| The Azad Pattan Hydropower Project is an important infrastructure project in the field of energy cooperation between China and Pakistan.The project is one of the large-scale and substantial investment assistance projects in China.The Azad Pattan hydropower plant project uses the overwater cofferdam diversion method.The project has the characteristics of long over-water period of foundation pit,large fluctuation of construction intensity,tight total construction period and complicated construction management.The paper carried out an optimization study for the above characteristics and the following conclusions were obtained:Chapter 3 explores the impact of diversion tunnel discharge on the water level of the river’s mainstream,based on practical project requirements.A model is proposed which uses the Arcsin function to fit the water surface line corresponding to the design flow and the over-weir flow.This model can be used to derive the water surface line upstream of the outlet of the diversion tunnel when the flow and water level relationship of the river is known.This model is easy to use and better reflects the top-supporting effect of tributaries on the over-weir flow in the confluence than the flow-level query method.In Chapter 4,after analyzing the applicability conditions of double dike closure,the critical slope of the river and the distance between the upper and lower bump dikes are considered as two important quantitative indicators of the applicability of double dike closures.The paper uses the above two quantitative indicators to construct a new parameter-the comprehensive applicability of double dike closures.This parameter is simple and easy to use,which is convenient for decision makers to select the closure dike.Based on the comprehensive applicability of the double dikes,Chapter 5 analyzes other decision-making indicators of the diversion tunnel sand barrier and the closure method.The scheme decision of diversion tunnel and closure dike is made by fuzzy comprehensive decision.The improved correlated schedule risk analysis model is used to calculate the work duration distribution in the network schedule.On the basis of obtaining the distribution of each working duration,the approximate calculation method based on the classical PERT method is used to determine the critical path of the initial diversion stage of the Pattan hydropower station project.Finally,Monte Carlo simulation is used to calculate the construction reliability of the initial diversion stage of the Pattan Hydropower Station project.In Chapter 7,a total of three alternative construction diversion schemes are designed.Through the TOPSIS method based on the comprehensive weight,the closeness of the three schemes is calculated.The final scheme is the construction diversion scheme of the foundation pit dry land construction period of 7months.By calculating the mechanical cost difference caused by uneven construction,it is found that the 7-month foundation pit dry land construction scheme has great advantages in this respect compared with the5-month foundation pit dry land construction scheme.In Chapter 8,a time-cost multi-objective optimization model is established for the diversion scheme of7-month dry foundation pit construction.The model uses the Monte Carlo method to simulate the construction time and effective construction time of the cofferdam,and generates the reliability of the completion of the cofferdam on schedule.Under the constraint of reliability,the non-inferior solution of the multi-objective model is delimited,and the final diversion scheme decision is made according to the free time difference.Finally,it is considered that the Azad pattan project is suitable for the scheme with a diversion tunnel diameter of 13 m and a cofferdam height of 32.9 m. |
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