Application of Six Sigma in the precision testing of standard soil mixes

Geotechnical index property test inputs are very important in foundation design in terms of soil classification and settlement calculations. It is therefore crucial to have accurate and reliable parameters for more reliable and safer foundation design. In this research, Six Sigma concepts were utilized and incorporated in the inter laboratory study (ILS) precision testing of standard soil mixes of Ottawa sand, Bentonite and manufactured sand. Specific Gravity tests, Sieve Analysis, Liquid Limit Test and Plastic Limit Test were conducted by Six (6) participating laboratories, including the Department of Public Works and Highways (DPWH), Bureau of Research and Standards laboratory. The conduct of the ILS shows that for the soil tests, only sieve analysis produced good repeatability and reproducibility values. Both Specific Gravity Test and Liquid Limit and Plastic Limit Tests showed high r and R values. To rectify this, the observed probable sources of errors during the conduct of the ILS were identified and quality control measures were employed for a retest conducted in a single laboratory. Retest results fell within the acceptable range of two results specifications of ASTM. Therefore, the quality control measures and procedures employed in the retest and ASTM precision statements were recommended to be followed for the proposed diagnostic testing for the DPWH Private Laboratory Accreditation and for the accreditation of laboratory technicians.