Abstract
When inner cavities of significant dimensions exist in natural rocks, problems arise when a shallow foundation for a building, bridge or other structure is builtonthem. Thus, taking one of the most representative cavity geometries in nature, the ellipsoidal horizontal shape, the main objective of this study is to obtain the ultimate bearing capacity of the foundation with cavities of different sizes and positions, on rock masses with different strengths and deformation characteristics. The study focuses on natural rocks of karst origin (in limestones, dolomites or gypsums) and of volcanic origin. The ultimate bearing capacity is determined relative to a situation without the existence of the cavity for different cavern positions and sizes, rock types (mi), strengths (UCS), and states (GSI) of the rock mass. The results showed that the most decisive parameter is the relative eccentricity. The influence of the rock type (Hoek’s parameter mi) is, for practical purposes, negligible (lower than 10%). The strength and condition of the rock mass (parameters UCS and GSI) have relatively little influence on the results obtained. This study aims to provide a simple design criteria for universal use, with different geometric configurations and qualities of rock masses that can be used directly without the need for sophisticated calculations by the designer.
Highlights
Introduction and ObjectivesCavities of significant dimensions may exist in natural rocks, mainly in evaporitic and carbonate rocks and in volcanic rocks
This high variability in cavities in karst environments is not related to the homogeneous types of sections and the resemblance in shapes found in lava tubes
It has been observed that the most influential parameter on the ultimate bearing capacity, relative to the bearing capacity that would be obtained without the existence of the cavity, is the position of the load with respect to the crown of the cavity
Summary
Cavities of significant dimensions may exist in natural rocks, mainly in evaporitic and carbonate rocks and in volcanic rocks. These cavities can represent a grave risk when a shallow foundation, such as for a building, bridge or other structure, is builtonthem. This fact may substantially determine the calculation results of the foundations. This is a relatively frequent problem worldwide, given the vast areas where these types of rocks appear. The volcanic rocks are mainly located in the Canary Islands, where there are important networks of lava tubes in which safety and stability measures for the vaults must be maximised [4,5]
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