Study On Dynamic Constitutive Model Of Fully-graded Roller-compacted Concrete And Anti-knock Risk Assessment Of Gravity Dams

With the development of RCC(roller compacted concrete)construction technology,a large number of RCC gravity dams have been built in China.As an important part of the water control project,the dam integrates the functions of flood control,power generation,shipping and irrigation.It has remarkable political and economic benefits and is easy to become an important target of explosion attack in a special period.When exposed to extreme explosion loads,RCC gravity dam may suffer serious damage or even dam break,which will bring disastrous impact to the downstream of the project.Considering the major disaster and huge losses of dam explosive damage,the problems of the anti-explosion performance and explosion safety risk of RCC gravity dams are becoming increasingly prominent.It is not only an important work content related to river basin security and socio-economic stability,but also an inevitable key topic in the construction and management of water conservancy projects.The analysis of the blast-resistance performance of RCC gravity dam is inseparable from the accurate understanding of the mechanical properties and dynamic constitutive model of the damming material.However,it is necessary to scale the aggregate to meet the assumption of stress equilibrium in laboratory tests,and thus it makes it difficult to carry out in-depth research on fully-graded and layered dam RCC through laboratory test methods such as SHPB tests,which restricts the development of the RCC dynamic constitutive model.In addition,the research on performance-based dam explosion damage evaluation is still in its infancy,and there is little research on the risk assessment method of dam anti-explosion safety under underwater explosion.In view of the above problems,aiming at the anti-knock performance and safety risk assessment of RCC gravity dam in special period,by means of meso-mechanical tests,theoretical analysis,and numerical simulation,a series of studies have been carried out on the mechanical properties of dam material,modification of dynamic constitutive model,evaluation of the anti-blast performance,and evaluation of engineering antiblast risk.The specific research contents and results are as follows:(1)Study on dynamic mechanical properties of RCC based on meso-mechanics.Based on the random aggregate algorithm,the mesoscopic model of RCC with continuous aggregate particle size was established,and the uniaxial dynamic compression/tension meso-mechanical tests were carried out.The influence of specimen size,layer structure,and coarse aggregate gradation on the failure modes and dynamic strength was systematically analyzed.It can provide a basis for the revision of the dynamic constitutive model of the fully-graded dam RCC.The results show that the layer structure under quasi-static loads reduces the strength of RCC to a certain extent,but the effect of layer structure on the dynamic strength can be ignored.The dynamic tensile/compressive strength of RCC with continuous aggregate gradation decreases with the increase of the maximum aggregate size,and this decreasing trend increases slightly at high strain rate.The strain rate sensitivity of the compressive/tensile strength,failure modes and size effect of RCC is similar to that of the normal concrete.Moreover,the quantitative relationship of the quadratic polynomial considering the strain rate effect of aggregate gradation is given,which provides a basis for further research on the constitutive relationship of RCC.(2)Modification of the dynamic constitutive model of fully graded dam RCC.Based on the laboratory tests and mesoscopic simulations,the triaxial mechanical properties of RCC under different aggregate gradations were studied.On this basis,the failure strength surface model is revised considering the influence of aggregate gradation on triaxial strength.The influence of the inertia effect on dynamic strength enhancement is quantified by meso numerical simulation,and the mathematical relationship of the true strain rate considering the aggregate gradation is derived.The damage evolution function is modified,and the damage equation parameters are calibrated by the single element simulations of the uniaxial compression tests.Based on the LS-DYNA software,the anti-blast performance of the concrete slab under the air blast loads is simulated.The simulation results verify the applicability of the modified K&C constitutive model of the dam RCC for the anti-knock analysis.(3)Study on the anti-knock performance of RCC gravity dam.Using the modified K&C constitutive model of fully-graded dam RCC,taking the influence of reservoir water and the weight of dam,the effect of the detonation distance,explosive equivalent,and detonation depth on the blast damage effect of a typical RCC gravity dam is explored.The damage modes and weak parts of the RCC gravity dam under underwater explosion loads are further analyzed.Furthermore,the classification standard of the explosion damage of the concrete gravity dam is suggested.The prediction curves of the dam explosion damage level under different underwater explosion scenarios are given.(4)Research on the performance-based explosion damage evaluation methods of concrete gravity dams.Based on the analysis results of anti-blast performance,the correlation between the particle peak vibration velocity(PPV)and the proportional explosion distance and the proportional explosion depth,and it is used as the index to evaluate the damage of the dam head.On the basis of the shear strength formula for the dam foundation surface,considering the impact of the blast damage on the dam foundation surface,an formula for the anti-blast stability of the dam foundation surface is proposed.Starting from the anti-blast safety of the structural performance,taking the importance of the crack penetration,upstream surface damage,and the damage location to the water retaining function and overall structure safety,the overall damage index is defined.For the concrete gravity dam,based on the vibration characteristics of the dam head,stability of dam foundation surface and overall dam safety,reasonable evaluation indexes are proposed and corresponding performance levels are divided.(5)Research on the explosive damage risk assessment of gravity dams in view of the downstream losses.Considering the uncertainty of the blast loads and mechanical parameters of dams,the failure probability of different damage levels is studied based on the Monte Carlo simulation method.The estimation methods of the life losses and economic losses corresponding to non-dam break failure and dam break failure are proposed.The explosive damage risk assessment method of dam explosion damage considering downstream loss is suggested,and the explosion damage risk assessment of typical RCC gravity dam project is carried out.