Claudio Tamagnini

Coupled nonlinear thermo‐hydro‐mechanical finite element simulations were carried out to investigate the behavior of energy micropiles subjected to thermal loading cycles. Two kinds of problems were analyzed: The case of an isolated micropile, for which comparison with previous research on medium‐size isolated energy pile is provided, and the case of large groups of micropiles, with the aim of investigating the interaction effects. In both problems, micropiles were considered installed in a thick layer of very soft, saturated clay, characterized by isotropic or anisotropic hydraulic conductivity. Two advanced existing hypoplastic models, one incorporating the thermal softening feature, were used to describe the clay behavior in both problems. The settlements of the micropile head were found to increase during thermal cycles under constant mechanical load, showing a sort of ratcheting. For micropile groups, the settlement increase rate was faster as the spacing between micropiles was reduced. The excess pore water pressures developed at the micropile‐soil interface played a significant role on the deformation and displacement fields of the soil‐micropile systems, especially in the case of micropile groups, affecting the shear strength developed at the micropile‐soil interface. The consolidation process was faster when the hydraulic conductivity was anisotropic, meaning that the development of excess pore water pressure was reduced in this case. As the spacing between the micropiles increased, i.e., as thermal interaction decreased, the heat flux exchanged by a micropile of the group during one cycle approached the heat flux exchanged by an isolated micropile in the same period.

The mechanics of cone penetration in CPTu tests in a silty clay was investigated with the PFEM, using a recently proposed finite deformation plasticity model for natural geomaterials – the FD MILAN model – which incorporates the bond strength Pt as an internal variable quantifying the effects of structure, and is equipped with a characteristic length ℓc to regularize the numerical solutions in presence of strain localization. The results of the PFEM simulations show that the deformations around the piezocone are strongly affected by the characteristic length. In particular, when ℓc/R is sufficiently small, the deformation field may be affected by clearly visible shear bands. The soil around the piezocone is subjected to a very strong destructuration process, which leads to the complete loss of bond strength in a large region around the cone tip and shaft. As a consequence, the use of literature empirical correlations in the interpretation of the CPTu test data in heavily structured soils could result in a significant underestimation of both the undrained strength and the overconsolidation ratio of the soil deposit.

This paper presents a critical review of results obtained over the last two decades concerning the application of shear band analysis to CloE and K-hypoplastic constitutive equations. A detailed scrutiny of the work done on this subject, along almost independent lines, by the research groups in Grenoble and in Karlsruhe shows that the general results outlined by Chambon & Desrues (1985) apply to both classes of constitutive models, and that the different approaches to shear band analysis in hypoplasticity can be reconciled, provided that no additional constitutive assumptions for the material inside the band are introduced.

Two classes of stress-point algorithms are used to integrate the incrementally non linear constitutive model CLoE, recently developed for granular materials. The paper compares the performance of the algorithms in terms of both accuracy and efficiency. An extensive program of numerical tests on some particular strain paths has been conducted in order to assess the effects of such variables as strain increment size and assumed error tolerance, as well as strain increment direction and initial stress state.