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Dynamic properties of crushed glass and tyre rubber in unbound pavement applications
Flexible pavements consist of treated unbound materials between the surface, typically bituminous, and the natural subgrade layer. A laboratory study was conducted to assess the dynamic behavior under the influence of repeated loads of the two most common global waste materials for their performance as road materials. The study investigated the behavior and properties of crushed rock (R) blended with waste glass (G) and tyre rubber (T) and evaluated them as alternatives to natural unbound materials. Preliminary tests included Modified Proctor compaction and Particle Size Distribution tests (before and after the compaction stage), and a more specialised test to determine the resilient modulus (Mr) and the permanent deformation values; the Repeated Triaxial Load Test (RLTT). The mixtures were prepared at different percentages of the whole specimen’s total dry weight: from 12 to 45 % waste glass, and from 5 to 15 % tyre rubber. To simulate typical in situ materials, the mixtures were also prepared at the lower target moisture contents of 70% and 80% of OMC. The moisture content and the dry density after the RLTT were measured. Results showed a positive correlation between permanent deformation and glass content, while glass content can improve Mr value of rock specimens by up to 50%. Under RLTT, the addition of tyre rubber to crushed rock decreased permanent deformation.
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‘Listening to the earth’: an unconventional approach to mapping basalt flows
Digitally recorded background ambient noise can be used to extract details regarding subsurface soil conditions. This unique methodology has been implemented to provide comprehensive assessments of geotechnical site conditions. Ambient noise is the persistent vibration of the ground in response to anthropogenic and natural causes. In many contexts, these background vibrations are classified as noise, and efforts are made to remove these signals from recorded data. However, these background vibrations also contain valuable information regarding the materials they travel through. The refraction microtremor (ReMi) technique separates these waves from noise recordings to determine soil shear-wave velocities. Interpolation of closely spaced one-dimensional velocity-depth profiles along linear arrays allow two or three- dimensional velocity-versus-depth representations to be produced, thereby mapping lateral variations and extending subsurface characterisations between more expensive spot borehole measurements. ReMi therefore provides a non- invasive and cost-effective way of characterising ground conditions across entire sites, with data acquisition able to take place in areas where drill-rig access is restricted. This paper demonstrates the contribution ReMi shear-wave velocity assessments can make towards obtaining robust subsurface models to mitigate risk from unforeseen ground conditions in Victoria’s booming construction industry. While traditional seismic refraction methods are unable to detect softer soils underneath harder material, ReMi was able to “see through” the basalt intrusions and delineate the upper and lower surface of the flows. This is particularly advantageous in Victoria, where multiple basalt flows are commonly interlain by soil horizons.
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Review Of Highwall Mining Experience In Australia And A Case Study
The highwall mining method was introduced in Australia in early 1991. Since then, at least 13 mines have used this method to mine coal. Abundant experience has been accumulated during the past 8 years, through some failures as well as successes. This paper presents a brief review of highwall mining experience at four Australian mines, with focus on geotechnical issues affecting mining performance. The paper also summarizes one case study, which involved major pillar/roof instabilities. The aim of the review and the case study is to assist the highwall mining industry to learn from past experience and to avoid similar instabilities in the future.
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Discussion of “Assessment of the Coefficient of Consolidation with Queensland Data”
This paper presents a discussion of “Assessment of the coefficient of consolidation with Queensland data” by Burt G. Look. https://doi.org/10.56295/AGJ5825.
The efforts of the Author are acknowledged in assembling a large dataset and attempting to make sense of the inherent noise. A limitation however is the anonymity of the locations from which the data was derived as it is very likely that over the 40 years of experience with soft soils in Queensland the Discusser (and perhaps others) would have been able to contribute with specificity.
It is the Discusser’s view that the generic relationships in the public domain referenced in the Paper are of limited if any utility and has never seen practitioners making use of them on real projects where the consequences were significant.
Some of the authoritative conclusions drawn and commentary in the Paper are worthy of further consideration: 1. the absolute rejection of U50 samples; 2. the variation in cv due to adoption of t50 or t90; 3. the expected range of cv; and 4. the singular bias and preference for cv guesstimated from piezocone dissipation tests.
Before discussing these, it is instructive to consider whether a regular or consistent pattern should be expected with the data presented given the inevitable variations, repeatability and reproducibility of any or all of the following:
- Soil structure, void ratio, Liquidity Index and sensitivity.
- Sample type and size.
- Sampling procedure.
- Transportation procedure.
- Storage procedure and conditions.
- Test specimen preparation.
- Test specimen parity – same material or adjacent tested for multi-test correlation purposes.
- Test procedure.
- Stress increments selected.
- Stress increments straddling the yield point by varying amounts.
- Interpretation and reporting.
In addition, real soft soils display a widely contrasting Jekyll and Hyde response depending on the stress level imposed i.e., whether stressed within the overconsolidated (OC) range or into the normally consolidated (NC) range post ruin of the soil structure on yield (Tavenas and Leroueil (1980)). Then there is the no small matter of Terzaghi’s simple consolidation theory premised on specimen vertical displacement alone assuming constant properties throughout the sample throughout the stress excursion during a consolidation test loading stage even though real soils behave differently. Given the above and when considering cv as a function of LL, it is unsurprising that graphs which the Discusser would colloquially describe as ‘measles plots’ are the result, indeed it is to be expected.
It is also no surprise that there are a significant number of extreme outliers if basic statistics as reported in the paper are applied to what is inherently a multitude of statistical data sets (or samples), rather than identifiable, statistically significant populations. The Discusser concurs with the paper’s general finding that such an approach is futile given the significant vagaries in the data.
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The Development Of Maccaferri’s Macres Reinforced Walling System With Steel Strip Reinforcing Elements
Of late there has been resurgence of interest, and in some quarters a preference to using steel inclusions as reinforcing elements in MSE (Mechanically Stabilised Earth) walls. An essential prerequisite for the effective introduction of any newly proposed system is to more accurately understand the pull-out resistance of the reinforcing elements and the specific nature of the reinforcement-soil interaction within the confines of prescribed select backfill requirements; an important concept fundamental to the design process. This paper originally presented at the 18th Southeast Asian Geotechnical Conference looks now at the strip development for Maccaferri Australia’s concrete panel and steel reinforcement retaining wall system, referred to as the MacRes System. It examines in detail the pull-out resistance of a newly developed steel strip as soil reinforcement in reinforced soil wall construction. The strip has indentations in an attempt to enhance the pull-out behavior. Large scale laboratory pull-out tests, using a pull-out box of 2 m in length, were conducted and the soil used was a silty sand from a borrow area. The testing program covered a wide range of overburden pressures from 15 to 120 kPa which enabled us to examine whether the calculated friction factor was dependent on the overburden pressure. Special dummy pull-out tests were conducted to correct the measured pull-out force and obtain the actual pull-out resistance. Independent consolidated drained triaxial tests, which measured dilatancy characteristics, were also conducted to characterize the properties of the tested soil.
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‘Value-adding’ to routine rock testing for underground excavation projects.
A geotechnical investigation will be enhanced by careful consideration, at its earliest stages, of the intended eventual construction methods and outcomes, and the expected time scales. This presentation will discuss the range of “routine” laboratory testing procedures for rocks that could be considered. Minor enhancements of standard testing and reporting procedures may yield valuable and subtle insights into potential rock mass behaviour and excavation efficiencies and contribute to beneficial improvements to eventual outcomes.
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Linking limit equilibrium analysis and landslide risk assessment
Current best practice for landslide risk assessment in Australia involves using the Australian Geomechanics Society (AGS) Guidelines for Landslide Risk Management (2007). However, many regulatory bodies (e.g. Councils) still adopt performance criteria relating to a factor of safety (FoS). Input parameters for limiting equilibrium analysis are often selected in a subjective manner. This can lead to significant differences in opinion between practitioners. Two issues are addressed in this paper, these being:
- Provision of a robust procedure for adopting modelling parameters and undertaking limiting equilibrium analysis.
- Linking limiting equilibrium results to a Landslide Risk Assessment (LRA).
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Design And Construction Of Plastic Geocellular Rain Water Harvesting/Stormwater Detention Tanks
Plastic voided modular structures (known as geocellular units) were first used in the mid-1980s in Europe below pavements to store stormwater. Its use has since spread to rainwater harvesting and on-site stormwater detention for residential, commercial and industrial developments. It is an environmentally friendly and sustainable solution. However, there are engineering pitfalls associated with the design and construction of plastic geocellular structures. The main pitfalls are associated with creep rupture of plastic structures, potential construction damage and the lack of care in wrapping the cells with filter fabric and backfilling procedure. As the scale and complexity of geocellular structures have significantly increased in recent years, guidance on appropriate design and construction methods has become more essential for these structures to be adopted as safe, yet economic and sustainable solutions.
In this paper, the author will describe his design and construction experience based on research associated with a court case on the damages associated with a major geocellular on-site stormwater detention project (approx. 8.5 Mega litres), and recent conversion of his backyard swimming pool to a 40,000 litre rainwater harvesting tank. References on design and construction guidance will be described together with the author’s personal opinion on the use of partial factors in the economic design of geocellular structures.