Safety Analysis Of Concrete Gravity Dams Considering Factors Uncertainty

Concrete gravity dams have played an important role in ensuring people’s life and stable socio-economic development,but once they fail,they will cause incalculable losses.In traditional concrete gravity dam safety analysis,deterministic analysis methods are often used.However,this method assumes that the factors affecting safety are deterministic and fails to consider the uncertainty of variables.Therefore,the results obtained by this method cannot fully reflect the safety status of the dam.This paper considers the uncertainty of influencing factors and takes an actual concrete gravity dam project as an example to conduct research on the analysis of factors affecting the safety of concrete gravity dams and the quantitative evaluation of reliability.The main research content and conclusions are as follows:(1)A sensitivity analysis framework for factors affecting the safety of concrete gravity dams has been proposed.First,according to the design specifications for concrete gravity dams,the safety factor of anti-sliding stability along the foundation surface,the stress at the dam toe and heel were selected as safety evaluation indicators,and corresponding loads and influencing factors were selected;Then,Sobol method,Garson method,Latin hypercube sampling and Gibbs sampling method are comprehensively used to analyze the sensitivity of the influencing factors;Second,consider the impact of different probability distribution forms,sampling methods,and value ranges of influencing factors on the sensitivity analysis results.The analysis results indicate that the main factors affecting the safety factor of anti-sliding stability include:anti-shear cohesion,upstream water level,anti-shear friction coefficient,and downstream water level;The main factors affecting the stress at the dam toe include:upstream water level and downstream water level;The main factors affecting the stress of the dam heel include:the upstream water level.The use of different probability distribution forms,sampling methods,and value ranges for influencing factors has a relatively small impact on the sensitivity results of factors affecting the safety of concrete gravity dams.(2)The main assumptions used in this paper were determined using literature statistics,orthogonal experiments,and comparative analysis methods,including:simplifying the model to a two-dimensional plane strain problem;The dam body concrete adopts a linear elastic constitutive model,and the dam foundation adopts an M-C ideal elastic-plastic constitutive model;Using thin layer elements to simulate the contact between the dam body and foundation;Assuming that the dam body is impermeable and the dam foundation is permeable,the water load is applied to the upstream and downstream surfaces of the dam body and the dam bottom surface in the form of surface force;Fixed constraints are applied to the bottom boundary of the foundation,and horizontal chain rod constraints are applied to both sides of the foundation.The size of the foundation model was determined using orthogonal experimental method:both upstream and downstream of the foundation,with a depth of 3 times the dam height;Using comparative analysis method to determine the grid division scheme of the foundation model:the size of the grid gradually changes from 2m at the bottom of the foundation to 50m at the boundary of the foundation.(3)A reliability calculation method for concrete gravity dams based on improved particle swarm optimization least squares support vector machine(IPSO-LSSVM)was constructed to address the problem of difficulty in accurately obtaining explicit nonlinear functional functions in solving the reliability of concrete gravity dams.The average particle distance,swarm fitness variance,inertia weight coefficient decreasing in parabolic form,and dynamic adjustment strategy of learning constants are introduced into the PSO algorithm to tune the hyper-parameters of LS-SVM regression models,so as to establish IPSO-LSSVM models reflecting the relationship between influencing factors and safety evaluation indicators;Based on this,functional functions for solving the reliability of concrete gravity dams is established,and the Monte Carlo method is used for reliability calculation.The results show that the IPSO algorithm has a significant improvement in performance compared to the PSO algorithm;The IPSO-LSSVM model can effectively solve the problem of implicit and highly nonlinear functional functions;The reliability calculation method for concrete gravity dams constructed can efficiently and accurately calculate the reliability of concrete gravity dams.