Safety First At Shepperton
Digmaster system improves productivity and safety at Home Farm Quarry
Shepperton Aggregates, a joint venture formed in 1991 between Tarmac and Brett Aggregates, operate Home Farm Quarry, a wet sand and gravel operation located alongside the B376 between Laleham and Shepperton Green in Middlesex. Until recently the company had been using a 71-RB dragline to extract material from the site, how-ever increasing difficulties in recruiting experienced operators, combined with the dragline’s inherent inability to follow localized undulations in the depth of the deposit, led the company to reappraise their extraction methods.
As part of this review, some 12 months ago Shepperton Aggregates approached Land & Water Services Ltd, the UK’s largest inland dredging contractors and specialists in contract aggregate extraction, to see whether they could offer a better solution. Among Land & Water’s specialist plant and equipment inventory is the largest fleet of long-reach excavators in the UK, with machines ranging from 4.5 tonnes to 88 tonnes in weight and offering extended reaches from 8m to 25m. During trials at the Shepperton site, both 20m and 25m versions were deployed to determine the most effective size of machine for the prevailing site conditions and to demonstrate how long-reach extraction methods could deliver improved productivity and efficiency.
Based on the success of these trials, Land & Water were recently contracted to carry out all extraction work at the site, operating on a cost-per-tonne basis. One of the company’s flagship machines, an 88-tonne Hitachi EX800H fitted with a customized boom, dipper and hydraulic arrangement to give a 25m reach and a 19.7m digging depth, is now fully operational at the site. Equipped with a 2m3 bucket, this machine operates, on average, for around 8h a day and extracts some 8,500 tonnes of sand and gravel a week.
With its extended reach and deep-digging capability, the EX800H is better equipped to follow any changes in the depth of the deposit, which averages 7–10m across much of the site but can be as deep as 12.5m in localized pockets. This improved flexibility is currently manifesting itself in more effective recovery of the mineral resource for Shepperton Aggregates as well as delivering increased void space for subsequent landfill operations.
Before Land & Water commenced operations at the site, consultants Knight Piesold were called in to conduct a geotechnical assessment of the land/water interface. They recommended a 2m stand-off distance and a 1:1 slope angle as a suitable margin of safety for the excavator and its operator. Accurate maintenance of this profile would militate any concerns about the stability of the bank or the possibility of the machine undercutting itself.
However, rather than relying solely on the skill and expertise of the excavator operator to achieve this profile, for extra peace of mind Land & Water’s long-reach EX800H was equipped with a Digmaster graphic depth- and profile-monitoring system supplied and fitted by Prolec Ltd, specialists in electronic safety and monitoring systems. This newly upgraded and easy-to-use system utilizes a range of ruggedized solid-state angle sensors, flowmeters and slew sensors mounted on the boom, dipper and excavator superstructure to provide the machine operator with a real-time representa-tion of the excavator’s boom, dipper and bucket movements via an in-cab colour VGA monitor. Flexible pan, zoom and bucket-tracking features provide the operator with accurate information on the elevation, reach, slew position, distance to target and bucket attitude against a pre-programmed animated target profile.
The Digmaster system’s multi-plane slope capability has been designed for quick, accurate and productive excavation work by allowing the operator to select a horizontal target terrain for basement work, slopes of any angle for grading work, or a user-definable multi-profile terrain for more complex applications.
In addition, in an adaptation to the regular Digmaster system, the excavator at Home Farm Quarry has also been fitted with a ‘fail-safe’ mechanism, whereby all machine movement is instantly suspended should the operator attempt to cut into his target profile. An override facility is also available for situations where the Digmaster system is not required.
As with all Prolec monitoring systems, Digmaster simply plugs into the Prolec CANbus sensor suite to provide operators with a wide range of features and ease of field replacement. Should more inputs be required, the user can simply plug in additional sensors or, if new capabilities are needed, can download new software. Up to 20 different bucket, grab and pump types can be stored, edited and selected from the standard software.
Prolec have also made Digmaster as user-friendly as possible, with all frequently used functions being available in just one or two key strokes. All controls are accessible via the monitor’s softkeys, with the relevant context symbols appearing above each of the five push-buttons as different options and features are accessed. In addition, the system’s software can be customized by Prolec to meet specific customer requirements, such as the need to incorporate communications or data-transfer capabilities.
Land & Water say the Digmaster system in use on their excavator at Home Farm Quarry has improved extraction productivity and efficiency at the site and, at the same time, overcome the overriding issue of safety when working alongside water.
