loading and humidity together into consideration was deduced.The differential thermo-visco-elasto-plastic constitutive equation of rock which considers the influence of humidity on elasticity, viscosity and damage has been established based on the Nishihara rheological model by introducing humidity expand coefficient, viscosity attenuation coefficient and damage variable. Creep equation, unloading equation and Relaxation Equation of rock considering humidity effect have also been derived,and the theoretical model of multiaxial creep which can fully reflect the visco-elastic-plastic quality of swelling rock in watered state been established.Base on FLAC3D software and take 82 fifth middle yard in Qi-nan coal mine of Huai-bei coal industry group for background, numerical simulation of creep characteristics on several models of dry and moisture weaken surrounding rock roadway with and without supporting was performed, several rules of these models such as surface displacement, principal stress distribution, shear stress distribution, plastic zone distribution etc. were researched. Conclusions about the effect of water on roadway supporting design were obtained which provided a reference for supporting design.