Research On The Seepage Behavior Analysis And Seepage Control Optimization For RCC Gravity Dams

Seepage performance is a key factor affecting the safety and stability of RCC dams.However,due to the particularity of the roller compacted concrete(RCC)dam structure,the complexity of the geological condition and the concealment of the seepage movement,it is difficult to accurately analyze and effectively control the seepage performance of the RCC dam.At present,the dam seepage behavior is analyzed using the seepage parameter inversion,seepage numerical simulation and seepage safety evaluation,and many meaningful research results have been obtained.However,there are still some deficiencies in the existing researches.Firstly,there is a lack of seepage parameter inversion methods that can both quickly and accurately invert the seepage parameters and fully consider the uncertainty in the inversion process.Secondly,it is difficult to accurately simulate the free seepage fields of RCC dams under complex geological conditions using the existing seepage simulation methods.In addition,the comprehensive safety evaluation model for the RCC dam seepage safety can't fully consider the uncertainty in the evaluation process.At the other hand,the seepage control structure optimization of RCC dams mostly use the single-parameter and single-target optimization method,which cannot fully consider the correlation between different design parameters,and it is difficult to obtain a seepage control structure design scheme that satisfies multiple target requirements at the same time.Therefore,to improve the reliability of the RCC dam seepage performance analysis and the effectiveness of the seepage control structure optimization,how to overcome the deficiencies in the existing researches is an important issue to be studied.In this article,we have thoroughly studied the seepage behavior analysis and seepage control optimization for RCC dams,and the achievements are listed as follows:(1)To solve the problem that the traditional Bayesian seepage parameter inversion methods can only consider the randomness,while neglect the grayness and unascertained uncertainty,and their solution efficiency and inversion accuracy are low,an improved seepage parameter inversion method is proposed by introducing the entropy-blind number theory,response surface model and Gauss-Newton method.Firstly,to fully consider the multiple uncertainties in the inversion process,the seepage parameters are regarded as blind numbers,and the entropy-blind number theory is introduced to analyze their uncertainties.Secondly,to improve the Bayesian parameter inversion efficiency,the response surface model(RSM)is used to replace the forward model which needs to be repeatedly invoked in the solution process.Thirdly,to improve the inversion accuracy of Bayesian inversion parameters,the Gaussian Newton(G-N)method is applied to optimize the inversion results.Then,the improved Bayesian seepage parameter inversion solution process is given.Finally,an example of the permeability coefficient inversion of a hypothetical two-dimensional rectangular earth-rock dam is used to verify the validity and accuracy of the proposed method.(2)To solve the problem that the RCC dam seepage simulation mostly uses Darcy law,which simplifies the seepage movement process and it is difficult to determine the free surface position effectively and accurately,and the geological conditions,dam details,and drainage holes are often greatly simplified in the modeling process,a numerical simulation method for the RCC dam seepage is proposed based on the fine geological modeling and CFD technology.Firstly,a modeling method for three-dimensional fine geological models,including the geological structure models and artificial object models,is proposed by effectively integrating the data sources of different scales and types.Secondly,a numerical model for the RCC dam seepage is established based on the CFD technology and the VOF method.Then,the seepage numerical simulation of RCC dams under complex geological conditions is later achieved through the coupling transformation between the three-dimensional fine geological model data and CFD model data,the finite volume method and PISO algorithm.In addition,an extended “fissure to represent line of holes” method is proposed to model the drainage holes with adjustable opening degrees.Finally,an RCC dam section is taken as a research object,whose seepage field is simulated and analyzed,and comparisons with in situ monitoring data demonstrate the reliability of the proposed methodology.(3)To solve the problem that the existing researches of the dam seepage safety assessment use the indicators that reflect the overall seepage safety and that can be monitored by existing technologies to establish an evaluation index system,ignoring the indicators that are difficult to monitor but have significant impact on local seepage safety,such as the dam overflow point elevation and the maximum hydraulic gradient of the dam foundation curtains,and they fail to fully consider the existence of ambiguity and randomness in the grade demarcation and data acquisition,a fuzzy comprehensive evaluation method for seepage safety of RCC dam is proposed based on the AHP-entropy weighting and cloud model.Firstly,on the basis of the conventional dam seepage safety assessment indicators(dam seepage flow,dam foundation surface uplift pressure,dam foundation seepage flow),two numerical simulation indicators are used as the evaluation indicators for the RCC dam seepage,which are difficult to monitor by existing technologies but have important impact on the local seepage safety,including the elevation of dam overflow point and the maximum hydraulic gradient of curtain,thus a multi-level and multi-index comprehensive evaluation index system for seepage safety of RCC dam is established.Then,a fuzzy comprehensive evaluation method of the RCC dam seepage safety based on the AHP-entropy weight and cloud model is proposed,which can overcome the dependence of subjective factors,consider the randomness and fuzziness in the evaluation process and quantify the degree of fuzziness of evaluation results.Finally,an RCC dam section is taken as a research object,whose seepage safety status is comprehensively evaluated,and the reliability and superiority of the proposed method are verified comparing with the traditional methods.(4)To solve the problem that the seepage control structure optimization of RCC dams mostly uses the single-parameter and single-target optimization method,which can't fully consider the correlation between different design parameters and it is difficult to obtain a seepage control structure design scheme that simultaneously satisfies multiple target requirements,and the current few studies that consider multi-parameters or multi-objectives still have problems with low solution efficiency or poor solution accuracy,a multi-objective optimization method is proposed for the RCC dam seepage control structures based on the surrogate model.Firstly,a mathematical model for the multi-objective optimization of the RCC dam seepage control structures is established through the analysis of the seepage control principles,design principles and design parameters of the main components of the RCC dam seepage control structures.Then,a model solution method is proposed based on the multi-objective particle swarm optimization(MOPSO)algorithm and the surrogate model,in which the MOPSO algorithm is applied to rapidly solve the Pareto solution set,and the surrogate model is used to establish an approximate relationship between the design parameters and the optimization objectives to replace the time-consuming seepage numerical model in the optimization process,thus the solution efficiency is improved,and the correlation between different design parameters is fully considered.Finally,the proposed method is applied to optimize the seepage control structures of a practical RCC dam and its effectiveness and advantage are demonstrated comparing with the traditional method.(5)Taking an RCC dam in southwest China as an example,the paper conducts an applied research of the proposed theory and method of the seepage behavior analysis and seepage control structure optimization of the RCC dam.Firstly,the project seepage parameter inversion is performed using the improved Bayesian seepage parameter inversion method.Secondly,the seepage parameter inversion results are used as the input parameters,and the RCC dam seepage numerical simulation method based on the fine geological modeling and CFD technology is used to simulate the project seepage field.Then,based on the seepage monitoring data and the seepage field simulation results,the dam seepage safety of the project powerhouse is comprehensively evaluated using the evaluation method based on the AHP-entropy weight and cloud model.Finally,to improve the project seepage safety performance,the multi-objective optimization method of the RCC dam seepage control structures based on the surrogate model is applied to optimize its seepage control structures.The project practice shows that the theory and method of the seepage behavior analysis and seepage control structure optimization for RCC dams proposed in this paper are scientific,effective and reliable,which can provide theoretical basis and technical support for the seepage analysis and seepage control design of RCC dam projects.