Cave ventilation

Concentration of carbon dioxide in the cave air as determined by a calibrated infrared CO2 meter is equal to, or only slightly higher than, the outside atmospheric value for this altitude (approximately 285 ppmv) and shows only minor variations in different parts of the cave. This is consistent with the sparse development of soil and vegetation above the cave, the long period of snow cover (8-10 months) and the good ventilation of the system. 

Spotl, C., Fairchild, I.J. Tooth, A.F. (2005) Speleothem deposition in a dynamically ventilated cave, Obir Caves (Austrian Alps). Evidence from cave air and drip water monitoring. Geochimica et Cosmochimica Acta, 69, 2451-2468. 

Site 14 in X Cave, which was tentatively classed as a vadose flow on the basis of its mean discharge greater than 10 m /s, is probably more related to the vadose seepages despite its variable discharge (only slightly more variable than site 8, see Table I) and low (which probably represents nearly complete ventilation in the cave environment prior to sampling). Its correlation between Ca and soil co, (as discussed earlier), the wide variation in CO2 relative to Ca (Fig. 4), and its supersaturation with respect to calcite (Table I) makes it resemble the vadose seepages more than the flows. 

It has also been possible to identify two types of vadose seepage. The first, which may be termed low-Ca vadose seepage, is derived from low-Ca soils and its degree of calcite saturation and Ca content are controlled by the available soil Ca and soil Pco, Such seepage does not appear to dissolve significant amounts of Ca as it transits the vadose zone, probably because it is closed to further additions of CO2 and may thus arrive at the aquifer substantially undersaturated if its co, remains at the high levels acquired in the soil zone. Further, some of this low-Ca seepage (such as site 4) will remain undersaturated even if ventilated to the Pco, of a cave atmosphere (Fig. 2). 

After normal stopping, face daily advance distance was 3.35 m, daily output was up to 86991, ventilation air methane was 26.9 mVmin, and during the mining process, gas concentration of upper comer in fully-mechanized caving face sometimes exceeded limit. 

For the 2303 fully mechanized caving face with W two ventilation system into a back. Two different air volume of goaf air leakage into the wind lane, stress field distribution, the oxygen concentration... 

Li Z.X. 2007. W type ventilation caving goaf flow field numerical simulation. Journal of liao ning engineering technology university 26(6)816-818. 

Wu YG Wu J.M. 2011. Pairs of fully mechanized top-coal caving goaf gas distribution of u-shaped ventilation system. Journal of coal 36(10)1705-1708. 

Jiang Wenzhong. 2008. The establishment of gas diffusion-convection model and calculation method of ventilation in gob caving zone. Safety in Coal Mine. (8) 81-83. 

Wu, Y.G., Wu, J.M. and Wang J.F. et al. 2011. The law of gas distribution in goaf of fully mechanized top-coal caving working face with double-U ventilation system. Journal of China Coal Society 36(10) 1704-1708. 

In most apphcations, the use of a round shaft, using a circular plan layout is far preferable. The smooth, round inside diameter that a circular cross-section provides improved ventilation flow while providing a geomechanically stable envelope that is resistant to caves and deformation in all but the most challenging ground conditions. As most shafts are concrete lined, the addition of the liner adds to the stability of the envelope, reduces ventilation friction losses, and provides for a consistent geometry to attached shaft sets. The pros/cons of these two main varieties of layout are shown in Table 1. 

Figure 5.6 shows the unattached fraction of radon (/ ,Rn) and thoron (/p,Tn) decay products as a function of the particle concentration of atmospheric aerosols. The fp values as a function of the particle concentration, Z, are measured by means of a condensation nuclei counter (CNC). Many working places have aerosol sources due to human activities and combustion and technical processes with a high particle concentration, Z > 4 X 10 particles cm , and therefore fp values below 0.01. The fp values are higher than 0.1 for places with particle concentrations <4 x 10 particles cm . This is the case in poorly ventilated rooms (ventilation rate <0.5 h ) without additional aerosol sources, rooms with an operating air cleaner and poorly ventilated underground caves. For the unattached thoron decay products in indoor air, the unattached fraction is estimated by the equation... 

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