Ground Improvement using deep vibro-compaction
Includes sequence, methods and equipment.
Purpose is to provide protection against liquefaction during a seismic event. Also provide a minimum ground bearing capacity. Using vibro-compaction the sand and gravel particles are rearranged into a more dense state by the combined actions of water flow and vibration. Vibro-compaction was use to compact the Dubai man made islands that were constructed from dredged sand.
Work Sequence
Set out a triangular grid with a 3 metre spacing using steel pins with a unique number marked label.
Pre-treatment C.P.T. that is, cone penetration testing, will be undertaken to access the existing ground strength
The vibroflot will be positioned over the compaction point and the bottom water jets and air jets opened to allow flushing. The vibroflot will penetrate into the ground under its own weight using the vibratory effect, assisted by the water flushing. The compaction will be carried out in steps of 0.5 to 1.0m each and the holding time at each step will be up to 60 seconds. As the soil is compacted, a crater will appear at the ground surface, which will be continuously filled with surrounding sand by the attendant loading shovel
Post-treatment C.P.T. will be undertaken to assess and monitor the compaction.
Load bearing tests will be carried out during the course of the works, using a 2.5m × 2.5m plate loaded to 1.5 times a working load.
Equipment
Vibroflot with extension tube, hydraulic power packs mounted on crane, diesel engine driven water jetting pumps, compressors, crawler cranes with 60 tonne capacity, water tank, de-watering pump
