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Assessment of the AS2870 standard designs for residential rafts on reactive clay
The standard raft designs set out in AS2870 are adopted for a significant proportion of residential buildings being built across Australia. Of recent years there has been increasing media coverage relating to the poor performance of footings for residential buildings, particularly in areas of Victoria underlain by Newer Volcanics basaltic clays. There are many aspects which govern the performance of footings founding on or in reactive clays, and questions regarding the appropriateness of the recommendations in AS2870 are being raised. One such question is whether or not the standard raft designs in AS2870 are satisfactory for the reactive clay sites they were formulated for. This paper presents the results of preliminary three dimensional finite element soil structure interaction analyses of the performance of standard type waffle and stiffened rafts founded on reactive clay with H2 classification. The analyses, based on simplified but reasonable assumptions, show that the waffle raft is substantially less robust than the stiffened raft. They also indicate that, for the assumptions made, the calculated performances of both types of raft do not meet the requirements for design of rafts by engineering principles, and that the rafts are unsatisfactory with respect to vertical differential movement and structural capacity when subjected to design characteristic surface movements. Whilst significantly more refined analyses and research are required to increase the absolute accuracy of these results, the results of these analyses cast doubt on the use of AS2870 standard raft designs for H2 sites and potentially for other reactive clay sites. This is particularly relevant in the greater Melbourne area given the projected levels of population growth in the coming years in areas which are underlain by highly reactive basaltic clays.
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Unbound granular base course with shallow foundation concept
This study aims to introduce alternative design procedures for a flexible pavement base course by utilizing the ultimate strength criteria with sophisticated laboratory results of base course materials. Current pavement design mostly avoids all complicated behaviours of an unbound granular base layer considered only as a layer transferring traffic loads to underneath layers regardless of the base course deterioration. Based on the design protocol, there are only the design criterion of the horizontal tension and the vertical compression occurring at the bottom of asphalt layer and at the top of subgrade, respectively. The real behaviour of a base course under traffic loads has been rarely accounted for in pavement design protocol. Nowadays, traffic is growing in terms of magnitudes and quantities and causing premature deterioration in a base course layer leading to major damage in pavements. The study presents theoretically the more suitable approach of the stress and strain distribution in a flexible pavement using the finite element method. An example of a conventional pavement structure consisting of a surfacing, a base course, a sub base course and a subgrade with a single wheel load of 750 kPa standard pressure was selected was established to investigate all pavement phenomena. The effects of uniform design pressure and material attributes which were generated by traffic were investigated. Moreover, the new design criteria for an unbound granular layer were defined as the ultimate strength design and the bearing capacity factor resulting from the application of the shallow foundation bearing capacity concept within the California Bearing Ratio (CBR) results. Our findings were reported and used to draw up the guideline and recommendation on the current pavement analysis and design.
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Rockfall Risk Assessment Burleigh Head National Park
An assessment of rockfall risk and control options for the Burleigh Head National Park, Queensland is presented. The park consists of a headland which rises from a basalt boulder beach to a rain forest covered plateau approximately 70 m above sea level at a slope inclination of 35o to 45o from horizontal. The basalt cap, which forms the plateau, is columnar jointed with the columnar blocks typically 1 m in diameter and 1.5 to 3 m long. Columnar boulders from the plateau occasionally fall, bounce, roll and slide down the lightly vegetated slope towards the beach with some of the boulders landing on or passing the Ocean View Circuit walking track near the base of the slope. Many of the recent rockfalls have occurred during or immediately after an intense rainfall event or period of prolonged rainfall. A quantitative assessment was undertaken to determine the risk to people walking along the Ocean View Circuit being struck by rockfalls and the risk reduction capabilities of various remedial work options. Probabilistic analysis of rockfall trajectories was undertaken using the computer program ROCKFAL3 to produce distributions of boulder kinetic energy, bounce height and stopping distance relative to the walking track. Both total annual risk and individual risk were calculated. Risk levels were compared with various published acceptable risk criteria to determine if remedial action is warranted. The risk reduction capability of scaling operations, rockfall catch fence construction and temporary track closure during high risk periods was assessed. Catch fence design requirements were determined from ROCKFAL3 probability distributions.
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Railway Engineering And Geotechnical Engineering Are They Married Yet?
Challenges for Geotechnical Engineering in Railways and the gap between research work and the needs and expectations of Rail Operators.
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Short And Cumulative Long Term Impacts Of Subterranean Cut-off Walls And Excavation Dewatering On Adjacent Structures In Urbanised Areas
This paper describes the hydrogeological and geotechnical assessment in relation to the short and cumulative long-term impacts associated with excavation, subterranean construction and dewatering in the Double Bay commercial area on the structural integrity of adjacent residential and commercial buildings. The paper comprises three main components, namely, (i) definition of groundwater study area and its geological and groundwater settings; (ii) assessment of potential cumulative impact of future developments on long-term groundwater change; and (iii) assessment of potential impact of short-term construction dewatering on risks of damage of adjacent buildings.
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Earthquake Dynamic Analysis Of A Hospital Building
This paper deals with the construction of the new Acute Care Hospital which forms part of the redevelopment of the Royal North Shore Hospital complex in Sydney. The hospital as a building essential to post-disaster recovery function has the highest importance level for a structure in accordance with AS1170.4:2007. This means that the structure requires dynamic analysis to be performed as the building is more than 12 m in height.
The Acute Care Hospital is 9 storeys high with allowance for 2 additional storeys. It is characterised with irregularities on the floor plate size and layout. The earthquake resistance elements of the building are the shear walls in the form of multiple lift and stair cores.
Using Finite Element Modelling (FEM) software namely Strand7, a three-dimensional computer model was developed and dynamic analysis was carried out using response spectrum method. Dynamic analysis output highlighted the different lateral load distribution among the cores when compared to static analysis and gives an indication of the true principal orthogonal directions of the building.
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Use of small unmanned aerial vehicles and related digital data in geotechnical and natural hazard impact assessment
Unmanned Aerial Vehicles (UAVs or drones) facilitate data collection that allows rapid and enhanced geotechnical assessment of the risks associated with landslides, slopes and structures during normal conditions and following natural hazard events.
WSP Opus has used UAVs over the past 10 years in New Zealand, and more recently in Australia, to assist engineering assessments for highways, railways, and infrastructure for local authorities, government departments and private clients. The early uses were mainly for occasional geotechnical slope and site mapping purposes. However, since 2011 UAVs have been systematically used for surveying and geotechnical applications. Examples are presented in this paper of the use of UAVs for assessment of slopes and existing landslides, as well as for post disaster assessments.
UAVs were utilized following the damaging February 2011 (M6.3) Christchurch Earthquake, the 2011-2015 storm events in central New Zealand, and the November 2016 (M7.8) Kaikoura Earthquake to inspect and provide damage records of sections of highways, slopes, and river stopbanks (levees), and to facilitate rapid development of remedial options.
The data gathered from UAVs have been used with post processing of imagery to create 3D terrain models. Comparison of periodic UAV derived models or comparison with previous LiDAR models enabled the detection and monitoring of slope change in areas affected by slope failures along transportation corridors. UAVs were also used to inspect and obtain geological data to assist with the assessment of rock slope stability. In the Blue Mountains Rail Corridor (NSW) in Australia, the use of UAVs provided a much safer alternative than having staff carry out observations directly (for example by rope access), given the hazardous nature of these locations. A comparison of geological and other data obtained from UAV inspections with those gained from conventional methods showed good correlation.
In addition to the safety benefits, the use of UAVs has enabled better and early decisions to be made to manage the risks associated with hazardous sites, and the rapid development of remedial solutions.
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Pile Testing Verification β an Alternative Approach
Dynamic pile testing is undertaken for a number of reasons including: 1. To confirm that the pile meets serviceability and geotechnical capacity requirements; 2. To assess pile integrity, either during installation (driven piles) or after construction (cast-insitu piles) and 3. To verify that the piling hammer delivers the energy required to satisfy the design criteria and that stresses during testing are kept within acceptable limits. In addition, testing allows us to establish and calibrate acceptance criteria – relationships such as resistance vs set curves, and/or correlated pile driving formulas. These relationships are premised on the interrelationship of capacity (C), transferred energy (E) and pile movement (M) which is represented primarily by pile set. These ECM relationships allow capacity to be inferred from measurement of transferred energy and pile movement and are used to infer the capacity of untested piles. However, for a variety of reasons, transferred energy can vary significantly between piles which, being undetected, undermines the reliability of ECM relationships. An alternative approach to using ECM relationships is proposed based on pile set and pile force (F). We demonstrate through parametric studies and review of project data, that these FCM relationships are reliable alternatives which bypass the problems with variable energy transfer. Of course, impact force will also vary with hammer performance, but impact force can generally be accurately determined from the measured impact velocity as a proxy. Pile velocity can be measured by attaching a single accelerometer to the pile, or by using a high frequency displacement monitoring device. FCM-based acceptance criteria have the significant advantage that both the necessary force (F) and displacement (M) inputs can be verified by simple measurements on all untested piles.
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Geotechnical stability assessment of the Mount Morgan fireclay caverns
This paper describes a qualitative geotechnical risk assessment of the stability of the Fireclay Caverns at the Mount Morgan Mine, located about 25 km south west of Rockhampton and comments on methods to manage and reduce geotechnical risk related to the caverns and nearby associated excavations.
Due to the discovery of dinosaur footprints in the roof of the caverns, the Department of Natural Resources and Mines (NR&M) propose developing tourism in the area by expanding visits to the caverns. Currently approximately 7,000 tourists visit the caverns per year.
The aim of the risk assessment was to assess the geotechnical stability of the fireclay caverns for the installation of boardwalks and staircases to provide access for tourism and as a guide to the interpretation, planning and long term management of the site to view dinosaur footprints expressed as impressions in the cavern roofs.
It was recognised that near the dinosaur footprints, subject to the stability hazard, the support of roof and walls using rock bolts or shotcrete would be regarded as a last resort.