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Session 5: The influence of geology on civil engineering

CONFERENCE PREVIEW

Jackie Skipper, Natural History Museum The papers in this session are loosely in three main categories.

Primary engineering geological observation There are a number of papers that follow in Skempton's intensely practical geological footsteps.

For example, in On subsidence and eustacy in relation to Venice, Butterfield analysed a wide variety of geological and archaeological data and erected a simple predictive sea level model. Used in with modern climate models, this work will have direct practical implications for any proposed tidal control schemes in Venice.

Despite work by Skempton as early as the 1940s on the importance of geology and geomorphology in engineering design, the science of applied geomorphology is still frequently misunderstood and regrettably underrated by engineers.

However, in Construction design data provided by the investigation of geomorphological processes and landforms, Griffiths et al, using examples from ongoing research in southern Spain, show how a wealth of data about landscape development, slopes and river systems can be obtained, all of direct relevance to civil engineering.

The role of geology in landslide risk assessment for civil engineering purposes follows a similar educational pathway. In this paper Hearn argues for a greater recognition of geological and geomorphological complexity in landslide assessment by developers and geoscientists alike.

He shows how engineering geology can contribute to landslide assessment, remediation and the development of models for future planning, yet sadly 'there are some cases in the developing world where geology and geomorphology are ignored during the entire planning, design and construction of infrastructure'.

In Geotechnics in south-east Hampshire, Hodges et al provide a useful summary of the 'apparently simple' Tertiary and Quaternary geology of the area around Portsmouth and its implications for engineering.

Historical engineering geology research on these materials, some going back 130 years, is of considerable use in interpreting modern ground conditions. A reminder that archive data is often just as useful as modern.

Techniques in geological site investigation In Site investigation and site conceptual models - the link between geology and engineering, Harding makes the case for the use of a site conceptual model for the characterisation of geology in engineering projects.

He suggests that the use of such a model would improve the link between geology and engineering by optimising the use of ground characterisation data for all stakeholders, instead of the current situation where constructors and other stakeholders often develop their own models, due to lack of data transfer.

In Modern reconnaissance methods for geohazard detention and monitoring in site investigation, Culshaw et al give examples of recent case studies where cross-hole seismic tomography, airborne thermal imaging, airborne electromagnetic (HiRes) and the scarily-acronymed PSInSAR (radar interferometry) were used.

I particularly liked the look of the thermal imagery example, in which 23 possible mineshafts were identified in a former coalfield area of Nottingham.

The second paper, Insitu investigation of problematical soils, focuses on the use of non-invasive shallow seismic and electrical resistivity methods. Evans et al review in detail some of the inherent problems of testing collapsible soils. They then give examples where assessments of compaction in loess and moisture content in a red soil were made insitu in large embankments using these methods.

Clays and soil behaviour I was particularly interested in the first paper in this category, Engineering geology of glaciated soils. Gareau et al are testing anisotropy in glacial tills from the Netherlands using a lateral stress oedometer, and are coming up with some interesting results.

They show horizontal reactions to vertical applied loads in these tills are anisotropic and that the direction of the horizontal stresses noted correspond with the direction of the depositing glacier.

In Geological evidence for widespread faulting and fracturing of clay-rich sediments during initial consolidation, Cartwright introduces a concept to engineering geology which has been developed in the petroleum industry in recent years.

Geophysical and geological evidence has shown that smectitic clays (such as London Clay) undergo intense polygonal fracturing and folding during early burial. This has led to the identification of 3D fault systems in sediments of this type worldwide. As Cartwright rightly states, this information poses some fundamental questions for the relationship between consolidation, stress history and strength in smectitic sediments.

In The origin and shear strength of kaolin-rich zones in Hong Kong and their implications for slope stability, Parry et al explore the nature of the kaolinitic clay zones which influenced two major, fatal landslides in Hong Kong in 1995. They conclude the shear strength properties of the kaolin infills vary with proportion of halloysite to kaolinite. The higher the kaolinite content, the lower the shear strength becomes.

This is a study in which good quality field observations (see Figure 2), shear strength testing and mineralogy have been used together to form some sensible conclusions - how very Skemptonian!

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