Foundation of the 'Los Tilos' arch bridge in La Palma Island

摘要

There are no simple procedures to estimate the bearing capacity of direct foundations on rock due to its anisotropy, as the criteria have to take into account different features concerning the rock discontinuities ( spacing, orientation, opening, persistence...) as well as other aspects concerning the rock matrix, particularly its strength when it is low. In this sense, the volcanic formations of the Canary Islands pose important difficulties to the designer of foundations given their highly anisotropic fabric, which is the result of a complex origin where the basalt sheets alternate with fragmentary material of pyroclastic nature. This volcanic building is frequently intersected by old vents, in the guise of pipes plugged with broken fragments of low compacity. In a valley of highly dissected steep slopes of such geology an arch bridge has been designed and built with a span between supports of 250 m. This paper describes the analysis that was carried out to take into account the particularities of rock anisotropy and the foundation geometry in very steep slopes. The construction problems are also addressed in the paper, describing the grouting treatment that was needed in one of the supports due to the presence of an old vent.