Abstract

FE formulation of solid mechanics problems typically require iterative strategies to solve the resulting nonlinear system. Basic strategies with prescribed load values, such as the Newton-Raphson method, are not valid in the presence of structural snap-back due to material or geometric non-linearity. In this case, the most common strategy is the cylindrical Arc-length method, which prescribes the norm of displacements as constraint, in order to obtain the load factor increment. However, because the constraint is quadratic, additional non-trivial criteria need to be introduced for choosing the appropriate solution, and the wrong choice may lead to potential spurious unloading among other problems. As a way to overcome these shortcomings, alternative methods have been proposed which are based on an energy dissipation constraint. Constitutive dissipation may be considered as an always increasing “time” parameter with the advantage that the corresponding constraint equation is always linear. Iterative methods based on a dissipation constraint can be found in the literature.]. But most of those formulations are based on specific constitutive models. In contrast, the present formulation is general in the sense that it is valid for any constitutive model, as long as the model subroutine provides, additional to the standard output, also the appropriate values of dissipation and dissipation derivatives. Some application examples in concrete structures with progressive fractures are also provided to illustrate the performance of the model proposed

Abstract

Assessing soil properties through geotechnical tests is a crucial activity to understand its behaviour. Field tests serve as a good approach to characterize the geotechnical behaviour of materials according to their in-situ condition. However, the interpretation of these tests often relies on empirical correlations, which can become complex when dealing with soils with notable heterogeneity. This paper objective is to determine the strength parameters and discuss the consolidation effects for a heterogeneous tropical soil deposit using data from field tests with different rates of penetration and laboratory tests. A layer identified as low-strength soil classified as silty-sand to silty-clay exhibited partial drainage during a standard-rate cone penetration. The approach proposed by Randolph and DeJong (2012) was used to determine the penetration rate necessary to mobilize an undrained behaviour of the material, since the cone penetration results shown that the material is mostly contractive and clay-like. CPTu tests were also conducted with penetration rates of 60 mm/s and 100 mm/s, to proper estimate the undrained shear strength (Su). These tests reinforced the presence of a preconsolidated upper layer, enabling the estimation for the overconsolidation ratio (OCR). For the normally consolidated portion of the residual soil, rapid tests that achieved a normalized velocity (V) associated with distinctly undrained penetration were used to derive the undrained shear strength (Su), with a cone factor (Nkt) estimated from standard-rate tests available. The geotechnical parameters estimated were then compared to the laboratory data results showing a convergence with the parameters estimated by the field tests.

Abstract

This paper presents an interpretation of cyclic pressuremeter tests with pore pressure measurement performed at Larivot bridge site (French Guyana). In cohesive soils, test results are in accordance with the pressuremeter theory. The times at 50% dissipation correlate closely with those obtained from dissipation tests performed using a piezocone in the immediate vicinity.