Eduardo Suescun-Florez

This review provides an overview of testing techniques related to high strain rate (HSR) loading of granular media, in support of the increasing interest in civilian and military applications related to transient loading on sand. The intrinsic properties of granular soils are shown to be rate dependent. The framework for assessing rate dependent behavior of granular soils is presented. Techniques for applying HSR loading including uniaxial and triaxial compression configurations are discussed. Critical issues related to inertial and wave propagation effects as well as boundary effects are highlighted. In addition, options for test setup and measuring response are described both with respect to capabilities and drawbacks. The most relevant studies are summarized, but gaps and inconsistencies remain in the available literature.

An experimental program was conducted to quantify the strain rate dependency of silica sand under different low to intermediate strain rates. Measurements of axial stress, axial strain and stiffness were explored to assess the sensitivity of mechanical properties to strain rate. Strain rates were applied on samples subjected to uniaxial compression stresses within a range of 0.01 to 100 %/s. The tests help facilitate the incorporation of strain rate dependency of soil response in geotechnical modeling of soil-structure interaction problems. Available observations of the response of sand under monotonic loading suggest that sand may exhibit significant strain rate dependency.

This paper reports on the results of several geotechnical engineering-related science activities conducted with elementary-school students. Activities presented include soil permeability, contact stress, soil stratigraphy, shallow and deep foundations, and erosion in rivers. The permeability activity employed the LEGO NXT platform for data acquisition, the soil profile and foundations activity employed natural and transparent soils as well as LEGO-based foundation models, and the erosion activity utilised a 3D printer to assist with construction of building models. The activities seek to enhance students’ academic achievement, excite them about geotechnical engineering, and motivate them to study science and math. Pre- and post-activity evaluations were conducted to assess both the suitability of the activities and the students’ learning. Initial results show that students gain a reasonable understanding of engineering principles. Moreover, the geotechnical engineering activities provided students an opportunity to apply their math skills and science knowledge.

Small-strain stiffness properties of soils, such as shear wave velocity, shear modulus and material damping, play a key role in the adequate design/analysis of unsaturated earth structures subject to static/non-static loading. Most conventional geotechnical testing techniques, however, cannot capture this small-strain behavior and, hence, vastly underestimate the true soil stiffness, mainly due to inaccuracies in small-strain measurements. Bender element technique has proved to be a viable way to investigate soil stiffness at very small strains, albeit mostly under dry or saturated conditions. Hence, there is a great need for assessing the feasibility of bender element technique in unsaturated soils as compared to fully standardized procedures, such as the resonant column and simple shear test methods. This paper introduces a suction-controlled proximitor-based resonant column device featuring self-contained bender elements for simultaneous testing of soils using both techniques. A comprehensive series of RC and BE tests were conducted on samples of silty sand at 50, 100, 200 and 400-kPa matric suction states via the axis-translation technique. Results show a reasonable good agreement between RC and BE test results. Both techniques showed the critical influence of matric suction on soil's small-strain stiffness response.