Compaction Grouting is a soil correction pressure system which increases the bearing capacity of soils. A compaction application is accomplished by pumping a very viscous (low mobility) grout, under pressure, into the ground which compacts the surrounding soil. Expanding grout displaces the under compacted soil to the side, forming a grout column. Grout columns can be sized as needed depending on the soil characteristics.
Displacement in the soil is produced by overburden pressure pushing back against all sides of the compaction grout column. A major advantage of using compaction grouting is that its top peak effect is realized in the weakest or softest strata of the soils underlying a building.
Compaction Grouting Applications:
- Pre-construction soil remediation
- Lifting structure approaches
- Raising: Roads, Bridges (pictured), Towers
- Raising and stabilizing existing structures
- Filling fissures in rock and subsurface voids
- Sinkhole remediation
Usually, grout (cement) is applied in measured stages beginning at the lowest point of a drilled shaft then working upward through the weak ground. On very shallow pressure grouting applications, compaction grouting can be injected from top down, building a cap. The “Top Down” method densifies the upper portions of treated area first so that it becomes a dense cap which helps to contain the expanding grout at lower levels.
When applied in a grid style layout, the pressure treated soil has a greater uniformity throughout its entire mass; this gives maximum soil stabilization and provides solid support.
Significant improvement can be achieved on the load-bearing capacity of problem soil. A lift can be achieved on structures that have settled due to problem soils.
Typical Grouting Sequence
Compaction grouting can be used as either end bearing or skin friction bases for lifting or stabilizing soils.
- Core through footing extensions, concrete slab, asphalt, or other obstruction.
- Drive casing into the soil stratum continuing down to bedrock or proper friction depth.
- A low mobility, mortar-like cementitious mixture (grout), less than two inch (2”) slump having more than 500 psi compressive strength, is pumped at pressures up to 1,000 psi contained within the casing to form a cohesive concrete bulb.
- The grout bulb is expanded to a one-foot diameter. Displacement of soil at the lower tip of casing is calculated and measured; the volume of grout is steadily maintained.
- The pressure grouting tube is raised one foot “lift”, and the grouting process is repeated.
- Injections continue as the casing is withdrawn up to the structure’s footing, which creates an in-place solidified grout pile surrounded by intensely compacted soil.