AKM Mohsin
MEng(Geotech), BSc Engg.(Civil), MIEAust, MASCE
Postgraduate Research student
Centre for Geotechnical Research
Research project - Automated Gmax measurement to explore degradation of artificially cemented carbonate sand
Supervisor: A/Prof David Airey
Since most oil reservoirs are contained in high-carbonate sediments and all offshore oil and gas exploration structures inevitably rests on ocean floor if it is not a floating platform, therefore the engineering properties of offshore calcareous soils have been studied rather extensively in recent years. Since the late 1970 there has been increasing interest in understanding the behaviour of cemented soils because of widespread occurrence of cemented calcareous sands in Australia’s offshore oil and gas exploration areas as well as other parts of the world. But a full understanding of the response of cemented sands have been hampered by the difficulties in obtaining high quality undisturbed samples of natural calcarnite covering a range of densities and degree of cementation and also by the high spatial variability in the degree of cementation. These difficulties have led researchers to study the response of artificially cemented soils
The main objective of this research was to investigate the stiffness (Gmax) and stress-strain behaviour of uncemented and cemented calcareous sand at very small strain to small strain level. Therefore putting this goal ahead it was essential to develop suitable equipments and triaxial test controlling program to serve the purpose. The technique followed in this study for Gmax measurement was the body wave propagation through the sample. The procedure was automated and applied to the triaxial test by using piezoelectric bender element.
The emphasis was given on the analysis of stiffness data to find out the factors influencing shear stiffness (Gmax) and to derive an empirical relationship of Gmax with those factors cemented carbonate sand. The experimental results of this research have been compared with published data and accepted theory of soil mechanics to validate the results, new procedure and observed soil behaviour. Preliminary analysis indicates that the mean effective stress, the stress ratio, void ratio and deviator stress and cement content are the most important factors, which influence the Gmax response of cemented carbonate sands. For cemented sand, Gmax is initially constant and independent of stress path. After yielding the modulus degrades due to the degradation of cementation, becoming increasingly stress dependent and eventually approaches towards the uncemented sand.
This project is funded by ARC (Australian Research Council) special grant. It is a COFS (Centre for Offshore Foundation System) project, conducted in collaboration with UWA, Perth. Below shows the layout of test setup and an input and output traces of shear wave through the sample, captured during the triaxial test for wave travel time calculation.
Selected Publications
- Mohsin A.K.M. & Airey D.W. (2003) Automating Gmax measurement in triaxial tests, 3rd International Symposium on the Deformation Characteristics of Geomaterials, Di Benedetto et al (eds), Lyon, France, pp.73-80.
- Mohsin, A.K.M, Donohue, S. & Airey, D.W. (2004). Development of a simple, economical, and robust method of estimating Gmax using Bender Elements. Proceedings of the 9th ANZ (Australia-New Zealand) conference on Geomechanics, ChristCharch, New Zealand
- Mohsin A.K.M. & Airey D.W. (2005) Degradation of cementation of an artificially cemented carbonate sand, International Symposium on Frontiers in Offshore Geotechnics (ISFOG), Perth, Australia.
- Mohsin A.K.M. & Airey D.W. (2005) Influence of cementation and density on Gmax for sand, International Conference on Soil Mechanics and Foundation Engineering (ICSMFE), Tokyo Japan.
Learning and Teaching
Tutoring duties
ENGG1801 Engineering Computing
CIVL2410 Soil Mechanics