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A detailed site characterisation was undertaken in order to assess methods that could be used to determine the depth and lateral extent of a potentially collapsible loessic brickearth deposit at a site in Kent. The investigation presented in this paper covers both geotechnical and geophysical evaluations, correlated to detailed lithological logs of trial pits at the site. This enabled cone penetrometer profiles to be compared directly with a suite of rapid geophysical survey techniques, which included electromagnetic (EM31 and EM34), electrical resistivity surveys and shear wave profiles, calibrated against the same soil profile. From this it was possible to determine the variability and extent of a collapsible loessic soil across the entire test site, thus demonstrating that appropriately calibrated geophysical techniques can provide a rapid indication of the presence at depth of a potentially unstable soil. [ABSTRACT FROM AUTHOR]

The Thames Water ring main extension is a 4·5 km long tunnel from Stoke Newington, in the London borough of Hackney, to New River Head in Finsbury, in the London borough of Islington. The 2·85 m i.d. tunnel was excavated by an earth pressure balance tunnel-boring machine (TBM) at depths between 40 and 60 m below the surface. Surface settlements along the route were measured by precise levelling, and were found to be small. It was therefore even more important to measure these settlements as accurately as possible, in order to provide informed estimates of subsurface movements induced in third-party underground structures much closer to the tunnel horizon. Because of the relatively large magnitude of the background movements measured, when compared with the small tunnel-induced settlements, it was necessary to adopt a rigorous statistical method to fit a Gaussian curve to the data. This exploited the analogy of the 'error function' to define the Gaussian curve parameters and . In all, 13 tunnels were underpassed successfully by the TBM, all within the 'conservative expected value' predictions, and without incident. The predictions and structural monitoring schemes undertaken for the High Speed 1 tunnels near Corsica Street and the Northern line tunnels near Angel station are described in the paper. It was found that the surface and subsurface trough width parameter did not vary with depth as predicted: therefore a new relationship is proposed. [ABSTRACT FROM AUTHOR]

The redevelopment of London Underground's King's Cross St Pancras Station in central London is being carried out to increase capacity from the current 55000 passengers per hour during the morning peak to an anticipated 82000, following the construction of the adjacent Channel Tunnel Rail Link (CTRL) terminus. The work will be undertaken in two phases: phase I works, currently nearing completion, which comprises a new western ticket hall and upgrade of the existing tube ticket hall; and phase II, which will comprise a new northern ticket hall and tunnelled links between the existing underground stations. This paper reviews the considerable amount of geotechnical work carried out for the project and will focus principally on three key areas: (a) developing an understanding of the potential hazards related to the stratigraphy of the site; (b) the use of advanced numerical methods; and (c) the role of instrumentation and monitoring within the design and risk management process. [ABSTRACT FROM AUTHOR]

The creation of the Olympic Park, commenced with the formation of the development platform, on which the venues and infrastructure was built. This was part of the enabling works, and included 2 million m of excavation, and the remediation of contamination. To enable the contaminated soils to be reused, a number of soil treatment techniques were adopted: soil washing, bioremediation, chemical stabilisation and material sorting. Soil washing was the main technique, treating around 700 000 m of soil by mixing it with water. This removed the fine grained fractions on which the contaminants were predominantly based, creating a filter cake, typically around 20% of the total volume of soil washed. Bioremediation and chemical stabilisation together treated less than 100 000 m of soil. A regime of chemical testing was established to test the materials at the excavation stage, manage the treatment and finally validate the final material. With the exception of the final validation, testing was carried out off site in MCERTS accredited laboratories, the bulk of the testing was undertaken in the site laboratory, which also handled geotechnical testing. [ABSTRACT FROM AUTHOR]

The present work has established a methodology that allows the user to determine areas susceptible to shoreline recession and cliff instability. This methodology includes the development of a qualitative loss estimation system which utilizes geotechnical field mapping observations and shoreline retreat predictions to estimate the exposition of critical infrastructure to hazards posed by cliff collapse and retreat. The technique identifies hazardous areas along coastal cliff environments. The assessment was undertaken along the cliff section between Brighton Marina and Portobello, East Sussex, UK. The cliff line was divided into 22 sections according to the cliff's geology. Each of these sections was mapped and described with respect to the lithology and possible failures that could occur. Historical shoreline recession analysis was used for the prediction of future shoreline positions. The prediction of future shorelines was performed by using the Digital Shoreline Analysis System, extension of ESRI's ArcView 9.x. The analysis was based on historical maps and aerial photographs dating from 1873 to 2005. The long term average cliff recession rates clearly show that cliff retreat has declined through time due to the presence of coast protection and cliff stability measures. Although these measures have delayed cliff recession to a great extent, they have not eliminated it. [ABSTRACT FROM AUTHOR]

A detailed borehole investigation has recently been undertaken for an extension to the Thames Water ring main in north London. Results of this were presented in a preconstruction geological model. This formed the basis for tunnel designers to assess ground conditions prior to construction and implement mitigation design and/or contingency plans in the event of adverse geological conditions being encountered. Previous sections of the ring main were constructed using open-faced tunnelling techniques. These allowed for inspection and continuous record of ground conditions at the tunnel face, enabling an identification of the geology and prediction of potentially adverse ground ahead. In facilitating such close geological supervision, tunnelling benefited from significant programme savings - in particular, a reduction of risk to the health and safety of underground personnel. In constructing the tunnel extension, a closed-face tunnel boring machine was opted for; this largely concealed the exposure of geology in situ during the excavation cycle. Apart from a limited number of tunnel face inspections, an indication of the geology was formed from observation and logging the spoil arising from the tunnelling machine, aided by an assessment of the performance of the machine itself in response to changes in geology over the alignment. These activities were necessary in validating the preconstruction geological model and in providing assurances to the on-site design and construction teams. [ABSTRACT FROM AUTHOR]

A site in central London called One New Change is currently being redeveloped. The new development has a basement that extends to approximately 14 m below ground level. Demolition of the building that formerly occupied the site, excavation of the new basement and construction of the new development have caused unloading and subsequent reloading of the ground. This change of loading has resulted in displacements occurring to the nearby London Underground Central Line tunnels that run parallel to the northern boundary of the site. The crowns of the tunnels vary from approximately 20 to 25 m below ground level. The piles and retaining wall for the proposed works are located at least 7 m clear distance to the south of the tunnel closer to the site boundary. The results of analyses carried out to assess the effects on the tunnels indicated that the imposed distortions caused by the proposed works were within tolerable limits. Monitoring was proposed to check that ground and structural movements were within the range of calculated values, and contingencies were identified in the event of agreed trigger levels being exceeded. Displacements measured during the demolition, excavation and construction phase of the project are presented. Conclusions are drawn from comparing the measured displacements with the tunnel deformation calculations. [ABSTRACT FROM AUTHOR]

A trial strain-monitoring system using Brillouin optical time-domain reflectometry (BOTDR) technology was set up to monitor joint movements in the concrete tunnel lining in an existing London Underground tunnel. The BOTDR strain sensor system allows the measurement of strain distribution along an optical fibre using the reflective technique, requiring access to only one end of the fibre. Measurements were obtained by a strain-sensing optical fibre installed along the tunnel lining. The joint movements were captured by measuring the strain along the fibre across the segment joints. The results show that there is good agreement between the joint movements evaluated by the BOTDR strain sensor system and those by conventional vibrating-wire strain gauges. Whereas conventional strain measurement gauges monitor the strain variations at discrete locations, a BOTDR strain sensor can provide a continuous strain distribution of the tunnel lining. The results demonstrate the practicality of using the BOTDR strain-sensing system to monitor the movement of tunnel linings. [ABSTRACT FROM AUTHOR]

The design, construction and monitoring of a 12 m deep basement for the Chapelfield Shopping Centre, Norwich, UK are reviewed. The extent to which data and reports from similar nearby construction projects allowed cost savings and reduced risks, particularly regarding solution features in the chalk, has been assessed. By having robust engineering solutions and contingency measures agreed at the start of construction, geotechnical works for the project were completed without delays or significant additional costs. Back-analysis has shown a good fit between actual performance and that predicted using the soil parameters chosen. Using hindsight, an assessment is made of whether all potential benefits from the prior knowledge of the performance of similar excavations in the area were realised. [ABSTRACT FROM AUTHOR]

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The article presents information on the performance of flood embankments in England and Wales. It discusses the geotechnical factors that can affect the performance of fluvial and estuarine flood defense embankments in the short and long term. The discussion considers the traditional methods used to construct flood embankments compared with modern techniques, the type of local materials used for construction, the range of possible geotechnical factors that can lead to a loss of performance and finally case histories of embankment breaches.

INTERVIEW Engineering beats Pisa's problem John Burland has been professor of soil mechanics at Imperial College London for 20 years and is recognized as a distinguished figure in geotechnical engineering. David Smith talks to him about his work. [ABSTRACT FROM AUTHOR]