geot revetments
TRANSCRIPT
1
Riverbank Protection
CIVE 717Assignment 4 Problem 2
Nathan Holste, Jon Renholds & Mick UrsicREF: http://project.jica.go.jp/laos/0245124E0/pdf/seminar_program_200603.pdf
Riverbank ProtectionPurpose - Usually defined as measures to strengthen the banks other than using riprapObjective - Show examples of many different types of riverbank protectionTypes
VegetationWindrows and TrenchesSacks and BlocksGabions and MattressesArticulated concrete mattressesSoil-CementRetaining WallsMany others possible
Sketches of different types of riverbank protection
2
Vegetation -3 Main Types Trees
REF: http://www.hastings.nsw.gov.au/resources/images/McInherny-004.jpg
Application of native
Mangrove trees along
Hasting’s River (near
Sydney, Aust.)
Estuary along with rock toe
protection
Shrubs
GrassesREF: http://www.sotir.com/case_studies/study_wilmington_detail.html
Application of small shrubs along with terracing the slope in Wilmington, North Carolina
REF:www.vetiver.org/TVN_past_pict_gallery_htm
Application of vetiver grass for bridge protection in Queensland, Aust.
Vegetation Structure- FascinesBundles of cuttings tied togetherPlaced in shallow trenches parallel to the bankPartially buried and staked in place
Creates log-like structure that will quickly root, grow and provide plant coverHolds soil in place to protect streambank from erosion
REF: Streambank Revegetation and Protection: A Guide for Alaska
3
Vegetation Planting MethodsLive Staking/Brush Mattress
Provides slope with protective vegetative coveringProvides erosion control with fish and wildlife habitatCreates good plant coverage and soil stabilityLabor intensive
REF: Stream Corridor Restoration: Principles, Processes, and Practices10/98 by FISRWG
Vegetation - Advantages
Least expensive of Riverbank Protection measuresImproves habitatAesthetically pleasing
REF: http://www.fws.gov/midwest/detroitriver/report_chapter2.html
Before & After planting grass on eroded slope on Ottawa River, Ottawa Canada
4
Vegetation - DisadvantagesOn high banks tree roots may be not able to stabilize toe and weight of tree will cause bank failure when undercutMay be hard to grow in some areasMay suffer wildlife or livestock damageOnly certain plants can withstand conditions (wetting/drying, freeze/thaw, etc.)Shrubs can result in significant hydraulic resistance during flooding
Sketch of bank failure due to undercutting and the weight of large vegetation
Windrows and Trenches
Windrows involve piling sufficient supply of erosion-resistant material on bankTrenches are similar except they are buried to be less unsitelyWhen bank erodes further, erosion-resistant material slides down and protects bank as the figure indicates.Advantages
Very little design work neededEasier to install on high banks
DisadvantagesWill lose more bank material until intersects erosion-resistant materialInconsistent results and steep side slopes result in high velocity rivers
Conventional Windrow placement
Trench
Trench exposed and protecting bankREF: Bottom two figures from Figure 8.8 in River Mechanics
REF: Top figure from WES Streambank Handbook CIVE717 website
5
SacksFilled with soil or sand-cement mixturePrimarily used for emergency work during floodsProtects streambanks when proper riprap isn’t availableAdvantages compared to stone riprap
Allow placement on steep slopesUse locally available materialsCreates smooth boundaryCobblestone effect may be more aesthetic
DisadvantagesHighly labor intensive (more costly)Susceptible to excess hydrostatic pressureUniformly sized – may require a filter materialVulnerable to environmental hazards
REF: Figure 8.9 in River Mechanics
Blocks
Manufactured with local materials or obtained commerciallyCast with openings to provide for drainage
Openings also allow vegetation to grow so that the root structure can strengthen the bank
Can be used with a filter if erosion is a concernAdvantages
Durable, less susceptible to freeze/thawEasy pedestrian access to riverLow channel boundary roughnessSufficient flexibility to conform to minor changes in bank shape
REF: www.wateronline.com/Content/ProductShowcase REF: http://www.incacape.co.za/landscaping.erosion.control.htm
6
GabionsRectangular wire boxes (baskets) filled with small-sized stonesUsed where flow velocities are too high for riprap of small stonesMade of heavy galvanized steel with PVC coating for corrosive environmentsStacked on relatively steep slopes to resist river flows and unstable banksNeed to be periodically inspected and maintained from damageAdvantages
Record of satisfactory performanceDisadvantages
Labor intensiveExpensive REF: Ohio Stream Management Guide
REF: www.ieca.org/photogallery/GabionIllustrations1.asp
Mattress GabionsShaped into shallow, broad basketsTied together side by side to form continuous blanket of protectionPlaced on a smoothly graded riverbank slopeMay still allow some natural vegetation growth
Site under construction 6 months later
REF: www.ieca.org/photogallery/GabionIllustrations1.asp REF: www.ieca.org/photogallery/GabionIllustrations1.asp
7
Articulated Concrete MattressesUsed in large rivers (Mississippi)Precast concrete blocks held together by steel rods or cablesAdvantages
Flexible, strong, and durableCompletely covers riverbank when properly placedCan be placed quicklyExcellent service record
Disadvantages~8% of surface area is open, allows fines to pass throughOpen spacing between blocks permits removal of bank materialDifficult to fit sharp curvesYearly inspection/maintenanceExpensive plant required for placement
REF: Figure 8.11 in River Mechanics
REF: www.greenvillebridge.com/1a1_jan_02.htm
Soil CementGood for arid
environments where freeze/thaw cycles are not likely to occur.
Works well with sandy soils where vegetation growth is difficult.
Has very little strength and is impermeable, both weaknesses may induce failure.
http://planning.co.la.ca.us/doc/case/TR53108_Vol5ApxB26_FinalTechMemoBuriedSoilCementEval.pdf
8
Retaining Walls
Three distinct types:
1) Gravity Walls 2) Cantilever Walls 3) Sheet-Piling Walls
http://www.stormcon.com/ecm_0401_retaining.htmlhttp://www.menlopark.org/creek/MPSection4.pdfDas, Baja M. 2004. Foundation Engineering, Fifth EditionThomson Brooks Cole.
Gravity Walls
Crib Structure on South Platte
Gravity walls resist active and passive forces by the mass of the structure.
Gabions - Waterton Glacier International Peace Park 2007
Figure 8.13 – River Mechanics
9
Cantilever Walls
Cantilever walls are used when there is a large amount of soil to be retained. The counterfort wall is an application that increases stability. These walls are typically made out of reinforced concrete. An anchor may also be used to increase stability.
Das, Baja M. 2004. Foundation Engineering: Fifth EditionThomson Brooks Cole.
http://www.humes.com.au/ctryimages/storage%20walls%20main.jpg
Sheet-Piling Walls
http://www.cmisheetpiling.com/img/bigwall.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Sheet_pile_New_Orleans-09-04-05.JPG/800px-Sheet_pile_New_Orleans-09-04-05.JPG
Advantages:
1) Easily installed
2) Highly effective
Disadvantages:
1) Limited height due to flexibility
10
Retaining Wall Stability
4 typical modes of failure (Cantilever):
a) Overturning
b) Sliding
c) Bearing Capacity Failure
d) Deep-seated shear failure
Design concerns for all vertical structures include:
1) Earth Pressure
2) Hydrostatic Pressure (Groundwater)
3) Soil Type (Erosive Capability and Strength)
Das, Baja M. 2004. Foundation Engineering: Fifth Edition Thomson Brooks Cole.
http://upload.wikimedia.org/wikipedia/commons/b/bd/Retaining_Walll_Type_Function.jpg
ConclusionsMany other types of riverbank protectionOther river stabilization measures
include riprap and river control structuresMany times these are used together,
however riverbank protection is a very important part of overall river stabilization to protect life and property
One of many tools for Riverbank Protection -
EPA guidebook for Riverbank Protection
REF: http://www.mtwatercourse.org