Nondestructive Vibrational Tests and Analytical Solutions to Determine the Young’s Modulus of Rammed Earth Material

Abstract

Rammed earth (RE) is a construction material which is manufactured from the soil. The soil is dynamically compacted at its optimum water content, inside a formwork to build a monolithic wall. The RE wall is composed of several layers, about 10–12 cm thick. In the last decades, RE material has been the focus of numerous scientific researches because of sustainable properties of this material: low embodied energy, positive hygrothermal behavior and a particular esthetic aspect. In several situations, nondestructive methods are needed to assess the mechanical characteristics of RE material, for both old and new RE constructions. This paper presents how in situ vibrational measurements can be used to identify the dynamic behavior of RE walls and to determine the Young’s modulus of the RE walls measured. To determine Young’s modulus from the dynamic characteristics, an analytical model based on Timoshenko’s beam theory is presented, both for flexural and torsional modes. Then, the proposed analytical model is verified with measurements on several walls having different cross-sectional forms: rectangle and L-shape. The walls’ natural frequencies were identified from the dynamic measurements by using the Frequency Domain Decomposition method. In parallel, for comparison, the Young’s modulus of the RE material studied was also determined by classical static measurements (on the walls, prismatic and cylindrical specimens). The displacements were measured by using the Image Correlation technique. The comparisons showed that the results from the proposed analytical method provided high accuracies and better than that obtained by measurements on the usual specimens (prismatic and cylindrical).