Tensile Fracture Mechanism Of Compacted Artificial Gravel Soil And Its Application In Ultra High Earth And Rockfill Dam

With the planning and construction of a group of ultra-high core rock fill-dam, artificial gravel soil is more and more attented for its high deformation modulus, good anti-seepage and so on. Many accidents of core rock filldam was caused by the deficiency tensile capacity of core wall material. The artificial gravel soil is not exception as the core wall, restricting its engineering applications and a key issue desiderated to be solved. Therefore, studying the tensile fracture mechanism of compacted artificial gravel soil has great significant to in-depth understand its tensile fracture mechanisms and expand its application. In this thesis, based on the previous research works, the basic mechanical properties and tensile fracture mechanisms of artificial gravel soil, the hydraulic fracturing of earth-rockfill dam was studied, then a numerical simulation calculation was established to analyze the production process of hydraulic fracturing. The main research and achievements obtained in the thesis are as follows:1.The600mm type compactor was developed. This apparatus can be used to study the compaction characteristics of large size soil material, its maximum diameter is120mm.2.The feasibility of artificial gravel soil was studied as the anti-seepage material of300m level core earth rockfill dam based on the basic nature of the soil of Nuozhadu hydropower Station. It was concluded that the artificial gravel soil was easier to compacted than natural soil, relevant mechanical index increased, and its resistance to penetration has not been reduced due to join gravel, seepage damage resistance increased. The artificial gravel soil, its gravel content was35%,was entirely feasible to be used as the anti-seepage material of Nuozhadu hydropower Station.3. A series of untriaxial tensile tests, conventional triaxial tests, and triaxial compression-tension combining tests on artificial gravel soil were performed. The uniaxial, triaxial tensile failure mechanisms of artificial gravel soil was studied, triaxial tensile breaking strength criterion, untriaxial tensile failure constitutive model and triaxial tensile failure constitutive model was be proposed. And the constitutive model can be used to describe the stress and strain whole process of artificial gravel soil in compression and tensile. 4. The hydraulic fracturing predisposing factors was researched in this paper. Hydraulic wedge splitting effect model was established based on the anysis of permeability soft belt, laboratory tests and numerical analysis verification the correctness of the model. The effect of arch effect and permeability soft belt in core rock filldam to hydraulic fracturing was studied by numerical analysis, laboratory test and theoretical calculation. The foundation reason of hydraulic fracturing was the tensile fracture damage of core material.5. The numerical simulation calculation of hydraulic fracturing was established by combining the smeared crack model with Biot’s consolidation theory based on the analysis of total stress numerical method and effective stress numerical method. Examples verified the correctness of the calculation method, and specific measures of anti-hydraulic fracturing of core wall in Nuozhadu hydropower station was generated.