Graduation Year


Document Type




Degree Name

MS in Civil Engineering (M.S.C.E.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Austin Gray Mullins, Ph.D.

Committee Member

Rajan Sen, Ph.D.

Committee Member

Michael J. Stokes, Ph.D.


dry soil mixing, wet soil mixing, FHWA, organic field surveys, organic case studies


Soil mixing is a procedure that has proven to be effective for loose or soft compressible soils. The method stabilizes the soil in-place using specialized augers, tillers, or paddles that inject grout or dry cementitious powders as part of the mixing process. The Federal Highway Administration design manual for soil mixing helps to estimate the required amount of cementitious binder to produce a target design strength. However, it is biased towards inorganic soils and only mentions caution when confronting organic soils which usually come with a high water table, moisture content and void volume.

The Swedish Deep Stabilization Research Centre cited studies with highly organic soils in regards to soil mixing and suggested that organic soils may need to reach a ‘threshold’ of cement content before strength gain can occur. The University of South Florida also conducted a study on highly organic soils and was able to confirm this concept. USF also proposed a threshold selection curve based on the organic content. This thesis extends this concept to the bench scale testing of multiple full scale field studies.

This thesis will conclude with the presentation of new threshold curves based on the new data from the added field case studies. Given that there were variable binders and soil types used in the data analyzed, these threshold curves are dependent upon soil type and binder type, thus expanding upon the curve previously suggested.