The seismic response of a fabricated subway station is a complex structural connection problem that depends on the mechanical properties of the joints. In order to obtain the optimal joint distribution of a fabricated station structure under earthquake action, three finite element models of a single ring structure of fabricated subway stations assembled with seven, five, and four prefabricated components were proposed. Seismic wave characteristics, peak acceleration, and coupled horizontal and vertical seismic components were considered to study the seismic response of the fabricated subway station structure with different forms of the joint distribution. The dynamic time history method was used to analyze the seismic response in three aspects: structure plastic strain, interlayer relative deformation, and internal force. The damage indexes and residual strength indexes of the joints were offered based on the concrete damage index to evaluate the joints’ damage degree. The results showed that the joints of the vault or bottom plate had little influence on the seismic response of the fabricated station structure. The sidewall joints had the obvious seismic response and the most severe damage under horizontal ground motion or coupled ground motion, which were the weak joints of the fabricated station structure. The existence of vertical ground motion aggravated the damage degree of sidewall joints, making the damage occurrence time of sidewall joints earlier and the damage end time extended. On the premise of meeting the mechanical load and site requirements, an assembly scheme with fewer prefabricated components can be selected.
The accurate identification of CO2 non-hydrocarbon gas layers plays an important role in the exploration and development of natural gas reservoirs. The logging response characteristics of layers containing non-hydrocarbon gas and hydrocarbon gas are very similar because there are gas fluids in both two kinds of layers, and this leads to the uncertainty in the interpretation results of gas types. In this paper, we present a comprehensive method for the identification of CO2 non-hydrocarbon gas layers by using CO2 relative content and apparent porosity. Firstly, based on the formation component bulk volume model of the coexisting reservoir of the CO2 non-hydrocarbon gas layers and the hydrocarbon gas layers, we develop an optimization algorithm to quantitatively calculate the CO2 relative content in the reservoir. Secondly, by analyzing and determining the logging response value of the CO2 non-hydrocarbon gas under the formation temperature and pressure conditions, we establish a qualitative identification chart using the difference between the calculated value of apparent porosity of CO2 and the hydrocarbon gas. Finally, we are able to accurately identify the CO2 non-hydrocarbon gas layers by comprehensively analyzing the calculation results of the CO2 relative content in the reservoir and the identification results of the CO2 apparent porosity identification chart. We apply the above workflow in Baiyun deep water area in eastern South China Sea, and it shows high efficiency in the identification of CO2 non-hydrocarbon gas layer.
Under the circumstance of soft fractured surrounding rock with high geo-stress, the support technology of tunnel has become a major challenge. Traditional I-shaped steel and bar lattice girder, which cross-sections are often designed to be left-right symmetrical, may have insufficient strength and stiffness. Based on the concept of symmetry, a new support technology of spatial steel tubular grid (SSTG) arch is designed with high strength and large stiffness. In order to clarify the mechanical properties and failure mechanism of SSTG arch used as primary support, through laboratory and numerical experiments, this paper carries out the bending tests for the circumferential joint of SSTG arch components combined with the excavation tunnel project of Panyu Square Station in Guangzhou, and the analyses of the ultimate bearing capacity, deflection displacement, failure modes, and stress–strain evolution laws of joint components are conducted in detail. The results show that during the whole process of loading, the arch components have experienced elastic growth stage, plastic development stage, and final failure stage. The average ultimate bending capacity of SSTG arches is 340.5 kN·m, and the joint opening is 13.9 mm. The joint form of high-strength bolt + rigid flange plate proposed in the paper has reasonable stress state and high safety redundancy, which can bear the load of surrounding rock effectively, and ensure the safety in tunnel construction. The research results could provide a theoretical basis for the design and application of SSTG arch support in related projects.
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