Compaction Grouting

Compaction Grouting is a displacement method of improving the bearing capacity of soil. Where low strength, low capacity or unstable soil does not have the required bearing capacity for a specific load, a high density, low slump grout is injected in the soil. The grout is injected at in a grid pattern at the at the at the elevation of the substandard soil. As a result, the viscous grout forms into a bulb displacing and densifying the soil, or “compacting” it resulting in an improved bearing capacity.

Applications

  • To treat soils prior to new construction
  • For remedial work to stabilize and if necessary raise existing structures
  • Improve stability of the soils by reducing water content
  • Karstic remediation

Advantages

  • Improves the bearing capacity of weak soils
  • Irregular fills or varying native soils become more uniform
  • Excellent control with the utilization of laser controlled monitoring equipment
  • Tendency to improve the weakest soils
  • Minimal disturbance to landscape, floors, roads or nearby structures
  • Portable equipment is available for limited access
  • Inexpensive and rapid compared to other soil stabilization techniques
  • Prove technique with a long history of successfully completed projects


To perform the work an injection pipe is drilled or driven to the lowest elevation requiring improvement. A low volume, high pressure pump is used to place the grout. The grout used for compaction grout is requires a specific rheology. The goal is for the grout to expand as a bulb and remain homogeneous exerting radial forces in all directions as it displaces and compacts the adjacent soil.

The low pumping rate is employed to prevent soil fracturing by allowing excess water to dissipate. Grout is placed until pre-established criteria are met. The refusal criteria usually include maximum volume, minimum flow rate, maximum pressure, or movement at the surface. After refusal is reached at a specific elevation, the injection pipe is raised to a shallower depth and the process repeated until the height of the zone is treated.

The ability of the soil to resist surface uplift or heaving usually limits the degree to which compaction grouting can effectively treat the soil. Precise instrumentation is used to detect upward movement at the surface or a structure. Building and structures can be stabilized or releveled to precise tolerances.

The effective radius of an injection hole varies with the soil type. For this reason generally a primary/secondary pattern is used with split spaced secondary holes midway between the primary holes.

TerraFirm’s staff of engineers and geologists can assist with determining if compaction grouting is the proper technique for your soil improvement project. Our resources of technicians can execute the work plan and adapt to changing field conditions for a successful result.