Ports Design Manual Part 1

8/13/2019 Ports Design Manual Part 1

1/99

PORT WORKS DESIGN MANUALPART 1

General Design Considerations for Marine Wors

Ci!il Engineering Offi"e

Ci!il Engineering De#art$ent

T%e Go!ern$ent of t%e &ong Kong S#e"ial Ad$inistrati!e Region


2/99

The Government of the Hong Kong Special Administrative Region

First published, Ma !""!

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!


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'OREWORD

The #ort ;or.s (esign Manual presents recommended standards and methodologies

for the design of marine *or.s in Hong Kong+ 1t consists of five separate volumes, namel,

#art ) to #art 9+ #art ) mainl covers design considerations and re:uirements that are

generall applicable to various tpes of marine *or.s+ #art ! to #art 9 are concerned *ith

specific design aspects of individual tpes of *or.s including piers, dolphins, reclamation,

sea*alls, brea.*aters and beaches+ This Manual supersedes the #ort ;or.s Manual, of *hich

the contents *ere prepared in the


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Woring Co$$ittee of Port Wors Design Man(al ) Part 1

The preparation of the document *as overseen b %hief &ngineer3Technical Services $

1r u. Fu.@man 7before 6 (ecember !"")8

1r Anthon oo

The document *as drafted b the follo*ing staff of the %ivil &ngineering 'ffice $

1r ee ;ai@ping

1r i Kam@sang

1r ;ong %hi@pan

Assistance and advice *ere provided b the follo*ing staff of the %ivil &ngineering 'ffice and Special

(uties 'ffice $

1r %hiu Mau@fat

1r Ko ;[email protected]

1r ai %heu.@ho 7before )! September !"")8

1r am %[email protected]

1r a* Man@chin

1r i uen@*ing

The document *as revie*ed b $

#rofessor oshimi Goda, o.ohama Bational 5niversit

#rofessor ee %hac.@fan, the 5niversit of Hong Kong

(r K*an K*o.@hung, the 5niversit of Hong Kong

&?tracts from -ritish Standards are reproduced *ith the permission of -ritish Standards 1nstitution

7-S18 under licence number !"")3SK"6)0+ -ritish Standards can be obtained from -S1 %ustomer

Services, 6


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CONTENTS

#age

Bo+

T1T& #AG& )

F'R&;'R( 6

%'BT&BTS 9

)+ 1BTR'(5%T1'B C

)+) #urpose and Scope C

)+! (efinitions, Smbols and References )"

!+ &B1R'BM&BTA %'BS1(&RAT1'BS ))

!+) General ))

!+! Tide and ;ater evels ))

!+!+) (atum ))

!+!+! Tidal %haracteristics in Hong Kong ))

!+!+6 Mean ;ater evels )!

!+!+2 &?treme ;ater evels )!

!+6 -athmetr )6

!+2 ;ind )6

!+2+) ;ind Stations in and around Hong Kong )6

!+2+! &?treme ;ind Speeds )2

!+2+6 (irectional (istribution of ;ind )9

!+9 ;aves Generated b ;inds )9

!+9+) General )9

!+9+! ;ave %haracteristics )0

!+9+6 ;ave #arameters )ed in Figure )+

Tides at various locations in Hong Kong displa a gradual change in tidal range and in the

time of occurrence of high and lo* tides from the southeast to the north*est across the

territor+ 1n a tidal ccle, ;aglan 1sland is tpicall the first to e?perience the high tide and

lo* tide *hile Tsim -ei Tsui is generall the last+ The mean dela is about ) hour and 6"

minutes for high tides and around ! hours 6" minutes for lo* tides+ The tidal range is largest

at Tsim -ei Tsui and smallest at ;aglan 1sland+ The mean tidal range is )+2 m at Tsim -ei

Tsui and about ) m at ;aglan 1sland and the ictoria Harbour+

The locations of tide stations under the control of the Hong Kong 'bservator are sho*n in

Figure !+ These tide stations provide long term measured *ater level data over ears+ General

*ater level information at the tide stations can be found in the Tide Tables published each ear

b the Hong Kong 'bservator+ 1n the tide tables, onl the times and heights of high and lo*

tides *hich occur each da are sho*n+ For more detailed predictions on hourl tide levels at

these stations, the Hong Kong 'bservator should be consulted+

1t should be noted that the *ater level information given in the Tide Tables of the Hong Kong

'bservator are based on normal meteorological conditions+ The observed *ater levels ma

differ from those given in the Tide Tables due to storm surges during tropical cclones+ The

*ater level information given in Tables ! to C described in Sections !+!+6 and !+!+2 is derived

from observed *ater levels and has account for the effect of storm surges+

+*+*0 Mean Water Le!els

The mean sea level, mean higher high *ater level, mean lo*er lo* *ater level at the eight

tidal stations together *ith the period of data are sho*n in Table !+ The mean higher high

*ater level is the average of the measured higher high levels and the mean lo*er lo* *ater

level is the average of the measured lo*er lo* levels+ The meaning of the higher high *aterlevel and lo*er lo* *ater level are sho*n in Figure )+

+*+* E2tre$e Water Le!els

5pdated e?treme sea level analses have been carried out b the Hong Kong 'bservator for

Ko au ;an, /uarr -a3Borth #oint, Tai #o Kau, Tsim -ei Tsui, ;aglan 1sland, %hi Ma

;an and o. 'n #ai+ &?treme sea levels for return periods of !, 9, )", !", 9", )"" and !""

ears for these seven locations are given in Tables 6 to C+ The period of records used in each

case is given in these tables+ At each location, the assessment *as carried out b fitting a

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Gumbel distribution to the annual ma?imum sea levels and using the method of moments in

parameter estimation+

Minimum sea levels observed at the < tide stations in Figure ! are sho*n in Table )"+

#robable minimum sea levels at /uarr -a3Borth #oint have been estimated b the Hong

Kong 'bservator using Gumbel=s method and are sho*n in Table ))+

+*0 3at%-$etr-

General information on the bathmetr of Hong Kong *aters can be found in the nautical

charts for the follo*ing areas published b the Hong Kong Hdrographic 'ffice $

ictoria Harbour eastern part

ictoria Harbour central part

ictoria Harbour *estern part

amma %hannels

Ma ;an and adLacent approaches

5rmston Road

Approaches in south eastern part of Hong Kong *aters

These nautical charts provide the *ater depths belo* the %hart (atum+ 1f other *ater level

data are used to calculate the *ater depth, care should be ta.en to ensure that both the

bathmetr and *ater level data refer to a common datum+

1t should be noted that, apart from the information given in the nautical charts, detailed

bathmetr surves are normall re:uired to determine the latest seabed levels and to

supplement information at and around the site area of a proLect+

+* Wind

+**1 Wind Stations in and aro(nd &ong Kong

A number of meteorological stations are operated b the Hong Kong 'bservator that

measures *ind data in different areas of Hong Kong+ Four stations in Huangmao Ihou,

Tuoning iedao, Beilingding and ;ailingding have also been installed in cooperation *ith the

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Guangdong Meteorological -ureau+ Figure 6 sho*s the locations of these stations+ (etails of

the *ind data collected at these stations should be chec.ed *ith the Hong Kong 'bservator+

+**+ E2tre$e Wind S#eeds

Mean hourl *ind speeds for return periods of 9, )", !", 9", )"" and !"" ears for three of the

main stations, namel, Kai Ta. Airport Southeast Station, %heung %hau Station and ;aglan

1sland Station are given in Tables )! to )2+ Mean *ind speeds for durations of !, 6, 2, 0 and

)" hours and return periods of 9, )", !", 9", )"" and !"" for Kai Ta. Airport Southeast

Station, %heung %hau Station and ;aglan 1sland Station are also given in Tables )9 to 6"+

The assessment *as carried out b the Hong Kong 'bservator b appling GumbelNs method

to the annual ma?imum mean *ind speeds for each duration and direction+ The period of

records used for each station is also given in the tables+ The follo*ing points about these

stations should be noted *hen appling their mean *ind speed data $

-oth the %heung %hau and ;aglan Stations are better e?posed geographicall

and not directl affected b urbani>ation+ Their *ind data are generall more

representative of the *ind conditions over Hong Kong+

The *ind data at Kai Ta. Airport Southeast Station are subLect to the shelter

effect of the mountains surrounding the harbour+ ;ind data at this station

should not be used for locations outside the inner ictoria Harbour area+

The mean *ind speeds given in Tables )! to 6" have been corrected to the standard height of

)" m above mean sea level+ Bevertheless, users are advised to consult *ith meteorological

e?perts for the latest information on e?treme *ind speeds+

&?treme *ind speeds for other *ind stations are not sho*n because of the relativel short

period of data collection+

For conversion of the mean hourl *ind speeds to mean speeds *ith durations of less than one

hour, the follo*ing conversion factors ma be cited $

)9


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Duration Conversion Factor

) minute )+)C

9 minutes )+))

!" minutes )+"9

) hour )+""

%aution should be ta.en *hen using the above values, as the conversion factors are greatl

affected b the surface roughness and topograph around a site of interest+

+**0 Dire"tional Distri.(tion of Wind

#ictorial summaries of the fre:uenc distribution of *ind direction and speed measurements at

Kai Ta. Airport Southeast Station, %heung %hau Station and ;aglan 1sland Station are given

for an annual basis in the form of *ind roses in Figure 2+

+*4 Wa!es Generated .- Winds

+*4*1 General

&stimates of e?treme *ave conditions at a site should ideall be obtained b e?trapolating a

series of *ave measurements made at or close to the site+ Ho*ever, because of the relativel

high cost of setting up a *ave recording sstem, and the need for records covering a suitabl

long period 7more than several ears8 to enable sufficientl reliable e?trapolation, direct *ave

record ma not be available for the design of marine *or.s or structures+

1n Hong Kong *aters, the most severe *ave conditions are usuall associated *ith storm

*aves and, in the absence of *ave records, *ave forecasting from *ind records can be used topredict such conditions, as outlined in later sections+ 1n some situations, particularl *here

there is direct e?posure to the South %hina Sea and longer period *aves are therefore

considered important, s*ell *aves from distant storms should be ta.en into account during

design+

-ecause of the comple? geographical features in Hong Kong *aters, *aves propagating into

such *aters are li.el to be transformed b processes such as refraction, diffraction, reflection,

brea.ing and seabed friction+ These processes ma have significant influence on the *ave

climate in the area to be studied+ The designer has to assess these factors at an earl stage to

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ascertain *hether more sophisticated analsis has to be carried out+ %omputer models are

available for such analsis and are recommended for use in studing the *ave transformation

in comple? areas+ These models have to be calibrated to ma.e sure that the are suitable for

that particular stud area+

+*4*+ Wa!e C%ara"teristi"s

%haracteristics of *aves that should normall be considered in design are given in the

follo*ing paragraphs+

7)8 ;ind ;aves and S*ells

;aves can be broadl classified as *ind *aves and s*ells+ ;ind *aves, also .no*n as seas,

are those under the influence of *ind in a generating area+ 1n general, *ind *aves are highl

irregular in appearance and tend to be short@crested+ S*ells, on the other hand, are *ind@

generated *aves that have travelled out of the region of their generating area+ 'utside the

generating area, no energ is supplied from the *ind, and therefore s*ells graduall deca due

to various energ dissipating and transformation processes, but their periods are elongated

during propagation+ S*ells have regular, long crest appearance, and are less steep than *ind

*aves+ A sea state ma consist of Lust *ind *aves or Lust s*ells or ma be a combination of

both+

;aves can also be broadl classified as deep *ater and shallo* *ater *aves according to the

*ater depth to *avelength ratio as follo*s $

(eep *ater *aves ;ater depth3*avelength ratio greater than "+9

1ntermediate@depth *ater

*aves

;ater depth3*avelength ratio bet*een "+"2 and "+9

Shallo* *ater *aves ;ater depth3*avelength ratio less than "+"2

7!8 ;ave #ropagation

For deep *ater *aves, the most important processes in the development of the *ave field are

usuall energ gro*th from the *ind, deep *ater *ave propagation and eventual deca of

*ave energ+ The seabed generall does not have an influence on the *ave field in deep

*ater+ ;hen *aves encounter an island, headland or obstacles during their propagation, the

diffract through these obstructions and such phenomenon should be account for in *ave

analsis+

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;aves entering into *ater areas *ith *ater depth generall less than about one@half of the

*avelength, ho*ever, are subLect to the influence of the seabed+ These *aves undergo

refraction b *hich the *ave height and direction of propagation var according to the

topograph+ The *ave height also changes as a result of the change in the rate of energ flu?

due to the reduction in *ater depth, even if no refraction ta.es place+ This is the phenomenon

of *ave shoaling+ ;ave attenuation *ill occur due to bottom friction and should not be

neglected in an area of relativel shallo* *ater that e?tends over a great distance *ith ver

gentle inclination in the sea bottom+ For *ave conditions inside tidal basins or tphoon

shelters, the effect of diffraction through the entrance and reflection inside the boundar of the

basins or tphoon shelters should also be considered+

As *aves approach the shore in shallo* *ater, the *avelength decreases and the *ave height

ma increase, causing the *ave steepness 7*ave height3*avelength8 to increase until a

limiting steepness is reached+ At this limiting steepness, the *aves brea.+ 1n the *ater

shallo*er than ! to 6 times the offshore *ave height, *aves begin to brea. and *ave heights

decrease graduall+ The region *here man *aves brea. is called the surf >one+ -rea.ing

*aves e?ert greater loading effects on the structures and it is therefore necessar to chec. in

design if the structures *ill be subLect to brea.ing *aves+

768 Tpes of ;ave #ropagation

Three classic cases of *ave propagation describe most situations found in coastal

engineering $

%ase ) $ Sea state *ith *ind *aves and s*ells A storm generates deep*ater

*aves that propagate across shallo*er *ater *hile the *aves continue to gro*

due to *ind+

%ase ! $ Sea state *ith *ind *aves onl ;ind blo*s over the *ater areas

around the site of interest and generates *aves that propagate to the site+ 1n this

case, there is no propagation of *aves as s*ells from a remote area+

%ase 6 $ Sea state *ith s*ells onl A storm generates *inds in an area remote

from the site of interest and as *aves cross shallo*er *ater *ith negligible

*ind, the propagate to the site as s*ells+

All cases ma happen at a site, but the first and the second cases are relativel comple? and

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re:uire mathematical model for reasonable treatment in particular *hen variable shoreline and

seabed topograph are present+ The use of mathematical model for *ave estimation is given

in Section !+9+


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The mean *ave period obtained b averaging the periods of all the *aves *ith

troughs belo* and crests above the mean *ater level is also called the >ero@

crossing period T>+

;ave height measurements in deep *ater have been found to closel obe a Raleigh

distribution+ For Raleigh distributed *ave heights, the ma?imum *ave height Hma?in a *ave

record can range from )+0H)36to !H)36$ a larger Hma?tends to appear as the number of *aves in

a record increases+ The relationship of other higher *ave heights *ith H)36 is sho*n in

Table 6)+ The Raleigh distribution is generall ade:uate e?cept for shallo* *ater *here no

universall accepted distribution for *aves e?ists+ ;ithin the surf >one, larger *aves are

graduall eliminated b the depth@limited brea.ing process and the *ave height distribution

becomes narro*er than the Raleigh distribution+ Thus, in the surf >one region, the Raleigh

distribution should not be applied and the method described in Section !+9+C ma be used to

estimate the relationship bet*een H)36and Hma?+

The *ave period does not e?hibit a universal distribution la* but the relationship of the

significant *ave period and the >ero crossing *ave period ma be appro?imatel related in a

general *a as follo*s $

T)36O )+!T>

The periods of other larger *ave heights 7see Table 6)8 ma be ta.en as e:ual to the

significant *ave period+

7!8 Spectral Method

5nli.e the *ave train method, the spectral analsis method determines the distribution of

*ave energ *ith respect to the fre:uenc and direction b converting time series of the *ave

record into a form of energ spectral densit function, *hich is called the directional *avespectrum+ The directional spectrum is e?pressed as the product of the fre:uenc spectrum and

the directional spreading function+ The *ave fre:uenc spectrum ma be obtained from a

continuous time series of the sea surface elevation *ith the aid of the Fourier analsis b

considering the *aves as a linear superposition of a large number of simple, small@amplitude

*avelets *ith different fre:uencies travelling independentl of one another+ The

representation of the *aves in the form of *ave spectrum is sho*n in Figure 9+ The

directional spreading function e?presses the degree of *ave energ spreading in the a>imuth

from the principal direction of *ave propagation+ ;ind *aves sho*s a large directional

spreading, *hile s*ells have a narro* spreading+

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The *ave spectrum gives an estimate of the spectral significant *ave height H m" b the

follo*ing relationship $

"m" m2H =

*here m"is >ero@th moment or the total area of the *ave spectrum+

The period parameter that can be obtained from a *ave spectrum is the pea. period, defined as

the period associated *ith the largest *ave energ 7see Figure 98+ An appro?imation of the

>ero crossing *ave period ma be obtained from the *ave spectrum b the follo*ing

relationship $

!

"

>

m

mT

*here m!is the second moment of the *ave spectrum in fre:uenc time domain as indicated

in Figure 9+

and T>is the >ero crossing period+

The >ero@crossing period from the spectral method is onl an appro?imation and the pea.

period can onl be obtained through the spectral analsis+ For *ind *aves in deep *ater, the

pea. period Tpma be appro?imated b TpP )+)T)36in the absence of realistic information+

The fre:uenc spectra for storm *aves ma sometimes be [email protected]+ 'ne pea. ma

correspond to s*ells occurring at lo*er fre:uencies 7longer periods8 and one or sometimes

more pea.s are associated *ith local *ind *aves at comparativel higher fre:uencies 7shorter

periods8+ The direction of s*ells ma also differ from those of *ind *aves+ 1n a [email protected]

spectrum, the effect of different pea. periods and the >ero crossing period calculated from

such a spectrum should be investigated in the design+

768 Relationships of H)36and Hm"

The principles of modern *ave forecast mathematical models and *ave recorders are

generall based on the spectral method providing outputs on the above spectral *ave

parameters+ Ho*ever, the significant *ave height H)36is commonl used to characteri>e the

*ave condition and therefore, it is necessar to understand the relationships bet*een the *ave

parameters derived from the *ave train and spectral methods+

;hile H)36determined from the *ave train method is a direct measure of the significant *ave

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height, Hm"from the spectral method provides an estimate of the significant *ave height+ A

number of field measurements over the *orld have ielded the average relationship of H)36P

"+C9 Hm" in deep *ater+ As *aves propagate into shallo* *ater, *aves e?hibit nonlinear

characteristics and H)36becomes e:ual to or even slightl greater than Hm"+ ;hen *aves

further travel into ver shallo* *ater and begin to brea., ho*ever, the spectral analsis loses

its effectiveness because *aves cannot be considered as a linear superposition of small@

amplitude *avelets+ Thus, the estimation of H)36based on Hm"should be made in deep to

relativel shallo* *ater onl+ ;hen the *ave information *ithin the surf >one is re:uired, it

is recommended to begin *ith the spectral data in the offshore and to evaluate the *ave

transformation b brea.ing as given in Section !+9+C+

+*4* Wa!e Conditions in &ong Kong

5nder normal *eather conditions, *aves are usuall mild in most parts of Hong Kong *aters+

;hen strong monsoon *ind prevails, higher *aves can be e?perienced at the more e?posed

locations and ma last for a fe* das or even longer in the presence of the monsoon *ind+

According to the Hong Kong 'bservator, northeasterl monsoon occurs from September to

Ma *hile south*esterl monsoon blo*s from Qune to August, and the northeasterl monsoon

is usuall stronger than the south*esterl monsoon+ Hence, *aves due to northeasterl

monsoon are generall higher than those generated b the south*esterl monsoon+

&?treme *ave conditions in Hong Kong are due to tropical cclones+ %clone is an area of

lo* atmospheric pressure surrounded b a circular *ind sstem attaining ma?imum *ind

speed near its center+ ;inds due to tropical cclones are characteri>ed b their high speed and

rapidl changing direction and the *ind field normall covers a large region+ The *ave

climate in Hong Kong *aters changes *hen a tropical cclone encroaches upon Hong Kong,

as described belo* $

;hen the cclone is far a*a, its *ind sstem has little or minor effect on the*ave climate in Hong Kong+ ocal *ind *aves are generall insignificant+

There could be a noticeable increase in the offshore s*ells from the southerl

and southeasterl directions travelling a long distance from the cclone+

As the cclone moves closer to Hong Kong, s*ells in Hong Kong *aters

become stronger and the local *ind speeds also increase at the same time+

(epending on the location of the cclone and its distance from Hong Kong, the

s*ells and the local *ind *aves are not necessaril approaching from the same

direction+

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;hen the cclone passes over or in the close vicinit of Hong Kong, ver strong

*inds can prevail, resulting in high local *ind *aves+ At the same time,

offshore s*ells continue to contribute to the local *ave climate for areas

e?posed to the southerl or southeasterl direction+

5nder normal *eather condition, the use of a constant uniform *ind field is considered

appropriate for *ave prediction+ 1n e?treme condition during tropical cclones, *ave

prediction using mathematical *ave models capable of handling time varing non@uniform

*ind field is regarded as the most realistic *ave prediction method in principle+ Ho*ever, this

involves significant calibration effort and difficult in getting comprehensive *ind data over

large area coverage throughout the period of tphoon development and propagation+ The use

of constant uniform *ind fields using the e?treme *ind speed data corresponding to various

incoming *ave directions given in Tables )! to 6" ma be considered acceptable as a

pragmatic alternative in *ave prediction for engineering design+

+*4*4 Wa!e Data and Data So(r"es

7)8 Measurement (ata

;ave information can be obtained directl from field measurement+ For general information

on *ave recording and analsis, reference ma be made to Section !0 of -S062C$#art )

7-S1, !"""8+

T*o bed@mounted *ave recorders have been installed near Kau i %hau and ;est amma

%hannel as sho*n in Figure 0 since )CC2 as part of %ivil &ngineering (epartment=s long term

*ave monitoring programme in Hong Kong *aters+ The follo*ing parameters are provided

from the outputs of the recorders $

Spectral significant *ave height Hm" +

Ma?imum recorded *ave height Hma? +

#ea. *ave period Tp +

Iero crossing *ave period T> +

Mean *ave direction+

Average *ater depth+

The average recorded *ater depths at Kau i %hau and ;est amma %hannel *ave stations

are respectivel about C m and )" m+

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A summar of the *ave measurement bet*een )CC2 and !""" is given in Tables 6! and 66,

and *ave roses on annual basis are sho*n in Figure + The *ave measurement over these

periods reflect that the prevailing *ave directions in the measurement locations are the south

and southeast, and e?treme *ave heights are generall aligned *ith the presence of tropical

cclone events+ 1t should be noted that the recorded spectral significant *ave height Hm"at

these t*o *ave stations ma be ta.en to be appro?imatel the same as the significant *ave

height H)36for design purpose+ More details of these data, such as the full set of *ave output

files, can be obtained from %ivil &ngineering (epartment if re:uired+

7!8 ;ave (ata from Storm Hindcasting

Storm hindcasting is based on the estimation of the *ave height at a particular location

associated *ith past storm events+ 1f there is a sufficientl long period of storm records, it is

possible to estimate the e?treme *ave heights based on the hindcast *ave heights of each

storm events b means of e?treme value analsis+

A hindcasting stud had been underta.en to estimate the significant *ave heights at t*o

offshore locations as sho*n in Figure < b means of a mathematical tphoon model *ith

reference to 2 tphoons occurred in Hong Kong bet*een )C2< to )CC2 7HK#5, )CC9

!"""8+ For each ear, the tphoon that most probabl generates the annual ma?imum *ave

height in Hong Kong *as chosen and its characteristics, including trac.s and pressure

distribution, *ere input to the model to estimate the significant *ave height+ -ased on the

significant *ave height computed each ear, an e?treme value analsis based on ;eibull

distribution *as performed to determine the significant *ave heights of different return

periods+ The results are sho*n in Table 62+ The estimated significant *ave height for given

return periods ma be considered for design purposes as the offshore *ave condition from

*hich the nearshore *ave conditions in Hong Kong can be calculated after due consideraton

of various *ave transformations, but the users are advised to see. for the latest information onstorm *ave prediction results+

1t should be noted that no specific direction and period information are given in Table 62 due

to data limitation in the hindcasting stud+ ;hen using the *ave information, it ma be

assumed that the *aves are travelling from directions approaching to*ards Hong Kong *aters

and the critical direction relevant to the site of interest should then be adopted in *ave

analsis+ For storm *aves, the *ave steepness, !H)3637gT)36!8, is generall in the range of

"+"6 to "+"0+ The range of period of the *aves given in the table ma be estimated b

e:uating the *ave steepness to e:ual "+"6 to "+"0+ The *ave period most critical for the safet

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of structure under design should be selected *ithin the above range+

768 Ship 'bservation (ata

isual observations of *ave conditions are reported from ships in normal service all over the

*orld, and sometimes these data are used to estimate the *ave conditions *hen *ave

information is absent+ 1n offshore area *here the *ave climate does not var :uic.l *ith

position, observations from a *ide area based on a large number of observations can be

gathered together and give a general indication of the *ave climate of the area+

Records of ship observed *ave data *ithin the area of the South %hina Sea bounded b

longitudes )""& and )!"& and b latitudes "B and 6"B are .ept b the Hong Kong

'bservator+ The areas covered b these ship observations ma include some relativel

protected inshore region+ 1f information on *aves is re:uired from ship observations for a

particular proLect, an open area should therefore be considered *hen approaching the Hong

Kong 'bservator for details of records held+ Ship observation *ave data of the South %hina

Sea can also be obtained from the Global ;ave Statistics 7Hogben et al, )C


26/99

mean sea level for this purpose+ Among the three *ind stations given in this

#art of the Manual, correction has been applied to the *ind data measured at

;aglan 1sland and %heung %hau *ind stations *hich have recording heights of

9 m 7

correction *as made using a relationship derived from measured *ind speeds at

;aglan 1sland and the measured *ind speeds close to the standard height of

)" m at Hong Kong 'bservator in the 9"=s 7%hin eong, )C


27/99

+*4*6 Wa!e Predi"tion fro$ Wa!e Meas(re$ent

&stimates of e?treme *ave conditions b e?trapolation of measured *ave data are onl

reliable if the original data are derived from a large number of ears+ The method of

prediction consists of plotting the initial *ave heights against the cumulative probabilities of

occurrence, using an appropriate probabilit function+ The obLective is to achieve a graph

*hich ma then be e?tended to give an estimate of the e?treme conditions+ An e?ample of

such method can be found in Section ! of -S 062C$#art ) 7-S1, !"""8+

+*4*7 Wa!e Predi"tion .- Mat%e$ati"al Modelling

The use of mathematical models to estimate the *ave conditions is recommended for *ater

areas *ith variable bottom topograph and shoreline configuration and subLect to the effect of

s*ells and *ind *aves+ (etails of the input re:uirements var among various tpes of models

developed b different organi>ations and therefore reference should be made to the user=s

manuals of these models accordingl *hen the models are used+ &?pert advice or input should

be sought *here appropriate as specialist soft*are and e?perience are usuall re:uired in *ave

modelling+

;here mathematical *ave modelling is applied, a modelling report should be prepared to

describe the *ave spectrum emploed and the modelling approach, procedures and results,

and should include the follo*ing information $

7)8 ;ave Spectrum

;ave transformation analsis should be made for irregular *aves e?cept for special cases such

as long@travelled s*ells approaching a coast *ith nearl parallel, straight depth contours for

*hich monochromatic *ave analsis ma ield reliable results+ -ecause transformations of

irregular *aves depend on the functional shapes of directional *ave spectrum, the fre:uencspectrum and directional spreading function emploed should be stated so that a chec. of the

analsis can be made after*ard+

7!8 Tpes of ;ave Models

The tpe of models and their principles, assumptions and limitations should be specified

because each tpe of model has its range of applications reflecting its theoretical basis+ For

e?ample, *ave propagation models ma not be able to give detailed description of the *ave

climate in a tidal basin, harbour or tphoon shelter due to diffraction and reflection and

!


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798 %alibration

The purpose of the calibration is to ensure that the computed results can realisticall represent

the *ave climate and is achieved b tuning the *ave model to reproduce the .no*n or

measured *ave conditions for a particular situation+ 1n this connection, evidence of

calibration for a particular chosen model, such as comparison of modelled results *ith

measured data, sensitivit tests on variation of input parameters and accurac achieved, should

be presented in the report+

708 %omputation Results

The results should be plotted and e?amined for an signs of computational instabilit or

unreasonable variations in *ave height or direction over short distances+ %hec.ing should

also be made if the values of the computed *ave conditions are consistent and reasonable *ith

respect to the shoreline or bathmetr configuration in the area being e?amined+ A summar

of the computed *ave conditions at the site of interest for various chosen design scenarios

should be given at the end of the report+

+*4*8 Wa!e 3reaing in S(rf 9one

The often :uoted figure of the ma?imum *ave height being e:ual to "+< times the still *ater

depth can be derived from the theor describing individual *aves+ Ho*ever, sufficient

difference e?ists in models bet*een results *ith random *aves and results *ith individual

*aves to indicate that the above figure is not an ade:uate estimate of the brea.er height in all

situations+ A method b Goda in Appendi? A ma be used to estimate the *ave heights in the

surf >one+

A design chart that relates the shoaling coefficient *ith the e:uivalent deep*ater *ave

steepness, the slope of seabed and the relative *ater depth is sho*n in Figure A) ofAppendi? A+ The dotted lines in the figure for the seabed slope demarcate the regions of *ave

brea.ing and [email protected]+ ;hen the intersecting point of the relative *ater depth and

e:uivalent deep*ater *ave steepness falls in the region above the dotted lines, *ave brea.ing

*ill occur+ This procedure ma be used to chec. *hether the structure lies in the brea.ing

*ave region or not+

The *ave heights in the brea.ing *ave region or the surf >one do not follo* a Raleigh

distribution as larger *ave heights brea. under the limited *ater depth+ 1f a structure is found

to be inside a surf >one, the Goda formulae or the corresponding design charts in Figure A! in

!C


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Appendi? A ma be used to estimate the significant *ave height and the ma?imum *ave

height in the surf >one+ 1n the event that the *ave condition is found to be marginal bet*een

[email protected] and brea.ing, it is suggested that both the [email protected] and brea.ing *ave

conditions be chec.ed in the design to determine *hich condition is more critical to the

structure+

+*4*1: Use of P%-si"al Wa!e Modelling

#hsical *ave models can be used as a predictive scale model for the prototpe or as a

verification model for a mathematical one+ As the present state of the art of mathematical

*ave modelling is often sufficient for general design purposes, phsical modelling is mainl

applied *hen a complicated bathmetr in front of a structure causes significant variations in

the near@structure sea state or *hen detailed structural design aspects related to run@up,

overtopping, toe scour or roc. movements have to be clarified+ 1t is mainl due to this

capacit to deal *ith comple? interactions that leads to phsical models being selected to

obtain the necessar design data+ For man of the tpical design problems, ho*ever,

mathematical model ma be the more economical and efficient option+ Therefore, e?pected

accurac must be balanced against the cost of both mathematical and phsical modelling+

+*4*11 Wa!e O!erto##ing

1nformation of the amount of *ave overtopping is needed to determine the crest level of

marine structures+ The methods for assessing the amount of *ave overtopping are given in

#art 2 of the Manual Guide to (esign of Sea*alls and -rea.*aters+

+*5 S%i# Wa!es in &ar.o(r

The *ave climate in the ictoria Harbour is dominated b ship *aves due to the movement ofmarine traffic+ According to an inner harbour *ave stud 7HK5, )CC8, it *as concluded that

the *ave climate in the ictoria Harbour, based on field measurements, has the follo*ing

characteristics $

The *ave climate is dominated b the ship *aves *hich are highl irregular in

nature+

The period of the ship *aves so generated tends to be short and is in the range of

about ! to 9 seconds+

;aves in the *estern portion of the harbour area are stronger than those in the

6"


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eastern portion+

;aves in the region off the north*est shore of Hong Kong 1sland are generall

the strongest in the harbour area+

;aves in bus navigation area are stronger than those in open areas *ith less

marine activities+

;aves during datime are stronger than those at night+

The distribution of *ave regions and the observed significant *ave height corresponding to

each *ave region are sho*n in Figure C and Table 69+ A tpical dail *ave height variation is

also sho*n in )"+ According to the inner harbour *ave stud, about


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over the *ater area+ Hence, the planning of the field measurement *or. and the period of

measurement should consider the meteorological and tidal characteristics of the area of

interest, and aspects of the stud for *hich the current data are needed, ta.ing into account the

follo*ing points $

T*o meteorological seasons prevail in the region of the #earl River &stuar $ the

dr season lasts appro?imatel from 'ctober to April in *hich the northeast

monsoon in the South %hina Sea dominates and the *et season lasts from

appro?imatel Qune to August in *hich the south*est monsoon prevails+ These

t*o maLor seasons are separated b a transitional period *hich generall e?tends

over the month of Ma and September+ (epending on the amount of rainfall

received *ithin the drainage basin of the #earl River, the amount of fresh*ater

discharged into the estuar varies significantl in these t*o seasons+ As a result,

the current velocities measured in these t*o seasons *ill also var significantl+

ariation of tide in the region is characteri>ed b the spring and neap tides

according to the relative positions of astronomical bodies+ Since tidal flo* is

one of the essential forcing conditions to the estuarine behaviour, each seasonal

field measurement should be conducted to cover a spring and neap tide+

The minimum observation period should be a complete tidal ccle, *hich is

about !9 hours for t*o high tides and t*o lo* tides in the semi@diurnal tidal

regime in Hong Kong+

Stratification in some areas ma be significant+ Field measurement should be

made in such a *a as to provide full information on the velocit and salinit

profile at the monitoring point+

The flo* conditions can be determined on site b means of the &ulerian and agrangianmethods+ The &ulerian method is a measurement of *ater flo*ing through an instrument *ith

fi?ed spatial coordinates such as a current meter or an acoustic doppler current profiler+ The

resultant current speed and direction at a specific point at different *ater depths can be

obtained b this method+ 1n the agrangian method, a number of floats or drogues are usuall

used and are released at pre@determined release point+ The paths of movement of the drogues

are then measured regularl until the are recovered+ This method enables the tracing of the

actual paths of the currents+ 1ts limitation is that onl the surface *ater movement is trac.ed

and heav marine traffic ma ma.e the method not feasible+ A combination of these t*o

methods can be emploed in a current surve for mathematical modelling to provide

6!


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measurements for calibration of a hdraulic flo* model and to provide information on the path

of the current for chec.ing the level of confidence of the modelling results+

+*6*0 C(rrent Predi"tion .- Mat%e$ati"al Models

Mathematical modelling is necessar to provide realistic estimation of the characteristics of

the flo* field in the coastal *aters as the flo* sstems in these *ater areas are usuall ver

comple? due to irregular shoreline, variable bathmetr and a number of interacting tidal,

*ind, pressure and densit gradient forcing conditions+ (etails of model application depend

on the tpes of models to be emploed, and e?pert advice and input are re:uired as these

models are normall not eas to appl+ General principles on mathematical flo* modelling

are given in the follo*ing paragraphs+

7)8 Model %ategor

1n coastal or estuarine situations, t*o@dimensional or three@dimensional models should

normall be used+ T*o@dimensional flo* models for use in coastal or estuarine situations are

generall depth@integrated+ The provide a single velocit vector representing the flo*

condition over the *hole *ater column in each hori>ontal cell of the modelled area+ These

models are generall used in situations *here the currents are appro?imatel uniform

throughout the *ater column or for studies in *hich the surface elevation are the primar

concern+ Three@dimensional models are used *hen the vertical structure of currents is not

uniform+ For Hong Kong *aters *hich is subLect to the effect of monsoon *inds and the

discharge from the #earl River, the use of three@dimensional models is essential *hen the

vertical distribution of currents is an important aspect of the stud+

7!8 Model Set@up

The setting up of a mathematical flo* model involves the establishment of the shoreline,bathmetr, model boundar and boundar flo* conditions, *ind field, computational grid

and values of other phsical parameters such as river discharges and bottom friction of the

seabed+ (etails of the input re:uirement should be consistent *ith the particular notation and

format adopted b the models+ 1n general, the follo*ing aspects should be noted $

The shoreline in the model should ta.e into account .no*n and foreseeable

reclamation or marine structures constructed along the shore+

The model boundaries should be set as far a*a from the areas of interest as

66


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possible, but *ithout covering too large an area that *ill affect the

computational efficienc as inaccuracies and uncertainties in the boundar

conditions *ill immediatel affect the model performance+ 1f the e?tent is too

small, the phenomena in the modelled area *ill be dominated b the boundar

conditions+ The natural effects of the geometr, depth and friction on the flo*

*ill not be able to be reflected in the computation+

The computational grid should be established in such a *a to reflect the details

of the shoreline configuration, bathmetr and to ield the re:uired resolution of

the current vectors in the area of interest+ As a general rule, small grids should

usuall be used around the harbour, channels and sensitive receivers, and a

relativel coarse grid ma be acceptable in remote areas and the open sea+

The seabed bathmetr should be accuratel schemati>ed in the model as the

*ater depth is an important parameters that determine the global and local

current distribution+ An overall picture should be in mind from a preliminar

stud of bathmetric records before starting the schemati>ation+

728 %alibration

The application of a mathematical flo* model should involve a calibration procedure in *hich

the model is run to compare *ith the hdrodnamic flo* field of a specific period in *hich

field data have been collected+ 1n calibration, model parameters such as seabed bottom

friction or depth resolution are adLusted to optimi>e the comparison of computed data to field

data+ %omparisons are generall made to *ater levels and velocities, and ma include

reproduction of temperature and salinit+ (iscrepancies ma be progressivel minimi>ed

through a number of simulation runs based on sensitivit analsis of the boundar conditions,

phsical and numerical parameters+ 1t is also necessar to chec. the performance of the

calibrated model in an alternate time period *ith another set of field data, *hich are collectedindependentl from the set used for calibration, b a verification process+ The verification

procedure ma result in some fine@tuning of the model input parameters+

798 Simulation %onditions

The flo* conditions to be simulated should ta.e into account the variabilit under different

seasons and tidal periods+ 1n general, the follo*ing situations should be considered in a

mathematical flo* modelling for Hong Kong *aters $

62


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+*7 Sedi$ents

1n general, the sedimentation rate at estuaries and coastal regions is dependent on river

discharge, land erosion, tidal current as *ell as the prevailing storm and *ave climate+ 1n

Hong Kong *aters, the natural long@term sedimentation rate is governed primaril b the

amount of sediments originating from the river discharges and tidal currents+ Since the

transport and deposition processes of sediments are ver comple?, analtical prediction of the

suspended sediment concentrations and the prevailing sedimentation rate at a given area of

interest is difficult+ Mathematical modelling is therefore used to simulate and assist in

predicting the outcome of such comple? processes+

Sediment models simulate the transport of sediments b advection, *ind, settling,

resuspension and random turbulent processes+ 1n most cases, sediment models use a

hdrodnamic database that is generated b a flo* model similar to that mentioned in

Section !++6 as the basic input+ To minimi>e computational effort *ithout compromising on

accurac, the computational grid of a sediment model is normall an optimum aggregation of

the flo* computational grid+ ;ith the hdrodnamic database in the bac.ground, other

phsical and control parameters are used as input to simulate the phsical processes involved+

The results of a sediment model stud are Lust as good as the calibration of these parameters+

Hence, phsical parameters such as settling velocit of the sediments and critical stresses for

resuspension and sedimentation have to be calibrated before the models can be reliabl used in

an sedimentation studies+

To calibrate the above phsical parameters, it is generall agreed that the follo*ing field data

*ill be ver useful in the calibration of a sediment model for sedimentation studies $

(ata on maintenance dredging in the vicinit of the area of interest+

Amount of sediment discharged from river+

ong@term data on suspended sediment concentration of the area+ Short duration time series of suspended sediment concentration under a .no*n

hdrodnamic condition+

1t should be noted that details of the model application and re:uired input data depend on the

tpes of sediment models to be emploed and e?pert advice should be sought *here necessar+

A sedimentation modelling report, *ith details similar to those described in Section !++6,

should be prepared after completion of the modelling *or.+

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6


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0* OPERATIONAL CONSIDERATIONS

0*1 General

This chapter gives guidance on general aspects such as the design life of structures, ship data,

re:uirements of approach channel and other operational considerations+

Man of the operational re:uirements of marine *or.s and structures are specific to their

particular functions+ Appropriate advice should be obtained from the client or the operator,

(irector of Marine, %ommissioner of Transport, other concerned government departments and

parties as appropriate on all operational matters+

0*+ Design Life

The design life of a structure is ta.en to be its intended useful life, and *ill depend on the

purpose for *hich it is used+ The choice of design life is a matter to be decided in relation to

each proLect+ 5nless special circumstances appl, the design life should be ta.en to be 9"

ears for all permanent marine structures covered b this Manual+ This does not necessaril

mean that the structure *ill continue to be serviceable for that length of time *ithout ade:uate

inspection and maintenance+ Rather, regular inspection and, *here necessar, repair are

re:uired under competent direction to ensure the stabilit and serviceabilit of the structure+

1n vie* of the variable and often unpredictable character of the forces to *hich marine

structures are subLected, it is fre:uentl unrealistic to e?pect substantial cost savings to result

from attempting to design them for short lives+ Generall, greater overall econom *ill be

achieved b choosing simple robust concepts and appropriate reliable construction procedures+

;here special circumstances appl, the determination of the design life should ta.e into

account the follo*ing aspects $

Bature and purpose of the proLect+

&ffects of factors *hich act against the stabilit and functions of the structure,

including fatigue loading, corrosion, marine gro*th and soil strength reductions,

and the corresponding maintenance effort re:uired to ensure that the stabilit

and functional re:uirements of the structure can still be met+

#robabilit level that particular limit states or e?treme events *ill occur during

the design life+

%ost benefit of the design life being considered, including an assessment of the

6


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capital cost and overall maintenance cost of the structure together *ith an

associated replacement cost re:uired+

1mpact on the design life due to future developments, changes in operational

practices and demands+

The probabilit level that an e?treme event *ill occur is related to the design life and return

period+ (esign life and return period are not the same and should not be confused+ An event

*ith a return period of TRears or longer is li.el to occur on average once in TRears+ The

relationship among the probabilit level, design life and return period is given in Figure ))+

Recommended return periods are covered in other sections or parts of this Manual+

0*0 S%i# Data

;here possible, details and dimensions should be obtained from the (irector of Marine, the

client, o*ners and operators of the vessels to be accommodated, and those li.el in the

anticipated lifetime of the structure+ essel characteristics *hich should be considered include

tpe, si>e and shape, ship handling re:uirements, cargo or passenger handling re:uirements,

and vessel servicing re:uirements+ A definition s.etch of the tpical dimensions of the vessels

is given in Figure )!+

-asic characteristics of local vessels ta.en from the ocal %raft Registr provided b the

(irector of Marine are given in Table 60+ -asic characteristics of the vessels o*ned b maLor

ferr operators are given in Table 6+ All values should be chec.ed *ith the (irector of

Marine, concerned government departments and the ferr operators as appropriate before

being used for design purposes+ 1nformation on other vessels using Hong Kong as a port of

call should be sought from the appropriate authorities *hen re:uired+

0* C(rrent Conditions

Reclamation, dredging *or.s and maLor sea defense such as brea.*aters ma cause changes

in the pattern of tidal flo* and conse:uentl affect navigation, mooring and berthing forces,

siltation and *ater :ualit in the vicinit of these marine *or.s, and possibl some distance

a*a from the site+ (uring planning of the proLect, advice should be sought from the %ivil

&ngineering (epartment and &nvironmental #rotection (epartment on *hether detailed

mathematical modelling studies *ill be necessar, and Marine (epartment on the current

conditions for navigation and other vessel operations such as berthing and mooring+

6C


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0*4 3ert% Conditions

Acceptable *ave conditions at berths for ferries and public vessels or *ithin cargo handling

basins and tphoon shelters can onl be determined after consultation *ith the (irector of

Marine and ferr or other vessel operators+ Guidance on acceptable *ave conditions for

moored vessels is given in Sections 6" and 6) of -S 062C$ #art ) 7-S1, !"""8+

0*5 T-#%oon S%elters

Tphoon shelters in Hong Kong are to provide shelter for vessels not e?ceeding 9" m in length

under e?treme *ave conditions in tphoons+ The recommended *ave heights under e?treme

*ave conditions should not e?ceed the follo*ing criteria $

Vessel Length Significant Wave Height

ess than 6" m ess than "+0 m

6" m to 9" m ess than "+C m

1t should be noted that the recommended design criteria should be ta.en onl as the target

design values instead of the absolute allo*able values+ ocali>ed e?ceedance of the design

values ma be permitted *ith due consideration of the site condition and the laout of the

mooring areas *ithin the tphoon shelter in consultation *ith the Marine (epartment+

0*6 A##roa"% C%annels

The depth and *idth of approach channels should be specified or approved b the (irector of

Marine+ The re:uired depth of channels can be calculated ta.ing into account the follo*ing

factors $

oaded draft of design vessel+

Tidal variations+

;ave induced motions of the vessel+

essel s:uat and trim+

2"


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An empirical factor giving an [email protected] clearance to facilitate manoeuvrabilit,

economic propeller efficienc and a factor of safet+

The *idth of the channel, defined as the *idth at the dredged level, should be determined

according to the follo*ing factors $

-eam, speed and manoeuvrabilit of the design vessel+

;hether the vessel is to pass another vessel+

%hannel depth+

%hannel alignment+

Stabilit of the channel ban.s+

;inds, *aves, currents and cross currents in the channel+

Availabilit of navigational aids+

The above factors are covered in detail b #1AB% 7)CC8+

;here the bottom of the channel consists of mud, it is usual in international ports to define the

depth for navigation as being that bet*een lo* *ater level and the level at *hich the densit

of the bottom sediment is e:ual to or greater than )!"" .g3m 6, since research else*here has

sho*n that the mud laers of lo*er densit do not significantl impede the passage of a ship+

The general practice to determine such a level in local port condition is to use an echo sounder

of !"" .H> to !!" .H> *hich, b e?perience, is able to identif the seabed of densit of

)!"" .g3m6in most cases for safe navigation+

;hen planning the location of approach channels, and approaches or fair*as in general,

account should be ta.en of future siltation and maintenance+ %onsideration ma be given to

dredging to a depth greater than the minimum re:uired navigation depth, *ith the intention of

eliminating the need for maintenance dredging in the first fe* ears after completion of initial

dredging+ &stimation of the amount of siltation *ithin the channel ma be determined fromsedimentation field measurement and mathematical modelling as described in Section !+e, location and details of fittings and fi?tures for navigation aids should be to the

2)


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re:uirements of the (irector of Marine+

General information and locations of e?isting navigation aids in Hong Kong *aters *hich

ma be referred to in design can be found on the nautical charts published b the Hong Kong

Hdrographic 'ffice 7see Section !+68+ The definitions of smbols, terms and abbreviations

used on the nautical charts can be found in Hong Kong %hart ) published b the Hong Kong

Hdrographic 'ffice 7HKH', )CC8+

2!


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26


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* GEOTEC&NICAL CONSIDERATIONS

*1 General

This chapter gives general comments and guidance on geotechnical investigation during the

planning and design of a marine *or.s proLect+ For details of geotechnical investigation, the

follo*ing documents issued b the Geotechnical &ngineering 'ffice should be referred to as

appropriate $

Geoguide ) $ Guide to Retaining ;all (esign 7G&', )CC6a8+

Geoguide ! $ Guide to Site 1nvestigation 7G%', )C


45/99

7!8 Tpical 'ffshore Subsoil #rofile

(etails of the offshore subsoil distribution and characteristics in Hong Kong are given in

G&' 7!"""b8 and a summar of the tpical subsoil profile is given in the follo*ing

paragraphs+

1n Hong Kong, the tpical offshore subsoil profile consists of a se:uence of soft to ver stiff

transported sediments, *hich ma be up to )"" metres thic., overling in@situ roc. in various

states of *eathering+ The offshore transported sediments have been subdivided into four

geological groups or formations, the Hang Hau Formation, the Sham ;at Formation, the

;aglan Formation, and the %he. ap Ko. Formation+ The distribution and sedimentar

characteristics are summari>ed in Table 6< and a schematic diagram sho*ing the general

se:uence of these geological formations is given in Figure )6+

Marine deposits of the Hang Hau Formation form the seabed over most of Hong Kong *aters+

The formation consist of a fairl uniform deposit of ver soft to soft, normall consolidated,

olive gre, clae silts that contain shells and lenses of fine sand+ These deposits are

commonl referred to as marine mud+ Ho*ever, the formation becomes sand to*ards the

base, particularl in eastern *aters *here the lo*est deposits represent the sand infilling of

tidal channels+ At the seabed, in >ones of strong currents such as the tidal channels of

5rmston Road and Kap Shui Mun, the Hang Hau Formation deposits become sand+ 1n the

deepest parts of the channels the deposits ma be absent *ith roc. e?posed at the seabed+

1n central and northeastern *aters, the Hang Hau Formation directl overlies the %he. ap

Ko. Formation, a mi?ed succession of clas, silts, sands, gravels and cobbles that ma be

uniform or poorl sorted+ The assorted sediments that ma.e up the %he. ap Ko. Formation

are predominantl of alluvial origin, *ith comple? geometrical relationships that reflect their

origin as river channels and floodplains+ &roded channels, ranging in *idth from a fe* metresto several hundred metres and up to !" metres deep, characteri>e the surface of the %he. ap

Ko. Formation+ This irregular topograph is important *hen determining the base of the

Hang Hau Formation for dredging or foundation purposes+

1n *estern and south*estern *aters, the marine Sham ;at Formation occurs bet*een the

Hang Hau Formation and the %he. ap Ko. Formation+ The Sham ;at Formation sediments

are tpicall soft to firm, normall to slightl over@consolidated, light gre silt clas *ith thin

sand bands+ The differ in appearance from the Hang Hau Formation being lighter gre in

colour *ith *hite patches of decaed shells and orange ello* o?idised mottles indicating

29


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subaerial e?posure and *eathering of the sediments+ The also have a higher cla content, a

slightl higher shear strength, and a lo*er moisture content than the Hang Hau Formation+

1n southeastern *aters, the Hang Hau Formation directl overlies the ;aglan Formation,

*hich is in turn underlain b the %he. ap Ko. Formation+ The ;aglan Formation comprises

a generall firm, normall to slightl over@consolidated, dar. olive gre, clae silt *ith shells

that is similar in appearance to the Hang Hau Formation+ Ho*ever, the ;aglan Formation has

a slightl higher shear strength and lo*er moisture content+ The formation becomes sand at

the base *ith interbedded shell sand and clae silt+ 1n a small area of southeastern *aters, a

restricted occurrence of the Sham ;at Formation underlies the ;aglan Formation+

768 -ehaviour of Marine Mud

The presence of soft marine mud underlain b highl variable alluvial deposits re:uires that

particular attention be paid to the site geolog *hen designing marine *or.s+ The properties

of the marine mud have been studied e?tensivel in recent ears and are sho*n in Table 6C

7Ho %han, )CC28+ ;hen the soft mud is loaded, the increase in e?ternal shear and vertical

stresses *ill cause deformation leading to stabilit problems and foundation failure if the

deformation becomes e?cessive+ 1n a reclamation *here the soft mud is left in place, mud

*aves ma develop if the loading is uneven or is applied too :uic.l+ %onse:uentl, careful

site control is re:uired to avoid rapid or irregular fill placement that ma result in e?cessive

soil displacement and possibl successive slip failures+ For foundations of marine structures,

the stabilit during and after construction must be chec.ed+ Soil improvement techni:ues,

piled foundations to transfer loads belo* the soft laers, or dredging and filling *ith granular

material can be used to improve the stabilit+ For environmental reasons, non@dredge

solutions should be emploed as far as possible+ The correct choice and effective

implementation of the fill placement and foundation methods, apart from cost, programming

and technical factors, relies heavil on a sound understanding of the strength properties of the

underling sediments *hich can onl be obtained through a comprehensive geotechnicalinvestigation+

An increase in vertical stress *ill also induce an e?cess pore *ater pressure in the sediments,

*hich *ill graduall dissipate as the pore *ater drains out+ This process is accompanied b

the consolidation settlement of the soil, *hich ta.es place until the e?cess pore *ater pressure

has completel dissipated+ Ho*ever, even after the e?cess pore *ater pressure has dissipated,

settlement ma continue for man ears at a graduall decreasing rate+ This phenomenon is

commonl termed secondar consolidation+ Settlement problems, such as differential

settlement, ma arise in a reclamation or marine structure if significant amount of settlement

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occurs after the *or.s are completed+ Hence, it is essential to ascertain the settlement

parameters of the soils in order to ensure that an residual settlement, due either to primar or

secondar consolidation, *ill not affect the future development of the reclamation or the

operation of the marine structures+

(etails of stabilit and settlement analsis for sea*alls, brea.*aters and reclamation are given

in #art 6 and #art 2 of the Manual $

#art 6 Guide to (esign of Reclamation+

#art 2 Guide to (esign of Sea*alls and -rea.*aters+

*0 Deter$ination of Soil Pro#erties

Geotechnical investigations should begin *ith a des. stud in *hich all e?isting site

investigation data and geological information are revie*ed, lead up to a thorough site

reconnaissance, and culminate in one or more stages of ground investigation+ From in@situ and

laborator tests of the sediments, the engineering design parameters can be determined+ The

procedures for carring out geotechnical investigations and laborator soil testing are

described in Geoguide ! 7G%', )C


48/99

in %hapter )" of Geoguide ! 7G%', )C


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strength as proposed b -Lerrum 7)C!8, add et al 7)C8 and Aas et al 7)C


50/99

stabilit of marine structures such as gravit or sloping sea*alls+

1t should be emphasi>ed that the specified laborator testing conditions should resemble, as

closel as possible, the field conditions in *hich the *or.s or structures *ill be constructed

and operate under various stages+ The initial state of the samples as *ell as the state of the

soils in the construction and operation conditions should be clearl specified+ Ade:uate

number of samples should also be tested under different stress conditions in order to determine

the shear strength and settlement parameters of the soils at different locations and depths+

* Deter$ination of Ro" Pro#erties

Tpical ranges of values of the unia?ial compressive strength of the most commonl

encountered roc.s in Hong Kong are given in Table )) of Geoguide ) 7G&', )CC6a8+ 5suall,

the strength of the intact bedroc. is not an important consideration in the design of

brea.*aters, gravit sea*alls and reclamations+ For marine structures supported b piles

founded on roc., it is necessar to chec. *hether the roc. strength is ade:uate to resist the

loads transmitted from the piles+ The roc. strength ma be assessed appro?imatel b

identification tests 7G%', )C


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4* LOADING CONSIDERATIONS

4*1 General

This %hapter describes the loading conditions *hich should be considered in the design of

marine structures and includes information on the loads to be ta.en into account+ Guidance is

given on the selection of relevant design parameters and methods of calculation to derive the

resulting direct forces on structures, ta.ing into account the nature and characteristics of the

structures+

1n addition to dead loads, superimposed dead loads, hdrostatic loads and soil pressures, the

other forces *hich ma act on marine structures are environmental loads, arising from such

natural phenomena as *inds, temperature variations, tides, currents, *aves and earth:ua.es,

and those imposed loads due to operational activities+ General imposed loads cover live loads

from pedestrians, vehicles, cargo storage and handling+ essel imposed loads cover berthing,

mooring and slipping+

5nless stated other*ise, the design loads given in this %hapter are unfactored+

4*+ Loading Conditions and Co$.inations

The structure as a *hole, or an part or section, should be designed and chec.ed for at least

the loading conditions given belo*+ 1f it is e?pected that other loading conditions could be

critical, the should also be investigated+ arious tpes of load should be combined in a

manner consistent *ith the probabilit of their simultaneous occurrence+

4*+*1 Nor$al Loading Conditions

These loading conditions are those in *hich normal operations continue unaffected b

environmental conditions+ A combination of the follo*ing should be considered $

(ead loads+

Superimposed dead loads+

ive loads due to normal *or.ing operations 7the most severe arrangement

li.el to occur simultaneousl8+

essel imposed loads 7berthing and mooring8+

Bormal environmental loads 7*inds, currents and *aves8+

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Soil pressures+

Hdrostatic loads+

Guidance on the calculation of environmental loads associated *ith normal *or.ing

operations is given later in this %hapter under each tpe of loading condition+ 1t should be

assumed that ma?imum imposed live loads can occur simultaneousl *ith ma?imum vessel

imposed loads from either berthing or mooring, *hichever gives the most severe effect+ 1t is

possible for mooring loads to occur at the same time as berthing for certain si>e and geometr

of the structure such as a Lett allo*ing berthing on one side and mooring on the other side+ 1n

this latter case, the most severe combination of berthing and mooring loads should be

determined b the designer and this combination assumes to occur simultaneousl *ith

ma?imum imposed live loads+

For normal environmental loads, it should be assumed that ma?imum loads from *inds,

currents and *aves can occur simultaneousl+ All directions should be considered *hen

assessing the most severe effects from these loads+

4*+*+ E2tre$e Loading Conditions

These loading conditions are associated *ith the most severe environmental conditions *hich

the structure is designed to *ithstand+ 1t is assumed that under these conditions most normal

operations, such as vessel berthing and mooring, pedestrian and vehicle movements, and cargo

storage and handling, *ill have ceased+ A combination of the follo*ing should be considered $

(ead loads 7same values as for Bormal oading %onditions8+

Superimposed dead loads 7these ma be different from Bormal oading

%onditions8+

Reduced live loads 7if an at all8 due to continuing operations+

Reduced vessel@imposed loads 7if an8 due to continuing operations+ &?treme environmental loads 7*inds, currents, *aves and temperature

variations8+

Soil pressures 7these ma be different from Bormal oading %onditions due to

variation of *ater table8+

Hdrostatic loads 7in some cases, these *ill be different from Bormal oading

%onditions, e+g+, due to difference in *ater levels8+

1t should be assumed for e?treme environmental loads that ma?imum effects from *inds,

currents and *aves can occur simultaneousl, but ma?imum effects from temperature

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variations should be considered separatel+ essel@imposed loads can be ignored under

e?treme environmental conditions from *inds, currents and *aves, as these *ill occur during

tropical cclone conditions *hen normal vessel movements *ill have ceased+ Ho*ever,

vessel@imposed loads should be combined *ith ma?imum effects from temperature variations+

Guidance on live loads to be considered under e?treme environmental conditions from *inds,

currents and *aves is given in later sections of this chapter+ Bormal ma?imum live loads

should be combined *ith ma?imum effects from temperature variations, as these variations

*ill not occur during tropical cclone conditions+

5nless stated other*ise, the e?treme environmental conditions for structures having a design

life of 9" ears should be ta.en as those having return periods of )"" ears+ ;here special

circumstances appl, resulting in a shorter or longer design life, the return period should be

adLusted accordingl+ The relationship of the return period and the design life is sho*n in

Figure ))+

4*+*0 Te$#orar- Loading Conditions

Temporar oading %onditions are those *hich arise during construction, to*ing, installation

or the carring out of unusual but foreseeable operations, such as the application of a test load+

For these conditions, a combination of the appropriate dead and ma?imum temporar loads,

together *ith the associated environmental loads, should be considered+ Temporar design

and environmental conditions should be appropriate for the location, and for the time of ear,

*hen the construction or operation *ill be carried out+

4*+* A""ident Loading Conditions

Accident oading %onditions are those *hich occur during accidental impact b a vessel+ For

these conditions, a combination of dead, superimposed dead and hdrostatic loads, soil

pressures, live loads and normal environmental loads, together *ith the appropriate accidentberthing load, should be considered+ Guidance on accident berthing loads is given later in this

%hapter+ The above combination is to some e?tent artificial, as an accident can occur at a time

of normal or e?treme environmental loading conditions+ Ho*ever, it is not normall

necessar to combine accident berthing loads *ith ma?imum imposed loads and e?treme

environmental loads because of the lo* probabilit of their simultaneous occurrence+ The

need for chec.ing of accident loading conditions *ill depend on $

1mportance of the structure+

ocation *ith respect to normal ferr routes and fair*as+

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(egree of e?posure to adverse environmental conditions+

&?pected degree of use if the structure is a pier+

Susceptibilit to damage of the tpe of design used+

#ublic and ferr piers should generall be designed or chec.ed for accident loading

conditions+ For such accident loading conditions, damage to minor structural members *hich

can be readil repaired, and to such items as fenders, can be accepted at the discretion of the

designer in consultation *ith the maintenance authorit+

4*0 Dead Loads

The dead load is the *eight of the structural elements of the structure, including an

substructure, piling and superstructure+ The *eight of the structure is its *eight in air+ ;here

parts are *holl, partiall or intermittentl immersed in *ater, upthrust on those parts should

be calculated separatel, as recommended in Section 9++

4* S(#eri$#osed Dead Loads

The superimposed dead load is the *eight of all materials imposing loads on the structure that

are not structural elements, and should include surfacing, fi?ed e:uipment, fenders, bollards,

handrails, ladders, *al.*as, stair*as, services, fittings and furniture+ For all loading

conditions, the possibilit of an of the superimposed dead loads being removed should be

considered+

4*4 Li!e Loads

4*4*1 Li!e Loads on Different T-#es of Str("t(res

The imposed live loads include all loads *hich the structure has to *ithstand e?cept dead,

superimposed dead, hdrostatic, soil, vessel@imposed and environmental loads, and should be

the greatest applied load li.el to arise from the intended use or purpose of the structures+ The

minimum imposed live loads that should be applied in a design are recommended in the

follo*ing paragraphs, and should be adLusted to ta.e into consideration the use of the

structures and the tpes of installations on them+

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7)8 #ublic #iers

The live loads for the dec.s of public piers, to include for the movement of pedestrians, hand

luggage, ship provisions and temporar stac.ing, should be ta.en as )" .#a+ ;here

emergenc vehicular access b an ambulance, police vehicle and3or fire engine as appropriate

is re:uired, the follo*ing additional re:uirements should be satisfied $

%oncentrated load to be applied on plan over an s:uare *ith a 6"" mm side

should be greater than 9 .B+

Total load to be applied on beams, uniforml distributed over span, should be

greater than )9" .B+

;here general access for pedestrians is provided to the roof, the live load should be ta.en as

9 .#a+

7!8 Ferr #iers

The live loads for pedestrian ferr piers should be no less than those given above for public

piers, but should in addition be chec.ed and agreed *ith the prospective ferr operators+ The

live loads for vehicular ferr pier *aiting areas and ramps *ill depend on the tpes of vehicles

allo*ed or e?pected to use the services, and should be agreed *ith the prospective ferr

operators+

768 'ther #iers

The live loads for other piers should be determined after consultation *ith the prospective

users, ta.ing into account the proposed use, possible cargo storage, cargo handling e:uipment

and vehicular access+

728 (olphins

The live loads for dolphins should be ta.en as 9 .#a+

798 Sea*alls

The live load on the area of the land behind the sea*alls should be determined ta.ing into

account the designated land use, and should be ta.en as follo*s $

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Footpaths, ccle trac.s, open pla areas and the li.e $ )" .#a

Roads and carriage*as 7normal traffic8 $ !" .#a

;hen assessing the loading conditions behind sea*alls, the effect of temporar loads, such as

those due to surcharge preloading in a ne* reclamation, should also be investigated in the

design+

708 -rea.*aters

The live load on the crest of the brea.*aters should be no less than those given above for

sea*alls, ta.ing into account the uses and operations on the brea.*aters+

4*4*+ Deter$ination of Contin(o(s Li!e Loads

Guidance on the determination of the live load due to continuing operations under e?treme

environmental conditions from *inds, currents and *aves, and of the live loads to be used in

accident loading conditions referred to in Section 9+!, is given belo*+

7)8 ive oads under &?treme &nvironmental %onditions

The live loads due to continuing operations under e?treme environmental conditions from

*inds, currents and *aves ma be ta.en as >ero for piers and dolphins unless there is a

specific need or re:uirement for the pier to be used during tropical cclone conditions, e+g+ for

emergencies or storage+ For sea*alls, the ma?imum live loads on the adLacent land due to

continuing operations under e?treme environmental conditions ma be ta.en as 9" of the

live loads due to normal *or.ing operations under normal environmental conditions, provided

that it can be ensured *ith reasonable certaint that the land behind the sea*all *ill not be

used for the storage or temporar stac.ing of materials+ For other structures, the live loads due

to continuing operations under e?treme environmental conditions should be assessed b thedesigner+ Bormal ma?imum live loads should be considered to appl under e?treme

environmental conditions relating to temperature variations+

7!8 ive oads under Accident %onditions

The live loads to be used in Accident oading %onditions for normal structures can be ta.en as

9" of the live loads due to normal *or.ing operations under normal environmental

conditions+ At the discretion of the designer, this percentage ma be reduced to !9 for

structures e?pected to be loaded infre:uentl, or increased to 9 for structures e?pected to

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structure, different loading cases, and different conditions, the critical still *ater level ma be

the minimum, ma?imum or some intermediate level the full range must be investigated b the

designer+

4*6 &-drostati" Loads

;hen considering the effects of buoanc, it is preferable to represent the buoanc and

gravitational loads as separatel applied loading sstems+ 1n this *a, the effect of changes in

*ater level can be seen more clearl, and it is possible in limit state design to appl different

load factors to dead loads and hdrostatic loads as appropriate+ The determination of

hdrostatic loads should ta.e into account *ater level variations and ground *ater profiles

mentioned in Section 9+0 and Section 9+< respectivel+

For calculating the hdrostatic loads, the fresh*ater and sea*ater densities ma be ta.en as

)""" .g3m6and )"!9 .g3m6respectivel+

4*7 Soil Press(re and Gro(nd Water Profiles

Guidance on the calculation of soil pressures is given in Geoguide ) 7G&', )CC6a8+ For the

purposes of calculating soil pressures $

;ater levels should be derived as described in Section 9+0+

Ground pore *ater pressures should be determined *ith reference to tidal

range, soil permeabilit, drainage provisions, and an artesian and sub@artesian

ground *ater conditions+

Allo*ance should be made for reduced passive resistance due to overdredging

or scour+

1n the case of a sea*all adLoining reclaimed land, the *all together *ith the bac.fill up to a

vertical plane above its heel 7i+e+ the virtual bac.8 can be treated as a monolithic bloc. for the

purpose of stabilit chec.ing+ Active soil pressures ma be assumed in the calculations and

suggested ma?imum values of mobili>ed angle of *all friction for active pressure calculations

are given in Table )2 of G&' 7)CC6a8+ #assive resistance in front of the toe of the structure

can be neglected for tpical gravit tpe sea*alls such as concrete bloc.*or. sea*alls resting

on a rubble mound+

The ground *ater condition is a critical factor in stabilit analsis+ (esigners should note that

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ground *ater profiles are site@dependent+ 1f possible, it is recommended that the design *ater

pressures should be evaluated from field observations and a detailed analsis considering $

Tidal variation at the sea*ard side of the sea*all+

;ater inflo* from land*ard and from sea*ard sides of the sea*all+

Rate of overtopping *ater under severe *ave climate+

#ermeabilit of *ater draining behind, through and under the structure+

Surface and bac. drainage provided to cater for surface and ground *ater+

1n relativel simple conditions, the ground *ater profiles illustrated in Figure )2 ma be used

as a reference+ ;here the land behind the sea*all is paved, the flo* from land*ard sources is

negligible, and ade:uate surface and bac. drainage behind the structure are provided, the

ground *ater profile in the fill behind the sea*all ma be ta.en as almost hori>ontal at a level

higher than the still *ater level+ 5nless there is clear evidence to the contrar, a tidal lag of

not less than "+ m and )+" m above the still *ater level under normal loading conditions and

e?treme loading conditions respectivel ma be used in design+

1n addition to the above *ater level lags, *here the land behind the sea*all is not paved and

the fill is highl variable, the ground*ater profile should ta.e into consideration the *orst

credible ground *ater conditions that *ould arise in e?treme events selected for design+

Guidance on the determination of the *orst credible *ater conditions are given in Geoguide )

7G&', )CC6a8+

;here the flo* from land*ard sources is significant, the effects of the ground *ater profile

should be evaluated b field investigations+

4*8 Wind Loads

For the assessment of *ind loads on marine structures and for the loading conditions referred

to in Section 9+!, the follo*ing design *ind pressures ma be assumed $

Loading Conditions Design Wind Pressures

Bormal )+! .#a

&?treme 6+" .#a

Accident )+! .#a

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61/99

For Temporar oading %onditions, the design *ind pressure should be assessed b the

designer for each individual case, ta.ing into account the follo*ing points $

The design *ind pressure of )+! .#a for Bormal and Accident oading

%onditions corresponds to a gust of about 22 m3s, *hich is the ma?imum gust

e?pected to occur *ith a mean hourl *ind speed of ) m3s 766 .nots8+ This b

definition is the ma?imum mean hourl *ind speed li.el to occur *hile

Tropical %clone Signal Bo+ 6 is hoisted or *ithin the first fe* hours of the

hoisting of Tropical %clone Signal Bo+ The design *ind pressure of 6+" .#a under e?treme environmental conditions

corresponds to a gust of about " m3s 7)60 .nots8, *hich is the ma?imum gust

e?pected to occur *ith a return period of about 9" ears in Hong Kong *aters+

;ind forces on structures and elements of structures ma be calculated in accordance *ith

Hong Kong %ode of #ractice on ;ind &ffects 7-((, )C


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4*1:*+ Wa!e Conditions

The *ave conditions that should be assessed in design should be Lointl described *ith the

*ater levels as these t*o variables are correlated 7HK#5, !"""8+ For marine *or.s *ith a

design life of 9" ears, the follo*ing *ave conditions and *ater levels should normall be

considered $

Loading Condi

Ports Design Manual Part 1

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