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Design Of Footings For Tilt-Up Panels At Boundaries
When a traditional shallow and wide footing is provided for tilt-up construction along the boundary of a property, the centreline of the footing falls on the inner side of the tilt-up panel thereby introducing a large moment due to load eccentricities. It is beneficial to provide a narrow and deep footing for tilt-up panels on a boundary for optimum utilisation of space. This study investigates the moment capacity of such footings with due consideration of the additional resistance provided by soil pressures on the vertical faces of the footings. A method for prediction of moment capacity was developed for narrow and deep footings that are subjected to eccentric loads. Three footings were tested at a construction site to develop the required insight for comparison of the failure load from field tests with the allowable load from the suggested method. Significant increase in eccentric load carrying capacity is possible if the resistance to moment due to the soil pressures on the vertical faces are included in the design equations. The suggested method to predict the allowable load of such footings for a given eccentricity is briefly outlined.
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Three-dimensional Slope Stability Assessments For A Large Translational Landslide
The factor of safety is often used to assess the stability of a slope. SVSlope is one of the software to calculate the factor of safety for both two and three-dimensional scenarios by using several Limit Equilibrium Methods options, including Morgenstern-Price, Spencer, Janbu and Bishop methods. Other geotechnical software such as FLAC and Plaxis use the Strength Reduction Method to calculate the factor of safety. When the authors recently analysed a large-scale translational landslide involving a large flat basal slip surface, it was found that different calculation methods for two-dimensional sections predicted a significantly different factor of safety for the same shear strength parameters. It became challenging for the design team to agree on the slope performance assessment from the various methodologies and the limitations of the two-dimensional analysis to massive translational landslides. The purpose of this paper is to investigate the stability of a typical three-dimensional large-scale translational landslide by applying different methods and comparing the differences between them. A typical large-scale translational landslide was modelled based on an actual project. It was analysed using 2D/3D SVSlope with different Limit Equilibrium Methods and FLAC3D with the Strength Reduction Method. The differences in the factor of safety from the various methods are presented. This paper highlights the strengths and weaknesses of a different factor of safety methods for a typical two and three-dimensional large translational landslide.
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Sustainable Engineering Solution for Slope Stability with Anchor Reinforced Vegetation System (ARVS)
Sustainability and resiliency are becoming more important in project design, with emphasis being placed on the environmental impact. Slope stability solutions should be designed to provide a low environmental impact to achieve long-term performance and overall project success. During design, it is important to consider factors such as durability, economics and environmental impacts. The Anchor Reinforced Vegetation System (ARVS) is recognised as a sustainable armouring and slope stability solution proving both surficial stability and erosion control at the same time. An ARVS is a component system consisting of a High Performance Turf Reinforcement Mat (HPTRM) to provide erosion protection and surficial strength, coupled with Percussion Driven Earth Anchors (PDEAs) for resistance to shallow-plane instability. The system is designed to optimise rapid vegetation growth and keep soil in place, thereby resisting mobilisation of soil masses associated with sliding failures of slopes. Key physical and material properties of the component system include optimal ultraviolet resistance, flexibility, and tensile strength of the HPTRM, along with its ability to promote vegetation establishment through increased soil and moisture retention. PDEAs can be selected in various lengths and strengths and are composed of corrosion-resistant material to ensure longevity while maintaining ease of installation. Design methodology of the ARVS for reinforcement against relatively shallow translational sliding failures consists of an infinite slope method solution adapted for the inclusion of PDEAs. Procedures for utilising the ARVS for relatively deep-seated rotational sliding failures include the modelling of stability using conventional limit equilibrium methods. Components of the ARVS are integrated into the model using slope stability modelling software. Results include the potential for an engineered ARVS solution for specific cases of reinforcement for slope stability. The sustainability of the ARVS solution including environmental parameters such as carbon footprint, economical and engineering aspects is analysed and compared with traditional solutions. An example of the practical application of the design methodology is demonstrated.
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Ground improvements and supports for embankments and structures of Regional Rail Link – City to Maribyrnong River
This paper discusses ground improvement and foundation support that were adopted in Melbourne’s Regional Rail Link development that was completed in 2015. The development included realignment of rail track within the existing rail corridor and additional bridges, viaducts, and embankments. The project site was a “brownfield” within a relatively complex geological domain of Yarra Delta Sediments including the recent marine deposits locally called Coode Island Silt (CIS) which is a highly compressible and very low strength clay. The presence of CIS and its variable thickness imposed special challenges for design and construction of the rail link and necessitated ground improvement and support works, including: a) preformed driven, bored and CFA piles for bridges, viaducts and underpasses; b) ground support using controlled modulus columns (CMCs) for the embankments with estimated long term settlement ≥ 150 mm; c) preloading and surcharging for embankments with estimated long term settlement <150 mm. The paper will first cover general geotechnical design considerations for ground improvement using CMCs. A case study will then be presented on the detailed design of the North Melbourne Flyover embankment widening.
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Uplift And Closure Of Brennans Creek Dam Due To Underground Coal Mining At West Cliff Colliery, NSW
This paper applies the new ACARP graphical method for predicting valley closure, upsidence and regional horizontal displacements to data measured at Brennans Creek Dam in order to review the effectiveness of the current dam monitoring programme. Analysis of the data shows that the embankment has been compressed by about 60mm and uplifted 50 mm. Regional horizontal movements of up to 7 mm have also occurred. We show that for a valley containing a dam embankment, a closer fit to the ACARP estimates of upsidence movement is obtained if valley depth is measured from crest level rather than from creek or floor of valley level. Dam closure movements are seen to be less predictable in terms of depth of valley, maximum incremental subsidence and in-situ horizontal stress regime. We conclude that the most recent mining by West Cliff Colliery of longwalls LW5A1 to LW5W3 does not appear to have damaged either the dam foundations or the embankment up to the present, and we have provided details of a better focussed monitoring progamme for analysing underground mining induced displacements in and around Brennans Creek Dam.
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Geotechnical Advances and Challenges in Urban Development
2020 AGS Sydney Golden Symposium
Prof Robert Mair, Dr Chris Haberfield, Paul Hewitt, Idy Li, Theva Muttuvel, Philippe Vincent, David Lees, Hashan Subasinghe, Helen Baxter-Crawford, Peter Sun, Antonio Ramirez Martinez and Bosco Poon & Rikito Gresswell
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The Role Of Tunnel Engineers In Implementing The Observational Method On Site
The observational method is widely used in tunnelling works. For successful implementation of the observational method in tunnelling, proper understanding of support system behaviour, an efficient monitoring regime, data evaluation and proper interpretation by an experienced site engineer is of prime importance. Site engineers play a key role in successful implementation of the observational method. Hence, it is very important for site engineers to understand the key behaviours to be observed, issues that could be resolved at the site and the systematic approach to be implemented to understand the tell-tale signs.
This paper describes the concept of observational method as described by Peck in 1969 and the development of its definition into CIRIA R185 and Eurocode 7. These serve as a basis for considering observational approach in the design and highlight the conditions under which the observational methods must not be used. To explain this, this paper discusses a case study on observational method implemented for a shotcrete-lined tunnel and observational “approach” implemented to adjust TBM compressed air pressures during TBM cutter head intervention to maximize the working man-hours in the cutter head chamber while ensuring face stability. For a shotcrete-lined tunnel, a practical procedure for predicting and comparing displacement behind the face in relation to face advance and time is presented along with spatial visualization tool for tunnel lining displacements. For TBM compressed pressure adjustment, an iterative procedure based on groundwater pressure monitoring and water ingress is presented in the paper.
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Soil strength estimation using free falling penetrometers
Obtaining soil strength parameters can be costly and time consuming for sites with low accessibility such as those offshore and at remote inland locations. A free falling penetrometer can be a cost effective solution for such sites and this has led to the development of numerous penetrometer systems. These penetrometers (retrievable or expendable) can be deployed from small vessels and be allowed to free-fall into the seabed. However, free falling penetrometer application is not widespread due in part to difficulties in data interpretation. There is a lack of appropriate theory and well controlled experimental data to estimate the rapid penetration resistance of the soil. This study has investigated the interpretation of free falling penetrometer through performing a series of laboratory model tests. A penetrometer of various tip diameters and masses has been dropped from different fall heights into kaolin with a range of undrained shear strengths. The effects of the influencing variables on the penetrometer performances are evaluated. Empirical equations are formulated to estimate the undrained shear strength of kaolin based on the measured dynamic penetration resistance and final penetration depth. The equations are successful in estimating the undrained shear strength in the model tests with reasonable accuracy. Good agreement has also been obtained in validating the empirical equations using a published case study.
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Groundwater And Deep Excavations
The presence of groundwater in deep excavations in soil and rock has the potential to profoundly impact both the stability of the excavation, and the impacts that the excavation can have on the areas surrounding the excavation. This paper is intended as a guidance based on the author’s experience to some of the key considerations and pitfalls that designers of deep excavations should take into account when designing deep excavations where groundwater is present. The paper focuses on the influences of Melbourne geology and hydrogeology on the design of deep excavations and provides a brief summary of some of the important groundwater features of the central Melbourne area, but the principles discussed have wider application to projects in similar geology. A series of generalised examples are presented to demonstrate some of the important impacts that groundwater can have on the stability of excavations and structural loads on buried structures, as well as some of the impacts that dewatering activities can have on areas surrounding the excavation.
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Repetitive Dynamic Loading Of Soils And Highly Weathered Rocks Due To Foreshore Construction Activities
Rockwall construction work was carried out on the foreshore of Port Phillip Bay at Mount Eliza in 1995 involving the delivery of many truckloads of boulders, the mass of each boulder generally being in the range of 0.8 to 3 tonnes. After being dumped onto the beach from tip-trucks, these boulders were then individually placed either in rockwalls at the back of the beach or dropped onto the beach sand to form a seawall for erosion protection purposes. Nearby residents complained that the foreshore construction activities generated noticeable ground vibrations at their houses. The occupants of one house, located 95 metres (m) from the point where trucks were dumping their loads of boulders, reported that hanging objects in the house were set swinging by the vibrations, which also could be distinctly felt when lying on lounges and beds within the house. The ground vibrations generated by the 1995 foreshore construction works were not monitored at that time, but on 13th November 1998 the 1995 foreshore works were replicated and monitored, so as to determine the magnitude of the resulting ground vibrations and their attenuation with increasing distance.
The 1995 works continued over a period of several weeks. The repetitive nature of the vibrations, involving about one hundred significant dynamic loadings each day, raised the possibility of fatigue weakening of the soils and highly weathered rocks in the cliffs behind the foreshore. The soils and highly weathered rocks in the area have unconfined compressive strengths less than 250 kPa. The adjacent cliff developed tension cracks just behind its crest, prior to completion of the foreshore construction works in June 1995, and failed on 8th July 1995. The cliff was not instrumented at the time of failure and hence the precise cause(s) of failure remain a matter of opinion. The aim of the 1998 test work was to ascertain if the vibrations generated by these foreshore construction works were sufficiently powerful for fatigue weakening to be a feasible, contributory failure mechanism for the cliff.
Comprehensive description of vibration requires measurement of the amplitude and frequency of the ground motion, and how these parameters vary over time, ie recording of a time series of the vibration rather than just the peak particle velocity. This allows for the recordings to be decomposed using Fourier analysis to show the frequency composition and additionally allows for conversion by differentiation or integration between displacement, velocity and acceleration. The ground vibration from each of the 1998 tests described in this paper was recorded as a time series.