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Phenomenon of Mud Pumping in Rail Tracks
Fundamental Concepts and Practical Implications
Distinguished Professor Buddhima Indraratna
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Annual Field Trip: Bakewell Underpass Project
Richard Herraman, Matthew Duthy, Tim Oborn, Mike Hirons
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Consolidation behaviour of Deep Cement Mixed Column Improved Ground during breakage of soil-cement structure
This paper investigates the behaviour of deep cement mixed (DCM) column improved ground during the breakage of soil-cement structure and subsequent consolidation incorporating the strain softening behaviour of cement mixed soils beyond yield. Numerical simulations were carried out using an extended version of the Mohr-Coulomb model. The ability of the numerical model in replicating the breakage of soil-cement structure was investigated using the physical model tests reported by Horpibulsuk et al. (2012) considering single cement mixed columns embedded in soft Bangkok clay. Numerical results clearly show that the sudden increase in settlements observed during the physical tests at higher applied loads is due to breakage of soil-cement structure during strain softening. During the strain softening, loads previously supported by DCM columns are transferred to the surrounding soft clay and excess pore pressures generated within the soft clay had shown a significant increase. Using the same model, the consolidation behaviour of the improved ground is investigated by varying the permeability of columns with respect to the surrounding soil. Results show that DCM columns will improve the consolidation behaviour of improved ground even when the column permeability is less than the permeability of surrounding clay due to higher coefficient of consolidation of columns compared to soft clay.
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Pilbara Cenozoic detrital sequences and associated geohazards
This paper presents two potential geohazards associated with Cenozoic detrital sequences in Western Australia’s Pilbara region.
The first considers carbonate rich calcrete layers, often reflecting the position of historic and current water tables. Observations of geochemistry of the calcrete layers compared with textural features in the resulting rock suggests a link between CaO, MgO and Loss on Ignition (LOI) abundance and the likelihood of cavities existing.
Geohazards in the form of sinkhole or doline formation may result from changes to groundwater by dewatering for mining or town-water extraction. Contributing factors that increase this likelihood are high water flow, presence of dispersive soils in the blanketing layer, a geochemical signature of >20% CaO in the calcrete and commensurate thicknesses of the calcrete layer (and potential void space) and the blanketing layer.
Relic rock slides have been recognised in several detrital valleys in the southern Pilbara and represent the second potential geohazard. The slides appear to represent a specific marker horizon in the detrital stratigraphy, attributed to a high rainfall, global warming climatic event in the Miocene. The slides consist of large rafted slabs/blocks of Archean bedrock with lesser cobbles and clasts of high strength rock. The voids between blocks are infilled with high plasticity, firm to hard kaolinitic clay, thought to be derived from subsequent lacustrine deposition. The preserved unit thickness varies from 10 to 80 m and can be buried by over 100 m of younger detritals.
The slides present a unique geohazard to mining operations, not simply due to the variability in rock mass strength which can impact slope design. A high variability in void and matrix size and distribution is noted, though size and distribution of these zones is typically too small to be “mapped” by infill drilling. The size is however sufficiently large to cause trafficability issues on haul roads.
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Full scale testing of ground remediation options for residential property repair following the Canterbury earthquakes
A series of full scale tests have been undertaken to assess the performance of ground strengthening methods to improve seismic performance of liquefiable soils in the Christchurch area. The tests used sequences of explosive charges to simulate seismic shaking at levels representative of SLS and ULS events and induced liquefaction and expulsion of sand. Monitoring included measurement of ground motion, pore pressure development and settlements.
The results have determined that the treatment of the upper crust by densification or cement stabilisation is an effective method of reducing settlements and preventing surface expulsion of liquefiable soil. Other options including deep soil mixing and a perimeter curtain wall were less effective but achieved the proposed design objectives and also have application.
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Utilization of fly ash in local Sarawakian peat soil stabilization
The present paper describes the utilization of fly ash (FA) for the purpose of soil stabilization of Sarawakian peat. The peat soil and FA samples were collected from Matang and Sejigkat thermal power station, respectively and tested in laboratory to evaluate their different physical and geotechnical properties mainly compaction, unconfined compressive strength (UCS) and the California bearing ratio (CBR) test. Different physical properties of peat soil and fly ash samples play an important role in the process of enhancing the strength of peat soil. The results show that UCS value increases with the increase of FA and curing periods. The CBR values also increase with the increase of FA at 96 hours soaking period. The results also demonstrate that, the UCS and CBR values were slightly decreased after addition of 20% FA. Therefore, locally available waste FA can be utilized with local peat for stabilization purposes which will reduce the disposal problem.
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Case history: Southern seawater desalination plant diaphragm wall construction
This paper provides a case history of Diaphragm Wall construction at the Southern Desalination plant. GFWA were contracted on a construct only basis by the Southern Sea Water Alliance (SSWA), to install the Diaphragm Walls forming the Intake Pump Station. Construction was carried out between September 2009 and April 2010. 38 No. 1.0m thick heavily reinforced diaphragm wall panels were installed to depths of 25.0m in variable ground conditions, totalling 6,250 m2. 15 No. 2.8 x 1.0m Barrettes were also constructed to facilitate support of ancillary structures.
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Arching in ground improvement
In some soil improvement techniques, such as dynamic replacement, stone columns, controlled modulus columns, jet grouting, compaction grouting and deep soil mixing, the ground properties are enhanced by introducing columnar inclusions to the required depths. Regardless of the technique used it is evident that the stiffness of the in situ soft soil and the inclusions are not the same, and the load distribution between the columns and soil must be determined as part of the process of the ground improvement solution. The distribution of load is a function of a number of parameters. This paper will discuss the mechanism of load transfer in the ground, will review a number of techniques for determining the stress and load distribution and will identify the parameters that affect the load distribution between the soil and columns.
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An embankment constructed using vacuum consolidation
Vacuum consolidation ground treatment has been used to facilitate timely construction of a road embankment on a 25 m thick deposit of soft to firm estuarine clay. This was the first application of the vacuum consolidation technique in Australia. This paper presents the vacuum consolidation technique, provides a summary of its construction and presents data during construction, consolidation and after decommissioning. A comparison with an adjacent embankment section constructed using the conventional surcharge and wick drain approach highlights enhanced stability obtained using vacuum consolidation.
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Investigation, Design and Approval of Foundations for the Cathedral Rocks Wind Farm in South Australia
The Cathedral Rocks Wind Farm is located on the south west coast of the Eyre Peninsula in South Australia, about 30 km from Port Lincoln (Figure 1). At this location the coast consists of cliffs up to 120 m high with the cliff top plateau gently falling away on the landward (NE) side to open grazing and farming country towards Port Lincoln.
The Wind Farm consists of 33 Vestas V80 2 MW wind turbines which have a tower height of 60 m and a three blade rotor 80 m in diameter (Figure 2). The adopted footing for each turbine tower is a buried reinforced concrete pad 14.5 m square weighing approximately 640 t. The wind turbines are spread over a distance of about 9 km along the cliff top plateau. Associated infrastructure includes access and service roads, buried power and control cables, a control centre, a transformer and switchyard and a 132 kV transmission line connecting to the South Australian grid.
The wind farm has been developed as a joint venture between Roaring 40s Renewable Energy and the Spanish company EHN (the hydroelectric corporation of Navarra) which has now been taken over by the Spanish based public infrastructure and renewable energy company, Acciona. Foundation design was carried out by the Hydro Electric Corporation of Tasmania (Hydro Tasmania).