Professor Stephen Fityus

The shrink-swell test, and its application in site classification and foundation design according to AS2870 (2011) has both advocates and critics. It has been used as the basis for many residential foundation designs in Australia for more than 30 years, and although examples of performance failures in residential structures are familiar to most practitioners, the incidence is relatively low compared with the number of structures that are constructed, and substantiated examples of widespread and systematic failures due to poor foundation design are few and far between. Nevertheless, there are those who advocate that the shrink-swell test is fundamentally flawed, generally on the basis that the reactivity index that results for any particular soil is affected by the water content of the soil at the time of measurement. Whilst there is anecdotal evidence to suggest this, the data usually put forward to demonstrate this assertion are seldom of high scientific quality, and not obtained under conditions that would allow the assertion to be rigorously and conclusively tested. In fact, scatter plots of shrink-swell index vs initial water content often put forward (eg Rogers and McDougall, 2020) as evidence do show a tendency for soils with higher water content to have higher shrink-swell index values, however, this paper demonstrates that this should actually be expected, and it does not, in itself, confirm that there is bias in the test. The paper discusses the alternative of basing foundation design on Atterberg limits, and recognises that whilst these give a good indication of the clay type and clay content of a soil, as they are determined on remoulded samples, they cannot account for soil structure which is a significant controlling factor in reactive soil behaviour. It goes on to consider what it would take to produce convincing data to demonstrate bias in the shrink-swell tests, and what would be needed to conclusively demonstrate that an alternative approach to site classification was more reliable.

This study aims at providing quality experimental data on the effects of temperature on tensile strength and small strain shear stiffness of two Australian mudstones. The objective is to provide multiscale data in view of developing a numerical model that can capture and simulate the complex multiphysics of underground coal fire propagation. Two mudstones were collected in the Hunter Valley, close to a known underground coal fire, referred to as ¿Burning Mountain.¿ The rock specimens were heated to a range of temperatures (maximum of 900¿°C) for 24¿h, and the materials were comprehensively characterized by X-ray diffraction, thermal gravimetric analyses, optical microscopy and scanning electron microscopy. In addition, mercury intrusion porosimetry was used in order to track changes in pore size distribution with temperature. Investigations at microscale were complemented by testing at the macroscale. In particular, the paper focuses on the evolution of the tensile strength and small strain shear stiffness as the materials are subjected to heating treatment. Results show that both parameters evolve in a non-monotonic manner with temperature. The observed mechanical responses are fully explained and corroborated by microstructural observations.

This study falls in the context of underground coal fires where burning coal can elevate the temperature of a rock mass in excess of 1000°. The objective of the research is to experimentally characterize the change in mechanical behaviour, mineralogy and microstructural texture of two sedimentary rocks when subjected to temperatures up to 1200¿°C for 24¿h. Specimens of local sandstone and mudstone were comprehensively characterized by X-ray diffraction and thermal-gravimetric analysis. These analyses were complemented by optical microscopy and scanning electron microscopy on polished thin sections. In addition, pore size distributions of these heated rocks were inferred by means of mercury intrusion porosimetry. These results were extended to an estimation of the intrinsic permeability using the Katz¿Thompson model. Investigations at micro scale were followed by mechanical testing (both unconfined and confined compression tests) on cylindrical specimens of heated rocks. Results show that the unconfined compressive strength (UCS) of both rock types tends to increase when the temperatures increases up to 900¿°C, beyond which the UCS tends to slightly decrease. As for the permeability, a clear increase in intrinsic permeability was observed for both rocks. The macroscopic behaviour was found to be fully consistent with the changes observed at micro scale.

Studies into rockfill have advocated the use of a tilt test to characterise the shear strength of coarse granular materials. The tilt test employs a simple split box, which is filled with rubble and then tilted until the upper box half slides off the lower box half. The angle at which this occurs is related to strength characteristics of the tested material, but the interpretation of this result is less than straight forward. This paper describes a systematic study of the tilt test on a series of gravels and mine wastes. The research shows that the tilt angle is sensitive to the tilt rate and the water content of the spoil, but that if the test is carried out in a systematic way, consistent results can be achieved. The results show that the tilt test is not a good discriminator of shear strength in waste rock materials. The tilt test is very sensitive to particle size, particle shape and relative density, but because of its very low confining stress, it is insensitive to the physical strength of particles. This means that the tilt test fails to discriminate reliably between weaker and stronger waste rock materials, for materials that are subjected to any significant amount of confining (normal) stress. It cannot be used as an alternative to direct shear testing to determine the shear strength parameters of mine spoil materials.

This paper deals with three grading entropy-based rules that describe different soil structure stability phenomena: an internal stability rule, a filtering rule and a segregation rule. These rules are elaborated on the basis of a large amount of laboratory testing and from existing knowledge in the field. Use is made of the theory of grading entropy to derive parameters which incorporate all of the information of the grading curve into a pair of entropy-based parameters that allow soils with common behaviours to be grouped into domains on an entropy diagram. Applications of the derived entropy-based rules are presented by examining the reason of a dam failure, by testing against the existing filter rules from the literature, and by giving some examples for the design of non-segregating grading curves (discrete particle size distributions by dry weight). A physical basis for the internal stability rule is established, wherein the higher values of base entropy required for granular stability are shown to reflect the closeness between the mean and maximum grain diameters, which explains how there are sufficient coarser grains to achieve a stable grain skeleton.

This paper documents a rock fall in the Hawkesbury Sandstone. Two distinct phases, preceding the ultimate rock fall event have been identified and documented; a creep-loading phase and a rock fracture phase. Water is identified as playing a significant role in the creep-loading phase. Over the long term, peak water pressures from intermittent heavy rainfall events have contributed to the slow, creeping movement of the overlying, joint-bounded block resulting in the progressive loading of the underlying rock mass. The rock fracture phase was extremely rapid and overlaps with the rock fall event. The kinematics of the rock fall has been interpreted from broken surfaces, scratches and positions of debris. From the timing of events, it is likely that wetting/saturation of the intact sandstone from sustained rainfall in the weeks preceding the rock fall would have significantly reduced the intact rock strength. Based on the site investigation and reconstruction of the failure mechanism, the rock fall is classified, in the Crunden and Varnes (1996) scheme, as a complex extremely rapid rock fall and rapid dry debris slide.

From a consideration of the concepts of geological weathering and structure, it can be expected that rockfall hazards should be characteristically different in different geological environments. This paper tests this idea by looking at the geometric characteristics of rock fragments formed on natural slopes in four different geological environments in Eastern Australia, where rockfall phenomena are often characterised by rolling of pre-detached debris. By measuring the three principle dimensions and making a systematic assessment of the shape characteristics of samples of rock debris in significant geological environments, it is found that the distributions of size and shape for the surface debris are statistically different. From the results, it is shown that the size and shape of debris is directly controlled by the rock type, its weathering characteristics and the structure of the parent rock mass. The severity of rockfall hazards is shown to be relatively lower in areas of Tertiary basalt, as the size of rolling fragments is limited by closely spaced fracturing inherited from its formation and the tendency to deteriorate further as it weathers deeply and rapidly. It is also lower in areas of Palaeozoic volcanics, since these tend to produce relatively angular fragments with higher proportions of fragments that are inherently more resistant to rolling. By contrast, thickly bedded sandstones form larger blocks with a larger proportion of shapes that are more prone to rolling. The size distribution of fragments is shown to be well approximated by a log-normal statistical distribution, and using the data provided in this study, it is possible to generate the size and shape data needed to undertake a stochastic assessment of rockfall trajectories in different geological environments. © 2013.

This paper explores the influence of the particle size on the water retention properties of a colluvial deposit derived from banded iron formations in the Pilbara region in Western Australia. A small-scale experimental program aimed at evaluating the water retentions curve of four particle fractions (1.18 - 2.36 mm, 0.60 - 1.18 mm, 75- 600 µm and < 75 µm) is described. Water retention curves, defined in terms of the gravimetric water content vs total suction, were obtained by exposing the specimens to a controlled wetting path using the vapour transfer technique. Total suction was measured using a dew-point psycrometer. The experimental results show an important increase in the maximum water retention capacity with decreasing the particle size. Finally, the influence of the water storage of each particle fraction on the water retention curve of mixed specimens, i.e. those composed by several fractions, is discussed.

This paper investigates the factors affecting the shear strength of granular materials by means of the tilt box test. The test involves the titling of a specifically designed split-box and measuring the angle at which the upper half of the box slides off. This angle can be interpreted as the peak friction angle of the sample for a low stress state. Experimental tests and numerical analyses using the Discrete Element Method (DEM) are carried out and compared. The study is carried out for two different materials, a rounded and an angular aggregate. It is shown that rolling resistance is needed to match the experimental results if only spheres are used but this is not the case for non-spherical particles. © 2015 Taylor & Francis Group, London.

The multistage oedometric relaxation test (MRT) with large bad imposition rate is studied. It is found that avery fast stress drop occurs at the beginning ofthe stages. Due to some regulation problem, the control system may cause a slight partial unloading at the start ofthe stage. The so resulted difference of the MRT compression curve and the standard compression curve is dependent on the soil texture. In case of 'large' partial unloading, locally negative effective stress can be caused in the sample in a stable way.

Two parameters are introduced being in unique, nearly linear relationship with each-other (density parameter (s0) and base entropy (S0o) which is an abstract mean diameter parameter). Data show that s0 is the asymmetric part of the minimum dry density smin in terms of S0. It is shown that the results of some direct shear and compression tests of sands with very loose initial state are significantly dependent on s0 with a sand data set where the dominant component of smin is s0.

The solution of non-linear inverse problems and the reliability testing of the solution may be impeded by noise in the data. Three methods are presented for addressing these problems. The first method recognizes that some parameters can be eliminated from the solution through sub-minimization. In the second method - To "clean" the merit-function - The concept of the closest noise-free merit-function ('follower') is introduced, which can be approximated by the real-life merit-function on a part of the parameter domain, on the condition that the shape of the noise-free merit-function is 'model invariant' being known a priori. In the third method the first method is used and it is shown that if all parameters are eliminated except one, then the transformed merit-function (depending on only one parameter) can be used for reliability testing. The complementary methods are illustrated by the example of the modification of the shark secant method and by the evaluation of a basic geotechnical test. © 2015 Taylor & Francis Group, London.

Shales and mudrocks undergo weathering in the near-surface geological environment, and degradation when directly exposed at the surface. Despite having superficially similar appearances, many shales have very different degradation behaviours. For example, some shales break down readily upon exposure whilst others remain more or less intact. Further, for those shales which break down, the style of degradation can vary greatly. A phenomenon is described where fresh shale blocks that are exposed at the surface undergo rapid breakdown to a fragmented texture which then persists for relatively long times, without further breakdown to finer soil particles. This is illustrated for some coal mine waste rocks. Furthermore, this metastable fragmented texture seems to be particular to each particular type of shale. The paper presents a conceptual model for this physical breakdown of shales which accounts for the differences in fragmental texture that are observed. The importance of several factors including strength, permeability and expansive clay content are identified for their contribution to the degradation behaviour of different shales.

The Hunter Expressway is a $1.7 billion road project in the Hunter Valley, NSW, Australia to provide a new east-west connection between Newcastle and the Lower Hunter. A large part of the materials encountered on site are expansive tuffaceous soils that would normally be discarded. However, because of increasing financial, environmental and space constraints, it is required to make use of these swelling materials in embankments. These materials include highly weathered claystone containing about 20% in mass of smectite. The highly plastic claystone is present in layers alternating with layers of nonplastic coal. Hence, when excavating the material, the claystone is mixed with the coal and it becomes relevant to consider the swelling potential of the mixture instead of that of the claystone alone. Some typical coal and claystone materials used in embankments were characterized by compaction curves and Atterburg limits. Then, a series of swelling tests were conducted on compacted specimens, of mixtures of coal and claystone, prepared in the laboratory with comparable initial conditions (suction and void ratio) so that any change in swelling potential could be solely attributed to the coal content. The results show that the addition of the coal has an effect in reducing the swelling potential of the claystone beyond a simple dilution effect. Some type of swell inhibition is implied. The addition of coal also significantly reduces the time taken for final swell strain to be reached. © 2014 Taylor & Francis Group, London.

In Australia there has been a significant increase in areas affected by dryland salinity over the 200 years since European settlement. As a result of land use and climatic changes this trend is expected to continue, with areas at high risk of dryland salinity predicted to more than double over the next 40 years. This presents a significant risk to road asset managers as concentration of salts within road pavements has been shown to cause damage to pavements and surfacings. The present study explores the impact of dryland salinity on road pavements by assessing the effect of naturally occurring salts on the tensile and shear strength of a sealed granular pavement. Tensile and shear strength testing was conducted on a granular pavement material at a range of salt concentrations. This testing confirmed that the presence of natural salts can have a positive effect on bitumen-sealed granular pavements in contrast to the negative impact salt crystallisation can have on bitumen surfacings. While in solution, salts were found to have a very small positive effect on tensile and shear strength, which is likely related to clay chemistry interactions. Upon crystallisation, salts were observed to form cubic bonds within the pores of the granular material which led to a significant increase in tensile strength. However, at interface between the surfacing and the granular material whisker-shaped crystals were observed to grow from the bitumen. The results suggest that increases in dryland salinity, while presenting a risk to the performance of road surfacings, may actually increase the tensile and shear strength of road pavement materials.

The grading entropy of a soil [S] is derived in terms of the more general concept of statistical entropy. It consists of two terms: the base entropy [So], arising from the difference in the width of the statistical cells in the conventional grading curve, and the entropy increment [¿S]. The goal of the research is to study which grading entropy plays the role of the "true" entropy in a thermodynamic sense (i.e. undergoes an increase during the crushing process being considered as an irreversible thermodynamic process): the entropy increment [¿S] or the sum of the base entropy and the entropy increment [S]. The soil samples are subjected to some crushing tests and direct shear test. The grading curve and the grading entropy are determined before and after each test. It is found that only the entropy increment [¿S] increases in the tests.