Winter 2009 Newsletter
2012 Olympic Park – Bridge Project
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:
- Dedicated project engineers and direction;
- Availability of data during the progress of works;
- Timely production and submission of interim and final reports.
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.
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
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.
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|
|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.
Summer 2009 Newsletter
History and Lineage
ESP currently undertakes hundreds of projects each year ranging from contamination assessments on small developments to large pathfinder projects. Senior Directors Stephen Rice and John Campbell have recently carried out project history reviews and the professional heritage of ESP has really become evident; Stephen first came to work in Wales in 1975 on the post-Aberfan tip stability programme and John Campbell was a resident geologist in the 1980’s employed on the stabilisation of the tips for the construction of the A470 Aberfan bypass.
Stephen and John have been active professional advisors in Civil Engineering and Engineering Geology in Wales for over 30 years and Roly Edwards (now retired as a Director) was technical advisor to Counsel at the Aberfan Tribunal. Our involvement has come full circle with ESP being retained as Geotechnical, Geoenvironmental and Flood Risk experts to the Local Authority on Project Riverside: the redevelopment of the Merthyr Vale Colliery and the source of the historic Aberfan coal tips.
BREEAM Advantage with ESP
Schemes funded by government departments currently require minimum levels of BREEAM attainment and in Wales, all new schemes are required to minimum standards from the Autumn of 2009 onwards. Current development guidance for sustainable buildings advocates a two stage process; The Design Stage and the Post Construction Stage, verified through confirmation of compliance and certification. BREEAM points can be obtained from a variety of design approaches and implementation to individual schemes.
With excellent experience in ground and environmental engineering we have a unique skills-set that enables us to focus on obtaining BREEAM points for development schemes to aid attainment and exceed compliance expectations. The range of applications ESP has experience of and can provide benefit to development schemes are as follows:
- Brownfield Redevelopment: Contaminated Land/Brownfield Assessment and Remediation;
- Renewable Energy Projects: Environmental Impact Assessments for Wind Farm schemes in upland areas;
- Sustainable Urban Drainage Systems: Field assessments for shallow trench or deep borehole soakaway design;
- Ground Source or Geothermal Heating and Cooling: Both shallow and deep, closed and open loop systems;
- Recycling: Proved excellent cost benefits through the sustainable use of aggregates;
- Site Waste Management Plans: Effective quantification and management of waste streams;
- Ecology: Assessment of benefits or protection requirements for ecological features.
While congregating prior to embarking on a Geological Society fieldtrip across the South Wales Church Village bypass project (the largest Welsh road project in progress at present) on a rare dry day during the summer, Group Chairman Paul Maliphant arrived with a special guest. Oscar winning British actor Jim Broadbent, famous for roles in Harry Potter, Bridget Jones and Iris, researching for an upcoming acting role as a Geologist, had contacted Geological Society headquarters in London to arrange some time to speak with practicing geologists and experience the varied environments and roles in which we work.
The Southern Wales Group excursion provided an excellent opportunity for this and ESP Associate Director Matthew Eynon had the pleasure of travelling around the site with Jim for most of the day describing some unique features of the South Wales geo-environments.
L-R: Mike Hughes, Paul Maliphant, Jim Broadbent, Matthew Eynon (ESP) & Craig Roberts.
Pyritic Heave in Aggregates
In our Winter 2009 newsletter we described problems and solutions associated with Dissolution in Limestone Terrains. Previously, we have published a paper on the risks from thaumasite: a calcium-silicate hydrate associated with sulphate reactions and concrete deterioration (In: Nichol, D., Bassett, M. G. And Deisler, V. K. (eds) 2004. Urban Geology in Wales). Continuing our description of unique geo-engineering problems, presented below is a short note on the potentially damaging effects of Pyritic Heave.
There are numerous processes which can cause swelling/heave of a rock or soil mass, these include: Frost heave; Release of strain energy from mineral crystals (massive rock); Hydration of anhydrite to gypsum or of expansive clay minerals; Adsorption of water onto mineral surfaces caused by changes in chemical conditions; Adsorption of water onto mineral surfaces caused by changes in relative humidity (swelling of clays); Pressure build-up of capillary air voids when unsaturated materials are wetted (slaking); Chemical reactions – oxidation of pyrite or sulphate attack.
Pyrite is found in black, carbonaceous deposits (mudstone and limestone) throughout the world. Expansion associated with oxidation of pyritic mudstones is well documented in the USA and has also been proved in England and Wales. We are currently employed as expert witnesses in an alleged Pyrite Heave case on a number of developments in Ireland.
Causes and Challenges
Problems due to expansion of pyrite shale were noted in the UK in the 1970’s, reported associated with fill. Pyrite oxidation can occur as a result of contact with oxygenated groundwater or gaseous O2 diffusion in the unsaturated zone. Low pH values cause a variety of minerals to precipitate including gypsum and humidity, temperature, surface area and morphology are also contributing factors. Formations in South Wales that have a known potential for pyrite formation include the Carboniferous Limestone and Lower to Middle Jurassic Formations. London Basin Formations are also known to have significant pyrite formation potential and are present beneath and around some of the UK’s most developed land and important infrastructure.
Heave usually involves formation of gypsum by the action of sulphuric acid on calcite which may be present in solid form or dissolved in groundwater. These reactions can be particularly damaging to fine grained sedimentary rock materials because the crystals frequently form in laminae and discontinuities. Susceptible pyritic shales and mudstones may be encountered as an in-situ rock, quarried fill, or colliery spoil.
Current consensus is that potential for swelling depends on the amount of pyritic sulphur, with values greater than 0.1% (tentative) having potential to cause structural damage. Swelling pressures developed depend on porosity and exposed surface area. Potential swelling pressures ranging from 70KPa to 2000KPa have been predicted.
In order for the production of gypsum to proceed, there must be sufficient pyrite, calcite and oxygen. Heave may possibly be controlled by capping immediately after excavation or by keeping groundwater level high. Great care must be taken to ensure anoxic conditions persist. Simple chemical testing and an ‘open eyes’ policy on the part of the designers can help avoid these effects, i.e. via obtaining and assessing laboratory data. If total sulphur exceeds acid soluble sulphate, unoxidised pyrites may be present – if contemporaneous with elevated calcium, the materials can be regarded potentially troublesome.
A visit to the quarry/fill source should be made and the material examined (by a geologist with a hand lens) for signs of gypsum crystallisation, provided the fill has been exposed in damp conditions for several months. Alternatively, laboratory samples can be kept in moist conditions for observation (simulation).
London & South East Services
Over the coming months we will be cementing our base in the South East of the UK based on our performance and the ongoing demand for our services. Our extensive work on the redevelopment of Reading Train Station along with numerous other projects along the M4 corridor and central London (including the 2012 Olympic Park Project) have presented this opportunity and more details will be provided in our next newsletter.