Water plays an important role in the mechanical properties of roadway surrounding rocks and poses a great threat to their stability. To study the damage and failure characteristics, and the fracture development laws of surrounding rock, a uniaxial compression test for prefabricated fractures in water-bearing surrounding rock was carried out. Results indicate that water-bearing prefabricated fracture specimens are in better development condition after failure. In water-bearing specimens, the propagation direction is more complex. There are more secondary fissures, and the fracture strength is significantly lower than in dry specimens. When immersed in water, the interior structure of surrounding rock is weakened and softened; thus, the intensity is reduced, and the development and propagation of fractures is promoted. For larger angles of the prefabricated fractures, the compression failure of surrounding rock changes into shear failure. As the angles approach 90°, the shear failure again prevails. Therefore, the strength of the surrounding rock firstly decreases and then increases. A new ultimate stress strength model is developed for fractures caused by shear slip failure in water-bearing surrounding rock. The model results are consistent with the experimental results, and the validity of the model is verified. These results are helpful for deeply understanding the failure process of water-bearing surrounding rock with prefabricated fractures. The proposed model could be used for the evaluation of water-bearing surrounding rock stability in coal mines, as well as dynamic risk monitoring. 相似文献
The genesis of Liangguo corundum deposit in the southern Gangdese magmatic arc, east-central Himalaya, remains unknown. The present study shows that the corundum-bearing rocks occur as lenses with variable sizes in the Eocene gabbro that intruded into marble. These corundum-bearing rocks have highly variable mineral assemblage and mode. The corundum-rich rocks are characterized by containing abundant corundum, and minor spinel, ilmenite and magnetite, whereas the corundum-poor and corundum-free rocks have variable contents of spinel, plagioclase, sillimanite, cordierite, ilmenite and magnetite. The host gabbro shows variable degrees of hydration and carbonization. The corundum grains are mostly black, and rarely blue, and have minor Fe O and TiO_2. The spinel is hercynite, with high Fe O and low Mg O contents. The corundum-bearing rocks have variable but high Al_2O_3, FeO and TiO_2, and low SiO_2 contents. Inherited magmatic and altered zircons of the corundum-bearing rocks have similar U e Pb ages(~47 Ma) to the magmatic zircons of the host gabbro, indicating corundum-bearing rock formation immediately after the gabbro intrusion. We considered that emplacement of gabbro induced the contact metamorphism of the country-rock marble and the formation of silica-poor fluid. The channeled infiltration of generated fluid in turn resulted in the hydrothermal metasomatism of the gabbro, which characterized by considerable loss of Si from the gabbro and strong residual enrichment of Al. The metasomatic alteration probably formed under Pe T conditions of ~2.2 -2.8 kbar and ~650 -700℃. We speculate that SiO_2, CaO and Na_2O were mobile, and Al_2O_3, FeO, TiO_2 and high field strength elements remained immobile during the metasomatic process of the gabbro. The Liangguo corundum deposit, together with metamorphic corundum deposits in Central and Southeast Asia, were related to the Cenozoic Himalayan orogeny, and therefore are plate tectonic indicators. 相似文献
1 Introduction Vegetation is an important component of terrestrial eco- system, it plays an important role in global matter and energy cycle, carbon balance and climate change. CO2 has effects on global warming, photosynthesis function, Net Primary Productivity (NPP) and earth environmental condition. NPP is one of the important biophysical variables of vegetation activity, and is a beginning link of biogeochemical carbon cycle. Vegetation absorbs CO2 from atmosphere through photosynthesi… 相似文献
Studies on Gelidium amansii agar fractionations were carried out in this paper. Gelidium amansii agar was fractionated on DEAE-Cellulose, and four fractions were obtained sequentially. The fractions were analyzed on physical and chemical properties, and IR and 13C-NMR spectroscopy applied for elucidating the chemical structure. Among the four fractions obtained, water fraction measured up to the standard of low EEO agarose. The sulfate content, ash content, electroendosmosis and gel strength (1%) of water fraction were 0.16%, 0.34%, 0.12 and 1 130g/cm2 respectively, similar to those of the Sigma products. 相似文献
Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were −7.4 and 5.4 g·m−2·d−1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were −12.8 and 5.8 g·m−2·d−1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m−2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m−2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m−2·s−1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature.