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Groundwater Control In Design And Construction Of Deep Basement Excavation In Singapore
In a highly built-up city like Singapore, newer developments revolve around constructing deep underground basements due to its limited land space. This constraint constantly challenges engineering methodologies especially in groundwater control and in the design and construction of deep basement excavation works. Most excavations below the natural ground water table will inevitably induce pore pressure reduction and drawdown in groundwater table. Some of the key factors that affect the change in water table are type of geologies, excavation support system and the excavation depth. Control of groundwater during deep excavation can also be attributed to reducing horizontal stress behind the retaining wall leading to pore pressure control, high permeability soil constituents underneath the toe of the wall and leakage through the gaps or openings. In this paper, three case studies are featured where 18m to 25m deep excavations were carried out for underground basement construction in the heart of Singapore City. How the control of groundwater was considered in design and implemented in construction methodologies of deep basement excavations is presented and groundwater behavior observed during the course of excavation in different soil conditions are presented coupled with the field monitoring results.
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Sustainability and Resiliency Implications of Underground Structures
Dr Raymond L. Sterling
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Consolidation And Creep Of Soft Estuarine Clay In Newcastle
Soil mixing and other intrusive ground improvement techniques are often go-to solutions for problematic soft soils. However, it is very much worthwhile to undertake detailed project specific studies and use advanced constitutive soil models to demonstrate that expensive ground improvement techniques are not always required. This paper looks at a case study where the Soft Soil Creep model was used in Plaxis to simulate the soft Estuarine Clay found at Kooragang Island, Newcastle and proves that deep soil mixing is not necessary for a rail embankment design. A review of field/laboratory tests and back analysis of field monitoring data from a trial embankment were undertaken to derive design parameters of the Estuarine Clay and understand its consolidation and creep behaviour. Site history and aging of the Estuarine Clay were then modelled using Soft Soil Creep model in Plaxis, which allows calibration of the stress state conditions at present time with field conditions. The calculated soil strength profile and past ground movements were able to be correlated with available data including cone penetration tests, shear vanes, inclinometer and extensometer readings. Predictions from the Soft Soil Creep model demonstrate a more sensible representation of current site conditions compared with using basic soil models. This realistic design approach assures confident in optimising the rail embankment design, which brings massive savings on construction costs from eliminating the need for deep soil mixing. The use of an appropriate advanced constitutive soil model, combined with a rigorous study of site specific data, has proven to reduce conservatism in design and increase the substantially benefit of real projects.
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AGS Brisbane Symposium 2024
Geotechnical Ingenuity for a Sustainable Future
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Impact Of Initial Conditions on the Effectiveness of Rolling Dynamic Compaction of Granular Soils
A finite element model (FEM) of rolling dynamic compaction (RDC) technology of a BH-1300 4-sided 8-tonne impact roller, developed previously by the authors, has shown to have reasonable agreement with that observed in the field. The use of this FEM is likely to provide high fidelity insights into the capability of the BH-1300 4-sided 8-tonne impact roller, namely in predicting the settlement and densification of an underlying granular material. A parametric study utilising this FEM with respect to initial density and shear strength parameters is undertaken to explore the relationship these properties have to the settlement and densification of a soil subject to RDC with a BH-1300 4-sided 8-tonne impact roller. The empirical relationships constructed within this study are validated against field trials from the literature of the roller improving sandy gravel fill at typical operating speeds of 10 km/h.
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Application Of Clegg Impact Value For The Evaluation Of The Properties Of Asphalt Concrete
The Clegg impact hammer is used to obtain a parameter relating to strength or stiffness of soil or similar type of materials. The parameter obtained is called the Clegg impact value (CIV). This study has investigated the relationship between CIV and bitumen content in a compacted bituminous concrete and the possible application of CIV for the evaluation of the properties of asphalt concrete. It was found that the CIV of compacted asphalt increases to a maximum value and then decreases with an increase in bitumen content. This relationship was similar to the stability versus bitumen content relationship determined in the Marshall method of mix design. Optimum binder contents determined using CIV, air voids and bulk density were comparable with those values determined using the standard Marshall method and the Austroads Pavement Research Group method.
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Rock fall case study: Hawkesbury Sandstone
This paper documents a rock fall in the Hawkesbury Sandstone. Two distinct phases, preceding the ultimate rock fall event have been identified and documented; a creep-loading phase and a rock fracture phase. Water is identified as playing a significant role in the creep-loading phase. Over the long term, peak water pressures from intermittent heavy rainfall events have contributed to the slow, creeping movement of the overlying, joint-bounded block resulting in the progressive loading of the underlying rock mass. The rock fracture phase was extremely rapid and overlaps with the rock fall event. The kinematics of the rock fall has been interpreted from broken surfaces, scratches and positions of debris. From the timing of events, it is likely that wetting/saturation of the intact sandstone from sustained rainfall in the weeks preceding the rock fall would have significantly reduced the intact rock strength. Based on the site investigation and reconstruction of the failure mechanism, the rock fall is classified, in the Crunden and Varnes (1996) scheme, as a complex extremely rapid rock fall and rapid dry debris slide.