The development and history of compaction grouting over the last 30-40 years has been well established by many distinguished researchers, design engineers and design/build contractors. It is interesting to note that upon researching data for this paper, there is a distinct lack of technical information to be found in Geotechnical text books. However, many technical papers have been published dealing specifically with the issues surrounding compaction grouting design, implementation and case studies. A short list of fundamental reference paper titles are as follows (see references for full citations):
"Compaction Grouting", 1973
"Planning and Performing Compaction Grouting", 1974
"Preliminary Glossary of Terms Relating to Grouting", 1980
"Compaction Grouting - The First 30 Years", 1982
"Compaction Grouting - A 10 Year Update", 1987
These and other important references are the main stream basis of knowledge for the highly specialized engineering and construction technique know as compaction grouting. Many diverse case studies and project examples also provide data on a wide variety of applications for the technique, such as:
Raising & re-leveling existing structures damaged by differential settlement.
Soil bearing capacity improvement for new construction of structures.
Soil bearing capacity increase beneath load bearing elements of existing structures.
Densification of loose sands beneath dams to prevent liquefaction during earth quake conditions.
Sinkhole stabilization and remediation of loose and raveled soil matrices.
The compaction grout method has some unique features which allow distinct advantages over other remedial methods of geotechnical construction. In many instances grouting is the only viable solution. Some of the advantages include:
Economy - Many times compaction grouting is the only feasible solution to foundation settlement problems, other than demolishing the structure and rebuilding with expensive deep foundation techniques.
Minimal Disturbance - During the grouting operations, the structure may remain occupied and in-service.
Minimal Risk - compaction grouting offers minimal risk of catastrophic structural failure while re-leveling structures or remediating sinkhole conditions.
Minimal Geotechnical Exploration - Once a basic reconnaissance round of geotechnical exploration has determined that compaction grouting is a viable solution, the process may be used as an exploratory tool and a remedial tool. Using drill logs to note density changes and total depth to competent bearing strata combined with grout injection pressures, rates and volumes versus depth, engineers can explore and remediate a site simultaneously.
Provide Greater Support for Structures - grouting on a pre-determined spacing along the perimeter of a structure develops an improved degree of added support between the grout points which serves to influence and improve a substantial footprint area as compared to steel piering a structure which only provides discrete point support .
Remediates the Problem - As opposed to building a structure on a pile, stone column or caisson foundation system which transfers the building load below the effected soil stratum, compaction grouting remediates the faulty layer, which minimizes the risk of future failures.
Ground Heave - Using a carefully planned and executed program, structures that have experience differential settlement can be re-leveled and stabilized. Large areas of a structure may be re-leveled without point loadings which may damage the structure.
It is also prudent to know and understand the limitations and other considerations associated with compaction grouting, when producing an engineering analysis. Some of these considerations include:
Damage to Underground Utilities - including pipelines, structures, vaults and wells may be sealed off or filled with grout during the operation.
Effectiveness Versus Permeability - Compaction grouting relies on the consolidation and mechanical densification of soils. Typically clays and other low permeability soils are not easily displaced or compacted.
Verification of Effectiveness/ Inspection - As the process takes place under ground, the main body of evidence for effectiveness are the grout logs produced during the operations and penetration testing before and after the process.
Cost Factors - Deep unstable conditions may exist which require extensive remediation in excess of the value of the structure, thus value engineering may determine that the process is cost prohibitive.