Abstract

The failure criterion of low-density volcanic rocks differs radically from that of conventional rocks by manifesting collapse under isotropic stress. In this way, the shapes of the failure model do not reveal a continuously increasing growth of deviating stress with the isotropic stress, but they reach a maximum value, after which they decrease until they vanish under the isotropic collapse pressure. As a consequence, engineering applications require the implementation of numerical codes and the resolution of associated numerical difficulties. This article presents the problem of the bearing capacity of a foundation on a low-density volcanic rock using the DLO (discontinuity layout optimization) numerical method. The analysis of results shows the ability of the DLO method to solve the numerical difficulties associated with the complex failure criteria, so that the convergence and stability of the solution can be achieved without generating high computational costs. Additionally, a discussion of the DLO results is also presented, demonstrating forms of failure on the ground following the real collapses in these volcanic materials. In addition, numerical validation was performed with the finite difference method, using FLAC, and with an analytical method using simplified configurations, obtaining good contrast results, with the DLO method performing better. In this way, an adequate and reliable resolution technique is provided to face the problem of bearing capacity in low-density volcanic rocks, overcoming limitations referred to in the technical literature regarding the difficulty of treating highly non-linear and non-monotonic numerical criteria, which allows the introduction of isotropic collapse failure.

Highlights

  • Magma fragments expelled by volcanic eruptions give rise to pyroclasts, which can be made up of: (1) small glass particles with a very highly specific surface area; (2) larger fragments that, when solidified, produce scoriae and pumices and contain inner gas

  • The unique geomechanical characterization of pyroclasts has been observed in various engineering studies that have been carried out in volcanic areas, such as in some dams, for example Campitos and Ariñez (Tenerife) [14,15], where a series of tests to determine the load conditions that produce mechanical collapse in their foundation materials were performed

  • Results and Discussion adopted parameters and the bearing capacity results obtained by the Discontinuity Layout Optimization Method (DLO) method are shown

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Summary

Introduction

Magma fragments expelled by volcanic eruptions give rise to pyroclasts, which can be made up of: (1) small glass particles with a very highly specific surface area; (2) larger fragments that, when solidified, produce scoriae and pumices and contain inner gas. As a consequence of this process, pyroclastic rocks have low density and, high porosity, such that the characterization and geomechanical applications are very special In this type of low-density volcanic material, when an external load of low magnitude is applied, the resistant and deformational characteristics resemble conventional rocks; by increasing the load level and raising the internal stress range, the links between the particles are broken and a destructuring process is induced, meaning that sudden deformations are inferred, generating a great danger for the structures that must be supported. Such failure law is implemented in finite differences, using FLAC [13], in order to validate the numerical solution obtained with DLO

Geomechanical Characterization of Pyroclasts
Formulation of the Failure Criterion
Parabolic criterion volcanic pyroclasts
Identification of the Failure Zones
Bearing Capacity
Analytical
Method
Hypotheses Adopted
Differences Method
Results and Discussion
MPa Pwith
Conclusions
Methods
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