Considering the extensive use of plasticity-based correlations in geotechnical practice to estimate soil parameters, the paper explores the influence of oven drying on the plasticity of two natural soft soil deposits: (i) Ballina clay, a marine structured soft clay from Australia and (ii) Bogotá clay, a lacustrine soft clay from Colombia. These two soils display extremely high plasticity when Atterberg limits are estimated using the natural soil. However, a strong reduction in liquid limit (up to 85%) is measured when the soil is oven dried before testing. The fact that the plastic limit seems insensitive to oven drying leads to a reduction in plasticity index close to 30% in Ballina clay and around 85% in the case of Bogotá clay. This behaviour is attributed to irreversible changes in soil fabric triggered by the oven drying process. The paper evaluates the consequences of neglecting oven drying effects in practice when adopting well-established relationships between mechanical parameters and soil plasticity. Plasticity-based estimates of index properties, compressibility and friction parameters are compared against values obtained from index tests as well as one-dimensional consolidation tests and ring shear tests.

This paper describes an experimental study aimed at evaluating the effects of mechanical and hydraulic paths on the compressibility and water retention behaviour of compacted loess from Xi'an, China. Suction-controlled oedometer tests, performed on statically compacted samples, are combined with mercury intrusion porosimetry (MIP) tests to evaluate the volumetric behaviour as well as the evolution of soil fabric for the compacted material. Oedometer test results are analyzed in the degree of saturation versus suction plane, using the water retention curve (WRC) for as-compacted material as reference. Negligible volume change, and hence no movement of the as-compacted WRC, is observed upon drying paths under low stresses. Wetting paths cause plastic deformations and hence the movement of the water retention curve. Soil densification shifts the WRC rightwards (in the degree of saturation versus suction plane), enlarging the air entry/air occlusion values and promoting steeper wetting and drying branches. MIP tests show that specimens subjected to drying and loading paths retain their as-compacted bi-modal pore size distribution (PSD). However, re-arrangement in soil fabric towards predominant mono-modal PSDs is observed in specimens wetted and loaded. Soil suction increases the compressibility and the yield stress of compacted loess. These experimental features are properly captured using an elasto-plastic constitutive model for nonactive soils that accounts for the evolution of the loading-collapse (LC) yield locus with plastic deformation.

The paper describes the results of an experimental study aimed at evaluating the evolution of the stress ratio under zero lateral deformation K 0 =σ h /σ v in compacted loess upon one-dimensional compression and wetting paths. The main features of a novel oedometer cell equipped with radial stress measurement are first presented. Statically compacted loess specimens where subjected to loading paths at constant water content as well as wetting at constant vertical stress in which measurements of horizontal stress were used in the estimation of K 0 . Results show an important dependency of the vertical stress prior to wetting on the measured stress ratio. This behaviour is caused by differences in soil fabric achieved before wetting. Experimental results are compared against previous studies of compacted loess behaviour.

The paper describes the results of an experimental study aimed at evaluating the evolution of the stress ratio under zero lateral deformation K-0=sigma(h)/sigma(v) in compacted loess upon one-dimensional compression and wetting paths. The main features of a novel oedometer cell equipped with radial stress measurement are first presented. Statically compacted loess specimens where subjected to loading paths at constant water content as well as wetting at constant vertical stress in which measurements of horizontal stress were used in the estimation of K-0. Results show an important dependency of the vertical stress prior to wetting on the measured stress ratio. This behaviour is caused by differences in soil fabric achieved before wetting. Experimental results are compared against previous studies of compacted loess behaviour.

Considering the extensive use of plasticity-based correlations in geotechnical practice to estimate soil parameters, this paper evaluates the influence of pore fluid salinity and soil drying on the plasticity of Ballina clay, a estuarine soft clay from northern New South Wales (Australia). A comprehensive experimental study which includes controlled leaching/salinisation paths applied to natural (remoulded) as well as oven-dried clay prior to the estimation of the Atterberg limits is presented. Plasticity tests are complemented with chemical analysis of the pore fluid carried out to evaluate the processes involved in the leaching/salinisation mechanisms for remoulded and oven-dried clay. Strong dependency of liquid limit on pore fluid salinity and oven-drying are observed in Ballina clay. Leaching modifies the soil fabric from an initially saline-sodic flocculated towards a normal flocculated arrangement. The experimental results show that changes in soil plasticity upon leaching are largely reversible upon salinisation paths. Oven-drying promotes the stacking of clay minerals (aggregation) which in turn reduces the water absorption capacity of the clay. The consequences of neglecting both salinity and drying effects in practice when adopting well-established relationships between mechanical parameters and soil plasticity are also briefly discussed.

Designing high mine waste rock piles for long-term behavior requires material mechanical characterization over a large range of stresses and variable environmental conditions. However, representative coarse samples cannot be handled by standard testing devices and the common approach is to test small-scaled samples at the laboratory, which might be affected by particle size effects when compared to the field material. Several reported results indicate that coarser samples present higher amount of particle crushing than small-scaled samples, thus lower dilatancy and higher compressibility. However, specific studies of size effects on time-dependent deformation are lacking. The aim of this paper is to identify the effects of particle size and suction on stressdeformation mechanism of partially saturated mine waste rock. Oedometric compression tests on two parallel graded samples are presented: the gravelly fraction (dmax=50 mm) and the sandy fraction (dmax=2.36 mm). Each stress increment triggers << instantaneous >> and delayed strains. The results reveal the combined effects of particle size and humidity on the mechanical behavior. Coarser samples exhibit higher total compressibility and creep deformation, which also increases with the material humidity. The results give empirical support for the development of scaling laws and suggest that total deformation can be decoupled considering a suction dependent index for creep deformation.

The paper describes the development of a high-pressure isotropic cell for studying the environmental degradation of low porosity clayey rocks. Air permeability measurements are used in this device as a tool to evaluate rock degradation in unsaturated rock specimens caused by mechanical, hydraulic and chemical paths. A modified equation, based on the air pressure decay method proposed by Yoshimi and Osterberg (1963), is presented. The proposed method is applied to an Australian clayey shale. Estimated values of air permeability are compared against those calculated using the original method which, in the case of low porosity rocks, seems to provide unrealistic values when the air pressure in the vessel decays beyond 50%.

This paper presents an experimental study on quantifying the effects of soil suction on the resistance offered by compacted unsaturated backfills to uplift of buried steel pipes and identifying the mechanisms that contribute to increased resistance compared to similar pipes buried in dry sand. This is achieved by means of 1-g physical model experiments, with the pipe buried in sandy loam–Kaolin soil beds of varying water content (suction), compacted to the same dry unit weight. The main experiments are supplemented by benchmarking experiments performed in dry sand of similar grain size distribution, as well as in compacted soil beds inundated with water to achieve conditions close to full saturation. The experiments are supported by a detailed characterisation study of compacted sandy loam–Kaolin mixtures and mini-CPT tests performed to evaluate the uniformity of the soil beds. Measurements of the reaction developing on the pipe as function of its uplift displacement are co-evaluated together with images of the failure mechanisms obtained using particle image velocimetry and continuous measurements of soil matrix suction. We conclude with a simplified method to predict the peak reaction to pipe uplift that allows considering the contribution of suction and the tensile–shear failure mechanism observed during the experiments.

The paper presents the results of an experimental study aimed at evaluating the stress-strain response of unsaturated tailings (Mixed Plant Reject and Dewatered Tailings) from a mine in Queensland, Australia, which can be applied to further optimise current tailings disposal strategies of the mine. Triaxialtests at constant gravimetric water content were performed on specimens prepared at different compaction states using dynamic and static methods, to determine their shear strength. The dynamically compactedspecimens display a higher strength than that statically compacted ones, which highlights the significance of stress history for tailings strength. As-compacted and post-testing suction measurements, performed using a high-capacity tensiometer, showed a reduction in matric suction irrespective of the material type, which is caused by mechanical wetting. The strength envelope was found to be non-linear, partly because of suction changes during testing. Post-testing suction measurement showed spatial variability within each specimen, with the central part of the samples experiencing the maximum suction reduction. The paper concludes with a discussion on the interpretation of such results.

This paper presents an air pluviation system, developed to facilitate 1g physical model tests in granular soils. The deposition process is fully automated and requires minimal input from the operator, thereby significantly reducing the time required to deposit large volumes of granular material, improving the uniformity of the prepared specimens and the reliability of test results. The components comprising the pluviation system have been calibrated to produce loose-to-very dense sand beds, of relative density that ranges between D r = 7% and > 100% of the maximum density achieved with the procedures described in the pertinent standards. The testing chamber where sand is deposited is instrumented with an array of pressure sensors, and the rig is equipped with a miniature cone penetration testing (mini-CPT) device. Measurements from the earth pressure sensors and cone tip resistance profiles are used to evaluate how friction at the sand–chamber interfaces affects the distribution of geostatic stresses inside the chamber, the uniformity of sand beds and boundary effects during deposition and during mini-CPT testing. The air pluviation system allows preparing layered sand profiles by adjusting the deposition parameters on the fly, and this feature is demonstrated through the analysis of mini-CPT tests performed in layered sand beds.

This paper describes an experimental study aimed at evaluating the influence of soil microstructure on air permeability in compacted clay. Air permeability measurements, estimated using the gas pressure decay method, were carried out for a wide range of compaction states. The evolution of the air permeability during wetting and drying paths was also evaluated. The experimental results show that, for an increase in the as-compacted degree of saturation, air permeability may either increase or decrease depending on the as-compacted dry density. Air permeability increases with increasing the degree of saturation in loose specimens, whereas the opposite trend is observed for dense specimens. Microstructural analysis, carried out using mercury intrusion porosimetry (MIP) tests, shows a strong dependency of the air permeability on the as-compacted soil microstructure. This behaviour is also noticed in specimens that experienced a large variation in the degree of saturation during wetting and drying. Microstructural data indicate that air permeability is mainly controlled by large pores that display high connectivity. The degree of saturation plays a dual role in soil microstructure which, in turn, affects the air permeability. Denser specimens (dry density ≥ 1·5 Mg/m 3 ) show a reduction in k eff due to the expansion of the clay aggregates with increasing the as-compacted degree of saturation. The increase in the as-compacted degree of saturation in loose samples (dry density ≤1·3 Mg/m 3 ) produces an enhancement in the proportion of macro pores, thus increasing k eff , as a consequence of modifications in the pore size distribution. A threshold value has been identified, above which further increase in degree of saturation causes a reduction in the proportion of macro pores, and therefore in k eff . A new proposal for estimating the air permeability is proposed in this paper based on the determination of a pore size parameter obtained from MIP data. The proposed approach seems capable of describing the evolution of air permeability for the whole spectrum of compaction states, including specimens subjected to wetting and drying paths.

This paper presents the results of an experimental study aimed at evaluating the effects of soil microstructure on volume change and wetting-induced collapse of a compacted loess from Xi’an, China. One-dimensional (1D) compression tests are combined with Mercury Intrusion Porosimetry (MIP) tests and Scanning Electron Microscopy (SEM) analysis to examine the collapse behaviour for different compaction states and applied stresses. A phenomenon of partial collapse occurs upon full saturation (wetting), whose magnitude depends on the as-compacted suction, the as-compacted microstructure and the stress level applied. Following partial collapse upon full saturation some of the initially meta-stable microstructure of the compacted soil is preserved which leads to higher compressibility in subsequent loading stages. Additional collapse tests carried out under isotropic conditions show that partial collapse upon full saturation takes place only under zero-lateral deformation (1D) conditions due to the residual (‘locked-in’) horizontal stresses maintained in the sample after compaction. Microstructural results and a simple macroscopic model for soil compaction are used to qualitatively explain the phenomenon of partial collapse observed in compacted loess.

An isotach elastoplastic constitutive model devised by Yang et al. (2016) and referred to as the Hunter Clay (HC) model attempts to capture a number of key behaviours of soft soils within a critical state framework, namely destructuration, fabric anisotropy and rate dependency, the latter often manifesting in creep settlement. Finite element implementation of the HC model is a useful means by which its application to practical problems can be facilitated. However, there are a number of significant challenges associated with the translation of isotach elastoplastic models into a finite element setting. In this paper, a detailed discussion of these challenges is undertaken and a new finite element implementation of the HC model is subsequently developed. This includes sophisticated numerical integration algorithms which employ automatic time substepping for solution of the governing finite element equations. The ability of the implemented HC model to predict the mechanical behaviour of soft soils under 1D compression is investigated via simulation of laboratory tests carried out on Ballina clay by Pineda et al. (2016) and Parkinson (2018).

Recent works have shown that delayed events of particle crushing are partially responsible of creep deformation in granular materials, and that Stress Corrosion Cracking promoted by high humidity within particles is the source of this mechanism. A number of experimental studies have focused on creep behaviour of water saturated samples and wetting-deformation after soaking dry material. However, there are few evidences of the effect of varying total suction in time-dependent deformation of partially saturated crushable material, and this mechanism have been rarely considered in constitutive models. The aims of this paper are to present experimental evidence of the effect of total suction on compressibility and creep of sandy sized samples from crushed rock, and to propose a simple one-dimensional elasto-plastic modelling approach based on the enhancement of an existing model. Oedometric compression tests at different total suctions are presented. The results show that compressibility and creep strains increase with both stress and humidity. The model proposed uses a time-dependent hardening law coupling suction with the amount of particle breakage. Based on preliminary calibrations, the model captures the effect of suction and time-dependent behaviour over a large range of total suction.

The paper presents preliminary results of an experimental study aimed at evaluating the influence of soil microstructure on the collapse behaviour of compacted loess from Xi’an, Shannxi province, China. Collapse behaviour was evaluated from one-dimensional compression tests in which compacted specimens were loaded to different vertical stresses, under constant water content conditions, prior soaking. Mercury intrusion porosimetry (MIP) tests and Scanning Electron Microscopy (SEM) analysis reveals a strong influence of the stress level on the soil microstructure formed by soaking under zero lateral deformation conditions.

An overview of the work done at the Ballina soft soil Field Testing Facility (NFTF), established near the town of Ballina (New South Wales, Australia) by the ARC Centre of Excellence for Geotechnical Science and Engineering (CGSE), is presented in this paper. The testing facility is aimed at carrying out fundamental research for providing solutions to problems associated with energy and transport infrastructure in Australia. Development of the field testing facility was driven by challenges with soft soil engineering at the nearby Ballina Bypass motorway project. The state road authority, the contractor and the designers helped to create the concept which was fleshed out and delivered by the CGSE. The main outcomes of comprehensive in situ and laboratory characterization studies are presented and discussed. Results of experimental studies carried out by the CGSE to assess sampling disturbance in the soft soil deposits encountered at the Ballina site are also presented. Last but not least, the paper discusses the main findings and lessons learnt from an international symposium organized by the CGSE in 2016 to assess current practice for predicting the behaviour of embankments constructed on soft soils.

shear calcareous silty soils, clay-sized Lehane the mechanical response of two carbonate sediments from Australia’s North West Shelf shown that fines content affects the undrained shear strength of these soils, by controlling the void ra-tio/density. However, published data on intact calcareous silty soils are still limited and there is a lack of guidance on how test results obtained from remoulded specimens may be used to infer the behaviour of intact soil. The aim of this paper is to make a contribution in this direction, by conducting an ex-perimental program on intact and remoulded calcareous silty soils, which includes microscopic and mechanical soil characterisation. ABSTRACT: Calcareous silts are encountered in many offshore areas where oil and gas exploitations are taking place (e.g., Arabian gulf, south east of Brazil, south east and north west of Australia). Understanding behavior of calcareous silts remains challenging as undisturbed silt samples are difficult to obtain, and most studies rely on remoulded silt samples. The purpose of this paper is to characterize the mechanical behavior of intact and remoulded offshore calcareous silts from two different water depths. The comparisons are done based on microstructure characterization using scanning electron microscopy (SEM) images supported by index tests, one-dimensional compression tests and undrained monotonic triaxial tests. The results have shown that, except for the critical state friction angle, the behaviour of remoulded silts differs from that

Neutron scattering techniques have provided a window into the structure and mechanics of solid materials for many decades. Recent work by the authors has demonstrated that these techniques can also provide tremendous insight into granular systems. Two prominent examples are presented; 1. The use crystallographic texture measurement techniques to uncover the evolution of fabric within clay soils as a function of deformation, and, 2. The use of neutron diffraction strain measurement techniques to examine the behaviour of force chain networks during the compaction of granular systems. In both cases, neutrons are able to provide quantitative measurements that are difficult (if not impossible) to obtain any other way. In the first case, this refers to the direct measurement of the average fabric tensor over a representative sample; in the second, neutrons are able to determine the three-dimensional stress state within individual particles and hence allow the calculation of the actual force network existing within an entire assembly of particles. 1. Background and Introduction Neutron scattering techniques have become a cornerstone of materials science and solid state physics for many decades [1]. The combination of penetrating power at wavelengths akin to atomic distances (e.g. 0.5-5Å), and distinctly different attenuation rates as compared to x-rays provide a unique window for the study of crystalline solids. The vast majority of these techniques rely upon coherent scattering of neutrons as described by Bragg’s law; nλ = 2d sin θ (1) which governs the angle of constructive interference, θ, for neutrons of wavelength λ, scattered from a crystal lattice with planes of separation d, where n = 1,2,3... . A typical neutron diffraction experiment relies upon the measurement of θ for a given wavelength (constant wavelength instruments), or the measurement of λ at a fixed angle (time-of-flight instruments), in each case to determine lattice spacings within a given sample. A typical experimental setup for a constant wavelength instrument (e.g. KOWARI at the Australian Centre for Neutron Scattering) is shown in Figure 1. An overview of such an experiment is as follows; From a polychromatic source (typically a fission reactor), a beam of monochromatic neutrons is formed via diffraction within a silicon crystal. This monochromatic beam is then shaped via neutron optics (e.g. slits and/or collimators) to an incident beam that is passed through a sample of interest. Scattered neutrons from this sample are detected, whereby the angle and intensity of the diffracted beam are measured and used to understand the crystal structure.