Posts by Katie Kennedy


Advice and Guidance on COVID-19

- by
Tags: Featured

The below advice and guidance is correct as of 3rd April 2020. This list will be updated as further guidance is published.

The current main advice from the Government is to:

Stay at home

  • Only go outside for food, health reasons or work (but only if you cannot work from home)
  • If you go out, stay 2 metres (6ft) away from other people at all times
  • Wash your hands as soon as you get home
  • Do not meet others, even friends or family. You can spread the virus even if you don’t have symptoms.

The Government has published guidance on working during the current period of restrictions which can be found at

Further updates from the Government can be found at

The Construction Leadership Council (CLC) published an updated Site Operating Procedures Version 2 on 2nd April 2020, however due to feedback, the CLC has re-issued version 1, which is the document the industry should be complying with.
Version 1 can be found at

On 31st March 2020, the Secretary of State provided a letter to the UK Construction Industry which can be viewed here.

The CLC has prepared a template of a letter that firms can adopt and adapt to issue to their workforces regarding travel to work.

For up-to-date guidance and advice, please visit, and


AGS Magazine: March/April 2020

- by
Tags: Featured

The Association of Geotechnical and Geoenvironmental Specialists are pleased to announce the March/April 2020 issue of their publication; AGS Magazine. To view the magazine click here.

This free, publication focuses on geotechnics, engineering geology and geoenvironmental engineering as well as the work and achievements of the AGS.

There are a number of excellent articles in this month’s issue including;
Update from the AGS regarding COVID-19 – Page 4
Are traditional sampling techniques really that bad? – Page 6
A Candid Look at Responses to SiLC Membership Questionnaire 2019 – Page 12
AGS Guide to Occupational Stress – Page 16
Q&A with Chaido Doulala-Rigby (Yuli) of Tensar International – Page 22

Advertising opportunities are available within future issues of the publication. To view rates and opportunities please view our media pack by clicking HERE.

If you have a news story, article, case study or event which you’d like to tell our editorial team about please email Articles should act as opinion pieces and not directly advertise a company. Please note that the publication of editorial and advertising content is subject to the discretion of the editorial board.


Q&A with Chaido Doulala-Rigby (Yuli)

- by
Tags: Featured

Full Name: Chaido Doulala-Rigby (Yuli)

Job Title: Business Development and Chief Civil Engineer Eastern Hemisphere (EH)

Company: Tensar International Limited

My engineering journey started in Greece where I was born, grew up and got my first degree in Civil Engineering. In my 26 years engineering career so far, that spans across the globe, including 10 wonderful years in Hong Kong working as a Geotechnical Engineer, I feel blessed to have been part of some extraordinary projects and to have met some truly amazing people both on a personal level and professionally.

Upon my return to the UK from HK some 14 years ago, I joined Tensar International and soon progressed to become the Chief Civil Engineer of the Company that invented Polymer Geogrid Technology and “revolutionised Civil Engineering” (as quoted in the ICE200 publication in 2018).

What or who inspired you to join the geotechnical industry?

I owe my initial ‘attraction’ to Geotechnics predominately to Dr Evan Passaris, who was a professor at Newcastle University upon Tyne back in the early 90’s and encouraged me to do their MSc in Rock Mechanics and Foundation Engineering. Upon my MSc completion in 1994, I joined the Jubilee Line Extension (JLE – Contract 102) that was under construction in London, working as a graduate tunnel engineer for Balfour Beatty/Amec JV. At the time, JLE was the largest Civil Engineering project in the UK and still remains one of the most expensive projects in the world of all times at over £4 million per meter of its 16km length!

Looking back, I can confidently say that, while my MSc intrigued my appetite for Geotechnics, it was joining the JLE tunneling project that cemented my decision to follow Geotechnics. It taught me to expect the unexpected when dealing with soil, which fascinated me and encouraged me to further explore the weird and wonderful world of Geotechnics. And here I am, just over a quarter of a century later, still in Geotechnics and still loving it!

What does a typical day entail?

There is no such a thing as a ‘typical’ day and I guess that’s the best part of being an engineer, no 2 days are the same! I love travelling and I love educating people from all backgrounds about the magnificent performance of geosynthetics and especially Tensar’s leading geogrid technology. My current role is largely a combination of both. It is quite a demanding role, that I enjoy enormously, but I have worked very hard to earn it and I still work even harder to keep up with its ever-expanding nature. Many people say I am ‘lucky’. But I don’t believe in ‘luck’. I believe we can all create our own ‘luck’, and I find that the harder I work, the ‘luckier’ I get, meaning the more I get invited to travel for Tensar. What the people that call me ‘lucky’ don’t know is the amount of preparation that goes behind the ‘glamour’ of travelling. There are many reasons for my work related travel: to present bespoke technical papers that I author to International Conferences, to deliver bespoke design training to Tensar’s various EH offices that I look after, to present our cost, time and value message to suit specific Clients’ requirements, to present our latest R&D research to technical forums, to participate to committee/panel meetings, to do STEM talks and/or activities with hundreds of school children and students, to review, interview and judge technical submissions of Industry projects’ entries on behalf of various independent Industry Awards such as Ground Engineering, ICE, Engineering Trust etc. What people that call me ‘lucky’ don’t see is the ‘red eye’ car, train and/or flight journeys that I take to get me to my destination on time and in the most efficient way and the weekends and early mornings or late nights that I spend on my kitchen table writing or assessing papers and preparing for my bespoke presentations. A large part of what I do is indeed voluntary and outside my normal, ‘day job’ working hours not because I ‘have to’ but because I choose to do so. Having gained so much experience in Geotechnics and in Engineering at large over the years, it gives me great joy and pleasure to be able to share my knowledge and give back to the engineering community, whether it is by participating in committee work, Industry award judging or getting involved in STEM work.

My ‘day job’ involves fast-track live project risk management by directing, advising, checking and indeed carrying out designs for Tensar’s multidisciplinary applications requests that land in my inbox daily from all over the world. Enquiries can vary from as simple as: “What fill can be used to build a 3m high car park retaining wall with your geogrids?” to “Can we build a 30m high dam with your geogrids?” to “Can you help us support a ~3,000ton crane over soggy paddy fields in Vietnam?!”. Or from: “Can you represent the ICE and talk about What Is Civil Engineering to students in an upcoming Engineering Day event at a University in Manchester” to “Can you come to Peru next month to present Tensar’s containment capabilities to a mining Client”! So two days are never the same and it is this unpredictable variability of what I do that I love the most, not knowing what soil type, request or idea tomorrow brings! Undeniably, there are times that managing my ever-evolving to-do list can get frustrating too, but after all these years, I have learned to know when to close my laptop and remind myself, and other like-minded colleagues, that ‘tomorrow is another day’.

Are there any projects which you’re particularly proud to have been a part of?

I take pride in every single project that I get involved with. But if I had to choose a single construction project that I got involved with in my career so far, it has got to be Tensar’s tallest geogrid reinforced soil embankment walls in Fujairah, UAE, that were constructed in 2011. The project was a massive cut and fill exercise whereby in-situ Gabbro mountains were blasted to create rock cut slopes with heights in excess of 100m, while the blasted rock was crushed and reinforced with our geogrids to form massive 60m high soil embankments to cross the valleys in between the mountains to support a new freeway connecting Dubai with Fujairah port. Our reinforced soil embankments replaced the originally proposed viaducts due to the surplus of blasted rock available and due to the access and construction difficulties a viaduct construction would pose in such harsh and arid environment. I am very proud to have led the design and supply team of Tensar Engineers to deliver this project, that included remote resource coordination, multicultural team engagement, and many site specific design alterations that I had to manage under very tight deadlines to best fit unforeseeable and challenging geomorphological conditions that were encountered during construction. And a few amazing trips to the site too!

The other ‘project’, that I take immense pride to be part of, is my voluntary role as a registered STEM Ambassador, for which I am grateful to have Tensar’s full support. My involvement with STEM started in 2018, thanks to the British Army that invited me to role model my career in Civil Engineering to young female school students, at the first ever Army-supported STEM careers’ fair. The event, that saw 900 female students aged 11-18 participating, was organised at the Military Royal Academy Sandhurst in May 2018 in support to the UK Government that declared 2018 as ‘Year of Engineering’ in an effort to help close the skill and gender gap our Industry is facing. The same event was repeated in 2019 but expanded over two days and attracted 2,000 school students of both gender and it is due to be repeated in 2020 scheduled to reach even more students from even more remote regions and form more underprivileged backgrounds, proving that there are no boundaries to engineering and that engineering is for all.

What are the most challenging aspects of your role?

On a Company level, as the inventors and leaders of polymer geogrid technology for over 40 years, Tensar’s greatest frustration is that, together with other manufacturers now,  despite the independently tried, tested and proven benefits of geosynthetics in reducing cost, time and carbon in earthworks construction, we are still trying to ‘convert’ vital sectors of our Industry like Highways and Railways and convince them to include geosynthetics in their design standards and codes, rather than still treating geosynthetics as a ‘departure’. In parallel, our added challenge is in trying to maintain top quality standards across the Industry and differentiate amongst the various geosynthetic products available in the market and their different functions. And although some companies, like Tensar, have invested a large amount of money to have our products independently tested, verified and certified in achieving a certain performance, unfortunately there are a lot of products available in the market that because they look the ‘same’, they claim that they perform the same. Our critical challenge is trying to keep up with defending our specification in our multiple live projects and trying to educate the Industry why ‘everything that looks like gold is not gold’. To this end, we have come together with other like-minded geosynthetics manufacturers and we succeeded in including some good guidance in two recent publications, namely the TWf Good Guide to Practice and the EFFC/DFI Guide to Working Platforms, whereby the advice to engineers is that, if they want to consider an alternative geosynthetic product, in a piling platform design for example,  they MUST seek an alternative FULL design rather than just swapping with cheaper geosynthetics alone; each geogrid or geotextile performs and interacts with the available fill material in a completely different and unique way, which has direct impact to the working platform design thickness and performance.

On a personal level, working for a company with Global reach comes with quite a few challenges from managing different time zones, different design codes and indeed different cultures to keeping up with local Industry updates by making time to actively participate in various technical panels and committees, often international. And while everybody is talking about ‘devolution’, most such committee and panel meetings still take place in or near London. And despite all remote digital aids available such as Webex, Skype and Teams, in a lot of such discussions, face-to-face interaction is still irreplaceable. My challenge is to plan as far ahead as possible and try to keep my diary up to date so I can fit in as many meetings as possible in a single journey, especially as I live and work ‘up’ North, in Lancashire.

What AGS Working Group(s) are you a Member of and what are your current focuses?

I am a member of the Geotechnical Working Group of AGS. Our current focus is trying to investigate, assess and compliment, if necessary, the currently Industry standards and guidance on ground improvement techniques and especially vibro stone column and dynamic compaction and their post-construction validation testing on site. Other areas of current focus of our working group is EC7-Part 2, improving sustainability in current site investigation process and the increasing volume and cost of BSI publications and its impact on SMEs, just to name but a few.

What do you enjoy most about being an AGS Member?

I enjoy meeting and interacting with like-mined professionals from our Industry and working together towards the betterment of our Industry by sharing knowledge and lessons learned, identifying knowledge gaps and filling such gaps by collectively and/or individually writing and disseminating papers and guidelines.

What do you find beneficial about being an AGS Member?

Personally, I benefit from knowing that I can contact other AGS members for professional advice that I can trust whether on project-specific or Industry-specific issues.

On a Company level, we find receiving and reading the AGS magazine informative as it includes current Industry updates. We also greatly benefit from participating in the AGS Conferences both for networking but also for having the chance to openly voice, share and discuss our concerns and issues with the Industry. To that end, I was extremely grateful to have the opportunity to organise and chair a panel discussion with representatives from all stake holders from our Industry including Clients, Consultants, Contractors and Academia that was aired at the AGS AGM in 2018 and included a lively audience participation. The objective of our panel discussion was about bridging the gap between designers and constructors and how do we make sure that the Engineers on site understand the importance of following the construction drawings’ specifications and what would be the implications, if, for example, they chose to use materials of lesser quality rather than the higher quality ones specified in the drawings. The panel discussion concluded that any such arbitrary replacement, which might lead to apparent cost savings, would most definitely lead to inadequate design and ultimately to an unsafe structure liable to collapse and even cause death and therefore our Industry must enforce stricter quality control and independent supervision on site.

Why do you feel the AGS is important to the industry?

Because it is run by Industry practitioners for Industry practitioners and as such it offers practical advice that is clear, unambiguous and easy to understand and follow. Or oppose to, we are always open to a good debate!

What changes would you like to see implemented in the geotechnical industry?

On the technical front, I would like to see more performance-based designs with confirmatory in-situ testing (i.e. observational method) being more widely specified and accepted by the Industry and in particular by the big Clients and Asset owners. Additionally, in order to increase the long-term resilience, value and sustainability of our assets, I would like to see a life cycle cost analysis of new or upgraded assets becoming a requirement in all tenders, in a way that would attract Tenderers’ interest and buy-in; and a way to achieve this, I believe, is by moving our Industry towards Project 13 new business model that is based on an ‘enterprise’ rather than traditional transactional arrangements. But until we adopt and embed Project 13, I would like to see more Contracts won not just on lowest pricing but on technical scoring as well as reputation scoring of the Tenderer.

On the cultural front, which is as important as the technical front in my opinion, the main change I would like to see in the Geotechnical and wider Construction Industry, is a change or rather ‘re-invention’ of individual behaviours from apathy to ownership and from routine acceptance to critical dialogue. As more and more disturbing details are coming to light from the Grenfell Tower tragedy, I think that our major focus as an Industry, should be to actively and loudly re-iterate and ‘re-enforce’ our ethical values to both practising young professionals and especially to students. Ethical behaviour, whether in personal or professional life can be taught. It is our responsibility to teach the future generations of engineers to be proud of their engineering achievements and to have a loud, firm voice when it comes to practising our professional code of conduct and our professional duty to warn. At any level. TECHNICAL EXCELLENCE must always come before any COMMERCIAL GAIN.




A Candid Look at Responses to SiLC Membership Questionnaire 2019

- by
Tags: Featured SiLC

A previous questionnaire was issued to the membership in 2009. As part of the SiLC Marketing Action Plan (2018 to 2021), it was proposed that a revised and updated questionnaire would be issued to the membership and this was done in 2019. Some questions remained the same as in the 2009 questionnaire, but the majority were revised, for example to include questions relating to the NQMS and the role of an SQP. The response to the 2019 questionnaire was 46% of registered SiLCs (90 responses), whereas in 2009 it was 43% (57 responses).

In general, those SiLCs who responded to the 2019 questionnaire consider that achieving SiLC registration had been worthwhile and had been a key factor in their professional development. It can be noted that 81% of respondents stated that SiLC is important to their area of work with comments indicating that generally the regulatory authorities recognise its credibility, it assists commercially with winning work and from one respondent a strong belief that it puts them ahead of those that do not have SiLCs. However, there were a small number of comments which referred to SiLC as not very active, feeling stagnant and in need of increased visibility in the industry to demonstrate why it is needed and why people should want to attain it. One response was even stronger saying it costs a lot of money and is of limited value. On the other hand it can be seen as encouraging in response to one of the other questions that there has been some requirement for SiLCs in pre-qualifications or specific project work from all groups across the industry, particularly Regulatory Authorities where 47 respondents out of the total of 90 indicated a requirement, but perhaps disappointing that only 28 respondents indicated a requirement from Environmental Consultants.

The responses to the question regarding how well-known is SiLC, indicate that a strong marketing effort is needed in order to increase the awareness of all groups other than Environmental Consultants and Regulatory Authorities and, even for these, some marketing effort would be beneficial. Suggestions of where marketing is needed were Scotland, legal advisers, insurers, private developers, large landowners, NHBC and non-contaminated land professionals.

It is perhaps a little surprising that 19% of respondents said that they do not have a professional development programme. For those that do, some indicated that SiLC forms a part of that programme. Although 46% of respondents said that they do not use the National Brownfield Skills Framework (NBSF), an encouraging proportion of respondents appear to be using it, particularly for their appraisal systems. One respondent suggested that in parts the NBSF is overly complex, but did not say which parts.

According to the responses, the SiLC website does not appear to be very well used with some members using it only every so often for specific things such as the Annual Forum or not at all. There seems to be doubt as to whether the Members Area has any useful purpose and there appears to be a general feeling that the whole website needs revitalising.

Positively, 61% of respondents consider that the National Quality Mark Scheme (NQMS) will achieve a raising of standards (which was the main purpose of the scheme – by getting things right first time), with 22% saying it will not. For some it is because of the limited take-up but others consider that until it is mandatory it will not reach its full potential. One respondent is not convinced that it will lead to faster planning applications as in their experience contaminated land issues are not generally the cause of planning delays. Another respondent said that there need to be positive case studies as to how the process has speeded up planning.

A disturbing comment came from one respondent who indicated that they had been specifically asked by clients not to include an SQP Declaration because they were concerned the site would be audited and this would cause delay. In reality, there is no intention to audit sites. Audits will cover only the basis on which the SQP has signed the Declaration and whether the NQMS process has been properly followed. There would be no interaction with or hold up of the site or the planning process and this respondent should inform their clients accordingly.

Although 25% of the responses indicated that they had received a requirement from Regulatory Authorities for an SQP Declaration in prequalification or specific project work, the overall number of requirements could have come from a much smaller number of authorities. Local Authorities have a right to check reports and they need to build up their own confidence in the scheme, but by ‘getting it right first time’ in the preparation of the reports and the Local Authorities ‘signposting’ to the scheme in their guidance there is a move towards ensuring that competent people prepare reports which in turn will help raise standards. It is also encouraging to note from the responses that some requirements are also coming from landowners, corporate organisations and the legal profession with uptake continuing to grow.

The SiLC PTP are resolved to improve the website in terms of its usefulness, including links to other sources of information and organisations. More marketing of SiLC is clearly needed. As inferred above, there is a SiLC Marketing Action Plan (2018 to 2021) in place which is kept under review at each PTP meeting. This now incorporates the feedback from the 2019 Questionnaire. Further marketing of the NQMS is underway by the NQMS Steering Group which includes dialogue with Local Authorities and Government Bodies. Many thanks are extended to those who took time to complete the survey and every effort will be made to bring about the changes suggested.

Article provided by Roger Clark, SiLC Chair of the Board and approved by SiLC PTP.

Article Business Practice

AGS Business Practice Working Group Update

- by
Tags: Featured

Sally Hudson, AGS Chair Elect and Leader of the AGS Business Practice Working Group, has provided an update on the top issues the AGS Business Practice Working Group discussed at their last meeting which took place on 11th February 2020.

Promoting and Enhancing Quality and Safe Practice within the Geotechnical and Geoenvironmental Industry

The AGS continues to promote and enhance quality and safe practice within the geotechnical and geoenvironmental industry. To increase awareness, it is our goal to increase AGS membership as widely as possible throughout the industry. The BPWG is working on updating the AGS Business Plan and is monitoring the services and benefits of the Association to ensure that members best interests are represented.

Updating AGS Publications

Some Client Guides and other publications are becoming out of date and so the BPWG is driving a programme of identifying and amending key publications. Although some recent updates have been published, such as the Selection of Geotechnical Soil Laboratory Testing guidance, the BPWG are working with the other Working Groups to continue this effort, starting with some of the most popular documents such as the Client’s Guide to Site Investigations. We are also continuously monitoring our website data to assess publication popularity.

New AGS Client Guides

It can be difficult for our clients to know what the geo-professional qualifications and designations mean and how they fulfil their requirements and what value they offer. The BPWG has instigated preparation of two Client Guides to summarise the meaning of geo-professional affiliations. We have produced two draft documents, which are at review stage, one each to cover geo-environmental and geotechnical professionals. We will promote the new guidance within the AGS magazine once available to members.

As a trade body dedicated to promoting best practice within the industry, we need to ensure that the advice we provide to our members is as current and accurate as possible and reaches as wide an audience as practicable.

We are always keen to welcome new members into the BPWG and so for those interested in the governance of the AGS and wish to know how you can contribute to the BPWG, please contact the AGS Secretariat at



AGS Category Award Sponsor at Brownfield Awards 2020

- by
Tags: Featured

The AGS are pleased to announce that they are the category sponsor for the Best Young Brownfield Professional at the Brownfield Awards 2020.

The Brownfield Awards 2020 will be taking place in De Vere Grand Connaught Rooms in London on 8th October 2020.

Entries for the 2020 Brownfield Awards including the Best Young Brownfield Professional category are open now. Entries will close on 17th April 2020.

More information about the Brownfield Awards can be found here.


“Are traditional Cable Percussion techniques really that bad?”

- by
Tags: Featured

Since the introduction of Eurocodes and the classification of samples with respect to disturbance, there has been much debate in the investigation industry as to the use of our traditional cable percussion sampling and in-situ testing techniques.  Whilst we at Soil Consultants are full advocates of improvements and increased quality there is, to our mind, still a relatively big unknown with regards to the benefits of high end in-situ testing techniques and/or rotary coring over the use of traditional cable percussion drilling methods.  This brief article is designed to stir some thought amongst the industry in comparing the use of ‘traditional methods’ over the more ‘improved’ sampling and testing techniques called for in EC7 and not to undo the good work put into improving quality within the industry.

Over the last few years, and major infrastructure projects aside, it is still apparent that the majority of engineering practices who specify ground investigation have little knowledge of Eurocode in relation to ground investigation, in what they are specifying, the methods available to achieve the geotechnical objectives and the scale of costs involved.  Thus, ground investigation is still all too commonly awarded on a combination of lowest cost and ignorance, which the specifiers [and by default the client] are willing to accept as ‘value for money’.  The Eurocodes are attempting to bridge this divide, but is the complexity and lack of understanding of these documents still preventing the advancement of quality and achievement of value?  From feedback in the industry [largely structural engineering practices], there appears to still be much work to do with regards to quality of investigation, quality of service and the value of ground investigation which only we as an industry can control and one which is constantly debated!

Since the publication of EC7 and its requirement for valid laboratory strength and deformation testing to only be performed on ‘Class 1’ samples, the use of the traditional U100 has been somewhat dismissed by the codes and consequently a stronger reliance has been put on SPT testing as a compliant technique along with ‘our knowledge of the geological formations’.  The use of the SPT has most likely been driven by our industry seeing this as a far less expensive alternative to rotary coring and a more practical method for congested and restricted access sites.  Indeed, this would be true as, in our experience, rotary coring averages about 200% more expensive than cable percussion drilling and few inner city sites offer the necessary access and working areas.  Pressuremeter testing also comes with a hefty price tag with an individual test averaging about £2,500 on a typical project.  The question which arises from this is: ‘Does the quality of sampling and specialist in‑situ testing provide the accuracy and reliability to justify their use and the expense?’.  The reality of this expenditure needs to be fully justified to provide confidence to the client and the design team that the results are more accurate and representative thus providing more valued engineering.  The counter argument to this being, ‘Is it better to obtain a greater data set, from say cable percussion techniques, to provide a more reliable average, which could be achieved through a higher number of boreholes and tests at significantly less expense?’

With traditional techniques, the introduction of the UT100 [thin walled sampler] has bridged the gap somewhat in the sample disturbance argument and has been rudimentarily accepted.  However, this sampling technique still does not fully comply with the requirements of EC7 due to the percussive driving of the sampling tube and it has important limitations in its practical use.  Energy efficiency measurements for SPT hammers has also been made part of the Eurocode requirement, but this still comes with problems as there is a demonstrable divide in consistency of the testing techniques and the measured energy efficiency, as the table below shows.  Arguably, and hopefully reassuringly, the majority of hammers seem to improve with age which could indicate that operators are looking after and properly maintaining their equipment.  However, erratic results are not defined by the Codes and this raises the question as to whether or not there should be some benchmarking to condemn poor performing equipment.

Table 1:  Different cable percussion hammer ratio records since 2012; colour coding represents the calibration test house.

In order to put the questions above into context, Soil Consultants have put together a data set of testing of the London Clay from our projects undertaken within central London using various sampling and testing techniques.  The data represent the ‘more traditional’ techniques adopted through cable percussion drilling as well as rotary coring and Pressuremeter testing.  In-situ CPT has not been included as we do not have access to a relevant data set at this time.  It is recognised that there are limited data available for pressuremeter testing and some of these data have been obtained from public open sources, but still relevant to the geology and geographical location.

Clearly, there are numerous arguments for and against the various techniques with regards to disturbance and testing orientation but it is acknowledged that there are flaws with all methods and the data have been presented on face value from ‘real’ projects.  In this data set, we have considered:

  • Cu derived from ‘metal’ UT100 and steel U100 sampling tubes – we are unable to segregate between thin wall and thick wall tubes although the majority of samples shallower than 15m have been obtained using UT100s
  • Cu derived from plastic U100 tubes
  • Cu derived from rotary core samples
  • SPTs, both uncorrected and corrected for N60 [Cu plotted as 5*N] and
  • Pressuremeter testing

Graph 1 shows the culmination of nearly 1,200 data points and whilst the number of points make the graph difficult to read, Graph 2 presents the envelopes of each of the data sets [lower and upper bound limits representing approximately 90% -95% of the data points ignoring anomalous low and high values].  On these graphs is also plotted ‘an average line’ which has been derived through simple visual assessment of the data set [based on the lines produced by four engineers assessing the data independently].  Whilst this is not technically a scientific average, we believe this is representative of ‘the designer’s’ approach.

Graph 1: All data points

Graph 2: Envelopes to individuals data sets

Graph 3 further simplifies the data by plotting the middle average of the envelopes and also includes the ‘average’ line from all data as a visual benchmark which, is continued through all graphs.  Graph 4 compares these data sets with the shear strength profiles for London Clay presented by Patel [1992] on 100mm diameter specimens.

Graph 3: Average profiles

Graph 4: Average profile and Patel’s envelope

Although this is not an exhaustive analysis, on face value, the following points are noted:

  • The Pressuremeter testing and Cu derived from rotary core show the widest scatter of data. Cu measured from samples obtained in metal sampler tubes also exhibits a wide scatter
  • Uncorrected SPT-derived Cu shows the narrowest envelope of all the data sets. Correcting the N value for energy efficiency, serves to further narrow this envelope
  • Whilst samples derived in plastic U100 sampler tubes gave a similar scatter in results to other ‘undisturbed’ measurement techniques, the overall strengths measured were greater, giving a higher average


Graph 3 plots the average of the envelopes which surprisingly produces a relatively tight group of lines, slightly divergent at shallow depth, tightening together at about 15m before diverging with depth.  Patel’s 1992 paper produced a set of data for the London Clay and shear strength measured from U100 samples [type of sampling tubes are not reported].  A refinement of Patel’s data has been undertaken with only the more central London sites being considered to provide a comparable data.  The average and lower bound envelope of this refined data set are shown on Graph 4.  The majority of the average data is seen to lie close to the lower bound line of Patel’s data, with only the measurements from plastic U100’s bucking the trend, with the results lying above the average line.  By comparison, Cu depth profiles published by Patel;1992, Skempton;1951 [U38 values corrected for 77% strength CW publication 1991] and Marsland;1974 are plotted on Graph 5.  Whilst there is a reasonable consistency with the gradients of the strength profiles, there is a significant divergence in measured Cu.

Graph 5: Cu profiles by various authors

So, what does this mean?  At this stage, it is arguable that the traditional U100 and SPT techniques are valid and show a no worse scatter than more ‘refined’ techniques.  That is not to say that any of the techniques do not have a place because this is very much ‘horses for courses’ and the overall geotechnical requirements of a particular project will dictate technique in certain circumstances.  For more routine investigations, the use of the more traditional U100 and SPT techniques, providing a greater data set could, in our view, give better value for money and a justifiable confidence in obtaining characteristic design values.  In saying this, quality of ‘workmanship’ is a considerable factor and investigation companies should ensure drilling operatives are suitably experienced and supervised along with ensuring equipment is well maintained and sampling tubes are clean.

The divergence of measured Cu profiles is proof that differences do exist in the London Clay and indeed, in our experience, the strength profiles around London do vary considerably, with some areas showing significantly weaker profiles than others; this should be accepted by the industry who should not be so quick to criticise the investigation contractor.  Design engineers, in our experience, continue to try and oversimplify this formation but, the London Clay is a variable deposit and the ground is not ‘Just London Clay’ as we hear on so many occasions.  Thus, investigation designers should be advocating a sensible level of investigation to provide a reliable and representative data set.

Whilst there is a wealth of information in the literature on the London Clay, on reflection, do we as an industry still need to put further research into sampling and testing techniques to provide the necessary confidence that routine ground investigation can provide reliable design parameters in light of the Eurocodes?

Article provided by Soil Consultants

Disclaimer: The contents of this article and the views represented within it are not necessarily reflective of the AGS as an organisation, or its Working Groups.

The AGS Geotechnical Working Group will be publishing a response to this article in a future issue of the AGS Magazine.




Urgent PPE support for the NHS

- by
Tags: Featured

With the ongoing situation with COVID-19, the NHS urgently need the following equipment:

• FFP3 Respirator Masks
• Full Face Visors (disposable)
• Full Face Visors (reusable)
• Safety Goggles/Glasses
• Hand Sanitiser
• Full Body (Hazardous Material) Suits
• Logistics/Transport support

If your organisation is able to help, could you please contact to provide your details. The AGS are collating the responses of organisations who are able to help and will pass these on to a central contact.


Update from the AGS regarding COVID-19

- by
Tags: Featured

With the ongoing situation of COVID-19, the AGS would like to remind AGS members of the current guidance. Businesses and workplaces should encourage their employees to work at home, wherever possible; if someone becomes unwell in the workplace with a new, continuous cough or a high temperature, they should be sent home and advised to follow the advice to stay at home for 14 days and employees should be reminded to wash their hands for 20 seconds more frequently.

The AGS are continually reviewing the situation and the decision has been made to postpone both the AGS Annual Conference which was due to take place on 2nd April and the Laboratories, Instrumentation and Monitoring Conference which was due to take place on 15th July. Further details about both conferences will be released in due course.

Currently, the AGS are looking to go ahead with the AGS Data Management Conference on 23rd September, however this will be monitored closely.

For those who attend AGS Working Group meetings, we will be using remote and conferencing technologies to hold these meetings until further notice and details of these will be circulated with the meeting notification as usual.

The AGS Secretariat are currently working remotely, but we are checking our voicemail twice daily and aim to get back to you as soon as we can. We can also be contacted by email


Important Notice: AGS Annual Conference 2020 Postponed

- by
Tags: Featured

The AGS have taken the decision to postpone the AGS Annual Conference to later on this year.

After much discussion, The AGS have decided to postpone due to the current spread of COVID-19. This will help to reduce the risk to all involved, and we wanted to give you as much advance warning as possible.

The AGS are looking to hold the conference later in the year and further details will be announced in due course.


AGS Magazine – February 2020

- by
Tags: Featured

The Association of Geotechnical and Geoenvironmental Specialists are pleased to announce the February 2020 issue of their publication; AGS Magazine. To view the magazine click here.

This free, publication focuses on geotechnics, engineering geology and geoenvironmental engineering as well as the work and achievements of the AGS.

There are a number of excellent articles in this month’s issue including;
AGS Annual Conference 2020 – Page 4
On Stoney Ground: Re-Visited – Page 8
AGS Commercial Risks and How to Manage Them: Conference Review – Page 12
Health and Safety – Lego style – Page 14
Emergency rescue from a trial pit: Are you prepared? – Page 16
Q&A with Phil Crowcroft of ERM – Page 20

Advertising opportunities are available within future issues of the publication. To view rates and opportunities please view our media pack by clicking HERE.

If you have a news story, article, case study or event which you’d like to tell our editorial team about please email Articles should act as opinion pieces and not directly advertise a company. Please note that the publication of editorial and advertising content is subject to the discretion of the editorial board.


Q&A with Phil Crowcroft

- by
Tags: Featured

Full Name: Phil Crowcroft
Job Title: Technical Fellow
Company: ERM

Phil Crowcroft is a Technical Fellow in the Asset Management team of ERM based in the Edinburgh office.  He has over 40 years experience in dealing with land contamination, brownfield regeneration and natural resources, combining his training as a civil and geotechnical engineer with experience on the broader aspects of the environment such as chemistry and hydrogeology. Phil was SiLC Chair of the Board (2011-2019) and the PTP (2008-2017). He is moving into retirement in 2020, and joining his wife in running a vintage department store in Berwick upon Tweed.

 What inspired you to get into the brownfield regeneration field?

My fear of chemistry pushed me to take maths, physics and geography A levels, and I realised then that the ground and what lies below was really where my interest and enthusiasm lay. This led on to a Bachelors degree in civil engineering and a Masters in geotechnical engineering. After 2 years work in mainstream construction, I moved jobs in 1978 to join a site investigation contractor, and discovered the huge variety of work and challenges that the ground poses to every building and civil engineering project. I also realised that I couldn’t leave chemistry behind because of the range of brownfield sites which were coming to development. Undertaking investigations on gasworks and landfill sites in the 1980s also highlighted the the very rudimentary state of understanding the challenges posed by such sites present.

What does a typical working day entail?

There is and has never been a typical working day, which is part of the fun of being in this business. Looking back over the last 45 years, I have enjoyed the challenge of helping to develop the approach to dealing with brownfield sites, whether as a contractor, a consultant or a regulator. But I’ve also tried to balance work with home life, so you won’t catch me working late into the evenings, unless I’m away from home, which perhaps was far more often than I ever expected.

Are there any cases which you are particularly proud to have advised on?

From a continuity point of view, I am proud to have worked on the contaminated land aspects of the EIA for high speed rail, starting in 1990 on the Channel Tunnel Rail Link from Folkestone to London, then since 2012, from London to Birmingham and Birmingham to Manchester and Leeds. I’ve worked alongside some brilliant people on this major project, and I am a huge fan of the railways, having spent far too much of my life sitting in traffic jams on motorways.

I am also very pleased to have worked on national guidance since the 1990s, including Industry Profiles, NFHA guidance, Model Procedures and the WDA Manual. I am sad that government policy has swept away great centres of excellence such as the Environment Agency Contaminated Land and Groundwater Centre, and has abandoned the production of guidance.

What are the most challenging aspects of your role?

I think that developing a capability in providing expert witness services has been the scariest thing I have done, but over time, it becomes less scary and more thought-provoking. I’m lucky to have developed an understanding of what we actually considered to be best practice at any moment of time since 1980, and I have most of the guidance since that time in my attic. I have a memo I wrote in 1985 telling fellow geotechnical engineers how to use ICRCL guidance. How sad is that? My career is finishing off with two cases in court, with the exciting prospect of being cross-examined by articulate barristers intent on your downfall. The battle commences….

What changes would you like to see implemented in the industry?

I would like to see the allocation of sensible government budgets to support development of relevant guidance covering the brownfield industry, and the support by public funding of research bodies such as CLAIRE, CIRIA and SiLC .

Why do you think SiLC is important to the brownfield regeneration field?

Lord Rogers and his Urban Task Force recognised in 1989 the need for competent people to work in a sector which embraces many different disciplines, and within 2 years, a working group comprising public and private sector bodies had developed the scheme and got it up and running. It continues to this day, and this is testimony to the need for and value delivered by such a scheme. My most recent litigation has centred on whether a consultant was negligent in dealing with a brownfield site, and much of the discussion has been around whether people were competent to carry out the roles they played. SiLC delivers confidence that an individual has core competence in their own subject area, whilst recognising and appreciating the parallel skills which are needed to deliver the reclamation and redevelopment of brownfield sites.

What has been one of the highlights of your career?

Over the last 40 years, I have been lucky to have worked with, and been responsible for, groups of talented people who deliver day in day out on brownfield projects. I don’t know how many job offers I have made, but I know many people who it has been my privilege to offer jobs to, who have then gone on to run their own teams, and lead the way in their own subject areas. I have managed, and then been managed by some, and they make me so proud to have helped them start their careers, and achieved success. Thank you to all of you.