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Estimating The Occurrence Of Rockfalls In Columnar Basalt
The occurrence of rockfalls from a columnar basalt cliff at the Lal Lal Falls reserve, near Ballarat, Victoria has been estimated using erosion rates and historical data. Erosion rates were calculated from the volume of material removed over the past 3 million years, based on the geomorphological history of the site. Historical data included a rockfall in 1990, which caused the death of two high school students, and another rock topple observed in 1992. A reasonable agreement is found between the volume of material involved in the observed events and the calculated annual erosion rate. In the absence of more reliable data, the method provides a useful estimation of event size and frequency.
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Ground improvement techniques for the treatment of high-speed railway embankments
A high-speed railway project is currently being constructed between Rawang and Bidor in Peninsular Malaysia. The ground improvement methods adopted in the project are vibro replacement with stone columns, dry deep soil mixing (cement columns), geogrid reinforced piled embankments with individual pile-caps and removal/replacement works. This paper provides a detailed look into the vibro replacement with stone columns and dry deep soil mixing treatment methods while also providing an overview into the other treatment methods implemented in the high-speed railway project. The use of plate bearing tests and field instrumentation to monitor the performance of the stone columns and dry deep soil mixing ground treatment methods is also discussed.
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Interface shear behaviour of coir geotextiles and sand using large-scale direct shear tests
The practice of soil reinforcement using natural products is attaining widespread acquiescence in developing countries due to its availability, cost effectiveness and also due to its ability in effectively replacing synthetic reinforcing elements. Coir is an eco-friendly, biodegradable, organic material which has high tearing strength, stiffness, and durability compared to other natural reinforcement materials. Frictional characteristics of geotextiles were analyzed through large-scale direct shear tests to knock out boundary effects and to reproduce the results in prototype scale. Detailed parametric study was conducted by varying the particle size, normal stress and type of geotextile. The improvement due to the provision of coir geotextiles is expressed in terms of a non-dimensional parameter called friction angle efficiency. The results indicate that coir geotextile inclusions enhance the peak shear strength, angle of internal friction and ductility of sand. Also, geotextiles with small mesh openings and higher tensile strength provide better performance in terms of increasing the shear strength of sand.
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Settling And Consolidation Behaviour Of Dredged Cohesive Estuarine Soil Using Column Testing Apparatus
Consolidation testing on in situ normally or over consolidated cohesive soils is commonly used to assess engineering parameters such as Cv, Cc and Cα. However, the application of conventional consolidation tests to reconstituted soil slurries is often unachievable. A column testing method for assessing the settling and consolidation behaviour of dredged soils was devised and applied to five samples of estuarine soil in a brackish (somewhat salty) water environment sourced from the South Coast of N.S.W, Australia. Test results show that void ratio and bulk density values after the settling phase of the test were comparable with results of in situ soil at the initial stage of standard laboratory oedometer testing. Calculation of compressibility coefficients Cc and Cα after the loading stage of the test revealed similar results to oedometer testing on the soils in the in situ state. The testing method was assessed to provide results within a more reasonable timeframe with sample thicknesses of approximately 100 mm. It was assessed that soil thicknesses greater than 100 mm in the columns were influenced by simultaneous primary and creep settlement and that an unreasonable test duration would be required to achieve meaningful results in an economic timeframe.
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Solid loads on cut and cover tunnels under high fills
In recent years precast concrete arches have been increasingly popular for use in applications such as drainage culverts, conveyor tunnels, rail and road tunnels and alternatives to short span bridges. The design of these structures for fill heights greater than about 10 metres over the crown presents potential problems that require experience and careful analysis to resolve. These include:
- High axial loads and shear forces that may be sensitive to the stiffness parameters of the foundation and backfill materials.
- Design of foundation structures for high vertical loads.
- Longitudinal differential settlement.
- Longitudinal loads on the structure due to steep fill slopes, inclined structural elements and longitudinal spreading of the foundations.
In this paper examples are given of structures that have exhibited these problems and design methods are presented that will ensure that problems will be avoided. Examples are presented of successful projects in Australia and overseas, with fill heights of up to 50 metres over the structure.
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Fatigue And Stability Characteristics Of Open Porous Cement Base Material
As large cities experience rapid growth, greater pressure is placed on existing infrastructure, in particular the construction and maintenance of roads and highways. ‘Permeable pavements’ are an economical and sustainable alternative to mitigate problems associated with current road structures. They allow water to percolate through the road structure reducing the impact of rainfall events, filtering of the stormwater, and provide a method of harvesting water whilst withstanding low to medium traffic volumes. Permeable pavements have become well established in the past thirty years in many countries around the world. However, its development and application has been limited in Australia as no national guideline from Austroads exists. The objective of the research summarised in this paper is to determine the structural and hydraulic performance of open porous cement stabilised materials. It is concerned with understanding the fatigue properties of cement stabilised permeable materials under real traffic conditions. In an attempt to fully understand the properties of the material, laboratory testing has been carried out to determine structural and hydraulic properties. These included the tensile and compressive strength, permeability, grading, effective void ratio, flexural stiffness and Young’s modulus. These tests were carried out on a group of samples with different aggregate sizes and shape to understand the relationship between the strength of the permeable material and the hydraulic parameters. Based on the results achieved, in obtaining optimum structural outcomes a balance needs to be established between structural and hydraulic properties. Further, based on fatigue characteristic of the samples, it was concluded that permeable stabilised material can withstand five million fatigue cycles without excessive cracking and deformation to the pavement structure. Hence, for low to medium traffic conditions, permeable pavements are a practical alternative to current impermeable design.
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Initial Moisture Content Bias In The Shrink-Swell Test Maintained
Following our presentation to the NZGS (Rogers and McDougall, 2020), a paper was published in Australian Geomechanics titled “On the Common Criticism of Initial Moisture Content Bias in the Shrink-Swell Test”, which sought to defend the shrink-swell test against our conclusion that it is flawed (Fityus and Burton, 2020). The present paper is offered by way of response.
Fityus and Burton offer interesting ideas related to the role of suction, and the variability of soil. However, our data analysis, since published in full (Rogers et al., 2020), still raises important concerns which have not been satisfactorily addressed. This is especially so with respect to the break-down of contributions from each of the shrink and swell strain components which readily show that in all cases (including Australian datasets) there is not an inverse relationship between the swell strain and the initial moisture content, which would be necessary for the shrink-swell test to properly remove the initial moisture content bias.
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Effect Of Enhanced Biodegradation On Settlement Of Municipal Solid Waste Landfills
Recent studies of municipal solid waste landfills have revealed the influence of biodegradation upon secondary settlement. Modern landfills, however, are designed with efficient containment systems which minimise moisture ingress and thereby reduce leachate and gas generation. The shortage of moisture means that these containment systems delay decomposition and stabilisation of waste. An alternative approach is to enhance biodegradation by designing and operating landfills as bioreactors. Leachate and gas are then produced during the early stages when the containment system is new and risk of failure is low. Additionally, accelerated stabilisation allows earlier re-use of the site. This paper describes an investigation conducted in a full-scale bioreactor cell at the Lyndhurst Landfill in Victoria, Australia, to demonstrate the effect of enhanced biodegradation upon secondary settlement. A hyperbolic settlement model is used to quantify the acceleration of settlement due to enhanced biodegradation and to predict the continuing settlement-time relationship.
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Recent experiences with soil nailing in deep cuts as part of level crossing removal works in Melbourne
The adoption of prudent soil-structure design parameters is a critical component of the design of soil and rock retention systems. Designs must also account for the influence of construction practices on performance. This paper discusses the adopted design soil parameters, construction practices and the measured response of soil nail retention systems at four sites in Melbourne as part of the Furlong Road, Main Road, Blackburn Road and Heatherdale Road level crossing removal project (FMBH LCRP). The project involved retention of near vertical cut faces up to 15 m high such that existing rail lines could be lowered to pass under local roadways. In the case of Furlong and Main Roads, the geological setting comprised Pleistocene age residual basaltic clay overlying basalt rock. At these two sites, a greater than expected degree of soil fissuring was observed. This paper presents a theory on the origin of the fissuring and construction methodologies that were used to reduce the risk of instability posed by the fissured soils. The geological setting at the Blackburn and Heatherdale Road sites comprised Silurian age residual siltstone clay overlying variably weathered siltstone rock. This paper describes some of the challenges involved in constructing soil nail retention systems in the two different geological settings, including the varying influence of drilling practices in both settings.