Viscoplastic cyclic degradation model for soft natural soils

Cyclic loading affects the long-term response of geostructures build on natural soils. Soft soils are particularly susceptible to the development of large deformations, induced by the repetitive nature of loading. A new viscoplastic cyclic accumulation model is presented, which is an hierarchical extension of the Creep-SClay1S model, to model the long-term permanent deformation resulting from undrained cyclic loading of natural soft clays. The cyclic cumulative strains are incorporated by means of an additional viscoplastic multiplier. This cyclic viscoplastic multiplier adds four additional model parameters that are derived from undrained cyclic triaxial tests. The model is calibrated using experimental data from undrained cyclic triaxial tests performed on high quality block samples of natural Ons\uf8y clay, at different average shear stresses, shear stress amplitudes and loading periods. The accuracy of the proposed model is demonstrated by comparing the element level simulations with the experimental data. The applicability of the proposed model is further illustrated with a boundary value problem, where an embankment submitted to cyclic loading is simulated. The use of the new model enables the simulation of the response of cyclic loaded foundations on soft soils, where the serviceability limit state over a long period of time is governing the design

Low amplitude strain accumulation model for natural soft clays below railways

An improved constitutive model for strain accumulation of natural clays under undrained cyclic loading is presented. The proposed model includes a formulation for the non-linear small-strain stiffness in the overconsolidated regime, along with a modified hardening law for cyclic accumulation to improve the tracking of strain accumulation at small stress amplitudes. To calibrate and validate the proposed model, a series of laboratory tests were conducted to study the cyclic response of natural Swedish clays, the effect of loading amplitude and pre-shearing history. Good agreement between predicted and measured accumulated axial strains and excess pore water pressures was obtained with different loading amplitudes. The findings reveal that the undrained pre-shearing has a substantial impact on the rate of accumulated strain, with pre-sheared samples exhibiting lower resistance values. The proposed and validated model opens up possibilities to study the monotonic and non-monotonic quasi-static response of soft clays below railway embankments over the lifetime of the structure, i.e. including the effects of construction, operation and decommissioning

The impact of soil variability on uncertainty in predictions of induced vibrations

Soil is by nature a variable, non-homogeneous material, which has implications for engineering problems involving wave propagation. This paper investigates the impact of the spatial heterogeneity of the stiffness of the soil on the three-dimensional wave propagation. A dynamic Random Finite Element Model is presented in which the soil variability is modelled by means of random fields, applied to the Young\u27s modulus of the soil, following a Monte-Carlo approach. The results show the importance of accounting for soil variability when making predictions on the maximum vibration level. Deterministic analysis is demonstrated to be insufficient when quantifying the maximum vibration level, because no information on the expected variability of the maximum vibration level is obtained. Furthermore, the scale of fluctuation and anisotropy of the random field strongly impact the estimation of the maximum vibration level, and the time of occurrence

Towards network assessment of permanent railway track deformation

The permanent railway track deformation caused by regular train traffic is important for infrastructure managers and railway contractors, as it determines the railway track quality. Although several successful approaches have been made to address the topic of the permanent railway track deformation, these have only been applied at specific locations, and have not yet been successfully applied at a network level. This paper presents a methodology that can be applied at the network level, by making use of a stochastic subsoil model to characterise the subsoil uncertainty and variability along the railway line, and by combining it with a dynamic train-track model and a cumulative cyclic deformation model. This methodology is illustrated by analysing a railway track section of 9 km in the Netherlands. The effects of the train service, such as train speed and axle loads, on the permanent deformation of the track are quantified. The proposed methodology has been partially validated against results of the dynamic stiffness obtained during the passage of a measurement train. The results illustrate the added value of this methodology for infrastructure managers and railway contractors as it allows for the quantification, at network level, of the consequences of train service changes for the future state of the railway network

Application of a second-order implicit material point method

In this work, we present the application of a newly developed implicit second-order Material Point Method (MPM) on offshore geotechnical applications. The presented second-order MPM uses a special set of piecewise quadratic shape functions to circumvent the well-known issue of producing zero nodal mass contributions. To mitigate the effect of the standard MPM to produce highly oscillating stresses across cell interfaces, we have carried over our ideas obtained from the derivation of the second-order MPM to the Dual Domain Material Point (DDMP) Method, too. The resulting second-order DDMP Method produces a smoother stress distribution across the entire computational domain while being able to profit from the improved convergence rates of second-order finite elements. In a numerical example from geotechnical engineering applications, we illustrate the practical application of our enhanced Material Point and DDMP Methods by simulating a cone penetration