P.R.N. Hobbs

Rapid observations to guide the design of systems for long-term monitoring of a complex landslide in the Upper Lias clays of North Yorkshire, UK

The Whitby Mudstone Formation has one of the highest landslide densities in the UK with 42 landslides per 100 km2. Landsliding at Hollin Hill in North Yorkshire, UK is complex and continuing, and includes shallow, retrogressive rotational failure on the upper slope, translation, and flow from the base of the Whitby Mudstone Formation over the scarp slope of the Staithes Sandstone Formation. Surface observations augmented by information relating to lithological, moisture and strength variation with depth allowed rapid initial interpretation of the masses affected by movement. These were provided by a single person operating portable probes providing depth logs of cone penetration resistance and soil moisture based upon dielectric property measurements in conjunction with a sampling auger. The gathered information was used to guide the design of further invasive site investigation and the configuration of permanent systems to monitor changes in dynamic moisture distribution and direct movement. At Hollin Hill, the near-surface materials in the upper 5 m interval are distinctly weathered or destructured, predominantly comprising silty clay in the Whitby Mudstone Formation, and fine silty, clayey sand and silty clay in the Staithes Sandstone Formation. Direct and secondary evidence was observed showing high moisture variation to be related to narrow intervals within the upper 5 m. Cyclic variation in moisture has played a key role in the movement and break-up of sliding materials, especially within the prograding lobes resulting from flow over the Staithes Sandstone Formation. Since these observations, permanent monitoring systems have been installed, including electrical resistivity tomography (ERT) arrays, which have successfully mapped the distribution of the Whitby Mudstone and the Staithes Sandstone, but will also be used in time lapse mode to image the near-surface moisture movement driving the landsliding processes. ERT array installations included a large area, low spatial resolution grid designed to investigate the potential coupling between the upper and lower slope hydrogeological processes and a small area, high spatial resolution grid designed to investigate the hydrogeological processes driving the earth flow.

A Robust Surface Matching Technique for Integrated Monitoring of Coastal Geohazards

At the dynamic coastal fringe, numerous processes interact with local morphology. In soft-cliff environments, this can often lead to the occurrence of coastal geohazards. These can pose a major threat to property and cultural heritage, and an effective monitoring strategy is therefore essential. While contemporary monitoring techniques have been applied, these are often unsuitable in isolation. This paper presents an integrated approach, with the development of weighted surface matching software enabling reliable dataset fusion and multi-temporal change detection, even where significant surface differences exist. Evaluation of this approach is presented and discussed.

Monitoring coastal change using terrestrial LiDAR

Abstract The paper describes recent applications by the British Geological Survey (BGS) of the technique of mobile terrestrial Light Detection And Ranging (LiDAR) surveying to monitor various geomorphological changes on English coasts and estuaries. These include cliff recession, landslides and flood defences, and are usually sited at remote locations undergoing dynamic processes with no fixed reference points. Advantages, disadvantages and some practical problems are discussed. The role of GPS in laser scanning is described.

Environmental geology maps of Bath and the surrounding area for engineers and planners

Abstract In March 1984 the British Geological Survey commenced an environmental geological study of parts of west Wiltshire and south east Avon for the Department of the Environment. The objective of this study was to collect the available geological data relevant to the area, and to present them as a series of thematic maps accompanied by a descriptive report and a database/archive of the data used. The output is intended to be used by land-use planners. It is designed simultaneously to be understandable by people not trained in geology and yet to contain detailed information required by specialists concerned with the environment and its development. The 14 maps which were produced describe themes which include solid lithostratigraphy, drift deposits, the inferred distribution of Great Oolite Freestone, the inferred distribution of fuller’s earth, groundwater, ground conditions in relation to groundwater, geotechnical properties of bedrock and superficial deposits, landslipped and cambered strata, distribution of slope angle, and mining. Although the task was primarily a desk study, it was found necessary to carry out a small amount of field survey to re-interpret the foundered strata to the north-west of Bath. This re-survey has been presented in a style consistent with the mapping of the rest of the study area. A fifteenth map showing the result of the re-interpretation of the foundered strata was produced as a supplement to the main report. This paper describes the methods and the results of this study and comments on the implications of the technique for land-use planning.

A GIS for the planning of electrical earthing

When creating an electrical earth for a transformer with vertically driven earthing rods, problems can arise either because the ground is too hard or because the ground is too resistive to achieve the required earthing resistance. To assist in the planning of earthing installations a geographic information system (GIS) layer has been created. In its simplest form it consists of a colour coded map that indicates the most likely earthing installation: a single vertically driven rod (indicated by dark green); multiple vertically driven rods (indicated by light green); a horizontal trench, where a rod installation is unlikely (indicated by yellow); for difficult ground, a specialist installation (i.e. drilling; indicated by red). However, the GIS can be interrogated to provide site-specific information such as site conditions, likely depth of installation and quantity of earthing materials required. The GIS was created from a spatial model constructed from soil, superficial and bedrock geology that has been attributed with engineering strength and resistivity values. Calculations of expected earthing rod resistance, rod or trench length, and all possible combinations of ground conditions have been compared with the ‘likely’ conditions required for each of the four proposed installation scenarios to generate the GIS layer. The analysis has been applied to the electrical network distribution regions of Western Power Distribution, in the English Midlands, and UK Power Networks, which covers East Anglia, London and the SE of England. Because the spatial model that underlies the GIS has been constructed from national databases the analyses can be extended to other regions of the UK.

Geophysical-Geotechnical Sensor Networks for Landslide Monitoring

In this study we describe the development of an integrated geophysical/geotechnical sensor network for monitoring an active inland landslide near Malton, North Yorkshire, UK. The network is based around an automated time-lapse electrical resistivity tomography (ALERT) monitoring system, which has been expanded to incorporate geotechnical sensor arrays. The system can be interrogated remotely using wireless telemetry to enable the near-real-time measurement of geoelectric, geotechnical and hydrologic properties.

Landslides at Volterra, Tuscany, Italy

Volterra is a delightful, vibrant medieval hill‐top town, situated at 550 m, on a narrow plateau, midway between Pisa and Siena, and 40 km from the coast (⇓Fig. 1). Originally, Volterra was a leading member of the 12‐city Etruscan federation, under the name Velathri. The town came under Greek cultural influence in the eighth century BC and subsequently under the Romans in third century BC. Important Roman remains include an amphitheatre. Major architectural features within the splendid walls date from the 13th century and include palaces and a cathedral. The town has been famous since Etruscan times for its fine alabaster, which is mined nearby. Fig. 1. Fig. 1. Location map. Remains of part of the Etruscan town are situated on a narrow spur of the plateau, about 0.5 km to the NW of the medieval town (⇓Fig. 2), called Le Balze (meaning ‘steps’, derived from the step‐like multiple slumps). This is the location of a spectacular active …

In situ measurements of near-surface hydraulic conductivity in engineered clay slopes

In situ measurements of near-saturated hydraulic conductivity in fine-grained soils have been made at six exemplar UK transport earthwork sites: three embankment and three cutting slopes. This paper reports 143 individual measurements and considers the factors that influence the spatial and temporal variability obtained. The test methods employed produce near-saturated conditions and flow under constant head. Full saturation is probably not achieved owing to preferential and bypass flow occurring in these desiccated soils. For an embankment, hydraulic conductivity was found to vary by five orders of magnitude in the slope near-surface (0–0.3 m depth), decreasing by four orders of magnitude between 0.3 and 1.2 m depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content, which can account for up to 1.5 orders of magnitude of this variability. Measurements of hydraulic conductivity at a cutting also indicated a four orders of magnitude range of hydraulic conductivity for the near-surface, with strong depth dependence of a two orders of magnitude decrease from 0.2 to 0.6 m depth. The main factor controlling the large range is found to be spatial variability in the soil macrostructure generated by wetting–drying cycle driven desiccation and roots. The measurements of hydraulic conductivity reported in this paper were undertaken to inform and provide a benchmark for the hydraulic parameters used in numerical models of groundwater flow. This is an influential parameter in simulations incorporating the combined weather–vegetation–infiltration–soil interaction mechanisms that are required to assess the performance and deterioration of earthwork slopes in a changing climate.

Chapter 8 Design and construction considerations

Abstract Relict glacial and periglacial environments are widespread, and the deposits that they are associated with mean it is inevitable that the design and construction of many projects will be influenced by their presence and nature. Tills and other glaciogenic deposits prove to be particularly challenging in this context for reasons that include: the spatial variability of the nature of the deposits; the wide range of particle sizes often included within a given soil, including large-sized particles; spatial variation in soil type and properties; variation in depth to rockhead and variable degrees of weathering and alteration; the presence of groundwater, that is misinterpreted as perched water, as well as sub-artesian and artesian conditions; the presence of solution features and fissures, partly or completely infilled with soft or loose material; and the presence of (often shallow) shear surfaces at residual strength. In this chapter, some of the more common problems and associated solutions associated with earthworks and man-made slopes, tunnels and underground structures, dams and reservoirs, foundations, and offshore engineering and installations are reviewed. It is important that great care is taken in addressing the influences of variability, complexity and uncertainty inherent in glacial/periglacial soil formations at all stages of the construction process, from feasibility to end-of-project activities, such as preparation of the as-built drawings.

Shrinkage limit test results and interpretation for clay soils

The shrinkage limit is one of the Atterberg limits and is a fundamental geotechnical parameter used to assess the settlement of engineering soils containing clays, yet is rarely tested for as part of ground investigation. This paper describes shrinkage limit test results on a variety of soils from Britain and overseas obtained using an improved laboratory testing procedure developed at the British Geological Survey. The co-relationships with the other Atterberg limits and with density are explored. In particular, the coincidence of the shrinkage limit with the water content at the peak bulk density achieved in the test is examined. The shrinkage behaviour for undisturbed and remoulded states and a three-way relationship between water content, density and suction are demonstrated. Some tropical residual and highly smectitic soils show a very wide range of shrinkage behaviour, albeit for a small dataset, when compared with the larger dataset of temperate soils tested. Consideration is given to limitations of the new and existing test methods.