دانلود رایگان مقاله انگلیسی خصوصیات ژئوتکنیکی توده سنگین رسوبی در CERN، ژنو - الزویر 2018

ABSTRACT

The European Organisation for Nuclear Research (CERN) in Geneva has extensive underground facilities, which were built over the past 70 years in a weak layered sedimentary rock called the red molasse. CERN has thus been continuously exploring its underground space and has gathered extensive geotechnical data from both laboratory and field tests. The data shows that the red molasse is composed of marls and sandstones forming 6 different geotechnical units with different geotechnical characteristics. The strength-stiffness relationship of the red molasse is lower than other molasses from other regions, and that the marls are significantly more ductile than the sandstones. Moreover, the intermediate rock units (sandy marls and marly sandstones) have similar strength but a different stiffness, a distinction which is not represented in the standard strength classification system. Although all rock units were subjected to the same diagenesis, one rock unit is found to be very weak with soillike properties. A mineralogy analysis shows that this unit is composed of high plasticity clay, whilst the other marls units are composed of medium-high and low plasticity clay. The field tests show rapid and progressive transitions between the different rock units, which makes field prediction difficult. This paper presents an overview of the geotechnical data gathered by CERN as well as the geotechnical characterisation of the site The geotechnical characterisation presented in this paper also compares laboratory tests with field tests.

 Conclusion

This paper presented a geotechnical characterisation of a weak sedimentary rock at CERN, Geneva. It is based on extensive data gathered in the past 70 years by CERN and consisted of exploration boreholes, laboratory tests and in situ tests. Although only a summary of the tests is presented in this paper, the results show the general characteristics of a weak sedimentary rock called the red molasse. This rock mass is composed of two rock units – marls and sandstones – and three sub-units exist for each rock unit. These sub-units form lenses in the bedrock with smooth transition between them making any prediction difficult. The rock mass is generally massive and can be viewed as a continuum solid. However, local fractured zones are observed and are mostly in very weak layers of marl and can be treated as a soil-like rock unit. The marls result from the diagenesis of clayey-silty Alpine detritus, and the sandstone of silty-sandy Alpine detritus. The strengths of the marls ranged from very weak (R1) to weak (R2). It was found that 1. very weak marl are composed of high-plasticity clays, 2. weak marl of medium-high plasticity clay and 3.medium-weak marl of low-plasticity clays. The strength of the sandstone ranges from weak (R2) to mediumstrong (R3) and relates to the grain size and their clay content. An overlap of strength is observed between the stronger marls and the weaker sandstones but has a different stiffness; the marls are found to be ductile and the sandstone more brittle. This difference is not captured by the International Rock Classification System, which is based on strength only. The 1. very weak marl were found to be significantly weaker compared to other units and are subject to slaking and swelling. It was also shown that the red molasse was more ductile than the molasse in Greece and South Africa.