Geomechanical characterization of the natural hemp - compacted clay interface -

Abstract

The interface parameters that govern the shear resistance mobilized between compacted clays and various solid interfaces are of interest in many geotechnical engineering projects. For example, the interface shear strength is essential for the design and safety assessment of deep foundations, offshore and onshore pipelines, mechanically stabilized earth walls, and fiber-reinforced soils, among others. Despite the wealth of data on the interface shear resistance between soils and solid interfaces, there is currently limited information on the interface resistance between clays and natural fibers which are currently being considered as a sustainable measure of soil improvement. In this study, a comprehensive experimental program is implemented to investigate the interface shear strength between a sandy clay and natural hemp fibers. A series of direct shear tests are conducted on both clay-clay and clay-hemp interfaces. The parameters that are varied in the experimental program are (1) the water content of the compacted clay, (2) the applied normal stress, and (3) the rate of loading and type of test (unconsolidated undrained tests versus consolidated drained tests). Another series of tests is implemented to study the interface shear resistance using single fiber pull-out tests at different rates of loading. Results indicate that the interface shear strength parameters that characterize the fiber-soil interaction are significantly affected by the test mechanism and the rate of loading. Results from interface direct shear tests that were conducted at fast rates to simulate undrained loading indicate that the interface strength parameters were found to be similar to those obtained using similar drained tests. This observation is important since it indicates that interface direct shear tests may not be optimal for characterizing the undrained response of the clay-fiber interface since drainage at the interface may be inevitable given the setup of the direct shear test mechanism.