Edward Derbyshire

Genetic influences on the properties of tills

Summary Tills are a distinctive geological and engineering group of soils which are characterized by a wide range of behavioural patterns and a high degree of variability. As a means of identifying the various geological types of tills, a classification system based on their modes of formation, transportation and deposition has been developed. To accommodate the inherent variability of tills, sub-division of these classifications has been carried out on the basis of their gradational characteristics. Further, the fabric features contributing to variability in engineering behaviour are identified. From this, extended classifications are tentatively suggested to aid the prediction of the engineering properties of tills and the selection of the most appropriate sampling and testing techniques for them.

Origin and Characteristics of Some Chinese Loess at Two Locations in China

Publisher Summary This chapter discusses the origin and characteristics of some Chinese Loess at two locations in China Edward Derbyshire. The Loess Plateau of Shanxi, Shaanxi, Gansu, and the neighboring provinces of central China has a strong claim to be regarded as the worlds type region for the loess formation. The terraces of the Hwang He rise above the floodplain to a height of about 100 m near Meng Xian. Samples taken 3 m below the surface of the uppermost terrace and 15 m below the second terrace were analyzed to determine their particle size, fabric, and clay mineralogy and consolidation characteristics. The loess is very poorly sorted on the Folk and Nard and is significantly different from the slightly sandy loessic alluvium of the present Hwang He floodplain which has a sorting coefficient of 1.34. The random open fabric of the silt skeleton and the presence of silt-sized aggregates of clay, on the other hand, are very similar to that found in the extensive Malan loess which is widely regarded in China as aeolian silt. It is found that although the greater age of the second terrace loess has produced an increase in clay percentage, the microfabric of the two terrace silts is essentially similar when due allowance is made for the difference in overburden and is consistent with aeolian deposition.

A synoptic approach to the atmospheric circulation of the last glacial maximum in southeastern Australia

Abstract Seven circulation types characteristics of present-day synoptic patterns are presented. Three are found to be important and recurring “cold outbreak” winter situations associated with either low temperatures, heavy snowfalls or both. In these situations, wind direction and strength differ notably in the areas of Pleitocene glaciation on either side of Bass Strait. Analysis of air flow over Tasmania in two recent winters is used to assess the degree of correlation between present-day snowfall and drifting and the orientation of Pleistocene glacial cirques. The stronger winter winds come mainly from north of west but bring relatively little snow at present. Given lower temperatures, such a source of strongly-drifted snowfall is considered as a possible explanation of certain apparent anomalies in the distribution of Pleistocene glacial ice in northwestern Tasmania. Some indication of the nature of the Pleistocene climate at higher altitudes is also deduced from the distribution pattern of cirques and their changes in morphology across the region. On the basis of the cold outbreak synoptic situations and the distribution of glacial landform evidence, model circulations are proposed for winter and summer seasons during the last pleniglacial.

LATE PLEISTOCENE PERIGLACIAL DEGRADATION OF LOWLAND BRITAIN: IMPLICATIONS FOR CIVIL ENGINEERING

Summary The geotechnical implications of the inherent complexity of glacial sedimentary sequences have been recently emphasized and it has been suggested that more extensive use be made of engineering geological and geomorphological mapping, especially in the preliminary stages of site investigations. The incidence of certain geomorphic processes beyond the ice margins, notably periglacial solifluction, obscures the relationship between glacial depositional landforms and glacial deposits, especially when periglacial activity has prevailed throughout a glacial period. In such a case, the level of discrimination and sophistication required of these techniques is higher than that demanded using a‘land system’ approach in ice-moulded terrain such as that of the last (Devensian) glaciation. This paper describes examples from the east Midlands of England, where recent engineering operations have encountered serious difficulties due to complex glacial assemblages or unstable bedrock being found beneath apparently simple morphostratigraphic surfaces. Surfaces mapped, for example, as late Tertiary‘erosional platforms’ and late Pleistocene river terraces can be shown to be the product of periglacial processes. Examples are described from recent engineering projects and suggestions are presented as to how similar problems may be avoided in the future.

Technical Developments in the Study of Particulate Matter in Glacial Tills

Some techniques in the study of the structural organization of glacial tills are described. The first of these employs a modified version of Harrisons method of studying mesofabrics (clasts 64-2 mm). A lightweight goniometer, suitable for expedition work, is described and some field results presented from a subglacial environment. A dry-brushing technique designed to accelerate fabric analysis and render it less selective is also described. Results of examinations of three-dimensional microfabrics of the same tills using the scanning electron microscope are also presented. The methods, used in combination, increase the diagnostic and analytical potential of till fabric analysis.