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The consolidation of soils is important to geotechnical engineering practice, such as when assessing the rate of settlement of shallow foundations, embankments, and landfills. In this paper, numerical analyses are performed to study the consolidation of unsaturated soils. The variations of excess pore-air and pore-water pressures and settlement with time are established by solving the governing equations. The flow and deformation of the different constituents of an unsaturated soil are fully coupled in the governing equations. The dependency of soil parameters, including the coefficients of permeability for air and water phases and the constitutive coefficients, is allowed to vary as changes to soil volume and suction occur. The effect of hydraulic hysteresis is investigated by considering different initial locations of the hydraulic states on the soil-water characteristic curve. It is shown that the different initial locations of hydraulic states result in different normalized instantaneous settlements and different initial excess pore pressures. The influence of the degree of saturation is also studied. It is shown that for the lowest degree of saturation, the most significant instantaneous settlement occurs and the total consolidation time is longest. The results of this study provide new insights into unsaturated soil consolidation. This is important because the hydraulic loading history and degree of saturation of the soil should be considered when assessing the rate and magnitude of consolidation settlement.

The mechanics of water retention in unsaturated granular media is of critical importance to a broad range of disciplines including soil science, geotechnical engineering, hydrology and agriculture. Fundamental to water retention is the relationship between degree of saturation and suction, referred to as the water retention curve (WRC). The majority of WRC models are empirically based and seldom incorporate physically meaningful parameters. This study presents an analytical model for the WRC that considers separate contributions from fully filled pores and partially filled pores containing liquid bridges. A recently established unique k-gamma pore volume distribution function for randomly assembled monodisperse granular materials is adopted to determine the contributions of fully filled pores. Calculation of the contribution of residual pore water retained in partially filled pores is undertaken by representing pores as individual cells shaped as platonic shapes of various sizes and determining the volume of all liquid bridges suspended between particles within the pore cells. Weighting factors for the various cell types are obtained from the pore volume distribution to determine the relative contribution of different pore cell geometries to the total residual pore water. The combined model accurately describes experimental data for monodisperse spherical glass beads for both wetting and drying, even though the underlying assumptions do not reflect exactly the complex, interconnected and highly irregular geometry of the pore space. A single parameter provides the lateral shift between the wetting and drying curves. The results of this study provide a geometric understanding of the mechanisms of water retention in granular media.

The anisotropy associated with the contact network in granular media is investigated. A unique expression for mobilised internal friction has been discovered using numerical simulations of monodisperse and polydisperse spherical assemblies under two-way cyclic axisymmetric and simple shear load paths. This uniqueness is described by a linear relationship between the macroscopic stress ratio and the geometric configuration of only the strong and non-sliding contacts, where strong contacts are those with a normal force magnitude greater than the mean normal force. A stress–force–fabric expression for arbitrary partitions of the contact network was derived analytically, providing a mathematical connection between the macroscopic state of stress and interparticle characteristics. Numerical simulations revealed that only strong and non-sliding contacts provided a non-zero contribution to the stress–force–fabric expression. Previous studies suggest the dominance of force anisotropy in the complete contact network, but this study indicates that geometric anisotropy of contacts is the dominant contributor in the stress–force–fabric relationship when particular subsets of the contact network are considered.

© The Authors, published by EDP Sciences, 2017. This paper considers the anisotropy associated with the interparticle contact network and interconnected pore space, which is quantified through a scalar quantity based on the fabric tensor. The study focused on the anisotropy associated with subsets of contacts and pores. It is shown that the stress ratio can be directly related to the geometric anisotropy of strong and non-sliding contacts, and that the anisotropy of pores is correlated with the anisotropy of contacts.

Cutter soil mix (CSM) walls are created by mixing soils with cement and bentonite slurry to produce a soil-cement mix with modest tensile and compressive strengths. CSM walls may be stabilised using internal steel beams. Presented here are the results of a CSM wall field trial and laboratory testing programme. Polypropylene fibres were added to the soil-cement mix in order to explore whether or not fibres increase wall resistance to bending, reduce the required quantity of steel and thus reduce cost and embodied carbon. The trial involved mixing fibres into a single CSM wall panel. Samples were taken and tested at 28 days and 2 years to assess unconfined compressive strengths, indirect tensile strengths and flexural tensile strengths. The fibre orientation distribution was also assessed. The testing confirmed that the mixing technique resulted in a uniform orientation distribution of fibres and significantly improved tensile strength. Also presented is a hypothetical design of a fibrereinforced CSM wall supporting an 8 m excavation to show that the steel quantity can be reduced while maintaining stability. A cost analysis, limited to the steel beams, fibres and anchors, shows that a CSM wall with 0.5% fibres by dry weight has a cost of $2930 AUD per linear metre of wall. This is significantly lower than the cost when no fibres were included, which is $4070 AUD per linear metre. The embodied carbon analysis, limited to the steel beams, fibres, cement and anchors, is also presented. The analysis shows that a CSM wall with 0.5% fibres by dry weight produces an emissions saving (having a total of 755 kgCO2e/m3) compared to the CSM wall without fibres (having a total of 929 kgCO2e/m3). Increasing the fibre content from 0.5% does not significantly alter the cost or embodied carbon when the cement content is constant. However, a higher fibre content does have the potential to reduce embodied carbon and cost further if an adequate tensile strength can be achieved with a low

Most shallow foundations are built in unsaturated soils above the groundwater table. Being able to evaluate the bearing capacity of these foundations is important in foundation design because the conventional bearing-capacity equations, which were developed for soils in saturated or dry states, are not directly applicable. This paper presents an effective stress-based finite-element formulation and shows how it can be used to compute the bearing capacities of shallow foundations in unsaturated soils. The mechanical behavior of unsaturated soil is described using the elastic-perfectly plastic Mohr-Coulomb model. It is shown that suction and hydraulic hysteresis directly impact the bearing capacity of unsaturated soil foundations. The effects of three different drainage conditions are also investigated, namely, a constant suction, a constant moisture content, and a constant contribution of suction to the effective stress and strength condition (also referred to as a constant xs condition). It is shown that the constant xs condition provides a good approximation to the other two and may simplify calculation of bearing capacity. When foundation loading occurs quickly, meaning a condition of constant moisture content prevails, a constant xs condition can be assumed without loss of significant accuracy. The xs magnitude can be taken as being equal to the initial in situ value.

This paper addresses the problem of hang-up in ore passes. A hang-up in a plane ore pass is analysed using the methods of discontinuous stress and velocity fields. The system consisting of broken ore material and a stiff ore pass wall is idealised as a plastic-rigid continuum satisfying the Mohr-Coulomb failure criterion and an associated flow rule. The influence of moisture in the ore, and its associated suction, is accounted for using the effective stress concept for unsaturated geomaterials. A simple failure mechanism consisting of three rigid blocks is assumed which is consistent with a bursting failure type and with the existence of a compressive arch underneath the hang-up section. Stress equilibrium and kinematic restrictions enable the derivation of simple algebraic expressions governing the stability of a hang-up. The separate influences of suction and cohesion are evident in the derived expressions. The paper then applies the derived expressions to a hang-up problem. Strength properties of an ore are determined experimentally using triaxial tests. The way water is retained in the ore is described using its fractal characteristics. It is shown how the ore pass size for hang-up instability is strongly dependant on moisture content and suction. An increase in suction increases the minimum ore pass dimension needed to avoid hang-up formation.

We examine spatial variations in the weekday-weekend pattern of NO 2 over the Los Angeles metropolitan area using the Ozone Monitoring Instrument (OMI) and then compare the observations to calculations using the WRF-Chem model. We find that the spatial pattern of the weekday-weekend variations of the NO2 column in the model is significantly different than observed. A sensitivity study shows that the contrasting spatial pattern of NO2 on weekdays and weekends is a useful diagnostic of emissions and chemistry. These improvements suggest that constraints from space-based observations of the processes affecting urban photochemistry (e.g., spatial patterns of emissions, ratios of VOC to NOx emissions, rate constants) are possible at a level of detail not previously described. © 2014 Author(s).

The San Joaquin Valley (SJV) experiences some of the worst ozone air quality in the US, frequently exceeding the California 8 h standard of 70.4 ppb. To improve our understanding of trends in the number of ozone violations in the SJV, we analyze observed relationships between organic reactivity, nitrogen oxides (NOx), and daily maximum temperature in the southern SJV using measurements made as part of California at the Nexus of Air Quality and Climate Change in 2010 (CalNex-SJV). We find the daytime speciated organic reactivity with respect to OH during CalNex-SJV has a temperature-independent portion with molecules typically associated with motor vehicles being the major component. At high temperatures, characteristic of days with high ozone, the largest portion of the total organic reactivity increases exponentially with temperature and is dominated by small, oxygenated organics and molecules that are unidentified. We use this simple temperature classification to consider changes in organic emissions over the last and next decade. With the CalNex-SJV observations as constraints, we examine the sensitivity of ozone production (PO3) to future NOx and organic reactivity controls. We find that PO3 is NOx-limited at all temperatures on weekends and on weekdays when daily maximum temperatures are greater than 29 °C. As a consequence, NOx reductions are the most effective control option for reducing the frequency of future ozone violations in the southern SJV. © 2014 Author(s).

We examine spatial variations in the weekday-weekend pattern of NO 2 over the Los Angeles metropolitan area using the Ozone Monitoring Instrument (OMI) and then compare the observations to calculations using the WRF-Chem model. We find that the spatial pattern of the weekday-weekend variations of the NO2 column in the model is significantly different than observed. A sensitivity study shows that the contrasting spatial pattern of NO2 on weekdays and weekends is a useful diagnostic of emissions and chemistry. These improvements suggest that constraints from space-based observations of the processes affecting urban photochemistry (e.g., spatial patterns of emissions, ratios of VOC to NOx emissions, rate constants) are possible at a level of detail not previously described. © 2014 Author(s).

The San Joaquin Valley (SJV) experiences some of the worst ozone air quality in the US, frequently exceeding the California 8 h standard of 70.4 ppb. To improve our understanding of trends in the number of ozone violations in the SJV, we analyze observed relationships between organic reactivity, nitrogen oxides (NOx), and daily maximum temperature in the southern SJV using measurements made as part of California at the Nexus of Air Quality and Climate Change in 2010 (CalNex-SJV). We find the daytime speciated organic reactivity with respect to OH during CalNex-SJV has a temperature-independent portion with molecules typically associated with motor vehicles being the major component. At high temperatures, characteristic of days with high ozone, the largest portion of the total organic reactivity increases exponentially with temperature and is dominated by small, oxygenated organics and molecules that are unidentified. We use this simple temperature classification to consider changes in organic emissions over the last and next decade. With the CalNex-SJV observations as constraints, we examine the sensitivity of ozone production (PO3) to future NOx and organic reactivity controls. We find that PO3 is NOx-limited at all temperatures on weekends and on weekdays when daily maximum temperatures are greater than 29 °C. As a consequence, NOx reductions are the most effective control option for reducing the frequency of future ozone violations in the southern SJV. © 2014 Author(s).