Data from ring shear strength testing of glaciolacustrine silty clay from the 2014, Oso, Washington landslide

We performed ring shear strength testing of three specimens from a glaciolacustrine silty clay unit involved in a large landslide that occurred March 22, 2014 near the town of Oso, Washington. Ring shear tests utilized apparatus DPRI-5 at Kyoto University, Japan and test results are presented herein. We refer to the specimens as the clay, clayey silt, and silt. Some tests were performed under controlled shear stress with shear stress increased at ~0.5 kPa/s until failure and failure was permitted to continue for decimeters to meters of cumulative shear displacement. These tests were performed on unfailed material and on fault gouge that developed during failure. Other tests were performed on fault gouge under constant shear displacement rates of ~0.001–10 cm/s. Nearly all controlled shear stress tests were performed in the undrained condition (specimen chamber water lines closed) and nearly all constant shear displacement rate tests were performed in the naturally drained condition (specimen chamber water lines open). Normal stress was controlled during all tests. Cumulative shear displacement, normal stress, shear stress, pore-water pressure, and specimen thickness were continuously measured during each test. Recording of these parameters continued during hold periods after shearing ceased for many tests. Recording similarly continued during many consolidation periods that followed shearing or hold periods. Consolidation involved opening specimen chamber drainage lines to permit excess pore-water pressure (if any) to dissipate and specimen thickness to stabilize under the applied normal stress.

File names indicate testing conditions. For controlled shear stress tests, file names are: specimen_”drained” or “undrained”_normal stress_”controlled shear stress”_”unfailed” or “gouge”.txt and subsequent hold and consolidation file names are: specimen_”hold” or “consolidation”_normal stress_”controlled shear stress”_ ”unfailed” or “gouge”.txt. For constant shear displacement rate tests, file names are: specimen_”drained” or “undrained”_normal stress_shear displacement rate.txt and subsequent hold and consolidation file names are: specimen_”hold” or “consolidation”_normal stress_shear displacement rate.txt. In some cases, recording was made to one file during shearing, hold, and consolidation periods. For these, file names indicate shearing conditions as described above with “hold” and/or “consolidation” appended to the end of the file name.