Grand Carre de Jaude: an exceptional building site of soil treatement by jet-grouting in the middle of a volcano

摘要

In the center town of Clermont-Ferrand, the building of real estate complex with 2 basement levels needed complicated substructure works. Because of the special geology and hydrogeology due to the volcano and its filling, the building designers were obliged to find very specific constructive solutions. During the stage of works the perimetral wall has been carried out from metal sheeting piles down a mixing-ground trench. In stage of use this wall has been reinforced by a concrete wall. To assure the bearing capacity, the equilibrium of the deep excavation and the retaining structures during scope of works and scope of services, a 3 meter thick injected bottom with secant jet-grounting columns and jet-grounting load-transfer colomns has been realized. To assure the 3 conditions of soil improving (bearing pressure, watertightness, increase of passive pressure) a specific target in terms of deformation unit, permeability and compression resistance, has been defined during the conception stage. At the begin of works, many testing boards have been used to confirm the type and characteristics for the concrete, diameters, resistance and deformation characteristics of the colomns, according to the types of soils (sandy, slity-clayey with some organic materials…). A program of works follow-up and control (compressive resistance, dilatometer, inclinometer, topography, water test, static loading test…) has been set up during the whole execution stage to achieve the earthworks and all substructure works.