The lines of evidence approach to challenges faced in engineering geological practice

Abstract

Establishing appropriate lines of evidence enables us to resolve the challenges faced in engineering geological practice. When considering the lines of evidence used to derive a conceptual site model (CSM), three interlocking themes are: (1) multidisciplinary working, (2) knowledge and experience and (3) lessons from the past. This is explored through case histories. There may be no standard approach and conventional engineering geological skills are not always sufficient; as during the decommissioning of cryogenic gas storage tanks at Canvey Island. Alternatively, there may be reservations about using a standard approach; which led to the unconventional use of chalk fill at Port Solent Marina. In the case of a major oil leak into the Permo-Triassic aquifer, understanding the basic science of the problem explained why the original CSM was too simplistic and informed a change of remedial strategy. Obtaining permits for an underground gas storage facility on a landslide complex on the Isle of Portland required numerous lines of evidence to assess the stability of the slope. Furthermore, new lines of evidence can be added to old data sets as technology develops, such as the use of LiDAR in mapping Cotswolds landslides. In his recollection of the early years of engineering geology in the UK, Professor Peter Fookes, the first Glossop Lecturer, wrote (Fookes & Lee 2017, p. 457): By the middle to the end of the decade [1970s], engineering geology was well established as a discipline in its own right. ... In the following decades new or improved field and laboratory techniques continued to support development of engineering geology as a discipline. But that is another story. Fookes was my PhD external examiner (Privett 1980). After my PhD I was employed as an internal consultant by a major UK contractor. I spend my subsequent working career with a number consultancy firms. My career has spanned the post-1970s period Fookes describes as 'another story' and I took up this theme for my (the nineteenth) Glossop Lecture.

Photographic feature: The Southwell Topple – reassessment of a very large coastal toppling failure on the Isle of Portland, UK

“…This alignment is consistent with mapped dips of bedding (Fig 2 in Brunsden et al 1996). Privett (2019) shows both of these 'axes' as forming part of the same gentle bowl-shaped plunging syncline, but the marker beds show a more definitive feature.…”

“…This means that the depression up through the wider northern part the Isle of Portland (described by Brunsden et al 1996) appears to be a structural feature of tectonic origin (Privett 2019). Our interpretation of the DORIS data is that this structure, itself part of the Shambles syncline, arises from the interference between the southwestern side of the Weymouth and Purbeck anticline and whatever was occurring further west to produce the Shambles syncline.…”

“…Our interpretation of the DORIS data is that this structure, itself part of the Shambles syncline, arises from the interference between the southwestern side of the Weymouth and Purbeck anticline and whatever was occurring further west to produce the Shambles syncline. Furthermore, taken with the absence of any geotechnical evidence for 'clay extrusion' or related mechanisms at East Weare (Privett 2019(Privett , 2020), it appears that the 'clay extrusion' hypothesis for the structural features of Portland is superceded by a tectonic explanation. Indeed, the Shambles syncline and the coastline parallel with the transform faults (or perhaps joints) intersect at an angle so they probably result from different phases of the regional tectonism, highlighting the underlying complexity of an apparently relatively simple geological context that influences or even determines the nature of the landsliding around the Isle of Portland.…”

“…Along the northeast-facing coastline compound slides dominate (Fig. 4), sometimes with basal shear surfaces at a higher level (Brunsden et al 1996), but much of the landslide morphology has been obscured by quarry waste dumped over several hundred years (Privett 2019). Where the rear scarps of such landslides are high and formed in Portland Stone (i.e.…”

Interprétation de l’hydrogéochimie de la Molasse d’Eau Douce Supérieure (Obere Süßwassermolasse) dans la région de Munich (Bavière, Allemagne) à l’aide d’une analyse multivariée et d’une modélisation géologique en 3D

“…Further, understanding the local groundwater chemistry means developing a conceptual model and constitutes a complex problem, which may be resolved by using different lines of evidence. Privett (2019) concluded that using appropriate lines of evidence allows one to increase the understanding and solve challenging geological problems. Also, Freedman et al (2019) stated that evolving a conceptual model should be associated with applying adequate lines of evidence and a suitable level of complexity to represent hydrogeological systems.…”