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The disasters caused by groundwater during underground cavern excavation, are inevitable and difficult to predict. In this study, transient seepage analysis was performed during the excavation of Qingyuan power station's underground caverns and drainage hole arrays. The drainage hole arrays around the caverns were simulated using a new method, and the groundwater surface during transient seepage analysis was confirmed with the hydraulic conductivity adjustment method, by using ABAQUS user subroutines USDFLD and GETVRM. By simplifying the drainage hole into face geometry, the proposed drainage hole simulation method could reach the accuracy of the widely used substructure method with half nodes of the computational boundary, and reflect the influence of drainage hole diameter on seepage analysis results. Moreover, a sensibility analysis of the diameter and space of drainage hole arrays could be conducted using one simulation model with the proposed finite element mesh type. Transient seepage analysis showed the evolutions of the groundwater level, flow rate and maximum hydraulic gradient of drainage holes and underground caverns, during the construction of Qingyuan power station. Such results could provide a reference for the creation of design and construction schemes. The previous excavation of the drainage hole arrays could control the seepage field, and reduce the flow rate and maximum hydraulic gradient of the underground caverns. This study may provide valuable reference to the design and construction of similar projects. [ABSTRACT FROM AUTHOR]

Finite element method (FEM) is usually used in dam and large underground cavern engineering to evaluate complex anti-seepage and drainage systems. In general, the substructure method is used to simulate the drainage hole array, but it becomes cumbersome when the number of drainage holes is large and the model is more complicated. In this study, the drainage holes were simplified and simulated as a line. The calculation results of the proposed method were then compared with those of the substructure simulation method and the well flow formula. This method has approximate accuracy, and it is easier to model with fewer nodes and elements compared with the substructure method. Based on the data of Heihe Reservoir, a three-dimensional equivalent continuum seepage FEM, reflecting the topography and geology of the dam area, was established, along with engineering layout and anti-seepage drainage system. The seepage field of nine different anti-seepage and drainage facilities were studied. The effects of drainage hole spacing and impervious curtain on seepage field were investigated. When the drainage holes were working normally and the drainage hole spacing was 2 m, the phreatic line in the dam body was the lowest and the drainage effect was the best. The analysis results showed that the failure of drainage holes on the left and right banks significantly influenced the seepage discharge of dam body and impervious curtain. According to the distribution of seepage field, a reasonable spacing of drainage holes is selected, and reasonable suggestions are put forward for anti-seepage and drainage in different parts. [ABSTRACT FROM AUTHOR]

The Qingyuan Pumped Storage Power Station is located in Liaoning, China and has large-scale water conveyance and underground powerhouse systems. In order to analyze the evolution of the flow rate, external water pressure, and hydraulic gradient of water conveyance and powerhouse systems or around them, a 3D equivalent continuum seepage finite element simulation model was established based on existing theories and a new drainage hole arrays simulation method was proposed in this study. The proposed method had approximate accuracy and was easy to model with fewer nodes and elements in comparison with the substructure method for complex hole arrays of diameter 5 cm. On the basis of four different conditions, the results show that the dehiscence of concrete lining lead to the peak values of the water conveyance flow rate, the water inflow of the powerhouse, and the water discharge of drainage hole arrays. The lapse of drainage hole arrays at a 50% rate resulted in the peak values of the external water pressure around the terminal of the diversion system and the hydraulic gradient around the upstream of drainage hole arrays. Besides, the hydraulic gradient around the downstream drainage hole arrays reached the peak value when the lower reservoir water level rose. [ABSTRACT FROM AUTHOR]

Check dams are applied worldwide as an effective approach for soil and water conservation. To improve the simulation accuracy of the hydrological processes in a catchment with a check-dam system, this study analyzed the applicability and accuracy of a formula for the drainage process of a perforated riser principal spillway based on observational experiments. The rainfall-runoff processes in a catchment with a check-dam system were also simulated with the recommended formulas for the drainage process of a perforated riser principal spillway. The deviations in the calculated discharge from the observed values of the experiment with the recommended formulas under normal and abnormal working conditions were within ±15% and ±5%, respectively. The hydrologic model used in this study needed only a few parameters to achieve a satisfactory simulation accuracy. The recommended formulas for the drainage process of a perforated riser principal spillway can improve the simulation accuracy of a flood peak by 7.42% and 19.58% compared with the accuracies of the technical code formula scenario and no drainage scenario, respectively. The results of this study are expected to provide a reference for flood warnings and safe operations of check-dam systems. [ABSTRACT FROM AUTHOR]

• Compare influence zone of cavern and drainage system with influence radius of well. • Statistical analyse the characteristics of 56 operational pumped storages. • Study the influence mechanism of model range on seepage analysis results. • Proposed the influence zone determination method for cavern and drainage system. The construction and operation of underground cavern and drainage system for pumped storage are threatened by groundwater seepage. Numerical simulation methods are commonly used for seepage analysis of cavern and drainage system. However, the method for determining the influence zone of the cavern and drainage system is unclear. The model range is difficult to confirm, and the accuracy of the analysis results is unwarranted. In this study, the engineering and geological characteristics of 56 operational pumped storages were summarised. Numerical simulation experiments were conducted based on steady seepage analysis of simplified pumped storage with cavern and drainage system. The influences of the model range on the groundwater level and flow rate of the cavern and drainage system were investigated, and a method for determining the influence zone was proposed for the cavern and drainage system. The results indicated that unclear influence zone of the cavern and drainage system existed in numerous pumped storages. Moreover, a small model range strongly overstated the results regarding the flow rate and groundwater level, as the groundwater drawdown at the computation boundary was ignored. Increased influence factors, including the right and left bank groundwater surface slope ratio, maximum water head depth above the cavern, and volume of the cavern, delayed the stable tendencies of the changes of the flow rate and groundwater level with an increased model range. With a receivable flow rate threshold, the proposed method could be used to predict the influence zone for the cavern and drainage system, and the optimal model range could be confirmed to improve the calculation accuracy of seepage analysis. [ABSTRACT FROM AUTHOR]