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Determining The Effect Of Ground Improvement Using Impact Rolling For Varying Site Conditions
Deep compaction techniques have been in use for a number of years. There are a number of deep compaction techniques that can be applied in ground improvement. These range from the traditional drop weight to eccentrically shaped (impact) rollers.
It is generally accepted that either of these techniques would affect some degree of ground improvement in noncohesive soils. The depth of ground improvement would be dependent on a range of factors including mechanical characteristics of the soil i.e. PSD, Atterberg limits and the location of ground water table.
To date anyone undertaking deep ground improvement using impact rolling techniques does not have a way of predicatively determining the depth of ground improvement in different soil and ground water conditions. It is the authors‟ intent to present a series of case studies where deep ground improvement using impact rolling techniques was successfully utilised across a variety of ground and phreatic conditions. The degree of improvement was evaluated in terms of CPT Tip Resistance (Qc), Young‟s modulus (E) and bearing capacity.
The intent of these case studies is to investigate relationships between the degree of improvement and potential contributing factors including the soil properties, the weight of the impact rolling module used, the number of roller passes and the location of the water table. These relationships are developed for a series of non-cohesive soil conditions specifically well graded sand, uniformly graded sand and crushed limestone, and are presented as nomographs. These nomographs can provide a guidance to predictively determine the number of passes required to effect ground improvement to a given depth for a particular soils type in various phreatic conditions.
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Characteristics of Vacuum Consolidation
Prof. Jin-Chun Chai, Department of Civil Engineering, University of Japan
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Unbound granular base course with shallow foundation concept
This study aims to introduce alternative design procedures for a flexible pavement base course by utilizing the ultimate strength criteria with sophisticated laboratory results of base course materials. Current pavement design mostly avoids all complicated behaviours of an unbound granular base layer considered only as a layer transferring traffic loads to underneath layers regardless of the base course deterioration. Based on the design protocol, there are only the design criterion of the horizontal tension and the vertical compression occurring at the bottom of asphalt layer and at the top of subgrade, respectively. The real behaviour of a base course under traffic loads has been rarely accounted for in pavement design protocol. Nowadays, traffic is growing in terms of magnitudes and quantities and causing premature deterioration in a base course layer leading to major damage in pavements. The study presents theoretically the more suitable approach of the stress and strain distribution in a flexible pavement using the finite element method. An example of a conventional pavement structure consisting of a surfacing, a base course, a sub base course and a subgrade with a single wheel load of 750 kPa standard pressure was selected was established to investigate all pavement phenomena. The effects of uniform design pressure and material attributes which were generated by traffic were investigated. Moreover, the new design criteria for an unbound granular layer were defined as the ultimate strength design and the bearing capacity factor resulting from the application of the shallow foundation bearing capacity concept within the California Bearing Ratio (CBR) results. Our findings were reported and used to draw up the guideline and recommendation on the current pavement analysis and design.
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Field Behaviour Of Fill Structures On The South West Rail Link
This paper provides a summary of the instrumentation and monitoring program implemented during the Glenfield Transport Interchange component of the South West Rail Link. Works included the construction of reinforced soil walls and fill embankments up to 9 m in height as part of the connection alignment between the existing East Hills Line and the Glenfield to Leppington rail line. The key challenge in the region was meeting the stringent long term settlement criteria specified by RailCorp. This was managed by preloading of the fill embankments, staged construction and a detailed instrumentation program which included inclinometers, magnetic extensometers, vibrating wire piezometers and settlement plates. Ongoing monitoring of retaining wall and embankment performance during construction allowed for confirmation of design estimates and management of preloading time periods. This paper provides a comparison of the predicted and actual ground behaviour, together with a discussion of the effectiveness of the techniques employed.
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GIS-based back analysis of riverbank instability in the Lower River Murray
Over the last 4 years or so, unprecedented low river levels, combined with current loading conditions, have adversely contributed to more than 137 riverbank collapse-related incidents and a long term metastable condition along the Lower River Murray, which have recently been considered as the dominating factors inducing bank collapse. With high resolution aerial photographs and digital elevation models (DEMs), this study has established the riverbank geometry prior to collapse of 26 2-dimensional cross section models. Based on government inventories, the collapsed riverbank sections were identified and vectorized using visual interpretation under ArcGIS. In order to obtain appropriate soil parameters for the study area, 5 back analytical models have been conducted at collapsed riverbank sections adjacent to Long Island Marina, Murray Bridge, South Australia. The slope stability analysis software SVSlope was employed in the back-analysis with soil data obtained from two nearby site investigations. Factors of safety were calculated to examine the potential for riverbank collapse with respect to varying river levels. The results indicate that, when the river levels return to 0 to 0.5 m AHD, a portion of the riverbank is close to collapse, whereas a large proportion of the banks remain quasi stable. A raised and maintained high river level will improve the stability but to a limited extent. Several remedial works may need to be conducted when the river level is about to decrease.
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Ground Engineering and the Law
Nicolas Gallina
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Deformation behaviour of ground improved by reinforced stone columns
Stone columns are extensively used for ground improvement for supporting various flexible and rigid structures. However, in very soft soil they encounter excessive settlement due to inadequate lateral confinement by surrounding soil. Reinforcing the stone column with geosynthetic enhances the performance of stone columns. The reinforcement makes the column stronger and stiffer. Also lateral squeezing of stone aggregate into surrounding soft soil is prevented and vice-versa. This paper investigates the load settlement behaviour of ordinary and reinforced stone column through laboratory model tests. Tests were performed with different geosynthetic modules for the reinforcement of stone column. The results from the load tests indicated a clear improvement in load capacity of the stone column due to reinforcement. The increase in the axial load capacity depends very much upon the modulus of the reinforcement and diameter of the stone column. FEM analysis was carried out to understand the behaviour of reinforced column. The findings of experiments are in conformity with FEM analysis.
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Two presentations
Dr David Harris & Professor Erich Bauer
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Contamination Management For Earthworks At Major Infrastructure Projects
During major infrastructure projects, management of potential and actual contamination issues is an important part of the approvals, construction and closeout phases of the overall works program. Planning for contamination may save considerable time and expense with the consultants and contractors working to ensure any construction activities are protective of human health and the environment while maximising the re-use potential of materials. While management of soils, spoil and water is common place during the building of major infrastructure, the impact of contamination from past land-use, acid sulfate soils or fibrous cement sheeting fragments (containing asbestos) is less quantifiable, but no less costly if poorly managed.
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Next Generation of Unsealed Roads
George Vorobieff