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This study investigates the stress–strain response of a novel high-porosity semi-bound soft–rigid permeable pavement blend prepared using rock- and tire-derived aggregates (RDA and TDA) bonded by a polyurethane (PUR) binder. A series of unconfined compression tests were performed on 36 mix designs (with different RDA and TDA proportions, PUR contents and curing durations) to identify the variables governing the stress–strain response. The greater the TDA content, the lower the mobilized strength (UCS) and stiffness (E50), both following an exponentially-decreasing trend. Meanwhile, an increase in PUR content (i.e. increase in the number of inter-particle bonds) and/or curing duration enhanced the UCS and E50. Unlike the UCS which often achieved a stabilized state at seven days of curing, the development of stiffness extended into higher curing durations. Applying the dimensional analysis concept, a practical modeling framework was proposed and validated (using an independent database) for the UCS and E50, allowing these parameters to be simulated as a function of the blend's basic properties – that is, RDA (or TDA) content and its mean particle size, PUR content, curing duration, and dry density. The proposed models can be used with confidence for preliminary design assessments and/or semi-bound soft–rigid optimization studies.

This experimental study investigates the response of vertical and battered minipiles to two-way symmetrical low-frequency (0.1 Hz) cyclic lateral loading. Laboratory (1-g) tests were performed on scaled-down minipiles in very dense cohesionless soil, for batter angles of 0°, 25° and 45°. The cyclic loading is classified into two categories: multi-amplitude and long-term single amplitude, where force-controlled load was applied at a constant frequency. The minipiles were instrumented with optic fibres, and strain profiles were obtained at each loading stage, in both compression and tension stroke. The results are presented in terms of hysteresis loops, variation of normalised stiffness, minipile strain and bending moments under cyclic loading. In the multi-amplitude loading category, backbone curves show a stiffer force–displacement response in tension stroke than in compression stroke. For the single-amplitude category, the area of the hysteresis loop is largest for 45° battered minipiles with the lowest accumulated deformation. The normalised stiffness at the end of 50 cycles is highest for 25° minipiles with a value slightly greater than one. The strain profiles along the minipiles show stabilisation of measured strain before the number of cycle reaches 50, for all three battered conditions. A multi-surface hardening constitutive model is used to explain the effect of shearing and cyclic loading, with increasing loading amplitude on 25° battered minipiles. These test results are indicative of better performance capability of 25° battered minipiles, in terms of secant stiffness, compared to the vertical and 45° battered cases.

This paper introduces a new technique that enables considering the impact of soil fabric on microstructure of internally unstable gap-graded soil. The influence of soil fabric on erodibility of fine particles was studied by transferring the real soil fabric from a micro-computed tomography (μCT) image to discrete element method (DEM) using a new image processing workflow. The pair correlation function (PCF), a two-point correlation between particles in images, was used as a microgeometrical parameter to assess the impact of image filters on the quality of the μCT image. Comparison between PCF and particle size distribution of the raw μCT and reconstructed images suggest that anisotropic diffusion and non-local mean filters reproduce the real soil fabric samples most effectively. DEM results showed lower coordination number but slightly higher stress reduction factor for the real fabric, indicating that the real contact geometry results in having fine particles more involved in force network.

Geotechnical structures made of granular material tend to be unsaturated during their service life. However, there is presently a lack of sufficient research and studies on their volumetric behavior under unsaturated conditions. In this study, loading and wetting induced volumetric behavior of granular materials in the unsaturated state was studied within a moisture content-based framework. Recycled crushed brick (CB) and excavation waste rock (WR) were the granular materials used in this research to promote sustainable construction. Several loading, unloading, and wetting state paths were investigated with respect to virgin compaction surfaces (VCS) developed using groups of compaction curves. The obtained experimental data was utilized to develop a constitutive model capable of predicting wetting-induced volume changes of granular materials in a net stress range of 100–4000 kPa and gravimetric moisture content range of 3.6% for WR, and 7.5% for CB to saturation. The model was verified by undertaking several independent state paths on independent materials and comparing the experimental responses with those predicted using the model. The proposed model is featured with simplicity in acquiring the model input parameters with the aim of filling the existing gap between the theoretical and real-life application of unsaturated soil mechanics. An application of the model can be the basis for the prediction of the settlement of a granular geotechnical structure that is being externally loaded and is subject to changes in moisture content due to climatic effects.

This study investigates the suitability of the swelling and collapse theory proposed based on a constitutive virgin compression surface (VCS) developed within the modified Monash Peradeniya Kodikara (MPK) framework. The modified MPK approach incorporates net stress, void ratio, and moisture ratio as state variables to interpret the swelling-collapse behavior of unsaturated soils. The soil selected for this research was an expansive Quaternary age basaltic residual clay located in Victoria, Australia. The experimental program included testing on unsaturated compacted clay specimens and clay specimens stabilized with lime at the optimum lime content (OLC). The OLC was obtained based on the swelling potential. Static compaction tests were conducted on untreated and lime-treated samples to establish the VCS and to propose the relationship between moisture ratio and net stress. Next, 1-D compression and consolidation laboratory tests were carried out to investigate and compare the mechanism of collapse and swelling based on well-established suction-based theories and the moisture content-based approach of this research. The swelling and collapse response obtained through both theories were very close which verified the suitability of the moisture content-based approach, being the Modified MPK framework. This study also investigated the application of suction-controlled experimental data extracted from the relevant literature within the modified MPK framework. The novelty of this study is proposing and validating a framework for conversion of the results between two different partial theories to interpret the volumetric behavior of expansive clay. Finally, a new method is proposed to estimate the swelling-collapse state of a sample through wetting without the need to establish the VCS.

The objective of this study was to evaluate the effects of geostatic stresses on the compressibility and strength development of submerged geopolymer stabilized columns. In this research study, modified 1D consolidation cells were developed to replicate deep mixed columns in the field when subjected to varying stresses at various depths. Various combinations of fly ash (FA) and slag (S) precursors were used and activated with a liquid alkaline activator (L) to form the geopolymer binder. Soil-column samples were cured under vertical stresses of 0, 50, 100 and 200 kPa for up to 28 days. The results indicated that by increasing the curing stress, the vertical strain and constrained modulus of soil-column composite increased. Moreover, by increasing the binder content, the vertical strain and stiffness of the composites were decreased and enhanced, respectively. The permeability of the composites decreased by increasing the curing stress. The results indicated that addition of the FA+S up to 25% resulted in an increase of permeability and further addition of binder content resulted in insignificant changes in the permeability values. For all the tested geopolymeric binder contents, increasing the curing stress resulted in the enhancement of strength development of stabilized columns. The rate of strength development was enhanced with curing time at an increasing rate, up to 28 days.

Porosity-dependent models can be used to predict the effective thermal conductivity (ETC) of particulate materials. However, they cannot directly account for microstructural features such as particle connectivity and interparticle contact area. Complex network theory can be used to extract network features as microstructural characteristics. However, these features have not been used to study heat transfer. In this work, both contact network and thermal networks are constructed for mono-disperse and poly-disperse sphere packings. Network features are extracted using complex network theory and machine learning techniques are applied to investigate the correlation between these features and the ETC. The most relevant thermal and contact network features for predicting thermal conductivity are identified. The network features capturing both interparticle connectivity and contact quality, such as “weighted degree”, show high correlation with ETC. Furthermore, random forest regression results show that involving multi-network features in a model enhances the accuracy in predicting ETC.

Mixtures of recycled tires and granular material have been used for a variety of applications in geotechnical engineering over the years. The characteristics and mechanical properties of s...

Permeable pavements can reduce the amount of surface runoff and peak flow rate and delay the occurrence of peak flow by allowing water to infiltrate underground similar to natural undeveloped catchments. Such suite of benefits of permeable pavements have made them one of the preferred stormwater control measures in most of the integrated land and water programs. Waste tire permeable pavements (WTPPs), as a relatively new permeable pavement technology, are designed with a surface layer made of up to 50% recycled tire particles. This study aims to investigate the hydrological performance of WTPPs to divert surface runoff and their impact on water quality. A large-scale trial in Australia was constructed and a comprehensive field performance monitoring program including double-ring infiltrometer tests and water quality testing was conducted to evaluate the performance of WTPP in real field conditions. Quality assurance tests on samples of the WTPP surface layer were conducted for permeability in the laboratory, and numerical simulations were done to estimate the surface runoff and investigate the sensitivity of the results to important design parameters. The physically-based models used for numerical simulations were developed in MUSIC X by replicating the layers of the constructed permeable pavement system as well as the impervious part of the trial site. The results indicated that the constructed system is capable of mitigating the surface runoff from the studied site, although only 25% of the discharge area was covered with WTPP. The infiltration rate of the WTPP over nine months with and without maintenance was studied. The results revealed that the infiltration rates even in areas without maintenance after nine months were found to be above the recommended values from ASCE permeable pavements task committee, but lower than the areas that were regularly maintained highlighting the importance of a regular maintenance regime for permeability recovery over time. Water quality tests were done on samples taken over a 17 month-long period indicating that the WTPP system successfully reduced most of the studied pollutants and chemical indicators, including most of the heavy metals, total suspended solids (69%) and turbidity (88%) by physically filtering the water.

Climatic events such as precipitation result in unbound structural layers of pavements being in a partially saturated condition during their service life. With unsaturated testing being relatively complex and costly, the presence of relatively low matric suction in granular geomaterials, practitioners have been reluctant to explore the utilization of unsaturated geomechanics in the analysis and design of the mechanical behavior of pavement structural layers. In this research, unsaturated mechanical characteristics of three types of recycled geomaterials were firstly investigated using repeated load triaxial testing and the incorporation of their soil–water characteristics in the analysis of their resilient moduli response. This was to demonstrate the importance of understanding the unsaturated mechanical behavior of compacted granular material. Next, a virgin compaction surface (VCS) was developed within a moisture content-based framework to interpret the loading, unloading and wetting-induced volume change of the compacted materials. Outcomes of this research, for the first time, extend the application of the well-established Monash Peradeniya Kodikara (MPK) framework, originally developed for fine cohesive soils, to granular materials. A distinctive attribute of the proposed approach is the relative simplicity in the testing methodology by utilizing the conventional geotechnical testing equipment. The findings of this research can be used for estimation of the settlement of a granular structural layer that is compacted, loaded and then wetted through precipitation or flooding.

Traditional pavements in urban areas are mainly rigid, impervious surfaces, resulting in augmented surface run off during rainfalls, thereby leading to flash-flooding and pollution of waterways. In comparison, permeable pavements permit percolation of water through surface layers, thus alleviating harmful environmental impacts. This study presents the authors’ recent experience in the development of an instrumented large-scale permeable pavement trial site—constructed using a combination of crushed rock (CR) and tire-derived aggregate (TDA), bonded by a polyurethane (PU) binder—located at a car park in South Australia. An area of approximately 400 m2 was paved using different TDA-based mix designs—different CR sizes, colors, and shapes, and different PU contents. Moreover, preliminary field performance monitoring results—including surface deflection measurements by the light weight deflectometer test, and strain measurements using optic fiber and strain gauge sensing techniques—are outlined and discussed in detail. The strength and stiffness of the TDA-based blend was found to be dependent on the TDA content, TDA-to-CR size ratio, CR shape, and PU content. The greater the angularity of the CR particles, the more effective the interlocking of the TDA and CR components, and thus the higher the developed strength and stiffness. The amount of strain generated in the permeable surface layer and at its interface with the lower screening layer were both found to decrease with a decrease in TDA content. Preliminary field observations indicate that the TDA-based system can indeed be a viable (and sustainable) solution to effectively mitigate flash-flooding while sustaining low–medium traffic loads.

Knowledge of particle morphology is vital to understand the behaviour of natural geomaterials including heat transfer. The effects of particle shape on heat transfer have been mostly quantified with two-dimensional (2D) particle descriptors or at most with a single three-dimensional (3D) descriptor. However, these particle shape descriptors may fail to capture the shape of all irregular particles. To redress this issue, we developed a method to reconstruct particles from micro-computed tomographic (μCT) images and to extract 3D sphericity and roundness of individual particles in the assembly. Sphericity and roundness of five real sand packings are calculated using the new proposed method. Furthermore, the effective thermal conductivity (ETC) of each sample is estimated using finite element modelling. Our results show that packings with higher sphericity or roundness tend to render higher ETC. A further examination of the microstructure in the assemblies indicates that sphericity or roundness corresponds to inter-particle contacts.

Suffusion is defined as the migration of fine particles caused by seepage flow through pre-existing pores of a soil structure made of coarse particles. This particle transportation changes the fine particle content and its distribution, possibly impacting the mechanical behaviour of eroded soil. Although limited research has been conducted on the post-erosion mechanical consequences under monotonic shearing, little attention has been paid to the impact of suffusion on the cyclic resistance and liquefaction potential of internally unstable soils. This paper investigates the cyclic and post-cyclic behaviour of a gap-graded cohesionless soil using combined triaxial-erosion apparatus. An internally unstable soil was chosen for the erosion test and was subjected to different seepage flow velocities and durations followed by cyclic loading and post-cyclic shearing. During cyclic loading, the eroded specimens with different residual fine contents behaved in a similar manner to a soil specimen constructed only of coarse particles. Regardless of the seepage velocity and duration, the erosion of fine particles resulted in significant increase in cyclic resistance. It is understood that eroded specimens with lower intergranular void ratios show higher resistance during cyclic loading, highlighting the importance of the intergranular void ratio in understanding the post-erosion mechanical behaviour of soils.

Despite extensive research on the behavior of unsaturated fine-grained materials, there is still a lack of understanding of the volumetric behavior of unsaturated granular materials. In this research, a model has been developed to predict the fundamental volumetric behavior of unsaturated granular materials through loading and wetting state paths. In this regard, a loading-wetting surface was developed in a space of void ratio-moisture ratio-net stress. A distinctive feature of the proposed model is the relative simplicity in obtaining the model parameters using conventional geotechnical testing equipment. Two types of recycled granular materials, commonly applied in unbound pavements were used, namely, recycled crushed brick (CB) and excavation waste rock (WR). The uniqueness of the developed surface was evaluated by employing a number of loading and wetting state paths. The results indicate that the developed surface is unique in its loading state paths; however, it only shows uniqueness in its wetting state paths for stress levels greater than 2000 kPa. The proposed model seeks to introduce the application of the unsaturated soil mechanics theory, for predicting the behavior of granular materials in the field, by providing a practical and cost-effective methodology.

A soft marine clay was stabilized with fly-ash (FA) and slag (S) based geopolymers. FA and S with combined contents of 10, 20 and 30% were added to the soft clay and activated with a liquid alkaline activator (L) at various contents. The clay was a marine clay which was dominated by quartz, illite and feldspar. The effect of a number of preparation and curing factors including water content and temperature variation, wetting-drying cycles and mixing time and method were evaluated. The objective of this research was to evaluate the effect of these factors that are likely to occur in ground improvement applications, such as deep soil mixing, on the unconfined compressive strength (UCS), microstructure and mineralogy of the mixtures. Results showed that increasing the FA + S content increased the UCS values significantly through the geopolymerization process, which was evident when increasing the FA + S content from 10% to 20%. Moreover, higher UCS values were achieved when the curing temperature was increased and the strength development was accelerated as a result of accelerated precipitation of FA and S. Furthermore, strength development was enhanced when the L/(FA + S) ratio was increased from 0.75 to 1.0, followed by a decrease at L/(FA + S) ratio of 1.25. Similar trends of strength development were observed by varying the water contents of 0.75, 1.0 and 1.25 liquid limit (LL) of the soil. The increased amount of liquid, L and water, caused less favorable environment, such as lower L molarity and less particle contact, for proper strength development. The UCS values decreased for up to 6 cycles of wetting and drying, where the geopolymeric network was not sufficiently stable, and remained almost constant afterwards. Increasing the mixing time caused more dissolution of FA and S, which resulted in enhancement of the UCS values. Adding FA + S and L to the soil separately resulted in higher UCS values compared to when FA + S and L were mixed together initially and then added to the soil. The microstructure and mineralogy analyses indicated that increasing the curing temperature, as well as the L/(FA + S) ratio resulted in more dissolution of FA and S and formation of calcium sodium aluminum silicate hydrate (CNASH) products.

The use of deep soil mixing (DSM) in ground-improvement projects, for structures subjected to low to medium loads, has increased over the past decade due to its convenient and practical implementation and its economic advantages. Traditionally, Portland cement and lime have been the most popular binders for DSM applications. However, the ground-improvement industry has been keen to explore environmentally friendly alternatives with low carbon dioxide emission. The aim of this research is to investigate the use of two stockpiled industrial waste by-products, namely, fly ash (FA) and slag (S), as alternative green binders in ground-improvement projects that would reduce the carbon footprint of these projects. In this research, combinations of FA and S, activated by a liquid alkaline activator (L), were evaluated for the ground improvement of a soft marine clay, namely, Coode Island Silt (CIS). The performance of the FA + S geopolymers was compared with that of traditional cement and lime control binders. The soil moisture content was set at 0.75, 1.0 and 1.25 of the liquid limit (LL) of the soil to replicate the field conditions. 10, 20 and 30% binders, by dry soil mass, were added to the soil, and the samples were cured for 7 and 28 days. Unconfined compression strength (UCS), flexural beam and scanning electron microscopy (SEM) imaging tests were conducted to evaluate the changes in the engineering behavior and the microstructure of the mixtures. The results indicated that the strength and stiffness of the soft clay were significantly increased by the use of these new FA + S binders, which substantiated them as alternatives to traditional cement or lime binders. The optimum binder content was found to be 20%, while CIS + 5%FA + 15%S was found to be the optimum mixture. Furthermore, correlations between the UCS and the modulus of elasticity (E50) and between the UCS and the modulus of rupture (R) for the geopolymer mixtures were proposed. They will be valuable to both designers and practitioners of ground-improvement works.

One of the leading causes of dam failure is internal erosion. The impact of erosion of non-plastic fine particles, known as suffusion, on the soil structure and strength has been studied experimentally. However, influences including sample size have not been thoroughly investigated. Internally unstable gap-graded cohesionless soil samples with various sizes were investigated using an erosion-triaxial apparatus. Samples were subjected to downward inflows of different seepage velocities. The results indicated that the potential for clogging increased with an increase in specimen length, leading to less fine particle erosion. Internal erosion changed the mechanical soil behaviour even after the loss of fines equal to 5% of the overall sample volume. Eroded specimens with similar intergranular void ratios showed similar undrained post-erosion behaviour. However, the magnitude of the post-erosion initial undrained peak shear strength is a function of coarse particle interlocking, residual fine content, and equivalent intergranular contact index. It was also found that the steady state line remained unchanged after erosion of fine particles and the mobilized friction angle at the steady state line is independent of the residual fine content.

Deep mixing using cementitious compounds are an in-situ ground improvement method for improving the strength and compressibility of loose sands. Low-calcium class F fly ash (FA) is a susta...

Effective thermal conductivity (ETC) is affected by interparticle connectivity in granular geomaterials, which can be characterised by coordination number. Complex network theory can be used to identify “features” that are also able to quantify the particle connectivity. However, this new class of variables have not been used to study the effective thermal conductivity in real sands. An advantage of some network features is that they can simultaneously consider both the particle connectivity and contact quality by adding a contact area or thermal conductance as a weight to connectivity variables. In this paper, weighted closeness centrality extracted from the computed tomography images of five natural sands is shown to be a good predictor of ETC of the sands.

In practice, it is quite common for soils to be mixed and compacted at moisture contents lower than the optimum moisture content (OMC) or lime content less than the optimum lime content (O...

It is believed that the relative density (Dr) can affect the internal stability of the gap-graded soils and hence the erosion of their fine particles (i.e. susceptibility to suffusion). This paper investigates the influence of Dr on the contribution of fine particles to soil fabric. A new procedure is proposed to produce samples with target Dr using the discrete element method (DEM). DEM simulations were carried out using spherical particles. Particulate scale analysis of variation of stress reduction factor (αDEM), the evolution of contact type and fine particle coordination number (Zfine) with Dr reveals how Dr affects packing stability. The results show that packings with a fine content of 35% and the gap ratio in a range of 4–7 are in the transitional zone in which they are unstable initially and become internally stable as Dr increases. The behaviour of gap-graded soil in the transitional zone is governed by fine-coarse contacts, but fine-fine contacts dominate the behaviour when soil becomes internally stable. Both αDEM and Zfine are reliable parameters in determining internal stability of gap-graded soils. Finally, the correlation between the results and macro-scale matrix phase diagrams confirms the validity of micro-scale information to describe the underlying phenomenon.

Shrink-swell behavior of expansive soils highly influences the performance of lightly loaded structures with shallow footings. Expansive soils often undergo heave and settlement due to soil moisture variation, which may cause differential movement in the structure. This phenomenon becomes critical when the changes in soil moisture are widespread due to climatic conditions. Indeed, there have been reports in the media regarding footing movements and cracks in new houses in Victoria particularly following the breaking of the last prolonged drought. As part of an ongoing research study on damage to residential structures caused by ground movements, a field site has been established on a vacant land in a western suburb of Melbourne. Soil moisture variation and corresponding ground movements are monitored using Neutron moisture probe and magnetic extensometers respectively. Soil suction variation is also measured from undisturbed samples in the laboratory. This paper describes the site selection, instrumentation and soil classification. The variations of soil properties with depth are discussed. Soil moisture variation is compared with climate data of the site and presented along with the corresponding soil layer movements.

Traditional permeable pavements are constructed with rigid aggregates and have low load-bearing capacity. The crack development due to loads and unpredicted ground movements reduces their service l...

The benefits of Permeable Paving Systems (PPS) in minimizing surface water run-off which in turn reduces the imposed pressure on stormwater collection systems at the time of flash flooding have been recently remarked profoundly. In addition, the PPS have additional advantages such as filtering the pollutants for downstream water collection systems and accommodating transformation of nutrients and water to the surrounding vegetation. Inclusion of end-of-life tire products in the mixture of PPS can adjust the flexibility of the final product. Tire aggregates will potentially enhance the final product performance in areas where the ground movement or intrusion of roots can cause damage to conventional rigid pavement systems. The effect of addition of waste tire and rubber aggregates to solid granular material have been investigated in the past; however, their focus have been mainly on creating highly compacted mixtures. In contrast; in this study; mixtures of soft (end-of-life tire aggregates) and rigid aggregates (crushed rock) with a relatively high porosity was tested to evaluate their suitability for construction of permeable pavements which require high porosity. The flexibility of mixtures and their stress dependant behaviour was investigated based on the volumetric fraction of soft aggregates in the blend. The transitional soft-rigid behaviour of the mixture can be utilized to mitigate the unexpected deformation induced on the pavement. The compressive behaviour of highly permeable mixtures under ko loading and deviatoric shear provides an insight on the formation of force chains in the mixtures between the rigid particles. In addition, monitoring the compressive behaviour of rigid-soft aggregates under ko loading explains soft aggregates cushioning impact on improving the compressibility and shear behaviour of the mixture.

Granular recycled Construction and Demolition (CD same generic evolution by increasing stress was observed irrespective of the material types or sizes.

Employing network science to understand particle interactions helps manufacture advanced materials with superior force transmission and heat transfer. However, knowledge of the dependence of networks on particle features such as shape is missing. This study computes particle shape ─ the average of three-dimensional sphericity and roundness, and multiscale network variables ─ degree, edge betweenness centrality and global clustering coefficient from unweighted/weighted contact and thermal networks ─ for three sands based on their X-ray computed tomography images. The dependence of network features on particle shape is explored for both individual particles and bulk sand samples. Results show that particle shape affects the degree in a network at sample and particle scales differently. In contrast, weighted edge betweenness centrality has a consistent inverse relationship with particle shape at both scales. The weighted edge betweenness centrality values from different samples consistently indicate that 20% of network edges (e.g., contacts) are responsible for 60% of the heat transfer in dry sands. Although unweighted edge betweenness centrality cannot reflect the heat transfer directly, it has a similar correlation with particle shape to the weighted feature. Global clustering coefficient from the thermal network increases in round particle packings and can indicate the mechanical rigidity of sands.

Laboratory testing methods are constantly being developed to simulate true field conditions in controlled laboratory environment. The aim of laboratory testing methods is to reproduce specimens whi...

Granular recycled Construction and Demolition (C&D) materials used in pavement structures and embankments experience static and dynamic loading during their service life. As a result, particle crushing causing serious issues such as settlements may occur. Particle breakage depends on different factors such as particle mineralogy, loading condition, particle size, and particle shape. A new insight into the importance and effects of particle shape on the degree of crushing is presented. In this study, breakage of individual C&D particles with different mineralogy and microstructure was studied. The fracture characteristics were found to be highly dependent on the particle shape factor. The particle behaviour at different scales from a single particle to particle assembly is presented and discussed. Discrete Element Method (DEM) was also used to clarify evolution of cracks through the particles. DEM assisted in measuring breakage energy more accurately by partitioning and tracking the energy dissipation especially through the creation of new surfaces during fragmentation. Precise three-dimensional particle shapes were generated by a large number of bonded spherical sub-particles and used to model single particle crushing and particle assembly crushing. The results demonstrated that brittle C&D granular materials with higher degree of sphericity and lower flakiness index would show higher resistance to breakage.

Lime stabilisation is a commonly used method for improving the properties of expansive clay subgrades around the world. This paper investigates the effect of curing on the behaviour of lime-stabili...

Results of optimization of an alternative alkali-activated binder (AAB) system based on two industrial waste products found in abundance in Australia, namely fly ash (FA) and granulated bla...

Dwellings constructed in mountainous areas can be vulnerable to rockfall hazards. Reinforced concrete barriers and rocksheds can be used to offer protection from falling boulders. Gabions (which refers to manufactured steel nets filled with geo-material) can be used to strengthen the protection. Mitigation of localised damage to the barrier due to the high impact force developed at the point of contact is particularly important in a design featuring the use of a slender stem wall forming part of the barrier. Vertical impact tests have been conducted with the core purpose of studying the total amount of force imposed onto the barrier as a whole. The distribution of pressure on the transmitting surface is also an important consideration when it comes to predicting localised damage that is inflicted on the frontal surface of the barrier. Experimental study is warranted to investigate the efficiency of the gabion in distributing the impact pressure. A series of small scale drop tests involving the use of two types of cushion materials has been conducted to study the pressure distribution behaviour. The volume of cushion materials that contribute directly to the transmission of force has also been studied for two different materials. The influence of friction between particles (which is dependent on many factors including the shape of the individual particles) is relevant to the performance of the cushion. This study is aimed at making recommendations on the selection of cushion materials for filling the gabion cells and developing simple calculation methodology which has been validated by comparison against experimentally recorded results.

The swell-collapse mechanism of residual basaltic clay in both untreated and stabilized with lime conditions was investigated. For treated specimens, the optimum lime content (OLC) was found based on swell potential reduction. Swelling and collapse potential were investigated using the virgin compaction surface, which is the backbone of the Monash-Peradeniya-Kodikara (MPK) framework. The suitability of the MPK was examined by applying different state paths. The swelling and collapse potentials were tested under a wide range of moisture contents and stress levels, with attention given to the effect of stress history and operational stress. Test results indicated that for the untreated and lime-treated clay (at OLC), the behavior of soil during loading, unloading, and wetting closely followed the MPK framework. However, the MPK did not extend to specimens with very low moisture content wetted under low stresses, and, consequently, a new improved model was suggested. Furthermore, a new method for predicting the swelling and collapse potential was proposed using the virgin compaction surface.

A novel approach has been used to simulate the true field performance of cement-stabilized recycled concrete aggregate in pavement bases using a unique, large-scale, fully instrumented pave...

This paper investigates the influence of lime stabilization of an expansive clay based on volumetric behavior and the soil- water characteristic curve (SWCC). The selected soil was a residual clay located in Victoria, Australia. Specimens treated with an optimum lime content (OLC) that was found to reduce swell potential were selected to investigate the SWCCs. Static compaction tests were conducted to establish the virgin compression surface. Hyprop (Meter Group, Pullman, Washington), filter paper, and the chilled mirror hygrometer were used to measure the SWCC at and below the surface at different net stress levels. To interpret the volumetric behavior of untreated and treated soil using the SWCC, swelling and collapse values were measured at various initial moisture contents and stress levels. The test results found that although the treated specimens were stabilized with lime at OLC, significant collapse and swelling potential were obtained when the lime-treated specimens were prepared at high suction value and wetted under low net stresses.

An experimental investigation involving the use of a full-scale pendulum device to deliver solid object impact on a reinforced concrete (RC) barrier specimen that was fitted with a layer of gabion cushion is reported in this paper. The deflection behaviour of the stem wall of the RC barrier including the tensile strains developed in the longitudinal reinforcement was of interests. Results recorded from the tests are compared with results from control experiments which were without the protection of any cushion materials. The introduction of a layer of cushion is shown to be able to have the contact force reduced by more than 95% and deflection demand reduced by about 70%. An analytical procedure employing the Hunt and Crossley contact model, Swiss code model and two-degrees-of-freedom (2DOF) system modelling technique is presented for calculating the flexural response behaviour of the cushioned barrier and validated by comparison with experimental measurements. An important outcome from the study is a simple hand calculation procedure featuring the use of a closed form expression along with a design chart which is illustrated by a worked example, to facilitate uptake in design practices.

Accurate and efficient prediction of thermal conductivity of sands is challenging due to the variations in particle size, shape, connectivity and mineral compositions, and external conditions. Artificial Neural Networks (ANN) models have been used to predict the effective thermal conductivity but they have not considered variables related to particle connectivity. This work uses computed tomography (CT) scanned images of four dry sands and network analysis to redress this significant shortcoming. Here sands are represented as networks of nodes (grains) and edges (interparticle contacts or/and small gaps between neighbouring particles) to extract network features that characterise interparticle connectivity. A network feature – weighted coordination number (WCN) capturing both particle connectivity and contact area – was found to be a good predictor of effective thermal conductivity in dry materials. Roundness, sphericity, solid particle thermal conductivity and porosity are other input parameters rigorously selected for an ANN model that predicts well the effective thermal conductivity of sands.

Subgrades of expansive nature are one of the main causes of damage to road network in Australia. Consequently, lime stabilization has been widely used to reduce the swell- shrink potential of these types of soils and thus reduce the associated damage. After stabilization and compaction, the subgrade will naturally be exposed to cycles of full swell and or partial shrinkage due to climatic cycles. This paper investigates this behaviour for lime stabilized compacted expansive soil from weathered Quaternary Volcanic geological deposits located in Western Victoria; Australia. These soils were stabilized with varying percentages of hydrated lime (2, 3, 4, 6 and 8 percent) and the swell-shrink paths of both untreated and treated soils were studied. Test specimens were compacted at optimum moisture content and maximum dry density. The samples were subjected to full swell-shrink cycles under a surcharge of 25kPa to reach structural stabilization and to simulate the impact of climatic wetting and drying cycles. Vertical deformation and swell-shrink cycle relationships for untreated and treated samples were obtained and analyzed. The results of lime stabilization indicate that equilibrium is reached after three cycles for both untreated and treated samples. In addition, results suggest that maximum deformation occurs in the second swelling cycle. Vertical deformation of untreated sample was reduced to a third after adding 2 percent lime and reduced to a sixth after adding 3 percent lime. The gradient of swelling and shrinkage path reduced to about a sixth and third when it is treated with 2 and 3 percent, respectively. The treated samples reached maximum swelling at a higher degree of saturation than the untreated sample.

Compaction of aggregates is an important part of the design, construction and research of pavement geotechnics projects. An important application of compaction is sample preparation for pavement design studies. Conventionally, the impact method of compaction is used for studies on pavement materials. However, recently, some researchers have been using other methods of compaction, such as static compaction, specifically for studying the unsaturated behavior of pavement materials. The objective of this study is to investigate the effect of compaction techniques on resilient behavior of compacted laboratory specimens. Studies show that the resilient behavior of unsaturated compacted road pavement materials is influenced by suction. In this regard, two types of recycled Construction and Demolition (C&D) material were selected and static and impact compaction methods were utilized for sample preparation. Further, accuracy of four predictive resilient modulus models with or without incorporation of suction was investigated. Test results show the impact of compaction method on particle breakage, matric suction and accordingly resilient behavior of C&D granular material.

Bearing reinforcement, which is composed of a longitudinal member (steel deformed bar) and transverse (bearing) members (a set of equal angle steel), has been established as an effective earth reinforcement material. The equation for estimating the pullout resistance of this reinforcement in coarse-grained soils has been previously developed but not for fine-grained soil. Claystone soil, abundant in Mae Moh mine, is a fine-grained material when crushed and compacted. It was proposed to be a backfill material in the Bearing Reinforcement Earth (BRE) wall for mining activities. The pullout resistance mechanism of the bearing reinforcement embedded in the claystone soil is presented in this paper. The total pullout resistance is the sum of the pullout friction and bearing resistances. The pullout friction resistance is approximated from soil shear strength and interaction factor α . The bearing pullout resistance of a single isolated transverse member can be approximated from the punching shear mechanism. The transverse member interference is classified into three zones, depending upon spacing and dimension of transverse member, S/B ratio. Based on a critical analysis of the test results, the pullout resistance equations for bearing reinforcement with different normal stresses, dimensions and spacing of transverse members embedded in claystone soils compacted at optimum point (optimum water content and maximum dry unit weight) are developed in term of total strength parameters.

Traditional pavements in urban areas are often impervious, resulting in augmented surface run-off during rainfalls, thereby leading to flash floods and pollution of waterways. In contrast, permeable pavements allow percolation of water through their surface layers, thus alleviating the harmful impacts associated with traditional pavements. This study reports on the mechanical performance of a large-scale permeable pavement trial site — constructed by tire- and rock-derived aggregates (TDA and RDA) bonded together using a polyurethane (PUR)-based binder — located at a car park in South Australia. An area of approximately 400 m2 was paved using different TDA-based mix designs, i.e., different RDA contents and sizes/shapes, and different PUR contents. A series of unconfined compression tests were carried out alongside a six-month field performance monitoring program — including in-situ light-weight deflectometer tests, and strain measurements by optic fiber sensing — to assess the pavement’s true potential under live traffic. The greater the TDA and PUR contents, the lower and higher the pavement’s strength and stiffness, respectively. Meanwhile, the development of strain (and hence deformability) was in favor of both the TDA and PUR contents. An increase in RDA size, which promotes an induced inter-particle frictional resistance in the soft–rigid matrix, was also found to enhance the pavement’s strength/stiffness while offering a further reduction in its developed strain. Moreover, the greater the RDA angularity, the more effective the mechanical interlocking (and hence interfacial friction) generated between the soft and rigid particles, and thus the higher the developed strength/stiffness. Although effective under low–medium traffic loads imposed by passenger vehicles inside the parking bays, the TDA-based technology (with the implemented mixture designs) was not as effective in sustaining high traffic flows within the parking aisles, e.g., U-turns imposed by light–medium trucks.

Swell-shrink movement of expansive soils due to seasonal wetting and drying can cause differential ground movements. This movement can inflict substantial structural damage above foundation level to lightly loaded infrastructure. To reduce this movement, techniques have been employed to either (i) chemically restrain the soil’s reactivity, (ii) control the moisture variation within the ground, or (iii) engage a footing system that can limit the impact of the stresses generated by such differential ground movements. Recently, a new concrete-free footing system has been developed in Australia in an attempt to sufficiently resist such ground movements. This system is comprised of an adjustable steel plate attached to the ground by multiple thin steel (hollow) battered mini-piles. The technology shows promise as a low-impact, cost-effective, excavation and concrete-free, innovative alternative to traditional footing systems. It is also quick and easy to install without the use of bulky and expensive equipment. Early field trial results have indicated that this new footing system can combat against and significantly reduce the transfer of the swell-shrink ground movements to a structure. This paper will describe this new footing system and report on an experimental field trial to date, which will include measured ground movements, moisture content and soil suction results vs. depth, as well as the performance of this new driven battered mini-pile group footing system.

Ground-source heat pump (GSHP) systems typically show higher efficiencies than conventional systems for space heating and cooling of buildings. However, the availability of GSHP systems performance data is still limited, especially in Australia due to the small number of GSHP systems installed and monitored. This paper provides some initial results from a GSHP systems monitoring project conducted on ten residential properties in the greater Melbourne region of Australia. The data measured reveals an estimated Coefficient of Performance between 2 and 4.9. The reasons for these variations in measured system efficiency with respect to design expectations are discussed.

This paper investigates the posterosion geomechanical behavior of internally unstable granular material due to removal of fines caused by erosive forces of water flow. Posterosion undrained behavior of a gap-graded internally unstable soil was investigated for a range of erosion durations and inflow velocities using a triaxial-erosion apparatus. Test results indicated that the undrained behavior of the original specimen changed from a strain hardening behavior to a flow-type behavior with limited deformation after internal erosion. The initial peak strength improved and the flow potential decreased during the initial stage of erosion. This observed increase in initial peak strength is believed to be the result of a better interlocking between the coarse particles posterosion. In contrast, the slip-down movement of the particles due to an increase in the posterosion void ratio postponed the dilation tendency. Test results also suggested that even erosion of a small percentage of fine particles improved the mechanical frictional behavior of the soil. However, there was a threshold value for the loss of fine particles at which this positive effect deteriorated. This might have been due to formation of local metastable structures and/or overcoming contractive behavior after loss of the semiactive fines and a considerable increase in the global void ratio. Shear strength results, rate of erosion, and local vertical strains together suggest that the intergranular void ratio is a powerful index in evaluating the posterosion mechanical behavior of internally unstable soils.

In this paper, a new design approach based on the principles of energy and momentum conservation is proposed for the design of free-standing rigid barriers subject to point impact. The nove...

Construction and Demolition (C&D) wastes are increasingly used as construction material in a range of civil engineering applications. Fine Recycled Glass (FRG) is collected at municipal kerbsides and its usage to date has been limited to unbound pavement layers. This research was undertaken to evaluate the performance of FRG as a supplementary material in blends with cement stabilized recycled concrete aggregate (RCA). Laboratory evaluation was undertaken on the RCA/FRG blends with 10%, 20% and 30% FRG content and stabilized with 3% medium setting General Blend (GB) cement. The laboratory evaluation was comprised of pH, plasticity index, foreign materials content, particle size distribution, linear shrinkage, California Bearing Ratio, modified Proctor compaction, Repeated Load Triaxial test, Unconfined Compressive Strength test and flexural beam tests. The cement stabilized RCA/FRG blends with up to 30% FRG content were found to have physical properties, which comply with the local state road authority requirements. The results of Repeated Load Triaxial tests indicated the RCA/FRG blends performed well with 30% FRG content just on the border line for bound pavement material. Unconfined Compression Strengths met the minimum requirement for 7 days of curing for all blends, while the 28 day strength of the blends showed a significant improvement with curing. The results of the flexural beam tests were noted to be consistent with past works with cement stabilized virgin quarry rock products. The modulus of rupture and flexural modulus for all the cement-stabilized RCA/FRG blends indicate that these blends are suitable for applications such as cement-stabilized pavement bases/subbases. The fatigue life was also within the range previously reported for quarry materials. The cement-stabilized blends with FRG as a supplementary material with up to 30% FRG content and 3% GB cement were found to have physical and strength properties, which would comply with road authority requirements.