Taking place at the prestigious Imperial College London, the annual Rankine Lecture always draws noteworthy discussion and this year’s Lecture on ‘Triggering and Motion of Landslides’ was no exception. Here, Philip Ball, group technical director, describes the day’s events and its links to SOCOTEC’s geotechnical business:
On the slide
When one thinks of ground investigation, a standard survey to ensure suitability of site is often what instantly springs to mind. But, it is also important to consider the possibility of more catastrophic responses from the earth, such as landslides. So it was apt, in Soil Mechanics 80th year to attend the Rankine lecture, by Professor Eduardo Alonso of the Universitat Politècnica de Catalunya, which sought to examine the factors that affect motion and landslides, with interesting results.
Landslides, although often under reported, are more common than people might think. In fact, they have been on the increase in recent times. Over the last year we have seen landslides cause far reaching damage, from a train derailment in Hertfordshire, to a collapsed by-pass in the Lake District. That said landslides are certainly not a new phenomenon. In fact the first job undertaken by the Soil Mechanics laboratory back in 1937 was to report on the embankment stability of Chingford Reservoir and was carried out by Karl Tezaghi.
A fast start
Back to the present day; this year’s Rankine Lecture began on the subject of physical phenomena and deformation mechanisms leading to fast sliding velocities. For Geotechnical Engineers it is important to be able to predict if rapid motion is likely to occur and it was rightly observed by Professor Alonso, that it is only after failures take place that enough attention is paid to the characteristics of soils. Subsequently, insufficient information is known about the geotechnical conditions of slopes and embankments which make predictions difficult.
However, in order to identify and even manage potential landslides, various methods can be used. One such method, the mechanism of thermal pressurization of pore water in the sliding surface, was discussed in detail and applied to sliding geometries. Other techniques such as flood risk assessment and landscape assessments can also be used to identify the likelihood of future landslides. It was also noted that temperature can have significant effects in failure zones and when combined with motion, this increases pore pressure which can lead to acceleration of the slide.
Slow and steady
Of course, no two landslides are the same, some begin fairly quickly, while others can present as a slow creeping motion in both natural and man-made environments. The second part of the Lecture examined slower landslides and posed questions including, “what will be their evolution in time?” and “what is the risk of sudden acceleration?” These questions were thoroughly addressed by the speaker for specific sliding mechanisms.
Making a point
Professor Eduardo Alonso went on to discuss The Material Point Method (MPM) at length. MPM has been used as a numerical technique to simulate the behaviour of materials, including soils. For the purposes of predicting landslides, the computational tool provides an opportunity to examine the transition from static impending failure to subsequent dynamic motion. From the discussion, it is clear that this technique could be more widely used as part of the geotechnical toolkit to provide detailed analysis on land mobility.
Feeling the strain
Back to home ground, the final part of the Lecture discussed landslides in partially saturated soils caused by excess groundwater, which is often the case with British landslides. Unlike other mechanisms of instability, where shearing strains concentrate in shear bands, unsaturated slopes exhibit mixed diffuse-shearing failure modes. Cone penetration testing has long been used to deliver high quality geotechnical results with minimum soil disturbance. As we continue to read headlines like, “Britain braced for floods”, it is clear that we will need to combine the tried and tested techniques with the new to ensure that the geotechnical industry is identifying possible landslides ahead of time.
In conclusion, it was very interesting to hear the advances that are being made in this particular area. We are confident that some of the learnings from today’s Lecture can be taken back to our businesses, were we will continue to update our techniques to provide our clients with the most robust results possible.
Save the date
As a long-standing member of The British Geotechnical Association, I will continue to support the Rankine lecture, as keeping up-to-date with the latest and greatest thinking from thought leaders in the geotechnical world is incredibly important to old hands like me as well as those embarking on the first steps into their geotechnical career.
The after Lecture dinner is also a positive opportunity to network with other stalwarts of the geotechnical industry, whilst providing the chance to thank our teams and our clients for their approach to continuous improvement. Yesterday evening we were lucky enough to host Michael Gavins, from Atkins, Matt Bellhouse and Emily Riley from Thames Tideway East. The usual networking took place during the dinner and we were also able to introduce two new graduates to the Lecture and the Dinner. In addition, to demonstrate our continued support to the Rankine event, SOCOTEC provided a raffle prize.
Did you attend this year’s Rankine Lecture and are Landslides something that the industry should have a more in-depth understanding of?