Sea Defences Dutch Guidelines on Dike Protection

8/13/2019 Sea Defences Dutch Guidelines on Dike Protection

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pre fe r r ed as base for c o r r e l a t i o n , if they are ava i l ab l e in s u ff ic in t amount .

It has to be a l so s t ressed tha t having quan t i f ie d even roughly)the fau l t t ree , it is p o s s i b l e to pay ex t r a a t t en t i on to thosemechan i sms wh ich con t r i bu t e mos t to the ove ra l l p robab i l i t y of fai-l u r e . Thus , t h i s app roach is an impor tan t e l ement in the a t tempt tothe to ta l qua l i ty cont ro l of the d ike des ign and di k e e x e c u t i o n . M o -r e o v e r, the p robab i l i s t i c app roach can be appl ied to some impor tan tpa r t s of the t o t a l de f ence s t ruc tu re e.g. r eve tmen t s ) whe re thenecessary input is a l read y ava i lab l e f rom the r e cen t i nves t i g a t i onsin the Ne the r l ands 9) 12) 31) .

The fu l ly descr ip t ion of p robab i l i s t i c a pp roach for d ike de s ignl ies to far beyond the scope of t h i s r epo r t . Howeve r the de ta i ledin fo rma t ion can be found in the Dutch repo r t s and p u b l i c a t i o n s 1),

9 ) , 3 1 ) , 3 5 ) . Taking knowledg e of the se r ecent deve lo pmen t s canbe r a the r p ro f i t ab l e e spec i a l l y for e s t ima t ion of pos s ib l e r i sk sinvolved in the re a l i z ed p ro j ec t s and for f ind ing the op t imum be-tween the r i sk s and the i n v e s t m e n t .

QU LITY COSTS

X

totalquality x normalcosts situation

optimumsituation.

failurecosts

\

ppr is lcosts

prvnt ioncosts

>ocu

low > highQUALITY LEVEL

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design water levetoading

Fig 6 LOADING ZONES ON A DIKE

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3. SHAPE AND HEIGHT OF A DIKE

3.1 Loading zones (26)

The degree of wave attack on a dike or other defe nce structure during a storm surge depends on the orientation in relation to thedirection of the storm, the duration and strength of the wind, theextent of the water surface fronting the sea-wall and the bottomtopogra phy of the area invo lved. For coastal areas there is mostlya certain cor relat ion between the water level (tide plus storm surge and wind set-up) and the height of the waves, because storm surge and waves are both caused by wind. Therefore, the joined fre-quency distribution of water levels and waves seems to be the mostappro priat e for the design purposed (also from the econom ical pointof view) .For sea-walls in the tidal region, fronting deep water, the follo-wing approximate zones can be distinguished (fig. 6 ) :I the zone permane ntly submerged (not present in the case of a

high level foreshore ) II the zone between MLW and MHW; the ever-present wave-loading of

low intensity is of importance for the long-term behaviour ofstructure;

III the zone between MHW and the design lev el, this zone can beheavily attacked by waves but the frequency of such attack re-duces as one goes higher up the slope;

IV the zone above design l eve l, where there should only be waverun-up.

A bank slope revetment in principl e functions no differe ntly undernormal circumsta nces than under extreme condit ion s. The accent is,however, more on the persistent character of the wave-attack ratherthan on its size . The quality of the sea-ward slope can, prior tothe occurrence of the extreme situation, already be damaged during

relative ly normal condi tions to such a degree that its strength isno longer sufficint to provide protection during the extremestorm.The division of the slope into loading zones has not only directconnection with the safety against failure of the revetment and thedike as a who le, but also with different applica tion of materi alsand execution- and maintenance methods for each zone (fig. 7 ) .

3.2 Dike shape (21)

The shape of the dike needs to be observed in cross-sect ion as well

as longitudinally.Cross-section

The gradint of the bank may not be so steep that the whole slopeor the revetment can lose stability (through sliding) These criteria giv e, theref ore, the maximum slope angle. More gentle (flatter)slope leads to a reduced w ave-fo rce on the revetment and less waverun-up; wave energy is dissipated over a greater leng th. By usingthe wave run-up approach for calc ulat ions of the crest height of atrapezoidal profile of a dike for different slope gra die nts , theminimum volume of the embankment can be obtained.However, this does not necessarily imply that minimum earth-volumecoincides with minimum costs. An expensive part of the embankmentcomprises the revetment of the waterside slope and the slope surface (area) increases as the slope angle decreases. The optimum

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BLOCK PAVEMENT5.50 m +

2 .50m + 015 m . r ^ f f f P * ^ O .SO roCLAYFIXTONE ^ \ \ l ^ J 3 . 4 0 m +

- . . 0 1 2 J l ^ K . COniCRETE SLAB

RIPI600

T|0 .20m\2W.L 0 .2 0 m + T T T *

wp 111 r 11 in i^ t ffB^ 1k g / m * j ^ S S B * * ^ 2 mT

FASCINE / REED / GEOTEXTILE

\^JS^^ \ -10m^ H f S A N D A S P H A LT

KSff L \ 2 m

\ PALE FENCE

N.A.P. - 0

4.00rv*trotrt ofconcrtt Mockl 050 xO.50 x 0.20

subtayar contlsts of clay 0.80 thick or mineitone0.70 thick undar crushad stona 0.10 thick

dimnion* in mktvtlt riatd to N A F

F/g. 7 EXAMPLE OF DIKE PROTEC TIONS

17
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cro ss- sec t io n (based on cos t s ) can be de te rmin ed when the cos ts ofear th works per m 3 and those of revetment per m 2 a r e known . Ca re fu la t ten t ion i s , how ev er, needed becau se the reve t ment cos ts are nota lways indep endent of the s lope an gle , e .g . for s teep s lopes theheavy pro t ec t i on i s neces sary whi l e for the mi ld s lop es the (cheap-e r ) g r a s s -ma t can p rov ide a su ff i c i n t p ro t e c t i on . Ano ther po in tof economie opt imal i sa t ion can be the ava i lab le space for d ike con-s tuc t i on o r impro vemen t .The common Dutc h p rac t ic e is to app ly the slop e 1 on 3 on the innerslope and bet wee n 1 on 3 and 1 on 5 on the oute r (seawa rd) s l op e.The minimu m cr es t wid th i s 2 m. The or i g ina l (o ld) Dutch d ikes weremade of loca l c lay and as s teep as pos s ib l e to min imi ze the quant i -ty of so i l . The s teep outer s lope s were pro te c ted aga ins t wave a t -t a ck by al l k inds o f ma te r i a l s l i ke wood , s t one , b r i cks , ma t t r e s se so f w i l l ow tw igs ba l a s t ed w i th s t on es , g r a s s , e t c . The co re o f amode rn d ike i s made of grea t qu ant i t i es of sand , brought in to p lacemost ly as hydraul ic f i l l . This sand i s covered m ost ly wi th a c laylayer of thic kne ss up to 1 m. In some rec ent wor ks the clay layerhave been rep laced by the layer of mi ne -s to ne . In both cases thedikes have been pro tec te d by a reve tmen t of p i tched s tones (basa l t )or p laced co ncre te b lo ck s . The need to repa i r grea t lengt hs of seadikes in a shor t t ime afte r the 1953 f loo d-d i sas t e r in the Net her -l a n d s , l ed to the in t roduc t ion of asphal t re ve t me nts . This has ne-ce s s i t a t ed en t i r e ly new d ike cons t ruc t i on w i th a spha l t r eve t men t sover ly in g d i r ec t ly the sand cor e . Depen ding on the type of asphal tmix tu re t he spec i a l r equ i r emen t s and r e s t r i c t i ons can be fo rmu la t edon the steep nes s of the slopes and the zone of ap pli ca t io n (underw at e r o f d r y ) , ( 2 7 ) .

The wate r-s ide berm is a common e lement in the Dutch d ike co ns t r uct io n. It could in the past lead to a red uct ion in the ex pe nd it ur eon s tone reve tm ents (on a very gent ly s loping berm a good g rass -mat

can be mai n ta ine d) and it p roduc ed an appr ec ia b le reduc t ion in waver u n u p .Present pra c t ic e in order to obta in a subs tan t ia l redu ct ion in waverun-up, is to place the outer berm at (or close to) water level ofthe des ign storm f loo d. If the berm l ies too much below that le ve l ,the highest s torm flood waves would not break beneath or on theberm and the run-up wi l l be inadequate ly a ffec ted , and the grass -mat on the upper s l ope too he avi ly loaded by wav es leadin g to po ss ib l e e ro s ion .For the storm flood be rms at high desig n l evel s as in the Ne th er -lands ( f req . 10 ^) there a re in gene ra l no pro ble ms wi th the grow thof gra ss on the berm and the upper s l op e . Howeve r there can be

c i r cu ms tan ces wh ich r equ i r e a l so t he app l i ca t i o n o f a ha rd r eve tmen t on the berm and even on a part of the upper s lo pe i .e . whenhigher f reque ncy of water leve l i s appl ied leading to more f requentove rwa shi ng of the upper part by sal t water du e to the run -up orwave -sp ray (a comon grass -mat t can surv ive only a few sa l ty eventsa y e a r ) . An important function of the berm can be i ts use as an ac-ce s s road fo r d ike ma in t enance .In gene ra l care should be taken to prevent e ros i on of the grass - matat the junc t ion wi th the rev e tm ent . The abrupt change in r ough nes smay lead to increase of bot tom t urbul ence and more loca l e r os i on .It is advi sabl e to c rea te a t ran s i t i on zone by apply ing the ce l l -b lock s , geog r id s or o the r sy s t ems a l l owing veg e t a t i o n .

Long i tud ina l p ro f i l e

Due to i r r egu l a r i t i e s i n t he l ong i tud ina l p ro f i l e o f an embankmen t ,

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S 1

S ,-settlement

^ seo level changes. frnat cres t heiqht __

, execution evet V

v seiche squall oscillation gust ^

run up

dike after construction

final dike shape

-toe protection

Fig 8 DETERMINAT/ON O F DIKE HEIGHT

construction

H s t Q 9 e H

settlement

i e 30yearsLOG time

primary

settlement

execution stage)

secundary

settlement

Fig. 9 SETTLEMENT A S FUNCTION O F TIME

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in con nec t io n wi th the top ogra phy of the te r ra in in f ron t or beh indthe bank , some reaches of the s lopes could be subjec ted to morethan normal wave or cur ren t a t t ack . Not al l reve tme nts a re equa l lysu i ta b le for use on a curved long i tud ina l p ro f i le , e .g . some ( ree-tang ular ) b lock sys t ems may leave gaping jo in t s go ing a round curved .A lso , the mec han ica l meth ods for p lac ing of b loc ks i s in prac-t ice l imi ted main ly to s t ra igh t l ines or to la rge rad ius bends wi thsu ff i c i en t l y l a rg e a r ea s .

3 .3 Dike he ight and wave run-up

3 .3 .1 Gene ra l cons i der a t i on on the he ight o f a d ike (1 6) , (21)

The he ight o f a d ike was for many cent ur i es based on the h ighe s tknown f lood level that could be rem emb ere d. It is evid ent that inth i s way the rea l r i sk of damage or the probabi l i ty of f looding we-re un kno wn . Li t t l e was known about the re la t ion be tween the cos t toprev ent f lood ing and the cost of the dam age that might resul t f romflo odi ng . In the 20 th cen tury it was found tha t the occ ur r enc e ofex t rem ely h igh water l eve ls and wave he igh ts could be descr ibedadeq uate ly in te rm of f requency in acco rda nce wi th the laws of probab i l i t y c a l cu l u s . Ho w eve r t he c u rve s o f ex t r em e va l ue s , b a s ed on ar e l a t i ve ly s ho r t p e ri o d o f o bs eva t i o ns , have to mo s t l y be ex t r ap o -la ted in to reg ions far beyond the fie ld of ob ser va t io ns wi th ther i sk fo r s o me u nc e r t a in t i e s .Af te r the 1953 d i sa s t e r , the f requ ency of the r i sk of f looding wass tud ied in the Net her lan ds in re la t io n to the econ omie a sp ec ts . F i -na l ly i t was dec ided to base the des ign of a l l sea d ikes fundamen-ta l ly on a water l eve l wi th a pro bab i l i ty of excee dan ce of 1 0 ~ 4 perannum. In the Net her lan ds the s torm-su rge i s mos t ly inc orpor a ted inthe es t imat ed water l ev e l . I f it is no t a ca se , the s tor m-sur geshould be ca lcu la ted sepa ra te ly and added to des ig n water l e ve l .Bes i des the des ig n f lood leve l severa l o ther e l eme nts a l so p lay aro le in de te r min i ng the des ign c res t l eve l o f a d ike ( f ig . 8 ) .- Wave run-up (2 of exc eeda nce i s appl ied in the Net her lan ds) de-

pending , on wav e he ight and pe r io d , angle of ap pr oa ch , r oughn essand pe r me ab i l i t y o f t he s l ope , and p ro f i l e sha pe (g r ad i en t s ,berm) .

- An extra mar gin to the dike heig ht to take into acc ount seic hes(osc i l l a t i ons) and gus t bumps ( s ing le wave s resu l t ing f rom a sud-

den violent rush of w i n d ) ; th i s marg in in the Net her lan ds var i es(dep ends on l oca t i on) from 0 to 0.3 m for the s eic he s and 0 to0.5 m for the gust bumps.

- A cha nge in chart datum (NAP) or a r ise in the mean sea level( a ssume d rou g h l y 0 .25 m ) .

- Se t t l ement of the subsoi l and the d ik e-b ody dur ing i t s l i fe t ime(at l eas t 30 yea rs ) , ( s ee a l so f ig . 9 ) .

The comb ina t ion of a ll these fac tors ment ione d above def ine s thef reeboard of the d ike (ca l led in Dutch as wak e-h e ig ht ) The recom-mended mi n imum f reeboard i s 0.5 m.

3.3.2 Wave run -up (15, (18)

The e ffe c t iv e run-up (R) , on an inc l ined s t ru c ture can be def ined

as R = Rn-YR-YB-YBwhere R n run-up on smooth p lane s lop es , def ined as the ver t ic a l

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iRu max/Hsup0^

down 1 -Rd max^s

I 2 -3h

Ru2Jsmooth slopes

l VR u m a x / Hs =0.9g p

2 4 6 8 1i0

^ ^ ^ /-np-rapgp=tana/]/2TcH s /gTp

2

Rdmax/Hs=031g p-0.17

smooth slopes;

Rd2 /Hs =0.33g p

rip-rap: 35/015= 2.25

D5o=2 0; 30;40mmIRREOUL R W VES

Fig. 10 RUN-UP AN D RUN-DOW N FOR SMO OTH ANDRIP-RAP SLOPES

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height above still water levelfYR 5* reduction factor due to sloperoughness and permeab ility, Y B * reduction factor due to berm andYR reduction factor due to oblique wave attack and breakerindex.For random waves R n can be expressed by

Rn , tana 1 .25

- a c

n / F 6 p - 2.5 C n ip where p - . . - ^ Tp tana < 2.5where C n a constant depending on the type of wave spectrum and ex-ceedance percentage, H g significant wave height, Tp - top periodand a - angle of slope . The values for C n C2% (run-up exceededby 2% of waves) estimated from the measurements are roughly equalto:c 2 % 0.55 a 0.60 - for a small spectrum and C2% a 0.70 - for awide spectrum.sing C2 % 0.70 and wave steepness of about 5% (typical. stormvalue for the North Sea Coast) one obtains the so called Old DelftFormula commonly used in the past for calcula tion of 2% run-up(

R2%)

o n t h e Dutch sea dike s, viz .

R2 % 8 H g tana

which is valid for ctga = 3 and relatively smooth revetment s.

As a safe approach it is recommended to use C2% 0.70 for deter-mining the run-up due to the wind-waves (smooth slopes) In thiscase2*2.% = 1.75 p or R 2% => 0.7 T p ]/ g H s ' tana for g p < 2 a 2.5

l

and

^2.% - 3.5 or R2% - 3.5 H g for ^ p S 2.5H7Some experimental results for smooth and rip-rap slopes are summa-r ized in fig 10.

The reduction factors for surface roughness and permeability,YRcan be roughly estimated as follows:

Covering layer _IBasphalt, smooth concrete 1concrete blocks, geote xtile -mats , 1 0.95open stone-asphalt, grass-mat

pitched stone , basalton 0.90rough, permeable block mats 0.80gravel, gabion s 0.70rip-rap (min. thickness 2XD50) 0.60In a case of slopes with a berm the run-up will be reduced by afactor B T n e effect of a berm with a constant width (B) is maximum when the berm is situated approximately at the average waterlevel (d B < 0.5 H, see definition scheme in fig. 11 ).It has furthermore been found that the run-up diminishes with in-creasing berm-width although the reduction rapidly falls off once acertain minimum width is exceeded, i.e. B 0.25 L 0 for non- andweak breaking waves, and B 4H for strong breaking waves,H/L0 > 0.03. The reduction factors Y B

f o r t ne berm width equal orlarger than the minimum width mentioned above, may be roughly esti

mated as follows:

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FIQ.ADEFINITIONS

-1.0 -0 .8 -0 .6 - 0 A -0.2 O 0 .5 10 1 5 2.0 2.5

Ro

FIG. B REDUCTION O F WAVE RUN-UP D U E TO BERMAS FUNCTION OF j- AND -RS~

H

V

1.0

0.9

0.8

(3 o.7

t 0,6

0.5

0,40.3

0.2

0.1

n1 2 3 4 5 6 7 8 o 9

YR s T ^- s c o s P ^ 2 - c o s 3 2 pO O

FIC f REDUCTION O F RUN-UP D U E TO OBLIUE WAVE APPROACH

Fig. 11 REDU TION OF W A VE R UN UP

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slope, c tga Y B at d B < 0,5 H)5 to 7 0.75 a 0.804 0.60 a 0.703 0.50 a 0.60

Oblique wave attac k, under an angle 3 can be roughly taken into account by Yp:

Yp c os |3 - 1 0 * ) , |5 = 65*

For |3 > 6 5 , R n = H s not less than H s t )N.B. 3 is reduced by 10* on account of variation of P ) .

Note 1 a recent inve stig atio n in Gerraany *} on the obliq ue waveattack indicates that in the range 0


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GRAVEL STATIC EQUIUBRIUMFILTER

TOPLAYER -S T O N E S - THICKNESS / WEIGHT ?BLOCKS GRANULAIR SYNTHETICDYNAMIC EQUIUBRIUM

DESIGN CRITERIA??? FLOW SLIDE?

C H O I C E P R OT E CT V E S T R U C T U R E A N D DE SI GN P R O C E S S

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a f a r c e s d i e t o down rush

b upl i f t p ressures d ue t o water i n f i l t e r

c upl i f t p ressures d u e t o approaching wav e f ront

d c h a n g e i n ve loc i ty f ie l d

Fig 12 FAILURE MECHAN ISMS OF 5L0PE REVETMENT

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circutar slides

G E O T E C H N I C L F ILURE M O O E S

suffosion

'/tiWtWfW/ZL

dtstruction toptaytr orlocal iliding due to wave impact piping under clay-laytr

trosion pattern * d i r t c t i o n

groundwater flow

b macro-mtchanismi

lifting up af prottctivt units cyclic compactian dut to wavi impact

dtformation_ - prof ile

s-shape

micro initability at tht surfact

y phreatic tin*


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4 . STRENGT H OP RBVETM ENTS

4.1 Gener al appro ach

Once the hydrau l i c des ign cond i t ions have been es tab l i shed , ac tua ldes ig n lo ads has to be for mul ate d. Por a g iven s t ru ctur e many di ffe ren t modes o f f a i lu re may be d i s t ingu i shed , each wi th a d i ffe ren t

c r i t i ca l load ing cond i t ion . Sche mat i ca l ly , th i s i s shown in f ig .12 and fig 13.For the dike as a wh ol e , in s tab i l i t y may occur due to fa i lure ofsu bs oi l , f ront or rear s l op e. Each of these fa i lure mode s may beinduced by geo te chn ic a l or hydro dyna mica l phe nom ena .

A modern (good) eng inee r ing p ra t i ce r e qu i res tha t a t t en t ion shouldbe given to a l l poss ibl e modes of fa i lure of the con st r uct ion underdes ign .

A b r i e f overv iew of the f a i lu re mecha n i sm s o f d ikes , dams or banksi s g iven be low (35) :

An over f l ow and /o r wave over topp ing at h igh wa te r- l eve l s i s a we l lknown mech ani sm, which le ads to water ent er ing the polder and tosoak ing o f the d ik e . The dange rous con sequ ence s r e su l t f rom thesoaking of the body of the dike and erosion of the inner slope.

Micr o - ins tab i l i ty o f the so i l ma te r i a l at the inner s lope may resul t due to seepage and a h igh phrea t ic p l an e.

A slip circ le at inner sl ope may be caus ed among oth er thi ngs by ahigh ph reat ic p lane in a d i ke . This wi l l be the case when the dura-t ion of the high water level i s long or permanent .

A s l ip c i rc le in the outer s lope may occur when a low water fo l lowsan extreme high water (or sudden d r a w - d o w n ) . The body of the dikeis heav y wi th water and s l ide s do wn .

A s l ip c i rc l e in the wat erw ay bank may obst ruct the fa i rw ay. Thisins t abi l i ty can be caused by a rapid draw -do wn of the water tablein the waterway or the presence of weaker or impermeable layers inthe subso i l .

A local shear fa i lure (s l id ing of a reve tmen t) para l le l to the s lope may a lso be the con seq uen ce of a rapid draw- dow n or hydr aul icg rad ien t s pe rpend icu la r to the s lop e .

Erosion ( removal of par t ic les) of the dike/bank protect ion or thebed may be caused by wave or current induced shear forc es somet imesass i s t ed by hydrau l i c g rad i n t f o rce s .

Piping ( in ternal er os io n) may occur i .e . the grad ual format ion of amat er i a l ent ra i ning f low under an impe rmea ble revetm ent or througha loca l concen t ra t i on o f pe rmeab le ma te r i a l in the d ike body / founda t ion . When the p ipe even t ua l ly r eaches the h igh wa te r s id e theprocess o f in te rna l e ros ion wi l l acce le ra te .

Migra t ion ind ica tes the t r anspor t o f ma te r i a l beh ind the reve tment . The t ranspor t may be para l le l to the bank causing local s lumping of the revetm ent or ver t i ca l resul t ing in an S-shaped pro-f i l e . Mat er ia l may also be los t through the revetment when f i l terrequ i rements a re no t me t .

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waves

water level

structure

externplg om try

extern lpressures

internag om try

intern lpressures

resultant

load

ig U SET UP OF B SIC RESE RCH NDST BIUTY COMPUT TION

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A l ique fact i on may occur in loose ly packed s ands under i nf luenc e ofa shock or a sudden d raw do wn . In this case the sudden incr ease ofpore pressure reduces the shear s t rength pra t ica l ly to zero and thesoi l behaves as a l iquid .

Pumping is seen when the revetment b ends under external press ureand thus gen era tes a f low of water u nde rne ath . The f low e ntra ins

pa r t i c l e s o f the so i l .Se t t l emen t s a re due to conso l ida t ion , co mpres s ion , mig ra t i on , ox i -dat ion of orga nic mater ia l ( i .e . peat l a y e r s ) .

Horizo nta l s l id ing or t i l t ing is most ly unl ike ly for a d ike or anear th dam, however for r igid str uct ure s i t is of par amo unt impor-t ance .I ce may seve re ly a t t ack the r eve tmen t du r ing win te r t im e .

Heave of the soil may be caused by the formation of ice crystalswi th in the gra in skele ton of the soi l dur ing the wint er .

Sh ip co l l i s ion aga ins t t he d ike /bank may cause cons ide rab l e dam age .

In the des ign p ro ce ss , one is most in teres ted in the u l t imate l imits ta te (U.L.S. ) of a fa i lure mecha nis m. This s ta te i s reached whenthe acting extreme loads are just balanced by the strenght of thes t r uct ure . If the u l t imate l imi t s ta te i s exc eed ed, the s t ruct urewi l l col l apse or fa i l . The conce pt of the u l t imate l imi t s ta te isgiven in f ig. 5.

The present sec t ion is res t r ic ted to the s tabi l i ty of the f ronts l o p e , moreover on ly ins t ab i l i t y a s a r e su l t o f hydrodyn amica l p ro -ces ses i s taken in to acco unt .The se t -up of the s tudies and s tabi l i ty computa t ion is shown sche-mat ica l ly in f ig . 14 .Star t ing wi th the hydra ul ic input data (waves , water leve ls) andthe descr ip t ion of the s t ructure , external pressures on the seawards lope a re de te rmined . Toge the r wi th the in t e rna l cha rac te r i s t i c s o fthe s t ructure (poros i ty of revetment and secondary layers) thesepre ssu res resul t in an in ternal f low fie ld wi th c orres pondi ngi n t e r n a l p r e s s u r e s .The resultant load on the revetment has to be compared with thes t ru ctur a l s t r eng th , which can be mobi l i zed to res is t these loa ds .If this strenght is ina deq uat e the revetme nt will deform and may

u l t i m a t e l y f a i l .

In many case s , the var i ous p roce sses can not be descr i bed as yet .The ref ore a b lack box approa ch is fo l iowed in which the re la t ionbe tween c r i t i ca l s t reng th pa ra mete r s , s t ruc tu ra l cha ra c te r i s t i c sand hydrau l i c pa ramete r s a re ob ta ined empi r i ca l ly .

The types of reve tment s which are present l y being s tudied are shownin f ig . 15 . in th is f igure the cr i t i ca l m ode of fa i lu re , the cor-responding determinant loads and the required s t rength are summari -zed qual i ta t ive ly. Resul ts obta ined for r iprap , p laced block reve tm en ts , asphal t and gra ss are d iscu ssed in more deta i l in the

fo l lowing sec t ions .

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sand/gravel

iii

cla y/g rass

rip-rap

gabions/(sand-,stone-,cement-)mattressesincl.geotextiles

placed blocksincl. block mats

asphalt

criticalfailure mode

inition ofmofion

transport ofmaterial

prof Ieformation

erosion deformation

inition of

motion deformation

inition ofmotion

deformation rock ing abrasion /

corrosion ofwires

u.v.

lifting bending deformation sliding

erosion deformation lifting

determinantwave loading

velocity fieldin waves

max. velocity impact

4P

max. velocity

seepage

^ \

max. velocity wave impact climate vandalism

^ P ^ s ^

overpressure impact

max. velocity impact overpressure

strength

weight,friction

dynamicstability

cohaesion grass-roots quality of

clay

weight,

friction permeabilityof sublayer/core

weight block ing wires large unit permeability

incl. sublayer

thickness,friction,interlocking

permeabilityincl. sublayer/geotextile

cabling/pins

mechanicalstrength

weight

Fig. 15 REV IEW OF SLOPE REVETMENTS WITH CRITICALMODES OF FAILURE

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4.2 Fa i lu re modes and de te rminan t wave load

Class i ca l s lope r eve tmen t s may be d iv ided in d i ff e ren t ca t ego r i e ssee fi g. 15) e .g .

- Natura l mat er i a l sand, c lay and gras s)- P ro tec ted by loose un i t s g rave l , r ip - rap )- Protec ted by in ter locki ng uni ts concre te b lo cks and ma ts)

- P ro tec ted by concre te and aspha l t s l ab s .In th is order the res is ta nce of the pro tec t io n is der ive d f romfr i c t ion , cohes ion , we igh t o f the un i t s , f r i c t ion be tween theun i t s , i n t e r lock ing and mechan ica l s t r e ng th . As a r e su l t o f thed i ff e rence o f s t r eng th p rop er t i e s , c r i t i ca l l oad ing cond i t io ns area l so d i ff e ren t .Max imum ve l oc i t i e s wi l l be de te rmine d for c l ay / g rass d ikes and g ra -ve l / r ip - ra p , a s they cause d i sp lace ment o f the ma te r i a l wh i l e up -l i f t pre ssu res and impa cts , ho we ve r, are of more imp or tanc e for pa-ved rev etme nts and s l abs , as they tend to l i f t the prot ec t i on .As these phen omen a vary both in space and in t ime , cr i t ica l loadingcon di t ion s vary both wi th respect to the posi t ion a long the s l opeand the t ime dur ing the pass age of a wa ve . Ins t abi l i ty for gras s /c l ay and g rave l / r ip - rap wi l l occur a round the wa te r l eve l , where veloci t ies are h ighes t du r ing up and down rush. Moreo ver , wave impact s are more in tense in the area jus t be lo w the s t i l l waterl e v e l .Ins t ab i l i t y o f paved re ve tmen t s wi thou t too much in t e r lock occursa t the p ink of maxim um down rus h, where upl i f t forces are h igher ,jus t before the ar r ival of the next wave f ront .If the pro tec t io n is perv ious upl i f t forc es are s t ron gly red uce d.Ins ta bi l i ty wi l l have occu rred due to the combined effec t of upl i f t - and impact fo rce s , jus t a f ter wave br ea ki ng .Conc re te s l abs and asphal t wi l l mainly respond to upl i f t forces a tmax imum se t -down. Due to the in t e rna l s t r eng th o f the p ro tec t ionwave loads are d is t r ibu ted more evenly over a layer are a , thus cau-s ing a h igher res i s tan ce agains t u pl i f t , compared wi th loose b lockp a v e m e n t .

4 .3 Wave loading and wave s t ru ctur e - in te rac t ion

The in terac t ion betwee n waves and s lopes i s depe nden t on the localwave height and per iod , the exte rnal s t ructu re geom etr y waterdepthat the toe , s lope wi th /w i th out berm, the cres t e l evat i on and thein te rna l s t ruc tu ra l geome t ry types , s i ze and g rad ing o f r eve tmen t sand secondary l a y e r s ) . The type of s t ructure wave in terac t ion is

conv en ie n t ly cha rac te r i z ed by the so ca l l ed b reake r pa ramete rdef ined as see a lso f ig . 1 6 ) :

where H inc ident wave heightL 0 = wave le ngth a t deep water

= 1.56 z in metr ic uni ts )T wave per ioda slope angle of the front face

For large values of the wave length or for large values of Xsteep s l o p e s ) , the wave behav es l ike a long w ave , which ref lec ts

agains t the s t ruct ure wi th out brea king - a so ca l led surging w av e.For shor ter waves and medium s lopes waves wi l l shor t and break,causing plungi ng brea kers for g valu es in the range of 1 3. Thisf igure i s common a long the Dutch coas ts wi th s lope a ngles of1 to 3 + I to 5, wave pe ri ods 6-8 s and wave hei ght s of 3*5 me tr es .

tg

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STABILITY

(STATIC EQUILIBRIUM)

ANDPROFILE DEVELOPMENT

(DYNAMIC EQUI LIBRIUM)

OF C O A R SE M ATERIALS . .

AND

THEIR APPLICATION

IN

COASTAL ENGINEERING

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For mild s lopes wave b reak ing becomes a more con t i nuou s p ro ces s ,r e su l t ing in a more g radua l d i s s ipa t ion o f wave ener gy. Th i s typeof b reak ing i s ca l l ed sp i l l in g .For the des ig n of s t ru ct ure s , surging and plunging breaker are ofm a i n i m p o r t a n c e .The area which suffers f rom wave - loa ding is bounded by the high ers

uprush and the lowest downr ush po int . Obv iou sly th is zone is vary-ing with the t i de . The value of max imu m up and down ru sh is shown inf ig . 10, both for imperv ious and pervi ous s l ope s . If the uprush ex-ceeds the c res t l eve l , f igures a re no longer app l i cab le .

No re l i ab le fo rmula a re ava i l ab le to p red ic t the max imum ve lo c i t i e sdur ing u prush and do wnr us h. Por surging and spi l l ing bre ak er, nume-r i ca l s o lu t ions have been ob ta ined , which a re , however not yetop era t io na l . A so lu t ion fo r the p lung ing b reaker has not ye t beenob t a in ed . Th us , the wave load ing on g rass /c l ay d i kes and g rave l( r ip - rap p ro te c t ion ) canno t yet be computed p rop er l y.

4 .4 S tab i l i t y o f loose ly ma te r i a l s

An ext ens ive resea rch program has been perf orme d recen t ly in theNeth e r l an ds on s t a ti c and dynamic s t ab i l i ty o f rubb le mound reve t -m e n t s , b r e a k w a t e r s and g r a v e l b e a c h e s ( 1 2 ) , ( 1 7 ) , ( 1 8 ) , ( 1 9 ) . T h e s etype of p ro tec t ion wer e s tud ied ex per i men t a l ly to de te r mine the re-l a t ion sh ip be tween the c r i t i ca l s t r eng th pa ram ete r, H s /A n (H wave he igh t , D n nomina l g r a in / s t one d iamete r and A spec i f i c den-sity p s - p w / p w ) , and the param eter descr ibing the type of wavea t t ack . Us ing H s / Dn pa ramete r, the rough c lass i f i ca t ion o f p ro tec -t ive appl ica t io ns is g iven in f igs . 17 and 1 8.

tpilling

Fig 16 BREAKER TYPES

borm dynomicallybreak- profil stabiwa tars S-shapa rock slopas groval baaches and btacto

1000 3000 500 0

* H s A D n 5 0

Fig 17 TYPE OF STRUCTURE A S FUNCTI0N OF Hs /A Dn50

New s tab i l i ty fo rmula have been de te rmined fo r d i ffe ren t app l i cat i o n s . An example of the gen eral s tabi l i ty cr i ter io n involving a l ldes ign var i abl es is presen ted for rubble mound reve tmen ts in f ig .19.

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prof ec f ion layer

rubble-mound breakwaters

strengthened part

"self adjusted" or bermprof i Ie

homogeneousrock-fitl

profile formation

homogeneousgravel

profile formation

1 20H AD n

static stability rock-fill

dynamic stability rock -f ill

dynamic stability gravel

sandy

beaches

(nourishment)

40

Fig 18 APPLICATION OF COARSE M ATERIALSIN COASTAL NGIN RING

- 35 -


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S/]/N

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

a impermeable core

. m permeab le coreThompson (1975)

permeable core

* homogeneous stru ctu re

S = A / D 2

SW L ^

' ^ l L 8B 8

B j ^ W

. J l l P l ^ ^

B /

B /

B / *

7 mB k B B

B / B

f '


39/125

,H. D ,nSO H , / A D n 5 0 - 4 .4 (S 2 / v / T ) 2 2 $ Z M

/ - / . r-\ 1/6 _0.1H / A D n 5 0 1 . 2 5 v 3 ( S 2 / y N ) , FORcotQ^3

H./ADnso- 1.25Vcota' S2 / \ Z H V S $J 1 FORcota3

- ^ j - t aa /N/z i fHt /gTi

0.5 ae a7 o.e 0.9 1 S 6 7 8 9 10

Fig, 19B RIP-RAP STAB IUTY FORM ULAE FOR N=3000 WA VESAN D AN IMPERMEABLE CORE

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0*\$& Dn50A/Dn50F 4.5 Dn50F/Dn50C = 4

^ B=oi

Dn50A/Dn50C=3.2 1 mm, h = waterd e p t h , c r = cr i t ica l ve l oci ty, i[t cr = c r i t i c a l S h i e l d s p a r a m e t e r,A zre la t ive dens i ty k = s lope r educ t ion f acto r = 1-sin 2a/sin 2) . 5 , angle of inte rnal fr ic t ion of m at er ia l , O, = slop e angle Bi =s tab i l i t y co ff i c i n t . The va lues o f | c r and Bi can be es t imatedfrom tables 1 and 2 below:

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A. RIPRAP

t r l5+2

B STONE OVERUYONE TOP-LAYERI

C. BINDERS ARE PL CEDPERPENOICUL R TOTHE SLOPE

INDERS

0. A U STONES ARE PLACEDWITH THEIfl LONGEST SlDEPERPENOICLLAR TOTHESLOPE

PLACEO STONES

FILTER RIPRAP)

E. STONE PITCHING BASALT)WITH OR WITHOUT GROUTING

G ROUTING

F. BASALTON

Fig 21 RIPRAP DESIGN A N D IMPROVING MEASU RES

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Tab le 1 Table 2

f l o w c o n d i t i o n s

ma jo r t u rbu l en t f l ow inc l . l oca ld i s t u r b a n c e s a n d c o n s t r i c t i o n s ;a l so outer be nds of r ivers

normal turbulence of r ivers andchanne l s

mino r t u rbu l ence ; un i fo rm f lowsmoo th bed cond i t i ons

1

5-6

7-8

8-10

s t a t e o f pa r t i c l e s

absolu te res t

s ta r t o f ins t ab i l i ty

movemen t

4>cr

0.03

0.04

0.06

I t has to be s t ressed tha t , whateve r method i s ada pte d , the exp er i -eno? and sound e ngine er ing judge ment p lay a la rge part in a properdes ign o f p ro t ec t i ve s t ru c tu re .

4 .5 p l i f t f o r ce s . B loc k - and impe rv ious r e ve tmen t s

The upl i f t forces a re of impor tanc e as wel l for the imperviou s (as-pha l t , conc re t e ) a s for t he pe rv iou s (b lock- ) r ev e tme n t s . Howeve rthe ca lcu la t ion methods of upl i f t a re qui te d i ffe ren t for the bothc a s e s .

Blocjt r e v e ^ n ^ s ^ arge_ .sca_lj5 u ^ t s jinder ra_ve att^cjc

The qual i ty of conc re te b l ocks was gra dua l ly improving in the las tdeca des and t he cos t d imin i sh ing ( a .o . due t o mechan ica l p l ac ing ) stha t , a t p resent conc re te b lock s of var iou s s izes and shape areused sa t i s fac tor i ly in coas ta l (d ike) pro tec t ion under a var ie ty of

cond i t i o s ( e spec i a l l y i n coun t r i e s w i th sho r t age o f na tu ra l ma te r i -a l s ) . Many d i f f e r en t k inds o f , o f t en pa t en t ed , r eve tmen t b locks have ac tua l ly been used . The fac t that des ign ru les a re s t i l l l imi tedin guan t i t y ha s s t imu la t ed i nves t i ga t i on s i n t h i s a r ea .

In respec t to the b lock re ve tme nts a d is t inc t ion can be made be-t w e e n :1. P ree b locks o f d i f f e r en t de s ign .2 . F l ex ib l e i n t e r l ocked b loc ks , i . e . due to g ro u t i ng , c ab l in g , e t c .

( i . e . B a s a lt o n b l o c k s , A r m o r f l e x - m a t s ) .3 . R ig id i n t e r l ocked b lo cks ( i . e . sh ip - l ap , t ongue - and g ro ove ,

etc . .The f i r st two sys t ems (see a l so f igure 22) have been recen t ly tes tein the Delta Wave Plume at the Delf t Hy dr au li cs La bor ato ry (DHL) inco -ope ra t i on w i th De l f t So i l Mechan ic s Labora to ry ( D S M L ) .The f ree p laced b locks were tes ted for both , permeable as wel l asumpe rmea ble (c lay) su bla ye rs . The la rge sca le tes t s have shown thatrec ta ngula r c lose d b lo cks p laced d i re c t l y on c lay form a verys t rong rev e tm ent . When there was good qual i ty c lay (no eros ionof the subla yer ) i t was im poss ib le to . c rea te dam age con di t ion swi th in the range of poss ib i l i t i es of the wave genera tor(H s 2.0 m, H ma x

2 * 6 m ' b locks D * 0.10 - 0.15 m t h i c k ) . Bes idesthe requ i rem ent of good and hom oge neo us c lay a very impor tan texecut ion requi rement i s the smoot ing of the s lope before theplac ing of the b loc ks . If the b locks a re to per form pro per ly, theymust adhere to the c lay wi thout the pres ence of too manyin ters t ices and cavi t ies . In the case of poor c lay ( sandy c lay) or

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PLACED STONES

(VILVOOROSESTONE)

STONEP I T H I N G

( B A S A LT )

PLACED BLOCKS T Y P E H A R I N G M A N

f ^

GOBI BLOCK

^ c ^ > B UILDING

F W ^ J B LOC KS

TONGUE

A N D

GROOVE T Y P

STEPPED

WAF FLE TYPE TYPE

interlocking blocks

MODIFIEC

TO N G U E

A N D G R O O V E

TYPE

SI fiEi wiiwrgi wwuf f wwT M

fijafc

ARMORFLEX BLOCK A N D M AT

A B L O C K

BASALTON

B A S A LTO NR E V E T M E N T

Fig 22A EXAMPLES OF BLOCKS TESTED ON LARGE SCALE

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45/125

6 f OROUTED, ~ t > 8AD

'GOOD' CLAY Jg > 7

A D

BARMORFLEX-MATD-0.11m

c tga3(B)-SPECTRUM

GROUTED, ? > 1 0I AD

mi BASALTON-PRISMS

D-0.1Bm

c tga3(O-SPECTRUM - F R E E PRISMS

l . l . l . l ,

SQUARE BLOCKS0.25 x 0.25 mO 0.15 m

SQUARE BLOCKS_ 0.25 x 0.25 m

OESTERDAM-PROFILE5=6

NAP+3mc tga4

(O-SPECTRUM

RIPRAP (OE.RJC.)etgo 3+4(REGULAR WAVES)

_ . _ a - 3

( S M A U SPECTRUMA-JONSIW B-PIERSOrTMCHHO

C- MAROLLEGAT (OESTER DAM)

-tga

\f vtH

F/g. 22B STABIUTY NUM BERS F OR SOME BLOCK REVETMEN TS

43 -
http://xn--2vth-zh6i/http://xn--2vth-zh6i/


46/125

Table 3 : S tab i l i ty o f concre te r eve tment3

H - c o s aV f

VF

for g z < 3 (breaking w aves)

c t g a > 2

ca tegory cover layer d e f i n i t i o n s

2 < ip < 3 ri p- N ivp -to le

rap (2 layers)3000 waves3 deno tes max .rable damage

II^ < 4

III< lp > 6

Pi tched s toneLoose blocksBlocks connec tedb y g e o t e x t i l e ;

B locks in te r lockedby f r ic t ionGrouted blocksconnec ted by geotex t i l eCabled blocks

Loose blocksdir ect ly on goodc lay

Grouted cabledb locksM e c h a n i c a l l yin te r locked b locks

ip s t rength cof f ic int def inedat e- = 1 . n _. lz =* tafia (2 t H g / g T z 2 ) - . 5

. D th ick ness of the block

. Por r ip-rap D - D S Q ( W 5 0 / p g ) V 3

. For long term loading effects thethi ckne ss D should be increasedby 25%a= s lope angle

. Fi l ter requ irem ents of the soi lhave to be met by the g eot ext i leand /o r g ranu la r sub- laye r (9 ) ,(26)

. B locks p laced d i rec t ly on geotext i le and wel l compacted sand:m a x . H s - 1.2 m

. Good cla y = acc ordi ng to requirements g iven in (26)

. Ca t . V mus t be ca re f u l ly des ignedand examined

Notes b lock s / sy s tems wi th a we l l de f ined in te r lock have go t a ve ryh igh s t ab i l i ty ( ca tegory V ) . The behav iour o f the sub- laye r / f i l t e rcan be a r e s t r i c t i ve f ac to r how eve r. The adequa te des ign c r i t e r i aon in terna l s tabi l i ty of sub - la yer s / f i l t ers re la ted to the level of

hydrau l i c load ing a re necessa ry.In all cases-, the exp eri enc e and sound en gin eer ing jud gem ent pla yan important ro le in applyin g these des ig n ru le s .

Research is now being di rected towards a bet ter de scr i p t i on of thet ime dependen t ex te rna l p ressur e dur ing the passage of the wav es .Once th is has been determined, the resul tant loads on the e lementscan be de te rmined .The s t ructura l s t rength of the block forms the f inal s tage of th iss tud y. More comp lica ted reac t ion s are being s tudying s tar t ing wi tha s ingle b lock, where the weight of the block del ivers the s tabi l i -z ing f orc e . With these data a pro bab i l i s t ic des ig n approa ch can bed e v e l o p e d .

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c w : p w . 9 l p t hc osa )

triangle-rule

schematization of the water pressureunder a sealed revetment

V *E v f e g ^~ x a r c t g ( n ) * ~ -

max Pv

n=1236

(slopej

1.0

0,9

0,8

0,7

0,6

0,5

0,40,3

0,2

0,1

Vi N

- - - - I

-

- -

-

.._

\

_.

-

_ -

- -

X

._..

\

-

..._

_..

^

- -

._..

/

^

--

-

1

/ r ' / i

i

ji

N f

^j

- i

.... -- -

-

11t

i

^

....

ji

\ v

X

-\

-

^

-

E ^V ^ 1

*4jX

C--

- - -

- -

- -

- . i . - .

. \

j

XX

\

-

-

^

X

n 0Z stationary flow

. 0 2 non-stationary

flow

a i= 1 - JL

triangle rule

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

H,

ig 3 SCHEM TIZ TION OF THE W TER PRESSUREUNDER AN IMPERME BLE REVETMENT


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Upl i f t fo rces for i rope ,v io jas r_ve t inent ( ie c o n c r e t e o r d e n s e a s - phT lt) ~ '

H y d rw a t et e rsur e- Qu

lawhgr

- Dyw hm eredi

T h eeve

Va ne l e m

t r i a

a u l i c u p l i f t p r e s s u r e s d e v e l o p un d e r a b s o l u t e l y o r r e l a t i v e l yr - i m p e r m e a b l e d i k e r e v e t m e n t a s a r e s u l t o f d i f f e r e n c e s in w a -l e v e l i n s i d e an d o u t s i d e t h e d i k e b o d y . H y d r a u l i c u p l i f t p r e s -s c a n b e c a u s e d b y :a s i - s t a t i c c o n d i t i o n s i . e . t h e g r o u n d w a t e r l e v e l i n t h e d i k eg s b e h i n d t h e e b b a n d f l o o d o f t h e t i d e o r a f t e r a s t o r m s u r g ee n t h e w a t e r l e v e l o u t s i d e t h e d i k e b o d y f a l l s r a p i d l y a nd t h eo u n d w a t e r in t h e d i k e f a l l s m o r e s l o w l y .n a m i c c o n d i t i o n s i . e . u p l i f t p r e s s u r e d e v e l o p s i n t h e d i k e b o d ye n t h e w a t e r l e v e l o u t s i d e i s l o w e r e d l o c a l l y, o v e r a s h o r e t i -p e r i o d , b y a p a s s i n g s h i p ( w a t e r d e p r e s s i o n ) or u p l i f t p r e s s u -s d e v e l o p w h e n w i n d w a v e s p r o d u c e c h a n g e s i n w a t e r l e v e l o n t h ek e f a c e .( q u a s i - ) s t a t i c p o t e n t i a l d i f f e r e n c e , p , at th e s u r f a c e of t h e

t m e n t c a n b e c a l c u l a t e d b y s i m p l i f i e d a n a l y t i c a l m e t h o d s ( i . e .d e Ve e r - m e t h o d ( 2 5 , ( 2 7 ) an e l e c t r i c a l a n a l o g u e or a f i n i t e

e n t c a l c u l a t i o n . T h e f i r s t a p p r o x i m a t i o n c a n b e o b t a i n e d b y th e

n g l e - r u l e ( f ig . 2 3 ) :

max

'wo J w

l i n e a b o v e s t i l l w a t e r l ei s k n o w n ) . T h e r e a l u p l i f t w a t e r

C Tw o , i s d e f i n e d b y ( f i g . 2 3 ) :g (p + h c o s a )

w h e r e 0 V i s a p o s i t i o n o f t h e p h r e a t i cv e l ( a s s u m i n g t h a t t h i s p o s i t i o np r e s s u r e ,

w h i c h i n d i c a t e d t h a t w h e n p = 0 , t h e u p l i f t p r e s s u r e

wo Pw h . c o s a

T h e d i m e n s i o n s of t h e r e v e t m e n t c a n b e o b t a i n e d u s i n g t h e f o l l o w i n gf o r m u l a s ( 2 7 ) :

1 . S l i d i n g c r i t e r i o nf wo

h > p a g (f c o s a - s i n a )

P2 . U p l i f t c r i t e r i o n

C woh >

p a .g . c o s a cosa

w h e r e APa -Pw

Pw

To p r e v e n t t h e r e v e t m e n t a s a w h o l e a g a i n s t s l i d in g , o f f t h e d i k eb o d y ( e q u i l i b r i u m c r i t e r i o n ) , t h e s l o p e a n g l e m u s t b e l e s s t h a n t h ea n g l e o f i n t e r n a l f r i c t i o n . P or r e l a t i v e l y i m p e r m e a b l e r e v e t m e n t ,t h e s l o p e a n g l e i n p l a c e s w h e r e w a t e r i s l i k e l y t o o c c u r b e h i n d t h er e v e t m e n t , s h o u l d be

3 . E q u i l i b r i u m c r i t e r i o nPw

tg a s tg (1 - H - )Pn

- 46 -


49/125

OIKES AND BANKSPROTECTION

SLOPE PROTECTIONOF DAMS

BOTTOM PROTECTION OF CLOSURE-STRUCTURES

W ^ W W ^ W T T T T I T J I i i i iTTfi r ivw i F i i - i r iy^PPP*

BOTTOM PROTECTION OF DISCHARGE SLUICES

SEALFUNCTIONS

" " ^ . . - S W I M : * *

RESERVOIRS/CANALS

'^":::S S? SW?OTW.O:U.V.' ^V.

BITUMINOUS SEAL OF DAMS

REDUCTION OF GROUNDWATER FLOW /HYDR AULIC GRAOIENTS

SANDASPHALTH.W.JJL zS

^ . Wl1 U 1 I 9 ^ S^ y mwmtmssr^^

f i i i i w i i i j l i ' i ' i i j i i I I i i iw i t i i - i W^ DAM CONSTRUCTION

H.W._LL > < ^

SANDASPHALT

[.. 11.' ".".. i .. i. i 11 iwi^r i 'wrrr-p ^w 1111 in i 'ri' i rrii'J" 11 iP i iWTTPPf

FILTER FUNCTIONS

STONE

< OPEN STONEASPHALT

SANDASPHALT

(FILTERLAYER)

BLOCK .

REVETMENT

SANDASPHALT [FILTERLAYER ^///,

OPEN STONEASPHALTSANDASPHALT

SAND

Fig. 2k APPLICATION A N D FUNCTIONS O F ASPHALT

47


50/125

h revetment thickness m) 7 wo maximum uplifta_* slope of dike face, p a con crete or asphalt

density

Symbols used:pressure N/m 2. _ . , _bulk density k g / m 3 ) , p w * density of water kg /m 3 ) , p nof wet soil k g / m 3 ) , g * acceleration due to gravity m / s 2 ) , f cofficint of fri ction: f tg 0 if c| > 0, els e f t g 9 , angle of internal friction of the subsoil and 0 angle of frictionbetween the revetment and the subsoil.More information hereabout can be found in 27 ).

4.6 impact fo rces . Asphalt revetments

Waves breaking on the slope cause high forces of short duration,called impacts. Apart from the wave conditions and the structuralgeometry, wave impacts are also affected by the physical propertiesof the water and the revetment, in particular the co mpressibi lity.For water this fig ure is determined highly by its air con ten t.Wave impacts cannot be computed, as yet. Although the basis equati-ons are available solutions cannot be obtained due to lack of mea-sured data for the material properties. Empirical data are usedtherefore, obtained from large scale model test performed in Holland and Germany. Results of these tests are summarized below, useddata mentioned in the guid elines for the design of asphalt 27 ).

Impact forces are of primarily importance for the impervious revetments i.e. dense asphalt) and to the less extend for the pervio usrevetments i.e. block revetments) .

A wave impact P) is in fact reg arded as a pressureover a certain width b) : P * p.b . The maximum pressure pgiven by pp w.g .q. H in which : p w acceleration due to gravity m / s 2 ) ,factor related to the slope e.g. qand q 2 for slope 1:6. The actingb = 0,4 H.

p) which actsV lil O A X Hl U dl ^ 1 C O O J T 6 P N / l i l ) X S

density of water kg /m 3 ) , g a

H wave height m) and q - a 2.7 for 1:3, q .2.3 for 1:4width is assumed equal to:

Plate thickness of an asphalt revetment can be determined using thecalculation model developed in 27 ), The formula reads:

h * 0.7527 1

.*1-V2) \ J b

490.2

in wh ich: h - thickness of revetment m)


51/125

r1 0 . 6

ij 0.4

| 0 2

1o107

slope

.to

: 3

H s ml

^ ^ 6^ - 5

4

- ^t109

0.8

0.6

0.4

0.2

010

slope 1

,7 10

: 2 / 1 : 4

\ H s l m l

^ 0 ^ 6-~Js^ ?

109

0.6

0.6

0.4

0.2

0107

slope

10

1:6

Hs(m)

: = =109

F/O A Necessary layer thickness for a revetment of dense stone asphalt plotted against the' modulus of subgrade reaction and for various significant wave heights and slopes

107 108 109 lO 7 10 a

modulus of subgrade reaction (N/m3)

Fig B Necessary layer thickness for a revetment of open stone asphalt plotted against themodulus of subgrade reaction and for various significant wave heights and slopes

10

i *

i .

4 -4 -

i\w\V.

W\A \^

flxtont on IMttr MankttI T . M l H CO T < 4.10 MCO T i S.12 MC

fixtont on wn atpnaH T i 3.03 MC T 4.10 MC T . RW MC

A


52/125

a U N M f t F I U C O MIX t INTERMEOMTE O V E M I U E O MIXFIUINO

I EITUMEN EZ3 MMEML AMMOATE Q v o * M

. 25 Z?/?f f ITUMEN FILLING O GGREG TE

In ove r f i l l ed mix tu r es the v i s c o - e l a s t i c p r o p e r t i e s of the b i tumend o m i n a t e , in u n d e r fi l l e d m i x t u r e s the p r o p e r t i e s of the mine ra la g g r e g a t e s are d o m i n a n t . The d e s c r i b e d o v e r f i l l ed m i x t u r e s aremas t i c a spha l t and ove r f i l l ed s tone a spha l t ; a spha l t conc re teb e l o n g s to the ca t ego ry exac t ly f i l led mix t u re s , under f i l l edm i x t u r e s are ve ry pe rmeab l e to w a t e r.

The large scale- and p ro to type - t e s t s ind ica ted tha t the o p e n - s t o n ea s p h a l t , if p r o p e r l y d e s i g n e d , can res is t the cu r ren t a t t ack up to6 m/s and the wave a t tack up to H s 3 m (6), 2 0 , 2 5 ) .It is a l so r easonab l e to expec t that open-s t one a spha l t r eve tmen ton the thick bed of s and-aspha l t can be des igned even to un f requen tloading of w a v e s of H, 5 m. However , in such ex t rem e ca ses ,specia l a t tent ion should be paid to the p r e p a r a t i o n of s and-body

c o m p a c t i o n ) .The re s i s t ance of the s a n d - a s p h a l t is l imi ted to the v e l o c i t y of 3m / s and the wave height of 2 m.

As an example of the ca l cu la t ion me thod men t ioned be fo re (fig. 2 6) ,for some asphal t rev etm en ts , with s lope 1 on 3 and the bed cons tan tc 10 8 N/m - 3 compao ted sand b e d ) , the fo l lowing layer th ic knesscan be g iven as an i n d i c a t i o n :wave height aspha l t open

*s m)

2345

concre te

0.0.0.0.

10203040

s tone asphal t

0.200.400.650.90

sandasphal t

0.400.80

The de ta i l ed in fo rmat ion on des ign and execu t ion me thod s for d i f f eren t app l i ca t ions of a spha l t can be found in (20) and (27).

4 .7 . Reve t men t s under sn ip 1 s induced load

Por des ign of bank p ro tec t ion of n a v i g a t i o n c h a n n e l s and harbouren t races is not only the laod due to the w i n d - w a v e s but a l so theload induced by sh ip move ment waves and c u r r e n t s ) of major iit ance .

Lmpor-

The des ign c r i t e r i a in r e spec t to th is aspect are s t i l l s ca r ce .H o w e v e r, in respect to the i n l and ve sse l s , the s y s t e m a t i c m o d e land p ro to type r e sea rach on th is subject is be ing carr ied out in theNethe r l ands . Refe rence shou ld be made to B laauw et al 1984) andPi larczyk 1984) , 3) .

The p ro to type measuremen t s took p lace in the Har te l Canal Rot terdam) j bot tom width 75 m, dep th 7 m. The fo l lowing t e s t em bank ment s ,equ ipped wi th geo t ex t i l e f i l t e r, were purpose ly cons t ruc ted ons lope 1:4 for the m e a s u r e m e n t s c a m p a i g n s (see fig. 2 7):

- 50 -


53/125

HARTELCAHAL

m*tingcabfn

poti tfOMnf tyi twn

F/j. 4 S chematized set up of prototype measurementssaing paraid te HM emtraliM . auo* i

MrMv X i M Ur

atarvaloetty meter f low dlractfon mtrm cho soundvr

F/V7.3 Cross profile t central m easurement stage5 0 0

F/p f Typical cross section of prototype embankments

F/g. 7 PROTOTYPE TESTS HARTEL CANAL (ship s waves)

fflPtaced btacks

Example of a Reno matt nns

ACZ 0tta mat

Fiitons (o.15m)-

Sand mattrass on gravel

-gaotaxti l*

F ix tone on s and -a spha l t

Fig.0 Examples of constructions tested


54/125

ononon

onon

clayClaysand

sandsand

1. r ip -ra p (5-40 kg)2 . blo cks (0.15 m)3 . b locks on g rave l ,4. b loc ks on sand5. basal ton (0 .15 m)6. r ip -ra p (5-40 kg)7 . coars e grav el (80-200 mm) on sand8. f ine grave l (30-80 mm) on sand9. basa l ton (0 .12 m) on s i lex/sa nd10. f ixton (0.15 m) on sand asph alt on sand11. s and-mat t r e s se s (0.20 m) on g rave l / sand12 . a rm orf lex -ma ts (0.11 m) on grav el /s and13 . PVC-Reno matresses (0 .17 m) on sand14 . ACZ Del ta b lo ck- mat s (0 .16 m) on grave l /sa ndThe tes t em bank ment s ( toplayer and subso i l ) , tes tsh ips and wetcross-sect ion of the tes t locat ion were equipped wi th var ious in-s t ruments . The tes ts have been carr ied out wi th tugs (700 hp and1120 hp) and with pu sh -to ws (pushing unit s 4500 hp and 5400 hp) .Bo th , four load ed and emp ty ba rge s and six loaded ba rge s in 3 x 2and 2 x 3 fo rma t ion have been used . These t e st sh ips sa i l ed bo thalong the central axis and close to the embankment of the canal atd i ff erent speeds to s tudy the re la t i onsh ip bet ween the- ship- induc edwater mot ion and the forces exer ted on the ba nk s . The typical ma ximum va lues o f wa t e rmot ion-c ompo nen t swere a s fo l low s : max imum ve loc i ty o fm a x i m u m w a t e r l e v e l d e p r e s s i o n , Zsecundary waves , H * 0 .85 m.The grave l emb ank ment s (30-80 mm andver i fy the model re la t i ons descr ib ing the begin ning of move ment andt ranspor t o f loose ma te r i a l s under sh ip - induced wa ter mo t i ons . Ithas been proved tha t , in ge ne ra l , ca lc ula t ion m eth ods based on mode l r e su l t s g ive a p rope r app rox ima t ion o f the p ro to type v a lu es .

The fo l lowing s t ab i l i t y c r i t e r i a have been es t ab l i s hed :

inducedreturn

m.85 m and

8 0-2 mm)

by thesef low, r

maximum

tes t sh ips 2 m s 1 ,

height of

were applied to

1 0 5 0 =T* r 2

2gSC O S 0C 1

t a n 2 c tta n2(|>

-1

where : , veloci ty of re turn f low [ms" 1 ) ,angle of in ternal f r ic t ion , R = s lope fac tor

a angle of s lo pe , $ =and 0 1.1 to 1.4.

2* Z m a x / A D 5 0 = 2.3

w h e r e : Z m a x * wa te r l e ve l depr ess ion in fron t o f t r ansve r se s t e rnwave

. Hi (cos B ) 0 . 53' S 1.8 to 2.3

AD50

whe re : Hi * height of sec unda ry w ave s , angle of wave appr oach ;ji s 55 ' , D50 " average s ieve value d iameter (50%) .

The hydraul ic components of ship induced water mot ion ( r , Zmax Hi) can be ca lcula ted accordingly to Blaauw, e t a l ( 1 9 8 4 ) , ( 3 ) .

The behavio ur of the o ther rev etment ty pes , used in the prot otypetes t s , was r a the r sa t i s f ac t o ry. Wi th some excep t ions , no ins t ab i l i -

ty was de tec ted .

- 52 -


55/125

CUTTING OF THE SOOS FROM DIKE

53


56/125

After the completion of the short-term measurements in the HartelCanal it was decided to keep all these prototype embankments forfurther studies on long term behaviour in the coming years.

4.8 Stability of grass-slopes

Some of the existing dikes along the Wadden Sea Northern part of

the Netherlands) need still reinforcement as these do not yet meetthe specific safety requirements. One of the options for reinforce-ment is a slope pcot ection of grass on a bed of cla y, rather thanstone, concrete or asphaltic protection. This option is feasiblebecause vast mud-f lats high foreshore) and grass lands stretch awayon the seaside of the existing dikes and are inundated only duringstorm surges. Moreover, the wave action in the Wadden Sea is muchreduced by a row of barrier islands. Due to these factors the design wave height does not exceed 2 m. The Delft Hydra ulic Labora to-ry was commissioned to assess the stability of such a grass dike bymeans of a full scale model study which was an absolute requirementas grass cannot be scaled down. Two investigations have been per-formed.In the Delta Flume, a five metre wide section of the grass dike wasreproduced on full scale. The model consisted of a sand core co-vered with a clay layer on a slope 1 on 8. Sods of grass with thedepth of the roots of approximately 40 cm were laid on top of theclay layer the gras s was taken from an existing d ike that was re-inforced ten years a g o ) . During the te sts, the wave heights and pe-riods and water levels tidal cyclus) were varied conti nuous ly ac-cording to predeter mined boundary con ditio ns during the designstorm surge. The maximum H s was equal to 1.85 m with Tp 5.6 sec .

plunging breaker falling on a water cushion) . The measured maximumvelocity on the slope 1:8) was about 2 m / s . After 30 hours of con-tinuous random wave attack the condition of the grass dike wasstill exceptiona l w el l. The surface erosion speed of clay protectedby grass was not more than 1 mm per hour . In a number of ad ditionaltests, the durability of the grass and the enlargement of holespreviously dug in the grass were studied. Although wave action con-siderably enlarged some of these holes, the residual strength ofthe dike was such that its coll apse was far from imminent 7 ) .The second inves tigat ion was carried out in a large site) f1urne onslope 1 on 4. Special equipment was used to simulate the run-up andrun-down ve locities on this sl ope. Two qualitatively differentgrass-mats on clay were used.The gra ss- mat s were tested with the average velocity of 2 m/ s average over 40 hours of test) and the thicknes s of a water layer ofabout 0.6 m. The maximum velocity was about 4 m/ s . Erosion speedof the clay surface w as 1 to 2 mm per hour up to 20 hours dependingon quality of grass-mat. After 20 hours of loading the erosionspeed started to grow much prog ressiv ely for a bad quality gra ss-ma t. Similar proces s took place for a good quality gra ss-mat butafter 40 hours of loading. The detailed information on the resultsand grass-mat specifica tion can be found in 8) .

Some additional information on resistance of unprotected clay-sur-face slope 1 on 3.5) were obtained during the investigat ion carried out for the Eastern Scheldt dikes 10 ). Also in this case twoquali tativ ely different clays were used fat and lean c lay) . The

surging-breaker conditions were applied to eliminate the effect ofwave impact H a 1.05 m, T p 12 s, max. velocity 3 m / s ) .The erosion on the upper part of slope was for both clay-types thesame and equal to about 2 - 3 cm after about 5 hours of load ing.

54


57/125

FULL-SCALE STABILITY TESTS OF A GRAS S DIKE

55


58/125

After the sarae t i me , the er osio n below S.W. L. w as about 7 cm for agood cla y, while for a lean qlay a local ca vi ty of ab out 0.4 mdepth was c rea ted a t the impact po in t . This la tes t p rob abl y beca useof the loca l non -ho mog eni ty of c lay . Also dur ing th is in ves t iga t i ona number of addi t iona l tes t s on the e ros ion of d i ffe ren t sublayers( i nc l . c lay) at loca l ly damaged topla yers ( some pro t ec t ive uni t swere r emoved) we re pe r fo rmed .

All the tests men tio ned above indic ated that the stre ngth of thegrass s lopes i s s t rongly a ffec ted by the gua l i ty of c lay and thecondi t ion of gras s and i t s root ing . The gene ra l des ig n ru le s cannotbe def ined ye t . How eve r, these in forma t ions can be of a grea t va luefor the des igning of grass d ikes a t the present t ime. Some addi t iona l in format ion on th is subjec t can be found in ( 5 ) .

4 .9 Example o f s emi -p robab i l i s t i c c a l cu l a t i on o f r eve tmen t

The de t e rmin i s t i c app roach i s t he mos t t r ad i t i ona l de s ign me thod( ) . The des ig ner se lec ts va lu es of load par ame ter s tha t a re a ssu-med to be ad eq ua te ly high and thus sa fe . The choic e of load ands t r eng th pa rame te r s is o f t en sub j e c t i ve , ba sed on t r ad i t i ona l p r ac -t i c e or t he de s ign e r ' s pe r sona l exp e r i e nce . The des ign me thod isbased on the assumption that the structure wil l not fai l i f theloads a re less than the s t re ngt h , provided a good (and ver i f ied )theore t ica l model i s ava i lab le . A fac tor of sa fe ty i s used to coveru n c e r t a i n t i e s .

The prob abi l i s t ic method i s a sys te mat ic a pproa ch us ing s ta t i s t ica lt e chn iques . Fo r cons t ruc t i ona l de s ign t he u se o f p robab i l i s t i c c a l -cu l a t i ons i s p r e f e r r ed . A p robab i l i s t i c p rocedu r e for r eve tmen t s i scur r en t ly under de vel opm ent , and a repor t wi l l be presen ted byPIANC worki ngg rou p no . 3 la te r in 1987. The re l iab i l i ty func t ion zmay be def ined as Z R (Xj) - s (X i) , where R * res i s tan ce func t io n , S load fu ncti on and Xi * basic v ar ia bl es . The l imit s tate ofthe cons i dered compon ent occ urs at Z * 0 ; the fa i lure s ta te i s re -lated to Z < 0.There a re three in t e rn a t i ona l ly agreed leve ls on which the l imi ts ta te equat ions may be so lved ( 3 1 ) , ( 3 5 ) :Le ve l I : jc[uS_i^j)rj3babil^Sjtic Pra c_h; pr es en t c o n st r u c t io n de -

sig n ~ me th od s witl relev ant par t ia l safet y fa ct or s .Lev el II : j^n-proj3aj3rlist_c apoa_cj ap pr ox im at io n me th od s are

applied* in whTch nor mal pro bab i l i ty d is t r ib u t i ons a reassumed for both s t rength and la odi ng:1. F i rs t o rder mean va lue app roa ch .

2 . F i r s t o rde r de s ign -p o in t app r oach .3 . Approx ima te fu l l -d i s t r i bu t i on app r oach .

Leve l I I I : Fu l l - d i s t r i bu t i on app roach ; t h i s me thod acco un t s for t heexac t j o in t p robab i l i t y d i s t r i bu t i on func t i ons i nc lud ingthe co r r e l a t i ons among the pa rame te r s . I t u sua l l y r equ i -r e s a cons id e rab l e compu ta t i ona l e f fo r t .

It goe s beyond the scope of this report to deal with al l the methods in de ta i l , bu t the mean va lue app roach wi l l be d iscu ssed because of i ts s implici ty and i ts i l lustrat ive value for s tudying theeffec t of the va lue of var ious s t rength and load p ara mete rs invol -ve d . In th i s method the re l i ab i l i ty func t io n Z i s l inear ized about

the expec ted mean va lue of the para mete rs invo lved . Mutua l ly independen t no rma l ly d i s t r i b u t ed va r i ab l e s a r e a s sume d . The mean va luez and Standard d evi at ion Cf z can be eva lua ted as :

56


59/125

ISITENOUGH

57


60/125


61/125

?

9


62/125

az H,

3Tp 2 cosa

- A D39

-vpAD

5 tand.

4 T p /Hs*

The following steps are taken to calcu late the mean v alue of Z (|i z)and theStandardof inputvariableHsA

ctga

Standarddeviationvariables

deviation G" z as a resultof each stochasticare as follows:

ofparameter

the weighed partial. The assumed values

D(assumed)

2.0 m1 .43 (cos a =0.955 s50,45 m

CT(Xi)0.25 m0.050 25

s0.50

or (0.10 n)

or (0.5 s)

0.0 1 m


63/125

3 * |

k(o) frcqucncy =

of toading | * *c *> o

(b) rspen*function

(e) damag

\

domogo S fcs.f.T

intcnsityof tooding(P)

intensityof loading(P)

in t tns i tyof lood ing (P)


64/125

Further research for lowering the probability of failure may thenfocussed on the characteristics of these parameters. In this casethe variab ility (or uncer taint ly) about the actual wave conditions(wave height and wave period ) is most i mportant (assuming that theaccuray of the form ule, thus , can not be improved) . Of course ifone takes a larger thickness of block, a more safe situation andthus, a lower probability of failure can be expected.

Assuming that in this case the prediction of the actual wave conditi ons can be improved nl . G H g=i 0,1 m and G T p 0,5 se c, the re-peating of this calculations provides p * 1.495 and the probabilityof failure equal to about 7%.The lay down of the criterion of acceptable probability of failureis mostly left to the responsible authorities. However, the bestway is to calculate the probability of failure for various designalternatives in combination with some economical studies regardingthe execution and maintance costs, and economical consequentes offailure. Such an approach can easily be used for decisional analy-sis, where the costs of each decision and its consequences are

weighed by the probability of these events.

The general outlines of the probabilistic approach are shown inFig. 29 One may relate this to the design of slope protection byloosely materials i .e . r iprap) . First of all one shoul'd be able to

predict the frequenc ies of occure nce of hydrauli c loads duringthe lifetime of const ructi on (Fig.29a.)Secondly, the response function should be obtained from hydraulicmodel tests or by applying known transpo rt relat ions hips (Fig.-29b) . The resultant damage (Sd) during the lifetime of the construction is obtained as shown in Fig 29c.

P

Sa I s.f.T.where: T * lifetime of the construction, f frequence of occurenceof a given load inten sity, s * damage per unit time and p inten-sity of load.If more than one type of loading is acting , the summation of thedamage should be computed by integration over the various load com-binatio ns and their pr oba bil iti es. The resulting total damage is ameasure of the expected maintance of the slope protection works fora given size of the top layer and revetment composition.A process of economical optimalization, based on the costs of construction and maintance, can further be carried out, leading to theselection of the optimum size of the rev etm ent . Besides this minimum integral cost criter ion, one should als restrict the expectedtotal dama ge .The maximumn acceptable damage depends on:

the relat ionsh ip between expected total dam age , which is anaverage over the total protecti on length and the maximum poss i-ble dama ge that may take place at a certain loca tion ,the type of constr uctio n and the vuln erab ilit y of the subsoi l,the risk of progressive damage if repair in time is impossiblefor te chnical , organisatio nal or financial reason s.

The actual state of the knowlegde allows to apply this approach on-ly for slope protection by loosely materials where the adequatetrans fer- funct ions (transport form ulae) have been developed in therecent years. However in general, there is still a lack of data and

insight in many of the above aspe cts . There fore the research programmes in the Netherlands for the coming years are being systema-tically directed towards economically justified design criteria fordifferent protective structures and different applications.

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boundarv conditions

technicQloptimalltern tive

finat designI

|alternafive design Ir i

see t fhe left

execution

Fig 31 DESIGN OEVELOPMENT

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te rmined m ost ly by mode l (or pro tot ype ) tes ts for each revet menttype under cons ide ra t ion . Por pe rmeab le r eve tmen t s on pe rmeab lesub laye r the ma th emat i ca l mod e l S tee nze t , a s deve lope d in theNe th er la nd s , can be used (9) .

Por the d im ens ion s of the reve tmen ts the fo l lowi ng (geneta l ) des igncri ter ia can be set out ( 26 , 27 en 28) :1 . S l id ing cr i te r ia : the revet ment should be des igne d so that it

does no t s l ide under f r equen t ly occur r ing load ing s i tua t ions .2. Equ i l ib r ium c r i t e r i a : t he r eve tmen t inc lud ing sub l aye r s and sub-

soi ls must be in equi l ib r ium as a wh ol e .3 . Up l i f t c r i t e r i a : in load ing s i tua t ions which occur r a re ly , such

as s torm su rge s , the compone nt of the weight of the r eve tme nt ,norm al to the d ike face should be greater than the upl i f t pr es-su re caused by wa te r.

4 . Sur f ace - r es i s t ance c r i t e r i a : the su r face pa r t i e l e o f r eve tmen tshould have enough res is tance agains t wave and current a t tack.

The mode l s se l ec ted to e s t ab l i sh the d imens i ons o f a s t ruc tu re wi l lhave to prove i t se l f in prac t ive to ensur e tha t th is repre sent s thepr i mary behav iour of the pr ot ot yp e, as wel l as to ensure that theused safe ty fac tor i s suff i c int to cover the seconda ry ef fec ts andinaccurac ie s in the used da ta and boundary cond i t ions .

5 .3 Choi ce of revet ment

From the c la ss i f ic a t i on of revet men ts (see f ig . 15) it i s obvi ousthat there are very many poss i b le c omb ina t io ns that can lead to al a rge number o f poss ib l e con s t r uc t ion s . Th i s does no t s impl i fy thecho ice o f a r eve tmen t . Bes i des , t he cho ice o f the ma in r eve tmen tcon st r uct ion has i ts own rep erc uss ion s for the t ra ns i t io ns and theother par ts of the d ike , and the execut ion and maintenance method.

To make a cho ice out of var io us and in a cer ta in s i tua t ion poss ib lea l t e rn a t i ves , c r i t e r i a fo r judg ing need to be fo rmula ted ( func t io -nal technical and f inancia l ) wi th the help of the demands that arema de . Even the bes t des ign may fa i l as a resul t of poor wor kma nsh ipand bad management . Thus , t he a spec t s wh ich a re conce rned wi th const ruct ion and wi th management and maintenance should a lso be invol-ved in th is s tag e . Bec aus e a l l the var i ous cr i ter ia have not beendef ined equal ly wel l and do not p lay an equal ly prominent par t inthe de f in i t e cho ice , sub jec t ive exper i enc es and /or p re jud ice canb e d e c i s i v e .It se ems to be wise to mak e the choi ce in a gr oup so that the subject ive aspect can play the leas t poss ib le par t . Por the d i fferent

aspe cts weighi ng fac to rs can be made so that a more objec t iv e cho ice might be po ss ib le . This problem is ac tu al ly t rea ted by a specia lwork ing g roup in the Ne the r l ands .Som e pos s ib le as pects and so lut i ons tha t can play a par t in thecho ice of the con st r uct ion of the revetment wi l l be me nt io ne d, in amore or less arbi t rary way below.

5.4 Com pos i t i on of d ike and re vetme nt

Compo si t i on of the con st ru ct i on (prof i le , yes /no berm, e tc . ) i s animportant cond i t io n for the des ign of a rev etm en t . On one s ide th iscan inf luen ce the d ivi s ion of the wave for ces on a d i ke . On the

other s ide th is can res t r ic t the f reedom of des ig n conc erni ng therev etm ent . The choice of a berm yes of no can be of a great inf luence to the choice of the upper par t of the s l op e . The hol low shapeof a s lope can increase the c lenc hing force s (and so s tabi l i ty) of

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g ot xtl

Fig 32 DESIGN PRINPLES

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G R A N U L A R F I LT E R S

F I LT E R R U L E S

G E O T E X T I L E S

T H I N T Y P E S

W O V E N

N O N W O V E N

M U LT I L AY E R T Y P E S

F I LT E R A N D

T H I C K N E S S F U N C T I O N

C O M P D S E D F I LT E R S

G R A N U L A R L AY E R

T H I C K N E S S D A M P I N G

FUNCTION

G E O T E X T I L E

FILTER FUNCTION

Fig 33 CHOICE OF FILTER/SUBLAYER

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concrete blocks

gravel

minestone

asphalt concrete

dumpedstone

penetration

A Penetration of sand info the m ine waste stonegeofexfile bet ween sand and minestone /gravelis necessary

separationbasalt b o a r d

columns

concrete

blocks

penetration

B Transition from basalt columns f o concrete blocksseparation board too short

Fig. 54 ILLUSTR TION OF TR NSITION PROBLEMS

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n e s s . P rope r exec t ion i s e s se n t i a l in o rde r t o ob t a in s a t i s f ac to ryj o i n t s a n d t r a n s i t i o n s .When the se gu ide l i ne s a r e no t f o l i owed the j o in t s or t r ans i t i on smay inf luen ce lo ads in te rms of forces due to d i f fe re nc es in stines s o r s e t t l emen t , m ig ra t i on o f subso i l f r om one pa r t t o ano the r

e r o s i o n ) or s t rong p re s su re g r a d i e n t s due t o a conce n t r a t e dg round wa te r f l ow.Example s t o i l l u s t r a t e t he p rob l em o f t r ans i t i ons a re g iven in f i -gures 34 and 35 .

BASALT traditional/old Dutch solution)

dumpedstonerubble)

^ - clay

^c lose p i le - row

geotextile

brick layers

rubble

PLACED BLOCKS

sea bottom77777 geotextile5-10cm gravel 5-20mm

broken stone)

spaced piles and wooden plank board)

blocks withpenetration

asphalt

concrete

geotextile

sand

\ - wooden sheetpile

F/g 35 EXAMPLES OF TOE PROTECTION

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technical

the modical check upas alarmbell

preventionis better than

cure

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6 . MANAGEMENT AND MONI TORING

Coas ta l zone manag ement invo lves managem ent and dec i s i on-ma kig re -g a r d i n g : a coas ta l p to tec t ion p la n , tha t i s a coheren t set of meas ur es ,

spec i f ied in time and sp ac e, to achieve a cer ta in extend of pro-t ec t ion aga ins t ex i s t ing o r an t i c ipa ted damage ;

a moni to r ing and con t ro l sys tem inspec t ion sys tem, meas ure -m e n t s ) .

Coas ta l zone manaFirs t ly, an in tegbecause of the int ion measures andin tegra l approachques are involvedpo ten t i a l so lu t ioland use planningmode l l ing t echn iqis required becauad jacen t coas ta l

geme nt is chra l approachter re la t i ons

the dai ly mis requiredin the anal

ns , for exam, env i ronmenues e tc . Thse of the pos e c t i o n s .

aracter ized by i t s in tegto the coas ta l p rob l ems

hip between land use , coanagement and con t ro l . S

s ince va r ious d i sc ip l inysis of the coasta l probple , coas ta l eng inee r ingt a l s c i e n c e , m a t h e m a t i c ai rd ly, a ce r t a in spa t i a lt en t i a l phys ic a l in te rac

ra l na tu re .is required

as ta l p ro tec -econd ly, anes and techni-lems and their, e c o n o m i c s ,1 and p hys ica l

inte grat iont ions be tween

In genera t i ng and ana lys ing a coas ta l p ro tec t ion p lan , the fo l lo -wing s t eps can be d i s t i ngu i sh ed :1 . de f in i t ion o f coas ta l sec t ions ;2 . c rea t io n of bas ic a l t e rn a t i ves ;3 . iden t i f i ca t ion o f coas ta l p ro tec t ion mea sur es ;4. s c reen ing o f mea sur es , by sec t ion ;5 . c rea t ion o f a l t e rn a t ive co as ta l p ro t ec t ion p la ns ;6 . impact asse ssmen t fu ll spe ci f ica t io n of a l l re lev ant e f f e c t s ) ;7. e v a l u a t i o n by t he d e c i s i o n - m a k e r s ) .

Informcoas tamentted winetworTo redsign sagenciA genem o n i t oc o n s i s1. ide

23

idedetby

4. cal5. exe

ation1 str uFig . 3th monks anduce thhouldes witra l lyr ing nts ofn t i f i e

n t i f i eerminathe necu la t icut ion

about thectures i s6 ) . Coasti tor ing a,/or specie, o f t enyield anh suff ic iapp l i cab le tworks bthe fiveation and

at ion oftion of ttwork ;on of the

of a cos

actuindi

al mac t iv ific fh igh ,opt iment ie meteingmain

quan

the rhe ef

costt- ef

al sspennaget iesield

cosal snf orhodactus teptif i

elevfect

tatesablment

andsur

ts oys teraatifora l lys :ca t i

antiven

of the coa sta l area in cludi nge fo r op t ima l coas ta l manage-, is the re fo re i n t ima te ly connec-

the des ign o f rou t ine moni to r ingv e y s .f the moni to r i ng sys tem, i ts dein which pro vid es the res pon sib leon a t min imal cos t s .the des ig n and opt ima l iz at i on of

deve loped in the Ne th e r l an ds

on o f the ob jec t ives ;

p r o c e s d y n a m i c s ;ess of the info rmat ion provi ded

s o f the moni to r i ng ne twor k ;f e c t i v e n e s s a n a l y s i s .

Based on the resul ts of analyse done in the second s tep, the neces-sary ins t rume nts for mon i tor ig can be de f i ned . It wi l l lead veryof ten to deve l opmen t o f the new types o f moni to r ing - in s t r ume nts .

A new ph i lo sophy in coas ta l moni to r ing invo lves the combina t ion o fmath emat ica l s imula t ion mode l s and me as ure me nts . in th is appro ach ,

which is s imi lar to that appl ied in the cont rol of indu st r ia l pro-c e s s e s , the resu l ts of me as ur em en ts are compare d wi th the foreca s to f th e m a t h e m a t i c a l m o d e l .

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A

Sea Defences Dutch Guidelines on Dike Protection

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