Four BSP RIC9000 Units for Prestigious Project in Qatar
For more than a decade the Rapid Impact Compactor (RIC), developed and manufactured by BSP International Foundations (BSP) at its facility near Ipswich, Suffolk, has become the preferred method for an increasing number of shallow ground improvement projects around the world.
In particular the RIC has been successfully used in the Middle East to compact large areas of infill sites including the world’s largest petrochemical refinery at Assalouyeh on Iran’s Gulf Coast and the huge Ras Laffan port extension in Qatar.
Qatar is again the focus of attention as RIC-Middle East, a contracting company based in the United Arab Emirates (UAE), has recently purchased four RIC9000 units which have been delivered to Doha, the capital of Qatar, to work on the Cultural Village Project (CVP) in the West Bay area of the city. This 99 hectare area (245 acres) is being developed by the government of Qatar and will ultimately provide 40 different types of low-rise buildings built to reflect a historical and cultural theme. The four RICs, mounted on two Kobelco LC480s and two Caterpillar 345Bs hydraulic excavators, began work on the project in March 2008 with completion of this phase of the project expected in June 2009.
What makes this project unusual is the scale and scope of the RIC treatment undertaken by the four BSP units. RIC-Middle East was initially contracted to treat 578,000m² of the sand and gravel fill at ground level. This ground, originally reclaimed from the sea some years ago, provides the base on which the CVP is to be built. The next phase is to raise the ground level in a succession of 4m lifts up to 30m height using granular fill imported from quarries across Qatar.
Compaction of the fill is again being carried out as each level is placed. Mounir Matraji, managing director RIC Contracting LLC, a division of RIC-Middle East, said “Our innovative proposal to employ the RIC method for compaction of the made-up fill has drastically reduced the cost and completion time as compared to conventional methods”. When completed later this year the new ‘hill-side’ will have a 30m elevation at its highest point enabling the developers to construct a large community with sea views and scenic outlook, an unusual situation in a country as flat as Qatar.
Looking at the project from a technical perspective, compaction indicators for the existing ground showed an improvement in Core Penetration Test (CPT) measurements from 1.5 Mega Pascals (MPa) to an average of seven MPa. The made-up fill granular material has average Standard Penetration Test (SPT N20) values of 30 following RIC compaction and the plate load modulus average was greater than 40MPa when taken at 0.9m intervals through the fill material.
According to BSP it is usual practice to input 100-200 T.m / m² energy into the ground during compaction to achieve the required strength, though in some extreme cases it has been known for contractors to put in 600-700 T.m/m² using multiple passes. The number of blows per point position and point spacing dictate the level of energy input. SPT or CPT’s being done to check the N values required by consultants. Different sites require different degrees of compaction. CPT targets can range from qc of 5Mpa up to 12-15Mpa depending on what is being supported.
A feature not so critical in the Middle East is the extent of ground borne vibrations that can be tolerated on European sites. From measurements taken on various sites it has been proven that the RIC can keep below the European residential threshold PPV of 20mm/sec when compacting as near as 5m to permanent structures. This can be further reduced by digging a cut-off trench. While typical daily coverage is up to 800m² based on single shift working, longer working practices in the Middle East mean that daily coverage can be greatly increased.
Commenting on daily coverage rates Mr. Matraji says: “On the CVP site we have been achieving an average of around 1400m² to 1500m² per day. However I believe there are instances, depending on the application and soil type etc, where the spacing of the impact points vary from 1.5m to 3m (centre to centre) thus affecting the achievable amount of coverage. In our case there are 3m between impact points resulting in an average coverage of 1500m² per 10-hour day shift.
Interestingly, BSP originally developed the RIC for the military to repair airfield runways following bomb damage. As a result of successful trials the company supplied 12 units to the British MoD which were mounted on Caterpillar 972G wheeled loaders. The RIC’s success in a military environment prompted BSP to develop the concept for civilian applications. Today’s operational units being used on civil engineering projects are now mounted on crawler excavators instead of wheeled loaders.
Available in five, seven, nine and twelve tonne dropweight sizes, the RIC is based on BSP’s hydraulic piling hammer technology and can be mounted on hydraulic excavators with operating weights from 30t to 65t. In operation the unit’s 1.5m diameter foot stays in contact with the ground, ensuring efficient energy transfer to the ground at all times. Energy is imparted by dropping the weight through a relatively small height of up to 1.2m at a rate of between 40 to 60 blows per minute.
It was recognised early in its development that the RIC technique, because of its faster blow-rate than the DC method used for deep compaction which usually involves dropping a large weight suspended from a crane, was able to compact ground to deeper levels than would be expected by just comparing the relative energies of the two methods. In some ideal ground conditions good improvement has been achieved to a depth of 10m. The key to maximising ‘depth-of-influence’ (DOI) is by no means an exact science and expertise in what ground can and cannot be treated has been built up over time and empirical evaluations developed.
Ideal ground conditions would consist of well graded gravels and sands. However, even the most controlled sites tend to have a certain level of silty material – which does not respond so well to compaction. The rule of thumb being the lower the silt percentage the better the material will consolidate. Moisture content in granular soils is not so critical and good compaction can be achieved even in water-logged conditions. The siltier the soil the more critical moisture content becomes.
Monitoring of RIC performance is an essential part of the process both to present proof of work done to clients and identify problem areas that may need extra fill. BSP has enhanced monitoring during the last year by the addition of GPS using the PCX-RIC system. This automates the logging of compaction work against site coordinates. The in-cab display can be loaded with site plans from a CAD program and a pre-determined pattern displayed to guide the driver and minimise setting out requirements. The finished RIC results can then be uploaded back onto the original plans to provide pictorial representation of work done to clients and identify problem areas that may need extra fill. BSP has enhanced monitoring during the last year by the addition of GPS using the PCX-RIC system. This automates the logging of compaction work against site coordinates. The in-cab display can be loaded with site plans from a CAD program and a pre-determined pattern displayed to guide the driver and minimise setting out requirements. The finished RIC results can then be uploaded back onto the original plans to provide pictorial representation of work done to clients.
ENDS