Stabilization Tests for Deep Mixing—Round-Robin Tests in Eight Finnish Laboratories

Stabilization tests in laboratory play an essential part of quality control and assurance of the deep mixing method. By preparing and testing laboratory soil specimens stabilized with different binder types and dosages (binder recipes), estimation of in-situ properties of treated soil can be made. The stabilization tests typically consist of uniaxial compressive tests of cylindrical specimens. However, there have not been any national guidelines in Finland on laboratory methods for stabilization tests until year 2018, when an updated Finnish stabilization design guideline was published by the Finnish Transport Agency. By means of this guideline, stabilization test results from different laboratories should be comparable. To study the comparability of the stabilization tests from different laboratories, a round-robin study (interlaboratory test) between laboratories was completed. The performed stabilization test series have been examined as the internal (within laboratory) coefficient of variation of the individual test series and as the external variation of the parallel stabilization test series performed in different laboratories. The internal variation of the stabilization test series was modest in most of the laboratories, but regardless of the national stabilization test guideline, a large variation was found in the results of the parallel test series of the laboratories. Based on the findings, additions to the Finnish national guidelines are needed and these additions are planned for implementation during 2023–2024.