Compaction Grouting

Compaction Grouting is a very specialized grouting technique designed to stabilize or densify the existing weak soils. This is accomplished by drilling/driving injection casing to the predetermined grout zone depth and injecting a low-slump, low-mobility soil/cement grout from the bottom of the grout zone up in designed stages. Each stage creates a grout bulb displacing the existing soils in all directions thus densifying the grout zone.

Compaction grouting can solve soil density problems. In this technique, a stiff mortar-like mixture is pumped into the soil. Rather than flowing through the soil, it forms an expanding bulb, displacing the soil while forcing out air and water. The resulting denser soil has a higher load-bearing capacity, thus stopping or preventing settlement. It can also be used to lift settled structures

It is typically carried out over a predefined grid pattern in a sequenced operation. The casing is driven or drilled on a design depth at each location, and the mixture is typically carried out in stages of 1 to 3 feet until refusal met. The spacing and steps of the grid pattern will determine by the depth of the grout zone, the overload of the grout zone, the types of soil and the pre-grow blow counts from the soil boring. The volume can be determined by an increase in the amount of the ground usually from 5% to 20% range.

●      Not suitable for soils with deficient permeability (i.e. clays)

●      Zone where limited overburden above the grout zone results in heaving. Usually, a minimum of 5 feet of overburden is required.

• Because every site is different, it is impossible to standardize compaction grouting probe spacing, placement procedures and sequences. Many factors including soil types, site conditions, and the results of soil tests influence the probe spacing, volumes, pumping pressures, and injection rates and sequence needed to correct the soil deficiencies. The mixture can be injected from the “bottom up” or “top down,” depending on the desired result. Grouting from the top down is more expensive because of the additional time required to drill through previously placed grout stages. However, top-downs typically work best for improving the ground at depths of 3 to 15 feet and when incremental releveling of a structure is required. Bottom-up placement is faster (due to continuous pumping) and, therefore, cheaper. It works very well to stabilize structures that require very little, if any, re-leveling. But it doesn’t compact soils less than 15 feet deep as well as top-downs. The two systems can be combined. Say a structure with a shallow foundation has settled and the soil is very soft to depths greater than 15 feet. In those areas where the structure requires re-leveling, do bottom ups from bedrock up to about 10 feet below the structural element. Then do top-downs until you encounter the bottom-up grout. With this sequence, the bottom-ups provide a stabilized base for the topdowns to push against. The topdowns can then lift the structure in increments. This system works well because in some cases if the bottom is not stabilized first, the top-down stages will add weight to the site and induce further settlement. Probes are typically spaced on 8- foot centers along foundation structural elements. However, the actual spacing should be calculated based on the spanning capabilities of the structure’s foundation system. When the total soil volume is stabilized beneath an entire building footprint, a triangular grid on 8-foot spacings often works best.

  When a grout casing has been drilled or driven to its appropriate depth, It is pumped at that location until:

  (1) a predetermined grout volume has been pumped,

  (2) a predetermined pumping pressure has been reached, or

  (3) undesired ground or structural movement is occurring.

  In most cases, the grout casing is then moved up, and pumping is resumed. Stage lengths may vary from site to site, but most work is pumped in 1-foot vertical increments

Contact the specialists at Geo Grout Ground Modification Specialist Inc. of Western United States for your compaction grouting project needs. Call us at (415) 285-2400 for complete information on our compaction services or email us at inquiries@gggms.com to discuss your Compaction Grouting needs today.