Ground Improvement

Ground improvement technologies are geotechnical construction methods used to alter and improve poor ground conditions in order that embankment and structure construction can meet project performance requirements, where soil replacement is not feasible for environmental or technical reasons, or it is too costly.

Ground improvement has one or more than one of the following main functions:

• Increase bearing capacity, shear or frictional strength
• Increase density
• Control deformations
• Accelerate consolidation
• Decrease imposed loads
• Provide lateral stability
• Fill voids
• Increase resistance to liquefaction

The following table lists the category of improvement, the function and potential methods of ground improvement.

Table 1. Ground Improvement Categories, Functions, Methods and Applications (NHI, 2004).

Category	Function	Methods	Comment
Consolidation	Accelerate consolidation, increase shear strength	1 Wick drains 2 Vacuum consolidation	Viable for normally consolidated clays.  Vacuum consolidation viable for very soft clays.  Can achieve up to 90% consolidation in a few months.
Load reduction	Reduce load on foundation, reduce settlement	1 Geofoam 2 Foamed concrete 3 Lightweight granular fills, tire chips, etc.	Density varies form 1 kN/m3 to 12 kN/m3.  Granular fills usage subject to local availability.
Densification	Increase density, bearing capacity, and frictional strength of granular soils.  Decrease settlement and increase resistance to liquefaction	1 Vibro-compaction using vibrators 2 Dynamic compaction by falling weight impact	Vibrocompaction viable for clean sands with <15% fines.  Dynamic compaction limited to depths of about 10 m, but is applicable for a wider range of soils.  Both methods can densify granular soils up to 80% Relative Density. Dynamic compaction generates vibrations for a considerable lateral distance.
Reinforcement	Internally reinforces fills and/or cuts.  In soft foundation soils, increases shear strength, resistance to liquefaction and decreases compressibility	1 MSE retaining walls 2 Soil nailing walls 3 Stone column to reinforce foundations	Soil nailing may not be applicable in soft clays or loose fills.  Stone columns may be applicable in soft clay profiles to increase global shear strength and reduce settlement.
Chemical stabilization by deep mixing methods	Physio-chemical alteration of foundation soils to increase their tensile, compressive and shear strength and to decrease settlement and/or provide lateral stability and or confinement	1 Wet mixing methods using primarily cement 2 Dry mixing methods using lime-cement	Applicable to soft to medium stiff clays for excavation support where the groundwater table must be maintained or for foundation support where lateral restraint must be provided or to increase global stability and decrease settlement.  Requires significant QA/QC program for verification.
Chemical stabilization by grouting	To form seepage cutoffs, fill voids, increase density, increase tensile and compressive strength	1 Permeation grouting with particulate or chemical grouts 2 Compaction grouting 3 Jet grouting, and 4 Bulk filling	1 Permeation grouting to increase shear strength or for seepage control, 2 compaction grouting for densification, 3 jet grouting to increase tensile and/or compressive strength of foundations, and 4 bulk filling of nay subsurface voids
Load transfer	Transfer load to deeper bearing layer	Column (pile) supported embankments on flexible geosynthetic mats	Applicable for deep soft soil profiles or where a tight schedule must be maintained.  A variety of stiff or semi-stiff piles can be used.

The Collin Group has been involved with ground improvement technologies for over two decades and has vast experience with column supported embankments, rammed aggregate piers, stone columns, vibro-concrete columns, deep mixing methods, and soil nailing.