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Impact Of Initial Conditions on the Effectiveness of Rolling Dynamic Compaction of Granular Soils
A finite element model (FEM) of rolling dynamic compaction (RDC) technology of a BH-1300 4-sided 8-tonne impact roller, developed previously by the authors, has shown to have reasonable agreement with that observed in the field. The use of this FEM is likely to provide high fidelity insights into the capability of the BH-1300 4-sided 8-tonne impact roller, namely in predicting the settlement and densification of an underlying granular material. A parametric study utilising this FEM with respect to initial density and shear strength parameters is undertaken to explore the relationship these properties have to the settlement and densification of a soil subject to RDC with a BH-1300 4-sided 8-tonne impact roller. The empirical relationships constructed within this study are validated against field trials from the literature of the roller improving sandy gravel fill at typical operating speeds of 10 km/h.
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Subsoil Pavement Drains: Panel Drains v Round Pipe Comparison
Liaison with Australian state road authorities in recent years has been the impetus for reviewing current accepted drainage practice, with tested, technically advanced, cost effective products now readily available in Australia. Premature pavement failure commonly caused by slow drainage response has benefited from design methods incorporating geo-composite panel drains, giving improved drainage response times, high flow infiltration, efficient filtration and economical installation.
Pipe stiffness test results highlight the difference in service performance to show that geo-composite panel drains are superior in structural capacity whilst their rigidity compliments efficient installation.
Comparison of factors affecting inflow capacity and outflow discharge identify the optimum flow performance of panel drains. Inflow considerations can be shown to be more relevant criteria than design for discharge capacity. Geotextile filtration performance is an integral part of geo-composite drainage systems with research highlighting the correct assessment of EOS being critical to efficient long term drainage sustainability.
Type of backfill used, permeability rates for in situ soil, pavement materials and drainage backfill play an integral part in overall design. Design practice should consider location of the system, permeability rates for in situ materials and geotextile filtration along with drainage inflow and discharge capacity.
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Crushed brick blends with crushed concrete for pavement sub-base and drainage applications
Demolition materials are generated by demolition activities and account for a major proportion of the waste materials present in landfills. Crushed brick and crushed concrete are major components of demolition materials. Recycled crushed concrete, crushed brick and crushed rock are however viable substitute materials for natural resources used as construction materials in engineering applications. This paper presents the laboratory testing results of various proportions of crushed brick blends with crushed concrete. The engineering properties obtained were compared with existing local authority specifications for pavement subbase and drainage systems to ascertain the potential use of crushed brick blends in these applications. The demolition materials for the experimental works were collected from a recycling site in Victoria, Australia.
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Effective remediation of groundwater in acid sulphate soil terrain
Acidic groundwater, generated from acid sulphate soil (ASS), is a major geo-environmental problem in Australia. Manipulation of groundwater through the use of weirs and gates in the nearby creeks and drains of ASS, which is being practised right now for preventing pyrite oxidation, is not effective in low land floodplains due to the risk of flooding. The application of a permeable reactive barrier (PRB) can be an alternative for remediation of acidic groundwater in such floodplains. Laboratory column experiments were carried out prior to installation of the PRB for examining the efficiency of the material. Results of these experiments have shown that recycled concrete could effectively neutralise the acidic water for longer periods with complete removal of aluminium (Al) and iron (Fe). Despite the reduction of the efficiency of the recycled concrete due to armouring by accumulated precipitates of Al and Fe, excellent performance was observed for an extended period under controlled laboratory condition. Following these results, a pilot PRB was installed in the Broughton Creek flood plains in southeast NSW to observe its performance under varying natural conditions of the field. The PRB has been maintaining near neutral pH with complete removal of Al and Fe from the groundwater of ASS matching with the results of column test. The promising performance of the pilot PRB for the last three years shows that PRB can be used as one of the cost effective and environmental friendly alternative to other recently utilised techniques in ASS.
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Australian Geomechanics – State of the Journal
It is my great pleasure and honour to introduce this issue of Australian Geomechanics. Following the resignation of previous Editor Bre-Anne Sainsbury, I offered to take on the Interim Editor role from the June 2023 issue to ensure continuity of the publication. The task duration has extended and based on the work completed to produce the latter three issues of the 2023 calendar year, this brief note presents some basic journal analytics, discusses current challenges facing Australian Geomechanics and aims to encourage the membership to prepare submissions for the benefit of the readership and the wider Australian geomechanics community. The sections about challenges and initiatives include references to discussions and brainstorming exercises held during my time at the AGS National Committee (2013-2019) and input from past Chairs and committee members during that period is acknowledged.
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Resilient modulus of some Victorian fine-grained soils at OMC, wet-of-OMC and soaked conditions
A typical flexible pavement structure consists of an asphalt wearing course and the underlying base and sub-base courses. The subgrade soil is the foundation of the pavement. In recent years, the resilient modulus has been recommended by pavement design guides as an important indicator for characterising the resilient behaviour of these pavement materials under dynamic traffic loading. The resilient modulus can be obtained from the repeated-load triaxial test in the laboratory. This paper reports and discusses some of the results from a study on the evaluation of the resilient modulus for eight Victorian fine-grained soils at different moisture contents and stress levels. The effects of the deviator stress, confining stress, moisture content and plasticity index of soils on the resilient modulus have been investigated, and a relationship has been established and discussed for the soils used in this study.
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Soil strength estimation using free falling penetrometers
Obtaining soil strength parameters can be costly and time consuming for sites with low accessibility such as those offshore and at remote inland locations. A free falling penetrometer can be a cost effective solution for such sites and this has led to the development of numerous penetrometer systems. These penetrometers (retrievable or expendable) can be deployed from small vessels and be allowed to free-fall into the seabed. However, free falling penetrometer application is not widespread due in part to difficulties in data interpretation. There is a lack of appropriate theory and well controlled experimental data to estimate the rapid penetration resistance of the soil. This study has investigated the interpretation of free falling penetrometer through performing a series of laboratory model tests. A penetrometer of various tip diameters and masses has been dropped from different fall heights into kaolin with a range of undrained shear strengths. The effects of the influencing variables on the penetrometer performances are evaluated. Empirical equations are formulated to estimate the undrained shear strength of kaolin based on the measured dynamic penetration resistance and final penetration depth. The equations are successful in estimating the undrained shear strength in the model tests with reasonable accuracy. Good agreement has also been obtained in validating the empirical equations using a published case study.
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Resilient Modulus Of A Stabilised Fine-Grained Subgrade Soil
Mechanistic design methods of pavement structures require the use of elastic moduli for each pavement material including subgrades. In the Austroads pavement design guide (Austroads, 1992), elastic characterisation of subgrades and cemented pavement materials is determined from empirical relationships based on California bearing ratio and unconfined compressive strength, respectively, while repeated load triaxial testing yielding resilient modulus is only mentioned as a recommendation for characterising unbound materials. However, in recent years, the resilient modulus of pavement materials has become a more important parameter in pavement analysis and design. This paper presents some of the findings of a continuing research project on engineering properties of a stabilised fine-grained subgrade soil. In particular, the variations in resilient modulus values due to the changes in additive content, dry density, moisture content and curing time were investigated. Laboratory repeated load triaxial tests yielding resilient moduli were conducted on stabilised fine-grained soil samples simulating the material properties at various levels. The resilient modulus results based on various stress levels were then analysed by using deviator stress and octahedral stress models. Resilient modulus values were calculated for an estimated in-situ stress condition using the octahedral stress model. The relationships between the resilient modulus values and each of the parameters mentioned above were defined by single regression analysis. Also, an equation that helps to estimate resilient modulus as a function of additive content, dry density, moisture content and curing time was established.