Rapid Impact Compaction is an innovative ground improvement method that uses controlled dynamic compaction.
Dynamic soil compaction methods have historically involved the use of tall cranes and free-falling weights, imposing inherent limitations on the types of sites that can be treated. The Rapid Impact Compactor is a significant enhancement to the dynamic compaction industry. Its carrier is a track-mounted excavator, allowing improved mobility and site accessibility.
The Rapid Impact Compactor was originally developed in the early 1990’s by B.S.P. in conjunction with the British Military as a means of quickly repairing damaged aircraft runways. Dynamic energy is imparted by dropping a 7.5 ton weight from a controlled height, onto a patented foot. Energy is transferred to the ground safely and efficiently, since the RIC machine’s foot remains in contact with the ground. Compaction parameters are automatically controlled and monitored from the RIC’s cab with an on-board data acquisition system.
The Rapid Impact Compactor is a welcome supplement the current suite of ground improvement tools available to the ground engineering community. Its’ versatility can provide engineers with a more cost effective means of dealing with poorly compacted or loose shallow deposits.
Rapid Impact Compaction – Ground Densification Solutions
The process involves dropping a heavy weight repeatedly on the ground at regularly spaced intervals.
Rapid Impact Compactor Specifications
Height of rig: 25 feet
Length of rig: 31 feet
Width of rig: 12 feet
Approx. working weight: 57.6 ton
Ram weight: 7 ton or 9 ton
Max drop: 4 feet
Max energy: 61,000 ft-lbs
Blows per minute: 40/60
Foot diameter: 5 feet
Key Features
The following are some key operational features of the equipment:
ON Board Computer
The Rapid Impact Compactor employs an on-board computer to control impact set termination criteria, and to record critical data. Acquired data at each impact point include: total energy input, total penetration, and penetration of final set. Measured noise levels are on the order of 88 dBA at 20 feet.
Ground Vibrations
At 100 feet the peak particle velocities have been measured to vary from 0.05 to 0.2 in/sec. Vibrations will vary with material type, and will increase as the degree of compaction achieved increases. Results to date indicate that without site specific testing, a safe working distance to structures can be on the order of 20 feet.
Versatility
Having the RIC mounted on a tracked machine gives it the versatility to move about in narrow and limited height spaces, such as within existing warehouses.
Applications
Versatility of the RIC equipment is such that we envision numerous applications. Essentially designed for compaction of granular soils, benefits have also been noted in random fills and mine wastes. Compaction of fills and loose natural deposits is the typical objective; however, the RIC equipment can also serve as a diagnostic tool, identifying zones that do not respond well to dynamic compaction. Such areas may include high-plasticity soils, buried tires (or other non compressible debris), or a host of other unexpected “surprises”. Identification of these zones allows the engineer to accurately localize areas for removal and recompaction, and can provide superior economy on sites where the only apparent solution is to replace all fills because investigations have indicated the presence of some undesirable soils.
Assessment of compaction achieved in random fills is typically more difficult to test (and hence quantify), the visual aspect of settlement of the surface supports the fact that ground improvement is being achieved. As use of the equipment expands, so will the database of test information.
Applications include the following:
- Compaction of loose granular soils to improve bearing capacity and reduce settlement.
- Mitigation of soil liquefaction potential.
- Densification of bulk fills (i.e. lifts of about 12 feet), eliminating the need for small lifts and possible use of compaction equipment within confined excavations.
- Compaction of foreshore fills, where granular material has been placed both above and below water table.
- Foundation compaction below footings and bearing walls.
- Densification of bridge end-fills and highway subgrades.
- Backfilling excavations at remediation sites, particularly where excavations extend below the water table, and groundwater pumping is not desirable due to pre-disposal treatment requirements.
- Compaction of loose native granular soils to limit the potential for liquefaction during seismic events.
- Use in association with deep compaction technologies such as vibro-flotation or stone columns to eliminate the need for confining fills, or excessive stone takes often required to meet the compaction requirements in the upper 12 to 15 feet.
Research
As use of the Rapid Impact Compactor has become increasingly popular, several studies regarding the process have been conducted.
The following is a partial listing of this research, including links to the source documents where available.
Results of Becker Penetration Testing, Chilliwack Fire Hall
Kristiansen, H. and Davies, M. (2003) AMEC Earth & Environmental, Inc. Burnaby, B.C., Canada, 14p.
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Ground Improvement Using Rapid Impact Compaction
Kristiansen, H. and Davies, M. (2004) 13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada, 10p.
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Rapid Impact Compactor Ground Improvement, Vibration Monitoring and Densification Assessment
Tara, D., and Wilson, P. (2004) Thurber Engineering, Ltd. Downtown Site, Squamish, B.C., Canada, 9p.
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