Sherong Zhang

Risk identification on hydropower project using the IAHP and extension of TOPSIS methods under interval-valued fuzzy environment

Risk identification on hydropower project, the first step of risk management process, is an extremely complex issue and has a significant impact on the efficiency of the following risk assessment and control. On the other hand, finding out some more possible risk factors among many risk ones is a multi-criteria decision making problem. This paper develops an evaluation model based on the interval analytic hierarchy process (IAHP) and extension of technique for order preference by similarity to ideal solution (TOPSIS), to identify exactly the more possible risk factors under a complex and fuzzy environment. In this paper, the IAHP is used to analyze the structure of risk identification problems in hydropower project and to determine weights of the criteria and decision makers, and extension of TOPSIS method with interval data is used to obtain final ranking of potential risk factors in hydropower project. Risk identification on an earth dam is conducted to illustrate the utilization of the model proposed in this paper. The application could be interpreted as demonstrating the effectiveness and feasibility of the proposed model.

Comparative Study of the Dynamic Response of Concrete Gravity Dams Subjected to Underwater and Air Explosions

AbstractThe response of dam structures subjected to explosion shock loading is a key element in assessments for the dam antiknock safety and antiterrorism applications. The physical processes during an explosive detonated in underwater/air and the subsequent response of structures are extremely complex, involving many complex issues such as the explosion, shock wave propagation, shock wave–structure interaction, and structural response. In addition, there exists a significant contrast in wave propagation phenomena in the water and the air medium due to their different physical properties and interface phenomena. In this paper, a fully coupled numerical approach with combined Lagrangian and Eulerian methods is used to simulate the dynamic responses of a concrete gravity dam subjected to underwater and air explosions. The shock wave propagation characteristics from explosions in water and air are simulated and compared. The damage profiles of concrete gravity dams subjected to underwater and air explosions ...

Risk assessment of earth dam overtopping and its application research

The problem of dam safety is one of the most important research topics of water conservancy projects, and many researchers pay much attention to study the risk of earth dam overtopping. This paper synthesizes in the definition of risk the probabilities of dam failure and the corresponding losses, including the probability estimation, losses evaluation and criteria exploring risk approaches. Then, a comprehensive risk assessment system of dam flood overtopping is established, which is widely applicable. Gate failure, randomness of flood, initial water level and time-varying effects are incorporated in the failure probability model. Many complex factors are simplified in losses estimation. In addition, thresholds of various types of losses are proposed and are adapted to the national conditions. The methodology is applied to the Lianghekou hydropower station in China to illustrate the assessment process of flood overtopping risk and to evaluate its safe loophole with a view to the failure of spillway gates. Monte Carlo simulation and JC method programs are adopted to solve the model based on MATLAB tools and DELPHI. The results show that the losses pose significant impact on the risk assessment and should be considered in the assessment of risk. Probability calculation and loss estimation could be well combined with standards, providing a basis for risk management and decision-making.

Bayesian-Based Hybrid Simulation Approach to Project Completion Forecasting for Underground Construction

AbstractReal-time simulation is powerful in forecasting the completion probability of long-term projects with repetitive tasks but fails to consider the time-varying uncertainty of inputs caused by construction process variabilities. In this paper, an improved method is introduced for predicting the time-varying probability of project completion of ongoing underground cavern group projects using Bayesian updating techniques. Within a tailor-made hierarchical simulation model, the Bayesian approach is adopted to constantly update duration distributions of unfinished project activities according to onsite data. The probability of project completion can therefore be increasingly refined during the process. The methodology is further explained in a case study where its feasibility and advantage over traditional approaches are verified. The success may also be replicated in addressing other similar time-varying uncertainty issues inherently present in almost all construction projects.

A Real-Time Online Structure-Safety Analysis Approach Consistent with Dynamic Construction Schedule of Underground Caverns

AbstractBecause of the uncertainties present in geology and construction processes, construction projects in underground cavern groups are typically characterized by high degrees of uncertainty. The real-time safety analysis of underground caverns during construction has been a key technological issue because previous three-dimensional simulations have commonly failed to consider the time-varying changes in construction schedules and geological conditions. Thus, this study couples a construction progress simulation with a real-time dynamic analysis of engineering safety. In this study, a real-time online safety analysis approach based on four-dimensional technology during the construction of underground caverns is introduced, and a dynamic visualization management system of safety information in underground caverns during construction is developed using the OpenGL (Open Graphics Library) Tao Framework and C#, with which integrated management of information related to safety, including geological informati...

Long-Term Structural Responses of Orifices in Gravity Dams Considering Thermal and Creep Effects

AbstractA numerical simulation method is presented to analyze the thermal and creep effects on structural performance of orifices in gravity dams during construction and operation period. Time-dependent conditions such as the changes of gravity load and water pressure, the concrete viscoelastic material properties, and the variations of environment temperature are all considered for numerical modeling. Compared temperature results obtained from heat transfer analysis with the monitored data around orifice, proposed model is verified to be a reliable tool for thermal-structural coupling analysis. This paper discusses temperature distributions of orifice concrete surfaces in contact with water or air. Tensile stress evolutions arising from temperature variations are investigated correspondingly. Subsequently, cracking risks of orifice with different environments and locations are calculated to evaluate orifice structural performance. Thermal and creep effects on the distributions of tensile stress and crack...

Real-Time Safety Evaluation for Slope during Construction Using Numerical Forecast and Sensor Monitoring Platform

Geology uncertainties and real-time construction modification induce an increase of construction risk for large-scale slope in hydraulic engineering. However, the real-time evaluation of slope safety during construction is still an unsettled issue for mapping large-scale slope hazards. In this study, the real-time safety evaluation method is proposed coupling a construction progress with numerical analysis of slope safety. New revealed geological information, excavation progress adjustment, and the support structures modification are updating into the slope safety information model-by-model restructuring. A dynamic connection mapping method between the slope restructuring model and the computable numerical model is illustrated. The numerical model can be generated rapidly and automatically in database. A real-time slope safety evaluation system is developed and its establishing method, prominent features, and application results are briefly introduced in this paper. In our system, the interpretation of potential slope risk is conducted coupling dynamic numerical forecast and monitoring data feedback. The real case study results in a comprehensive real-time safety evaluation application for large slope that illustrates the change of environmental factor and construction state over time.

Influence of Ground Motion Duration on Responses of Concrete Gravity Dams

ABSTRACT This study investigates the duration effect on the responses and damage of a dam–reservoir–foundation system. A group of 95 recorded accelerograms with a wide range of durations are adopted in the analyses. A novel global damage index that takes into consideration the consequences of damage at different locations on the overall dam safety is proposed. Nonlinear analysis results show that the duration is positively correlated with the accumulated damage of the dam system. An amplification coefficient that relates the response of the concrete gravity dam from short-duration and long-duration ground motions is proposed.

BIM-Based Collaboration Platform for the Management of EPC Projects in Hydropower Engineering

AbstractEngineering, procurement, and construction (EPC) contracts are becoming the most common form of contracting in the hydropower trade for large-scale hydropower projects. Because of an increa...