Characterization of the Soil-Timber Interface by Laboratory and In Situ Testing Methods

Abstract

As part of a larger study on the use of laminated timber foundations, a field and laboratory study of the interface behavior of soil and timber was undertaken to better understand the interaction of the two materials. Limited test data is available in literature for soil-timber interface performance, and as laminated timber piles have different surface characteristics than traditional timber piles, there is a need for characterization of the interface behavior.

This thesis summarizes the development and initial testing of a wood CPT friction sleeve to measure the soil-timber interface properties in situ. This thesis also summarizes the results of a series of laboratory interface direct shear tests on a soil-timber interface to provide data useful in the design of timber foundations. The results of a surface metrology study are presented herein, and the results are compared to existing models for interface behavior developed for steel and concrete piles. CPT soundings using the wood friction sleeve have been performed at well-characterized sites, and the results have been compared to adjacent soundings using a conventional CPT. A study of the surface morphology of timber during shearing is performed, and hypotheses of potential influencing factors are proposed. The findings of this research suggest that the relative influence of surface characteristics and friction mechanisms of a soil-timber interface is different than that of soil and steel or concrete. There is a need for further study of the influence of the surface characteristics of timber, and further testing and development of the wood CPT friction sleeve is required to measure interface strength in situ.