This paper describes a comprehensive set of experimental data concerning the one-dimensional, time-dependent behaviour of organic clays and peats. The experimental analyses concerned three different peaty soils (either undisturbed or remoulded) with fairly different index properties (the organic content ranged between 20% and 70%) that were submitted to various kinds of one-dimensional consolidation tests. The experimental data confirm that peats and organic clays have many aspects of their delayed behaviour in common. The main outcome of this work is a good-quality, comprehensive and meaningful set of data for use in developing and calibrating constitutive models for simulating the delayed response of soils, with an emphasis on organic clays and peats.

The use of passive piles can be an effective method for stabilising unstable slopes. Unfortunately, no rigorous analytical solution has so far been proposed for assessing the ultimate, lateral pile–soil pressure distribution under drained conditions for the design of passive piles in a slope. The present work focuses on the reliability of a finite-element model (FEM) used to assess the ultimate limit state conditions of passive piles in frictional soils. The paper also provides an estimate of the ultimate load of a single pile and a row of piles in a slope of frictional soil. The results are obtained with a series of two-dimensional analyses (evaluating the role of boundary conditions) and three-dimensional analyses on an infinite slope (to evaluate the role of the embedment ratio, the influence of slope inclination and the arching effects in pile rows). The analyses were performed using the Abaqus finite-element code associated with a couple of user-defined subroutines for defining the initial and boundary stress conditions. The computed ultimate loads are compared with theoretical findings obtained from a simple extension to drained conditions of Viggiani's approach to undrained conditions. Depending on pile embedment and soil layer thickness and strength, three rupture mechanisms are discussed from a theoretical standpoint. The FEM converges very efficiently and reliably in one rupture mechanism and for deep pile embedments, whereas convergence is slow and difficult in the other cases and requires a very high elastic soil stiffness.

Soil-retaining structures, such as anchored, gravity and diaphragm walls can be used effectively to stabilise unstable, shallow slopes. The present work focuses on assessing the passive soil pressure that can be mobilised by passive and active retaining structures used for slope stabilisation purposes; passive structures are taken to be those left free to move and find their own equilibrium against the soil pressure, and active structures those equipped with pre-stressed ground anchors that lead to an upward movement against the unstable sloping soil. The numerical analyses performed with the Abaqus finite-element code and the comparison drawn with available theoretical solutions show that, in the case of passive retaining structures, the maximum horizontal soil pressure that can be exerted by the unstable soil layer on the retaining structure is independent of soil–wall friction and coincides with Rankine's passive value. However, in the case of active retaining structures, the passive soil pressure may be much greater than Rankine's value and should be evaluated as suggested by Eurocode 7 (geotechnical design). Such a high soil pressure is only meaningful for the purpose of sizing the retaining structure, however, because (just uphill from the stress region perturbed by the soil–wall friction and ground anchor) the stress state at rupture coincides with Rankine's theory in the case of active retaining structures too. Thus, even in the case of anchored retaining structures, the maximum soil pressure that can be exploited for slope stabilisation coincides with Rankine's value. These conclusions have important consequences for the dimensioning of soil-retaining structures for slope stabilisation purposes. A practical application for slope stabilisation is discussed in the final part of the paper.

Accurate modeling of the time-dependent behavior of geomaterials is of great importance in a number of engineering structures interacting with soft, highly compressible clay layers or with organic clays and peats. In this work, a uniaxial constitutive model, based on Perzyna's overstress theory and directly extendible to multiaxial stress conditions, is formulated and validated. The proposed constitutive approach essentially has three innovative aspects. The rst concerns the implementation of two viscoplastic mechanisms within Perzyna's theory in order to distinguish between short-term (quasi-instantaneous) and long-term plastic responses. Similarly, elastic response is simulated by combining an instantaneous and a long-term viscous deformation mechanism. The second innovative aspect concerns the use of a bespoke logarithmic law for viscous eects, which has never been used before to simulate delayed soil behavior (as far as the authors are aware). The third concerns the model's extensive validation by simulating a number of dierent laboratory test results, including conventional and unconventional oedometer tests with small and large load increments/decrements and wide and narrow loading/unloading cycles, constant rates of stress and strain tests, and oedometer tests performed in a Rowe consolidation cell with measurement of pore pressure dissipation.