results of shear strength during early portion of the life of the soil cement. Many times, the owner and engineer understand that the material is acceptable, yet they are concerned that an oversight agency will not accept the judgment made. Perhaps, there should be additional dialog up front about what happens if test results are not consistent and then how to evaluate the final product. The mixed material will never be completely ‘homogeneous’ unless the in-situ soils were homogeneous from the onset. Ultimately, the desire of a soil mixing operation is to provide a good, thorough blend of in-situ materials and binder material. Each of the items discussed above, in addition to others, would allow the client flexibility to apply engineering judgment to the results and to ‘put it all out there on the table’ using the drilling records, cores, videos and evaluation of the results. If there is difficulty coming to a consensus whether it is an acceptable project, one should look at the work globally, in that, if 90% of the QC boxes are checked, the work is likely In cab monitor display (photo courtesy of Condon Johnson) adequate for its proposed function. However, if there was no quality control, no care in the blending, no control over rotation/drilling speed and no grout control, then it will be quite difficult to be able to convince an owner or engineer that what’s in the ground is acceptable. That is, it will be difficult to convince someone of the quality unless the installed work is excavated and exposed, which is not practical or financially prudent. Conclusion A QC program is an extremely beneficial tool, which has been enhanced using a com- puterized operation system, and has brought about a better understanding of the results. With the available tools and methods, real data is obtained to verify that the installation of each element was performed consistently and in similar manner compared to the test program. Soil mixing is an extremely valuable, useful technology that can enable infrastructure to be placed atop some of the least favorable ground conditions. It has been proven that soil mixing has reliable strength gain over time while minimally affecting the environment. In sum, soil mixing can be priced reasonably and competitively if the work is monitored carefully, has a reasonable QC protocol and verification requirements, and can apply engineering judgment where necessary. A. David Miller, P.E., is an independent geotechnical consultant with more than 30 years of hands-on, practical soil mixing experience. He is chair of the DFI Soil Mixing Committee, and he co-authored the DFI and ADSC Guide Specifications on Soil Mixing. 72 • DEEP FOUNDATIONS • JULY/AUG 2017
