Preferred Design Procedure

There are three different design approaches for compaction grouting:

• Designs based on experience
• Designs based on mathematical models
• Designs based on numerical modeling

The first method is by far the most commonly used. Schaefer et al. (2016b) concludes that there is no way to accurately design a compaction grouting program using mathematical modeling. While there are some applicable models, they often are difficult to use and many input parameters often requiring assumptions to be made that can lead to further inaccuracy. Numerical modeling can be performed, but as with mathematical models it can be difficult to choose input parameters and ways to properly model the grout‑soil interaction.

 

The experienced based method is the preferred method and is often preferred in practice and recognized in the FHWA-NHI publication Schaefer et al (2016b). A lot of specialty contractors keep these design methods proprietary, but there is some published information on this design approach. Mathematical and numerical modeling may be used in addition to the experience based methods for critical projects requiring higher performance post-grouting.

The Federal Highway Administration (FHWA) has a set of design documents for this technology. The documents are summarized below.

 

Publication Title	Publication Year	Publication Number	Available for Download
Ground Modification Methods	2016b	FHWA NHI-16-028	Yes1

 

1. https://www.fhwa.dot.gov/engineering/geotech/pubs/nhi16028.pdf

Table 1 provides the typical inputs and outputs of the design and analysis procedures.

 

 

Table 1. Typical inputs and outputs for design and analysis procedures.

Performance Criteria/Indicators

Increase in SPT N-value
Increase in CPT tip/sleeve resistance
Heave at the ground surface
Decrease in volume grout takes
Peak pressure measurement
Increase in shear wave velocity

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Subsurface Conditions

Delineation of Stratigraphy
Permeability/Hydraulic Conductivity
Liquefaction potential
SPT N-Values
CPT Tip Resistance and Sleeve Friction
Coefficient of consolidation
Presence of Voids
Relative Density
Gradation
Groundwater elevations

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Loading Conditions

Embankment loading
Structural loading
Earthquake loading

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Material Characteristics

Gradation of sand in the grout mix
Grout strength
Slump
Permeability of the grout mix
Internal friction

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Construction Techniques

Grout pressure
Flow rate
Monitoring instruments & procedures

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Geometry

Vertical or battered
Grid shape
Injection spacing

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