A to Z Geotechnical Services

CGL offers a wide range of specialist skills, providing advice and support on geotechnical engineering issues.


Basement Impact Assessments
Basement Impact Assessments

Due to high land values and limited development space in London, basement extensions are becoming common.  It is increasingly recognised that these may have an impact on local flooding, groundwater flow, and ground movements, potentially generating long term stability issues for neighbouring properties.  In April 2011, the London Borough of Camden adopted CPG4, as official planning guidance, for their use in the consideration of planning applications involving basements in the Borough.


The document presents a structured, formalised approach to identifying the potential risks, both from and to the development, in a five stage Basement Impact Assessment (BIA) process from original screening by the applicant through to review and  decision making by the Council.


The BIA process incorporates a holistic review of surface and groundwater conditions, and incorporates geotechnical analysis, where appropriate, to establish ground movements arising from the basement development and therefore its potential impact on neighbouring properties.  This is particularly relevant where party wall foundations are to be underpinned.  CGL has undertaken a number of BIA reports to date and one of the very first ‘test’ cases of the new process is currently under consideration within the Council.

Recent experience suggests that other London Boroughs are likely to adopt the BIA methodology with frequent requests from Local Planning Authorities to assess the hydrogeological and hydrological impacts of large basements elsewhere in London.  CGL’s extensive experience within the London area makes us well placed to address these queries, and provide an holistic analysis to accurately determine the potential risks and support the planning process.


For further information about Basement Impact Assessments please contact Richard Ball at our Head Office on 01483 310600 or email Richard at RichardB@cgl-uk.com.

Construction Monitoring and Supervision
Construction Monitoring and Supervision

The key to successful implementation of engineering designs is good site management. The complex nature of geotechnical and geoenvironmental designs and the frequent requirement for third party certification requires skilled engineers to support client teams during construction. CGL employs dedicated engineers who understand construction and the importance of timely integration of ground-related solutions into development and building projects.

CGL’s activities during the construction process may be broadly divided into two main elements: firstly,monitoring and supervision of remediation measures on contaminated sites, and secondly,inspection of earthworks and building formations.


Activities on contaminated sites range from simple inspection, testing and certification of capping layers in domestic gardens, to supervision of large-scale hydrocarbon remediation projects. Some sites necessitate the use of innovative methods, requiring detailed knowledge of soil chemistry and engineering properties to arrive at successful conclusions. For instance, the use of e-clay stabilisation and in-ground barriers to avoid issues with regards to migration of groundwater contamination that would entail several years of monitoring to satisfy the regulator.


On a more routine level, CGL engineers direct and validate the removal of old underground fuel storage tanks, or assist in classification of waste materials to minimise waste disposal costs. Because of our independence during these operations, clients and regulators alike are confident that the remediation solutions are pragmatic and implemented to meet or exceed programme timings and limit costs.


Geotechnical engineers employed by CGL are experienced in supervision of earthworks, and the assessment of monitoring and compliance data from earthworks operations. Their involvement and ability to make immediate decisions can lead to the avoidance of costly delays in the event of unplanned circumstances. Our pragmatic recommendations provide confidence that construction conditions are appropriate for support of foundations, floor slabs and sub-structures. Recently, at the Woolwich site, CGL’s involvement has allowed higher foundation levels to be adopted, and material to be re-used rather than discarded, saving the client both program time and material handling costs.


So, when it comes to the construction process, both contractors and developers can benefit from the capabilities and skills of our engineers accompanied by our independence that is valued and respected by regulators. CGL take pride in providing ground solutions for difficult sites and then assisting the construction teams to implement the necessary measures to make the projects a success.


For further information about Construction Monitoring and Remediation please contact Ian Marychurch at our Head Office on 01483 310600 or email Ian at IanM@cgl-uk.com.

Earthworks Design and Control
Earthworks Design and Control

Designing of earthworks for schemes of various sizes under a variety of ground conditions, and in ensuring that these are implemented under proper construction control, is another of CGL’s capabilities. Our senior staff have substantial experience in the design of major highway and rail schemes, some of which have necessitated detailed engineering analysis to overcome difficult ground conditions and ensure long term stability and serviceability.


Our capabilities include assessment of sources to identify material suitability, the effective re-use of materials, and minimisation of the cost of imported fill. Our approach uses the principle of ‘relationship testing’ where complex engineering parameters can be correlated to routine on-site test procedures; a simplified but robust approach to compliance testing resulting in confidence in the construction and savings in earthworks programmes.


Specialising in the design of earthworks over soft alluvial soils, CGL has expertise in the design of ground improvement methods to enhance settlement rates beneath embankments. Typically these permit settlements that would ordinarily take 12 or 18 months under normal conditions to be completed within as little as 3 to 6 months, substantially reducing construction programmes and associated costs.


In addition, careful design of earthworks with geotextile reinforcement can lead to the creation of vertical walls and development platforms that can allow highly constrained sites to become developable. We have been involved in a number of schemes in which levelling of sloping sites has been recommended to allow the construction of residential development. Similarly, the judicious use of test data and detailed specifications can be used to allow placed fill to support structural foundations.


Where earthworks necessitate the removal of contaminated materials, CGL’s in-house waste experts are able to refine disposal classifications to substantially reduce off-site disposal costs. Our contribution often leads to substantial savings which make otherwise marginal schemes financially viable. An example of this is our recent involvement with the Wandsworth project. Our clients often seek our independent advice during early tender evaluation to enhance their competitive position and, ultimately, their success rate.


Supporting our design, we provide construction quality assurance services to monitor and validate the formation of different types of earthworks ranging from simple capping layers to large reinforced earth structures. This independent validation and certification offers confidence to clients that their asset conforms to the relevant design codes, providing posterity for the future.


For further information about Earthworks Design and Control please contact Ian Marychurch at our Head Office on 01483 310600 or email Ian at IanM@cgl-uk.com.

Expert Witness

Unfortunately, dispute resolution is an ever present part of today’s construction industry. The ability to identify technical issues, provide clear and pragmatic advice, well versed in current practice and published guidance and codification can provide timely solutions. Technical experience and familiarity with the role of an expert witness are essential.


Our very experienced senior staff at CGL have been instructed by legal teams from a number of practices specialising in construction dispute resolution and have experience of mediation, arbitration and giving court evidence. Our staff attend training and awareness of court procedures, dispute resolution and reporting on a regular basis.


Senior staff include Nick Langdon, Ian Marychurch, Jo Strange and Andy O’Dea of CGL have been involved as Expert Witnesses on many cases in the last few years on matters such as:


  • Remediation of brownfield sites effectiveness;
  • Retaining wall and river wall failures;
  • Sludge hopper or failure;
  • Collapse settlement of chalk fills and failure of fill;
  • Foundation settlements and failures including impact of solution features;
  • Liquifaction of foundation soils due to dynamic;
  • Failure of ground improvement;
  • Contamination classification;
  • Slope movements during construction;
  • Waster ingress into gas holder bases; and
  • Floor slab failure due to expansive slag.


Over the years CGL has been appointed by solicitors from Hill Dickinson, Beale & Co, Berryman Lace and Mawer, Dewey & Le Boeuf, Beachcroft LLP, Addleshaw Goddard and others. Settlements have resulted in favourable agreements for instructing parties and on occasion seeing key judgements made in favour of the instructing party.


For further information about our Expert Witness service please contact Nick Langdon at our Head Office on 01483 310600 or email Nick at NickL@cgl-uk.com.

Foundation and Substructure Designs
Foundation and Substructure Designs

CGL’s team has strong foundation design and engineering expertise.  Collectively, our senior staff have over 60 years’ experience in this field.  Value engineering bespoke solutions has recently seen CGL win the Ground Engineering award in 2011 for best UK project with a geotechnical value over £1million for our involvement in the Guildford Radisson hotel.  The contribution of CGL’s value engineering in realising this project for the client was specifically identified by the judges.  Having local knowledge and experience, we understood the quality of the Upper Chalk in the area, enabling the basement to be constructed in open cut; removing a contiguous pile wall from the design, and allowing final structural loads to be carried on shallow pad foundations, rather than bearing piles.  CGL developed a strategy to use the Observational Method on this project, and, working closely with the main contractor Galliford Try, and the structural engineer Walsh Associates Ltd., the basement was delivered well within programme with over £1 million saved from the basement costs alone.

Soil-structure interaction analysis of raft foundation options has enabled the removal of pile foundations from design, with the associated benefits of decreased cost and programme time.  Analysis is typically undertaken using Oasys VDISP software to assess ground movements within the basement and around the perimeter of the site, with spring stiffness values provided for inclusion in structural analysis software.  Basement retaining walls are analysed using WALLAP retaining wall software to assess deflections and prop loads.  From the combination of these two methodologies a reliable indication of ground movements can be established and serviceability conditions required by the new European codes assessed.

Where financial implications are high, or soil structure interactions are complex and critical to establish movements and bearing capacities, we have the facility to use sophisticated finite difference software (FLAC) to establish critical deflections, and ground movements, forces and moments in structural members, and satisfying third party interests (party wall engineers or local planning authorities).

For further information about Foundation and Substructure Designs please contact Nick Langdon at our Head Office on 01483 310600 or email Nick at NickL@cgl-uk.com.

Geotechnical Desk Studies
Geotechnical Desk Studies

CGL provide desk studies to our clients in the construction industry for projects both large and small. These desk top surveys can be tailored to meet the requirements of each client as either individual reports submitted as part of the planning process, or part of the intrusive investigation documentation.


Desk studies form an essential part of the investigation process for all sites whether brownfield or greenfield. CGL have long championed the cost effectiveness of the holistic site investigation that encompasses both the substructure design and contamination mitigation. All desk studies will require Conceptual Site Models (CSM) for contamination risk and need to consider past land use, geology both published and unpublished, and environmental incidents in context and with a view to eventual construction.


CGL do not provide simply a web-based generic collection of data without project context, but incorporate the requirements of industry based standards from the Association of Geotechnical and Geoenvironmental Specialists (AGS) and the current BS5930 and BS10175. The reports provide guidance for the intrusive investigation and support the development of the geotechnical process under the European Standard EC7.


Typically, such desk studies can be assembled, and in a matter of a few days at relatively low cost by our experienced geotechnical and geoenvironmental staff and are quality audited by highly experienced staff. Such investigation has the potential to save clients considerable amounts of money and time in both the planning and construction process.


For further information about Geotechnical Desk Studies please contact Nick Langdon at our Head Office on 01483 310600 or email Nick at NickL@cgl-uk.com.

Geotechnical Site Investigations
Geotechnical Site Investigations

"You pay for a site investigation whether you have one or not” Prof Stuart Littlejohn (1991). These words are as true today as they were two decades ago and, where value engineering is needed, investment in below ground design information is vital.


At CGL we focus our clients concerns on investing time and money into one of the least visible elements of the construction process with experienced guidance on risk reduction and what can be achieved with the knowledge a good site investigation provides.


Our experienced geotechnical engineers and engineering geologists work across the UK on site investigations ranging in size from a few £1000’s to £0.5million for clients as varied as individual householders, to major residential developers and commercial organisations, and to the power and rail industries.


Our experience and knowledge of the industry ensure we use appropriately experienced and quality driven investigation contractors and soil and contamination testing laboratories so that our factual information, compliant with BS5930, BS10175 and EC7, supports the interpretative and design reporting that is usually our final product.


Recently completed CGL site investigations have included the investigation of 74 pylon locations over 153km of moorland in the north of Scotland, Seager Tower, and a comprehensive investigation to allow value engineered options for a rafted basement. Over the years we have provided site investigations on unstable slopes, low height basements, active markets requiring night shift work and the demanding conditions around electricity sub stations and alongside railways.


Our tailored and cost effective investigations allow us to enhance the value added solution from the skills we can bring with geotechnical design using numerical analysis to predict serviceability limits required for European Code compliance.


For further information about Site Investigations please contact Nick Langdon at our Head Office on 01483 310600 or email Nick at NickL@cgl-uk.com.

Hydrogeological Assessments
Hydrogeological Assessments

Hydrogeological assessments consider how sites may be affected by groundwater and nearby surface water bodies, in terms of flood risk and impact of foundation selection.  They can be used to model how the site or proposed development may impact groundwater beneath the site and nearby surface water bodies.  This type of assessment is increasingly being requested by local planning authorities, particularly where proposed developments include basements that may alter regional groundwater flows in urban areas, giving rise to settlements and ground movements or local flooding.

At CGL, we consider the first and most critical step in such an assessment to be a desk study review followed by the building of a site conceptual model (CSM) by our experienced geological and geoenvironmental engineers to guide any intrusive site investigation and monitoring that may be required.

The CSM is refined on completion of the intrusive works and subsequent groundwater monitoring, and forms the basis for geotechnical recommendations regarding foundation design and design groundwater levels for retaining walls, floor slabs and more.  In this regard, the hydrogeological assessment provides both information and guidance to Local Authorities and the Environment Agency, and can also deliver significant cost savings in retaining wall design by establishing realistic design ground water levels.

Hydrogeological assessments are also used in environmental investigations to support numerical modelling of contaminant flow to derive remediation targets for submission, generally to the Environment Agency at planning stage.   In this connection, CGL use both the Environment Agency’s publically available remedial target methodology, and ConSIM software.  We also have the facility to model groundwater flow using FLAC finite difference software where the ground and groundwater conditions are particularly complex.

CGL’s advice and guidance at Belvedere is an example where hydrogeological assessment played an important part in the environment assessment and modelling of contaminant flow.  The work carried out for this project included the determination of the risk to water, the level of remediation required and agreement with the Environment Agency to the most appropriate remediation option.

For further information about Hydrogeological Assessments please contact Jo Strange at our Head Office on 01483 310600 or email Jo at JoS@cgl-uk.com

Mining, Cavity Investigations and Remediation
Mining, Cavity Investigations and Remediation

In the UK, mineral extraction through the years has resulted in a legacy of abandoned shallow mine and quarry workings dating as far back as Roman times. Mining of coal, ironstone, sandstone, limestone, chalk and metalliferous minerals to great depths has caused destabilisation of the surface in a number of ways including  and tailing lagoon failures, ground instability, shaft or adit collapses and tip and tailing lagoon failures.  Apart from the obvious engineering impacts on buildings and infrastructure, mine failures can also cause environmental damage through release or redirection of pollutants.  In addition, natural cavities can form in the ground through the dissolution of soluble rocks such as chalk, limestone or salt causing   environmentally sensitive sites.  At CGL, we are aware that this legacy can have a significant impact on our clients’ proposed development schemes if not identified at an early stage.


With our extensive experience of investigating, and designing and implementing appropriate remediation of such features to ensure the suitability for site development, CGL are well placed to provide ground solutions for our clients.   Commencing with the feasibility and acquisition stages of projects, we are able to assist with the calculation of associated abnormal development costs providing an independent, cost effective solution that meets the requirements of both the client and regulators.  Our work often follows through to the design and implementation of remediation schemes, along with the design of pragmatic yet resilient foundation and infrastructure solutions.


Our specialist staff at CGL include mining and geotechnical specialists, engineering geologists, and geoenvironmental and remediation engineers who possess the skills necessary to provide solutions to a wide range of ground instability issues.  This wide range of skills across the company allows our clients to have confidence that our advice and ultimate solution is founded on expertise and experience.


Examples of our involvement with mining or quarrying projects include Morley, Wass for English Heritage, Fife Towers, Halton East, Leeds School and Ebbsfleet, Kent.


For further information about Mining, Cavity Investigation and Remediation please contact Richard Pennock in our Harrogate Office on 01423 276000 or email Richard at RichardP@cgl-uk.com.

Numerical Modelling of Ground Movements
Numerical Modelling of Ground Movements

CGL has the benefit of the sophisticated finite difference programme (FLAC) specifically developed for geotechnical applications which will assist in making designs EC7 compliant. This software is highly flexible and capable of modelling complex geometries, construction sequences, and both linear and non-linear soil behaviour, as well as modelling fluid flow through soils and large-strain plastic deformation.


At CGL, we offer FLAC as a solution in situations where ‘engineering approximations’ derived from combining simpler methods of analysis are not adequate.  These occur for interested third parties (utilities operators, rail companies, party wall engineers) where explicit calculations are required to quantify and control the risks to adjacent or buried infrastructure.   FLAC is highly versatile and has allowed CGL to provide:

  • Assessment of the impact of a proposed new build over historic brick lined sewers in North London: the analysis calculated stress changes developed in the sewers from the proposed construction of piled foundations very close to the sewers.  Tunnel moments were reported and ‘ovalisation’ was calculated throughout the construction sequence.

  • Modelling of the flow of soil gases from a landfill to assess the effectiveness of proposed remedial measures: the model was calibrated to comply with gas monitoring data available for local properties and was provided to the Local Planning Authority.

  • Determination of the form of slope failure for a site involving ‘varved’ clays, using a specialist soil model built into FLAC: the analysis was used to support a litigation case regarding significant movements on a historic culvert.

  • Slope stability and loads generated in soil nails for a railway cutting in chalk: the model allowed a significant reduction in the number of soil nails required.

  • Predictions of ground movements arising from the excavation and construction of a new basement in London Clay, immediately adjacent to existing properties:  the analysis accounted for the combined effect of soil heave, and retaining wall deflections, provided prop loads and retaining wall deflections, settlement beneath underpins, and was submitted to party wall engineers.

  • Assessment of the impact of laterally loaded piles installed close to a Network Rail piled structure in very soft alluvial soils: the analysis was used to satisfy both the structural engineers and Network Rail that the impact of the new piles would be minimal


FLAC represents the state of the art in geotechnical analysis and, correctly applied, can generate significant savings in analytical time and effort; particularly where third party interests are involved.


For further information about Numerical Modelling of Ground Movements please contact Nick Langdon at our Head Office on 01483 310600 or email Nick at NickL@cardgeotechnics.co.uk. Alternatively, contact Richard Ball on 01483 310600 or email Richard at RichardB@cgl-uk.com.

Retaining Wall Analysis
Retaining Wall Analysis

Over many years CGL has provided structural and civil consultants as well as contractors with analytical capability and advice on retaining wall design. The recent introduction of EC7 in the construction industry, together with a need for confidence that structural movements will meet more onerous serviceability criteria, is placing greater demands on designers to predict wall movements than ever before. In this regard, CGL can provide a multiple layered approach to the analysis of retaining structures applying appropriate software for the solutions needed.


In-house software based on first principles of soil mechanics can be economical where movement or moment calculations (serviceability limit state) are not critical, such as with reinforced soil walls and gravity walls, or are low height; Category 1 Structures. We can also use gravity wall analysis software, GWALL, in these circumstances.


CGL uses the more sophisticated retaining wall analysis program WALLAP for cantilever and propped retaining walls; Category 2 Structures, where it is important to establish design movements, bending moments and strut or prop loads.  WALLAP allows the user to specify a staged construction sequence with props at any required level, water pressure profiles (both hydrostatic and non-hydrostatic) and allows berms to be modelled as part of a construction sequence.  In serviceability limit state mode, WALLAP enables an assessment to be made of horizontal and vertical ground movements arising from the construction sequence. This information can be used for building damage assessments.  WALLAP can also calculate bending moments in the wall to facilitate reinforcement and section design.


Use of the finite difference software, FLAC, allows modelling of structural elements, complex soil geometries and specific structural formulations for rockbolts, anchors, piles, and beams, amongst others, all of which may be attached to frictional or cohesive interfaces to model the interaction between the soil and the structure more completely than other methods. 


Our approach is calibrated to the needs of the project and is mindful of constructability and cost, particularly in the current economic climate.


For further information about Retaining Structure Analysis please contact Nick Langdon at our Head Office on 01483 310600 or email Nick at NickL@cgl-uk.com.

Slope Stability Analysis
Slope Stability Analysis

Slope engineering - the formation of both cutting and embankment slopes - is an important element of development and infrastructure design. Maximising slope angles often allows increased developable areas and the reduction of construction materials. The key to successful slope design is based on a strong knowledge of soil behaviour coupled with an understanding of the analytical approaches necessary to balance safety with cost efficiency.


CGL has a long established track record in the assessment of slopes, based on experience established from road and rail embankments/cuttings, design of reinforced earth slopes and platforms, and remedial works on failed slopes. On occasion senior staff are called in to advise on slope failures, either regarding emergency stabilisation measures or providing expert opinions in respect of the causes of failures.


CGL’s investment in sophisticated analytical software allows the company to make detailed assessments of magnitudes of ground movement as well as undertaking routine overall slope stability assessments. These high level capabilities, which involve the use of finite difference software, have assisted clients in satisfying sensitive third parties, ranging across the spectrum from affected house owners to Network Rail. They have been assured that robust solutions can be developed whilst maintaining safety as a priority, thereby protecting structures and the general public.


Analyses can be undertaken in all material types, from soils to rock. The application of slope stability assessments can relate to temporary as well as permanent cases, allowing steep temporary slope angles for short-term construction conditions which may lead to savings against the use of conventional temporary support. An example of this is the GE Award-winning Guildford Radisson Hotel, where a careful assessment of the chalk slopes within a basement excavation allowed the removal of a perimeter bored pile wall support and saved £1 million on the cost of construction of the basement, together with a significant reduction in programme and overall build costs.


CGL’s understanding of ground behaviour, together with a commercial appreciation of the benefits that steepening slopes can bring in terms of space generation or material minimisation, and an ability to respond to situations that may develop during siteworks, allows clients to be confident that their assets will remain safe in both the short and long term, with the added benefits of cost savings and reductions on programme.


For further information about Slope Stability Analysis please contact Ian Marychurch at our Head Office on 01483 310600 or email Ian at IanM@cgl-uk.com.

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