In deep stormwater tunnel systems (DSTSs), entrapped air pockets are prone to pressurization and deformation during rapid filling, resulting in pressure surges that threaten system security. This study investigates the effects of structural and inflow parameters on peak pressures. To simulate the pressure surges of entrapped air pockets, a rigid-column model was developed for a simplified DSTS configuration comprising two shafts and one tunnel. The global sensitivities of the air pocket, system structure, and inflow parameters were calculated using the Extended Fourier Amplitude Sensitivity Test (EFAST), which employed indicators of the maximum pressure and relative increment. The results indicate that parameters related to the shape and initial state of the air pocket exert a substantial and direct effect on pressure surges in rapid filling, whereas tunnel system parameters tend to exhibit minimal influence. Notably, compared to the total inflow discharge, the flow difference between two shafts imposes a more significant and direct impact. For the maximum pressure of air pocket, the initial pressure and the maximum water level height of shafts demonstrate more pronounced effects. The proposed sensitivity analysis could be integrated into methodologies for system safety assessment, while the rigid-column model may be extended to accommodate multiple shafts and air pockets.

The Urban Drainage Network (UDN) is a type of underground municipal infrastructure responsible for transporting sewage and rainwater. To keep abreast of the hydraulic and water quality conditions of the pipes and to detect problems such as pipe clogging, pollution and leakage, real-time monitoring sensors have been widely adopted, accomplished with the development of IoT technologies. However, the intricate topology and numerous nodes of drainage pipes complicate IoT sensor placement strategies, especially in the selection of sensors and the location of monitoring points. This review examines application cases of IoT sensors in UDNs and some other hydraulic networks, evaluating the characteristics and applicability of various optimal placement methods and theories. A general framework was proposed applicable to the optimal placement of IoT sensors in the UDN, including object classification–method selection–quantitative evaluation. Currently, the quantitative evaluation of monitoring schemes lacks a systematic process, and existing layout methods may not be optimal. Future research can explore dynamic optimization strategies through phased deployment and feedback iteration, which can enhance the accuracy and objectivity of sensor layout design and evaluation.

The pressure surges for water filling in deep stormwater storage tunnels (DSSTs) with entrapped air-pockets seriously threaten the safety of pipeline structures and even lead to the destruction of urban water infrastructure. Hence, this paper develops a volume of fluid (VOF) model to study pressure surges in a two shafts and one tunnel system. Research works under different initial air-pocket parameters are carried out, while the VOF model is verified by the empty tunnel water filling experiment in the same system. The results show that the maximum pressure increases with an initial length/diameter ratio decrease or air volume fraction increase. Also, the extreme pressure with entrapped air-pocket at a certain scale can reach 1.6 times the static pressure (30 m). With the increase of initial air volume fraction, the frequency of pressure surges slows down, while the maximum pressure gradually increases and approaches a specific value within a fixed air volume fraction range (0.2–5.0%). The maximum pressure of air-pocket at different initial positions shows a downward trend from the middle of the tunnel to two sides, while the pressure of the air-pocket near a higher shaft will be slightly higher. The proposed model can be extended to systems with multiple shafts or air-pockets, and the conclusions have reference significance for structure design and water filling control in the DSST.

Long-distance water supply systems are important measures to improve the water resources distribution, and the water hammer protection devices such as air vessels are usually added in the project to ensure the safety and stable operation. However, the sediment particles are always ignored in the design. Hence, a numerical model and program were established for sediment laden water hammer based on the method of characteristics (MOC). Using the proposed model, the water hammer protection influences of sediment particles parameters are simulated for the same pipeline system of a water supply project. The result shows that the resistance loss of sediment-laden water in pipelines is larger than that of water, and the initial head of pump needed to be increased to ensure the water levels of downstream reservoirs are consistent. After power failure and pump stopping, the negative pressure wave of sediment-laden water is 2.97 m higher than that of water, and the theoretical minimum internal pressure along pipelines is 7.8 m lower. With the same air vessel protection, the lowest minimum internal pressure heads along pipelines decrease with the increase of quantities of sediment, while the results show no obvious influence by changes of median particle diameters. The lowest absolute pressure of pipeline could reach −0.69 m under the condition of 50 kg/m3 quantity of sediment and 0.05 mm median particle diameter. The relevant research results are of great significance sediment-laden water hammer numerical simulation and water hammer protection design.

Deep tunnel systems are characterized by large burial depths, long distances, and free-surface pressurized flows, operating under complex inflow conditions that can lead to strong pressure oscillations, particularly in the transitions between the main tunnel and shafts. This paper focuses on the deep tunnel system in Shanghai, China. A physical model was established based on the gravity similarity, and a corresponding one-dimensional mathematical model for free-surface and pressurized flows was established. The entire process of water inflow was observed in the experiment, and several inflow conditions, including different discharge and inflow schemes, were conducted to analyze the maximum pressure at the junction between shaft and deep tunnel, as well as the pressure along the tunnel. The deviation degree was introduced to validate the reliability of the numerical model. The impact of inflow distribution on deep tunnel pressure was studied with numerical simulation. The results indicated that simultaneous inflow from both shafts leads to a more pronounced phase difference. The pressure downstream after stabilization was higher than the pressure upstream. Simulations of pressure variations with the same discharge under different inflow scenarios revealed that symmetric inflow results in higher pressure at both the midpoint of the tunnel and in front of the downstream shaft. Asymmetric inflow only creates localized high pressure in front of the downstream shaft, with symmetric inflow producing greater pressure overall. When upslope inflow exceeds downslope inflow, it can also reduce the maximum pressure within the pipeline. The greater the difference in inflow on both sides, the smaller the pressure.

Scroll vortex dropshafts have been adopted as an effective tool to convey flow from higher to lower elevations in drainage systems. To ensure the reliability of these dropshafts, the approach channel would normally need to achieve uniform inflow conditions through a minimum channel length requirement. In dense urbanized cities, however, these conditions are occasionally unattainable due to land space constraint. Hence, further investigation is needed to examine the effect of non-uniform inflow conditions on the flow regimes and hydraulic performance of scroll vortex dropshafts. This study aims to quantify the effect of various non-uniform inflow factors on the non-dimensional head-discharge relationship and minimum air core size of the scroll vortex dropshaft by means of computational fluid dynamics simulations. Three-dimensional numerical models with different approach channel lengths are first constructed, and simulations in uniform inflow conditions are then performed and validated by experiment data. Subsequently, simulations with non-uniform inflow conditions are carried out with varying discharges as well as cross-sectional velocity distributions. The results showed that the effect on the performance of the dropshaft depends more on the distribution profile than its peakiness. A higher water level at the entrance and dilated minimum air core size in the dropshaft are typically observed for biased inflow conditions with inward velocity distributions toward the vortex chamber center, while outward distributions toward the outer wall of the vortex chamber lead to an opposite effect. A shorter approach channel would aggravate the disparity magnitude as expected. Finally, regression equations are established based on the simulation results to enable the assessment on the effect of non-uniform inflow conditions in the design stage.