The Challenges of Field Measurement of Suction Within Free-Standing Mainline Railway Embankments

For over 100 years, adequate performance has been observed for free-standing mainline railway embankments despite the typically rudimentary earthworks techniques used. Notwithstanding this performance, use of effective stress limit equilibrium analyses often do not satisfy the design criteria adopted today. Embankments on the Main Southern Railway are frequently up to 20 m high and have been subjected to environmental events; including drought, intense rainfall, flooding on their upslope side and substantial earthquake loading over the last century. In addition, these same embankments can be subjected to the influence of subsidence from underground mining. One feasible explanation of their adequate performance is the presence of suction within the body of the embankments. The phenomenon of suction has attracted much study and is thought to be understood by the geotechnical profession. Nevertheless, recognition of suctions within engineering analysis are seldom attempted. What is known as suction can be measured under laboratory conditions and its presence is accepted in the field. However, its measurement in the field, especially at depth, is technically challenging. There is a dearth of research and reported installations of this nature, particularly for embankments and the authors are endeavouring to correct this. The hope is that this paper will stimulate discussion within the geotechnical profession by providing an update on the authors attempts to measure suction at depth in the field with commercially available instruments, and whilst illustrating the challenges faced.