Analysis of the influence of cyclic loading on the settlement of clay base of tank

Introduction. The soils at the base of tank foundations are subject to loading and unloading cycles during tank filling and emptying. The construction of such constructions is often carried out in areas with overwatered clay soils. The purpose of the study is to investigate the change in vertical deformations of water-saturated clays under the influence of “loading – unloading” cycles. This will make it possible to identify the values of additional settlements of water-saturated clay subgrade under loading and unloading cycles. Materials and methods. A series of laboratory tests was performed in an odometer with cycles of loading and unloading with specimens of firm, soft-firm and very soft clays. The values of mechanical parameters of the studied clays obtained during laboratory tests were used in numerical calculations of the settlement of the base of a vertical steel tank in the PLAXIS 2D software package. Results. The influence of clay consistency on the value of settlement under cyclic loading of samples in a compression device was studied. The ratio of plastic and elastic deformations was determined for clays of firm, soft-firm and very soft consistency. Additional settlement of clays with firm, soft-firm and very soft consistency caused by cyclic loading and unloading (within the first 10 cycles) amounted to 10 % of the total soil settlement. The results of numerical experiments showed that the additional settlement of the tank base at 20 cycles of loading and unloading amounted to 2.4–4.1 % of the total settlement. Conclusions. Laboratory and numerical studies have shown that loading and unloading cycles of water-saturated clays lead to the development of additional settlement. The amount of additional settlement depends on the number of cycles and the consistency of the clay. During the whole period of the tank operation the number of filling and emptying cycles can be more than 2000, therefore, additional soil deformations in the foundation base should be expected.