• Nie Znaleziono Wyników

Dredging - past, present, and future

N/A
N/A
Protected

Academic year: 2021

Share "Dredging - past, present, and future"

Copied!
22
0
0

Pełen tekst

(1)

DREDGING - PAST, PRESENT, AND FUTURE

Arthur L. IkKnight

Chief, Operations Division, Jacksonville District Corps of Engineers, U. S. Army

ABSTRACT

This paper traces the history of dredging from a primitive dredge invented by Leonardo da Vinci to the most modern and powerful equipment. Emphasis is given to the modern hopper dredge and recent development in connection with the use thereof. The possibility of application of hopper dredges to beach nourishment work is discussed with an account of current experiments being made in an effort to develop the

practi-cability of such usage.

+ + + +

+

+ + + + + + +

Dredging is, of course, the science of excavating materials which are submerged underwater. As a matter of fact, Hebster does not give the word the dignity of calling it a science. It has long been considered by the average person as a rather uninteresting, prosaic, unsophisticated, and perhaps dirty subject. I have no argument with the source of these feelings but, having been engaged in this subject for over 30 years, I must take the other side of the fence since dredging is actually a most challenging field in which we are dealing with a medium which we cannot actually see in its insitu condition and in a field in which there are so many variables that accurate, simple, and firm determination of a given engineering problem is not susceptible of posi ti ve solution. The flUlctior of an engineer is not just to perform engineering work but to perform it in the most

economical manner. Although this branch of engineering certainly is not as highly technical as some other branches, I know of no field that offers any more rewards in the field of method improvement and cost reduction as does the field of dredging.

(2)

C e r t a i n l y dredging has been and continues t o be a necessary science t o p r o g r e s s . From the b e g i n n i n g o f h i s t o r y men must have performed some type o f dredging and we know t h a t the Egyptians c o n s t r u c t e d t h e o r i g i n a l Suez Canal some 4,000 years ago and must have excavated by one means or another v a s t q u a n t i t i e s o f submerged m a t e r i a l . I n 1289 K u b l a i Khan completed the 1,000-mile Grand Canal f r o m Hangchow t o P e i p i n g which i s s t i l l one o f the l o n g e s t canals i n the w o r l d . I hope t o demonstrate t h a t i n dredging as i n a l l o t h e r sciences , the p r i m i t i v e methods o f our f o r e f a t h e r s were a f a r c r y f r o m the modern s o p h i s t i c a t e d equipment i n use today.

Because o f the low nature o f t h e i r land and t h e i n d o m i t a b l e w i l l of t h e Dutch people f o r s e l f - p r e s e r v a t i o n , mechanical methods o f subaqueous e x c a v a t i o n became a n e c e s s i t y o f l i f e i n the Netherlands many, many years ago and i t i s f o r t h a t reason t h a t the Dutch i n f l u e n c e v ; i l l be predominant i n the s l i d e s which I am g o i n g t o shovf.

Leonardo da V i n c i i s reputed t o have developed t h e f i r s f ' d r e d g e wheel" i n about 1500. You see from t h e s l i d e t h a t the source o f pov;er was manpower c r a n k i n g over the m u l t i - b u c k e t e d wheel which can be seen. ( S l i d e l )

Some years l a t e r the "spoon and bag" dredge was developed. This dredge^is the d i r e c t ancestor o f the dipper dredge and on the n e x t two s l i d e s you w i l l see ti/o types o f spoon and bag dredges. Crude though these machines be they r e p r e s e n t the e a r l i e s t attempts t o gain mechanical advantage by simple e n g i n e e r i n g m e t h o d s . ( S l i d e s 2, 3 )

A manpowered s c r a p e r - t y p e dredge i s seen n e x t . T h i s dredge was used I n H o l l a n d i n 1565. Note t h a t we begin t o see some advances i n mechanical d e t a i l s . ( S l i d e k)

I n 1600 we f i n d t h a t the Dutch had what they c a l l e d a "mud m i l l " which you see now. T r u l y manpowered, t h i s dredge u t i l i z e d f o r the f i r s t time an endless chain bucket and discharged dredged m a t e r i a l i n t o scovfs. ( S l i d e 5 )

A manpowered predecessor t o our c l a m s h e l l dredges today vras i n use i n 1617. T h i s once again I l l u s t r a t e s the i n g e n u i t y o f t h e Dutch i n p r o v i d i n g t h e e x c a v a t i n g equipment w i t h mechanical advantage. A p p a r e n t l y the dumpscows were pushed under the b u c k e t l o c a t e d between the two halves o f what we would today c a l l a catamaran type h u l l . ( S l i d e 6 )

(3)

Manpower a p p a r e n t l y became i n s h o r t supply even i n those days and horsepower came i n t o use. V/e see noiv a horsepowered dredge, v i n t a g e 1650. The house-type s t r u c t u r e s on the deck are a c t u a l l y s h e l t e r s f o r the horses v;hich are p r o v i d i n g the motive power f o r the endless chain buckets. I n order t o get a b e t t e r i d e a o f how t h i s equipment works t h e n e x t s l i d e shows the cut-away o f a v e r y s i m i l a r dredge and i f you w i l l look c l o s e l y you can see the horses i n t h e t u r n s t i l e . The spoked wheel was a p p a r e n t l y used t o a d j u s t the d i g g i n g h e i g h t o f the endless chain bucket l a d d e r . ( S l i d e s T , 8 )

I do not have the date o f t h i s n e x t dredge b u t i t i s an i n t e r e s t i n g cut-away o f another type o f manpowered machine. The method o f e x c a v a t i o n a p p a r e n t l y i n v o l v e d a c i r c u l a r wheel w i t h buckets r a t h e r than an endless c h a i n . ( S l i d e 9 )

So much f o r the development o f e a r l y dredging equipment.

Various and sundry improvements continued t o take place i n subsequent years but the r e v o l u t i o n i n mechanical dredging equipment came w i t h the i n v e n t i o n o f the c e n t r i f u g a l pump by Papin i n 1705 and the steam engine by Watt i n 1795. Records have been found i n d i c a t i n g t h a t tv;o Germans, Hofmann and S c h w a r z t c o f f , developed a h y d r a u l i c dredge f o r l a n d f i l l i n g around B e r l i n i n 1855 , b u t d e t a i l s are n o t a v a i l a b l e .

Dredges today come i n two c l a s s i f i c a t i o n s - h y d r a u l i c and mechanical. Both o f these b a s i c types are broken down i n t o d i f f e r e n t a p p l i c a t i o n s and the n e x t 6 s l i d e s w i l l merely p r e s e n t the types which are i n use t o d a y . F i r s t , we see a p l a i n s u c t i o n h y d r a u l i c type dredge. This dredge i s w i t h o u t c u t t e r power and merely sucks m a t e r i a l o f f the bottom and discharges through a s t e r n connected pipe l e a d i n g t o a s p o i l d i s p o s a l area. T h i s type of dredge i s the predecessor o f the dustpan dredges which are used today i n some p a r t s o f the U n i t e d S t a t e s , p a r t i c u l a r l y a l o n g t h e M i s s i s s i p p i 6 M i s s o u r i R i v e r V a l l e y . ( S l i d e LO)

Next we see the cutterhead p i p e l i n e dredge w i t h which I am sure most o f you are f a m i l i a r . A r o t a t i n g c u t t e r on t h e end o f the l a d d e r p h y s i c a l l y excavates t h e m a t e r i a l from i t s i n s i t u c o n d i t i o n and f r o m there i t i s pumped h y d r a u l i c a l l y and d i s c h a r g e s through a s t e m connection t o pontoon and shore p i p e . The dredge i s c o n t r o l l e d on s t e r n mounted spuds and i s swung f r o m one s i d e o f the channel t o the o t h e r by means o f a swing gear. ( S l i d e 11)

(4)

Next comes a mechanical type dredge o f t h e c l a m s h e l l o r grapple t y p e . Larger dredges o f t h i s type are going out o f f a v o r b u t they have played an i m p o r t a n t p a r t i n many l a r g e p r o j e c t s i n the p a s t . On some p r o j e c t s today t h i s same p r i n c i p l e i s used but by mounting mobile t y p e cranes on barges. ( S l i d e 1 2 )

The n e x t type i s the mechanically operated endless chain bucket dredge which was f o r many years probably t h e most used type o f equipment i n Europe, I t was a l s o u t i l i z e d i n the U n i t e d S t a t e s b u t never t o the degree t h a t i t was i n Europe. Dredges o f t h i s t y p e a s s i s t e d i n the c o n s t r u c t i o n o f the Panama Canal b u t they are "as scarce as hens t e e t h " i n the United States today b u t are s t i l l used i n Europe as we w i l l see l a t e r . ( S l i d e I 3 )

The mechanical d i p p e r dredge i s n e x t . Machines o f t h i s type are s t i l l i n use i n the U n i t e d States and serve an e x c e l l e n t purpose i n e x c a v a t i o n o f rock and other q u i t e hard m a t e r i a l s . ( S l i d e ih)

F i n a l l y , we see the s e l f - p r o p e l l e d h y d r a u l i c hopper dredge. I n normal o p e r a t i o n a hopper dredge sucks up the bottom m a t e r i a l through drags mounted on the sides o f a v e s s e l and i n t o the hoppers w h i l e making one or more passes through the dredging area. Then, the dredge proceeds t o sea o r some o t h e r assigned dump area and discharges t h e m a t e r i a l through doors i n t h e bottom o f the hoppers. This type o f dredge i s normally employed where the water i s t o o rough f o r a p i p e l i n e dredge o r where s p o i l d i s p o s a l areas f o r use by a p i p e l i n e dredge are n o t a v a i l a b l e w i t h i n economic d i s t a n c e .

( S l i d e 1 5 )

Before proceeding w i t h a d i s c u s s i o n o f r e c e n t i n o v a t i o n s w h i c h are t a k i n g place i n the hopper dredge f i e l d , I w i l l spend a few moments on the c u r r e n t t r e n d i n the development o f c u t t e r h e a d p i p e l i n e dredges. This type o f dredge i s c e r t a i n l y the most numerous here i n t h i s country and i s the b a s i c t o o l o f the p r i v a t e d r e d g i n g i n d u s t r y . Although the Corps o f Engineers owns and operates a l i m i t e d number o f these dredges throughout the U n i t e d S t a t e s vre l a r g e l y look t o the c o n t r a c t o r s f o r the performance o f the type o f vjork which i s s u i t e d t o the h y d r a u l i c p i p e l i n e or c u t t e r h e a d dredge. P i p e l i n e dredges are V f e l l s u i t e d t o o p e r a t i o n i n s h e l t e r e d waters and where a d i s p o s a l area i s a v a i l a b l e w i t h i n reasonable d i s t a n c e . These dredges vary through a wide range o f s i z e s from q u i t e s m a l l and sometimes "Rube Goldberg" items o f p l a n t used f o r s m a l l r e a l e s t a t e f i l l s on up t o those having discharge pipes 36 inches i n d i a m e t e r . The s i z e o f the discharge pipe i s the n o r m a l l y u t i l i z e d method o f r e f e r r i n g t o the s i z e o f a p i p e l i n e

(5)

dredge. C o n t r a c t o r ov;ned equipment i n the United States today v a r i e s f r o m 10-inch dredges w i t h 300 h . p . on the dredging pump t o 3 6 - i n c h dredges w i t h as much as 10,000 h . p . P i p e l i n e s f r e q u e n t l y exceed 10,000 f e e t i n l e n g t h and boosters are r e q u i r e d i f necessary i f discharge l i n e s are t o o l o n g . C u t t e r horsepower v a r i e s from 75 h . p . o r l e s s on q u i t e s m a l l dredges t o as much as 2500 h . p . on the l a r g e r ones.

P i p e l i n e dredges can excavate a remarkable range o f m a t e r i a l s and have s u c c e s s f u l l y dredged l a r g e q u a n t i t i e s o f hard r o c k . I t i s i n d i c a t e d t h a t rock w i t h a Hohs scale hardness o f 2 and 3 can be excavated by a w e l l designed p i p e l i n e dredge w i t h o u t b l a s t i n g . Rock o f harder c l a s s i f i c a t i o n r e q u i r e s b r e a k i n g up by c h i s e l or b l a s t i n g , the l a t t e r method b e i n g w i d e l y used on numerous p r o j e c t s .

The next s l i d e shows a t y p i c a l 27-inch c o n t r a c t o r owned dredge as operated here i n the U n i t e d S t a t e s . This p a r t i c u l a r dredge has 4500 h . p . on the pump and i s f o l l o w i n g the modem tendency t o e l i m i n a t e crevis q u a r t e r s . Anchor booms which are a r e l a t i v e l y r e c e n t development can be seen extended f r o m t h e bow. V/ith these booms the s w i n g i n g anchors can be handled w i t h much more convenience and w i t h much l e s s time than w i t h the o l d method by which a t t e n d a n t d e r r i c k boats had t o p i c k up and r e l o c a t e swinging anchors as necessary. ( S l i d e l 6 )

This n e x t dredge i s a very l a r g e and modem dredge. This dredge has a t o t a l connected horsepower o f 8,000 and i s o f 27-inch s i z e discharge p i p e . I n t h i s view the a f t e r spud frame has been lowered f o r t r a n s i t under r e s t r i c t i v e b r i d g e s b u t I n the n e x t s l i d e we see the same dredge i n o p e r a t i n g c o n d i t i o n . You w i l l note t h a t crew's q u a r t e r s f o r a crevf o f about 85 men are i n c l u d e d . ( S l i d e s 1 7 , 1 ^ ^

Now we come t o a few Dutch designed p i p e l i n e dredges. This f i r s t one has a 26-lnch discharge l i n e , 4,000 h . p . on the pump, and 900 h . p . on the c u t t e r . A d i f f e r e n t type o f l a d d e r A-Frarae w i l l be seen and the swinging booms are t u b u l a r i n s t e a d o f

l a t t i c e d as on the American dredges which you j u s t saw. No q u a r t e r s are p r o v i d e d and the swinging and h o i s t i n g gear i s l o c a t e d on deck. One o f the d i f f e r e n c e s o f Dutch dredges i s i n the spud system and you w i l l note here t h a t they do n o t have the massive spud frames which you saw on the American type dredges. F u r t h e r , the d i g g i n g

spud i s l o c a t e d on the c e n t e r l i n e o f the dredge i n a c a r r i a g e ^ ) which i s moved f o r e and a f t by screw j a c k s i n such way t h a t i t ( S l i d e ^

(6)

i s r e s e t .

Vllt.^'^l^^l^lTZ^^^^ --^^^^

mounted i n f i x e d w e l l s and thl Zl^ ^^^^ o f f c e n t e r and

one spud up and one s ^ u f d o ™ as f ^ i r ^ ' h T ' " ' " ^ ^ ^ " ^ t h e c u t . ^ ^"^"Ss back and f o r t h across

the p ï p ' a n l Tso h T ' o n t h e ' ^ u t f ' ^ " ^ ^ "^^^ ^'P

-The gallows frame f o ^ the Ï a d d e r " ' ' " ^ " ^ ' ^ discharge l i n e . American, d o d g e s a n ^ t h e ^ a n ^ l ^ b ^ ^ ^ ^ e ^ T t t S d '^1 f e a t u r e i s the " T J h^h ï e v e X I f t V ? i n t e r e s t i n g seen r u n n i n g a l o n g ^ t h e l i d e ^ ^ S t t t u s l ! = S e ^20^ = ^ E u r o p f a n ' r i f e l T i ^ ^ t o ' e r ' ^ f ^ " ' ^ ^ " ^ ^ ^ ^ ^ ^ ^ ^

-=

r

s

- i L p

t h a t scow i s f i l l e d ^ o t L r L w x l l ^ b e ^ ' a ^ o n l - d 'r'"^' of t h e dredge and m a t e r i a l d^no J ^ . H ^ " " g s ^ d e on the near s i d e dredge i s powered Tuh a Joo h n e ?°"*^n"0"3ly. The chain on t h i s 26 buckets p e r minute Fa°h u'^i a t a r a t e o f and bucket dredges 2 ^ r S S Ï n t h " ' ' ^ ^ " ^ ° ^ - ^ ^ - " ^ gca d r e r a t e d i n t h i s manner. ( S l i d e 2 1 )

t h a t the Steamer HENRY BURnFM " ^ ^ " " ^ ^ ^ 1872 dredge and operated f L T u '^""^^'^ted f o r use as a hopper S t . Johns Revert S o r L a C h a ^ i r s t ' T l ^ " ^ ^ ^ " ^ ' ° ^^e Savannah Harbor Georgia* Ï r L ^h^^^ I C a r o l i n a , and

(7)

been c o n t i n u o u s l y developed by the Corps o f Engineers up t o the stage of our modern p l a n t vjhich I am coming t o . The n e x t s l i d e i s o f the Dredge MARKHAM which was c o n s t r u c t e d by the Corps o f Engineers i n 1960 and i s the newest and most s o p h i s t i c a t e d hopper dredge c u r r e n t l y i n s e r v i c e by the Corps. The dredge was

s p e c i f i c a l l y designed t o handle p r o j e c t s on the Great Lakes. I t i s d i e s e l - e l e c t r i c and has 5300 h . p . f o r p r o p u l s i o n and hoppers w i t h a c a p a c i t y o f 2,681 cu. yds. The MARKHAM operates b a s i c a l l y as a c o n v e n t i o n a l hopper dredge b u t i s a l s o equipped w i t h

c a p a b i l i t y o f pumping out i t s own hoppers through an overboard discharge l i n e o r the c a p a b i l i t y o f " d i r e c t pump-ashore" which i s a process which I w i l l describe i n g r e a t e r d e t a i l l a t e r . The two dredge pumps are arranged so t h a t they can be connected i n s e r i e s w i t h 2,000 h . p . made a v a i l a b l e f o r pumping o u t i n t o a shore discharge p i p e . The l a y o u t o f the MARKHAM i s t y p i c a l o f our modern dredges w i t h the b r i d g e f o r w a r d , the hoppers a m i d s h i p , and machinery spaces a f t . I t , t o g e t h e r w i t h the ESSAYONS vfhich you

see on the n e x t s l i d e , i s p a r t o f the c u r r e n t f l e e t o f 15 hopper dredges i n o p e r a t i o n by the Corps o f Engineers. They range i n s i z e from the ESSAYONS v/hich you see h e r e , which has a hopper c a p a c i t y o f 8,270 c u . yds. t o the 500 cu. y d . PACIFIC which operates on the West Coast. During FY 1964 t h i s f l e e t o f dredges dredged over 85,000,000 c u . yds. o f m a t e r i a l a t a n e t u n i t cost per c u b i c y a r d o f almost e x a c t l y 30*. ( S l i d e s 2 2 , 2 3 )

V/e i n t h e Corps are proud o f the f a c t t h a t although the o p e r a t i n g cost o f our dredges has increased i n r e c e n t years i n approximate conformance w i t h the E n g i n e e r i n g News Record I n d e x , the cost per c u . y d . has remained v i r t u a l l y c o n s t a n t . T h i s i s a t t r i b u t e d t o the r e t i r e m e n t o f o l d e r dredges , the g r e a t e r e f f i c i e n c y o f newer dredges, and i n c r e a s e d concern w i t h t e c h n i c a l aspects o f dredge o p e r a t i o n .

The cutaway view o f the ESSAYONS shows the b a s i c f e a t u r e s o f the t y p i c a l seagoing hopper dredge w i t h which I am sure most o f you are f a m i l i a r . The q u a n t i t y o f m a t e r i a l loaded depends p r i m a r i l y on i t s c h a r a c t e r , t h e pumping t i m e , the hopper c a p a c i t y , and the d i s t a n c e t o which the m a t e r i a l has t o be c a r r i e d f o r dumping. I n heavy coarse types o f m a t e r i a l which r e a d i l y s e t t l e s out most i f n o t a l l o f the s o l i d s are r e t a i n e d . Conversely, i n l i g h t and s i l t y m a t e r i a l s a good p r o p o r t i o n o f the s o l i d s f l o w overboard through the hopper o v e r f l o t ' / . On each assignment the most economic load has t o be determined.

(8)

The problems presented i n m a i n t a i n i n g the Delaivare R i v e r a t P h i l a d e l p h i a some years ago l e d t o the development o f i-;hat v;e c a l l a sump r e h a n d l i n g u n i t vfhich l a t e r has evolved i n t o d i r e c t pump-ashore and I vrould l i k e t o describe those processes. S p o i l areas f o r use by p i p e l i n e dredge vjere not a v a i l a b l e v d t h l n reach of the area s u s c e p t i b l e o f s h o a l i n g and a haul t o sea o f 50 m i l e s or more vfould have been r e q u i r e d t o e f f e c t d i s p o s a l i n deep vrater by hopper dredge. T h e r e f o r e , f o r many years the s h o a l i n g was removed by hopper dredges and dumped i n prepared basins some d i s t a n c e from the shoal a r e a . From those b a s i n s the m a t e r i a l was rehandled by p i p e l i n e dredge and discharged ashore behind r e t a l n i r » ^ d i k e s . Although t h i s method vfas used f o r over h a l f a century i t became c l e a r t h a t only a s m a l l p r o p o r t i o n o f the s h o a l m a t e r i a l a c t u a l l y reached the upland s p o i l areas where i t was r e t a i n e d . The m a t e r i a l i s a l i g h t s i l t weighing about 1300 grams per l i t e r and s t u d i e s showed t h a t from 20 t o 25 m i l l i o n cubic yards o f

m a t e r i a l was b e i n g dredged each year from the Delaware R i v e r wher^^^^ only approximately o n e - t h i r d o f t h i s amount was e n t e r i n g the

e s t u a r y as new m a t e r i a l . I t was determined t h a t a method o f p r o v i d i n g f o r the p o s i t i v e c a p t u r e , r e t e n t i o n , and permanent d i s p o s a l o f dredged m a t e r i a l was e s s e n t i a l and a f t e r v a r i o u s s o l u t i o n s were s t u d i e d there evolved the i d e a o f u n l o a d i n g a

hopper dredge through a s e l f - c o n t a i n e d and e l e v a t e d discharge l i n ® i n t o a r e h a n d l i n g v e s s e l moored a t a s u i t a b l e l o c a t i o n from w h i c l ' p o i n t the m a t e r i a l could then be pumped ashore. One o f our r e g u l ' * * ' f l e e t o f hopper dredges, the GOETHALS, was converted t o enable i t : t o pump out i t s hoppers and discharge the m a t e r i a l through an

e l e v a t e d " s n o r k e l " i n t o a companion v e s s e l . For t h e companion v«3S-=

the o l d and obsolete hopper dredge NEW OPJjEANS was converted i n t o vjhat v;as c a l l e d a sump r e h a n d l e r . The p r o p u l s i o n and o r i g i n a l dredging machinery v;as removed and 6,000 h . p , pump power i n s t a l l © ' ^ f o r pumping the m a t e r i a l deposited i n t o the v e s s e l by the G O E T H A L ' ^ t o shore d i s p o s a l areas through a p i p e l i n e i n the same manner as ^ employed by a p i p e l i n e dredge. The sump r e h a n d l e r vessel was moO'^ t o e s t a b l i s h e d d o l p h i n s i n the Delav;are R i v e r and connected by a p i p e l i n e t o the shore d i s p o s a l area. The next s l i d e w i l l show a close-up view o f the Dredge GOETHALS w i t h i t s s n o r k e l extended o ' - ^ ^ t o t h e sump r e h a n d l e r . ( S l i d e 2h)

This system was placed i n o p e r a t i o n i n l a t e 1954 and had remarkable success i n m a i n t a i n i n g the Delav/are River beto/een

P h i l a d e l p h i a and the sea. I t has a l s o been used at o t h e r l o c a t i ' ^ ' * ^ I n b r i e f , the sump r e h a n d l i n g system and the p o s i t i v e d i s p o s a l orS^ dredged m a t e r i a l have reduced the r e q u i r e d dredging e f f o r t t o approximately o n e - h a l f o f i t s former l e v e l .

(9)

The Hopper Dredge COMBER was a l s o converted f o r use i n c o n j u n c t i o n w i t h the GOETHALS and t h e NEW ORLEANS and t h i s team o f UIO hopper dredges and the sump r e h a n d l e r worked very e f f i c i e n t l y . Hov;ever, as always happens when we progress w i t h developments, i t soon became apparent t h a t the sump r e h a n d l e r would be unnecessary i f the dredges themselves had t h e c a p a b i l i t y o f connecting t o a shore discharge l i n e and pumping ashore d i r e c t l y . T h e r e f o r e , the most recent development along these l i n e s has been t o c o n v e r t both the GOETHALS and the COMBER t o p e r m i t d i r e c t pump-ashore and t h i s system has now replaced the sump r e h a n d l i n g system i n the Delaware R i v e r and the MEW ORLEANS has been r e t i r e d . The n e x t s l i d e shovjs the COMBER moored alongside a mooring barge and pumping d i r e c t l y ashore through a connected pontoon l i n e . A Wellons p i e r barge was acquired and m o d i f i e d f o r a mooring barge. The barge i s more or l e s s permanently moored t o s u b s t a n t i a l d o l p h i n s l o c a t e d at s e l e c t e d p o i n t s along the Delaware R i v e r . When the dredge f i n i s h e s accumulating a load o f m a t e r i a l i n the dredging area i t s drags are r a i s e d and the vessel proceeds t o the mooring barge. Through p r a c t i c e i t has been p o s s i b l e t o reduce the connection t i m e t o 5 o r 6 minutes and the d i s c o n n e c t i o n time t o about 3 minutes upon completion o f the d i s c h a r g i n g o f the m a t e r i a l . The d i r e c t pump-ashore procedure i s c u r r e n t l y being used w i t h a g r e a t degree o f success and w i t h advantageous economy. ( S l i d e 2 5 )

The development o f d i r e c t pump-ashore immediately i n t e r e s t e d many o f us i n the p o s s i b i l i t y o f a d a p t i n g t h i s type o f o p e r a t i o n t o beach nourishment and since I know t h a t many o f you gentlemen are very I n t e r e s t e d i n t h i s s u b j e c t I w i l l t e l l you a l l t h a t I can about t h i s p o s s i b i l i t y . As you knov/, c u r r e n t t h i n k i n g i s t h a t a r t i f i c i a l nourishment o f eroded beaches i s c e r t a i n l y one o f t h e best approaches i n endeavoring t o overcome our p r e s e n t e r o s i o n d i f f i c u l t i e s , and i t appeared l o g i c a l t h a t a hopper dredge capable o f p i c k i n g up a load o f good beach sand a t some a v a i l a b l e l o c a t i o n and w i t h the a b i l i t y t o pump the m a t e r i a l onto the beaches might p r o v i d e an economical and speedy method o f beach nourishment. Serious thought has been given t o t h i s problem by the Corps since e a r l y 1963 and progress i s being made. The d i f f i c u l t y has been i n the mechanical problem o f p r o v i d i n g a d e q u a t e mooring f a c i l i t i e s i n an exposed sea area near a beach which w i l l p r o v i d e s a f e and economical o p e r a t i o n o f a hopper dredge. The typ& o f o p e r a t i o n which I described i n the Delaware R i v e r p e r m i t t e d

r a t h e r c o s t l y mooring d o l p h i n c o n s t r u c t i o n a t s e l e c t e d p o i n t s . But i n n o u r i s h i n g beaches so many discharge p o i n t s would be r e q u i r e

(10)

n o r m a l l y o c c u r r i n g t ^ ^ s h a n ' ^ :

t

^ ^ L '

T/f T ''''''Tr

p r o b l e m s o f c o m i n g in anri m ; , n ^ • , • "'"^^^^ ^^^ch the m o o r i n g f a c i l i t y L o b ' x o u s l v f a r T f f — e c t l o n to a i n t h e p r o t e c t e d Dela^^are R i v e r o r o ^ h e r ^ i m i l " e x p e r i e n c e d

- r r : : t r L : i ; - i f S ; ^ ^ ^

p r o m p t

connections

Ttl

t h e d r e d p e " o f f s ' h ' ' ' ^ " h l c h w o u l d p e r m i ? f o r t a n k e r s h a v e b e e n i n use f o r a " n u m L T ""^"^^^"S f a c i l i t i e s e s s e n t i a l . P'^°™Pt h o o k i n g up and d i s c o n n e c t i n g are ^ e - ^ - - L r b - ^ g e ' ^ r ' ^ ' ^ s o n ^ t i m e n L t s p r i n g . H ^ w e t e T t h i ' e x p e r i m e n t s u n t i l c o n n e c t i o n are b e i n f purchased'and t h K ' ' " ' ^ ^ P^''*' " f ^ ^ ^ ^ " ^ e x p o s e d ' s u r f c S l t i o L

makrnrör

t " ' ' ' ' ^ ' ' ^ ^ ^ ^ a l o a d o f s a n d o n t o t h e

beal"'

We

know'th^^t^b^eb'

^ ^ - ^ a r g i n g t h e GOETHALS have t h e caDahiVi'i- T^^* ^ ° t h the COMBER and a r e l a t i v e l y s h o r t t i m e "^S^r ' n l ' ' k ^ ' ^ ^ " ' " ^ ' ^ ° f ^ ^ " ^

c o n n e c t i o n s ^ o p e r ^ m l t ^ ^ ü c h T u m T l h ^ o Ï " o n t ^ ^ ^ ^ I Z C ^^^^^^^^

R e s e a r c h l \ t ™ e % ^ r f

: a n r £ : e n \ t : T r f f s h "

^ " - ^ - ^ " ^

o f f t h e e a s t c o a s t o f t h e U n i t e d Spates ? h " ^ " " ^ " ^ ^ ^ i n v e n t o r y is t o l o c a t e ^ « . ^ 0 - ! ^ ^ " ^ s . The p u r p o s e o f t h i s

(11)

procedure v f i l l p r o v i d e a much more economical and e f f e c t i v e method of beach nourishment than has so f a r been d e v i s e d .

My mentioning o f the experiments w i t h r e s p e c t t o beach nourishment by hopper dredge i s n o t i n t e n d e d t o d e p r e c i a t e the p o s s i b i l i t y o f beach nourishment by p i p e l i n e dredge. I t i s my o b s e r v a t i o n t h a t sand bypassing a t ocean i n l e t s has not y e t been developed i n t o an easy, s i m p l e , and e f f e c t i v e procedure and I t t h e r e f o r e appears t h a t a r t i f i c i a l nourishment from borrow p i t sources i s almost a must. There are not u s u a l l y too many areas where p i p e l i n e dredges can operate i n p r o t e c t e d waters and pump the proper type o f sand t o a beach a t economical c o s t . Hov;ever, n e c e s s i t y i s the mother o f i n v e n t i o n and i t i s f e l t c e r t a i n t h a t

the i n g e n u i t y o f the American dredging c o n t r a c t o r s w i l l develop economical means o f beach nourishment by p i p e l i n e dredge. A p r o j e c t which i s now underway and d e l i v e r i n g m a t e r i a l t o the Newark A i r p o r t a t Newark, New J e r s e y , i s i n t e r e s t i n g because o f i t s p o s s i b i l i t i e s along the l i n e s o f beach nourishment. I n t h i s case m a t e r i a l i s being dredged by a p i p e l i n e dredge and discharged i n t o s p e c i a l l y designed d i s t r i b u t i o n b a r g e s . These barges i n t u r n are towed s e v e r a l m i l e s t o a p o i n t where another dredge has been e s p e c i a l l y developed t o remove the m a t e r i a l from the barge and d e p o s i t i t on the f i l l a r e a . Such a system might v m l l have beach nourishment a p p l i c a t i o n i n some l o c a t i o n s .

Another r e c e n t development i n dredging i s s i d e c a s t i n g from a hopper dredge. T h i s system was f i r s t developed a number o f years ago by the N a t i o n a l Bulk C a r r i e r s i n an e f f o r t t o m a i n t a i n the mouth o f

the Orinoco R i v e r i n Venezuela. A T2 t a n k e r was converted w i t h an extended boom o f f the s t a r b o a r d side through which the dredge pumped m a t e r i a l d i r e c t r a t h e r than going through hoppers. The boom

extended 250 f e e t outward from one s i d e o f the vessel and the dredge had f a n t a s t i c a l l y s u c c e s s f u l r e s u l t s i n p r o v i d i n g a usable channel i n t o the mouth o f the Orinoco vfhich no p r e v i o u s equipment had been able t o do. I n a l i t t l e less than 3 years t h i s dredge removed over 104 m i l l i o n cubic yards o f m a t e r i a l from the Boca Grande entrance channel and the success o f the dredge was so g r e a t t h a t the same company b u i l t i n Japan a t a cost o f some $15 m i l l i o n the g i a n t dredge ZULIA f o r o p e r a t i o n i n the channels o f Lake Maracalbo, Venezuela. The ZULIA was p r o v i d e d w i t h c o n v e n t i o n a l hopper dredge c a p a b i l i t y b u t was also f i t t e d w i t h a boom 415 f e e t i n o v e r a l l l e n g t h and capable o f b e i n g r o t a t e d ISQo so t h a t discharge could

(12)

be .jchieved on e i t h e r the p o r t or s t a r b o a r d s i d e . The boom extends 328 f e e t beyond the side o f the v e s s e l . The next s l i d e i s a head on view o f the ZULIA dredging i n Lake Maracalbo. The discharge pipe i n the boom i s 57 inches i n I n s i d e diameter. The v e s s e l i t s e l f i s 548 f e e t l o n g , has a beam o f 95 f e e t , and a d r a f t of about 263^ f e e t . I t has 11,000 h . p . on t h e p r o p u l s i o n machinery and 12,000 t o t a l h . p . on i t s 4 dredge p u m p s . ( S l i d e 2 6 )

The ZULIA has made an o u t s t a n d i n g r e c o r d at Lake Maracalbo and has p e r m i t t e d t h e maintenance o f a usable deep d r a f t channel f o r the heavy volume o f tanker trade i n t o t h a t p o r t . Records o f t h e I n s t i t u t o N a t i o n a l e de Canaliziones o f the Venezuelan Government sliow t h a t d u r i n g the p e r i o d heU-ieen 17 February 1960 and 17 J u l y 1962 the ZULIA pumped through the boom a t o t a l o f 104,663,000 c u b i c meters o f m a t e r i a l and by c o n v e n t i o n a l hopper dredging 2,801,000 c u b i c meters f o r a t o t a l o f 107,464,000 cubic meters. I n place surveys i n d i c a t e d the removal o f 70,462,000 c u b i c meters i n d i c a t i n g an average e f f i c i e n c y o f 67.32 p e r c e n t . With t h e t r u l y f a n t a s t i c pumping r a t e s a c h i e v e d , over 7,000 c u b i c meters per h o u r , i t can be seen t h a t very e f f e c t i v e and economical dredging w i t h the ZULIA has been p o s s i b l e . The cost o f t h e dredging d u r i n g the p e r i o d c i t e d was some 23i American money p e r cubic meter^

The success achieved by t h e ZULIA prompted c o n s t r u c t i o n o f a somewhat s i m i l a r s i d e c a s t i n g dredge, the ICOA, which i s a l s o o p e r a t i n g i n South America.

The Corps o f Engineers has become convinced t h a t s i d e c a s t dredging o f f e r s very d i s t i n c t advantages under proper c i r c u m s t a n c e s . I t i s e s s e n t i a l l y an improved method o f a g i t a t i o n dredging which i s performed t o some e x t e n t by a l l hopper dredges. The term a g i t a t i o n dredging i s used t o denote the e f f e c t o f s o l i d p a r t i c l e s which have been d i s t u r b e d from t h e i r i n s i t u c o n d i t i o n b e i n g c a r r i e d by p r e v a i l i n g c u r r e n t s o u t s i d e the dredging area where t h e y are l a t e r d e p o s i t e d . Under c e r t a i n c o n d i t i o n s a g i t a t i o n d r e d g i n g has always been e f f e c t i v e and economical and w i t h t h e h i g h volume o f m a t e r i a l which can be pumped by a modern

s i d e c a s t i n g dredge and the a b i l i t y t o i n i t i a l l y discharge the

m a t e r i a l e n t i r e l y o u t s i d e o f the channel p r i s m the advantages are gre l y m u l t i p l i e d . Although boom dredging must be l i m i t e d i n a p p l i -c a t i o n , i t has unquestioned a p p l i -c a b i l i t y i n areas where the m a t e r i a l i s r e l a t i v e l y f i n e and where t h e r e i s a p r e v a i l i n g c u r r e n t away f r o m the a r e a .

(13)

I t may occur t o you t h a t i n d e s c r i b i n g the sump r e h a n d l i n g and d i r e c t pump-ashore techniques and then f o l l o v d n g t h a t d e s c r i p t i o n v ; i t h a d e s c r i p t i o n o f the s i d e c a s t i n g technique t h a t I have

c o n t r a d i c t e d m y s e l f . I n the d i r e c t pump-ashore technique i;e are going t o g r e a t ends t o get the m a t e r i a l e n t i r e l y out o f t h e estuary v;hereas i n the s i d e c a s t i n g technique we are d e l i b e r a t e l y d i s c h a r g i n g m a t e r i a l very close t o the channel a r e a . This a p p a r e n t l y c o n t r a d i c t o r y s i t u a t i o n only serves t o p o i n t up the vast d i f f e r e n c e i n the s i t u a t i o n s which always face an engineer engaged i n d r e d g i n g . A procedure v;hich w i l l be extremely e f f e c t i v e i n one l o c a t i o n w i l l be completely i n e f f e c t i v e I n another.

Some thought has been given t o u t i l i z i n g boom dredges f o r beach r e s t o r a t i o n work b u t so f a r the method has not appeared t o o f f e r much prospect f o r success. Beach experts t e l l us t h a t unless m a t e r i a l i s deposited i n water o f 6 f e e t o r l e s s i n depth I t i s not e f f e c t i v e i n beach nourishment and so f a r none o f the boom dredges which have been b u i l t are capable o f o p e r a t i n g t h a t close t o a beach.

The Corps o f Engineers had p r o m i s i n g r e s u l t s w i t h e x p e r i m e n t a l s i d e c a s t i n g performed by the Dredge HAINS i n the Great Lakes and l a s t year converted a s u r p l u s YSD secured from the Navy i n t o a s m a l l s i d e c a s t i n g dredge w i t h o u t hoppers. This dredge, knovm as the MERRITT, i s c u r r e n t l y i n o n e r a t i o n i n our W i l m i n g t o n , N . C . , D i s t r i c t and can be seen on the n e x t s l i d e . As you w i l l see the tCRRITT i s a q u i t e s m a l l v e s s e l w i t h l e n g t h o f o n l y 107' 10". A c o n v e n t i o n a l r o t a t i n g crane which was already on the YSD has been u t i l i z e d t o support the boom. The v e s s e l has two 10" side drags and discharges through a 12" i n s i d e diameter boom 80 f e e t i n l e n g t h . With the t r a j e c t o r y o f the m a t e r i a l t h i s p e r m i t s d e p o s i t about 90 f e e t f r o m e i t h e r s i d e o f the dredge. The boom can be svmng t o e i t h e r side and the n e x t s l i d e w i l l show an a d d i t i o n a l view w i t h discharge b e i n g e f f e c t e d through the boom. ( S l i d e s 27, 28)

Although the MERRITT has been i n o p e r a t i o n only a l i m i t e d

p e r i o d i t i s i n d i c a t e d t h a t i t w i l l serve an extremely u s e f u l purpose. There are s e v e r a l ocean I n l e t s along the coast o f North C a r o l i n a which are o f such shallow depth as t o preclude o p e r a t i o n by even the s m a l l e s t Corps o f Engineers hopper dredges under u s u a l l y p r e v a i l i n g circumstances. The areas are t o o rough

(14)

f o r the economical use o f p i p e l i n e dredges. I n recent o p e r a t i o n s a t Oregon I n l e t , North C a r o l i n a , under q u i t e adverse circumstances the MERRITT dredged 76,847 c u . y d s . o f i n place m a t e r i a l a t a cost of 5 7 . 6 i per c u b i c y a r d . The d r e d g i n g c r e a t e d a p i l o t c u t

through the ocean bar a t Oregon I n l e t o f s u f f i c i e n t dimensions to p e r m i t the s a f e o p e r a t i o n o f the l a r g e r and c o n v e n t i o n a l Hopper Dredge HYDE. Although the t-ERRITT i s e x p e r i m e n t a l i n nature we look f o r s p l e n d i d b e n e f i t s from i t on s m a l l ocean b a r s .

As a m a t t e r o f f a c t , the Corps i s c u r r e n t l y c o n v e r t i n g another s u r p l u s Naval v e s s e l , a YF, f o r use i n the New Orleans D i s t r i c t . The conversion work i s now underv;ay and t h i s v e s s e l w i l l be f i t t e d w i t h a r o t a t i n g boom s i m i l a r t o t h a t which you saw on the ZULIA.

Going s t i l l f u r t h e r and s a v i n g the b e s t f o r the l a s t , the Corps of Engineers c u r r e n t l y has under c o n s t r u c t i o n a t Sparrow's P o i n t , Maryland, what v;e t h i n k w i l l be the most advanced and s o p h i s t i c a t e d piece o f d r e d g i n g equipment ever b u i l t . The l a s t s l i d e w i l l g i v e you an a r t i s t ' s conception o f t h i s dredge t o be kno™ as the McFARLAND. I t v ; i l l have f u l l hopper dredge c a p a b i l i t y , c a p a b i l i t y to pump ashore through a discharge l i n e as was p r e v i o u s l y d e s c r i b e d i n c o n n e c t i o n w i t h the COMBER and the GOETHALS, and i n a d d i t i o n V f i l l have a boom f o r s i d e c a s t i n g purposes. This dredge w i l l be assigned t o the G a l v e s t o n , Texas, D i s t r i c t and i t i s expected t h a t the s i d e c a s t i n g c a p a b i l i t y can be used t o d i s t i n c t advantage on some o f the entrance channels along the Texas coast which a p p a r e n t l y have c o n d i t i o n s i d e a l f o r t h i s type o f o p e r a t i o n . The McFARLAND w i l l have an o v e r a l l l e n g t h o f 300 f e e t , a beam o f 72 f e e t , and a loaded d r a f t n o t t o exceed 22 f e e t i n order t o p e r m i t e f f i c i e n t o p e r a t i o n s i n some r e l a t i v e l y shallovf areas i n the Galveston D i s t r i c t . The boom w i l l have a t o t a l l e n g t h o f 221 f e e t , 10 inches and w i l l extend over the side a p p r o x i m a t e l y 140 f e e t . The boom w i l l be c o n s t r u c t e d o f aluminum and when n o t i n use w i l l be stov;ed i n the a f t p o s i t i o n . The p r o p u l s i o n system w i l l c o n s i s t o f 4 d i e s e l engines d r i v i n g tv;in c o n t r o l l a b l e -p i t c h -p r o -p e l l e r s . Each o f the 4 engines w i l l be r a t e d a t 1600 h . -p . g i v i n g a t o t a l p r o p u l s i v e h . p . o f 6,400. The dredge pumps w i l l be e l e c t r i c d r i v e from separate d i e s e l g e n e r a t o r u n i t s , each pump b e i n g 2800 h . p . P i p i n g arrangements w i l l p e r m i t connecting t h e pumps i n s e r i e s f o r use i n pumping ashore o r boom d i s c h a r g i n g . The maximum hopper c a p a c i t y w i l l be 3100 c u . y d s . ( S l i d e 29)

(15)

The McFARLAND v d l l be f i t t e d w i t h a l l o f the l a t e s t types o f i n s t r u m e n t a t i o n , c e n t r a l engine room c o n t r o l , and a l l modern developments known t o the s h i p b u i l d i n g a r t . V/ith i t s a b i l i t y t o operate as a c o n v e n t i o n a l hopper dredge, t o s i d e c a s t m a t e r i a l a t r a t e s never b e f o r e a v a i l a b l e i n the U n i t e d S t a t e s , and t o

discharge through as much as 10,000 f e e t o f shore d i s p o s a l l i n e s , we expect g r e a t t h i n g s o f the McFARLAND.

REFERENCES

"Dragado de A g i t a c i o n con Brazo en e l Canal de Maracalbo, Venezuela," 1962, I n s t i t u t o N a c i o n a l de C a n a l i z a c i o n e s , Republic o f Venezuela, Caracas, Venezuela.

"Sidecast (Boom) Dredging - Foreign Experience and Local A p p l i c a t i o n , " Henry G. A. Hayward, American S o c i e t y o f C i v i l E n g i n e e r s ,

F a l l M e e t i n g , New Y o r k , N . Y . , 1961.

" L a t e s t Dredging P r a c t i c e , " Ole P. E r i c k s o n , T r a n s a c t i o n s , American S o c i e t y o f C i v i l E n g i n e e r s , V o l . 127, 1962, P a r t I V .

"Hopper Dredge D i s p o s a l Techniques and Related Developments i n Design and O p e r a t i o n , " Louis J . M a u r i e l l o £ Lewis Caccese, Corps o f E n g i n e e r s , U . S. Army, Federal Interagency Sedimentation Conference, 1963.

"The Hopper Dredge," Corps o f E n g i n e e r s , F r e d e r i c k C. S c h e f f a u e r , Government P r i n t i n g O f f i c e , Washington, D. C. , 1954.

(16)
(17)

'•)0

Slide 9

Hyfli*a.ulica.Ily' operated dredsres

(18)
(19)
(20)
(21)
(22)

Cytaty

Powiązane dokumenty

In order to “harvest” this enormous energy resource, the laddermill uses large controllable kites to ascend and descend to drive a generator.. A regular kite will fly up without much

sampling procedure, metabolic activity quenching, intracellular metabolite extraction (endometabolome), extracellular metabolite (exometabolome) and analysis procedures

These ‘socio-technical’ systems are of a hybrid nature because they are constituted by different kinds of elements, intentional and non- intentional: social institutions, human

W przypadku dynamicznego rozwoju kraju i realizacji zapla- nowanych inwestycji infrastrukturalnych oraz utrzymania dużego tempa prac inwestycyjnych do 2020 roku wydobycie

Celem przeprowadzonych badań była analiza związków pomiędzy cechami oraz oszacowanie bezpośredniego i pośredniego wpływu wybranych cech, w tym kompo- nentów plonu, na plon nasion

Ta ostatnia wydaje się mieć pod- stawowe znaczenie dla gospodarki kreatywnej, przyczyniając się do wytwarzania dóbr (towarów i usług) o wysokiej wartości kulturowej,

Odbiorca staje tu bowiem przed dylematem, czy prowokacyjny tytuł jest raczej subwersywnym przekroczeniem perspektywy muzealnictwa ludzkich ciał, czy niechcący się w nią

W doktrynie chrześcijańskiej pustka wiąże się przede wszystkim z tajemnicą grobu Chrystusa (jako znak zmartwychwstania), przez co manifestuje „obecność