Field Seismic Assessments of Microbially Induced Desaturation (MID) Ground Treatment Method

The objective of this study is to investigate the effectiveness of the Microbially Induced Desaturation (MID) ground improvement method in reducing liquefaction potential of silty soils. Field studies were conducted at the Sunderland site in Portland, OR. Tests conducted at the site includes: (1) a Direct-Push Crosshole (DPCH) test, (2) four liquefaction screening tests, (3) series of crosshole tests using an embedded sensor array, and (4) series of stage-loading, shaking tests using an embedded sensor array and a screening sensor. Two NHERI@UTexas hydraulic mobile shakers named T-Rex and Rattler were utilized in this study. The DPCH testing was conducted first to obtain the P-wave and shear wave velocity profiles of the test site. The screening tests were conducted to evaluate the potential of excess pore-water pressure generation in the soils over a range of depths. A sensor array consisted of eight 3-D ground motion sensor (geophones) and four pore-water pressure transducer (PPT) were installed based on DPCH and screening tests results. Crosshole tests and series of stage-loading, shaking tests were conducted to evaluate P-wave velocities and the excess pore-water pressure induced by cyclic loading from T-Rex and Rattler. Crosshole tests and series of stage-loading, shaking tests were repeated after the MID treatment was applied through the soil mass in the sensor array. Results before the MID treatment shows the treatment is highly effective in reduce P-wave velocity in saturated soil; hence, the treatment is effective is desaturating silty soils. More studies are needed to determine the effects of MID treatment on the excess pore-water pressure induced by cyclic loading.