The foundation of a 40-storey tower in jointed basalt

A 132.70-m-high tower (above foundation) has been successfully completed at Tenerife Island. The foundation of the tower, a 2-m-thick reinforced concrete slab, is supported by jointed, vesicular and weathered basalt, and scoria. A three-dimensional, elastic finite element program has permitted to calculate the displacements of the tower and the stresses in the slab. The installation of rod extensometers at different depths below the slab and clinometers at the lower basement has provided comparison between measured and calculated displacements, and the estimation of in situ deformation moduli. A first stage prediction (before construction) has allowed establishment of an upper limit, based upon pressuremeter modulus, and a lower limit, based upon Bieniawski's equation [The geomechanics classification in rock engineering applications. In: Proceedings of the fourth cong. ISRM congress, Montreux, vol. 2. 1979. p. 41–48], of the settlements of the tower slab. The geometric mean of these values comes close to the measured settlement. The moduli deduced from the simple empirical equation proposed by Gokceoglu et al. [Predicting the deformation modulus of rock masses: a comparative study. Int J Rock Mech Min Sci 2003;40:701–10], and Hoek and Brown [Practical estimates of rock mass strength. Int J Rock Mech Min Sci 1997;40:701–10] as a function of GSI provide a good fit with the measured settlements in this type of rock. A good correlation is also obtained with the empirical equation presented by Verman et al. [Effect of tunnel depth on modulus of deformation of rock mass. Rock Mech Rock Eng 1997;30(3):121–7] that incorporates the influence of the confining stress in the deformation modulus.