Study on critical water pressure of hydraulic fracturing and its correlation with strength parameters of cement mortar under chemical solution erosion

The chemical erosion has a significant influence on the induction of the instability of cement mortar structure under high water pressure conditions. In this study,the cement mortar is tested on the three-field coupling test system and servo-controlled testing system. The hydraulic fracturing morphology,the evolution regularities in tensile strength and critical water pressure of hydraulic fracturing are analyzed by long-term chemical corrosion. The research results indicate that the effects of four solutions on the macro-performance of cement mortars are different. At the later stage of immersion stage,the damage deterioration of the cement mortar specimens soaked in pH=3 Na₂SO₄ solution increases with the immersion time. The degree of damage deterioration in pH=1Na₂SO₄ solution is the greatest,followed by those in pH=3 Na₂SO₄ solution,and then in pH=7 Na₂SO₄ solution. There are significant differences between tensile strength and the critical water pressure of hydraulic fracturing for corrosion degree under the action of water chemical solutions. As to the same condition,the corrosion degree of critical water pressure of hydraulic fracturing is greater than the tensile strength. Meanwhile,there is an obvious correlation among the critical water pressure of hydraulic fracturing and tensile strength of cement mortar under different chemical solution circumstances. In addition,the damage variable of fracture length and material strength are defined in terms of the failure criteria on critical stress of hydraulic fracturing which can be presented. Moreover,the functional correlation between the critical water pressure of hydraulic fracturing and tensile strength is presented,and a great quantities of experimental data are used to prove the analysis results. Finally,the applicable condition of functional relationship between critical water pressure of hydraulic fracturing and tensile strength is given.