The Fuller's Earth formation is an overcon-solidated, jointed, randomly Assured, calcareous mudstone with some thin to medium, jointed argillaceous limestone bands. South of Bath, the formation contains the commercial (montmorillonite rich) Fuller's Earth bed. This Paper reviews the effect of the proportion of calcite present on the moisture content, Atterberg limits, particle size, and residual shear strength. Attention is drawn to the importance of appreciating that the calcite percentage and the clay mineralogy are both likely to change with time as a result of weathering processes. This will affect the stability of natural slopes and man-made cuttings, excavations, etc. La formation de terre à foulon est un limon compact calcaire surconsolidé jointé et fissuré au hasard qui contient des bandes de chaux argillacée jointées d'épaisseur faible ou modérée. Au sud de Bath la formation comprend la couche de terre à foulon commerciale qui est riche en montmorillonite. L'article examine l'influence de la proportion de calcite presente sur la teneur en eau, les limites d'Atterberg, la grandeur des particules et la résistance au cisaillement résiduelle. On attire L'attention sur la nécessité de comprendre qu'il est probable que le pourcentagc de calcite et la mineralogie argilleuse changeront au cours du temps ce qui entraine un processus d'effritement cela influencera la stabilité des pentes naturelles, des déblais, des excavations, etc.

BS 5930 offers little assistance to engineers wishing to use residual strength parameters in slope stability analysis. It wrongly suggests the ring shear gives lower parameters than the shear box.BS 5930 does not mention the fact that the residual strength is stress dependent, hence the failure envelope is curved and the parameters must be assessed using an appropriate effective normal stress. For this reason the correlation charts relating ϕ′R to plasticity index or clay content need replacing with a series of charts in which these properties are plotted against ϕ′R values obtained at a number of effective normal stress loadings. Even then such correlations should be treated with caution.

Summary This paper gives details of the foundation problems at a housing development on a 4–7° slope of Blue Lias limestone, overlying Rhaetic and Keuper Marl. Cambering in the past has produced extension gulls with cavities up to 1 m wide and zones of disturbance over 5 m wide. These structures were not visible on the surface or on the aerial photographs and presented unforeseen problems when discovered in foundation trenches. Extensive site checks have been undertaken, the foundations for each building plot being inspected by one of the authors. A simple classification of the extension gulls on this site, based on the mode of opening along joint and bedding surfaces and any subsequent collapse or infilling, is presented. The overall stability of the hillside is discussed with reference to the residual strength of the Rhaetic, which here is a highly plastic, montmorillonitic horizon containing well marked shear planes. The presence of the gulls necessitated several changes of the site layout in an attempt to avoid the most highly disturbed ground. The developer suffered a 150ss in the proposed number of units.

Summary From the literature and the geological maps it is known that superficial structures occur extensively associated with the Jurassic strata in the south Cotswolds. There is some discrepancy in the representation of superficial structures on the small-scale geological maps (1:63,360 and 1:50,000 scales). Examples from the Bath area have been selected and engineering geomorphological maps of some superficial structures are presented. It is concluded that valley bulges and cambers are difficult to delimit using this technique but landslips, especially the more recent, large-scale ones, and mudflows can often be clearly depicted. An important consideration is the subsequent ‘smoothing’ of natural features by hillwash or intensive agriculture and associated ploughing. It is concluded that this form of mapping is no substitute either for geological mapping or for a proper site investigation; it can, however, add valuable data.

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.