End of the Line for Longham Quarry -
CASE CX210B Excavator Finishes the Job
A Case CX210B excavator was used to remove the final material at the Longham Quarry, near Poole, Dorset . The quarry, under extraction license to CEMEX UK, building materials supplier, is now being wound down after more than 12 years operation, during which time over 1.8 million tonnes of sand and gravel have been removed.
The company has ceased extracting material and over the course of the next two months will process existing stockpiles. The land will then revert back to the local authorities at which time the stocks of top oil and overburden will be used to create bunds to form a 100-acre reservoir with a capacity of 1.4 million cubic meters to serve the Bournemouth and Hampshire areas.
Three times a year, Southampton based plant hire company, Jeff Townsend, is hired in to remove the 300 mm topsoil and then to finely grade the next 100 mm for archaeological purposes. J Townsend also does the extraction and bulk hauling. Extraction is to a depth of 3.5 m.
The topsoil is stored in temporary bunds around the perimeter of the gravel pit; the overburden is stored separately. Both will be used in construction of the reservoir and for landscaping purposes.
Steve Smith, CEMEX quarry manager reports that the CASE CX210B is the ideal size for this type of work. With a ditching bucket, it can quickly remove the topsoil with the high level of precision required. This fine control is even more useful in examining the underlying layer for archaeological remains. The machine also has the reach and the production capacity to keep the haul units busy.
With an operating weight of 21,500 kg, the CX210B is designed for productivity. Maximum bucket capacity is 1.26-m³ and lift capacity up to 14,923 kg. The bucket digging force of 15,200 daN makes the CX210B an efficient excavator in gravel and sand applications.
With a maximum digging depth of 6.65 m, dump height of 6.84 m and forward reach of 9.73 m, the demand at Longham Quarry was well within the operating envelope of the machine. This allowed the excavator to work large areas, feeding a common stock pile without tracking the machine. However, a maximum travel speed of 5.6 km/h meant it could travel between locations quickly.
There have not been significant archaeological finds but some artefacts dating back to the Bronze Age have been found.
The gravel and sand is taken by two wheel loaders from stock piles to the processing plant which is a BL Pegson 900 cone crusher working with a Finlay mobile washing and screening unit which has a Williams lignite separator on both the sand and stone screens.
Processed materials are conveyed to stockpiles of sharp washed sand (<55 mm); 20 mm stone, 10 mm stone and oversized rejects. The oversized material is then passed through the crusher and reprocessed. Silt from the sand washing plant is pumped to settling ponds.
A large proportion of the material is used in the decorative stone market. The plant was processing up to 140,000 tonnes per year.
CEMEX is in the close down phase on site with all extraction stopped. There are 5 workers on site – 2 operating loading shovels, 1 excavator operator, a plantman and a foreman.
Apart from managing the Longham quarry, Steve Smith is also responsible for two wharfs, one in Poole and one in Southampton , which process material brought in by dredgers.
Geology and the Environment
The River Terrace deposits where laid down during the Mid-Quaternary period (approx. 800,000 years ago). London clay forms the basement to the terrace deposits. The topsoil can be up to 800 mm thick, the overburden 700 mm overlying a 3.25 m average depth of mineral river terrace deposits. The underlying London Clay is up to 35 m depth.
During the working of the quarry, CEMEX has had to ensure that the operations did not disturb the extensive wildlife. During the spring, due to the abundance of ground nesting birds, the gravel beds could not be worked. Badger sets also had to be protected.
Over the years, CEMEX has been able to hand back sections of the quarry pit, which have already been converted into a reservoir known locally as the Longham Lakes . Due to the environmental measures being implemented and nature conservation works, the lakes are already popular with birdwatchers.
Over 3,500 trees will be planted during the regeneration works, carefully selected to provide food and nesting for birds. The reservoir will be a nature reserve and although public paths will exists, the reservoir will not be used for pleasure activities.
