Article Laboratories

Use of Standard Laboratory Tests in the Assessment of Slope Stability of Peat

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In December 2006 the Scottish Executive (SE) published a best practice guide for proposed electricity generation developments entitled “Peat landslide hazard and risk assessments”. The SE document includes a requirement for slope stability analysis using the infinite slope equation. While there is nothing wrong with the equation, it pre-supposes that the conventional effective stress parameters are appropriate for peat and furthermore, by implication, that they can be obtained from standard laboratory testing.

In his major work on peat, Hobbs specifically excluded any discussion on shear strength noting that it is clear that the strength depends not only on effective stress but also on time as the void ratio continuously decreases under maintained load. Other authors have reported exceptionally high drained strengths and regard the effective stress tests as problematic.

Notwithstanding the foregoing paragraph, there has been a noticeable increase in demand for effective stress triaxial and direct shear tests on peat to satisfy the requirements of the SE document. Inevitably these tests create major difficulties for the test laboratory and then provide strengths which are not credible to the engineer doing the assessment.

The following comments need careful consideration prior to scheduling what can be time consuming and expensive laboratory tests :

  • Assessment based on compressive or shear stresses may be insufficient for peat in which the main strength may well be tensile due to fibrous structure.
  • For effective stress triaxial and direct shear tests the rate of strain in shearing is derived from the preceding consolidation stages. For peat there are well documented difficulties in identifying primary and secondary compression, and their associated parameters. Standard test procedures rely on data for primary consolidation only in order to calculate compression rates. In peat, secondary compression may be more dominant.
  • In undrained compression, pore pressures increase rapidly and are sustained very close to the applied total stress, thus producing very low effective stresses, often within the uncertainty of measurement of standard testing. This is particularly true where the stresses are initially very low as would be the case for superficial peats. Such low effective stresses are inherently inaccurate and lead to derivation of very high effective angle of friction, 50o to 80o have been reported.
  • In drained compression or direct shear the rapid flow of water from specimens often produces an untypically concave upward trend in the stress/strain curve without achieving failure even at very high deviatoric stress, again producing a very high angle of friction.

 

This cautionary note should not detract from the main requirements and recommendations of the guide, but needs to be given serious consideration when assessing the method of analysis to be used for slope stability in peat. If such laboratory testing is to be used, it is prudent to discuss individual requirements with the laboratory prior to scheduling, but still expect the test results to be problematic.

Peter Keeton, Environmental Services Group Ltd

Article Contaminated Land Laboratories

The problem of made ground

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The categorisation, analysis and reporting of ‘made ground’ is a recurring nightmare for the modern laboratory. Traditionally a by-product of land reclamation schemes, a container of the stuff can contain traces of anything from steel, concrete and brick to nappies and Coke cans – and that’s on a good day.

Ask anyone from the engineer taking samples at the coalface to the men in white coats analysing them, and you will find that there is no all-encompassing approach to deal with the ‘made ground’ conundrum. Nevertheless, with brownfield sites being universally hailed as the sustainable way forward, now, more than ever before, is the time to seriously evaluate the methods employed both on-site and in the laboratory and try to circumvent the insidious ‘no easy answer’ maxim.

Much of the confusion goes back to the introduction of the Environment Agency’s Monitoring Certification Scheme (MCERTS) for the chemical testing of soils. Any laboratory operating under this banner has to submit results that fulfil both the general requirements of ISO/IEC 17025 and the specific method validation and performance requirements of MCERTS. The latter is problematic for laboratories dealing with made ground, inasmuch as it requires samples to conform to specific sample matrices in order for the results to become accredited. For relatively unadulterated soils, this has meant the creation of soil classification categories such as ‘loamy soil’, ‘sandy soil’ or ‘clay type soil’. It is worth noting that while some geotechnical engineers may see this as a tenuous oversimplification, it is widely regarded as the best available approach and has the full endorsement of the Environment Agency and UKAS – albeit based on economical drivers. Made ground’s inherent ambiguity throws a rather obtrusive spanner in the works when faced with these basic matrices and prompts all manner of interpretive stances and questions. Some good starters for ten: can you report made ground results as accredited? Is it possible to report them as ‘unaccredited’ to make it clear to the engineer that the sample does not fall into a clear defined matrix?

It isn’t just an issue of categorisation – the whole process, from preparation to final report, is divested of any consistency as laboratories adopt their own approach by asking questions such as do we dry the sample? Do we mill the sample to uniform particle size? Do we discard anything over 2mm? Do we ignore everything that is not soil? None of these methods will provide an inaccurate result per se, but each has the potential to give a misleading picture of the site.

If, in addition to that head-scratching list of questions, you consider the fact that the commercially driven nature of redevelopment schemes has turned laboratories into high-tech, scientific conveyor belts, the complexities of the problem becomes increasingly pronounced. It is a crossroads situation reliant on good judgement, experience and, above all, a decent sample. It is impossible to overstate the critical nature of the latter point: without a comprehensive sample, the laboratory cannot do its job. In other words, it cannot capture the essence of a site’s industrial legacy and act as a signpost to the appropriate action.

Though MCERTS has to a certain extent raised the standards in the laboratory, it missed an opportunity by not offering any guidance to the geotechnical engineer on the best available techniques (BAT) for sampling, storage and transportation; nor does it elaborate on the consequences of incorrect, inappropriate or inadequate sampling. The reason the EA has put the onus on the laboratories is understandable – to allow continuity of testing pre- and post-MCERTS – but the resultant confusion and knowledge deficit, particularly with regards to sampling, is less than satisfactory.

As throwing legislation at the problem is unlikely to be constructive, the best achievable course of action is to engender a milieu of interdisciplinary compatibility fuelled by open lines of communication, intellectual communality and the symbiotic sharing of knowledge. Geoscientists should learn how to adequately describe their sample, how to make the sample manageable for the laboratory and to understand the laboratory machinations of sample preparation, analysis and reporting. By the same token, chemists should acquire some field experience, learn about the conditions engineers face on-site and educate themselves on the processes that inform geotechnical sampling techniques.

If the question of how to produce consistently accurate results from made ground is reducible to a single answer, it can only be to ask more questions: what are the limitations of the selected analytical method? If there are limitations, do they matter in this case? On what basis is the data reported? Does it match the basis on which my acceptance criteria are calculated? Has the sample data been generated in ideal conditions using ideal standards which are unlikely to represent the conditions on my site? Add a soupçon of communication, wait for MCERTS to catch up and we’re well on our way.

Andrew Buck PhD, MSc, CSci, CChem, FRSC is the Technical Director of Envirolab (www.envlab.co.uk)

Article Contaminated Land Laboratories

MCERTS

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The Environment Agency’s Monitoring Certification Scheme for the Chemical Testing of Soils:
What it is. How it affects you. What you need to do.

MCERTS Monitoring Certification Schemes were first introduced in industrial sectors with regulated processes that resulted in stack emissions. The scheme requires those companies to deliver monitoring results that are “valid, reliable and accurate”. To get to this position depends on using the appropriate resources – correct test methods, competent personal, accredited organisations and suitable equipment and planning.

The MCERTS scheme for chemical testing of soils was introduced by the Environment Agency to support their regulatory activities and make informed, quality assessments on the management of contaminated land under a number of regimes, including, Part IIa of the Environmental Protection Act 1990, Pollution Prevention and Control Regulations 2000 and the Waste Management Licensing Regulations 1994.

The scheme is applicable to all testing laboratories and procurers of analytical services, where results generated for the chemical testing of soil are submitted to the Agency. In order to gain accreditation on the scheme, laboratories are required to have their processes, essentially test methods, in a quality management framework, by both the United Kingdom Accreditation Service (UKAS) to the international standard ISO 17025 and also MCERTS requirements.

There are increasing pressures on businesses to comply with Environment Agency regulations and European and international standards. Using a laboratory with MCERTS accreditation alleviates some of this pressure because it guarantees the proper use of suitable methods, standards, services and equipment, trained and qualified personnel, quality assurance and quality control all leading to reliable data. MCERTS accreditation also assures users that the laboratory meets performance standards set out in current international standards and the growing requirements of EC directives.

Failure to meet the regulations can be costly, both financially and to a company’s reputation. An MCERTS accredited laboratory assures the user that they have met standards in a number of areas including:

  • The selection and validation of test methods

  • Sampling pre-treatment and preparation

  • The estimation of measurement uncertainty

  • Participation in proficiency testing schemes

  • The reporting of results and information

The benefits of the scheme include:

  • Providing assurance to stakeholders of the quality of data from testing

  • A level playing field, based on the Agency’s requirements, is established

  • Identifying that the chemical testing of soil is a critical component in producing defensible data for regulatory purposes.

In order to guarantee reliable data from the chemical testing of soils and therefore reassurance that risks are minimised, procurers of testing should:

  • Ensure the chemical analysis results submitted to the Agency for regulatory purposes conform to MCERTS requirements.

  • Check that the laboratory conducting the testing has MCERTS accreditation for all the parameters requiring analysis. Accreditation is given on a parameter-by-parameter basis. If they do not have the correct accreditation sub-contracting of the test required to another MCERTS laboratory may be required. If a suitable laboratory does not appear to be available, contact the Environment Agency for advice.

  • Check that the test methods employed by the laboratory are appropriate and fit for purpose in terms of the parameter, the Critical level of interest (CLI) and the matrix. The CLI may be a soil guideline value or a regulatory limit.

  • Check with the laboratory that the sampling processes, preservation and transportation are appropriate.

  • In collaboration with your chosen laboratory, have complete audit trails available that address aspects such as sample location, depth of sample, date and time of sample, reference identity and the laboratory used.

The MCERTS scheme for the chemical testing of soils was phased in, but has been fully operational since 1 March 2005. Therefore, all data for regulatory purposes should now be to the MCERTS standard. Laboratories and the procurers of testing need to work together to ensure that the test data provided meets the requirements and satisfies the needs of the ultimate client.

Cliff Billings Group Technical & Quality Manager STL UK

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EA’s position on MCERTs

From 1st March 2005, the Environment Agency has required accreditation to our Monitoring Certification Scheme (MCERTS) where laboratory soil testing results are submitted to us as part of a regulatory regime for which we have statutory responsibility.

We strongly recommend that MCERTS accredited methods are used for soil testing in activities to do with site remediation, whether carried out on a voluntary basis or to comply with planning requirements. This is particularly important in relation to any waste management issues on the site.

Jackie Harrison Environment Agency

Contaminated Land Working Group Meetings

In recent meetings of the Contaminated Land Working Group, it has been clarified that the EA is a consultee but not a Statutory Regulator for planning applications. This means that MCERTs data may not always be required at the planning stage. Although the EA recommend MCERTS, the final decision is up to the Local Authority.

Some AGS Members feel that all tests should be to MCERTS so that the reports can be used at a later date. At present, the EA is expected to take a pragmatic approach to historical data obtained before the introduction of MCERTS and take account of whether the laboratory is now accredited, and other relevant factors. However, this may not always be the case, particularly for data collected after March 2005, and the need to ‘future proof’ data should be seriously considered.

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Meet NHBC Requirements with MCERTS

The NHBC welcomes MCERTs accredited testing and supports it’s use in association with robust and representative soil sampling strategies when investigating sites affected by contamination. It brings transparency and consistency to the analytical testing techniques and encourages discussion between the consultants and testing laboratories which can only be a positive step forward.

Article Laboratories

MCERTS implementation still set for 1 March 2005

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In view of the fact that many companies will find that no laboratory has MCERT accreditation for all the tests they require, the EA has been asked for clarification and guidance about what interim measures may be applied.

The response indicates that moving implementation deadlines has not proved productive in increasing the number of MCERTS laboratories, and may in fact be counter productive, as some labs may believe the scheme will never be fully implemented and enforced. Therefore, the scheme will be fully implemented from 1st March.

The EA concede however, that some pragmatism may be required in the short term. In general, procurers of analytical services will be expected to choose the laboratory that best meets their requirements, i.e. the one that can carry out the highest percentage of the required Annex A parameters to MCERTS standard. In order for this to be accepted, evidence may be required in order to demonstrate that steps were taken to find the most appropriate laboratory.