Construction Field Monitoring of a COB Prototype Building

Cob is an earthen building material made by soil, fibres and water used for millennia. However, cob construction disappeared out during the nineteenth century. These last years, it is experiencing a renaissance in Northwestern France and Southern England. Due to a limited technical knowledge, the investigation of engineering properties is important for modern design practice and code requirements. Moreover, to ensure building properties, it is necessary to have same quality mix along the building phases. The aim of this study is to determine material variation during the monitoring of a cob prototype building in Normandy (France). This study investigated structural cob mix composition, water content, density, mechanical properties and thermal conductivity. Specimens shape used were cylindrical 110 x H220 mm and prismatic 300 x 300 x 70 mm. Results indicated a variation in cob mix (water content, materials proportions) between three different lifts. These variations lead to different densities and, consequently, to variables compressive strengths: 0.99 to 1.38 MPa and thermal conductivities from 0.610 - 0.816 W.m-1∙K-1.

Detection of the Phoma pathogens Plenodomus biglobosus subclades ‘brassicae’ and ‘canadensis’ on wasabi, and ‘canadensis’ in Europe

Phoma stem canker / blackleg is an internationally important disease of Brassicas including B. napus (oilseed rape, OSR), caused by multiple genetic subclades of the fungi Plenodomus lingam (formerly Leptosphaeria maculans) and P. biglobosus (L. biglobosa). In Spring 2021, Phoma-like disease symptoms were observed on leaves and stems of Eutrema japonicum (wasabi) crops at three UK sites (Northern Ireland, Southern England and the West Midlands). Fungal isolation from wasabi leaf spots yielded colonies with two distinct phenotypes on potato dextrose agar (PDA). Isolates from the Northern Ireland and Southern England sites had white colonies with abundant pink cirri that were confirmed (based on ITS rDNA, beta tubulin and actin sequences) as P. biglobosus subclade ‘canadensis’ (Pbc). Those from the West Midlands site, however, had yellow pigmented colonies and were confirmed by sequencing as P. biglobosus subclade ‘brassicae’ (Pbb). Greenhouse pathogenicity testing showed that Pbb and Pbc wasabi isolates were pathogenic not only to this host but also OSR, B. oleracea (cabbage), and B. rapa (pak choi). Re-isolation of the fungi was attempted and confirmed from lesions that developed on inoculated OSR and wasabi, thus completing Koch’s postulates. These findings represent new discoveries for both Pbb and Pbc on wasabi, plus for Pbc in Europe. The crop health implications of these results are briefly considered.

Immature Insect Assemblages from the Early Cretaceous (Purbeck/Wealden) of Southern England

The record of immature insects from the non-marine Purbeck and Wealden groups (Lower Cretaceous) of southern England is reviewed and expanded. Fossils of adult terrestrial insects are locally common, but terrestrial immature remains are restricted to transported hemipterans, most of which are sessile nymphs or puparia resembling those of extant whiteflies (Aleyrodidae). Remains of immature aquatic insects are more diverse and comprise the extant orders Plecoptera, Ephemeroptera, Odonata, Trichoptera, Hemiptera and Diptera. The Trichoptera are represented by larval cases constructed from a variety of materials corresponding to several ichnogenera. The Wealden immature insects were preserved in predominantly freshwater fluvial settings, whereas the Purbeck ones occur in lagoonal palaeoenvironments, ranging in salinity from brackish to hypersaline. The composition of aquatic immature insect faunas in the latter offers potential for palaeosalinity analysis, although there are complicating factors relating to habitat stability. Uncommon trace fossils such as beetle borings in wood provide evidence of immature insects not represented by body fossils.

The deformation history of southern England, and its implications for ground engineering in the London Basin

Structures in the basement beneath the London Basin affect the geology of relevance to geotechnical engineering within London. Unfortunately, the basement beneath London is covered by Cretaceous and Tertiary sediments. It is cut by major faults linked to the compressive phases of the Hercynian and Alpine Orogenies and to the regional extension that occurred during the Mesozoic between these compressive events. Evidence is presented that movement on basement fractures beneath London played a major role in the distribution and deformation of sediments within the Basin, causing local folding and faulting significant to engineering works. Basement rocks are exposed in SW England where the type and orientation of these fractures (faults and joints) can be examined in outcrop. This study, complemented by seismic sections in the southern UK, enable the architecture of this fault network within the basement to be determined. Understanding the fracture system in the basement provides a basis for (i), interpreting the lateral facies variations of sediments in the Basin and hence provides a means for predicting from a ground investigation the likely presence, activity or influence on site of such structures at depth and (ii), understanding the extent of local, steeply inclined and sub-horizontal planar zones of shearing when encountered on site.Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/cc/london-basin