Off-fault Plasticity and Earthquake Rupture Dynamics: 1. Dry Materials or Neglect of Fluid Pressure Changes

We analyze inelastic off-fault response during earthquakes. Spontaneous crack-like rupture, with slip weakening, is modeled in 2-D plane strain using an explicit dynamic finite element procedure. A Mohr-Coulomb type elastic-plastic description describes the material bordering the fault. We identify the factors which control the extent and distribution of off-fault plasticity during dynamic rupture. Those include the angle with the fault of the maximum compressive prestress, the seismic S ratio, and the closeness of the initial stress state to Mohr-Coulomb failure. Plastic response can significantly alter the rupture propagation velocity, delaying or even preventing a transition to supershear rupture in some cases. Plastic straining also alters the residual stress field left near the fault. In part 1, we consider “dry” materials bordering the fault, or at least neglect pore pressure changes within them. Part 2 addresses the effects of fluid saturation, showing that analysis procedures of this part can describe undrained fluid-saturated response. Elastic-plastic laws of the type used are prone to shear localization, resulting in an inherent grid dependence in some numerical solutions. Nevertheless, we show that in the problems addressed, the overall sizes of plastic regions and the dynamics of rupture propagation seem little different from what are obtained when we increase the assumed plastic hardening modulus or dilatancy parameter above the theoretical threshold for localization, obtaining a locally smooth numerical solution at the grid scale. Evidence for scaling of some localization features with a real (nongrid) length scale in the model is also presented.Earth and Planetary SciencesEngineering and Applied Science

Long Term Failure in Compacted Clay Slopes

The results of field, laboratory, and analytical investigations of recurring slope failures along the Mississippi River Levee are presented. Observations from slide trenching operations are described. Laboratory measured shear strengths are compared to effective strengths at failure back-calculated for two slides. Factors influencing the long term behavior of the levee materials and the mechanism of failure are discussed

Lessons learned from a Tiger Worm Toilet implementation project in Sierra Leone

This paper discusses the implementation of Tiger Worm Toilets (TWTs) as a sustainable alternative to pit latrines in areas with challenging environmental conditions. The study was carried out in Koinadugu, Sierra Leone, where TWTs were installed in 200 households, providing safe sanitation for approximately 1,200 individuals within a 17-month period. The study reveals that TWTs offer several benefits over traditional pit latrines, including higher cost efficiency. Despite some setbacks, TWTs have been well-received by the local communities, resulting in a significant reduction in open defaecation in areas where latrines are not viable. The study presents areas of further research and concludes with recommendations for future TWT designs based on the lessons learned

Off-Fault Plasticity and Earthquake Rupture Dynamics: 2. Effects of Fluid Saturation

We present an analysis of inelastic off-fault response in fluid-saturated material during earthquake shear rupture. The analysis is conducted for 2-D plane strain deformation using an explicit dynamic finite element formulation. Along the fault, linear slip-weakening behavior is specified, and the off-fault material is described using an elastic-plastic description of the Drucker-Prager form, which characterizes the brittle behavior of rocks under compressive stress when the primary mode of inelastic deformation is frictional sliding of fissure surfaces, microcracking and granular flow. In this part (part 1), pore pressure changes were neglected in materials bordering the fault. In part 2, we more fully address the effects of fluid saturation. During the rapid stressing by a propagating rupture, the associated undrained response of the surrounding fluid-saturated material may be either strengthened or weakened against inelastic deformation. We consider poroelastoplastic materials with and without plastic dilation. During nondilatant undrained response near a propagating rupture, large increases in pore pressure on the compressional side of the fault decrease the effective normal stress and weaken the material, and decreases in pore pressure on the extensional side strengthen the material. Positive plastic dilatancy reduces pore pressure, universally strengthening the material. Dilatantly strengthened undrained deformation has a diffusive instability on a long enough timescale when the underlying drained deformation is unstable. Neglecting this instability on the short timescale of plastic straining, we show that undrained deformation is notably more resistant to shear localization than predicted by neglect of pore pressure changes.Earth and Planetary SciencesEngineering and Applied Science

Biodesalination: an emerging technology for targeted removal of Na+and Cl−from seawater by cyanobacteria

Although desalination by membrane processes is a possible solution to the problem of freshwater supply, related cost and energy demands prohibit its use on a global scale. Hence, there is an emerging necessity for alternative, energy and cost-efficient methods for water desalination. Cyanobacteria are oxygen-producing, photosynthetic bacteria that actively grow in vast blooms both in fresh and seawater bodies. Moreover, cyanobacteria can grow with minimal nutrient requirements and under natural sunlight. Taking these observations together, a consortium of five British Universities was formed to test the principle of using cyanobacteria as ion exchangers, for the specific removal of Na+ and Cl− from seawater. This project consisted of the isolation and characterisation of candidate strains, with central focus on their potential to be osmotically and ionically adaptable. The selection panel resulted in the identification of two Euryhaline strains, one of freshwater (Synechocystis sp. Strain PCC 6803) and one of marine origin (Synechococcus sp. Strain PCC 7002) (Robert Gordon University, Aberdeen). Other work packages were as follows. Genetic manipulations potentially allowed for the expression of a light-driven, Cl−-selective pump in both strains, therefore, enhancing the bioaccumulation of specific ions within the cell (University of Glasgow). Characterisation of surface properties under different salinities (University of Sheffield), ensured that cell–liquid separation efficiency would be maximised post-treatment, as well as monitoring the secretion of mucopolysaccharides in the medium during cell growth. Work at Newcastle University is focused on the social acceptance of this scenario, together with an assessment of the potential risks through the generation and application of a Hazard Analysis and Critical Control Points plan. Finally, researchers in Imperial College (London) designed the process, from biomass production to water treatment and generation of a model photobioreactor. This multimodal approach has produced promising first results, and further optimisation is expected to result in mass scaling of this process