Development of an in situ dynamic liquefaction test

A new field-testing technique has been developed in which liquefaction and pore pressure generation characteristics of soil are measured in situ. The in situ dynamic liquefaction test utilizes a large, hydraulic shaker to load dynamically a soil deposit. The soil response is measured with embedded instrumentation. The embedded instrumentation includes newly developed liquefaction test sensors that incorporate velocity transducers (geophones) and pore pressure transducers in a single case. The recorded data are used to describe pore pressure generation and liquefaction characteristics in terms of the relationship between shear strain and induced pore pressure ratio. The analytical techniques used to compute shear strain from particle velocity measurements are discussed and compared. The results from testing a 1.2-m by 1.2-m by 1.2-m reconstituted field test specimen are presented. The shear strain - pore pressure relationships at selected numbers of loading cycles that were determined from the in situ dynamic liquefaction test are compared with those measured by other investigators in the laboratory. The field-measured relationships show the same shape as the lab-measured relationships, but the field data indicate a smaller threshold strain for pore pressure generation (∼0.005 %). This difference is attributed to the low effective stresses in the reconstituted field specimen.