AMEC Canada uses BSP’s Rapid Impact Compactor for ground improvement in British Columbia

When BSP International Foundations launched the Rapid Impact Compactor (RIC) it was considered as a major breakthrough in ground consolidation engineering and, as a result, this innovative development is now being used by foundation engineering contractors in an increasing number of countries around the world.

AMEC’s Canadian subsidiary AMEC Earth & Environmental is just one contractor to use the RIC recently. The company was retained to provide geotechnical consultant services for the design and construction of a new fire hall and office building with a rectangular footprint of approximately 40m by 80m in the town of Chillwack, British Columbia. When completed the fire hall will be two storeys high with five apparatus bays and a three storey hose tower, while the office building will be four storeys.

Based on the results of a geotechnical investigation carried out last Autumn, it was clear that ground improvement works would be required to remediate water bearing susceptible soils on the site. Rapid Impact Compactor Ltd, BSP’s agent based in Delta, British Columbia, was selected to compact the granular soils as part of the ground improvement programme using the RIC in 7 tonne mode mounted to a 40 tonne Hitachi 400H hydraulic excavator.

Following a pilot programme using different compaction frequencies and patterns, it was decided that 6m by 6m areas should be compacted with a minimum of two passes with each pass having a minimum of 9 blow locations on the first pass and 13 locations on the second pass. In addition, each RIC blow location was compacted by enough blows to achieve a final 5mm set.

Because of wet weather conditions, it was necessary to sub-excavate and replace upper soils containing sufficient fines. Generally, the sub-excavations extended to a depth of between 0.5m to 1.0m which were backfilled with a sand and small gravel content followed by compaction with a Caterpillar 10 tonne smooth drum ride-on compactor.

Quality control Becker Penetration Testing (BPT) was carried out after completion of the ground improvement works which confirmed the RIC’s success in densifying the granular soils to a depth of around 6m. Henrick Kristiansen, AMEC’s project manager, says: “The use of compactor has been very successful on this site and is proving to be a very cost-efficient ground improvement method.”

Joe Miller, managing director of Rapid Impact Compactors, says: “We first saw BSP’s compactor working in Manchester, England and immediately recognised its potential for the North American market where there is no machine capable of densifying existing ground down to six metres. Following discussions with BSP, a unit was delivered in July 2001. However, it has taken about a year to establish the principle through perseverance and excellent results obtained on sites requiring ground improvement. As a result, word has got around with civil engineers now requesting the compactor to be included in project specifications and has led to an increase in the number of enquiry’s about its availability,” explains Mr Miller.

Interestingly, the compactor’s performance at the Chilliwack site clearly demonstrated its potential as we were asked by AMEC to densify the ground to a depth of 4.5 metres but after testing, densities had actually been increased to nine metres. The results we have been obtaining in Canada are certainly impressive and we are now looking forward to expanding throughout North America,” adds Mr Miller.

Available in seven or nine tonne modes, the RIC has been designed around a modified version of the Ipswich-based company’s popular BSP 357 hydraulic piling hammer. Mounted on a suitably sized hydraulic excavator, the RIC attachment has proven to be much more efficient when compared to the slow and archaic method of suspending a 10 to 15 tonne weight from a crawler crane and dropping it from a predetermined height of between five and 15 metres.

In operation, the RIC’s 1.5m diameter foot stays in contact with the ground, ensuring efficient transfer of energy 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 and 60 blows per minute. Although the energy per blow is small in comparison to conventional dynamic compaction, the rapid blow frequency amply compensates and can result in a much greater total energy input per unit area of a site.

Because it is in constant contact with the ground, there are no flying debris and no danger from a large falling weight. These safety advantages over conventional dynamic compaction allows other activities in the immediate vicinity to proceed during the compaction process.

David Redhead, BSP International Foundation’s managing director, says: “We have been highly encouraged by the acceptance of the construction industry in our RIC concept, bearing in mind that ground consolidation is such a critically important starting point for so many contracts. Feedback from contractors around the world using our RICs indicates a speed up in operation generally, with a more efficient and cost-effective outcome.”