Gain Skills to Champion Excellence in the Geoprofessions at GBA’s Annual Conference

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Geoprofessionals from across North America will gather at Geoprofessional Business Association’s (GBA) 2024 Annual Conference, April 18-20, 2024, at the JW Marriott, Anaheim Resort in Anaheim, California. With a theme of “Champion Excellence,” conference participants will gain the skills and knowledge to actively promote and support the pursuit of exceptional performance, quality, and success in all aspects of their firm.

Keynote speakers include New York Times best-selling author and innovation consultant Diana Kander and famed one-handed Major League Baseball pitcher Jim Abbott.

The event offers opportunities for development of highly sought-after skills such as communication, innovation, and overcoming adversity, as well as Business Round Table Sessions – the unique chance to discuss problem-solving, best practices, and strategies with geoprofessional peers about the issues impacting the industry.

Those who are newer to the geoprofessions can engage with executive-level industry leaders, connect with new mentors, and boost their professional profiles. Mid-level geoprofessionals can unlock new leadership opportunities, exchange best practices for risk management, and network with hundreds of like-minded professionals. Seasoned geoprofessionals can share strategic insights as they address industry challenges and contribute to the elevation of the profession with their invaluable experiences.

The GBA Annual Conference offers up to 6.5 professional development hours.

Early registration rates are now in effect, but rates will increase on March 1.

Learn more and register here.



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Name: Peter Widdowson

Job title: Director Business Development

Company name: Igne Group Limited

What does the company do and what areas does it specialise in?

Igne is the new brand for six combining businesses which share a group history of 350 years’ service in site investigation, materials testing, unexploded ordnance threat mitigation, water well drilling, geothermal borehole drilling and geo-environmental consultancy.

We know our collective services must be delivered more effectively and sustainably than ever which is why the businesses have fused together to respond more efficiently to our customers in the pre-construction and construction phase environments.

Our vision is to become the most trusted tier-one partner for environmentally sustainable site investigation and drilling services across the entire construction and infrastructure lifecycle in built environments throughout the UK.

Any single part of Igne can respond to customers’ needs in each of our specialist areas, simplifying the process for clients and consistently ensuring the provision of the same level of service and expertise.

Where is Igne located?

Igne has offices in Aberdeen, Airdrie, and Hamilton in Scotland; Preston, Chester le Street, Birmingham, Aylesbury and Gillingham in England; and Presteigne in Wales.  Our head office is Ross on Wye, a beautiful part of Herefordshire.

How many people does the company employ?

We employ circa 300 full time staff and rely on many exceptional contract staff who support us when we need to call on them.

How long have you worked at Igne?

I joined Igne in a brand-new role for the company in June 2023 (so 6 months and happily counting.)

What is your career background, and what enticed you to work for Igne?

I am a professional Civil Engineer and a member of the Institution of Civil Engineers.  My background has been in tier 1 and 2 civil engineering and building construction contracting, working across Scotland principally, but also supporting businesses in the North of England, around Manchester and Warrington.

Over the last 10 years, my roles have focused more on business development and work winning.

When the opportunity came to join Igne ahead of its official launch on 2nd October 2023, I was really excited for a variety of reasons.  Firstly, I would be able to expand my own knowledge across a number of new sectors.  I was most commonly on the receiving end of site investigation reports – now I would get to promote best practice in site investigation for clients.

Secondly, I would be able to start working more directly in an area that I believe is one of the future solutions to decarbonising heat in the UK, harnessing geothermal energy.

Finally, I would be able to start practising what I have always preached; that the greatest risk to any construction project lies in the ground.  Understanding the ground conditions early on can help project teams understand the hazards and provide mitigation solutions to problems that can otherwise cause severe delay, disruption and additional costs to a project.

At Igne, I now represent a business that gets its hands dirty, so to speak, and does the work that I know is critical for a project’s success.  We are one of the specialist contractors, and consultants, who will lead with the advice and intelligence that we can provide, backed by the expertise that we have, to ensure our clients’ successes.

What is your current role within Igne and what does a typical day entail?

There are several threads to my role within Igne as I support each of our business units and service streams.

I led on the communication to all current and previous customers relating to our change to becoming Igne from 2nd October 2023.  Some parts of the now-combined business had incredibly well-established names and were known by many as the ‘go to’ supplier for their work.  Changing the brand to Igne is significant but has been well-supported by all involved.  The communication piece was critical to tie up all loose ends.

My key role day-to-day is to support each business to identify and secure the opportunity to negotiate and tender for future work.  We need to share our broad capabilities with our current customers who may know us primarily for one service – such as UXO or site investigation – but not realise we can now offer them so much more.

We need to understand our customers and future customers and the markets in which they operate, so that we can continually improve for each individual customer.  My role looks at how we deliver today but also how we might deliver tomorrow in partnerships and alliances or through acquisitions.

I truly believe, with a passion, that we can help all clients, whether they are developers, consultants, contractors or individual homeowners, to understand their project better to reduce cost, stay on programme, improve safety, reduce environmental and ecological impact and carbon intensity, and the demand on natural resources.  It is my role to communicate that passion to our future customers and show them what we can do for them.

What are the company’s core values?

Our purpose is to enable sustainable communities and advance positive change. We do this through our values:

Reliability: Whatever the job, we focus on what matters, do things the right way and deliver real results. Dependable, positive and hugely knowledgeable, we provide skills and experience that people can rely on.

Partnership: We work in partnership with clients and stakeholders to find answers and reach shared goals. We build long-term relationships by being open, transparent and easy to work with. We are full of practical ideas that people can put into action.

Quality: We are dedicated to our work and passionate about quality. We set high standards and work hard every day to meet and advance them. We speak up, act with integrity and offer honest advice people can trust.

Are there any projects or achievements which Igne is particularly proud to have been a part of?

Delivering sonic drilling solutions to site investigation challenges in remote and inhospitable parts of beautiful Scotland, whilst also working in environmentally sensitive locations without damaging precious flora and fauna.

This demonstrates our core values in action:

Reliability, we can get the job done no matter the challenges we may need to overcome.
Quality, we deliver the highest quality works maintaining sensitivity to the environment or communities within which we are operating.
Partnership, to work with our client to determine the best way and best value option to deliver the information they need.

Another example is clearing unexploded ordnance from a 5-hectare area of the Dorset coast for the National Trust.  The area had been badly damaged by and exposed several hundred items of live and inert ammunition.  We cleared this former training area, rendering it safe for public access once again.

How important is sustainability within the company?

Incredibly important – sustainability is at the heart of our purpose and is our vision.  In everything that we do today, we are thinking about tomorrow.  It is the very purpose of our business, to provide the data to inform our customers about the most sustainable way to develop their project.

It is also important to us that we continually improve how we go about achieving this, to minimise our own impact.  For example, as we transitioned to become Igne, all our old PPE was recycled with 0% going to landfill.  This ensured we reduced CO2 emissions by 13kg per 1kg recycled – and we reduced water consumption by 1litre per 1kg recycled as the old workwear become new garments.

How does Igne support graduates and early career professionals who are entering the industry?

Our CEO, Rob Hunter, is committed to advancing social mobility and does a lot of work in a voluntary capacity to advance the cause.  Therefore, it is unsurprising that Igne has an acute focus on developing early talent at the heart of its workforce plan.

We have various routes to support young people entering the industries and specialisms we span.  We have graduate and apprentice routes into roles such as engineers, geologists, administrators, marketers, HR professionals, drilling crews and many more.

We go into colleges and universities to teach and help young people understand what the industry is like.  We don’t sugar-coat what life can be like as a driller for example, but for the right people, it is a hugely rewarding career.

We do need to improve how we communicate the available careers to young people, to get them interested in what we do at Igne and in the wider industry.  If we can do this successfully, it will help us to stem the recruitment and people-resource issues that we face.  Attracting the right people in the first place, and nurturing their talent is the route to a more sustainable workforce solution.  It is a core company focus for us.

How has COVID-19 impacted Igne today? Are there any policies which were made during the pandemic that have been kept to improve employee wellbeing and productivity?

Yes, absolutely.  The flexibility we developed across the businesses, which was generated as a result of COVID-19 and the ways of working that we had to adopt, has demonstrated that a hybrid working practice is both possible, in appropriate circumstances, and beneficial to employee wellbeing and therefore productivity.

Our move to hybrid has helped us reduce our carbon footprint through reduced commuting, and our employees continue to demonstrate their commitment to the business reciprocating the trust the business puts it them.

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

I am a firm believer that the ground holds the greatest risk to any construction project no matter how large or small.  It is a constant source of challenge whether through geotechnical ground conditions, historic uses, contamination or protecting sensitive receptors.  If everybody worked in isolation, we would not deliver the results we need to develop our industry.  We must work collaboratively, share best practice and allow ourselves to learn from each other for the good of the planet, our employees and the communities in which we work – and we must enjoy a collective voice.  For me, AGS helps to facilitate the foregoing across our industry, so, it is a ‘no-brainer’ – AGS is critically important to our industry.

What are Igne’s future ambitions?

Our ambition is to consolidate the capabilities from across the group, to enable us to deliver more than the sum of our parts through shared learning and commitment to delivering a holistic and integrated service for our customers.  We are also committed to continuing to grow our capabilities in the direction led by our customers’ needs.  This is what excites me the most.  In doing so, we will become the most trusted partner to the construction industry, providing pre- and post-construction services they can absolutely rely upon.


Article Safety

AGS Welfare Guidance, a step in the right direction

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Image provided by AECOM

The industries expectations to all health, safety and wellbeing requirements have changed through the years, as we understand and acknowledge the negative impacts work activities and environments can have. In the late 1980’s and into the 1990’s I recall working on construction projects where the requirements to wear a safety helmet and safety boots were not amongst the site rules, where all materials were required to be carried up a ladder, normally by young inexperienced labourers, and the idea of leading-edge protection was an alien concept.

With all of these examples and many, many more, through the demonstration of the harm captured within accident statistics, the Health and Safety Executive working with industry stakeholders have developed new legislation, approved codes of practice and guidance to reduce the risk of being harmed while at work. This approach has been transformative to the construction and many other industries and benefited those working within them.

Although successful in achieving its outcomes, this change has not always been viewed as positive at the time of its introduction, although few would retrospectively now challenge the requirement to wear a safety helmet where there is a risk of falling objects, etc., as the benefits are clear.

Thinking back to my experience of construction site welfare in my earliest career, most projects I worked on had no welfare. Breaks were taken in the back of your van and public toilets, or other alfresco arrangements were used to relieve yourself. Where some form of welfare did exist, the quality and upkeep of it was poor by todays standards.

I worked with a bricklaying contractor on a project on the outskirts of London where a hotel was being constructed. The only welfare on site was a single 16ft canteen with a gas stove, a kettle, tables and chairs, and a solitary portaloo, all of which was supplied by the groundwork’s contractor. I do not recall how many groundworkers there were on the project, but I know there were ten bricklayers and labourers, more than the welfare could cater for by today’s standards. Welfare maintenance was limited to the emptying of the portaloo once a week by the supplier.

It was winter so everything was covered in mud. A few of the groundworkers tools and cans of petrol were stored in the back of the canteen. As expected at the time, there was no soap, detergent, hand towels, cups, tea, coffee, toilet roll, etc. Worst of all and why it sticks in my mind, was the frying pan. At the 10 o’clock break, the groundworkers used to cook a fry up in this massive frying pan on the gas stove. Due to the lack of washing facilities the pan was reused daily without being cleaned, so it was black and charred and there remained a 5mm layer of congealed animal fat in the bottom of the pan. On a few occasions in heavy rain, the bricklayers used to stop work and take shelter in the canteen, the groundworkers didn’t, they just worked through it. If shelter was taken before 10 o’clock, on inspection of the countertop you could see the rat footprints in the frying pan fat, where they had been feasting on it through the night. The pan was always used and never cleaned!

I am glad to say that such situations are a thing of the distant past, and those coming into the construction industry today have an improved experience. Recognising the impact insufficient welfare can have, today’s welfare provision must be suitable to the workforce size, serve the needs of both male and female workers, be well equipped with food and drink receptacles, have supplies of hygiene and cleaning sundries, a supply of fresh drinking water and means of heating food and drink. It should provide storage for clothing, changing areas and heating for the drying of workwear, toilets and wash basins with hot and cold running water, hand health creams, sun protection and ample waste control. Cleanliness and maintenance of welfare must be daily, with replenishment of consumables, etc. to ensure the workforce have everything they need to their work and health.

However, this is not always the case in the pre-construction site works, such as ecology, archaeology, utility mapping, ground investigation, etc.

It is fair to say, depending on the size, scope and location of geotechnical and geoenvironmental projects, our industry has very varied levels of compliance to what should be expected with regard to welfare. While I haven’t seen any frying pans and rat footprints, I have seen inadequate on-site welfare or an absence of it entirely. There are several justifications put forward for such situations, however, none which have the welfare of those working on geotechnical and geoenvironmental projects at its core or which align to legislative requirements. Such justification could include; if welfare is provided, we would price ourselves out of the project, the client has pushed back against the cost of welfare, the project is not long enough to warrant having welfare, etc.

In reality, none of this reasoning will stand up to scrutiny by the enforcement authority, as legislation is clear, Construction Design and Management Regulations 2015 (CDM15), regulation 13.4. ‘the principal contractor must ensure that—(c) facilities that comply with the requirements of Schedule 2 are provided throughout the construction phase’, or within the Workplace (Health, Safety & Welfare) Regulations 1992, regulation 4.1. ‘Every employer shall ensure that every workplace, modification, extension or conversion which is under his control and where any of his employees works complies with any requirement of these Regulations…….’

There are weaknesses within the regulation and guidance, which on their casual reading seem to justify not having on site welfare. Within the CDM15 Schedule 2 (which the above quote relates to) it uses the term ‘….must be provided or made available at readily accessible places.’, and then there is the Provision of welfare facilities during construction work, HSE information sheet 59, which introduces the term ‘transient worker’ and states that ‘it may be appropriate to make arrangements to use facilities provided by the owner of existing premises, in which the work is being done, local public facilities or the facilities of local businesses’.

Considering ‘readily accessible places’ within CDM15. The statement is part of a much longer statement, which includes regulation 13.4.c, stating that ‘the principal contractor must ensure that facilities that comply with the requirements of Schedule 2 are provided throughout the construction phase’. The use of the phrase ‘….must be provided or made available at readily accessible places’ in this context allows the principal contractor to provide the welfare or arrange for a third party to provide it, as long as it is readily accessible. A 7th December 2022 prosecution of Adler and Allan Ltd, highlighted the expectation of the Health and Safety Executive for onsite welfare for brownfield / contaminated sites. However, the context of this case surrounded a worker contracting leptospirosis due to a lack of onsite hygiene facilities, so it should be noted that the contraction of leptospirosis is not linked to brownfield / contaminated sites, but any sites where rats (all year round) or cattle (spring and summer) are present.

HSE information sheet 59 was published 13 years ago, the corresponding construction regulations were the Construction (Design and Management) Regulations 2007, which is referenced within the document on page 1. It goes on to state, ‘principal contractors should make sure that suitable welfare facilities are provided from the start and are maintained throughout the construction phase’ and that contractors ‘should ensure that there are adequate welfare facilities for workers under your control’. The document sets out in significant detail what welfare should consist of and contain.

However, this is ignored by those using it as an argument for using off site publicly accessible facilities, their focus instead turns to the section titled, ‘Use of alternative facilities for transient construction sites’. This states that ‘when undertaking short duration work (up to a week), it may be appropriate to make arrangements to use facilities provided by the owner of the premises in which the work is being undertaken, local public facilities or the facilities of local businesses.

What is not quoted by those using Information sheet 59 as an argument for using off site publicly accessible facilities, is that it then goes on to state ‘clear agreement should be made with the provider of the facilities; it should not be assumed that local commercial premises can be used without their agreement. In all cases the standards above (welfare standards detailed in document) must be provided or made available. Facilities must be readily accessible to the worksite, open at all relevant times, be at no cost to the workers, be of an acceptable standard in terms of cleanliness and have handwashing facilities’. The use of garages, supermarkets, public toilets, etc. whilst often providing basic toilet and hand washing facilities will struggle to meet all the remaining requirements, with issues such as cleanliness, chairs with back support, means of heating food and drink, changing rooms, free of charge to the worker, all preventing facilities being deemed suitable and sufficient before even looking at the definition of readily accessible.

To improve welfare across the industry, providing clients with an industry benchmark and contractors a level playing field to price against, the AGS has published new Welfare Safety Guidance which is available via the AGS Website. This guidance takes into consideration the vastness of scope, duration, workforce and environment variations which are present across the industry and puts into place a set of welfare standards to ensure the health and wellbeing of those working within the industry. The guidance addresses the application questions posed by conflicting regulations and guidance and provided the industry a simple, clear and concise framework to support the diversity of the workforce.

Our industry should be one that welcomes in early careers and supports existing staff by providing them with suitable and sufficient welfare, ensuring their wellbeing. The work the industry engages in is physical, dirty work, which is undertaken in all weather conditions, year-round. Those that deliver this work deserve the comforts that basic welfare delivers as a minimum.

Article provided by Jon Rayner – AECOM SH&E Director & AGS Safety Working Group Chair

Article Laboratories

Calibration of Whatman Grade 42 filter paper for soil suction measurements

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The correlation between the water content of filter-paper disks and the porewater suction in soil samples is used to determine soil suction, and various equations have been proposed to model it. To verify whether the equations in BRE IP 4/93 for determining soil suction based on the water content of Whatman Grade 42 filter paper remain valid and can be used with currently available batches of Whatman Grade 42 filter paper, SSL and i2 Analytical laboratories confirmed experimentally that NaCl solutions can be used to calibrate Whatman Grade 42 filter-paper disks and the equations in BRE IP4/93 remain valid. The method is inexpensive and reliable. Filter paper from different manufacturers or other than NaCl solutions also can be used after calibration.



Soil suction is the result of the interaction between soil, water and air, and is important in understanding the strength and behaviour of soils, in general, and unsaturated soils in particular. There are numerous direct and indirect methods for measuring soil suction in situ and in the laboratory (e.g. Ridley 2015; Esmaili and Hatami 2017). The filter-paper technique is the most commonly used indirect method for estimating soil suction because of its low cost, simplicity, and wide range of suction values (0-5 MPa). The method evolved in Europe in the 1910s and USA in the 1930s (e.g. Frendlund et al 2012; Fondjo et al 2020).

Soil and filter paper (direct contact), or porewater vapour and filter paper (indirect contact), are equilibrated for several days in an airtight container. Subsequently, the water content of the filter paper is determined, and the soil suction is calculated by using equations that relate the filter paper water content and soil suction (e.g. BRE IP 4/93; ASTM D5298).

The total suction ψ in soil is the sum of the matric suction (ua – uw) and osmotic suction π determined by the direct and indirect contact of soil and filter paper, respectively,

ψ = (ua – uw) + π,

where ua is the pore-air pressure and uw is the porewater pressure.

The calibration of filter paper involves either equilibration of filter paper in a suction or pressure plate at different applied pressures or by non-contact equilibration of filter paper over salt solutions, e.g. NaCl, KCl, Na2SO4, or MgCl2, with different salt content, and then independently determining the filter paper water content (WCFP). The data from various calibration studies suggest that for suctions greater than ca 1000 kPa the total and matric suction calibration curves converge but diverge at lower than 1000 kPa (e.g. Fredlund et al 2012).

Whatman Grade 42 or Schleicher & Schuell No. 589-WH filter papers have been used in soil suction tests, and many studies have established and evaluated calibration equations. Even though filter paper is an industrial product manufactured under strict control, it is not clear if the manufacturing process and thus quality of the filter papers remains the same over the years or if the published calibration curves are applicable to the currently available filter paper batches. Thus, calibration of each batch of filter paper is recommended (Marinho and Oliveira 2005).

This paper describes the calibration study undertaken by SSL & i2 Analytical to demonstrate for accreditation purposes that filter papers can be inexpensively calibrated by using salt solutions, and the equations in BRE IP 4/93 (Crilly and Chandler 1993) can be used with currently available Whatman Grade 42 filter paper batches.



  • Ash-free Whatman Grade 42 filter paper (CAT No. 1442-070 & Lot No. 16971096) 70 mm in diameter
  • Thermometer (±1 ⁰C accuracy)
  • Laboratory balance with an accuracy of 0.1% of the weighed mass
  • Oven capable of maintaining the temperature at 105 ± 2.5 °C
  • One pair of metal tweezers
  • 200 ml terrine jars, with mouth size of 100 mm to allow for the filter papers to be placed inside without touching the jars
  • Corrosion-resistant metal or plastic pipe to act as a support for the filter paper disks
  • Glass beads to secure the supports
  • Six aluminium circular tins
  • A large glass flask with distilled or de-ionised water
  • Desiccator
  • Cooler box



Salt solutions were prepared by dissolving table salt in distilled water (Table 1). All equipment but the thermometer and filter papers were thoroughly cleaned by carefully washing and rinsing them with distilled water, and then dried. Latex gloves and tweezers were used to prevent the transfer of any oils or other contaminants and handle the filter-paper disks. The filter-paper disks were dried and kept at 105 ± 5 ⁰C.

Clean glass shards or beads were placed at the base of the jar to support the plastic or metallic pipe upon which the filter paper disks were placed. Prior to placing the filter-paper disks, the glass jars were filled with the salt solutions.

Two filter papers were placed above the salt solution on the supports so they had 2 cm clearance from the surface of the solution and protruded more than 1 cm past the support in all directions but were not in contact with the jar. The jar contents were then secured with a water tight  lid. The configuration is shown in Fig. 1.

A set of six jars was placed within a cooler in a temperature-controlled laboratory room (23 ± 2 ⁰C) and left undisturbed for two weeks to equilibrate. Room temperature was maintained at 23 ± 2 ⁰C.

After equilibrating for two weeks, the jars were removed and the filter papers were placed into aluminium tins for initial weighing; this part was performed by two technicians who worked on each jar together to reduce the amount of time that the filter papers were exposed. The aluminium tins were then placed in a dry oven set at 105 ± 2.5 °C for a minimum of 16 hours with the lids half-off to dry completely. The following day the lids were replaced and the aluminium tins containing the filter papers were left to equilibrate in the oven for 5 min before being removed and allowed to cool in a desiccator. After this second dry weighing, the water content was calculated.


The data from the calibration tests at the SSL Bristol and i2 Analytical laboratories are given in Table 1. The 0% NaCl solution was deionised water. The filter-paper water content data suggest good reproducibility and repeatability between and within laboratories, respectively. The suction values at 23 ⁰C were calculated using the online molality calculator of

The osmotic suction π values in Table 1 are compared with the values generated by using the equations in 1) BRE IP4/93 for matric suction and 2) Leong et al. (2002) for total and matric suction (Fig. 2):

1a) log kPa =  4.84 – 0.0622 × WCFP                    15% ≤ WCFP ≤ 47%

1b) log kPa = 6.05 – 2.48 × WCFP                   WCFP > 47%

2a) log kPa = 8.778 − 0.222 × WCFP             WCFP < 26%

2b) log kPa = 5.31 − 0.0879 × WCFP             WCFP ≥ 26%

The data in Fig. 2 suggest that the non-contact calibration data represent total suction values and agree with the convergence of matric and total suction values at approximately 1000 kPa (log kPa = 3) and at about 25% WCFP.

At filter-paper water content greater than 25% the calibration data well agree with the Leong et al. 2002 equation for total suction, suggesting that the Whatman Grade 42 filter paper produces data consistent with published calibration equations.

The equations in BRE IP 4/93 and Leong et al. 2002 for matric suction are in good agreement, which suggests that the equations in BRE IP 4/93 can be used to calculate soil suction, with currently available batches of Whatman Grade 42 filter paper.

There are no calibration data for matric suction; however, considering the agreement between the test data and equations 1a and 2b above, it is reasonable to argue that the currently available calibration equations, including the ones in BRE IP4/93, can be trusted to return reliable suction values.


NaCl solutions can be used to calibrate ash-free Whatman Grade 42 filter paper. The calibration method is simple and non-expensive. Furthermore, the results strongly suggest that the equations in BRE IP 4/93 can be used to determine soil suction in the laboratory, with currently available batches of Whatman Grade 42 filter paper.


Tabetha Hellard, Elizabeth Hort and Kellon Booker at SSL and Dariusz Piotrowski, Ewa Plona, and Aleksandra Jurochnik at i2 Analytical kindly agreed to perform the calibration tests.


ASTM D5298-16 (2016) Standard test method for measurement of soil potential (suction) using filter paper, ASTM International, West Conshohocken, PA, 2003, DOI: 10.1520/C0033-03,

Crilly, M.S. and Chandler, R.J. (1993) A method for determining the state of desiccation in clay soils, BRE information paper, IP4/93. HIS BRE Press, Bracknell, UK.

Esmaili, D. and Hatami K. (2017) Comparative Study of Measured Suction in fine-grained soil using different in situ and laboratory techniques, International Journal of Geosynthetics and Ground Engineering, 3:27

Fondjo, A.A., Theron, E., and Ray. R.P. (2020) Assessment of various methods to measure the soil suction, IJITEE, Vol. 9, Issue 12, pp. 2278–3075 (online).

Fredlund, D.G., Rahardjo, H., Fredlund, M.D. (2012) Unsaturated soil mechanics in engineering practice, pp 939, John Wiley & Sons, Inc., Hoboken, New Jersey.

Leong, E. C., He, L., and Rahardjo, H., (2002) Factors Affecting the Filter Paper Method for Total and Matric Suction Measurements, Geotechnical Testing Journal, Vol. 25, No. 3, pp. 321–332.

Marinho, F.A.M. and Oliveira, O.M. 2005. The filter paper method revisited, Geotechnical Testing Journal, Vol. 29, No. 3, pp. 1–9.

Ridley, A.M. (2015) Soil suction — what it is and how to successfully measure it, Proceedings of the Ninth Symposium on Field Measurements in Geomechanics, Australian Centre for Geomechanics, Perth, pp. 27-46.

Fig. 1. Test configuration for (a) a single jar (left) and (b) six jars during the two-week equilibration period (right).

Fig. 2. Filter-paper calibration test data compared to published calibration equations.

Article provided by Dimitris Xirouchakis, Director at Structural Soils Ltd

Article Geotechnical

Bitesize Guide – Geotechnical unit, Ground models and Geotechnical Design Models– what are these, what do they cover and who is responsible?

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This note has been prepared based on a review of the draft prEN 1997 dated August 2022.

Geotechnical Unit

A geotechnical unit is defined in prEN 1997-1 as a ‘volume of ground that is defined as a single material’. Ground can be soil, fill or rock existing in place before any construction works, each with its own hydraulic conductivity.

A unit will have a description and classification based on designation of material parameters and identification of the data used in the selection of representation values of ground properties.

These units are normally identified prior to the start of the ground investigation as part of the initial desk study, site inspection and preliminary investigation (prEN 1997-2, 5.2.2 to 5.2.4). These are required as part of the planning of the design investigation (5.25) and develop as the project cycle evolves. The ground investigation should identify strength, stiffness, anisotropy and geometrical variation of the units.

Normal UK practice would give responsibility for these initial works either to the Specialist Ground Investigation Contractor, or sometimes to a Geotechnical Consultant appointed at an early stage in the Project.

Ground model

The concept of the Ground Model is familiar to all practitioners site specific outline of the disposition and character of the ground and groundwater based on the results of ground investigations and other available data. These conditions will have an influence on the site (and this may also need to include the recognition of potential ground conditions and sources outside the site boundary), on the design itself, and finally the construction of the project.

The draft prEN 1997-2, 4.1 states that a Ground Model shall comprise the geological, hydrogeological and geotechnical conditions of the site as determined by the ground investigation, and is one of the main outputs to be included in the Ground Investigation Report (GIR). The Ground Model also forms the basis for development of Geotechnical Design Model [GDM] for each geotechnical design situation and each geotechnical structure (prEN 1997-1, 4.2.3).

As an example, the Ground Model should consider, but not be limited to, the geomorphology of the site, geometrical and geotechnical properties of the geotechnical units, but also discontinuities and weathered zones. The Ground Model shall state the variability and level of uncertainly of the conditions and properties alongside derived values from relevant ground properties of all geotechnical units encountered.

Without the Ground Model, the GIR would not be able to identify the derived values of the geotechnical units.

As the Ground Model is one of the principal outputs from the initial desk study, site inspection, preliminary or design investigations and is to be included in the GIR, development of the Ground Model is usually the responsibility of the Specialist Ground Investigation Contractor, or is sometimes passed to a Geotechnical Consultant appointed at an early stage in the Project.

The draft prEN 1997-2 states the Ground Model shall be developed and updated as new potential information is made available. Without the ground model, a GDM cannot be developed and validated. Any changes to the ground model shall be documented in the Geotechnical Design Report (GDR). Updating the Ground Model at this stage may therefore fall to the Geotechnical Designer rather than the original Specialist Ground Investigation Contractor.

Geotechnical Design Model

The GDM is a conceptual representation of the site derived from the ground model for the verification of each appropriate design situation and limit state. It is based on the Ground Model which has verified against the variability and uncertainty of the ground conditions.

The GDM should include, but is not limited too

  • tabulation or graphical cross sections of the geotechnical units
  • representative values of ground properties for all the geotechnical units encountered in the zone of influence.
  • inclusion of groundwater table
  • and the process of compiling the GDM.

The GDM should also consider the

  • variations of groundwater in all directions within each geotechnical unit. There may be occasions where groundwater pressures may be classified as accidental actions, as detailed in prEN 1997-1, 6.1.
  • identification of any spatial trends

Normal practice in the UK is that the development of individual GDMs would be the responsibility of the Geotechnical Specialist appointed to design each geotechnical structure for the appropriate geotechnical design situation and then included in the GDR. On most projects, there may be multiple GDRs often prepared by different designers. Guidance on the content of the GDR is given in prEN 1997-3. The individual GDRs may be collated into a single Project GDR.

The reliability of the GDM must be validated using the guidance given in prEN 1997-1, Table 4.6 for the appropriately selected Geotechnical Category [GC]. The GC would have been selected as part of the GIR. Table 4.6 has been reproduced as follows:

The validation process should also review the quantity, quality and appropriateness of the information taken from the GIR.  This is done to determine sufficient confidence in the GDM to ensure the level of reliability required by prEN 1990 is obtained, and additionally, that the measures taken to validate the GDM according to the GC are adequate. If neither condition is met, or there is insufficient confidence in the level of reliability then additional ground investigation shall be performed.

The GDM is reported in the GDR for each geotechnical design situation and for each geotechnical structure. Guidance on the content of the GDR is given in prEN 1997-3.

The AGS Geotechnical WG are preparing a number of other Bitesize Guides covering various Second-Generation EC7 topics, and if anyone has a burning desire to say something, get in touch with Katie, Alex Dent or Chris Raison via

Guide produced by Emma Cronin, SOCOTEC.



Article Geotechnical

AGS Bitesize Guides – Introduction – prEN 1997:202x

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The second-generation of Eurocodes is proposed as the first major revision of the Eurocode suite of standards since original publication in 2004. This process has been underway for at least 10 years. Initially this comprised a series of Evolution Groups, set up by all the major National Standards Bodies [including BSI], tasked with reviewing the first-generation Eurocodes and identifying area where improvements, clarification, simplification, and harmonisation could be applied to improve the documents. Proposals were then passed to Task Groups for updating and preparing new drafts. The final process was a series of reviews by both the public and by the National Standards Bodies themselves [in UK by the BSI Committee B/526].

The Structural Eurocodes are a series of interlocking standards that interact as a whole and require designers to have access to and understand many different codes which link to yet more material, execution, and testing codes. The draft prEN 1997 is a work in progress and currently comprises three parts as follows:

prEN 1997-1:202x         Eurocode 7: Geotechnical design — Part 1: General rules

prEN 1997-2:202x         Eurocode 7: Geotechnical design — Part 2: Ground properties

prEN 1997-3:202x         Eurocode 7: Geotechnical design — Part 3: Geotechnical structures

prEN 1997 in turn is dependent on the over-arching Eurocode EN 1990, now titled ‘Basis of Structural and Geotechnical Design’. EN 1990 is an integral part of design to prEN 1997. BS EN 1990:2023 was published by BSI in August 2023.

Details of the timeline for final completion and publication of prEN 1997 has been given by Andrew Bond [chair of B/526 and past-chair of TC250/SC7] in a recent article published in Ground Engineering [November 2023 pp30-32]. Some topics were covered by the recent AGS webinar [September 2023] and parallel webinars held by NEN [Nederlands Normalisatie Instituut], acting as Secretariat for the revisions to prEN 1997.

Because of the imminent publication date and the large number of new topics, revisions to layout and structure and introduction of some new concepts, the AGS Geotechnical Working Group thought it timely to issue a series of Bitesize Guides covering prEN 1997. These are intended to introduce topics selected from the current drafts and to give personal views and understanding of the requirements gleaned from the code as actually written. It is believed that review and comments from representative members of the target audience rather than knowledgeable experts closely involved in the development will help to identify areas of ambiguity or lack of clarity. Finally, the publication of bitesize guides will hopefully generate some discussion and dialogue from other members of AGS.

The bitesize guides can be downloaded from the AGS website here.

Article provided by Chris Raison, Raison Foster Associates

Article Business Practice Contaminated Land Data Management Executive Geotechnical Instrumentation & Monitoring Laboratories Loss Prevention Safety Sustainability

Early Career Professionals: Call for Posters

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The AGS is holding a sustainability-themed poster competition at this year’s Annual Conference, and we’d like to see how Early Career Professionals are applying sustainable practices in the workplace.

Whether it’s applying SuRF UK’s sustainable management practices, using mobile data capture, using ethically sourced PPE, we’d like to see your ideas and practices for how you’re improving sustainability.

The poster should be colourful, eye-catching and aim to inspire businesses to become more sustainable. Submissions can cover any of the 17 UN Sustainable Development Goals:

The winner will receive a Selfridges hamper worth £85, free entry to this year’s Annual Conference on 25th April in London, plus have their poster printed in AGS Magazine which reaches over 6,000 industry professionals 6 times a year.

All posters submitted will be displayed at the Annual Conference.



Posters should be submitted in a high resolution, A4 format and can be created in any means, from drawing by hand, utilising photography, to computer-generated artwork. 

Please note that all submitted posters will be printed and displayed at the AGS Annual Conference.

To enter, please email your poster alongside your full name and company to Caroline Kratz at with the subject title ‘AGS Poster Competition’. The deadline for entries is Friday 5th April at 9pm.



The Annual Conference is the flagship event in the AGS’ calendar. Taking place on 25th April 2024 at One Great George Street in London, the event will see over 200 geotechnical and geoenvironmental professionals in attendance.

This year’s Annual Conference has an overarching theme of sustainability and the AGS will be donating a percentage of profits made to Projects for Nature, an initiative which aims to restore nature recovery in the UK.

For further information and to register click HERE or email



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Name: Dave Woods

Job title: Technical Manager

Company name: Huesker Ltd

What does the company do and what areas does it specialise in?

Manufacturer and designer of geosynthetics.

Where is HUESKER located?

UK office in Warrington, production facilities in Germany, USA & Brazil

How many people does the company employ?

10 UK employees, 600+ globally

How long have you worked at HUESKER?

Approaching 4 years

What is your career background, and what enticed you to work for HUESKER?

Civil / Geotechnical Engineer with 30 years of experience in UK, Asia and Europe. Geosynthetics have always been a major area of interest and expertise for me, and Huesker were a company whose materials I had known and worked with over my entire career from my very first project widening the M25 motorway.

What is your current role within HUESKER and what does a typical day entail?

Technical support for sales and design of the company products, advice on site installation, business development, external training through CPDs, conference papers and presentations, university lectures etc and representation of the company and industry on industry and technical committees. No two days are alike.

What are the company’s core values?

Imagination, Progressiveness, Excellence, Attractiveness & Reliability.

Are there any projects or achievements which HUESKER are particularly proud to have been a part of?

We are proud of all our projects from small retaining walls and foundations to huge infrastructure schemes. Most recently the development and implementation of geogrid with integrated fibre optic cables to monitor ground movement and warn of sink holes prior to failure on HS2 and the development of active composite textiles which treat contaminants within soils in situ rather than condemning them to landfills.

How important is sustainability within the company?

Sustainability is at the core of all we do. Our products offer up to 85% reductions in embodied carbon content versus conventional construction methods whilst we continue to lead the market with advances in the use of post-consumer recycled materials in our products and increasing use of renewable energy in our production facilities.

How does HUESKER support graduates and early career professionals who are entering the industry?

Where possible we offer external lectures to students at undergrad and postgrad level within universities globally. We seek to employ the very best young engineers and through continuous internal training, mentoring and the sponsorship of Masters and PhDs seek to advance the careers of our employees to reach their full potential.

How has COVID-19 impacted HUESKER today? Are there any policies which were made during the pandemic that have been kept to improve employee wellbeing and productivity?

Options for remote working and flexibility of working hours were always part of Huesker’s working practices, but during and post Covid, these options were made available to more staff members. The increased use of video conferencing has reduced both in house and external face to face meetings helping to improve sustainability and increasing productivity whilst introducing more regular global meetings and training sessions to better share individual knowledge.

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

The AGS is a valuable source of information and networking opportunities within the geotechnical field through in person events, webinars and published guidance.

What are HUESKER’s future ambitions?

To continue to innovate within the geosynthetics field with an aim to improving the sustainability, safety and economy of geotechnical projects whilst providing solutions to both existing problems and questions which are yet to be asked.

Article Instrumentation & Monitoring Sustainability

Assessing the Possible Sustainability Benefits of using Instruments and Monitoring on Site

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The AGS has asked each of its working groups to discuss sustainability issues at their meetings and the Instrumentation and Monitoring Working Group is no exception. From the Group’s perspective there are obvious sustainability, cost, time and carbon benefits in not having to go to site regularly to monitor Geotechnical or Geoenvironmental parameters. Instead, remote monitoring equipment can be installed, and the data downloaded periodically or streamed in real time to your office computer.

Such a philosophy is also very much in keeping with the AGS data management philosophy – require input of data only once and get the most appropriate person (ideally the producer) to do it.

Unfortunately, many practitioners have had bad experiences with continuous remote monitoring, which can be tricky to establish, maintain and interpret effectively without sufficient experience. Regulators may also not accept on-site analysis of data without prior approval (difficult to obtain with current regulatory response delays), significant oversight and complementary analysis.

There remains a seeming lack of understanding on the part of some practitioners and regulators as to what can be done these days with remote monitoring, the range of equipment that is available and what guidance is available for the use of that equipment (usually precious little and out of date…). The skill lies in the ability to determine exactly what to do and what equipment to use for any particular project, depending on one’s perspective, competence and defined sustainability goals.


In terms of sustainable development, the Brundtland report (UN Report of the World Commission on Environment and Development: Our Common Future, 1987) defines sustainable development as ‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs’.

Sustainability is the combination of several different considerations including environmental, economic and social factors, which can sometimes be even more important than simply reducing carbon. Offsetting is a commonly misused word in the context of sustainability as it rarely is in practice and most people will only come across it in relation to carbon footprints, credits and the fuel in the plane that takes you on holiday.

In fact, the basic concept underlying sustainability is that it is best achieved using a process involving quantification of a combination of potentially related factors from each of the identified key areas as expressed for example in UN sustainability guidance.

This process lead methodology and approach is absolutely key to determining and calculating the positive and/or negative elements identified and quantified to achieve the “best” result – for a given value of “best”.

There have been several attempts to undertake sustainability calculations by both AGS members and others, and several more attempts are currently in the process of being determined, tested and calculated, including at least one for UK regulators. This is in part a response to the engineering sustainability initiatives being developed within the development/building industry at the request of groups like ICE.

However, this is far from a simple task in practice, especially when one starts including considerations of total life cycle carbon, recycling and waste elements, which are very difficult aspects to attach precise and accurate quantifications to.


So, how does one actually go about proving or justifying the use of on-site methods, equipment, analysis, remote monitoring and costs against more traditional methods such as laboratory analysis?  One of the easier ways to at least start the process is to determine the benefit primarily on the basis of cost, especially as the carbon intensive travel to site element is becoming ever more expensive.

For example, six gas monitoring visits (minimum recommended by CIRIA document C665 ‘Assessing risks posed by hazardous ground gases to buildings’ for residential low risk) may cost in the order of £3,000 and 1.2 tonnes carbon dioxide emissions.

Compare this with a remote continuous monitoring system at two visits (one to install and one remove) over a week of falling low pressure continuous monitoring at a total cost in the order of £2,200 and 0.2 tonnes carbon dioxide emissions.

Issues Identified

However, if the regulator treats the CIRIA C665 requirements (for example) as strict requirements and not as guidance, they may not accept the possibility of remote monitoring data and conclusions as continuous monitoring for gasses largely postdates the original publication of that guidance.

This could increase the costs beyond that for the proposed six visits. This is where the socio-legal aspect of the sustainability calculation comes in, along with our professional duty of care to our clients, and perhaps explains why this is not taken up as much as it could and should be, to improve the sustainability of the industry when using newer technologies and alternative, but equally valid and proven methodologies.


As a regulated industry, we can fail on sustainability when it comes to presentation, guidance and especially the regulation itself, which is often many years behind the current realities of what can now be achieved on site.

We hope that this article will provide an initial spur to tackling some of the issues raised by the working group and that with the help of its members and others, the AGS can produce influential and informative guidance to practitioners, clients and UK regulators regarding the options available, new ways and examples of how to achieve regulatory compliance, and how remote monitoring and analysis can contribute to the overall sustainability of our Client’s projects and the industry as a whole.

Whilst in fact the determination process can be fairly simple (at least in theory), to determine what is probably the best, greater or more sustainable method of undertaking current site tasks and analysis, it may not be attainable using a method currently accepted by the appropriate UK regulator or society.

The Instrumentation & Monitoring Working Group will be exploring this topic further and will aim to provide additional case studies and examples of how this can be successfully achieved in practice. If any AGS members have relevant examples, case studies and critiques on any of the above or related topics then please send them to the group via the AGS Secretariat and thanks for listening.

Article provided by Chris Swainston on behalf of the AGS I&MWG

Article Business Practice

Unconscious bias in recruitment

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Whether we think so or not – we are all biased. Decisions we make about people are impacted by our unconscious bias without us even being aware of it. This can have consequences when we are recruiting people into the workplace as well as in appraisals, training and development, networking and mentoring.

Things we notice about a person when we meet them for the first time include their skin colour, age, gender and disability. Our experiences and influences (such as family, peers, media, education) lead us to unconsciously group people into categories which form the basis of stereotypes*, which can lead to prejudice and discrimination. Once we acknowledge our bias, we can take action to reduce its influence.

There are several types of unconscious bias which can strongly influence who we recruit. A couple of examples include:

Affinity bias: where you unconsciously favour someone because you share similar interests, backgrounds and experiences. We feel more comfortable around people who are like us.

Confirmatory bias: where we look for evidence / information that confirms our beliefs and values and we ignore evidence that disproves them.

When it comes to recruitment, examples of how our unconscious bias could influence our decisions include:

  • Employing someone who is not the most qualified;
  • Not recruiting people with differing views;
  • Following ‘status quo’ as a ‘safe’ option;
  • Not asking someone to interview due to a name not sounding ‘English’;
  • Not recruiting someone because they are not a good ‘cultural’ fit;
  • Assuming that a mother won’t be able to commit enough time to work;
  • Assuming an older worker will not be open to learning new skills.

If we want to create an inclusive environment where everyone can flourish, we must address unconscious bias.

There are a number of ways to reduce unconscious bias in recruitment:

  1. Define the job role;
  2. Redact information on the application form / CV that identify key characteristics of a person such as age, gender, ethnicity. This will remove unconscious bias while short listing potential candidates.
  3. Have a diverse hiring / interview panel.

Even by following these steps, it is unlikely that we will be completely unbiased.

Unconscious bias can sometimes be difficult to self-identify and to assist with that there is a test called the Implicit Association Test (IAT). The IAT measures the strength of associations between different groups of people and your immediate thoughts and unconscious stereotypes about those groups of people. The test’s purpose is to specifically highlight bias, this does mean that you may be confronted with some results that you may find upsetting or do not agree with; however, it can be a great method to understand your unconscious attitudes and beliefs.

You can take part in the anonymous test or learn more about it here:

*Stereotype: a fixed idea or image that many people have of a particular type of person or thing, but which is often not true in reality and may cause hurt and offence

Prepared on behalf of the Business Practice Working Group by Vivien Dent (Groundwater and Land Quality Technical Specialist, Green Growth and Delivery, Environment Agency) and Bradley Falcus (Senior Geo-Environmental Administrator, Central Alliance Pre-Construction Services Ltd)


Some insights into the geotechnical implications of pyrite and its consideration and management

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The assessment of ground aggressivity and suitability of construction materials are fundamental aspects of geotechnics. Ground hosted sulfide and sulfate minerals are known to produce unwelcome implications for ground engineering. Confidence in selection of the most appropriate form of construction and mitigation methodology, must be based on the results of meaningful site-specific material characterisation and assessment of performance in the likely construction environment. It is apparent that many ground engineering practitioners do not fully appreciate that certain rocks and soils are liable to contain sulfur species that may negatively impact ground engineering projects. In practice assessment procedures are often followed without a clear understanding of the issues and how to best manage them. This approach is not always suitable for managing the extensive variability encountered in the UK. Furthermore, an appreciation of how the construction activities may bring about undesirable changes are necessary for design of appropriate mitigation and long-term management. This short article discusses some of the issues that may occur, particularly where pyrite is concerned and considers how these characteristics and associated risks may be managed.

Causes of construction groundwork damage brought about through physical deterioration of ground and engineering materials are attributed to a wide range of factors that involve physical, chemical, and biological processes. In the UK a high proportion of such occurrences in the engineering environment result from the presence of sulfate ions in groundwater, brought about through dissolution or reaction of sulfur compounds. Pyrite and gypsum are the most commonly occurring sulfur compounds likely to be encountered during construction works.  In certain locations, the source of the sulfate ions is clearly through dissolution of evaporitic deposits, but in many cases, covering a much wider geographical area, these are derived from the oxidation of iron sulfide minerals, particularly pyrite. Pyrite, and the other infrequent iron sulfide minerals are unstable in oxidising and damp atmospheric conditions typical of the construction environment and will rapidly weather, producing insoluble orange-brown hydrous iron oxide, with release of hydrogen (H+) and sulfate (SO42-) ions into solution as mobile sulfuric acid. This has a significant negative impact for ground engineering when reaction occurs consequent of ground disturbance, creating conditions that are aggressive to ground material including buried steel and concrete and, in some cases, raising sulfate to harmful levels.

Reaction of the sulfuric acid with other calcareous minerals such as calcite or concrete, give rise to selenite-gypsum as discrete crystals, and this involves expansion. The replacement of pyrite and calcite by selenite involves a volume increase of around 103%, developing ground stresses and causing differential heave due to indiscriminate crystal growth. This chemical alteration is frequently accompanied by rapid deterioration in engineering properties of the host material and the volumetric gain often causes disturbance in filled ground, and failures of foundations, earthworks, underground excavations, tunnels, and slopes. Observations have also documented abiotic pyrite oxidation where the pH of pore fluids was around pH >12, indicating that this reaction mechanism can also occur when pyrite bearing ground is treated using lime and cement.

The oxidation of pyrite is complex, it occurs through various reaction stages, at different rates, which conclude in a range of products. Ultimately reaction depends on various aspects including the crystalline form and grain size of the pyrite, the mineralogy and fabric of the host, and environmental conditions, including the exposure to weathering brought about by the engineering work. To manage any negative impacts to design and construction, the possibility of changes promoting the potential for pyrite oxidation during and after construction needs to be considered.

Sulfur is an abundant element in the Earth’s crust and occurs in geological materials of all ages and origins, in a variety of forms. Sulfur is highly reactive and readily combines with most non-noble elements, particularly under reducing conditions, to form metallic sulfides of which the iron form, pyrite (FeS2) is the most widely occurring, along with its less common dimorph marcasite (FeS2), and occasional pyrrhotite (Fe1-xS where x = 0 – 0.2). Gypsum tends to be the most widely occurring sulfate mineral and is frequently encountered during ground works. Gypsum occurs as a primary accumulation in evaporite deposits such as the Mercia Mudstone Group and forms through evaporation of saline waterbodies. But it is more widely occurring as the crystalline ‘selenite’ form, which tends to develop as a ‘secondary’ product of contemporary weathering action on pyrite in the presence of calcite. The oxidation of pyrite will also give rise to high concentrations of sulfate ions which are mobilised by groundwater. Not all forms of sulfur are troublesome in engineering situations, although this depends upon the environmental conditions. Some recalcitrant mineral sulfates, such as barytes, celestine, and organic sulfur are relatively stable in weathering environments, and do not contribute to the sulfur present in groundwaters, unless conditions are unusual, so they are unlikely to impact significantly in construction and geo-material applications. Therefore, knowledge of the likely occurrence and attributes may help to manage potentially adverse conditions that could occur during and after construction.

Pyrite is remarkably widespread in its occurrence and is found as a minor constituent in a wide range of naturally occurring materials. It occurs in rocks and engineering soils, ranging from ancient sediments to Recent deposits, igneous and metamorphic rocks and hydrothermally deposited mineral veins. Pyrite occurs as diverse forms including variously shaped grains, nodules, and well-formed crystals, ranging from microscopic to several cm across; the morphology of pyrite has an influence on its potential for atmospheric oxidation. Therefore, its appraisal may help to determine its potential reactivity and the suitability of pyrite bearing ground and geomaterials for particular applications.

The different forms of pyrite and their combinations all share the same internal arrangement of iron and sulfur atoms but conditions during formation affect the crystal form. Well-crystallised pyrite occurs in the brass-yellow macroscopic form as large masses, veins or as large discrete often striated cubic, octahedral or pyritohedral crystals a few millimetres to a few centimetres in dimension and are commonly referred to as the ’non-reactive’ form of pyrite.  Typically, these are found in rocks that are well indurated and / or have been subjected to moderate to high-temperatures and pressures.  These well-crystallised forms of pyrite have a densely packed structure and relatively small specific surface area such that they tend to respond slowly in weathering environments. Macroscopic forms of pyrite occur extensively in igneous and metamorphic rocks and some hard-rock limestones, sometimes in substantial concentrations distributed through the host and tend to be relatively stable in construction environments.  These deposits are widely worked in the UK for construction aggregates in which slow oxidation or combination with cementitious binders may lead to problematic chemical reactions. In less-well indurated sedimentary rocks, pyrite may occur as visible nodules or smooth faced crystals, but more typically, it takes the form of disseminated microscopic framboids that are very difficult to recognise.

The microscopic framboidal form of pyrite is of greatest concern to ground engineering. Framboidal pyrite tends to form in sedimentary environments under anoxic reducing conditions through microbial activity where it remains stable, but when exposed to oxidising and damp atmospheric conditions it may rapidly deteriorate with consequentially detrimental effects.  It is commonly found in dark coloured (grey and dark grey), fine-grained sedimentary deposits including clays, mudstones, argillaceous limestones, siltstones, sandstones, and low-temperature hydrothermal deposits. The microscopic reactive forms of pyrite may also occur in newly formed sediments, including marine sands and gravels and river flood plain deposits, which are widely used as construction aggregates. Framboids are raspberry-like spherules, typically 2 – 80 μm diameter, comprising of ordered agglomerations of microcrystalline pyrite grains that are themselves <0.3 – 2 μm in diameter. They occur as disseminated spherules, clusters, or dark greenish-grey coloured concentrations along partings. The framboidal structure results in grains with a large surface area in proportion to their volume, making them highly susceptible to oxidation in an oxygen and water bearing atmosphere and oxygenated water.  This reaction may be mediated and greatly accelerated by microbial intervention from bacteria such as the ubiquitous Acidithiobacillus sp., which rely on electron transfer between Fe2+/Fe3+ for their metabolic process and this functions as a key mechanism in the oxidation reaction. In the ground engineering discipline, this form of pyrite is often referred to as the ‘reactive’ form of pyrite.

It is cautioned that the allusion to the visible form of pyrite as ‘non-reactive’ is not strictly true, the well-crystalline macroscopic forms of pyrite are still susceptible to oxidation following exposure, but depending on their surface condition, reaction generally will occur over a much slower timescale and may not be considered significant where construction is concerned, although it may be expedited where physical damage occurs to the crystals and through reaction of less stable forms. Therefore, potential reactivity must be assessed, with judgement also relying on previous experience of that material.

In the UK, framboidal pyrite is widely found in the dark coloured deposits of marine and fluvial origins of Carboniferous, Jurassic, Cretaceous and Eocene age. These account for a large part of the near-surface stratigraphy that contains many major urban centres. Through weathering, sulfate minerals can be present at shallow depth, whereas sulfide minerals may predominate at greater depths where oxidation has not occurred. Weathering involves physical and chemical changes to the natural material as it adjusts to different overburden pressures and the presence of atmospheric gases.  The change in pressure results in development of fissures and joints which facilitate the movement of oxygenated groundwaters. Water movement promotes chemical adjustments including hydration, dissolution and alteration of certain minerals and the formation of other minerals.  The distribution of sulfate varies within the weathered zone, with the top few metres having negligible amounts due to removal by rain leaching, but elevated levels may be present at the base of the root zone at around 2 to 3 metres depth, decreasing towards the base of the weathered zone, and this is identified by presence of brown staining on fissure and bedding surfaces, and presence of selenite. The weathering state is revealed by the colour changes of the iron forms present. In weathered horizons, the orange-brown colour of ferric iron predominates, whereas with depth the grey colour of ferrous iron represents less weathered lithology and indicates an increase in the presence of unreacted sulfide minerals.

Although British, European, and other standards promote good practice in carrying out investigations, potential problems are often not adequately anticipated and catered for. Historically the Building Research Establishment have provided guidance for routine UK assessment of potential ground aggressivity based upon water and acid soluble sulfate content and acidity of soil and groundwater samples. This worked well for many decades with few instances of sulfate attack on buried concrete reported.  However, following investigation on several cases of sulfate attack on construction materials and disruptive ground heave during the 1980s-1990’s, it was realised that the consequences of pyrite oxidation were not being considered and had been attributed to various other assumptions. Precipitation of new minerals such as gypsum provoke possibilities of ground heave. As the process of dissolution and precipitation will not generally occur in the same location, both expansion and void creation may produce differential movements and heave causing structural damage. This necessitated revision of testing standards, and guidance advocating a staged approach based on initial review of the geological setting, followed by a planned investigation programme and detailed ground assessment. This requires an awareness of potentially aggressive material and importance of focused chemical testing. The severity of pyrite oxidation depends not only on the crystal form but also on the permeability and chemistry of the host deposits as well as the groundwater conditions. The site investigation may confirm the presence of significant quantities of pyrite, gypsum, and calcite but these values alone do not facilitate assessments of the reaction rate and significance to construction. Assessment also requires that the consequences of the construction activity and weather-related issues in the construction period and beyond are fully addressed to provide an adequate basis for the design of structures.

The consequences of pyrite reaction may become a significant hit for the construction budget and progress when unsuspected. The oxidation of pyrite bearing deposits during earthworks and construction has been observed to progress rapidly over a matter of weeks or months, producing conditions chemically aggressive to engineering materials. Therefore, to avoid or manage potential problems attributed to pyrite oxidation it is necessary to know not just that it is present, but also its distribution, its form and reactivity. Investigations and construction may overlook the potential for material deterioration, but this can be determined at a site level through observation of changes following exposure and targeted chemical testing. The distribution of sulfur compounds in soils and rocks can be highly variable so testing must ensure that sulfur-bearing horizons are not missed, and a suitable characteristic value selected for design. Material selected for laboratory testing should focus on the construction zone but also evaluate other strata that may be affected.

Knowledge of the mechanical behaviour of the host material and the changes brought about through exposure during construction may expedite management of the construction process by facilitating re-use of a favourably weathered product that would otherwise constitute an unsuitable material. Ultimately, management of material avoiding costly offsite disposal, may be achieved through informed investigation with pre-weathering of pyritic fill to mitigate the risk of heave through conversion of pyrite to selenite or by blending, encapsulation, or provision of targeted drainage and impermeable barriers.

Article provided by Mourice A. Czerewko, Associate Engineering Geologist, AECOM Ltd


AGS Photography Competition 2023 – The Results

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In March 2023, the AGS launched their fourth photography competition.

Members of the AGS Executive and Business Practice Working Group including Vivien Dent, Sally Hudson, Jo Strange, Bradley Falcus and Steve Hodgetts took on the challenging task to judge the images by scoring across the following criteria;

  • Originality
  • Composition
  • Colour, Lighting, Exposure and Focus
  • Overall Impression, Impact and Visual Appeal

Four images were shortlisted, and we’re pleased to announce that Shannon Wade of Strata Geotechnics was the overall winner of the competition and won a luxury Fortnum and Mason Hamper.

Our three runners up, who each won a bottle of Champagne are Shannon Wade (Strata Geotechnics), Matthew Cook (Environmental Protection Strategies Ltd) and Aaron Stokoe (Brownfield Solutions Ltd).

The AGS would like to thank all those who took the time to enter the competition.


Shannon Wade, Strata Geotechnics

Image description: Truly highlights the highs and lows of rural GI. An additional scheme of work for The Coal Authority at the site of the Esgair Mwyn, Metal Mine near Pontrhydfendigaid to again improve water quality and prevent it leaching through metal mine spoil. The weather had been foul for days with limited shelter, our team worked their hardest in the conditions to get the works done safely and on time and were rewarded by a little bit of sunshine and a glorious rainbow.


Shannon Wade, Strata Geotechnics

Image description: Working nights with our Comacchio 305 on the M1 Southbound, J35 for National Highways undertaking works to inform design for addition PRS lay-bys on our existing Smart Motorways network.


Matthew Cook, Environmental Protection Strategies Ltd

Image description: The drilling of windowless sample boreholes at an RAF site in Cambridgeshire with RAF jets in the background, boreholes were being drilled to to provide information for use in improvements to site.


Aaron Stokoe, Brownfield Solutions Ltd