Vertical-Facing Loads in Steel-Reinforced Soil Walls

The paper investigates the influence of backfill soil, foundation soil, and horizontal joint vertical compressibility on the magnitude of vertical loads developed in steel-reinforced soil concrete panel retaining walls at the end of construction. Measurements of toe loads recorded from instrumented field walls are reviewed and demonstrate that vertical toe loads can be much larger than the self-weight of the facing. In extreme cases, these loads can result in panel-to-panel contact leading to concrete spalling at the front of the wall. Vertical loads in excess of panel self-weight have been ascribed to relative movement between the backfill soil and the panels that can develop panel-soil interface shear and downdrag loads at the connections between the panels and the steel-reinforcement elements. A two-dimensional finite-element model is developed to systematically investigate the influence of backfill soil, foundation soil, bearing pad stiffness, and panel-soil interaction on vertical loads in the panel facing. The results show that an appropriately selected number and type of compressible bearing pads can be effective in reducing vertical compression loads in these structures and at the same time ensure an acceptable vertical gap between concrete panels. The parametric analyses have been restricted to a single wall height (16.7 m) and embedment depth of 1.5 m, matching a well-documented field case. However, the observations reported in the paper are applicable to other similar structures. The general numerical approach can be used by engineers to optimize the design of the bearing pads for similar steel-reinforced soil wall structures using available commercial finite-element model packages together with simple constitutive models. (C) 2013 American Society of Civil Engineers.139914191432Universitat Politecnica de Catalunya-BarcelonaTech (UPC)Ministry of Education and Innovation of Spain [BIA2010-20789-C04-01]Ministry of Education and Innovation of Spain [BIA2010-20789-C04-01

Advective gas flow in bentonite: Development and comparison of enhanced multi-phase numerical approaches

Understanding the impact of repository gas, generated from degradation of waste and its interaction with the host rock, is essential when assessing the performance and safety function of long-term disposal systems for radioactive waste. Numerical models based on conventional multi-phase flow theory have historically been applied to predict the outcome and impact of gas flow on different repository components. However, they remain unable to describe the full complexity of the physical processes observed in water-saturated experiments (e.g., creation of dilatant pathways) and thus, the development of novel representations for their description is required when assessing fully saturated clay-based systems. This was the primary focus of Task A within the international cooperative project DECOVALEX-2019 (D-2019) and refinement of these approaches is the primary focus of this study (Task B in the current phase of DECOVALEX-2023). This paper summarises development of enhanced numerical representations of key processes and compares the performance of each model against high-quality laboratory test data. Experimental data reveals that gas percolation in water-saturated compacted bentonite is characterised by four key features: (i) a quiescence phase, followed by (ii) the gas breakthrough, which leads to a (iii) peak value, which is then followed by (iv) a negative decay. Three models based on the multiphase flow theory have been developed. These models can provide good initial values and reasonable responses for gas breakthrough (although some of them still predict a too-smooth response). Peak gas pressure values are in general reasonably well captured, although maximum radial stress differences are observed at 48 mm from the base of the sample. Here, numerical peak values of 12.8 MPa are predicted, whereas experimental values are about 11 MPa. These models are also capable of providing a reasonable representation of the negative pressure decay following peak pressure. However, other key specific features (such as the timing of gas breakthrough) still require a better representation. The model simulations and their comparison with experimental data show that these models need to be further improved with respect to model parameter calibration, the numerical representation of spatial heterogeneities in material properties and flow localisation, and the upscaling of the related physical processes and parameters. To further understand gas flow localisation, a new conceptual model has been developed, which shows that discrete channels can possibly be induced through the instability of gas-bentonite interface during gas injection, thus providing a new perspective for modeling gas percolation in low-permeability deformable media