Investigation of change in shear wave velocity with increasing applied stress for two samples from Holme Pierrepoint

The development of capability in the measurement of superficial deposit thickness has required laboratory testing to integrate with values obtained from field trials of a number of methodologies and equipment. The use of shear waves to detect the base of a deposit depends on an accurate knowledge of the internal velocities of the material in the deposit. It is also important to know the shear wave velocities of the materials at the deposit interface. The site used for initial assessment of equipment and methodologies was a series of sand, silt and gravel layers overlying a weathered mudstone. There are a number of interfingered facies within the body of the deposit, which may have differing interval velocities. The object of this laboratory study is to determine the shear wave velocities through undisturbed samples of the deposit material and the underlying solid geology. The samples under test are silty fine sand and the weathered mudstone. The gravel layers could not be sampled in an undisturbed state and have not been included in this study

Subgrade geology beneath railways in Manchester

It is not sufficient to identify fine-grained soils, only, as locations for potential subgrade problems as could be done using a traditional 2D geological map. More information is required about the geological structure, lithological variability, mineralogy, moisture content and geotechnical properties of the soil, much of which can be supplied by modern 3D geospatial databases. These databases can be interrogated at key depths to show the wide variability of geological materials and conditions beneath the ground surface. Geological outcrop and thickness of bedrock an superficial deposits (soils), plus the permeability and water table level are predicted from the Manchester geospatial model that is based on 6500 borehole records. Geological sections along railway routes are modelled and the locations of problem soils such as alluvium, till and glaciolacustrine deposits at outcrop and shallow subcrop are identified. Spatial attribution of geotechnical data and simple methods to recast sections in engineering geological terms are demonstrated

An evaluation of combined geophysical and geotechnical methods to characterize beach thickness

Beaches provide sediment stores and have an important role in the development of the coastline in response to climate change. Quantification of beach thickness and volume is required to assess coastal sediment transport budgets. Therefore, portable, rapid, non-invasive techniques are required to evaluate thickness where environmental sensitivities exclude invasive methods. Site methods and data are described for a toolbox of electrical, electromagnetic, seismic and mechanical based techniques that were evaluated at a coastal site at Easington, Yorkshire. Geophysical and geotechnical properties are shown to be dependent upon moisture content, porosity and lithology of the beach and the morphology of the beach–platform interface. Thickness interpretation, using an inexpensive geographic information system to integrate data, allowed these controls and relationships to be understood. Guidelines for efficient site practices, based upon this case history including procedures and techniques, are presented using a systematic approach. Field results indicated that a mixed sand and gravel beach is highly variable and cannot be represented in models as a homogeneous layer of variable thickness overlying a bedrock half-space

A comparison of trackbed design methodologies: a case study from a heavy haul freight railway

One of the major roles of railway trackbed layers is to reduce vehicle induced stresses applied to the underlying subgrade to a level that limits the progressive build up of permanent deformation. The ability of trackbed layers to satisfy this requirement is dependent upon the materials used for construction and their thickness. Numerous design methods, (both empirical and analytical), have been developed across the World to evaluate trackbed design thickness. However, where there is limited information or experience of previous trackbed design with the specific materials or site conditions under consideration, the choice of methodology becomes one of engineering judgment, in assessing the significance and reliability of the design input parame-ters. This paper describes a number of design methods which were assessed in a recent project to design a new heavy haul freight railway trackbed, founded on moisture sensitive subgrades, using locally available materials for the track support layers. The produced design thicknesses for each of the methods are compared for differing subgrade conditions. The results show considerable variation of thicknesses from each method with little consistent pattern to the variation. Reasons for these variations are suggested and the choice of the final design used for specific subgrade conditions are presented together with appropriate justification. Concluding on these issues, recommendations are made for a more considered approach to trackbed design

Determination of the shrinkage and swelling properties of the Lias clay : oedometer consolidation testing

This report presents the factual results of laboratory tests into the one-dimensional consolidation properties of clays from the Lias group. Two sets of tests were carried out, one loading to 4400 kPa and the other loading to 1776 kPa, based on the size of sample available. The lowest range of volume compressibility was 0.021 m2/MN and the highest 2.302 m2/MN. The lowest range of consolidation coefficient was 0.27 m2/year and the highest 159.54 m2/year