Study On The Evolution Of Bearing Capacity And Failure Mechanism For Water Bearing Concrete Media

The physical and mechanical properties and long-term service characteristics of concrete materials are significantly affected by the water environment.This thesis uses a combination of theoretical research,experiments,and numerical simulation to deeply explore the evolution of bearing capacity,failure mechanisms,as well as characteristics of ultrasonic and acoustic emission activities of concrete with different moisture content from macro and micro perspective.(1)Uniaxial compression tests with four moisture content conditions of 0%,2%,4%,and 5.5%(saturated),and ultrasonic and acoustic emission monitoring techniques are combined to study the impact of moisture content on the ultrasonic and acoustic emission characteristics of concrete samples.The research results show that the uniaxial compressive stress-strain curve of concrete samples have experienced the compaction and elasticity,the stable crack development,the accelerated crack development,and the failure stage.With the increase of moisture content,the crack initiation stress and strength of concrete first increase and then decrease,while the elastic modulus and Poisson’s ratio first decrease and then increase.The inflection points were observed in the fitting curves for moisture contents within 1.15–1.65%.With the increase of moisture content,the ultrasonic waveform of concrete media gradually becomes sparse,the wavelength increases,the amplitude decreases,and the velocities of P-wave and S-wave gradually increase.The acoustic emission activity of concrete materials gradually decreases with the increase of moisture content,and exhibits a time lag characteristic.The frequency of acoustic emission signals gradually evolves from medium and high frequency to medium and low frequency.(2)Based on acoustic emission moment tensor inversion,the damage types and stress state characteristics of concrete in different moisture content conditions were studied.It is found that with the increase of moisture content,the proportion of shear damage events gradually increases,and the damage mode changes from tensile during drying to shear during saturation.The T-axis direction of the main tensile stress gradually evolves from vertical to a vertical angle of about 30 °,consistent with the macro fracture surface.(3)Based on discrete element numerical simulation,the entire process of crack initiation,development,and penetration of concrete samples during uniaxial compression was studied.From a microscopic perspective,the causes of changes in the macroscopic bearing capacity of concrete specimens under different moisture content conditions and the damage evolution process were revealed.It is found that cracks first occurred in the transition zone of concrete media,then the development of shear cracks leads to the generation of tensile cracks,and the accumulation of the latter dominates the failure of the sample.With the increase of moisture content,the proportion of shear cracks in concrete samples gradually increases in the peak stress,while the proportion of tensile cracks decreases.In terms of energy,before the peak stress,the adhesive energy mainly increases,and after reaching the peak stress,the adhesive energy rapidly transforms into friction energy and damping energy.The adhesive energy of the sample at the peak stress is the largest when the moisture content is 2%,and it is the smallest at the saturated state.Combined with the laboratory test of acoustic emission monitoring technology and acoustic emission moment tensor inversion,this thesis deeply studies the mechanical properties of concrete under different water content conditions,and reveals the failure mechanism of concrete materials in different moisture content based on the evolution of ultrasonic and acoustic emission characteristics.Discrete element numerical simulation is used to reproduce the process and mechanism of material fracture at the mesoscopic level,and the above conclusions were compared and supplemented to verify each other.The results obtained are of great significance for revealing the physical and mechanical properties and damage mechanisms of concrete materials in the water environment,as well as ensuring the healthy operation of concrete projects.