Engineers Australia

AGS NSW Research Award 2018
for Research in Geotechnical Engineering or Engineering Geology Presentations

Dongli Zhu, Liet Dang, Ruoshi Xu, Subhani Samarakoon Jayasekara Mudiyanse and Xinyu Ye

As part of their ongoing support of academic institutions and students, the Sydney and Newcastle Chapters of the Australian Geomechanics Society are offering the prestigious AGS NSW Research Award for research in Geotechnical Engineering or Engineering Geology.

The award aims to provide a forum for research students from NSW universities to showcase their research to the wider Geotechnical Community. Abstracts for the below presentations can be viewed over page.

Finalists

This year five (5) research award finalists have been chosen to provide their presentations to the wider geotechnical community and they are:

Dongli Zhu

Liet Dang

Ruoshi Xu

Subhani Samarakoon Jayasekara Mudiyanse

Xinyu Ye

 

Their presentations:

 

Dongli Zhu – University of Wollongong

A study on pile-pvd interaction in soft clay

Abstract
Soft soils are often encountered in Australia, particularly in the coastal areas., Their low strength and high compressibility are considered by engineers to be problematic as foundation material. To construct structures on soft soil, piles and prefabricated vertical drains (PVDs) are often used by geotechnical practitioners as ground improvement techniques. It is well known that pile installation effects can adversely influence the pile performance by inducing additional movements and stresses into the piles. Especially for displacement piles, undesirable soil-pile interaction often leads to the development of excess pore pressure, excessive soil displacement during pile installation and negative skin friction (NSF) caused by the settlement of compressible soil surrounding the piles. Additional drainage by PVDs prior to the installation of pile could reduce excess pore water pressure, lateral soil movement, and negative skin friction on the pile. In this paper, a research on pile-PVD interaction in soft clay is reported. The research has three major components: full-scale field testing, laboratory model testing and Numerical simulation. The full-scale field testing program includes the construction of two embankments on soft soil. PVDs were installed underneath one of the embankments. The ground was allowed to consolidate and then one pile was driven into the soft soil at the centre of each embankment. The pore water pressure, lateral soil movement, surface settlement and strain of pile shaft were recorded. The laboratory model test was design to investigate the influence of pre-consolidation and PVDs on generation and dissipation of excess pore water pressure due to pile installation. The numerical analyses is adopted to perform parametric study. The outcome of this research indicated that pre-consolidation with PVDs before piling can effectively reduce the excess pore water pressure, lateral soil movement and downdrag on a pile.

Liet Dang – University of Technology Sydney

Engineering characteristics of expansive soil stabilised with bagasse ash, bagasse fibre and hydrated lime

Abstract
Bagasse fibre and ash are readily available waste by-products of the sugar-cane refining industry; their improper disposal can cause adverse environmental effects. Therefore, bagasse fibre and ash are considered in this assessment to investigate the possibility of utilising them as additives for treatment of expansive soil. The main objective of this study is to experimentally investigate the influence of hydrated lime, bagasse fibre and bagasse additions on engineering properties of expansive soil. Several series of geotechnical experiments were conducted on untreated and treated soil specimens mixed with different additive contents and curing for various times of 3, 7, 28 and 56 days. The geotechnical experiments included swell potential, swelling pressure, unconfined compressive strength (UCS), California bearing capacity (CBR), and consolidation tests. A comprehensive study on the microstructure development of untreated and treated expansive soils was also carried out using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) techniques. The results of this experimental study reveal that the additions of bagasse ash (BA), hydrated lime (L), and combined bagasse ash-hydrated lime (BAL) effectively improved the compressive strength, the stiffness, the swell potential and the compressibility of stabilised soils. Meanwhile, a combination of bagasse fibre (BF) and lime resulted in the remarkable improvement in the swelling pressure and the bearing capacity characteristics of reinforced soils. The findings indicate that the application of bagasse ash or bagasse fibre without or with lime stabilisation of expansive soils can not only enhance the geotechnical properties of expansive soil but also address the coming environmental impacts of bagasse disposal, while providing cost-effective construction materials for civil sustainable infrastructure development.

Ruoshi Xu – University of Technology Sydney

Novel application of Geosynthetics in Seismic Protection of Buildings Considering Soil-Foundation-Structure Interaction

Abstract
Seismic design is moving from imposing limits on forces and moments acting on the structures and foundations, to performance-based design allowing more sensible evaluation of building performance during and after earthquakes. Foundation rocking which can function as energy dissipaters to absorb seismic energy and prevent it from being fully transmitted to superstructures is a common phenomenon observed during earthquakes. However, the permeant foundation rotation and settlement are the issues produced by this foundation movement. On the other hand, employing end-bearing pile foundations may result in enormous shear forces developed in the structure and at the connection between the foundation slab and pile heads, as the foundation rocking mechanism is prevented. In this study, a geosynthetic reinforced composite soil (GRCS) foundation system is proposed to resolve the rocking induced issues for shallow foundations. In addition, a geotextile reinforced cushioned pile foundation is recommended to extend the use of foundation rocking as an energy dissipater to pile foundations. To evaluate the seismic performance of the proposed foundation systems, a fully nonlinear three dimensional numerical model is developed to perform time history analysis considering seismic soil-foundation-structure interaction employing FLAC3D software. The numerical predictions indicate that a GRCS foundation system can provide design engineers with an alternative option to limit excessive settlement, and maximum and residual inter-storey drifts induced by seismic loading. Moreover, for buildings requiring pile foundations, a geotextile reinforced cushioned pile foundation can offer design engineers another solution to control the shear forces that develop in a superstructure, as well as reducing the structural demand of the pile foundations.

Subhani Samarakoon Jayasekara Mudiyanse – University of Wollongong

Coupled Bio-Geo-Chemical clogging in low-lying Permeable Reactive Barriers (PRBs)

Abstract
Acid Sulfate Soils (ASS) occur sporadically in the coastal floodplains throughout the globe. They contain a shallow layer of pyrite (FeS2) that oxidizes in the presence of oxygen. During pyrite oxidation, sulphuric acid is generated and the soil pH is lowered to levels below 3, while toxic Al3+ and total Fe cations are leached into the groundwater. This acidic groundwater flow dilates the acidified land area, deteriorating the quality of soil terrains and waterways over large areas. These acidic effluents have been shown to be detrimental not only to flora and fauna, but also to buried infrastructure, because sulphuric acid is highly corrosive and can cause severe damage to pipelines, culverts and foundations. Thus, remedial measures are required to neutralise the acidic groundwater, the conveyor of acidity. Several engineering solutions have been implemented in Australian low-lying areas, and after numerous trials, Permeable Reactive Barriers (PRBs) have proven to be the most economical and efficient method. Nevertheless, the main factor potentially compromising the performance of PRBs is the chemical and biological clogging of their pores and associated reduction in permeability due to mineral precipitation and bacterial activity, respectively. Chemical clogging has been extensively investigated by past UOW researchers, whereas the bio-clogging of PRBs in ASS terrains, which has not been critically analysed in previous studies, is associated with acidophilic bacteria which promote the biofilm growth while catalysing the chemical reactions and mineral precipitation. Therefore, both chemical and biological factors affect the hydraulic characteristics such as porosity and permeability of the reactive granular assembly of the PRB while reducing its longevity. These bio- chemical clogging mechanisms should be critically analysed, as research into these novel aspects are advantageous in developing an advanced Bio-Geo-Chemical (BGC) computational model and a proper PRB design criteria, which is vital in controlling soil and water acidity, to mitigate negative environmental impacts and diminish the extra maintenance and replacement costs associated with infrastructure in low-lying acidic belts.

Xinyu Ye – Newcastle University

Experimental study of a new developed grouted soil nail

Abstract
This report presents a new developed grouted soil nail. Primary study for grouting was performed to investigate the grout propagation during pressure grouting. A physical model system were subsequently established to investigate the pull-out performance of this soil nail at different GP (GP) and degree of saturation. The comparison of the new soil nail and the conventional soil nail was also conducted. Some of the conclusions can be drawn: Firstly, the grout propagation, including the fracture or compaction pattern and shape of formed grout bulb, during pressure grouting are various at different water/cement ratio and grouting pressure. Secondly, the pull-out force of a compaction-grouted soil nail induces hardening behaviour after a sharp increase with a relatively constant hardening rate. In addition, the higher GP results in higher pull-out force significantly. Thirdly, comparing to the conventional soil nail, the pull-out force of compaction-grouted soil nail can be enhanced more effectively by increasing GP. Fourthly, although the pull-out force of a compaction-grouted soil nail is higher with a lower degree of saturation, the initial pull-out forces are the same for the same GP regardless of the degree of saturation and the subsequently diameter of grout bulb. Because the soil pressure closely propagates in the soil sample of lower degree of saturation, a prediction that smaller spacings between grout bulbs along nail rod are manufactured to increase the total pull-out force effectively can be made in the soils of lower degree of saturation.

For further information and submission please contact:
Stefano Pirrello via: [email protected]

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