Pile stabilisation of large landslides

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment


Large scale land-sliding regularly causes damage to our infrastructure, including buildings and property, pipelines and cables, roads, railways and sea defences. The presence of infrastructure within or adjacent to the zone of sliding requires that the slides are stabilised. While the cost of this may be considerable, it is often less than the cost of continued damage and loss of use, or of re-routing the infrastructure concerned.Increasingly, discrete piles are used to increase the stability of landslides, and are often favoured because they can be directly targeted at the infrastructure to be stabilised, i.e. piles can be placed immediately upslope and downslope of infrastructures such as railway lines and roads crossing a slipping mass, providing direct support to the infrastructure. In heavily built up areas, piles can be fitted around existing buildings, or where redevelopment takes place they can act both as foundations for the new building and to stabilise lateral movements.The size and extent of the slipping mass often mean that the forces acting on the stabilising piles (for the required design increase in factor of safety) are very large. The large pile bending resistance needed can only be provided by large diameter piles, often installed in several rows. The economic design of piles on this scale requires a better understanding of the interaction between the multiple rows of piles, in particular how load transfers onto the different rows. Under large slope loads plastic hinges may form within the pile section, and these change the mechanism by which further load is then carried by the pile. The formation of the plastic hinges is a complex soil structure interaction problem, and it can be difficult to predict their exact location, particularly where there are large variations in soil stiffness over the pile depth.While simple elastic analyses are commonly used in design to predict pile bending behaviour, interaction between the failing mass and multiple rows of piles may be better analysed using simple (2D) finite element analyses of the slope. However, there is a need for more monitoring data of real pile behaviour, to instil confidence in the use of more sophisticated elastic or finite element analysis in design. Compared with other large scale geotechnical constructions (such as retaining walls and basements), there is very little high quality monitoring data to show how rows of discrete piles behave with ongoing slope movements.Instrumentation will be installed into a large landslide near Telford that is to be stabilised with discrete piles, with the aim of developing a comprehensive understanding of the interaction between the climate, slope movements, and the rows of installed piles. The instrumentation will include inclinometers to measure ground and pile displacements, strain gauges to measure pile bending, piezometers to measure pore water pressures and a weather station to record climate parameters such as rainfall, temperature, and solar radiation. The landslide and piles will be back analysed using elastic (beam on spring) and full two and three-dimensional finite difference analyses. The proposed research will also consider how simpler finite difference analyses could be used in the design of landslide stabilising piles. The measured data and numerical models will then be used in a critical appraisal of pile design, and how it may be improved.
Description Discretely spaced piles are a means of stabilising failing or potentially failing natural and man-made slopes. The piles pin through the slipping soil mass into underlying stabilising ground, thus resisting further movement of the ground above the sliding plane.

Instrumentation was installed to monitor the performance of a large pile stabilisation scheme in the Ironbridge Gorge, constructed to prevent further damage to existing housing and a road through deep-seated ground movements. This has led to insights about the performance (working forces, and displacements) for long and relatively slender piles installed to stabilise deep movements, and the design approach used for these piles. Numerical analyses were also carried out to explore the mechanisms of failure and serviceable performance of piles of different installed lengths/arrangements.
Exploitation Route The findings will influence the approaches used for design of major slope stabilisation schemes.
Sectors Construction,Environment,Transport

Description The findings of the research have influenced the design approach used by engineering consultants for discrete pile schemes, and have provided greater confidence in use of discrete piles in landslide stabilisation.
First Year Of Impact 2012
Sector Construction,Environment,Transport
Impact Types Societal,Economic

Description Mouchel Group PLC
Amount £25,000 (GBP)
Organisation Mouchel Group PLC 
Sector Private
Country United Kingdom
Start 11/2007 
End 11/2009
Description ICSGE 2015, Singapore 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Prof Powrie gave a keynote lecture on discrete passive piles for infrastructure slope stabilization to international conference in Singapore.
Year(s) Of Engagement Activity 2015
URL http://www.geoss.sg/icsge2015/tp.html