Strength Deterioration And Chemical Mechanism Of Sandstone Under Dry-wet Cycles In Acid And Alkali Environment

The occurrence of geological disasters,such as landslide and collapse,were closely related to the long-term effect of water.Rock mass engineering will be unstable under the action of physical and chemical effects.Water-rock interaction is very important for engineering,relating to the crag,dam foundation,slope,cultural relic protection,which are basic research topics.In view of the complexity of sandstone deterioration mechanism under the action of dry-wet cycling in acid and alkali environment,supported by“the Research Fund of Ministry of Education for the Doctoral Program of Higher Education”and“National Natural Science Foundation of China”,summarized by the findings of predecessors,The uniaxial compression test,triaxial compression test,fracture mechanics test,ion concentration test were conducted under the action of dry-wet cycling in acid and alkali environment.Chemical thermodynamics,chemical kinetics and law of porosity evolution were introduced to explain the deterioration of sandtone.Main researches are described as follows:?1?In the soaking environment with pH=4,7,9,the sandstone samples were tested with 1,3,6,10 cycles?4 stages?.After uniaxial compression test,triaxial compression test and tensile test in each cycle stage,the Mohr-Coulomb strength criterion parameters and Hoek-Brown criterion parameters were obtained,and the degradation effect was analysised.According to the relation of partial stress space stress and strength criterion parameters,The failure curves changing with different number of cycles in?plane were obtained in different pH?pH=7,9,4?and cycles?n=1,3,6,10?.?2?The peak strength of SCB samples with inclined crack were obtained by fracture mechanics test with different pH?pH=7,9,4?and cycles?n=1,3,6,10?.The SCB specimen with thickness B=30mm,diameter D=76mm,span s=38mm,a=19mm crack,and the crack angle have degrees of 0,15,25,40,respectively.The I/II composite fracture toughness were measured by calculation of peak intensity with different PH values?pH=7,9,4?,dry and wet conditions?dry and saturated?and number of cycles?n=1,3,6,10?.The crack tip parameters?T stress,critical radius and crack initiation angle?were obtained through the improved maximum shear stress fracture criterion with different PH values and dry and wet conditions,and comparing analysis of test and improvement curve.By fitting the experimental data,the fracture criterion for engineering application is obtained.?3?Through the analysis of the mineral composition of sandstone,main minerals in sandstone:quartz,feldspar,calcite,biotite were selected as the research object.The main equation of chemical reaction of minerals in the sandstone are obtained in neutral,alkaline,and acidic environment,calculating the Gibbs function of the main mineral composition of dissolution reaction in acid and alkali environment using of basic principle of chemical thermodynamics,the main direction of sandstone mineral dissolution reaction was confirmed.Chemical dynamics was introduced to study the reaction rate of mineral and aqueous solution.Ion concentration(SiO₂,K⁺,Na⁺,Ca²⁺,Fe²⁺)were tested for each cycle.the ion generation rate was calculated by sandstone mineral dissolution in each stage,and the ralation between ion generation rate with cycles was obtained.The micromechanism of chemical action was explained.?4?The dissolution volume mineral quartz,potassium feldspar,albite,calcite,biotite and incremental in each stage were calculated by ion concentration(SiO₂,K⁺,Na⁺,Ca²⁺,Fe²⁺)of after the action of different pH?pH=7,9,4?and cycles?n=1,3,6,10?,respectively.to the and then get the.Relations among porosity increment and cohesion,internal friction angle,fitting compressive strength,the relationship between Hoek-Brown strength parameters were analysised,and the mechanism of sandstone deterioration was explained...