Numerical simulation of surface subsidence after UCG including groundwater effect

Underground Coal Gasification (UCG) is a method that allows for the extraction of energy from hard to access coal seams (i.e. very thin or deep underground). One of the greatest advantages of UCG is that it eliminates the need to put humans underground, thereby reducing the risk of injury and fatality, which are significant concerns during conventional underground coal excavations. UCG currently has two main hurdles that are affecting its potential industrialization: the risk of surface subsidence and groundwater pollution. The existence of groundwater is particularly a challenge because of implications to both pollution and its influence on mechanical processes underground. Two mechanical effects of groundwater should be considered: changes in effective stress and in volumetric strain. Additionally, at any UCG site, the influence of groundwater should be analyzed together with the thermal impact of coal combustion. To couple the fluid, thermal and mechanical analyses, the commercial software FLAC3D by Itasca is utilized. The modelling results are compared with the field measurements at the Shatsk UCG station in the Moscow Basin. The site at hand is complicated by six aquifers in the overburden above the UCG reactor. The relative performance of the models with and without groundwater and thermal effects is evaluated based on predictions of the surface subsidence. The groundwater increases the depth and narrows the width of surface subsidence closing the modelling results to the measurements, whereas the high-temperature decreases the depth without changing the shape of the surface subsidence

Rivaroxaban with or without aspirin in stable cardiovascular disease

BACKGROUND: We evaluated whether rivaroxaban alone or in combination with aspirin would be more effective than aspirin alone for secondary cardiovascular prevention. METHODS: In this double-blind trial, we randomly assigned 27,395 participants with stable atherosclerotic vascular disease to receive rivaroxaban (2.5 mg twice daily) plus aspirin (100 mg once daily), rivaroxaban (5 mg twice daily), or aspirin (100 mg once daily). The primary outcome was a composite of cardiovascular death, stroke, or myocardial infarction. The study was stopped for superiority of the rivaroxaban-plus-aspirin group after a mean follow-up of 23 months. RESULTS: The primary outcome occurred in fewer patients in the rivaroxaban-plus-aspirin group than in the aspirin-alone group (379 patients [4.1%] vs. 496 patients [5.4%]; hazard ratio, 0.76; 95% confidence interval [CI], 0.66 to 0.86; P<0.001; z=−4.126), but major bleeding events occurred in more patients in the rivaroxaban-plus-aspirin group (288 patients [3.1%] vs. 170 patients [1.9%]; hazard ratio, 1.70; 95% CI, 1.40 to 2.05; P<0.001). There was no significant difference in intracranial or fatal bleeding between these two groups. There were 313 deaths (3.4%) in the rivaroxaban-plus-aspirin group as compared with 378 (4.1%) in the aspirin-alone group (hazard ratio, 0.82; 95% CI, 0.71 to 0.96; P=0.01; threshold P value for significance, 0.0025). The primary outcome did not occur in significantly fewer patients in the rivaroxaban-alone group than in the aspirin-alone group, but major bleeding events occurred in more patients in the rivaroxaban-alone group. CONCLUSIONS: Among patients with stable atherosclerotic vascular disease, those assigned to rivaroxaban (2.5 mg twice daily) plus aspirin had better cardiovascular outcomes and more major bleeding events than those assigned to aspirin alone. Rivaroxaban (5 mg twice daily) alone did not result in better cardiovascular outcomes than aspirin alone and resulted in more major bleeding events