Direct in-situ soil liquefaction testing

The objective of this testing procedure is to evaluate the earthquake-induced liquefaction susceptibility of an in-situ soil deposit. This is accomplished by determining how much excess pore water pressure can be developed for given shear strain levels and number of cycles. This approach is ideal because it directly characterizes the behavior of soil during large strain cyclic loading conditions, which are the same conditions expected during an earthquake.

The raw data for this project was in the MATLAB .mat file format. The data files loaded to the unprocessed folders are converted to ASCII file format with headers added in and are the voltage time series recorded by the dynamic signal analyzer.

The converted data files simply convert the voltage to engineering units and remove the zero offset for the velocity time series (the zero offset in the pore pressure transducer is useful information and therefore not removed).

The corrected data files involve the filtering of the velocity time series using a Butterworth filter to remove frequencies below three hertz; the pore water pressure data is not filtered.

The derived data files include the shear strain time series that is calculated at the center of the four-node isoparametric element using eight of the velocity time histories (the remaining four velocity time histories corresponding to horizontal movement perpendicular to the direction of shaking is not included because its contribution to shear strain is negligible).

The shear strains are calculated using the displacement-based method that described in Rathje et al, 2004. The word document titled “Shear strain calculation method” in the Analysis folder includes a more detailed explanation of the calculation steps.