A geo-environmental Desk Study was undertaken by Geotechnics Ltd at a disused railway embankment site on the western side of Beckets Park in Northampton to assess the potential risks associated with developing the site for housing.  The desk study and site walk over identified the following potential sources of contamination:

• Hydrocarbons from ash, clinker, coal, lubricants, oils, sleeper preservatives and imported embankment materials
• Hazardous Gases from coal, ash and imported embankment materials
• Metals from waste, rolling stock, ash, clinker, sleeper preservatives and imported embankment materials
• Asbestos from brake linings and fittings on rolling stock
• Aggressive chemicals (acids, cyanides, sulphates) from coal and ash
• Hydrocarbons (including gas generation) from current use of filling station on adjacent site
• Pathogens from previous historical use of adjacent site as Livestock Market

We decided that network diagrams would be the clearest way to present how the identified potential sources of contamination would affect users, buildings and controlled waters.  

We ended up completing three network diagrams using KeyCSM simply because it only takes a click or two to produce them once you have the data in the program.  

The model creation and diagram creation process took around 20 minutes using KeyCSM and Envirocheck Analysis.

The initial network diagram from the Conceptual Model showed all the potential linkages.  However this model assumed that housing would be constructed with the embankment materials retained.  

Removal of the embankment as a source would, by definition, remove it from the model and leave fewer remaining linkages as clearly shown in the second network diagram.

Once we had taken away the embankment we were only left with two possible sources and relatively fewer contaminants to show, making the model much clearer for the client to see.

Records indicated that the redevelopment of the Cattle Market had included extensive tests to show that no significant Pathogens existed in the soil which left the Filling Station as the main source to investigate.  Liquid hydrocarbons were discounted on consideration of the underlying geology and the recent age of the development.

This left gas as the only potentially significant risk to be investigated along with an analysis of the soil underlying the embankment to determine if any significant leaching had occurred.

In the past we would probably have used AutoCAD for the production of the site conceptual model.  Using KeyCSM and Envirocheck Analysis in this way saved several hours of work and gave us a simple and understandable model to build further phases from.  The KeyCSM network diagrams definitely helped advance the case for the investigation and subsequent risk assessment.

The landslip impacted on one of the outbuildings and stabilisation works were required to address both the slope behind the building and the slopes and buttress associated with the viaduct.

Remediation needed to recognise the historic environment, access constraints, sustainability issues and the maintenance of stability of the viaduct throughout the construction.  Reinforced Soil was seen as providing the optimum solution. 

Site investigation, analysis and conceptual design was undertaken by Geotechnics Limited, detailed reinforced soil design by P and S Consulting Engineers and the construction by WM Longreach. 

 The scope of the works included: 

• Removal of failed material from the slope and formation of a temporary batter
• A drainage layer below and behind a reinforced soil wall comprising 16 layers of Heusker geogrid interleaved with imported compacted granular material and excavated soil to a height of 8 metres
• An upper slope grading into the natural ground some 13 metres above the driveway level
• A wall feature in Wenlock stone to the lower section of reinforced wall to blend with the character of the mill.

Critical to the success of the project was the use of long reach plant both for excavation and construction on a very constricted site.  

Maintenance of close working relationships between all the parties concerned including the mill owners, Severn Valley Railway, the designers, the contractor and the client was also essential to minimise disruption and to maintain access for visitors wherever possible.

In pursuance of improving traffic flow on the A46 further improvements are under consideration for the Toll Bar Island, Coventry.

Geotechnics Limited have recently completed an investigation for sign gantries on the A45 and A46 (£60,800).  This work involved drilling boreholes on the verges, which for the A46, required working at night under Traffic Management and lane closures.

Twelve boreholes were required to be drilled using mini tracked rotary rigs, due to space limitations, with dynamic sampling/SPTs in overburden and rotary core drilling in Mercia Mudstone bedrock.  Boreholes were generally completed in a single shift, making maximum use of traffic management, except for a 25m deep hole which took two shifts.  Drill flush was contained using sand bagging around the borehole location and recirculation techniques.

At three locations, boreholes were located behind barriers which precluded drive on access.  In order to access these, the rig was brought to and lifted onto location using a hi-ab lorry.  Dismantling of the barrier was discounted as an option as at least one post would also have had to be removed and these could not be returned to working condition within the permitted night closure times on the A46.

Dynamic Sampling and Rotary Core drilling achieved full recovery permitting full strata descriptions and sample availability for subsequent laboratory testing.

In order to do achieve this, several methods of ground investigation were required, along with in-situ and laboratory testing and instrumentation.  However, the access to site was quite restricted and needed to be carried out within traffic management with specific time constraints.  The slopes of the wing walls were relatively steep and sections of crash barrier also had to be removed to gain access.

The investigation comprised trial pitting, hand held window sampling and hand excavated inspection pits on the slopes of each wing wall, windowless sampling and dynamic probing at the crest of the wing walls.  Subsequent laboratory testing to obtain specific details on the properties of backfill, such as effective angle of internal friction was also undertaken.

In order to measure and monitor the rotation of the walls in the vertical axis, six uniaxial Tiltmeters were installed on three of the walls at approximately 1/3^rd and 2/3^rd height.  The cables were routed and hard wired into a datalogger mounted on one of the wing walls.  These were installed using a scissor lift enabling access to heights of over 6 metres up the faces of the walls.

An existing datalogger with solar panel, installed in 2000 for use with strain gauges, was inspected and deemed to be unsuitable for monitoring of the tiltmeters.  This datalogger was removed, but the solar panel was suitable for keeping the battery in the new multi-channel datalogger fully charged. 

Remote monitoring was made possible by equipping the datalogger with a GSM modem, which transmits data to an off-site server.  Argus monitoring software then processes the data and presents it on a website for real-time viewing by the Client.

The wing walls will be monitored for movement for 18 months and the data collected will hopefully confirm whether the walls are actually moving!

The Clients’ project proposals include for the design and construction of a new rising main along Booth Lane and an 18m deep, 15m diameter storage detention tank.

The site was underlain by a variable thickness of Made Ground over Glacial Till of firm to stiff clays with sand and gravel lenses.  Solid strata comprising Mercia Mudstone was encountered at a depth of 33.5m below ground level.

The investigation comprised eleven cable percussive boreholes, one with rotary Geo Bore S Wireline techniques and one with rotary follow on together peizometer installations and in-situ material testing.  Ground protection mats were required to prevent damage to grass surfaces at some locations.

A further three boreholes were commissioned for the purpose of acting as water wells to observe groundwater drawdown within an aquifer during a pumping test.  Monitoring wells were installed within the boreholes at depths between 17m and 26m below ground level within the aquifer.  The pump tests were designed to obtain information on the aquifer properties to allow the design of temporary groundwater control during construction of the detention tank.

A microgravity survey was also carried out by the specialist geophysical contractor Terradat on behalf of the Client.  The microgravity survey was carried out over an area around the proposed location of the storm water detention tank on recreational ground off Warmingham Lane.  The aim of the survey was to locate potential voids associated with salt workings in the area – none were encountered. 

All site works were supervised by Engineers, John Harrison and Jonathon Gray under office project management by Paul Hayes.

During pre-contract meetings between Skanska, Amey and Geotechnics Ltd, the design requirements were discussed and proposals for the desired monitoring arrangements and collation of data were explored.  Amey’s primary criteria was for the installation of a number of Vibrating Wire Piezometers (VWP’s), Inclinometers and Hydrostatic Profile Gauges (HPG’s) to deliver real-time ground movement data to allow them to constantly analyse the overall construction performance.  The priority of Skanska, the Main Contractor, was to complete the instrumentation installation without affecting the programming of the embankment works, and within a set budget.

 The original specification was for the various instrument types to be manually monitored during construction works, which would have required an onsite team of up to 6 technicians each day.  Initial meetings soon highlighted that not only would this entail considerable costs, the Health and Safety Risks associated with working amongst active construction plant were too great. 

Geotechnics prepared a proposal based on the remote monitoring of all VWP’s and inclinometers and manual monitoring of just the two HPG’s, thus greatly reducing the number of man-hours required on site.  This option was approved by all parties involved and Geotechnics Ltd were commissioned to carry out the works.

Remote monitoring was made possible by installing multi-channel dataloggers equipped with GSM modems which transmitted data to an off-site server.  This processed the data and presented it on a website for real-time viewing by Amey at their offices in East Sussex.  The dataloggers were situated outside the construction zones to minimise the risk of damage. 

Thirty six Vibrating Wire Piezometers were installed to provide pore water pressure measurements during the building up of embankments. 

Twenty three Uniaxial In-Place-Inclinometer (IPI) strings (comprising a total of 126 sensors) were installed to varying depths to allow monitoring of the lateral movement of large embankments and structures. 

Two Hydrostatic Profile Gauges (HPG) were installed (197m and 121m in length) to monitor the settlement characteristics and response of the ground beneath embankments as they were built up.

Five multichannel datalogger boxes were installed, linking up all the remotely monitored instruments to an automated monitoring system.  Each box comprised a watertight enclosure containing a multichannel datalogger, relay multiplexers (for increasing the number of channels), a cellular GSM modem with transmitter and a lead acid rechargeable battery.  Geotechnics worked alongside Skanska to install instruments in several phases in order to fit around the construction programme and progress on site, which required Geotechnics to be flexible to adapt to changes in the programme. 

Geotechnics Ltd’s knowledge of the ground conditions along the new road route (we undertook the main ground investigation in 2007, together with previous investigations along earlier proposed routes) enabled the most effective drilling methods to be adopted, ensuring the costs of installing instrumentation were kept to a minimum.  Both Skanska and Amey were open to technical suggestions and advice from ourselves, which we consider was key to providing an effective monitoring scheme on time and to budget.

The investigation comprised rotary percussive sampling carried out using a tracked Klemm drilling rig and supervised by Geotechnics’ Engineer, Ben Tucker.  The work was carried out over several night shifts under Network Rail possession.  An overhead 20kV electricity cable had to be isolated as it ran directly over where the shaft was predicted to be.

Following Skanska’s excavations to locate the shaft visually, the drilling rig was set up over the centre of the shaft.  Due to the uncertain nature of the chalk backfill material the rig was positioned on a steel platform, usually used for mining investigation projects, that extended across the shaft preventing the rig becoming unstable should the shaft collapse beneath.  This had to be manoeuvred into place by a tracked 360^o excavator.  Railway sleepers and boards were laid across the steel platform for the drillers to work on.

Once drilling had commenced the borehole made good progress and we were aiming to finish within two or three shifts.  However the weather had a difference of opinion.  The temperature dropped, the snow fell relentlessly and the country came to a stand still.  As most major roads were blocked by thick snow, Network Rail required the use of the line overnight to keep at least some parts of the country running.  This meant permission to drill was not given for several nights until Network Rail could grant us rail possession again.

After two nights of heavy snow we were granted re-possession to complete the borehole to a depth of 22.50m.  A control borehole was sunk adjacent to the shaft to provide information on the natural chalk material nearby.  On completion a plain standpipe was inserted into the shaft borehole to allow a Geophysical Logging survey (Gamma logging) to be carried out to determine the relative density of the backfilled chalk and the location of any possible voids or remaining structure of the old access shaft.

Geotechnics were employed by South West Water under the direction of Consulting Engineer, Pell Frischmann, to carry out site investigations along the pipeline route and at the proposed treatment works.   A three phase investigation was undertaken which included 37 trial pits to maximum 4.80m depth and 12 rotary open-hole and cored boreholes to up to 15m depth, with in situ variable head permeability tests.

The main constraints on the project were associated with the location.   The site was located in an area of outstanding natural beauty and access to the locations needed careful consideration.   In particular, one pumping station site was located adjacent to Tintagel Visitors Centre with only a narrow track normally used by the centre to transport tourists to and from the Castle by Landrover.   A small tracked rotary rig was mobilised, and ground guards were used extensively throughout the site to prevent the already wet fields from deteriorating due to tracking.

Given the nearby location of Tintagel Castle, a watching brief was carried out by local archaeologists while several of the trial pits were excavated.

A range of geological materials were encountered during the investigation including foliated slates, phyllites and micaceous schists.   The proposed treatment works at Trevalga included the construction of an 8m deep, 20m diameter activated sludge tank.   Detailed rock core logging by Geotechnics identified the tank area to be underlain by weak to medium strong sub-horizontally dipping slate with generally very close to medium spaced fractures.   This enabled the temporary slopes to be designed with 1:1 gradients and the tank base to be cast directly onto the fractured slate bedrock with no piled foundations and only minimal steel mesh reinforcement.

The project is currently under construction by BAM Nuttall and is due to be completed in Spring 2010.

Fullabrook Down

Devon Wind Power proposes to construct a major new onshore wind farm at Fullabrook Down, North Devon.  Twenty two new Wind Turbine Generators (WTGs), each 110 metres high, with 45m long blades and 65m from ground to hub will be constructed.  The new wind farm is understood to have an installed capacity of 66 megawatts and is expected to produce the equivalent of over 80% of domestic electricity consumption in North Devon and will serve the needs of nearly 30,000 domestic customers.

Geotechnics Ltd was approached by Magna Project Services Ltd on behalf of Devon Wind Power to undertake a site investigation and provide geotechnical advice for the design of the foundations for the new WTGs.

Tim Thornburn and Gareth Lewis from the Exeter regional office carried out a Preliminary Geotechnical Appraisal comprising a desk study of the site together with trial pitting to assess geotechnical risks at each turbine location.  A Multi-Channel Analysis of Surface Waves (MASW) geophysical survey was undertaken at ten of the locations to obtain dynamic stiffness moduli to assist in foundation design for dynamic loadings.  The Preliminary Appraisal included an assessment of risks from natural and man made cavities, seismic and landslide hazards, liquefaction and soft ground.  Outline foundation options were provided for each WTG, in addition to excavatability and information on re-use of site won material as haul road aggregate. 

A rotary core borehole investigation together with the preliminary assessment and trial pit investigation will provide detailed foundation design parameters for the WTGs once the final specification for the turbines is formulated.

Mostyn Docks

In the North West, Geotechnics Chester office has undertaken an investigation at Mostyn Docks on the Dee Estuary where the main structural columns for the enormous off shore North Hoyle wind farm development are stored prior to shipping to site.  The project comprised cable percussion boreholes and plate load testing and was managed by Ray Macklin, with Keith Nicholls assisting in developing a foundation scheme for the temporary racks which will carry the columns.  The work was done for Port Dredging Ltd, and their Engineer MT Hojaard (of Denmark).

Workington

The Dunblane team has been involved with wind farm developments in Workington in Cumbria over some time but more recently has completed their engineer-intensive investigation for a proposed 20 turbine (900ha) wind farm and associated 30 kilometre haulage road in a beautiful, but remote location above the western bank of Loch Awe in Argyll and Bute.  Under the supervision of Engineer, Mott Macdonald, for Client, Greenpower (Carriag Ghael) Limited, more than 400 Trial Pits with CBR determinations have been excavated and over 650 peat probes sampled, by up to five Geotechnics Engineers.

The wealth and diversity of natural habitats, particularly nesting birds, even rare ospreys and golden eagles, meant that the changing ecological considerations have taken priority, necessitating continual review and revision of fieldwork planning to optimise productivity and protection to the environment.

Although generally fortunate with the weather and midge swarms, there have been days where the natural elements have powerfully demonstrated the suitability of this site for its proposed development as a source of wind energy!  Further logistical challenges relating to limited vehicular access and the large scale of the site have also been conquered; all terrain vehicles were used where practicable to help transport engineers, operators, soil and rock samples; but walks of several hours through the undulating terrain, which includes dense managed forests, peat moorland, rock outcrops, lochans and burns were not uncommon before ‘starting work’!  Remarkably, where access was available, the team led by Site Agent, Greg Anton, still managed to achieve their tendered target of 8 trial pits or more per machine day.

In addition Keith Nicholls and Len Threadgold have contributed some design ideas to the Carbon Trust for innovative foundation solutions for the next wave of development of offshore wind farms.  The new generation of turbines will be sited in water in excess of 30m deep and the marine foundations will require innovative foundation design strategies.