An Alternate Compaction Grouting Technique

This paper describes an alternate compaction grouting system. It also provides the theory and a mathematical model to assess and quantify the degree of soil improvement caused by compaction grouting. It further discusses a field application where this system has been successfully used. The most common objective of compaction grouting is the densification of the soil whereby the grout does not permeate or fracture the soil matrix. This is typically accomplished by using low mobility grouts. Predictable results can also be obtained for some applications by utilizing the further described alternate method. The alternate method involves the following: Regular sleeve pipes (similar to those used in permeation grouting) are installed to the required depth, through the soil strata that need to be treated. Geotextile bags are strapped ("concertinad" on the sleeve pipe) straddling all or some of the sleeves. The geotextile bags are inflated via a double packer with a balanced, stable, low viscosity cement based suspension grout with high resistance against pressure filtration. Several bags (on different pipes) are inflated at the same time. The inflation process is done in stages to allow the water to slowly (pressure) filtrate through the geotextile bags. During each grouting stage the pressure is systematically increased. Because the compaction process is time related (with reference to Terzaghi's time settlement equations) the compressibility of these layers is gradually and systematically reduced. The spacing between the grout pipes has to be such that the soils are subjected to vertical stresses in excess of those they will eventually be subjected to. The volume reduction of the surrounding soils under the grouting pressure, as well as the influence radius of the compaction grouting can be mathematically estimated with the method described in this paper. This in turn dictates the spacing between the grout pipes. By not attaching a geotextile bag on every sleeve, hydrofracturing or permeation grouting in conjunction with hydrofracturing can be conducted via these sleeves, after the compaction grouting has been completed.