Young Geomechanical Professionals’ Night

Mehrnoush Rafiei, Michael Egan, Ken Chen and Hamid Mortazavi Bak

(Now Closed) Call for Abstracts

The Sydney Chapter of AGS is calling for presenters for the Young Geomechanical Professionals’ Night on Wednesday 14 June 2023. The best applicants (from industry and universities) will be chosen to give a 10-minute presentation on their preferred topic. Successful applicants will be selected based on a half-page abstract on the subject that they propose to present (deadline 17th April). Following selection, final presentations would be due by 22nd May for AGS review. Talks need not be overly technical or theoretical, but should reflect interesting and challenging aspects of the presenter’s work that would be of interest to the geotechnical community. Participation is open to industry participants under the age of 35 as of 1st January 2023.

This exciting opportunity includes: 

Further information

Entries will also be reviewed for the potential to be presented at the AGS Symposium later in the year and shortlisted applicants may be invited to prepare a paper for the AGS journal. Applicants who are chosen to present at the YGP Night will be ineligible to apply for the 2023 AGS NSW Research Award on the same topic.

Who should attend

Engineering Geologist and Geotechnical Engineers.


Mehrnoush Rafiei Engineering Geologist – Jacobs

“Secular Change In Mineral Composition Of A Mesoproterozoic Shale Controlling The Primary Rock Properties”

A key transition in the history of the Earth’s biosphere is from the lifeless terrestrial surfaces to the biologically mediated weathering environment of soils. Primary clay minerals formed in soils that are ultimately deposited in continental margin sediments comprise > 60% of the sedimentary record in the Phanerozoic. The Mesoproterozoic Velkerri Formation provides a contrasting record of continental margin shale before the advent of terrestrial life and soils. Mineral mapping of black shale intervals within the Velkerri Formation shows that while clay minerals and clay-sized grains are of similar abundance, petrographic relationships showing intergrowth of expansive illite- smectite and quartz identify a post-depositional and not primary origin for this fraction that controls shale properties. These results show shale lamination and porosity is extensively controlled by cementation and mineralogy. Silica and illite as the major cement have largely occluded the porosity, decreased permeability and increased brittleness in some laminae. Further burial and alteration of these shale intervals resulted in the formation of pyrite and apatite that are limited to the open porosity or organic-rich laminae. Organic carbon is primarily found in laminated mats as well as a significant pyrobitumen fraction found in fractures and shelter porosity. The limited fraction of primary mineral assemblage is consistent with the absence of soil chemical weathering influence during physical sediment production before the advent of terrestrial life. Key rock properties in the Velkerri Formation such as organic carbon enrichment, cementation and porosity are thus dominated by post-depositional processes that modified a distinctly non-uniformitarian initial suite of primary grains.

Michael Egan Senior Geotechnical Engineer – JK Geotechnics

“A Case Study On The Geotechnical Challenges Of A Deep Excavation Parramatta, New South Wales, Australia”

A 60 storey tower underlain by a 30m deep basement is currently under construction within the expanding central business district of Parramatta, NSW. The tower is surrounded by and abuts two multi-storey buildings with basement levels, a heritage listed church, a 100 year old water main, and is set back approximately 50m from the Parramatta River.

The tower is supported by a 900mm thick hydrostatic slab with internal thickenings at the column locations, as well as eight 1.5m diameter (tower) piles integrated into the western basement shoring wall. More than 200 threaded bars (57mm diameter) with a minimum length of 8m are connected to the hydrostatic slab to resist uplift forces during construction. A further 53 rock anchors ranging between 24 and 37 strands and supporting jacking forces in excess of 7.5MN are installed below the central lift core. The retention system consists of anchored and internally propped secant pile shoring walls terminated within competent bedrock approximately 15m below ground surface level. To limit seepage inflows both during construction and in the long-term, a grout curtain extends below the toe level of the secant pile walls to a maximum depth of approximately 50m below ground surface.

A comprehensive site investigation program was carried out to characterise the complex geotechnical conditions of the site, including deep cored boreholes, insitu permeability testing and borehole imaging. From the results of the investigations and cognisant of the many design and construction challenges, detailed numerical analyses were undertaken to model the soil-structure interactions of the shoring system, tower piles, lift core rock anchors, water main and hydrostatic slab. An instrumentation and monitoring (I&M) program was implemented to assess actual basement wall movements against those predicted from our numerical analyses. This paper presents details of the geotechnical investigations, numerical analyses and I&M program, and the engineering solutions implemented to overcome the challenges faced during the design and construction phases.

Ken Chen Associate Geotechnical Engineer – WSP

“Strain Softening And Navigating Karstic Risks In The Design And Construction Of Large Retaining Walls”

Metronet, the single largest investment in public transport in Perth, Australia, is currently being constructed through regions well known for its karstic limestone conditions. The subsurface conditions are characterized by frequent voids, vugs and pockets of loose sands below the rockhead, limestone pinnacles as well as the formation of sinkholes and caves in nearby areas. The occurrence of such karstic features has led to several “near miss” incidents on historic projects. Collectively, these ground conditions present a significant engineering challenge to the design and construction of this landmark railway project.

This presentation will focus on the Yanchep Rail Extension (YRE) portion of the project, which comprises over 30 km of retaining wall structures, 3 new stations precincts and over a dozen new bridge structures. The key geological features will be highlighted, and an efficient and pragmatic approach used to mitigate risks during design and construction will also be presented.

Additionally, the alignment is proposed within a large cut setting, which requires bulk excavation in the order of up to 10 m to 15 m below the existing ground level. Due to project and site constraints, contiguous piled walls without propping, anchoring or tiebacks have been proposed to support the ground within these large cuts. Fully cantilevering piled retaining walls of this height are unconventional and requires consideration of post-peak strength loss associated with high strains and large lateral wall movements. The potential impact of this phenomenon has been modelled by considering “strain- softened parameters,” whereby strength reduction is selectively applied within the geotechnical analyses based on the ratio of lateral movements at the pile crest to the pile retained height. The presentation will also discuss the development, application, and limitations of this innovative “strain-softening” based design approach.

Lessons learned throughout the design development and field observations during construction will also be discussed. This presentation aims to provide a valuable case study for the design and construction of large cantilevering retaining walls within a highly variable, karstic geological setting.

Hamid Mortazavi Bak PhD Candidate – UNSW; Team Lead, Geotechnical Design – Geotesta

“Enhancing Soil-Construction Material Interface Shear Strength Parameters Through Bio-Cementation”

The behaviour of various geo-structures, such as retaining walls, floating piles, embankments, and reinforced slopes, is significantly influenced by the response of the soil-structure interface. Therefore, improving and controlling the strength characteristics of the soil-structure interface is critical for successful implementation of many geotechnical engineering projects. This study investigates the use of microbially induced calcite precipitation method to strengthen the interface between soil and construction materials, i.e., steel and concrete. Modified direct shear tests, designed using the Taguchi design of experiments method, are conducted to examine the strength parameters of the bio-cemented soil-steel interface. The ANOM and ANOVA approaches are used to analyze the primary test results, and the predictions of the Taguchi method are compared to the test results. The study shows that introducing the bio-cementation process to the soil-construction materials interface effectively enhances interface properties, i.e., increasing the sand-steel interface shear strength by 3 to 7 times, depending on the normal stress used in the tests. Moreover, the study presents a new culture medium for the bacteria that utilizes waste material, resulting in a cost-effective bio-cementation method suitable for large-scale geotechnical engineering projects.

Judging Panel

Idy Li Principal – Geotechnics; Team Leader – EIC Activities (a member of the CIMIC Group)

Behzad Fatahi Associate Professor; Head of Discipline-Transport and Geotechnics – University of Technology Sydney (UTS)

Tanya Strate Senior Associate Engineering Geologist – SMEC

AHM Kamruzzaman (Zaman) Principal Engineer Geotechnical – Transport for NSW (TfNSW)

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.