Epidemiological and virological studies indicate that noroviruses-contaminated groundwater was the primary source of four acute gastroenteritis outbreaks in South Korea between 2008 and 2012. Furthermore, cabbage kimchi was first identified as the vehicle of transmission between groundwater and infected patients in an outbreak in 2011. The proper treatment of groundwater sources prior to use for drinking or in food preparation is necessary to prevent further outbreaks.
An acute gastroenteritis (AGE) outbreak was reported in May 2013 in Gyeonggi Province, South Korea. Eight students who had eaten breakfast on 21 May 2013 at a high-school restaurant exhibited AGE symptoms. Our case-control study showed that a strong association was observed between AGE symptoms and fermented oyster consumption. Virological studies also indicated that noroviruses (NoVs) were detected from both clinical samples and fermented oyster samples, and multiple different genotypes (genogroups GII.4, GII.11 and GII.14) of NoVs were present in both samples. The nucleotide sequence similarity between the strains found in the clinical samples and those in the fermented oysters was more than 99·5%. Therefore, to prevent further outbreaks, proper management of raw oysters is necessary and the food industry should be aware of the risk of viral gastroenteritis posed by fermented oysters contaminated with NoVs.
For an underground excavation at depth in highly stressful conditions, it is important to mitigate the risk of stress-induced failure, e.g., rockburst, and improve miner safety concerning the stability of underground workplaces and the prevention of fatalities. In general, the cause of rockburst is classified into three categories: strainburst due to stress-induced fracturing, rock ejection by seismic energy transfer, and rockfall associated with mining-induced seismicity. In this study, the Split Hopkinson Pressure Bar (SHPB) modified configuration of bar drop apparatus was developed by attaching a direct shear test box and a long bar. As a result, the modified bar drop system enabled to replicate and control of a seismic velocity that was an incident on the joint rock surfaces installed in the direct shear testing box. The long bar installed in the modified bar drop system provides a longer stress wavelength to overcome the relatively shorter duration of the stress waves in the SHPB system. The dynamic shear test on the jointed rock samples using the bar drop apparatus also provided the information to estimate the rock joint shear strengths. 1. INTRODUCTION The rock structures stability depends on the distribution characteristics and mechanical characteristics of discontinuous surfaces such as faults and joints in the rock. Underground excavation has high-stress conditions, and such workplaces are causing stability and fatalities of underground workplaces due to rockburst. In general, the cause of rockburst is classified into three categories: strainburst due to stress-induced fracturing, rock ejection by seismic energy transfer, and rockfall associated with mining-induced seismicity. In order to understand the behavior and stability of such rock structures, it is necessary to understand the shear characteristics of the joint surfaces. The direct shear test and multi-stage shear test are methods to measure the shear characteristics of the joint surfaces. The direct shear test measures the shear characteristics of a joint surface by generating shear displacement with different load conditions from each specimen and requires samples with the same roughness. However, it is difficult to obtain samples with the same roughness in the field, so a multi-stage shear test is conducted. A constant normal load section is set as a specimen in the multi-stage shear test. The shear characteristics for each normal stress stage are measured by generating shear displacement while increasing the normal load. In the case of the multi-stage shear test, the International Society of Rock Mechanics and Rock Engineering (ISRM, 1981) recommends the discontinuous surface test method for rock. However, it has been pointed out that the joint surface of the specimen is damaged due to an increase in shear load due to the normal load, resulting in a lower shear strength than the direct shear test (Zhao and Zhou, 1992).
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