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Soil Behavior Type Classification System Based On Cone Penetration Test
A soil classification system is used to group soils according to shared qualities or characteristics based on simple cost effective tests. The most common soil classification systems used in geotechnical engineering are based on physical (textural) characteristics such as grain size and plasticity. Ideally, geotechnical engineers would also like to classify soils based on behavior characteristics that have a strong link to fundamental insitu behavior. Existing textural-based classification systems have a weak link to in-situ behavior since they are measured on disturbed and remolded samples. The cone penetration test (CPT) has been gaining in popularity for site investigations due to the cost effective, rapid, continuous and reliable measurements. The most common CPT-based classification systems are based on behavior characteristics and are often referred to as a Soil Behavior Type (SBT) classification. This paper presents an update of popular CPT-based SBT classification systems to use behavior-based descriptions. The update includes a method to identify the existence of microstructure in soils and examples are used to illustrate the advantages and limitations of such a system.
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Melbourne Metro Tunnel Project – Numerical Analysis Of Anisotropic Rock Mass For State Library Station
The Metro Tunnel Project is delivering twin nine-kilometre rail tunnels in Melbourne, Australia. In addition to the tunnels, five new underground stations are being constructed. Two of the new stations – State Library and Town Hall – are complex cavern and adit excavations located in Melbourne’s City Centre which will directly connect to the existing City Loop Stations.
The State Library station, located predominantly underneath Swanston Street and a busy tram route, was surrounded by a mixture of modern, educational and heritage developments requiring the excavation sequence and primary support to be designed to ensure minimal surface impacts.
To simulate the anisotropic rock mass response to the excavation of the State Library Station, FLAC3D numerical analysis was undertaken. The analysis adopted the ubiquitous joint constitutive model approach and was used to assess the performance of the primary lining design and to determine the impacts the predicted ground displacements may have on the surrounding structures.
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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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Groundwater Drawdown Related Settlement and Pump Text Interpretation
Settlement associated with groundwater drawdown can be an important design factor for construction below the watertable. As a result, prediction of the extent and magnitude of groundwater drawdown is an essential part of the evaluation of potential impacts of deep structures. Pump test analysis is routinely employed to for assessment of hydraulic properties of aquifer units affected by deep excavation. Interpretation of pump tests makes use of the rate of groundwater extraction and the drawdown measured in the pumping bores and at other locations. Settlement is not usually considered during interpretation of pump tests. This paper discusses settlement due to dewatering and proposes use of settlement monitoring for interpretation of pump test results.
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Geotechnical risk assessment and management for maintenance of water conveyance tunnels in South Eastern Australia
In SE Australia it is estimated that there are more than 500 km of large diameter rock tunnels constructed over a period of more than 50 years for water supply, hydro-electricity, sewage and other purposes. Owners are required to implement an inspection and maintenance program for these critical assets to ensure ongoing reliability of performance and in particular to prevent tunnel blockages from rockfalls. Major cost and time goes into the planning of a tunnel outage for inspection and repairs. Thus it is critical that the frequency between outages is determined on the basis of sound engineering and commercial principles. A critical aspect is the assessment of geotechnical risk at the planning stages for tunnel outages. A Quantitative Risk Assessment (QRA) is considered the most defensible method for prediction of risk of collapse to guide the timing for inspection and repair work.
This paper presents a straight forward QRA method adopted recently by the author on a range of tunnel projects in SE Australia during the planning stage to determine the annual probability of collapse and key geotechnical issues required to be considered during repairs. It also discusses procedures adopted to manage geotechnical risk during an outage with due regard to the range of likely treatment methods that may be required and safe access for personnel.
This risk assessment approach applied in recent years in Australia for dams and slopes can also be adopted for tunnels. This method represents a powerful geotechnical tool as it attempts to quantify the annual probability of failure in numerical terms. It also forces the practitioner to look closely at the range of failure mechanisms possible and their individual contribution to the combined probability of failure. The method may also be applied for the preliminary design for new tunnel projects.
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The CBR test – A case for change?
The origin of this paper lies in a perceived inconsistency between the laboratory CBR’s poor reproducibility and the CBR’s special place within pavement technology. The paper summarises the reproducibility and repeatability of the laboratory CBR and discusses the implications of the poor reproducibility on design and product quality decisions. It shows that the load-deformation properties assumed for the standard crushed rock (CBR=100) differ significantly from the measured properties of crushed rocks and that this inconsistency results in an undesirable bias in the reported CBR. It explores the laboratory test’s ability to replicate the in situ CBR and investigates the practicality of replacing the CBR of cohesive subgrades with the undrained shear strength. It contends that continuing reliance on the CBR hinders the development of pavement technology.
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The development of a fatigue transfer function for in situ foamed bitumen stabilised pavements
This report reviews the results of research undertaken into the stiffness and fatigue performance of in situ foamed bitumen stabilised pavement materials at various sites in the Cities of Canning and Gosnells in Western Australia. The aim of the research was to assess if a design relationship could be developed to predict the fatigue life of in situ foamed bitumen stabilised pavements and if the visco elastic properties of the bitumen binder were reflected in the stiffness and fatigue performance.
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Soil-Structure Interaction Of Battered Minipile Groups In Sandy Soil
Battered minipile groups mimicking tree root networks have been gaining popularity as a footing solution for light structural applications in residential, commercial and infrastructure sectors, recently. Battered minipile group configurations are recently in the limelight due to advantages such as ease of installation and environmentally friendly nature. The lateral load resistance of battered minipile groups is investigated in this paper through a combination of physical and numerical modelling. Two-unconventional battered minipile groups with configurations representing the root network of trees with the capacity of engaging a larger volume of soil compared to conventional battered minipile group configurations are studied. A conventional battered minipile group is also included in the study to draw a direct comparison with the new minipile group configurations introduced in this paper. The conventional battered minipile group has two positively and two negatively 25° battered minipiles. The second type of group has one 25° perpendicularly battered minipile in the leading and trailing row each. Another unique orientation of the battered minipile group is also introduced in this study which has four diagonally outward 25° battered minipiles. The third type of minipile group with four diagonally outward battered minipiles offered the highest lateral resistance among the three groups. This better performance capability was attributed to the engagement of a larger volume of soil in resisting lateral load applied at the minipile head. Through this study, the industrial application of the unconventional minipile group configuration with better performance capability in terms of lateral load resistance can be advocated more confidently.
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Engineering Waterproofing Solutions For Underground Civil Infrastructure
Australia is fortunate to have built some of the driest tunnels in the world over the past 20 years with a very strong track record in achieving the highest specification requirement of ‘no damp patches’ over many hundreds of kilometres of tunnel construction. However, this hasn’t always been the case. In fact, early tunnels built in the 1980s and 90s suffered from severe water damage and cost contractors hundreds of millions of dollars in rectification works.
This paper will discuss how the Australian tunneling industry transformed itself by adopting international standards and a strong engineering approach to waterproofing solutions and details. We will review practices from other parts of the world, relevant standards, specifications and experiences using various membrane solutions.
Every tunnel project has its own unique circumstances and requirements which need to be considered during the design phase. Material selection in particular plays a key role in successful outcomes for waterproofing of underground structures. In this context we will review options for station boxes, shafts, caverns and TBM nozzles covering the benefits and limitations of various available materials. There is not a one-size fits all solution when it comes to tunnel waterproofing. We will analyse various projects completed over the past 20 years and the learnings from each of the different applications.
In more detail, the study will reflect on how our industry has managed to create dry cross passages locally, specifically in the most challenging area of terminating the membrane to the TBM segmental lining. We will investigate the engineering design of these terminations and how a robust solution, which is appropriate for underground applications, has been adopted.
With the confidence our industry now has in tunnel waterproofing, we will propose that an Australian Standard be considered with the development of a technical committee. A new local standard would be appropriate for local conditions and be reflective of the skills and knowledge that have been developed over the past two decades.
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Digital optimisation workflow in early project phases and what it can bring when looking at the MacLeamy curve
It is known from the MacLeamy curve that early effort in project developments pays off. Any change in early project phases takes less effort and is more effective in impacting cost and success of the project than a change that incurs later. This contribution points out possible savings by employing numerical optimisation for achieving the optimal design with respect to both code-conforming performance and construction costs for common geotechnical systems such as ground improvements. One of the bottlenecks for the widespread use of numerical optimisation for design is perhaps the lack of a workflow management program. In the present paper, a structure of a functional workflow management program based on Python, its standard library, third-party packages, and external APIs will be detailed. In addition to that, some fundamentals of how optimisation works will be presented. One meaningful use case of the automated optimisation applied to the design of ground improvements for LNG tank foundation is presented. Extensions to digital ground model provided by the BIM process and seamless information transfer to the construction site purposed for the implementation of the observational method in geotechnical design will be drawn.