2012 Olympic Park - Bridge Project
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During the latter part of 2008 and early 2009, ESP have been working with Hochtief (UK) Construction to deliver an assessment of ground conditions on part of the very large London Stratford Olympic Park site. The project has involved a series of boreholes to assess ground conditions beneath an existing rail track-bound embankment for a proposed piled bridge link between Stratford Regional Station and the “gateway to the games” – the new Aquatic Sports Centre. Ground conditions proved challenging, with variable River Terrace Deposits, Woolwich and Reading Beds overlying the Thanet Sands; a glauconitic quartz sand which is one of the oldest sediments in the London Basin. Key elements of our contribution to the project included:
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Contributions to Geoscience
Geological Society Award Winner
In May 2008, the Southern Wales Regional Group of the Geological Society invited entries for the inaugural Early Career Geologists Award. Following a presentation lecture at Cardiff University, ESP Associate Director Matthew Eynon was presented the award based on strength of content and presentation of the paper to a peer group. The award was judged and presented by the current chairman of the Southern Wales Regional Group, Paul Maliphant. The paper can be downloaded from the Corporate and Community Events section.
Endorsed Professional Training/CPD
During January 2009, in a reprisal of earlier presentations, Matthew Eynon was invited to represent ESP as a guest speaker with fellow professionals to a Geological Society CPD Symposium, again at Cardiff University, titled Visualising the invisible - Conceptual ground modelling: the foundation of best practice geoscience.
University of Wales Lectures
ESPs commitment to supporting higher education has continued through 2008, most recently with our annual presentation to Swansea Metropolitan University Construction Students on principles of geo-engineering and aspects of development projects. This has become a regular fixture in the diary, having been invited back each year since 2005.
Commencing during Lent Term 2009, ESP Director Giles Sommerwill has been invited to provide a programme of lectures to MSc Civil Engineering Students at the University of Wales, Newport. The theme of the lecture series is Contaminated Land: hazard identification, principles of risk assessment and selection of appropriate remedial/reclamation solutions. Having the input of an ESP practicing professional will no doubt enhance the knowledge of the upcoming civil engineering professionals in South Wales.
Dissolution in Limestone Terrains
Background
Over the past six months, ESP has been retained as the principal geo-consultant and engineer on a number of schemes where we have been tasked with providing engineering guidance on solution features within natural limestone deposits. The karstic nature of the subsurface limestone bedrock in South Wales gives rise to a number of unique geotechnical problems that require consideration and action during development (and sometimes retrospectively if an emerging condition).
Causes and Challenges
Solution features are commonly encountered at geological contact zones between the Carboniferous Limestone, adjacent bedrock units (commonly the Carboniferous Coal Measures and Triassic Marginal Facies) and superficial deposits.
These features are formed by chemical weathering of carbonate or saline rocks and subsequent collapse. They are commonly in-filled with material derived from the overlying deposits; which is typically soft or loose in nature, and may result in voids.
The presence of solution features can be a significant challenge for both civil engineering construction works and existing structures with settlement of structural foundations, road pavements and infrastructure. Limestone can be a risk even where not present at surface and hence not indicated on geological plans. Notably, solution of saline rocks can be rapid.
Features in the Field
Where superficial deposits are thin, solution features can be easy to identify by topographical features such as a surface cone shaped depression (in non-urban environments). Where superficial deposits are thicker, or solution has occurred along a vertical/sub-vertical fissure, the feature can be deeper and more difficult to identify using field mapping techniques. Intrusive investigation work is often required to prove the geometry. Definitions vary by region and these features are referred to by many names including; Gulls, Cavities, Dolines, Sinkholes, Swallets and Whiskey Holes.
Treatment Options
Depending on the objectives of the treatment, different remedial options are available. The importance of understanding the problem at an early stage is essential in ensuring Value Engineering options are obtained and implemented for the client, as shown below:
| Method of Treatment | Structures | Roads | Infrastructure | Relative Cost |
| Excavation/Replacement | • | • | • | Low Cost |
| Ground Treatment - Compaction | • | • | • | Moderate Cost |
| Ground Treatment - Grouting | • | • | • | High Cost |
| Reinforced Capping | • | • | Low/Moderate Cost | |
Modified Foundations |
• | Moderate/High Cost |
| We are currently acting as Expert Witnesses on several schemes where full appreciation of the karst hazard was not achieved prior to construction. Commonly, and to the benefit of the development project, an awareness of these issues at project conception would likely have diverted significant remedial costs. In addition to our work where Limestone Solution Features contribute to development risks, ESP are also currently retained as Expert Witnesses on a number of other cases including excavation problems, deep basement construction/hazards and pyritic heave in aggregates. |
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