CASE STUDIES OF STONE COLUMNS IMPROVEMENT IN SEISMIC AREAS
Soil improvement with stone columns is often implemented in seismic areas in particular as a countermeasure against liquefaction. The efficiency of stone columns can be explained by the compaction effect during their execution, by the reduction of the seismic stress on the soil, and by their draining effect as well. A historical evolution of the first realisations is presented, followed by an inventory of the observed performance of such systems in seismic conditions. Then, recent applications of stone columns combined with pile foundations are presented. Key-Words: seismic area, stone columns, liquefaction, case study, pile foundation.
NUMERICAL STUDY OF THE SOIL-STRUCTURE INTERACTION DURING STRONG EARTHQUAKES
The non linear dynamic soil-structure interaction of three reinforcement concrete building frames (3, 6, and 12 levels) subjected to strong earthquakes is studied using the FEM. The soil behaviour is modelled with hypoplastic and visco-hypoplastic relations which are able to model the response of cohesionless and cohesive soils under alternating and dynamic loading, for drained and undrained conditions. The behaviour of reinforced concrete is modelled using an elastic-plastic constitutive law for the plain concrete and elastic-ideal plastic for the steel bars. It is assumed that the buildings are founded on a layered ground from Treasure Island, San Francisco Bay (Seed et al., 1991). An acceleration record at Yerba Buena Island during the Loma Prieta 1989 earthquake is used as bedrock excitation. In order to quantify the influence of the soil-structure interaction, the ground motion at the foundation depth due to the bedrock excitation is first calculated without considering the structure (“free field acceleration”). This ground motion is then applied to the base of the buildings to evaluate the internal forces and deflections of the structure. In a third analysis, the dynamic response of both structure and soil due to the same bedrock excitation is considered. Based on the comparison of the numerical results it is concluded that the proposed numerical model is a powerful tool to quantify the influence of soil-structure interaction on the response of buildings during strong earthquakes.
The Inca Occupation of the South Coast of Peru
like the others, however; it forks into several nearly parallel ravines of which the largest are Huayuri, Rio Grande-Palpa, Ingenio (called Collao in ancient times), Nasca proper (the ancient Caxamarca), Taruga, and Poroma. Due to peculiarities of the local topography, the irrigated areas in Ica and the ravines of Nasca are located inland, at the foot of the mountains, rather than at the mouths of the rivers as is more usual in Peruvian coastal valleys. No sharp natural or cultural boundary separates the valley of Chincha from the valleys of Cafiete (ancient Huarco and Runahuana), Asia, and Mala, the next valleys going up the coast to the northwest. At the other end of the area we are considering, however, there is a sharp break; beyond Yauca the Andean foothills reach out to the sea, natural conditions are quite different, and there are important differences in the archaeological picture as well. The historical sources which mention the south coast are not particularly helpful, except in so far as they provide us with a few dates. To begin with, no chronicler gives an explicit account of the political organization of the south coast at the time it came into contact with the Incas. It can, perhaps, be inferred from Cabello Balboa's statements about common policy toward the Inca invaders that there was some sort of political connection between the valleys of Mala, Cafiete, and Chincha, but the connection need have been no more than a temporary military alliance. Cabello makes no mention at all of Pisco. The valleys of Ica, Nasca, and 125