Interpretation of Secant Shear Modulus Degradation Characteristics from Pressuremeter Tests

Nonlinear shear modulus degradation characteristics are of interest in many geotechnical engineering applications, such as ground deformation caused by seismic shaking and deep excavations in clay, weathered rock, and stabilized soil. This paper presents an approach to derive the secant shear modulus degradation characteristics from in situ pressuremeter tests, which is based on a digital filter algorithm. The algorithm is described, and data preparation procedures are presented. Use of the algorithm is illustrated by means of pressuremeter data for soils stabilized with deep mixing methods on the Boston central artery/tunnel (CA/T). The nonlinear secant shear modulus degradation characteristics from the digital filter approach are shown to be in good agreement with those from the curve fitting and transformed-strain approaches. They also compare favorably with the results of other in situ and laboratory tests performed in conjunction with the CA/T stabilized soils. The algorithm is implemented by a 26-line MATLAB code in an appendix of the paper.