广州地铁设计研究院股份有限公司

ObjectiveThe energy consumption of metro station ventilation and air-conditioning systems accounts for more than 30% of the total operating cost. During non-air-conditioning seasons, refrigeration units are still required to operate for equipment rooms, resulting in energy waste. To reduce energy consumption, it is necessary to investigate the feasibility of applying free cooling technology of cooling towers in metro station small cooling systems is investigated and the cooling tower schemes suitable for different scenarios are explored. MethodBy analyzing the air-conditioning load characteristics of metro stations, five cooling tower-based cooling system design schemes are proposed, including open cooling tower indirect cooling, closed cooling tower direct cooling, open cooling tower direct cooling, series-connected cooling tower direct cooling, and variable-frequency cooling tower direct cooling. Considering the water circuit characteristics, heat exchange efficiency, and applicable conditions of different system configurations, their advantages and disadvantages are compared, and key issues such as water treatment, pipeline optimization, and control strategies are discussed. Result & Conclusion Studies show that the cooling load of metro small systems is mainly sensible heat. During winter and transition seasons, adopting an open cooling tower indirect cooling system is the optimal solution for small cooling systems in metro stations, so as to reduce energy consumption significantly. It is recommended to select the optimal scheme based on climatic conditions, initial investment, and operation maintenance costs, and to implement intelligent control strategies to maximize energy-saving benefits.

ObjectiveWhen metro station is constructed in combination with a municipal bridge, the station structural stress stage can be divided into pre-bridge and post-bridge parts. At present, there is a lack of systematic summary and analysis of the stress characteristics of the metro station structure in these two stages. Therefore, it is necessary to analyze the deformation and stress characteristics of the metro station structure during the two stages of combined station-bridge construction. MethodBased on the actual engineering project and referring to a certain standard metro station, a load-structure calculation model is established. Focusing on structural components such as the station roof slab, roof longitudinal beam and transfer beam, numerical simulation and calculation are carried out using MIDAS GEN software. The structural stress and deformation characteristics of the metro station constructed in combination with a bridge are comparatively analyzed between the pre-bridge and post-bridge stages, according to the standard section and the end-shaft section respectively. Result & Conclusion The bridge load and transfer beam may alter the stress state of the roof slab and roof longitudinal beams of station structure, with the primary influence range concentrated on the spans adjacent to both sides of the transfer beam, with relatively minor effect on the intermediate spans. For the roof slab of a combined station-bridge structure, except for the side supports of adjacent spans—which should have reinforcement strengthened according to the internal forces during the post-bridge stage—the transverse reinforcement in other areas can be done following the standard station design. During the pre-bridge stage, the roof slab on both sides of the transfer beam experiences larger longitudinal bending moments and shear forces; therefore, it is recommended to set haunches between the transfer beam and the roof slab and to strengthen the longitudinal reinforcement of the roof slab in adjacent spans along the bridge. The spatial stress in the end-shaft section is significant, due to the bridge load, the pier-under columns may undergo large deformations, causing tension on the roof slab at the column support positions and the lower part of the longitudinal beams, which may lead to cracking or damage. Hence, bridge piers should be arranged to avoid the end-shaft area.

ObjectiveThe construction conditions in water-rich soft soil strata are unfavorable, and the construction of metro shield tunnel link passages may significantly affect the integrity of the existing tunnel structure and the stability of the surrounding strata. To enhance the construction safety, it is necessary to study a construction scheme that combines the freezing method with prestressed support. MethodBased on the link passage and pump station project in Pingxi Station-Low Carbon City Station interval of Shenzhen Rail Transit Line 3, a construction scheme utilizing freezing method + prestressed support is proposed. The freezing parameters and construction steps are described. Finite element simulations are conducted to systematically analyze the bearing performance of the frozen wall and the prestressed support system, while field monitoring is performed to evaluate the effectiveness of construction disturbance control. Result & Conclusion According to the finite element simulation results, the maximum tensile, compressive, and shear stresses of the frozen wall are 0.07 MPa, 1.31 MPa, and 0.50 MPa, respectively, all meeting the safety factor requirement of 2.0. The maximum deformation of the frozen wall in the regular link passage section is 21.0 mm, approximately 3.9 times that of the frozen wall in pump-station section. Under uniform and non-uniform working conditions, with prestress load of 500 kN at the nodes, both the strength stress ratio and the stability stress ratio of the support structure remain below 0.7, indicating excellent spatial stability and load-bearing performance. Field monitoring results show that adopting the freezing method + prestressed support can effectively control the link passage construction induced disturbance to the ground structures and existing segmental lining.

In the construction of underground engineering with complex surrounding environment, reasonable prediction and evaluation of the influence of precipitation on the surrounding environment is a key problem to control the feasibility of the project. At present, the calculation of dewatering-induced settlement using the layered summation method heavily relies on empirical coefficients, leading to significant variability in predictions and deviations from actual observations. To predict the precipitation settlement of loess reasonably and accurately, based on the analysis of the physical properties of saturated loess, the void ratio and liquid index were introduced as key indicators to characterize both deformation potential and the deformation’s difficulty in the dewatering process. The practical calculation method of dewatering settlement of saturated loess stratum was established, and settlement verification was carried out at multiple sites. The results show that depending on the overlying pressure and groundwater action mode, saturated loess can form uncompacted saturated loess and compact saturated loess. The physical properties and dewatering settlement deformation of the two types of loess are different. The main physical property indexes affecting dewatering deposition deformation are the porosity ratio and liquid property index in the initial state, reflecting the deformation potential and the difficulty of deformation of saturated loess, respectively. The comparison between the calculation and measurement of six sites shows that the dewatering subsidence in the loess area mainly occurs in compact saturated loess where the macroporous structure still exists. The proposed e-IL method, incorporating void ratio and liquid index, effectively captures the settlement behavior of saturated loess. This study provides effective technical method for designing and constructing dewatering engineering in the loess area.

[Objective] The capacity bottlenecks and parallel operations throughout the full-process of integrated train dispatching from metro vehicle bases are not fully touched in existing section-based dispatching capacity studies. Therefore, it is necessary to focus on the complete process of trains operating from the stabling and inspection garages to the mainline platforms, systematically analyze dispatching capacity bottlenecks, and propose a calculation method for the integrated dispatching capacity of metro vehicle bases during morning peak hours, providing theoretical support for the evaluation and optimization of depot dispatching capabilities. [Method] Based on the section division method, the throat area passing capacity within vehicle depot under train routing and coordinated dispatch-routing modes, as well as the additional train insertion capacity at connection stations under different insertion routes, a detailed capacity calculation model is established by introducing operational timetables and time-distance diagrams. Further analysis is conducted on the capacity bottlenecks of different sections and the parallel operation processes. For both single-track and double-track dispatching scenarios, an integrated dispatching capacity calculation method for metro vehicle bases is proposed. Theoretical calculation results are compared with actual operational data from the Luogang Depot of Guangzhou Metro Line 6 to verify the reliability of the method. [Result & Conclusion] Under the double-track dispatching mode at the above-mentioned depot, the theoretical minimum dispatching interval during morning peaks is 223.6 seconds, corresponding to a maximum dispatching capacity of 17 trains per hour. In actual operation, the observed dispatching headway during morning peaks is 222.6 seconds, with 17 trains dispatched, resulting in a deviation of only 0.45% from the theoretical value, thus verifying the reliability of numerical calculation.