Vertical cycle karst zone has been studied for more than 100 years, however karst subzones in the zone have never been divided and affected depth of CO2 from rainwater in the zone has never been studied. On the basis of field observation, survey and chemical analysis, the difference of karst processes indicated by CaCO3and pH values in fine and loose sedimentary strata as well as limestone strata, and the vertical cycle zone ascertained by predecessors can be divided into three subzones, that is, the upper first subzone, characterized by unsaturated water solution and strong dissolution processes, the middle second subzone, characterized by supersaturated water solution and precipitation, and the lower third subzone, characterized by unstable water solution and weak dissolution or weak precipitation. The three subzones can indicate the vertical co2 cycle. In fine and loose sediment strata, the bottom of the first subzone is the lower boundary strongly influenced by co2 from rainwater, soil and air; all co2 from rainwater, soil and air is almost exhausted in the second subzone. In the early developmental period of karst process in limestone strata, karst funnels and vertical caves do not form, vertical seeping of rainwater and soil water is very slow, and co2 from soil, rainwater and air almost can reach the third subzone, but in the middle and late developmental periods, karst funnels and vertical caves occur, co2 from soil, rainwater and air can reach deep seasonal change zone and horizontal cycle zone and quicken development of karst morphology. Deep karst morphology near groundwater level under vertical cycle zone develops better in the middle and late periods of karst process. 相似文献
Viscoelastic artificial boundaries are widely adopted in numerical simulations of wave propagation problems. When explicit time-domain integration algorithms are used, the stability condition of the boundary domain is stricter than that of the internal region due to the influence of the damping and stiffness of an viscoelastic artificial boundary. The lack of a clear and practical stability criterion for this problem, however, affects the reasonable selection of an integral time step when using viscoelastic artificial boundaries. In this study, we investigate the stability conditions of explicit integration algorithms when using three-dimensional (3D) viscoelastic artificial boundaries through an analysis method based on a local subsystem. Several boundary subsystems that can represent localized characteristics of a complete numerical model are established, and their analytical stability conditions are derived from and further compared to one another. The stability of the complete model is controlled by the corner regions, and thus, the global stability criterion for the numerical model with viscoelastic artificial boundaries is obtained. Next, by analyzing the impact of different factors on stability conditions, we recommend a stability coefficient for practically estimating the maximum stable integral time step in the dynamic analysis when using 3D viscoelastic artificial boundaries.