STUDY OF COMPATIBILITY OF METHODS FOR LIQUID LIMIT MEASUREMENT ACCORDING TO CZECH STATE STANDARD AND NEWLY ADOPTED EUROPEAN STANDARD STUDIE KOMPATIBILITY METOD PRO MĚŘENÍ VLHKOSTI NA MEZI TEKUTOSTI DLE ČSN A NOVĚ PŘIJÍMANÉ EVROPSKÉ NORMY
The goal of the publication is a correlation between the methodology of liquid limit determination using Casagrande bowls according to the Czech state standard being valid as yet and the methodology on a principle of the conical test according to a newly adopted European standard. It allows a better link of utilization of an extensive statistical set of investigations realized for purposes of foundation engineering in past that are available in Geofond for newly conducted engineering geological studies according to the new European standard related to water contents at the liquid limit for wide-spread clay soils. The sample values ranged from 21.49 to 49.56 % according to Casagrande and in the conical test they ranged from 24.11 to 51.07 %. The difference of the results for identical samples reached values from 1.15 to 4.19 %. The studied mean difference coefficient between methods amounts to 2.55 %.
Liquid limit of low- to medium-plasticity soils: comparison between Casagrande cup and cone penetrometer test
For liquid limit determination, the European Standards require the cone penetrometer technique or, alternatively, the Casagrande cup method; but the latter is widely used in practice. As most European soil classification systems are not adapted to the new European Standards, a systematic study was carried out to verify the differences between the two techniques for liquid limit determination, examining clayey soils from various geologic units. Comparison of 100 liquid limit values ranging between 20 and 50% indicates that the liquid limit obtained by the fall cone method is generally 2.2% points higher than that obtained by the hard base Casagrande apparatus. Comparison of data from different sources consistently indicates that the equation proposed in this study may be useful in revising existing soil classification systems, avoiding problems of soil classification due to the technique used for liquid limit determination.
Pyrite multiple-sulfur isotope evidence for rapid expansion and contraction of the early Paleoproterozoic seawater sulfate reservoir
Abstract Earthʼs oxygenation is often described in terms of two unidirectional steps at the beginning and end of the Proterozoic Eon, separated by a long-lived intermediate redox state. Recent work defines a more complicated path to oxygenation, exemplified by an apparent drop in oxidation state following the early Paleoproterozoic Lomagundi carbon isotope excursion. The timing of this proposed drop in oxidation state is not well constrained, and it is not clear how it relates to redox conditions during the remainder of the Proterozoic. Here we present a study of pyrite multiple-sulfur isotopes, supported by Fe speciation and organic carbon isotopes, from early Paleoproterozoic black shales. We find evidence for the rapid expansion of the seawater sulfate reservoir during the Great Oxidation Event at ca. 2.3 Ga followed by a subsequent contraction in the size of the seawater sulfate reservoir at ca. 2.05 Ga. This scenario is consistent with the emerging view of a rise and fall in surface oxidation state during the early Paleoproterozoic. Comparison of our new data to other records of the seawater sulfate reservoir suggests that the elevated sulfate concentrations that characterize the early Paleoproterozoic did not return until the late Neoproterozoic.