one side exposed to waves - hidraulika's blog · • lee-side cover layer – if minor overtopping...

One Side Exposed to Waves

Both Sides Exposed to Waves

Preliminary Geometry

Refined Geometry

Evaluation of Construction Techniques

Selected Construction Technique

Evaluation of Materials

Redesign?

Preliminary Choice of Armor Units

Evaluation of Preliminary Design

Functional Evaluation

Economic Evaluation

Environmental/AestheticEvaluation

Modify DesignsOr Abandon Project Final Design

Geometric Design Aspects• Crest elevation and width• Concrete cap• Armor layer thickness• Primary layer bottom elevation• Toe berm• Structure head• Lee-side armor• Underlayers• Bedding/filter layer• Scour protection

Preliminary Design Phases

1. Structure geometry2. Evaluate construction technique3. Evaluate design materials

• Crest Elevation– Prevent excessive overtopping rates

• Depends on height of runup

– Excessive overtopping causes• Lee-side choppiness

• Serious top-bank erosion (e.g. behind revetments)

• Excessive waves in navigation channels

Smooth Impermeable Slopes

Additional Factors

γγγγr - Influence of surface roughnessγγγγb - Influence of fronting bermγγγγh - Influence of shallow waterγγγγββββ - Influence of approaching wave angle

Impermeable Rock Slopes

Permeable Rock Slopes

Coefficients

Generally expressed in the form...

Typical CEM Table(one of six)

Critical AverageOvertoppingDischarges

Crest width:

• Depends on overtopping• Best evaluated with model studies• Little guidance available• Minimum is 3 armor stones wide• Consider use of crest

• Vehicles • Equipment

• Concrete Caps (Superstructures)– Strengthens the crest

– Deflects overtopping away from leeward slope

– Increases crest height

– Provides roadway access for vehicles and equipment

Failure Related to Superstructures

• Concrete Caps (Superstructures)– Requires cap & structure stability studies

– Economic evaluation of cap versus higher rock structure

Armor layer thickness:

Riprap layer thickness:

(whichever is greatest)

Bottom Elevation of Primary Cover Layer:Extend downslope to elevation below SWL equalto the design wave heightH when the structure is in aDepth > 1.5 H.

Extend to the bottom if Depth < 1.5 H.

Bottom Elevation of Primary Cover Layer:To prevent underlayer rock from being pulled through the armor layer,

D15 (cover) < 5 D85 (under)

Failure Due to Toe Berm Erosion and Scour

Toe Berm for Cover Layer Stability

Minimum Height of Toe

Minimum Width of Toe

(where W in these equationsis 1/10 the size

of armor layer stone)

W

Failure Due to Overtopping and Toe Erosion

Failure Due to Other Toe Problems

Backside Slope Failure Due to Overtopping

• Lee-side Cover Layer– Based on

• OVERTOPPING

• LEE-SIDE WAVES

• POROSITY

• HYDROSTATIC PRESSURE

• Lee-side Cover Layer– If minor overtopping present,

• Lee-side armor should be the same as seaward side

• Extending down to SWL or -0.5H (preliminary)

• Model tests recommended.

– If significant overtopping present,• Extend to bottom


Secondary Layer

• Secondary Layer• As thick or thicker than primary• Example:

• Primary: 2 stones thick• Secondary:

• n = 2.5 (between –1.5 &–2H)• n = 5 (below –2H)

•Interface slope as shown

• UNDERLAYERS


• FILTER LAYERS

• STRUCTURE HEADS•At the head and up to15m to 45m on the leeward side, the seaward side armor stone should be used.

Coastal Engineering Practice CommitteeCEM Preview

Movement of armor units• Rocking• Displacement from layer• Sliding of layer• Settlement of layer

Not armor unit breakage


Parameter Stability Equation


Sea State Variables• Wave height• Wave length• Wave steepness• Wave angle• Wave Asymmetry• Spectrum shape• Water depth• Water density

Structure Variables• Armor layer slope• Freeboard• Armor density• Armor gradation• Armor weight• Armor shape• Packing density• Layer thickness• Porosity of layers


Classified by:• Type of armor unit• Water depth• Superstructure• Dynamic• Crest elevation

• Non-overtopped• Low-crested• Submerged

• Based on small-scale physical models• Testing of designs is recommended• Always test unusual designs

Model Testing


Design Guidance for These Situations

Hudson’s Equation


where


Gradation Range:

with


Design guidance for:• Sloping trunk and head• Vertical trunk and head

Toe berms…• Support main armor layer• Prevent damage by scour


Both Sides Exposed to Waves


Geometric Design Aspects• Crest elevation and width• Concrete cap• Armor layer thickness• Primary layer bottom elevation• Toe berm• Structure head• Lee-side armor• Underlayers• Bedding/filter layer• Scour protection

Preliminary Design Phases

1. Structure geometry2. Evaluate construction

technique3. Evaluate design materials


Crest width:

Armor layer thickness:

Riprap layer thickness:

(whichever is greatest)

SUMMARY: ARMORSUMMARY: ARMOR--LAYER STABILITYLAYER STABILITY

1. Hudson (1974) SPM (1984)1. Hudson (1974) SPM (1984)•• Limited applicabilityLimited applicability

-- ONLY permeable structuresONLY permeable structures-- ONLY nonONLY non--overtopping wave conditionsovertopping wave conditions

•• Factors not consideredFactors not considered-- Wave period, Wave period, TTpp-- Variable structure permeability, PVariable structure permeability, P-- Damage level, SDamage level, S-- Storm duration (number of waves), tStorm duration (number of waves), tdd

SUMMARY: ARMORSUMMARY: ARMOR--LAYER STABILITYLAYER STABILITY

2. CEM (2000)2. CEM (2000)•• No limitationsNo limitations

-- Includes wave overtopping and Includes wave overtopping and submerged submerged condtionscondtions

-- Includes Includes TTpp, P, S and t, P, S and tdd factorsfactors•• Methods easy for EXCELMethods easy for EXCEL•• Includes partial safety factors for designIncludes partial safety factors for design

Use CEM (2000) methods to estimate armorUse CEM (2000) methods to estimate armor--layer stability.layer stability.

A COURSE INCOASTAL DEFENSE SYSTEMS IITIDES, STORM SURGE and WAVESJack E. Davis, PhD

van der Meer.pdf11-coversheet.pdfA COURSE INCOASTAL DEFENSE SYSTEMS ISTRUCTURAL DESIGNBy DAVE BASCO, PhD

one side exposed to waves - hidraulika's blog · • lee-side cover layer – if minor overtopping...

Documents