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Technical Note On Pseudo-Static Seismic Pressure Applied To Retaining Walls With Linear Surcharge In C-Ø Soils
This study has explored seismic pressure applied to retaining walls with linear surcharge effect in cohesive-frictional soils, assuming three general approaches. The first approach provides a formulation. This formulation is able to calculate the seismic pressure, the seismic pressure coefficient, and the angle of failure wedge. The second approach provides dimensionless graphs for designers. There are three general graphs for calculating the seismic pressure applied to the wall and four graphs for determining the minimum and maximum seismic pressure levels. The lower limit of each graph shows the minimum active soil pressure coefficient (kase(min)) at the lowest surcharge distance, and the upper limit shows the maximum active soil pressure coefficient (kase(max)) at the highest surcharge distance from the wall. Five comprehensive graphs are presented to determine the angle of failure wedge. These graphs show the changes in the internal friction angle of the soil, cohesion, linear surcharge, horizontal acceleration coefficient, surcharge distance from the wall, and the friction angle between the soil and wall. In the third approach, all specific and unique wall analyses can be performed by referring to MATLAB software and using programming codes. Compared to other methods, the proposed method has the advantage of considering soil parameters such as cohesion, soil internal friction angle, friction angle between the soil and wall and linear surcharge in elasto-plastic soil and in seismic conditions. Other advantages include the calculation of excess stress distribution due to surcharge, the distribution of total seismic stress, and the calculation of depth of tensile crack. Comparison of the results of the proposed method with previous methods and numerical software shows the accuracy of relationships and graphs.
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Temporary Support Of Deep Basement Excavations In Rock
Deep basements have become common in our modern cities. Whilst the analysis and design of retention systems for deep basements in soil are relatively well established, the same cannot be said for deep basement retention systems in rock. In many instances the design of retention systems in rock are based on a soil mechanics approach and as a result often ignore unique aspects of rock mass behaviour that can significantly impact the performance of these retention systems. It is important that the characteristics of the rock mass are well understood and are quantified during the ground investigation. Some of the aspects of retention system design and analysis that are set out in this paper only became apparent following unsatisfactory performance of a retention system. Due to the sensitivity surrounding such unsatisfactory performance, it has not been possible to include the specific case studies. As a result, this paper provides an overview of the many aspects involved in respect to ground investigations, analysis, design and construction of deep basement retention systems in rock that are required to mitigate against unsatisfactory performance. This paper is restricted to temporary embedded wall retention systems that are installed to allow the construction of the permanent basement structure.
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Seismic Analysis For Open Pit Mines
Open pit mines are of a dramatically different scale and nature to most civil works, so seismic analysis techniques required for open pit mines are also very different to those for civil works. This paper demonstrates two important aspects of the seismic behaviour of open pit mines; site response effects resulting from large scale man-made and natural topographical features, and the effect of earthquake ground motion on seismic stability assessments for steep and high slopes. An understanding of the first aspect is a prerequisite for understanding the second aspect.
The effect of topographical features is generally to amplify ground motion at the crests of pit slopes and ridges, and up through spoil piles. These effects will alter response spectra for infrastructure design. Slip mass scale effects mean that, during an earthquake, the maximum average acceleration within a slip mass is less than the maximum surface acceleration. The combination of these two effects means that the appropriate value of acceleration for use in slope stability calculations is highly dependent on topography, and the size and location of the potential slip mass under consideration.
Seismic analysis techniques for open pit mines are not well established. Two case studies, one of an open pit slope, and one of a large ore spoil pile on a ridge, demonstrate that meaningful insights, based on sound engineering principles and consistent with the literature, can be obtained with the use of appropriate and thorough seismic analysis techniques. It is suggested that dynamic analysis is required to assess seismic behaviour at open pit mines.
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Geotechnical Lessons From An Extreme Geo-disaster: Visit To The May 2008 Wenchuan Earthquake Zone, China
This paper summarises key geotechnical findings arising from studies by others and from a visit to the Wenchuan earthquake zone in China. The magnitude and scale of the May 2008 Wenchuan earthquake classifies this event as an extreme geo-disaster. Such events do not often attract the technical attention of the geotechnical profession due to their low probability-high magnitude nature which is outside the normal design codes and construction standards for engineering structures. However, study of these extreme events can provide valuable insight to the performance of natural and engineered systems under severe loading which can lead to improvements in geotechnical models and engineering design under normal loads.
The geology of the Wenchuan earthquake is described including the surface rupture and ground shaking features. Seismic damage to structures including buildings, dams and tunnels is discussed, highlighting the role of design codes and construction standards on damage control. Coseismal geohazards such as landslides, debris flows and landslide dams are summarised including mechanisms and impacts on life and property. Overall, the primary controls on the extensive devastation suffered include the high magnitude, shallow depth and long duration nature of the seismic event, the strong vertical component of movement due to the imbricated thrust tectonic control on movement and the fact that deformation was not constrained to the main rupture plane but also occurred along secondary structures between bounding faults within a structural zone some 50-70 km wide and 500 km long.
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Geotechnical Challenges In Design And Construction Of Bridge Foundations And Approaches In Hilly Granite Formation
This paper presents a case study of geotechnical design and construction challenges of bridge foundations and approaches in a hilly granite formation in northern New South Wales, Australia. Firstly, the geological formation and existing cut slope conditions which have high risks of rock fall will be described. The original design was based on the available geotechnical information and assumed construction methodology. Reinforced concrete cantilever retaining walls founded on mass concrete were adopted for the bridge southern approach to resolve constructability issues over hilly terrain. The design considered retaining wall block sliding stability while overturning and internal stabilities were satisfied. Slope treatments using a rock fall fence together with individual boulder stabilisation or removal were also considered. It was found during construction that the actual ground conditions were different to that originally inferred and modifications to pad footing designs were deemed necessary. Additional investigations were undertaken, and the subsurface ground models updated to inform the revised design. For the northern bridge abutment foundation, a piled foundation was introduced to optimise the design with due consideration of temporary piling platform and access along a new geotextile reinforced approach embankment. The revised design was developed in close collaboration with the Contractor and the Principal. The foundation design of Pier 2 was revised using micro-piles to address the presence of a weak rock layer intrusion. In the end, key lessons learnt from this challenging project have been summarised for future project references.
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Prediction of collapse potential for silty glacial sand
This paper examines the wetting induced collapse behaviour of three different silty glacial sands from South Australia. Single-oedometer collapse testing was applied to determine the wetting induced collapse settlement. For each soil, three different initial dry unit weights (one close to the field dry unit weight) were used to investigate the effect of dry density ratio. For each dry unit weight, specimens were inundated at varying pressure to investigate the effect of wetting pressure. Dry density ratio, percent of clay fraction, wetting pressure and the initial degree of saturation were found to be the key factors controlling the collapse behaviour of soil. A new empirical equation was proposed to predict the collapse potential of soil depending on the aforementioned factors. The empirical equation gave good predictions for the South Australian silty sand. Verification of the proposed equation was performed using existing data from the literature. The proposed equation gave much better estimates than that obtained from existing prediction equations.
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Embodied Carbon Assessment of Geotechnical Works
In the light of rising construction sustainability concerns, embodied carbon assessments are often one of the main engineering tools to identify the best “green” option. Embodied carbon assessments provide a simple way to quantify and measure the summation of all the greenhouse gases generated from the built environment. It includes a whole life carbon cycle assessment of a given project from the impacts of materials production, transportation, installation, maintenance, and any waste or disposals during and at the end of design life. This paper aims to allow geotechnical engineers to quickly determine the embodied carbon of their design, and more profoundly form the basis of an innovative and efficient design approach with the consideration of intelligent and alternate material choice to achieve the same performance. In this paper, the methodology of embodied carbon calculation will first be introduced, followed by a summary of carbon emission factors (CEF) that are applicable for geotechnical designs. The discussion herein will focus on the initial portion of the embodied carbon life cycle assessment which comprises of the “before use stage” only for a particular project. Case studies on the use of embodied carbon calculations were provided for a variety of geotechnical projects including foundation for road embankment, trench excavations, and tunnel design. These case studies will show the significance of carbon calculations during the initial design stages and its value in recognition of projects’ sustainability goals. Alternative real-life solutions in achieving de-carbonization will also be presented as a concluding remark, highlighting the possibility of sustainable design in geotechnical practice.
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Geotechnical Offshore Site Investigation And Reclamation Design At Port Kembla
Port Kembla is an active seaport situated approximately 90 kilometres south of Sydney. The majority of the current port activities are focussed in the Inner Harbour area of the Port. However, as this is reaching capacity, the port authority is turning its focus onto the planning of the development of the mostly undeveloped Outer Harbour. Stage 1 and 1A (Phase 1) development of the Port Kembla Port Corporation (PKPC) Outer Harbour master plan would create one additional bulk cargo berth and approximately 10 hectares of reclaimed land. In February of 2010, PKPC awarded Snowy Mountains Engineering Corporation (SMEC) the contract to undertake Phase 1 detailed geotechnical site investigation works, and the associated reclamation and berth designs.
The Outer Harbour has been subjected to deposition of materials from five previous disposal campaigns, whereby dredged sediment from the Inner Harbour was disposed of within the Outer Harbour. Underwater containment bunds of uncrushed blast furnace slag were constructed for one of the disposal campaigns, and the contained areas were filled with spoil that typically consists of unconsolidated, very soft, compressible clay. This is consistent with geotechnical interpretation based on site investigation data which found that unconsolidated dredged fill, up to eight metres thick, underlies the majority of the Stage 1A and 1B development, generally thickening towards the east and southeast.
Phase 1 geotechnical design for the Outer Harbour development includes the design of containment bunds and land reclamation design associated with subsequent infilling with appropriate select fill material. Various design options were considered for both the bund and reclamation construction. Instrumentation and monitoring were proposed as part of the detailed design in order to confirm design assumptions and monitor the performance of the reclamation.
As the detailed design progressed, PKPC made the decision that the conforming design, which satisfied the original scope of works and settlement criteria, would not be constructed. Their preference instead was for a reclamation design that eliminated the need for removal of any of the underlying dredged spoil and did not utilise ground treatments other than passive preloading and surcharging techniques. The developed design has since been issued for tender and a constructor selected with construction about to commence.
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Pit slope failure evaluation in near real-time using UAV photogrammetry and 3D limit equilibrium analysis
Slope failures are an inevitable aspect of economic pit slope designs in the mining industry. Large open pit guidelines and industry standards accept up to 30% of benches in open pits to collapse provided that they are controlled and that no personnel are at risk. Rigorous ground control measures including real time monitoring systems at TARP (trigger-action- response-plan) protocols are widely utilized to prevent personnel from being exposed to slope failure risks.
Technology and computing capability are rapidly evolving. Aerial photogrammetry techniques using UAV (unmanned aerial vehicles) enable geotechnical engineers and engineering geologists to work faster and more safely by removing themselves from potential line-of-fire near unstable slopes. Slope stability modelling software using limit equilibrium (LE) and finite element (FE) methods in three dimensions (3D) is also becoming more accessible, user-friendly and faster to operate. These key components enable geotechnical engineers to undertake site investigations, develop geotechnical models and assess slope stability faster and in more detail with less exposure to fall of ground hazards in the field.
This paper describes the rapid and robust process utilized at BHP for appraising a slope failure at an iron ore mine site in the Pilbara region of Western Australia using a combination of UAV photogrammetry and 3D slope stability models in less than a shift (i.e. less than 12 hours).
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Guidelines On Settlement Criteria For Design Of Highway Projects
This paper examines the implication of post-construction settlement and differential settlement on highway pavements constructed on soft soils by considering a number of a factors including: type of pavement, rate of settlement, ride quality, and likelihood of pavement distress. The main purpose of this paper is to provide some guidance and clarity on how differential settlement criteria should be specified and allowance made in the design, and in the selection of pavement types. Experience is drawn from monitoring and maintenance records gathered on various sections of the Pacific Highway Upgrade and other NSW roads. Extensive research has been carried out by the Roads and Maritime Services of NSW (RMS) and we have quoted extensively from their draft RMS (2009) “Guide for design and performance of concrete pavements in areas of settlement”. Structural performance of the pavement is considered in addition to ride quality functionality, and guidance is provided for designers to select the appropriate settlement and differential settlement criteria for highway projects. The RMS document uses radius of curvature as a basis for design, which is strictly speaking correct but difficult to predict when designing embankments on soft soils due to small allowable post-construction settlements. This paper provides some guidance on the correlation between the more commonly used limits on “change in grade” specified on recent road projects and “radius of curvature” and provides warning on the potential misuse of these values in assessing the length of transition zone required behind bridge abutments.