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Vibro Compaction

Ground improvement techniques are geotechnical construction methodologies that modify and enhance the engineering properties of the soil mass by improving one or more of the following parameters: Increase in the soil density and shear strength, Decrease of the compressibility, Reduction of settlement (total and differential), Increase in the soil bearing capacity, Acceleration of the consolidation process, Increasing the factor of safety against liquefaction in case of an earthquake, and generally Re-strengthening of the soils. There are a number of Ground Improvement techniques available for different types of soils, different purposes and project requirements.

Methods

Vibro Compaction/Replacement

Vibro Compaction is a densification ground improvement technique that rearranges the soil particles into a denser state. Vibro Replacement is a reinforcement ground improvement technique that strengthens the soil by means of the construction of a stone column.

Dynamic Compaction

Dynamic Compaction is a Densification ground improvement technique that uses a heavy weight “tamper” suspended from a crawler crane boom that is dropped repeated number of times into the ground to densify the soil.

Rapid Impact Compaction

RIC is a ground improvement technique consisting of an excavator-mounted, hydraulic pile-driving hammer of 9-16 Ton hydraulically raised and then allowed to free-fall; thus, delivering energy to arrange soil particles into a denser state.

High Impact Roller Compaction

HIRC is also a “dynamic” compaction technique consisting of a triangular, rectangular or hexagonal ”wheel” mounted on a trailer that is pulled by a Tractor with a constant speed, making several passes compacting the soil.

Vibro Compaction/Replacement

Vibro Compaction is a technique that enables the rearrangement of soil particles into a denser configuration with vibration by the use of powerful downhole deep vibrating probes.

Vibro Replacement (Stone Columns) uses the same principle of the Vibro Compaction (powerful vibroflots that generate vibration to re-arrange soil particles) but in soils where the VC is not possible due to higher fines content (higher than 10% and typically less than 40%); thus, the densification is achieved by displacement of the soils radially by the vibrator, refilling the resulting space with granular material which results in the construction of stone columns at the treatment locations.

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Applicable Soils & Depth of Improvement

The Vibro Compaction technique is most suitable for loose medium to coarsegrained sands with silt / clay content less than 10% (less efficient with fines content between 10% and 15%). Can be applicable to depths up to 45m (or more depending on Crane capacity)

The Vibro Replacement (Stone Columns) are most suited for sands with fines content greater than 10% and typically less than 40% or for clays which require some level of bearing or lateral reinforcement. Can be applicable to depths up to 45m (or more depending on Crane capacity)

Applications

  • Nearly all reclamation projects
  • Buildings
  • Offshore and nearshore man-made islands
  • Pipelines
  • Road and rail embankments
  • Power plants
  • Infrastructure in general
  • Stone columns for embankments on soft soils that need to accelerate drainage, increase stability, and reduce settlement

Advantages

  • Increases the allowable bearing capacity of the soil
  • Limits (minimizes) total and differential settlements
  • Mitigates the risk of Liquefaction (to the design depth) in case of seismic event
  • Reduces the size of foundation due to reinforced ground
  • Can densify deep soils up to 45m depth

Disadvantages

  • Vibro Compaction has a diminished effectiveness if sand has fines content between 10% to 15% and definitively is not applicable if fines content in excess of 15%, unless combined with other G.I. approaches.
  • For Stone Columns, in very soft clays with undrained shear strength of 20 kPa, stone columns cannot be applied due to lack of lateral support
  • Stone Columns are also not recommended for high loads on a very limited footprints

Dynamic Compaction

Dynamic Compaction (DC) involves the repeated dropping of a 10 to 30-Ton tamper multiple times from heights of 15 to 30 m, transforming potential energy into a densification effect to the soil particles

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Applicable Soils & Depth of Improvement

The DC technique is most suitable for loose medium to coarse-grained sands with silt / clay content less than 15% (somehow efficient with fines content between 15% and 20%). Can be applicable to depths up to 12m (but typical ideal effective depth is down to 10m).

DDC is effective both above and below the ground water table although vertical drain elements (such as wick drains) are typically used to assist with pore water dissipation when the water table is relatively shallow.

Applications

  • Reclamation projects
  • Densification of fills, mine refuse, collapsible soils, sanitary landfills, and soils loosened by sinkholes
  • The method works best on granular soils where the degree of saturation is low, the permeability is high and the drainage is excellent

Advantages

  • Relatively inexpensive method
  • Increases the allowable bearing capacity of the soil
  • Mitigates the risk of Liquefaction in case of seismic event
  • Can densify deep soils down to 12m

Disadvantages

  • DC is not suitable if water depths are shallower than 1.5m
  • Not effective when soils have fines content in excess of 20%
  • Limitations where highly sensitive structures susceptible to ground vibrations are nearby
  • Limited effective depth typically of 10m although can improve to 12m
  • Cannot be used near underground services
  • Cannot be applied if soft cohesive soils are located in the upper part of the compaction

Rapid Impact Compaction

RIC is a ground improvement technique consisting of an excavator-mounted, hydraulic pile-driving hammer of 9-16 Ton hydraulically raised and then allowed to free-fall; thus, delivering energy to arrange soil particles into a denser state. RIC is both a densification and a reinforcement technique, it uses the same principle of the Dynamic Compaction (weight dropped into the ground to densify the soil) but in a more controlled manner (less height, less weight, but faster). On the one hand, it is a densification technique because it rearranges the soil particles into a denser state; on the other hand, it can also be a reinforcement technique because when combined with soil replacement or stone backfill at the point of impact, it develops re-strengthening columns that are built and compacted with the method; thus, increasing the bearing capacity, limiting the settlement (total and differential) and increasing the shear strength.

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Applicable Soils & Depth of Improvement

The RIC technique is most suitable for loose medium to coarse-grained sands with silt / clay content less than 20% (less efficient with fines content between 20% and 25%). Can be applicable to depths up to 5-6 m with hammers of 9 Tons and up to 8-9 m with hammers of 16 Ton. Depth of improvement is highly dependent on soil conditions.

Applications

  • Nearly all reclamation projects
  • Buildings, offshore and nearshore man-made islands
  • Pipelines, road and rail embankments
  • Power plants, infrastructure in general but due to the depth limitation, care should be given to the depth limitation

Advantages

  • Fast, relatively inexpensive
  • Increases the allowable bearing capacity of the soil
  • Limits (minimizes) total and differential settlements
  • Mitigates the risk of Liquefaction (to the design depth) in case of seismic event
  • Minimum disturbance to superficial soils, only grading work required

Disadvantages

  • Marginally effective when soils have fines content in excess of 25%
  • Compaction limited to 5-6m with 9T hammers and 8-9m with 16T hammers, (it is not suitable for moderate or deep compaction of soils)

High Impact Roller Compaction

HIRC is a “dynamic” compaction technique consisting of a triangular, rectangular or hexagonal ”wheel” (typically between 8 to 12 Tons) mounted on a trailer that is pulled by a Tractor with a constant speed, making several passes over the soil. The effect of the speed combined with the “tampering” of the irregular “wheel” creates a waving effect that densifies the soil particles. The effect of the speed combined with the “tampering” of the irregular “wheel” creates a waving effect that densifies the soil.

Unlike the principle of the weight dropped from a height (i.e. Dynamic Compaction and High Impact Compaction) the “weight” of the HIRC is “pulled” from a tractor, making each turn of the odd shape “wheel” an energy impact wave delivered into the ground; thus, densifying the soil. The depth of densification is less than the Dynamic Compaction or Rapid Impact Compaction, thus HIRC is considered a superficial compaction method.

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Applicable Soils & Depth of Improvement

The High Impact Rolling Compaction technique is applicable in sands with fines content not in excess of 10%, but can be used also (with less effectiveness) with slightly greater fines content. HIRC has a limited depth of improvement to the top 1.5m to 2.0m; it is ideally implemented as complementary to other deep compaction methods like VC or DC, which are poor in compacting superficial soils.

Applications

  • Economic and fast way of densifying large extensions of land whereby the top 1.5m to 2.0m needs to be compacted in one effort, as compared to layer by layer compaction
  • Employed as compaction technique for superficial soils, complementary to VC, and DC in reclamation projects, buildings, offshore and nearshore man-made islands, pipelines, road and rail embankments, power plants, infrastructure in general.

Advantages

  • Fast, relatively inexpensive compared to compacting by layers
  • Does not require multiple lifts of material placing, can compacted one layer of up 1.5-2.0 mt in one single effort

Disadvantages

  • Limited to depth of improvement of 1.5 to 2.0m (maximum)
  • Not intended for smaller projects (less than 1 Ha) as it requires certain speed and looping cycle
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