L4-Landslides_Mitigation - The Unstable Earth: Landslides...

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Unformatted text preview: The Unstable Earth: Landslides Part 4: Landslide Mitigation Whistler Creekside debris flow barrier system. h l k d d fl 1 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 Landslide Learning Goals IV By the end of this lecture, you will be able to: 1) Relate the type of landslide damage expected as a function of its velocity. 2) Identify tell-tale signs of an unstable slope. 3) Compare and contrast avoidance, prevention, and protection strategies for dealing with landslide hazards. h d 4) List the mitigation techniques commonly used for avoidance, prevention and protection strategies. 2 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 1 Landslide Cause & Effect Triggers Cause geological mechanical hydrological geomorphological biological human intense rainfall rapid snowmelt water-level change volcanic eruption l earthquake shaking rapid erosion anthropogenic Trigger Effect rock slide soil slide mud flow rock fall debris flow Having identified a landslide hazard, this then leads to mitigation (trying to fix the problem). 3 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 Rate of Landslide Movement 4 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 2 Cumulative Frequency-Magnitudee FrequencyCumulative Frequency: The total number of events that occur per year. Magnitude: A single number, showing the scale of an event. (for quakes: Richter scale; for landslides: volume). 5 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 Landslide Mitigation Landslide analyses allow for the comparison of various mitigation solutions, including their comparative effectiveness and costs. In general, approaches to landslide mitigation can be categorized as follows: Avoid the Problem: involves relocating a facility, structure or route of a planned new road or rail line to avoid areas along which landslide hazards may be a problem. Prevention: works towards preventing a landslide from occurring. This is usually done by reducing the driving forces or by increasing the resisting forces. Protection: accepts that the landslide hazard will occur, but works to minimize any impact it may have. This is done by employing protective structures that divert or stop the moving mass before they do any damage. 6 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 3 Landslide Prevention - Avoidance Landslide hazard maps may be used to plan the “best” route for a new highway, pipeline or rail line; i.e. one that minimizes the number of major landslide hazard areas encountered. 7 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 Landslide Prevention Since the forces tending to cause movements downslope are essentially gravitational, a simple approach to increase stability is to reduce the mass of soil/rock within the slope or remove the unstable material all together. 8 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 4 Landslide Prevention Another general method used to stabilize a landslide is to increase the resisting forces by applying a resisting force at the toe of the landslide... ... and/or by adding anchors. 9 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 Landslide Prevention - Anchors normal force FS = resisting forces driving forces 10 of 22 = friction cohesion [n–] Landslides: Erik Eberhardt EOSC 114 – 2009/10 5 Landslide Prevention - Drainage Because seepage forces act to increase the driving force on a landslide and pore pressures reduce the effective strength, control of both surface and subsurface water is of major importance. Installation of drainage ll f d control structures. 11 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 Case History – Campo Vallemaggia The usual method for reducing water pressures in massive unstable slopes is to drill drainage holes at the toe of g f the slope or from an adit/tunnel, to create a series of outlets for the water. The Swiss village of Campo Vallemaggia sits atop a deepseated landslide, from which movements have been measured for over 100 years. If the landslide movement is allowed to continue, the village would eventually be pushed over the front scarp. 12 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 6 Deep Drainage – Campo Vallemaggia unstable (slide) zone transition zone stable zone 13 of 22 Installation of subsurface drainage control structures. Landslides: Erik Eberhardt EOSC 114 – 2009/10 Velocity (mm/day) y 788.8 788.6 drainage adit opened 788.4 788 4 788.2 Borehole Head (m) d Geodetic Mo ovement (m) Deep Drainage – Campo Vallemaggia 788 1989 4 3 2 1 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1400 1350 critical threshold at 1390 m 1300 1989 14 of 22 1990 1991 1992 1993 1994 Landslides: Erik Eberhardt 1995 1996 1997 1998 EOSC 114 – 2009/10 7 Mitigation – Rockfall Protection An effective method of minimizing the hazard of rockfalls is to let the falls occur and to control their distance and direction of travel. Barrier Systems Rockfall Nets 15 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 Mitigation – Rockfall Protection Such dynamic barrier systems are now able to cope with impact energies of up to 3000 kJ. Such such systems try to minimize costs by making yielding elements replaceable following a rockfall event. 16 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 8 Mitigation – Debris Flow Protection Objectives: Whistler Creek 1. Remove debris from the flow mass (barriers) 2. Prevent more debris from being g entrained (concrete-lined channel) 3. Decrease flow’s velocity & erosive capabilities (boulder-embedded channel) The 1983 Alberta Creek debris flow prompted the building of a concrete containment flume. 17 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 Landslides – The Unstable Earth 18 of 22 Landslides: Erik Eberhardt EOSC 114 – 2009/10 9 ...
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This note was uploaded on 04/01/2010 for the course EOSC 114 EOSC 114 taught by Professor Stull during the Spring '10 term at The University of British Columbia.

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