A deep study of geotechnical characterization has been carried out with low density volcanic pyroclasts. More than 250 samples have been tested and the strength and deformability of these materials has been studied. Many interesting results have outcome from this study, one of them being the different shapes of failure of the samples obtained both theoretically and empirically. These shapes are mainly the following ones: In uniaxial compression nearly vertical failure planes; In triaxial compression, failure planes forming angles of 45+ψ/2 with the major principal stress, being ψ the dilatancy angle of the material; For high values of the confining stress the plasticity theory does no longer verify and the sample loses completely its structure; In the frontier zone of high confining pressures when the plasticity theory is about to stop verifying horizontal or nearly horizontal failure planes are formed. It is considered that these results may also be of interest and extended to other types of rocks.

1. Introduction

An extensive study has been done recently with the main objective of advancing in the understanding of the stress-strain behavior of low density pyroclasts, determining the most influential factors in it, such as its structure or alteration (Conde 2013). Particular attention has been paid to examine aspects considered paramount such as: macroporosity (size and morphology of the pores, their relative size in relation to the particles, etc.), alteration of the particles or the partial or complete filling with deposits of crystals or particles due to the circulation of fluids, in the macropores of altered materials. More specifically, the study performed was intended to obtain:

  1. A failure criterion of these materials, based on a few parameters.

  2. A geotechnical classification of the main types of low density pyroclasts, useful for defining a type of behavior and typical ranges of values of the main parameters for each defined group.

  3. More test results of low density volcanic materials, in order to improve the accuracy of the different correlations obtained in previous studies (Serrano et al. 2007) and useful for obtaining others for their practical use in civil works.

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