The Heartlands/Polkemmet reclamation scheme covers a total site area of some 470 hectares and includes around 120 hectares of derelict land in the form of coal mining spoil bings which stretch from Greenrigg in the west to near Kepscaith Farm in the southeast. The remaining areas mainly consist of low-grade agricultural land and coniferous forestry, together with the upland heath of Polkemmet Moor. To reclaim the site, Minrec the contractrors excavated the remaining shallow coal reserves by opencast methods, with the spoil within the excavations recycled to create a new landscape. The result is the removal of the derelict land allowing the existing polluted burns to be cleaned up and routed via new open watercourses.

Opencast mining in simple terms is like turning over a garden (only with bigger shovels). The first “shovelful” you dig goes above the ground (the overburden dump) this hole is now called the “operational void” You then take the next shovelful and put it in your previous hole/void. This way you always have an “advancing face” an “operational void” and a “backfilling operation” and when you get to the end the “final void” (your last operational void) with your above ground overburden dump (the first shovelful) The next question that’s asked is “but if you’re taking out tonnes of coal surely the ground will be much lower” – No not normally. Here is a good example – if you take a tray of toffee, the one’s with the hammer, and you smash it up, you can not fit all the pieces back into the tray to give you the same flat surface that’s because the toffee has “bulked” up due to the voids between the particles. This “bulkage factor” ( which varies dependant on material type) can be calculated and transposed into final restoration contours. This graphic explains, in a very simplistic way, how Open Cast Coal Mining or Strip Mining is performed. In reality it is much more complex as will be seen from the various photos in this web site.

The coal was extracted using tracked hydraulic excavators, loaded into articulated site based coal trucks and then transported Minrec's Coal Processing Area just adjacent to the access road on the western edge of the site, near Cult Farm. The processing facilities consisted of the coal screening and crushing plant, together with stockpiles of both raw and processed coal, with the mounds being of different qualities, from the best grade to the poorest, depending on which seam the coal came from. There were many seams being coaled but the four main ones were the Mill, Armadale Ball, Armadale Main & Colinburn. Both Armadale seams virtually ran the full length of the open cast site from north to south and because they were on different levels in the ground, they overlapped each other. The Mill seam followed the route of Coal Extraction Area (CEA) “A” down to the western side of CEA “C”. Lastly, and deepest of the four main seams, was Colinburn which occupied the eastern side of the site and was covered by CEA “B1 – B19” and CEA “D” and the eastern side of CEA “C”. Just over 1.6 million tonnes of coal were excavated with the last of the coal being removed in February 2008.

The Dry Coal Screening & Crushing Plant or CPP (Coal Processing Plant for short) could go through 300 tonnes in one hour and up to 3500 tonnes in one shift with wheeled shovels and other equipment working continuously. The machine was set up so that the coal coming out at the end of the crushing and screening was no more than a maximum of 40 mm in diameter. The coal was blended to comply with an agreed specification and random samples were taken from the output of the CPP and then bagged & tagged and sent away to nearby laboratories for analysis. The coal was analysed for volatile material, ash, sulphur and calorific value. (The heat of combustion or the calorific value of a sample of coal is defined as the amount of heat evolved when a unit weight of the coal is completely burnt and the products of combustion cooled to a standard temperature of 298 degree K) and the results determined how the coal would be blended into the final customer product. Most of the coal went to power stations to generate electricity meeting the agreed specification hence the testing. Sampling and testing was later carried out at the face cutting down the time and cost to the operator.

Dust emissions were minimised by water spray on conveyor transfer points, the moving belts were covered and the stocking ground was kept damp. Road going transporters, working between 8 am and 6 pm were loaded by wheel loaders at the stocking grounds prior to being sheeted before leaving the site. Even though coal extraction has a relatively low potential for dust emission due to the inherent moisture content of the coal reserves the nature of the operation was such that coal was very carefully lifted to ensure a clean product was obtained, ensuring that the potential for dust emission was greatly reduced. Coal excavation also took place at depth within the working void and this provided shelter, which reduced windborne emissions. Overburden from the initial excavations was used to create the main site haul roads and the overburden mound located in the centre of the site. The overburden was then backfilled into the de-coaled voids.

Compacting

To make the worked out & backfilled land suitable for development it must be compacted. The Polkemmet reclamation scheme employs a revolutionary method of compacting called the HEIC (High Energy Impact Compaction) system. Developed by South African firm Landpac the HEIC consists of providing high energy impacts on the surface by pulling along heavy (10 - 12 tonnes) rotating pentagonal or cam shaped steel drums. The HEIC system improves the engineering properties of soils increasing its strength and reducing its compressibility i.e. further settlement is reduced. Referring back to the toffee analogy, the backfilled areas have bulked up due to air voids in between the rocks and these air voids need to be removed otherwise the ground will be unsuitable for further development due to the soils being loose and diverse in nature. The HEIC system compresses the soil particles together by forcing out the air and substantially reducing the voids resulting in a in a more uniform nature. Compaction makes the soil denser by the removal of air. In simple terms it is the process in which soil particles are forced closer together due to the reduction in air voids. The process requires mechanical energy, a lot of it and the HEIC is proving to be the ideal tool to provide it.

The drums ride up and down as they are pulled along by a tractor unit and the compaction is created when the drum drops from its highest height to its lowest usually only about 15 - 23 cm. However, with up to 12 tonnes slamming down, the ground underneath the drums is subjected to a great deal of energy. Roll a 50p piece between your fingers along a desk to get a basic idea of how the principle works, then imagine if that 50p was suddenly a 12 tonne weight. The simplified graphic shows how the principle operates. The Polkemmet reclamation scheme employ both the cam shaped and pentagonal shaped drums as can be seen in the pictures. In technical terms the HEIC process changes heterogeneous soil (soil with a diverse range of properties) into a medium which is more uniform and increases the capacity of "foundations" constructed over the affected soil which has higher strength, reduced permeability (liquids can't pass through as easily) and reduced settlement. In other words it has the engineering properties suitable for foundation work i.e. housing and business development. As the HEIC unit goes around the same area layer by layer the soils underneath are being continually monitored by an innovative system called CIR (Continuous Impact Response) again developed by Landpac. The CIR is a specialised technique for digitally recording real time soil response during the HEIC process. HEIC ground response is measured using an accelerometer attached to the HEIC impact drum tube axle. Each impact, during drum rotation, is recorded relative to its position on site as determined by an integrated GPS tracking system and the results are plotted on a colour coded map. CIR is used to effectively identify relative variations in soil strengths, stiffness or density across the whole site. Landpac headquarters are in Johannesburg, South Africa but have key operating centres in the UK, Australia and China and the HEIC & CIR systems are being used all over the world as a revolutionary method of speeding up and increasing the effectiveness of the compacting process. While the 10 & 12 tonne units are to be seen on the Polkemmet site, Landpac are developing an even larger 15 tonne unit here on site. Another first for the Heartlands / Polkemmet development.

Testing

Once an area, or cut, was mined and the backfilling process begun testing was undertaken to ensure the correct level of compaction was achieved. Compacting and testing is currently ongoing as the final pockets of land are brought up to pre-coaling levels. The testing is carried out by various methods on an almost day to day basis on site but the two most noticeable tests are the Plate Bearing Test and the Maintained Load Test. Both these tests are carried out at different stages of the backfilling of any individual cut.

The Plate Bearing Tests are undertaken on each individual layer of backfill at a ratio of one for every 5000m3 of material placed, this roughly equates to two a day. This test involves a 16 ton trailer that is towed and positioned at predetermined locations on the backfill. The weight of the trailer is transferred to the backfilled material using a steel plate of a precise diameter and thickness. The weight is added in increments over time until the maximum load is achieved, the load is then take off gradually before the test is repeated. This test enables the engineers to monitor the settlement of each individual layer.

While the Plate Bearing Tests are carried out on each individual layer the Maintained Load Tests are only undertaken when an area has been backfilled to the final ground level. A large steel plate is placed on the final layer of the backfill and large weights are added over time and settlement of the plate is carefully monitored. Again this test enables the engineers to determine the settlement of the backfill, however because the weights added are roughly equal to the load imposed by housing it gives a better idea of how the final engineered platform will react to construction on it.The locations of both tests are dictated by the engineers (WA Fairhurst & Partners) and carried out by Landpac personnel. The testing is supervised by Discovery GE and any surveying s undertaken by specialists Fox McMaster.

Another control measure implemented to monitor settlement over the entire development platform will be metal settlement pins which are driven into the ground and then surveyed on a regular basis to assess what settlement, if any, has occurred and this is checked against pins that are in original adjacent ground. There are other tests that are undertaken to ensure satisfactory compliance but the aforementioned are the more intense.

The layout of the site has been influenced by existing features, namely the location of a suitable site access point and the bings, together with the underlying geological structure, which has determined those locations from coal will be worked. Access to the site is made from the B7066 approximately half way between Whitburn and Harthill (opposite but westward of the entrance to Polkemmet Country Park and then via the country lane which is the existing access to Cult Farm. The lane between Cult Farm and the entrance at the B7066 has been upgraded to an appropriate standard for use by HGVs serving the Polkemmet reclamation scheme. Beyond Cult Farm the existing lane to Polkemmet Road is closed to through traffic for the duration of site operations and access to Rigghouse Farm from the east via Polkemmet Road is also blocked..
Cult Farm is used as the site offices and the site plant yard, workshops and coal processing area are close by. This area also accommodates the weighbridge, wheelwash and HGV sheeting platform as well as security (you have to sign in to access the area). Please note it is not recommended that the general public use these roads due to the nature of the work involved.

In addition to the coal reserves, the site also contained an extensive reserve of brick-making fireclay and this fireclay was recovered and transported to the Ibstock Brick factory at Tannochside.