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A Photographic Essay On Landslides Across Southeastern New South Wales Triggered By The Rainfall Events Of 2022
Eastern Australia has experienced a significant magnitude rainfall event of extended duration in the first 7 months of 2022. Across the east coast of New South Wales (NSW) a series of troughs and East Coast Lows occurred during a La Nina weather cycle bringing above average rainfall to the region. As this first half of 2022 La Nina event was drawing to a close the Indian Ocean Dipole entered a negative phase which coincided with another intense East Coast Low in early July 2022 impacting the Illawarra region of NSW. These events caused widespread flooding and significant landslide damage to road and rail infrastructure across the state networks and local government infrastructure across NSW. During this extended wet period in the first 7 months of 2022 more than 200 landslides have been recorded across the Illawarra, Southern Highlands and Blue Mountains regions of NSW whilst many more have occurred across the north coast region. This paper presents a brief and albeit preliminary summary of the rainfall and provides a series of photographs with very brief descriptions of some of these landslide events within southeastern NSW. The intent of the paper is to provide early guidance to AGS members of the nature and form of landslides that have occurred across the Illawarra region. This paper does not discuss the dual fatality resulting from the Wentworth Falls area rockfall of the 5th April.
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Geological constraints on Mmax values from Western Australia: Implications for seismic hazard assessments
Although Western Australia is commonly viewed as a Stable Continental Region with low rates of earthquake activity, geological and geomorphological evidence indicates that active tectonic processes are occurring. A zone of intraplate transpressional shear (the Western Australia Transpressional Belt—WATB), extends southwest from near Savu Island, Indonesia across the North West Shelf through the Cape Range and the Gascoyne alluvial plain to the Mt. Narryer fault zone (~-27.5˚S). The North West Shelf is accommodating crustal flexure and shallow faulting due to the collision with the Banda Arc, the central west coast exhibits evidence of active fold growth since Marine Oxygen Isotope Stage (MIS) 5e and the Murchison region has evidence of Quaternary tectonic deformation and a record of two large magnitude historical earthquakes.
Geological data to constrain maximum earthquake magnitude (Mmax) estimates for individual seismogenic sources within Stable Continental Regions (SCRs) are lacking. However, within the Stable Continental Region (SCR) of Western Australia, individual morphotectonic structures exist that can be parameterized for inclusion in seismic hazard analyses. Recent studies of the WATB have identified a number of morphotectonics structures that provide structure specific seismic source data. Reverse reactivation of normal faults is manifest as surface expression of faultpropagation folds in the Murchison region. These individual blind-reverse faults are capable of generating earthquakes in the range of Mw6.4-7.4, which is consistent with the largest historically observed earthquake in the region, the 1941 Mw 7.1 Meeberrie event. The rupture of combined fault segments could push these Mmax values up to Mw 7.4-7.7, which would be similar to the 2001 Mw 7.7 Bhuj India event. Ongoing characterization of these features within the WATB has implications for probabilistic seismic hazard analyses (PSHA) in the region. Where these types of structures exist, Mmax estimates may differ from the Mmax values previously suggested in the Brown and Gibson (2004) and Clark et al. (2011) domain models.
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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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Woolgoolga To Ballina Pacific Highway Upgrade – Reliability Assessment Of Soft Ground Treatment Design
Eleven road sections with an approximately 20 km total length out of the 155 km Pacific Highway Upgrade project between Woolgoolga and Ballina (W2B), NSW traverse areas having significant depths of soft soils. At Maclean Interchange or Clarence River Interchange, soft soil thickness was up to 20 – 25 m under the road alignment. Soft ground treatment design for the identified soft soil areas was undertaken in 2014. The main objectives of the soft ground treatment were to provide certainty of delivery of the highway upgrade within a given time during the main contract with a satisfactory long-term pavement performance.
The highway section between Whytes Lane and Pimlico Road of approximately 3.85 km is one of the longest road sections underlain by up to 8 m thick soft soil that required ground treatment. Due to the significantly length of the soft ground treatment for this road section, one of the main objectives was to reduce or optimise the cost of soft ground treatment.
During the detailed design stage, soft ground treatments using preloading with or without Prefabricated Vertical Drains (PVD) were considered. Due to issues such as sample disturbance during soil sampling and transporting, limitations of the adopted soil testing methods and equipment, limitations of the available geotechnical investigation information, there was a possibility that the actual ground behaviour could be different from the predicted behaviour using the design soil parameters. Reliability analyses were carried out to assess the potential variability of material parameters on embankment settlement and ground treatment requirements.
The reliability assessment provided quantitative confident levels of the ground treatment designs and suitable contingency measures. The reliability assessment provided indication of the cost and risk balancing. The target confidence level was minimum 70% for the soft ground treatment design with the proposed observation method and contingency measures such as placement of additional surcharge or additional preloading time to respond to changes during the preloading period. The reliability assessment also effectively assisted the client’s decision on the preferred soft ground treatments.
The adopted reliability assessment method as described in Duncan (2000) and the assessment results for the soft ground treatment design were presented. The embankment settlement was monitored during the preloading stage and was back analysed. The reliability assessment results, which were analysed in the design stage, and the ground treatment design were reviewed against the actual embankment settlement performance.
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Excavations and the Next Door Neighbour
I have recently seen an increasing number of geotechnical reports that imply that using Ko=1-sinφ’ (the coefficient of earth pressure at rest) to design basement retaining walls is appropriate and will, to a large extent, prevent movement of neighbouring properties. Can this be justified?
Ko, as we all know, is the ratio of the horizontal to the vertical stress in the ground. Although it is generally accepted that Ko = 1 -sinφ’ applies to normally consolidated soils (Bishop 1958), it is a function of stress history. Since most Australian soils are the product of complex weathering and desiccation processes, they are generally over-consolidated and it is probably wrong, more often than not, to assume Ko=1-sinφ’.
Alternatives are available and guidance can be found in papers such as Mayne and Kulhawy (1982), from which the expression Ko =(1 – sinφ’).OCRsinφ’ might be chosen as a more rational alternative. This could present problems if, as is so often the case, testing has been omitted to save money and neither φ’, nor OCR, are known. In this case it might be better to guess a plausible, but conservative, value of Ko based on experience and a knowledge of the local geology. In most cases a “conservative” value of Ko is a high one, but the specific application needs to be considered and a high, or low, value chosen as appropriate. Ko=1 may not be unreasonable, at least as a starting point, in many situations.
It is simple enough to design a retaining wall to withstand Ko stresses, but this does not mean they will eventuate, or that the resulting wall will prevent ground movement. If the objective is to try and minimise movement then analysis of the entire construction sequence is required, using realistic values of the basic parameters. It may be worth keeping the following thoughts in mind:
- Ko stresses will only be maintained if zero ground movement occurs. Even with diaphragm walls and very stiff, top down, construction this is hard to achieve in practice, so actual stresses are nearly always less than the Ko ones.
- Relatively small movements of a wall during excavation and anchor installation are enough to cause stresses to drop to the active (Ka) value. This can be demonstrated using WALLAP, FREW, or a finite element/difference program to model the construction sequence.
- Walls are often allowed to cantilever as much as they can before the first row of anchors is installed. This causes movement that is usually close to the maximum that the wall will experience on completion and the stresses drop to the active value.
- Stressing anchors to high levels, once a wall has been allowed to deflect, increases stresses in the wall, but does little to redress ground movements that have already occurred.
- In practice, ground movements are more likely to be limited by undrained conditions during excavation, than by anything that the engineer can do to stiffen the restraint. Whether this can be relied on in a particular instance to limit ground movements needs careful evaluation.
- Where a basement is built in open cut, ground movements will have occurred during excavation and cannot be reversed. In this case earth pressures on the wall are more likely to be governed by the level of compaction given to the backfill, as suggested by Ingold (1979), than by the original Ko condition.
To me this illustrates that design, of even a commonplace construction element such as a basement wall, requires very careful consideration and my concern is that there is a modern tendency to ignore the complexities. This may be due to a lack of time, a lack of money, or even to a lack of interest in the subject, as Tim Sullivan’s recent discussion of post- graduate study might suggest (Australian Geomechanics, December 2003). Whatever the cause, geotechnical engineers are paid to give advice that is reasonable and appropriate in relation to every one of their projects. This requires site specific data and site specific thought. Relying on “off the shelf” reports with little or no data can have dire consequences and the excuse that it was only a “cheap” investigation holds no water when things go wrong. I urge any of you who provide geotechnical design advice to keep your thinking cap on at all times – to lose it is to court disaster!
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Assessment Of Existing Foundations For Building Upgrade Projects
Building owners are often faced with the question of whether to demolish and rebuild to gain extra floor space, or to assess if existing buildings can support additional levels. Aside from the adequacy of the superstructure, consideration must be given to the capacity of the existing foundation system to cater for the increased loading. Douglas Partners (DP) has employed a range of portable equipment for use in often congested basements and poor access areas, to investigate and develop a geotechnical model for such sites.
Where no records exist, or where the assessment of the existing pile foundation is required for QA purposes, low-strain pile testing techniques may be used to determine pile lengths. The geotechnical model and existing foundation details are subsequently combined to assess the capacity and expected settlement performance of the existing foundation system. In most cases, increased confidence in parameters and advances in foundation analysis and design methods has permitted extra floors to be added, thus realising a large capital benefit for the owner of the building.
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Relative compaction: In search of a rational method for specification
The primary purpose of compacting engineered fills is to expel water and air from the soil matrix to achieve an increase in stiffness, thereby reducing the likelihood of post construction settlement.
Engineers and earthwork contractors are accustomed to adopting ‘relative compaction’ as a means of compliance testing. Specifications relating to earthwork construction control are commonly expressed as:
γd field / γd max x 100 > R (%) (1)
where γd field is the material density of the material measured in the field , γd max is the maximum dry density obtained from a known energy input and R(%) is the required relative compaction. Despite being widely accepted, relative compaction does not have any direct correlation with the known properties of a material. Hence, there is no rational method for selecting an acceptable percentage R(%) for a particular purpose (Gue and Liew, 2001).
The intention of this paper is to the investigate the rationale behind the perceived need within the construction industry to specify a minimum density ratio R(%) and consider what rational recourse a civil engineer or technician has when a compaction specification cannot be met.
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Ground Investigation In The Sydney CBD — A More Sustainable Model For The Future
Below Sydney’s central business district (CBD) lies a complex network of transport and service tunnels competing for space with building basements and confined by changes in topography. Although the geological setting is well understood and documented, potentially millions of dollars are spent each year on new ground investigations. Why?
Over the last 50 years, NSW Government departments have spent millions of dollars on substantial engineering and geotechnical site investigations within the Sydney CBD and are estimated to have drilled thousands of boreholes.
The majority of existing geotechnical information was collected by government departments and geotechnical consultancies and stored in libraries or archived. Over time this data may become misplaced or in many cases disposed of. There are many government departments and consultancies that preserve data in systematic electronic GIS type databases. Indeed, if the basic information was attributed (e.g. grid coordinates, borehole No., Department, and Project No. etc.) the stored data could be assessed quickly to determine if any data is located within a project area by interrogating a central GIS database (or GIS web service) and therefore retrieved from the relevant storage achieve or geotechnical consultant at minimal cost. The NSW Government is planning on making it mandatory to apply for permits to drill, but also to record information from any borehole that encounters groundwater or potentially water bearing rocks. Permits and recording of boreholes is also the case within mining and mineral exploration in NSW. It is therefore envisaged that much of the geotechnical investigation data produced across the Sydney CBD could be centrally stored in a GIS database. A data model based on the British Geological Survey – National Geoscience Data Centre model is proposed to more efficiently store large amounts of geotechnical data. Access to this information could then be provided through a secure, GIS-based Internet web portal. In many cases, planning for new projects could rely heavily on accessing existing data through this single point-of-truth database and over time, new geotechnical models could be added to further develop an evolving 3-D geological model of the Sydney CBD and other key locations.
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Digitalisation and Automation of Road Materials Compaction: SPARC Intelligent Compaction Kit
‘Intelligent Compaction’ (IC) broadly refers to the compaction of road materials, primarily using advanced sensing and automation, which achieves the target performance over their design life. Our recent international workshop on intelligent compaction highlighted that countries like US and China have implemented IC technology in practice as a mandatory requirement for contractors almost 6 years ahead of Australia. Our online questionnaire survey results indicated that the slow adoption of IC technology in Australia is mainly due to the lack of standards or specifications for the use of IC technology and the lack of confidence among contractors who already have an existing fleet of conventional rollers for compaction. There are some retrofittable kits available in the market that can facilitate IC with conventional rollers. However, the main limitation of these kits is that they provide only one parameter out of various intelligent compaction meter values (ICMVs). We are developing an innovative kit with cutting-edge hardware and software tools to facilitate performance-based compaction of road materials. The key features of our kit include [i] facilitating simultaneous visualisation of multiple ICMVs on both onboard and remote systems in real-time during compaction, [ii] providing versatility to retrofit a conventional roller, [iii] flexibility to incorporate corrections for different ICMV indicators, [iv] facilitates customising to construction specifications in line with the ongoing industrial digitalisation, and [v] integrable with the existing post-processing software such as Veta to view and analyse the collected IC data. In this paper, we provide the basic design concepts of the kit, its functionalities and capabilities with initial test results. The design concepts of the kit prototype will be further refined in the future based on the field trials undertaken on different materials using different roller types. The experiences gained through using our kit in actual construction projects will pave the way to develop robust and data-oriented specifications for IC to be used by the Australian road construction industry.