Presentation on theme: "Folkestone Warren landslips Friday 10 th March 2006 Chris Pantling and Andrew Buck."— Presentation transcript:
Folkestone Warren landslips Friday 10 th March 2006 Chris Pantling and Andrew Buck
Folkestone Warren Situated on the south coast of England between Folkestone and Dover. The Warren is an extensive area of under cliff situated between the rear ‘High Cliff’ and the sea. Area suffers from land slips and rock falls. The Folkestone to Dover railway runs across the top of the lower cliff. Is one the most expensive railways to maintain in UK.
Geology Underlying bed is sandstone. Undercliff consists of chalk and clay. High cliff consists of chalk. Sand lies above the high cliffs. Chalk Cliffs at Folkestone Warren
Landslip History Major slip in 1915. Railway line displaced by 50 metres. Took 4 years to reopen. Borehole investigations identified the slip started at the base of the Clay. Folkestone beds have a high hydrostatic head placing uplift on the base of the Clay and providing lubrication. Major slips followed in 1936, 1937 and 1940. Folkestone to Dover railway
Recession Movements at survey stations and slip boundaries
Causes 1.Coastal erosion of the cliff toe. 2.High winter groundwater tables creating a hydrostatic head. This places uplift on the base of the clay and provides lubrication along the slip plane. 3.Rock falls from the high cliff above falling onto the slide-head. Creates rotational land slips along the clay bedding plane. Folkestone Warren rotational slumpRock falls Upper and lower cliffs
Protection of Folkestone Warren Regrading of the undercliff Sea wall construction Beech Groynes Construction of toe weights Drainage Toe weighting Groynes Additional rock protection at base of sea wall
Alternative Solutions Cliff Foot StrategiesCliff Face Strategies Hard EngineeringRevetmentsCliff pinning Beach PumpingGabions BreakwatersCliff Drainage Dental Masonry Soft EngineeringBeach FillingCliff Modification Beach NourishmentVegetation
Summary Land slips occur as a result of local geology and coastal erosion. Only beneficial result has been the uncovering of large numbers of fossils. Shoreline protected by sea wall, groynes. Slope stabilisation of cliff regrading, toe weighting, cliff drainage. Movements now reduced to very low levels. Railway line one of the most expensive to maintain in UK.