$/ ;>. 23rd Annual y� Highway Geology Symposium

GUIDE BOOK FOR FIELD TRIP NORFOLK, VIRGINIA

APRIL 27, 1972

I I I I I I I I I I I

I

I

23rd A rum al

Highway Geology Symposium

FIELD TRIP

to

The Second Hampton Roads Bridge-Thnnel Crossing

Apnl 27, 1972

Norfolk, Virginia

GUIDE BOOK PREPARED BY

George S. Meadors, Jr.

FIELD TRIP L EADERS AND CONTRIBUTORS

Cal vm R. Moxley, Jr. Roger B. Stevenson Robert E. Kell Arthur C Munyan

- Virginia Department of Highways Parsons, Brmckerhoff, Quade and Douglas V1rg1ma Department of Highways Old Dominion University

SPONSORS

Virginia Department of Highways Virginia Highway Research Counc il

Vugini.a Div1s1on of 1\fineral Resources Old Domimon Un iversity

I I I I I I I I I I I

I I

FOREWORD

On behalf of the sponsors and the Steering CommitTee. welcome to the 23rd Annual H1ghway Geology Symposium field trip. Tlus year1s lTip not only IS 111 one of 1he most. mterest.mg geological areas of t11e state, but offers chal­lenge and mtr1gue to all who ha• e de\•eloped the technology to construct. a high­way faC"llny such as t.he Hampton Roads Bndge-Tunnel.

The rnp hrst includes a srop at a local fossil pit ha' mg strata similar to the older ones of the bay. A boat w1ll be urihz eel to make an mspectwn of the tmmel ronstrut'tJOn and waste areas, and for a general harbor cruise.

11 JS hoped that �ou will profit from lhe trip by sharing m our experienres.

lll

t\hrhael A. Ozol Burrell S. Wlu11ow George S Meadors Arlhur C l\Iunyan James L. Cab.-er

11 11 I I I I I I I I M

I

TABLE OF CONTENTS

FOREWORD ; I o • t t t t I e • t • I I' o • • ' • t '" t • I '"' t I I I I t 0 t I • I I 1 t t 1 1 1 1 0

INTRODUCTION .. . . . . . . . . . . . . . . . . . . � . . . . . . . . . . . . . . . . . . . . . . . .

HJSTORY OF THE CHESAPEAKE BAY . . . · · · · · · · · · · · · · · · · · · · � · ·

HAI\IPTON ROA DS BRIDGE -TUNNEL PROJECT , . • . . . . , . . . . . . • . . . . • •

The Ftrst Hampton Roads Bndge Tunnel Tunnel ....

Trestle

. . . . . . . . ' . . . . . . . . . . . ..

o a I I I I I I ' I I 9 t t t t I t I I I I I t I I •

OperatJon . , . . . . . . . . . . , . . . . . . . . . . . . . . • . . . . . . . . . . . . . .

The Second Hampton Roads Bridge Tutmel . • . • • . . . . . . . . • . . • • • . • •

GEOLOGICAL PROVINCES OF VIRGINIA • • • • • • • ' • t • • • • • • • • • • • • • •

GE OLOGY OF THE AREA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . • •

RICE 1\IEI\IORIAL I\IUSEUI\1 AND FOSS IL PIT (STOP NO. 1)., . . . . . . • . •

SOIL AND HYDRAULIC STUD IES • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. - . . ' . . . . . . . . . . . . . . . . . . Sml Study .....

H\ drauhc Stud) • • • • • • f • • • • • • • • • ' ' • • • • • • • • • • • • • • • • • •

SITE CO!'\DITIO!' • . . . . . . . . . . . . . • . . . . . . . . • . . . . . . . . . . . . . . . . . . . .

Page No.

lii

1

1

3

3

3

3

4

4

6

6

10

10

1 0

12

13

RIGHT-OF WAY REQUIREMENTS . . . . . • • • • . . . • . . . . . . . . . • . • . . . • , • 15

DRED GING AND BORROW AREAS (STOP NO,

OYSTEH AND FISHING AREAS (STOP NO 3)

NORTH AND SOUTH PORTAL ISLANDS ...

North Portal Island (Stop No 4) • • • • • .

2) • . " . . . . . • . . . . . • . . . •

. . . . . . . . . . . . . . . . . . . . . "'

SoUih Portal Island (Stop No 51 • t t I I t t t ' • t e t t t t e t e t t t t t t t t t �

1\Iethods of Construcuon • • • • • • • • .. . .. ' • • • • • • • • . . . . . . . . ... 0

Sheotpile Trench Construction

Dredge and Ftll Constructwn .

15

1 5

16

16

16

16

16

18

Sand Drams and Surcharge Construction • . • . . • • , . . . . . . • • 18

,.

TABLE OF COI\TE�TS (Cominucd1

SOIL PROFILE - LABORATORY A�D 1); SITU TESTING . . • . . • . . . • .

Cohcs1on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Consolidauon . . . . . . . . . • . . • . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . • . . . . .

Increase m Cohesion with Consolidation . . . . . . . . . • . . . . . . . . . • . . • • .

Field Obser\·a· �ons . . . . . . . . . . . . . • • . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TRESTLE DESIGN -- SECOND CROSSING ........................ .

Clearance and Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Span Lengths

TU��EL DESIG� - SECO�D CROSSI�G .......................... .

Dt.SI'l'ip' :on ................................................. .

Design Cri�er:a. . . . . . . . • . . . . . . • . . . . , . . . . . . . . . . . . . . . . . . . . . • . . .

PHOBLEl\IS OF CO!'\STHUCTING l�TERSTATE ROUTE 64 ALONG WILLOCGHBY SPIT (STOP NO. G) • • • • • • • • • • . • • • • • • • • • • • . • . • • • • • . •

\''

I Page No.

19 I 19

19 I 20

20 1 2 0

21 � 2 1

2 2 I 2 2

2 2 I 2 2

28 I I I I I

•

• • • • • 'I • I I I I I I I

INTRODUCTION

The field trip for the 23rd Annual Geology Symposium is focused on the second crossing of Hampton Roads by a bridge-tunnel that will strengthen the tie between Hampton and Norfolk, Virginia. The crossing will be at the contact of the James River with the Chesapeake Bay (see Figure 1) .

The field trip will begin with an orientation period at the Chamberlin, which will include movies of the existing structure showing the tube placement, etc. From- the hotel� a bus will carry the group to a local fossil pit that displays the local geology. From the fossil pit, the group will journey to a tour boat which they will board for the afternoon trip to the construction involved in the new tunnel •

IllSTORY OF THE CHESAPEAKE BAY

In the 17th century, John Smith entered the mouth of one of the world's finest estuaries - the Chesapeake Bay - and wrote: "The North Cape is called Cape Charles in honor of the wealthy Duke of York. Within is a country that may have the prerogative over the most pleasant place of Europe, Asia, Africa or America, for better and pleasant navigable Rivers: heaven and earth never agreed better to form a place for man's habita­tion. Here are mountains, hills, plains, valleys, rivers and brooks all running most pleasantly into a fair bay composed but for the mouth with fruitful and delightful land. In the Bay and rivers are many isles both great and small, some woody, some plain and most of them low and not inhabited. 11

The present. Chesapeake Bay IS about 10,000 years old. Its ong�n came during Pleistocene times. Durmg a period in the late Miocene or early Pleistocene, the seas had receded and dry land extended almost to the present day continental shelf. In late Pleis­tocene times, little or no land cXIst.ed m the area of the Eastern Shore peninsula, as a re­sult of the advance of the Atlanhc Ocean. Dunng this advance of the ocean, the combined action of waves and shore currents formed spits and barriers across the shore from Mary­land to North Carohna. The resultmg enclosed area contained lagoons and marshes simi­lar to the Pamlico and Albemarle Sounds of North Carolina. After the retreat of the sea, this barrier was continuous to the extent that it forced the Potomac and Susquehanna drain­age southward to its present outlet mto the Atlantic Ocean. When the sea advanced west­ward again, 1t drowned the complete area except for the Eastern Shore peninsula. Thus the Chesapeake Bay represents the drowned valleys of the Susquehanna River. The Bay at present has a length of 190 miles and IS from 4 to 40 miles wide. The tidal shore-line of the Bay and its tributaries has been estimated at 4 , 600 miles. The Bay and tributaries have a surface area of about 4, 300 square miles. The coastal plain contains 7 major rivers - the Patuxent, Potomac, Susquehanna, Patapsco, Rappahannock, York and James � wh1ch feed rnr.o the Bay from the west. These are in addition to 40 other main tributanes that are fed by 102 mam branches and creeks.

These waterways have a combmed navigable length of approXlmately 1, 800 miles.

Newport News

r:! I

I ,J-f.l- -/ _''----.! I \ I

Chcsa�eo�r

V1rgin10 Beach

Figure 1. Location plan for second Hampton Roads bridge-tunnel crossing.

-2-

I I I I I I I I I I I I I I I I I I

I

• • • I I I I I I I I I I I I I I

HA i\IPTO\. ROADS BRIDGE TUNI\TEL PROJECT

The f1rst Hamp1 on Road s Bndge Tutmel. between West Ocean Vww Street m Norfolk and 1 he Hamp1 on sho rei 1 ne near Old Pomt Comfor1 m Hampton. was con­struc1ed d urmg 1he penocl '\o' ember 1954 through November 1957. The project \\aS fmanced by part of a $95 ml]l 1011 bond 1ssue and replaced the Newpor• News and Old Pomt Comfort. fernes. The ero�smg c·ons1sts of 23 rubes totahng 6 . 859 feel 111 leng .. h •

2 man-made 1slancls. open approaches each approximately 600 feet m length and 2 ap proaf'h trestJes - the \rnr1h tJ·estle 3, 250 feet m lenglh and the south 6,150 feet The ex1stmg crossmg IS opel'ated w1th stale h1ghway funds and wnh tolls rhat will rct•re the or1gmal bond 1ssue b\ the end of 197-1- The uprommg ehmmauon of these tolls and the mcrcased t rafft c 'olumes mcl1<. atecl•o stat e highway offlc1als the need for a second crossmg

The tunnel portion ol •he proJCI t cons1sts of prefabrJcated 1uhcs. ru1 and ro' er box secltons, 'e1111l alton hu1lc.IJn�s. and open approaches The 23 prefahncatcd tubcs were sunk 111 plate 111 a d redged 11 enr h and baC'kf11lecl to pro\ 1de a 5 · foot mumnum l o• er O\Cl' the tunnel At earh 0nd of the JJI'Ciabncated tube sec1.1on, box sernons. wh1ch arc each abOlll 90 fee• long unci were c·onsn·uttecl by t he cut-and -co\er method. r•onncc1 the prefahncated tube scuton to 1lw 1 cn•t!atton blllldmg strucl.ures The open approadws ra.rn the nmnel roaclwa\ to 1he •restle seC'LJons.

The tuJm<'l roadwa\ de::.• ends on a <l. (I pert cnt grad e f rom a roaclwav el e' at 1011 of -11\ -l mean sea le• el (msll at the north trestle to a low pomt of c}e\. atton 105 -!- msl in 1.he tunnel. ascend s on a �racle of 11 5 pei·ccnt und er the mam channel. and ·hen ron 1.1 nues on an a st. end t ng gr acle of 4. IJ pcr1'en• 1 o a roadway el e'· atwn of -HL -l ms I at the south trestle The w tthh ol roacl\\a\ through 1 he tunnel and open approaches 1s 2j t eet bct:ween rurbs. and the mmJmum 'el'llcal <lca.:lllce between the roa lwa\. and '•1C l eJ]Itlg 111 1nu t.unnel IS 14- feet

Electnc powe1· for \enttlaiJon. d rainage, ancl lighnng ts pro\.ldecl b\ submarmc cables from each shore. and water tor f1re pro1.ectiOn and c1eanmg IS J.llped 0' er earh nest.Je. The roadwa\ ''"'h•n •he tunnel ts a flex1ble bttummous conf'rete pa' ement on a reinforced conere•e slab. and the •ntcrwr flmsh conststs of ceramiC" ttlecl walls ancl a

porcelam�enamelled alummum }•an 1·el1mg

Trestle --· --

The tunnel aJJproaL·h ' ' estl<.?s hot h nor•h and south. are precast. pres1ressecl beams. 50 feet long SUJ.lported on preLasl. prestressed concrel"e plle hents The w1clth of roadv.·a\ IS 30 feet between Lurh::.. 1hus perm11ung trafftc m e1ther cllreuJon to b�pass d 1sabled 'eludes T\\O loot w1d e :><.�.fet\· walks are pro,Ided on each sJcle of the 1restles. and t.he concrete pa1·a}Je1 waJJs are surmounted b\· alummum posts and railings,

Operatton

The br1dge-tunnel crossmg JS operated b.} the Department as a two-way traffic facthry. Curren! datlr r.raffH' \olumes c ompnse about 15,000 \ehirles. The adminis­tration of t he proJef't 1s earned on at a bUlldmg l ocated at t.he roll plaza i n Hampton, V1rg1ma. where < ol l ect10n and recordmg equtpmenr are housed. Shell.ers at the end of each open approach on the tslancls house trucks and service equipment such as waslung \ elucles. Garages and s1 orage for mamtenancc equipment and materials are pro' tded adJacent to Imersfalc Roure 64 lll Hampion. abou1 one-half mile west. of the toll plaza Bus service O''er the project IS provided by publ J c bus l ines.

Th� Sel'ond Hamp1 on Roads Brtdge- Tunnel

The second Hampton Roads Brtdge-Ttllmel wtll be locat.ecl mshore (west.) of the extstmg (Interstate Route 641 crossmg. The proJect w:tll start on Willoughby Sp1t m t.he VlClmty of the old ferry lermmal. where n w1l l connect to proposed Interstate Route 64. The JOO-foor approach lughway w11l be transmoned to the trestle m accordance w1tb a cl earance d1agram furmshed by the Department. The south approach trestle� about 6. 000 fee1 long. w11l termmate at 1he enlarged Sout..h Port.al 1sland. The roadway on rhe tsland wtl l be t1 anstnoned to the south tunnel portal. and descend rJu-ough the south open approach structure. The roadwa\' w1l1 1hen descend 1.hrough the sour.h vennlation and gar.ehouse s1ructure 10 the precast. trench tunnel. The t:rench tunnel will pass be­neath the Hampt on Roads main slup (hannel and ascend to an enlarged NortJ1 Portal Island. where n. Will reach t.he grade o f the t .restle after passmg through t.he north ven­rl1atJOn and l.tde gate structures and the norrh open approach sn·ucture. After crossing t he .1, 250-foot north approach trestle. rhe projet t will termmate on the Hampton shore approxnnately 650 feet he�ond the CXJSllng toll pl aza. where 11. wi)] jo i n ex.ishng Inter st ate Rout e <>4.

The second bndge ·tunnel crossmg w11l be operat.ed as a dual lil!le. umdJr ectJOnal t;rafhc facJllly. Under eme1·gency cond1110 ns. each tunnel ean be opera1ed as a t.wo-way. smgle lane facthry.

The pl an of both the ftrst and s econd Hampton Roads crossmgs and the prohle of t.he proposed second crossmg arc tl1 ustrated on Ftgure 2.

. I .

I I I I I I I I I I I I I I I I 1 I I

-

HAMPTON

).

- - - - - -

" " '

' l,

•• o PU•�ll ul.�"'•"

I

.... ,.

- - -

,, • • ,,. • ._.. I

- - - - - -

/ f I·�· t,r; .,.� .. •11 .SO. A'4�· ··-·•l"' .. ,...

I . --- � -------- �--� -

____ - ..... --:------:----------�------..:.. --�--- • PR('PQSt D T-.•;t,\1

I •

�!Ji[�''T'IIIt''litj;!-'I'IIJI1illm1lii .... llftlllf h.tl t t I I tttll"t

. . I

'• .... " •..

I

jy I<' I R{iPOSlf) PtFit.J\f\'1

PLAN

, ....

. . . '

PROFILE

/1['11'1' mm'I'Jir''j l'j'j;l ·,i: iJ'Il!JII!Jll'I'J. IIl'jfiJ!il'JIIIIPill!ll n;to·, 1!iliJrrn urrl r ttl tt I" wu . . H • •mil 111lttl . u.-.. .

L----------------------------·--- -

Figure 2. General plan and profile of second Hampton Roads bridge-b.tnnel crossing.

- -

GEOLOG1C:\L PRO\T>:C'ES OF VJRGINJA

Virgima boasts of havtng rocks 1 1 om t.he oldest to the youngest, runmng t.he geologic time scale from PreCambnn.n to recent. The state cont�ms many classic examples of sed1men•.atwn. straugraphy, strurtural geology, and metamorphtc and igneous activity. Based on rock type. VJrgJiua IS d1v1ded 1mo 5 physwgraphic prov­i nc•es .

The Coastal Plam JS on 1he east and consists pnmanly of unconsolidated sands! gravels, clays and m arls.

The Pi edmont borders the Coastal Plam on rhe west and cons1sts primarily of deeply weathered metamorplnC's,

The Blue Ridge Moumams lJe to the west of the P1edmont and arc made up of crystalline rod\. The AppalaC'htan Valle.\. betler known as the She nandoah Valley of Virginia, cons1sr.s oi highly fo1ded and fault.ed sechmenfary rocl-.s. The 5th prov mce. the Appalachian Plateau , IS Ill Lhe far southwesi corner of the state. ''here shales. sandstone and coals are found isee Figure> 3\.

GEOLOGY OF THE AREA

The Hampton Roads area 1 s loc·at ed m the Coastal Flam. The surface of the Coast.a.l. Plain of Vi rgm m generallv slopPs eastward towards the Ar.lo.nt1c Ocean. It continues to the east beneath the :\Jlart\1' Ocean , where 1t forms the contment:al shelf that extends approx imatel y 2u0 m 1les offshore.

The bedrock of tl1e Coasial Plam is composed of parnally consohdar.ed sedi­mentary rock that d1ps to 1.he e:1s1 a1 s1eeper angles than rhat of the surface, The rocks consist of Cretaceous. Eocene uml .M.1ocene marme sands. commonly contauung a large percentage of glaucorute. gl'a 'els, clays. shell marls. and diatomaceous sediments. In turn, these sediments a1 e sp: ra<..h cally Oller la m b) Pleistocene, Recent and possibly Phocene sand and grave l deposns thar may constitute marme terraces.

The CretaC'eou s sed1 men1 s we 1 e denved fl om weathermg and erosiOn m areas to the west Durmg the tnnes of advanemg seas. the sediments were deposited through­out the coastal reg1ons These s·�d1me•1tarv rorks are composed mamly of sand and clay with minor gravel lenses. In some loca1ions. the rock formations contam numerous plant fosslls. Cretaceous maienal ma) o .. ceed 1, 500 feet m depth m the Norfolk­Hampton area.

Followmg the C1 etaceous pe::t'lod was the Paleocene. The re IS no e''Idence or exposures md1canng that any Pal�octme .sed1men1 s were deposned, wh1C'h suggests a period of erosiOn and/or wnhdrawal I)( Th(;' seas Howe\ er, H has been argued that pos.::ibly the lower and older Eoc·ene sed1menr:s !of the ne:>.1 penod) rna) represent t.he Paleocene Penod.

I I I I I I I I I I I I I I I I I I I

I I I I I I I I I I I I I I I I I I '

- 7 -

. _. .;..: �

...... l:..D :... ..... ;;:.. .... 0 til � ('..) ::::: ..... > 0

('..) ... .-0. � :... :.0 0

·-

The Eocene Penod began approXlm ately 60 milbon years ago durmg another penod of ad' ancmg seas . Depths of the sediments from the Eocene range from 150 feet m the west to 850 feet. between Norfolk and Cape Charles. The sediments are tomposed of glauconlflC sand beds w1t.h dist•ontmuous mterbedded days. The formation abounds m fossil remams such as shark teeth and whale bones .

The absence of Ohgocene matenal m the column indicates another era of e1ther nondepos1t10n or active eros10n and recessed seas.

To t.he east. around Norfolk, the Miocene sediments reach t hicknesses greater than 900 fee1 The composmons of t he Miocene formations vary from sand t.o d i ato­maceous cl a) s wlth some glauconinc clays and some very shelly marls. As ran be expected. rhe formanon abounds m fosstl s of whales. seals. porp01 ses. mul lusks. shark. I'a' and other fish.

The most recenl S) stem of rocks to be deposited came durmg the Pletst.ocene per10d. The lnhol og) of rlus formanon may Simply be descnbed as unconsolidated, yell ow. rrossbedded sand and gra•.el up ro 100 feet thn·k near the Eastern Shore. Shallow seas were probably responsible for the depos1hon

S1l1. sand and gra" el compr1 se the most recent ma1 er1al depos1 ted m the Coastal Plam This regohth was derned from wmd, beach, lagoon and stream de­posits (see F1gure 4)

The surface I S onh shghtly dissected by streams Swamps and marsh lands are com mon. wlth the G1·ear Dismal Swamp bemg the large st.. Because the coasrlme JS so deeply cut bv branclung bays and estuaries. the appearance has been de scribed as that of a "frmge of penmsulas". Blu ffs up to 100 feet high commonly border the estuanes. Fme natural harbors, s and) beaches, and barr1er beaches arc abundant along the (•oastJ me_

- � -

I I I I I I I I I I I I I I I I 1 I I

I I I I I I I I I I I I I I I I r I

H1CE l\IEl\IORlAL l\IUSEUl\I A 1\JD FOSSIL PIT ( STOP NO. 1)

The p11 shows an excellent secuon of 1.he local geology. The museum ad· jacent. 1.0 RH·e Pn cont.ams mam exC'ellentl� presen ed macrofossils collected from the pit. The pit IS operat.ed commercially as a borrow pit and as an outdoor edu­cauonal laborat.or� for schools and colleges It IS approxJmat.ely 50 feer. deep.

The silt� sand facies of the Yorktown IS exposed m the plt. The texture of the sediments ranges from cla�ey sl1t. and sand near the base to sl1t.y fme sand m the upper part, Quartz. calcne. and glauconite are r.he dommant mmeraJs Calc1te ranges from less than 10% of the sed1ment 111 the basal part of the pit t.o more than 30% locally 111 t.he uppermost beds. The mcrease m calc1te reflects the mcrease 111 the fossil content upward m the ser11on. Beddmg IS lackmg or poorly de\ eloped m thls facies. Lammanon IS present locall� wnhm the p1t but biOturbation has destroved much of t,he ongmaJ beddmg. Cursory samplmg of the pJt has yielded over 175 spec1es of mollusks. arthropods, foranmufers. bryozoans and ot.her groups. The fauna IS dom­inat.ed b� molJusks. A baleen whale was reLO' ered from the upper part. of the formatwn (U. S Geol Sur' e\, 1 965. p. A-ll) The lower beds cont.am a rest.nct.ed macrofauna with man.} burrowu1g bent.hos and few predators Although tlun -shelled pelecypods are present throughout the sequence. the) are relanvely more abundam. in the lower se­quenee. The uppE>r beds contarn a d!'.erse rommumt\' of \agrant. bemhos. mC'ludmg carmvorous gasr.ropods. erlun01ds. and pelel"'\'pods Bot.h populauon densm and faunal dp ersll.\ mcrease upward through the sectJon lmenSI\ e stud1es of the fauna are bemg conduC'i ed b\ personnel of tl1e Umt.ed States National Museum and Un11 eel States Geologieal Sur' ev.

The Yorktown Formatwn 1s 0' erlam by G to 10 feet of PleiStolene sedunems. A gra"elly sand less than 1 foot rluck rest.s upon the Yorloown. The gra' elly sand grades upward mto well sorted med1um sand and then mt.o a heterogeneous mixture of sand. s1lt. and clay. The upper parr has been weat.hered and, durmg the present penod of weat.hermg. the upper few feet of the Yorktown has been alt.ered to a nonralcareous, mottled s1h\ sand. Locally Iron ox1des ha\ e accumulated 111 t,he gra,·elly zone and pro­duced an mdurated pebble bed.

The sedimems. fauna. and strat1grapluc relauonslup of the York1.0WIJ sed1ments m R1ce PJt and m surroundmg areas mclware t.hat the lower end of t.he Pemnsula was co' ered by normal marme war.ers 50 to 150 feet deep durmg the late Miocene Durmg lat.e l\'Iwcene and early Phoeene ume the Yorlv own sea became progressn ely shal­lower as the sea le\ el fell and tJ1e basm f1lled wJth sed1mem. The upper part of rhe Yorktown format;1on was truncated lw Pletstocene manne eroswn. A t.hm \,eneer of Pleistocene sedmwnt.s was deposned clurmg the late Sangamon or early W1sconsm Sr.age

SOIL AND HYDRArLIC STl..-DIES

�0 tl s tl!_cb_

I I I I I I I I I I I

The strauftcanon of the silt -cla\ and upper sand deposus was explored durmg I the desJgil of the first Hampton Roads rTossmg by 46 bonngs as shown m Figure 3.

1 10

I I I I � � I I I I I I I I I I I I I :;:

0 � "-"!' <: -

I

...

••

•• •

--·

� .

•

�·

- 11-

Undisturbed .,. .. t.nples of sOJJ were :::<.em eel ::mel tested 111 the laborat.ory 10 obtain data on the sml properties. An aclchu onal program . eon:::istin g of 1Cl borings. was undertaken tn the c ourse of the studws lor the second Hampton Roads l'ros:Smg w further venf\ the sod prof1le along t.he ali gnmen t. of t.he cross ing and 1.o oht.ain furt.her informat:ion on soil C'haracren�ti('S an d their effects on d esi gn and con­sr�·u ctwn.

The sod prof ile re', ealecl b\ these boi· ings was m close a greement wjt,h t.hat b ased on t.he f1rst bormg program. In The ar eas of the nort.h approach trestle� The !\'orth Portal Island . and the nonh 2. oon feet. of the precast rube tunnel the soils are sandy. These sotls do not }Jresent any speciaJ problems 111 rhe design or con­structJon of the proJect.

To the south, howe\ er. there 1;5 a 1.h1ck layer of compress i ble organi1.· sil� cla� Generalh, 1J1is silt� da\ 1s O' erlain by a clepos !l of sand. The ele\·atJon of the hottom of the siltv r:la.\ range s from ·-<30 ar the south trestle to -1'10 at. rhe deepest pornon of the channe] . Dense. sanch soil� are found below the stlt�· clay. The s1lty elay presents problems! part 1<. ularl� at t.he South Portal JslilncL

The proper•.1es of the silt\ lla� ST.t·ata \\'Cl e 111' esttga1ed by m eans of field\ ane shear 1es1.s and lahot·atory 1es1 s of ltnc!Jsr.urhed samples consi sr.ing of uncon fuwcl rom press 1011 �e�ns and •-'onsoJ 1ela1 eel und ram{:(l t.nax ial 1.es1 s On the basts of t.hese test resul t s ! a shei..lr strenp.th prol Jlc \\US ciC'\'elopL•d, wi1.h :::ihear st.reng.Ths • at·y in g !rom J(IO t.o 'l0(l psf from t.he i.op to honom of the SilT\ day la�·er .

Tlw eom]Jn�sslhilit.\· duu·a< terist.ies of the stlt. \ day were in·. es t igu ted b.\·

mean s of laboratoi'Y t•onsol lclat lon 1 �St:::i tn c:oniutwl.l on '' Jt.h e ·.: alua i ion:;; ol se1 .1 l ement s ohser,·ed at the exi st.ing Sou1.11 Por1 a l lslaucl Tlw 111 e.sr Jga'ton 1miJ C ared l.hat tJJe slit� <.lav layer IS h1ghl.\' (·ompressd,Je,. and henr e impo :::ecl load� '' 1 l l resu lt 111 sul>st a nt 1al se11:1em en' ::: . Furthe1·more. the J'; .. l.le at \\hlfh <.mholld...ttJon Ol'(·ur:. r:3 \ c�n s]o,,; then.! fore . an� des1gn \\hH·h is dependent on ]Jn:loacllng of the eompress1hle sod "Ill requ1t·e some mc:ans of W.'l'e]eral.ll?f.!; the ''onsulrdanon

The ln·st Hampton Roads l'r ossJ ng. w..ts clvs1 gned t.o JWO' 1de JWOrel'tJon agamst floods and hurr i('anes to an <.:le,·at.wn · 14 feet abo e mc.•an SPa le el (m�l) lor 1]w tres1Je approat'hes and portal 1slands The en1 Llat10n hu d dmgs are \\Uter11ght to an ele\at.ion of �17.25 msl, and t1de gates are pro' 1clecl at e..tch ponal 10 pre1 ent floodmg of The t.unnel 111 the e';ent. of a major munclanon An anaJ� :>J:::. ol reu�nl stuchcs made by t.he L. S. Arm�· Corps of Engint:E'l'-5 :.mel the l S W<.:atJwr Bu reau on 1he subjel t ol hurr icane and st,orm (;haracl.et·isou;, tn 1J1L Hamp1.on Road::. are..t has l'onfJrmecl and \ahcla1.ed the des 1 gn critena tor r.he 1 '<IS1ll1g ll'OSSlllg An c 1 alual Jun of thL� ope1·a• JOnal records for 1he llrs• Hampton Roads cro::,smg and lor 1hc Chesapeake Ba,'. vros!:img ha s l1kewise conflrm�d a nd �·aliclat,ecl the ongmal des1gn c I'Jtet·ia for f lood , hu1·nc.·w1c and storm prot CH't.k�no

I '

u I I I I I I I I I I I I I I I 1 I I

I I I I I I I I I I I I I I I I I m -

In H.IGU t.he South Portal Island nprap protection was remforced, and in 1965 the undenvater slope protection for t·he tunnel requ1red mmor repan·s for 1, 600 feet offshore of the NortJ1 Portal Island. In 1969, the South Portal Island seawall was restored to its origmal elevatiOn to compensate for local settlement of 0.8 to 2 0 feet occurring since the project was opened in 1957.

Annual mspectlons of the project, reviews of operational records durmg hurricanes and storms, and records of maintenance costs over a period of 13 years clearly mdlCate the adequacy of the orIginal hydraulic design criteria and justify their adoption for the second crossmg.

SITE CONDITION

The existing South Portal Island is located partially in the lea of Fort Wool and is protected against storms by a riprap dlke and a concrete seawall along its northeast face. The North Portal Island is sheltered from storms by Old Point Comfort. Outshore (east) of the existing crossing, there are telephone and govern­ment commurucation cables between Fort Monroe and Willoughby Sp1t via Fort. Wool The Hampton Roads channel passes between the portal islands and is abutted by nu ·

merous leased oyster-fishing grounds in the shallow waters surrounding the trestle approach structures. Borrow material requLred for the construction of the exisJJng South Portal Island was obtained from Willoughby Bank by hydraulic methods. {See Figure 6 )

The second bridge-tunnel crossing w11l be located 200 to 300 feet. mshore (west) of the existing crossing. A 6. 000-foot bndge-trestle structure will connect Willoughby Spit to an enlarged South Portal Island. The new i. 270··foot precast tunnel will pass under the Hampton Roads channel between the ISlands, and will pro\ Ide a hor­Izontal clearance of approximately 3. 800 feet between the six-fathom channel ltnes and a vertical clearance of 58 feet below mean low water.

The top of the tunnel st:ructu re is to be locat.ed at the same ele'' atjon as that of the existmg tunnel, thus providing an equal or wider channel width. m accordance wnh recommendations of the U. S. Army Corps of Engmeers. The Hampton Creek channel. approximately 1. 000 feet west. of the center lme of the existing trestle, was relocated durmg the construct.ion of the first. crossmg and w1Jl not be affect.ed by a second one. S1m1larly. the Willoughby Spit channel will not require modlftcation, as 11. ts suffiCiently remote from the construction area.

- 13-

I I I I I I I I I I I I I I I I I I

. . '

. . . .

' .

� .

.•

!.' ,_, ,' -1·

,. .... \ ,. ' \ '•.

.,

. .,

i .

·-­,\T •,_. ·. :1

'• ;1 ' ....

.. / ' � "'·�

. .

t .,

I,

.:

•

...

.f..,£� j�

:.

-. J •

' , ,

r. I

• � � .!! ..

. ,

: .

� � :

�

; � '

;r •

t : .. _,

. � -: " -. .: � : :

r

.. �

,. .

,., :. ·�� ,' \, '! ....

'•

..

� •'

.. ... . � _,"'"'"= • . _ . ,.. .. L--... . .-.-. , .. , � . ,,

,.. I ,�_: - � : ' � . .-� ;h . � t'..:r - � .. ,

·.

'·

-=

.·

RIGHT O F WA Y HEQUIRE 1\1E�TS

At the nort h and south t ermuu of t he projec t , the new approach roadwa� s can be constru .::t.ed wJ thm t he nght s - of wa� of the ex1sting project and the rurrentJy planned constJ'UC't Jon of RoUH.:! I ll4 on \\"t ll oughby Sptt . Consequen t ly. no add i u onul propert\ w11 l be needed for cons t n tc•t t on on land . Destgn and consu· uctt on requt r e ­ments mdtc•ate t.hal. a per manent easement. shouJd b e acqutr ed between the \Vt1loughb� and Hampt.on shores . to he 500 l eet west of t he cent er l i ne of t.he new cros s mg and 500 feet east of the cent er l m e of the ex 1 sn ng erossmg . Tlu s easement. woul d pro ­'I. Jde adequaT e space for <.. onstru<.. • •on and, upon L ompJ erwn o f the project , wtll permn operatwnul ' antral to pre' em clamagl to the t re st l es and submarine power cabl e s .

DHE DGING A N D BOR ROW .AREAS (STOP � 0 . 21

Conferem·es w11h t he U. s . A r m \ Corps o f Engmeor .s , the L S Na' � , the li. S. Coast. Guard and locuJ Ponn·aNors ha' e establi shed r.hat adequate clreclgmg spo t l and borrow areas at·e a\ rulable for •he project The U. S Go\ ernmcnr. has a dtspos.al area at Crane\ Island (about ;; m l l e s from the proJctL) \\ lu eh t an aL rommodat<> pumped or bor1om dump mat.er1 al

The H1gh\\'a\ Depat t men· , dunng t he cou r:5e o f t i s stuclws lor Jnwt· st.at c Route H-L Ill' est 1gat ed a horro\\' at·ea a• Scwc l l s Po mt Spt t . An c· alual l on of t he bonngs ancl sod t est s made du t mg t h l S Ill' c::.: JgatJon ha� md . l'al ed that sutl rctcnt qua111 1 t ws o f sand suJ t abl o l or {'Ol1::.l l ltl.. t Jon of t lw Smt t h Ponal l:: ; l ancl could not he obtamed ceonom J Cal ly tn tht s area It should hl' not l•d t hat t h ese mawt·ral s are sull.able l or orclmary back f11l and. If requl l·ed . t ould be u.:>etl l or f r l l D' et· tJ1e p 1·ecast tu bes . Addruonal bonngs ha' c mdll' at.ed ' ha1 adequal<. qu ant tt t c::. ol Slutahl e borrow maten al for the new South Isl and ma) he obr amed f rom Wt l loughl)\ Bank. t he sou n· c o f sand J i l l lot· the Sou t h Portal Island o f the e'\tSl lng t'l'os stng

0\ ST.E.H A"\D FJSHl "-:G A R EA S tSTOP �0. a '

The l ot al Jons o f l eased O \ stet· beds and puhl t c I 1 Sl11ng at•eas m thc ' H ' J n l l \ o f t he p1·ojcct, as well as t.he ch·eclgtng lnn tts and cllsposal and borrow at·ea;; for t he second cross tng. arc shown on Ft glll'e n The Depar t ment SC'C'td'ed t t·om t he Stat.e Deparmwnt o[ 1\laJ' me Resour ces . and ot het· •tual t f , ecl sou rC'es, )Jl'IOl' t.o consll'li( ' 'Oil. a su r' m of O\ srer bed O\\ ner sh . p and ) teld \V1•h t h t s mfo r ma t 1011, cons!derahJc <..:on s t rn t l 'Oll economt�s { an be effected In rechw mg t he ''ont ractor ' s nsk and l ! abt h l \ , wlw h other w1 se would be l'elle<•Jccl m t he lncl::; lor L o n stTut 1 1on t'onn·ar:l.s.

. 1 :>

KORTH AND SOUTH PORTAL ISLANDS

NortJ1 Portal lsi and (Stop No. 41

The eXJ st.mg North Portal Island will be enlarged to accommodate the new crossing by hyd rau!J c f1ll pl aced on the e:d stmg sand bottom . The flll will be con­tai ned 10 pre..., ent s1lung w1thin preplac ed stone d1kes between an appr oxnnate bott o m elevation o f 1 7 m s l and a top elevation o f rhe t sl and a t - 1 2 msl .

_ The exlent t o wh1ch the island J s t.o be Widened IS the mimmum ch st ance bet ween the exi s t mg and proposed tunnels such that. the CXl snng tunnel fill wi l l not be dJst.urbed durmg construcnon. The result i ng approxunate \Ucl1"11 o f 235 feet between tunnel center l i ne s pro1 1des adequate space for the new su·ucrure s and roru:hva�·s w n h m a lengt h al­most Jdcnllcal to t.hat of the cxistmg I S l and .

The exJstmg South Portal Isl and wtll be enl arged by construcnon o f a new 1 sl and immedi ately adjace111 t o t he exist.mg one to au·ommoclat e rhe new tunne l . The s i te of the new South. Island. unl1ke tJ1a1. for the Nor t h I s l and , J S u.nder l am with a sofi Silt depos1t forming the upper port1ons of the natural bou:om o f Hampton Roads as shown 111 Figure 7 ( in back en\ elope) . Afrer l ompl et.i on, t he new and e:-ost mg i sl ands w1ll be conne c t ed t o form a smgl c one .

Methods o f C'!_n_st ruc non

A s t he const ruC't Jon of the new 1 sland WJ) J 1mpose la1·ge add1110na1 load s on the compressible subs0 1 l s . t hrte schemes oi l'Onstrut tton were studi ed to dete1·mme t he method t.ha' would result 1 n 1,he muu mum t ost and mm1mum nsk to the exlStlllg t unnel These schemes . as di seussed m the followmg sectwns � are (1) t.he sheetp1le t.rench met hod . (2) the dredge and (I l l met hod . and (J) tJw sand drams and surcharge method The 3 met hods are I llust rated m Figurt; R

Sheet p!le Trent h Construl l.lon

W 1 1 h the sheetplle t r eneh met.hod of const:ruf't.wn . t h e new tunnel and open approach su·uc·tu res would he loc at.ccl about �n feet mshore (west.1 of t he e:·o st m g center l t nc of t he t u nnel on the South Port a] Isl and . Construt 1 1011 of the new fac1 l lt 1 es would be carried out wlthm an open sheetp1le n·ench parallel to tJ1e ex 1 st 1ng t lllmel and wnlun the confmes of the ex1stmg dredged and f1lled Jslancl. Th1 s method would l l m n t he need for e'>1 endmg the ex 1 s tmg I sl and and hence h mn t.he new l oad s resul tmg from sand f11l on the t om ­pressJble substrata. Howe• e r . t he cofferdam m erhocl reqm res the al ignment of t h e new t unneJ t o b e so c l ose t o t h e ext st mg t unnel that rhe t rcnc_ h exea· atwn would unt'O'- el' the top of t!w extst mg t.u bc . Thereior e . am lunher cons1dera11on of t h 1 s method was abandoned b�c:1use of the bJgh n sk of cl t s tu!'1JUJ1C'e.

·· Hi -

I I I

I I I I I I I I I I I I I

...... --1

l11161llrl�,.:.:" c��

• l � l t D , � ,,,,,,.,.,,":l.rkL �

l i L T • CL.A'f

StLTT S O li D

SHEETPILE TRENCH

·� '" du,.,, _ _,,,.., ML ........_ M...;uu-,tc.\�· .. ,. _ __ II -...

l. pa:;ucuc PD

Sti..T Y CLAY

! lll�fY S A " O

EXCAVATION AND SAND FILL f ... O,OII.D 1UIIIIIL

't ·� ...--•.!_•,!! _ - 1 1

.......... .._ !Ut< ..... .... __:_ ...... t.[_ . .!:,!!f.._j ' ........ ... ..

:.J 0 10 100 ����.� •• �.��==�

� llfl <L PII'

-- ·-- ----:;c .... _.,, ......... _�_:· ...... J' ..

' _ ,.,,,.

JILTT C:\.. A T

l l l..T T I A N O

ndffH NtTCW- t 1 .. l..c::::::J • .............._-- --... -· ...... I I I �Tr'J""''·t - 1-lLH.... n-,......,. " t: tc !: ;. !t • f- I l :..iii l• --�_:.......-"1, - ... , ___ .,.,. - � •••• � �lntn••.nTDII

.... -�·-- 250'

SAND DRAINS AND SURCHARGE

I I L T T C L A Y

I I L T T IAIID

Figure 8 . Construction methods for South Portal Island on second bridge-tunnel crossing.

Dredge and F 1 l l Construct Jon

The construction of t.he ex1stmg South Portal Island was accomplished by the dredgmg and di sposal of 9 0 feet of compressible, and hence unsuitabl e . founda­tion matenal s . wluC'h were replaced With sand fill by hydraulic m ethods. Smce completwn of the construct ton 13 years ago, settlements have been Witlun the pre­dicted acceptable val u es . and ha'- e r esulted i n minimal corrective measures to the I sland and ns protectiOn , with no significant damage to the structures. Enlargement of the ex1stmg I Sl and bj dredge and fill methods would require that the center hnes of the existmg and new I s l ands be 300 t o 400 feet apart m order to avmd problems of slope stabi1 i ty durmg the dredging of the enlarged island. This m ethod of construct Jon. wnh suit able separanon of the Islands. wlll present no undue hazards to t he existmg structures, but wtll requ1re the remo\ al and di sposal of about 1, 000, 000 cubic yards of silt and replacement Wit h approximately 1 , 500, 000 cubic yards of hydraul i c sand fi1 1 . Disposal at sea of unsmtable mal erial 1 s no longer economical and d i sposal in the Corps of Engmeers CI·aney Jsland cl1sposal area 5 miles distant requires a sub ­stantial rehandlmg charge. Further . the hydraulic fill to a depth of 20 feet below t he new structures will require v i bro-compaction for a distance of 25 feet each s1de of the runnel center J J ne. The total e stimated cost is $5 million.

Sand Drams and Surcharge Constru ction

I I I I J I I I

W1demng of the exi s t mg I s l and util izmg tllis third method of consu·uctwn wi l l I require placmg hydraul i c f1 l l between the existing bottom (elevation -15 m s 1 J and t he top of the Island (ele' atJon - 1 2 m s l) w1tlun the enclosure of previously placed stone dikes. Till s procedu re Wil l l im J t siltmg and w11l provide a dry land surface from I which sand drams can be Instal l ed prior to surchargmg to elevauon �37 m s l . A ft e r campi ell on of t he consohda1 10n perwd, U1e surcharge will b e removed and used as tunnel backfilL Settlement analyses were made using the Boussinesque Theon . and t.hese were venf1 ed bv the Fmne Element tvlethod usmg computer techmques. Tht•sc stud1es indicate negl lg1ble additi Onal settlement under the ex1st mg structu res when

I the cent er l me s between ISl ands are 250 feel apart. Tlus met hod would rcqu1rc � 1 , 350 , 000 cub1 c ,; ards o f f1l l , 250 , 0 00 cubJc ,; ards of surcharge remo\ al , 525, 000 l m . ft . of sand dram s , und instrumentanon Estimated cost: $4 . 05 milliOn.

Upon evaluat iOn of t he above factors it was decided to use rhe surcharge unci I sand dram method o f construct wn. No dredgmg and d1sposal o f unsuitable matenal I S required m t.lu s metlwd. Howe\ er, the dredge and fill method is a pos1 t 1ve and rel at.Jv ely foolproof pl an wlu l e the s and dram construction and operation requ i re I considerable care and control of iechmque to produce completely sau sfactor,; r e -sul t s , The South Isl and was constructed under a separate advanced contract ro pel'l11 1 t . under a subsequent cant raC' t . t he trench to be dredged and deposited to construct the I North Isl and and the tubes t o be fabncated while the 1 2 months of surcharge on the Sout.h Island progressed.

The problems . after the selectiOn of the surcharge and sand drain method, IIi became t.he c n t J C'al!n of des1gn. care m mstalhng Ute saud drams, and the c\ aJ u - � at1on o f f1eld mstrument readmg s .

- l " -

I I I

I I I I I I I I I I I I il I I I I

SO I L PROFILE - LABORATORY AND I N SITU TESTING

In general ter m s . the s01l prof1 l e at t.he South Island s1t.e cons1st s of a t h m layer of loose silty sand at. the ha) bottom a t about cl evai lon - 1 5 Tht s 1 s fol lowed by a layer of clayey slit wJt.h seams and pocket.s of sand down to el evanon -90 The lower portwn of the s tl t.y cl ay contams some orgamc matter Below tl1e s l lt.} cl a) are l ayers of dense silty sand and sand .

The clayey s1lt 1 s sl 1ghily o��erly consohdatecl at the upper porilon and normally consoliclat.ed lower down. Jr vanes graclua1 l y 111 consi stency from soft at the top to stiff at the bottom.

The presence of till s c l aye\ s1lt. laver presents problems of stabJl l t� and settle-ment.

Laboratory test,s of LIDdJ stm·bed samples of U1e cl ay silt were made 111 1 954 for t he fi r st. bl'Jdge -t.u iDlel . Add11..10nal l aborato1·v tests a s well as f1eld " ane t est s were made m 1 96 9 . The 1 9 5 4 tests cons1 sted of unconfmed compresswn t.est s and t r t ax t al test s . Only Uw 1 9 54 unconfmecl rompresswn t e st resLLlts were used for t he deSJ giL

In the 1 969 test 2 consolidated. unclramed tnaxial tests were made at chamber pressures equal to 1 1 2 the overburden pressure . These yielded resu]t·s l ower than those of the unconfmed comp1·esswn te st s of the same sample tubes

A plot. of peak cohes10n results versu s d epth showed that soil cohes iOn m ­creased with depth, From thi s fi nchng . p l ou.mg values o f cohesiOn were assumed for design. The basis of the assu mption was to fol low t.he U' erage lower 1 1 m 1 t of the t e st results. negl ect mg extreme \ alues,

From a plot of A t.te1·berg l i m i t s and natut·a] water content versus e l e\ atJon and stress- strum cur' es for .l aboratory ancl \ anc shear tests, 11. appeared t hat the daycy s1l •. was qu ttc senstt l ' e rartt culaJ·J� 111 the uppe1· la) ers

Consol tdat 1 011 .. .. ______ _

Consol tclat Jon tes ts were performed clurmg both the l 95-! and 1 969 m � e s t tgallons Consolldat.ton cun es were produl'ecl b� plotting preconso] 1datwn pressure and exJstmg ov erburden pressure \ ersus depth and coeffic ient, of consol idation, Cv. at appl t cabl c pressm·e ranges ' e rsus el e1 ation,

From these test s tt appeared that :

1 . The cl aye\ s1J t IS somewhat O" erly consoli dated from Its surface at l 3 to ele'.'at.wn -50 and normall) consol lclated below rhat

- l !) ..

2 The time rate of consolidation I S much higher for the soi l s above -50 than for those below.

For consohdatlon by means of sand drains, it i s conservatively assumed that the horizontal coefft ciCnt of consolidation is equal to the vertical. Field permeability and pumpmg tests were performed durmg the mitial stages of con­su·uct lon. It was planned that If ir was confu·med that the horizontal coeffici ent of consolidatwn was subst antially greater . the sand drain spacing would be revised. The sand drams were installed by jetnng for nunimum displacement, nunimum smear _

Increase m Coheswn w1th Consolidation

On the basis of the relatwnslup of the cohesion test results with overburden pressure and preconsolidanon pressur e . 1t was assumed that

c - 0 . 3 p.

The 1rut1al cohesiOn IS the product of existmg preconsohdation, whether under existmg O\ erburden pressure or other geologiCal preconsol idation pressure. When the soil consohdares under t he imposed load to a value lugher than Its 1m0al coheswn, an mcrease m consohclanon wJ l l t ake place.

were:

Field Obsen at Ions

The de'-· I ces u sed t o momror t.he consohdanon of the in situ foundation matel'lal

Casagrande Piezometers

Pneumatic Pwzometers

Deep Settlement Pomts

Conti·oJ Stakes

Incl mometer Casll1gs

_Slope S1abl1J t r Analvses

Slope stabll JL) anal) ses were performed for various stages of t.he proposed const ruct wn. These consisted of eomplete solutions of the Swedi s h Shde Ctrcle and manual soluuons of sl1dmg wedg e s .

- 20 -

I I I I I I I I I I I I I I I I

I I I I I I I I I I I I I I I I I m

The m1 1 mum factors o f safet\ are t a bulated below:

Maxi mu m F1l1 El evation

-5

- 1 2 •20 - 31) -37

1\Imunum F . S • • whtch melucles fl l l 1,0 1he mruumum elevauon

Shde Circle Wedge

1 . 09 1 . 1 7

1 . 1 8 1 . 23

1 . 3 7 1 . 20 1 . 44 L G5 1 . 27 1 . 27

11 should be noted that an approxmlale slope stabll i ty analys1 s b\ means of Taylo r ' s charts mchrat es that the fi1l to · 1 2 requires t.he same a\ cragc cohes i On 1 alue as did the exea\ at JOn fo r rhc cx1 s t mg South Island. It was report eel t hat the excava1.1on was made \vit hou1, any pr obl ems of 1nstabil i ty.

For fil l s above ele\ a1. 1on - l 2 . the mcrease m cohesiOn due t o conso]JCianon of the sand ·dramecl area was constclcred m the s1a.bJl l t.� analysis

The faC J or s o f safet.} t abulated abo 1 e are consJclered adequate m \ tcw of t he fact that the fill I S t.o he ker>t under rarefuJ observatiOn It should be noted that t he lowest factor s or safe!\ OL cur at earl\ s t ages m the const ruct ton For tlu s reason, remechaJ aC't ton suc-h as ext endmg berms W 1 1 l be possible J ( the need IS md 1 cat ecl

TRESTLE DESIG \J � SECO�D C ROSSING

The horizontal roadwa\ dec.�.runce hel\veen bottoms of brush c urhs f01 the proposed trestl es will be .36 t eet , pro' 1dmg 2 l anes of 12 feet earh . plus shoulders on each s 1cle The normal roaclwa\ sertJ on w1ll be crowned at a rat e of :3 1 6 mrh per fool, wluC'h wl l l J.J ::;o be t he ma.xmwm superele1 at wn rate. The prof t l e of t he proposed t res1.le has been l'stahl t shecl l o pro• ttlc t he sanu. '- err tr al cl earance between the bottom of the structure and mean low water (mlw) as rhar for rhe ex1 st Jng trest l e ( 13 feet 3 mrhes) The roaclwa\ g 1·ade w1l l be le' el . except a1 t he l and abu t ment s and approarhes t o the t sl uncls C1·oss clramage wtl l be pro' Jdecl to as sure a safe and comfortable drt • mg condP ron

• 21 -

Span Lengths

Studies were made using an American A ssociation of State Highway Officials (AASHO) HS20 loading plus alternate m ilitary loading for 50-foot, 75-foot and 100-foot trestles. The spans consisted of prestressed concrete beams supporting a cast-in­place concrete deck founded on 54-inch diameter prestressed concrete cylinder piles. The r e sults of these investigations, plus experience on the fir st Hampton Roads crossing and other projects, and soil investigations in the area, all indicate that a maximum pile loading of 200 tons is both feasible and prudent. Based on this pile capac1ty, investiga­tions indicate that the 50-foot span r equires 2 piles at each bent, the 75-foot span re­quires 3 piles, and the 100-foot span requires 4 piles. A d esign study was made, setting the prestressed beams at a spacing of 6 feet - 9 inches , This spacing is the approximate maximum for a 1 00 -foot AASHO Type 4 beam and a 7 5-foot AASHO Type 3 beam. The same spacing was used for the 50-foot span since the Department's high­way design criteria specifr 6 feet - 9 inches as the maximum spacing of stringers for a total slab thickness of 72 inche s .

TUNNEL DESIGN - SECOND CROSSING

Description

The tunnel portion of the project consists of precast tubes, open approache s . and ventilation buildings . The portal-to-portal length of the tunnel is approximately 7 , 270 feet, of which the precast tubes compr ise about 6, 875 feet. The depth below mlw to the top of the tunnel at its lowest point will be about 79 feet.

Design Criteria

The tunnel design criteria are itemized as follows:

1 . The maximum grade in the tunnel is 4 percent.

2 . Since stopping sight distance does not govern along the vertical sag curves in the tunnel, the proposed length of 200 feet for the 2 vertical curves is compatible with a 50 mph design speed based on driver comfort.

3 . Flooding of the tunnel and the open appr oaches during periods of extreme high tides is prevented by constructing the side walls of the open approaches to a height 14 feet above mean sea level and by providing portal tide gates.

-! . The crown slope in the new tunnel is 1/ 4-inch per foot.

- 22 -

]

I I I I I I I I I I I I I I

• I I I ,_ -I I I I I I I I I I I I I

5 . The eXIsting and proposed tunnel structures were destgned on the basJs of the following assumptions:

Weight of :Matenals

Water - 64 pcf

Saturated soil - 110 pcf

Submerged soil - 70 pcf

Structural concrete - 147 pcf

Tremie concrete - 83 pcf (submerged)

Ballast - 70 pcf (submerged)

Lateral coeff1cient active earth pressw:e - 0. 27

Factor of Safely ( Buoyancy)

At smking (not including ceiling, ledge, sidewalk, roadway pa1, ement or wall finish weights) - 1 . 06

After dewatering and removal of bulkheads (prior to placing interior joint concrete and backfill) - 1 . 02

Final design condition (tube completed with 5-foot minimum backfill in place - no allowance made for shear or s1de frictwn prov1ded by the backfill) - 1 . 25 .

The following photographs illustrate the techniques by which the tubes for the first crossin& \".'ere fabr iC'ated , outfitted and sunk into posibon .

- 23 -

(!) t\1-.":!':"J!· e tr-;,- ... !:..r. :� 'tet., ,.: ::ifl""".ry!l ICl:l •• 't>y • •

- 2l -

� lY J•!" ,. :r. t 5 :!· :-.;:.=..!n. I!. �r -je5. : • • t tt' �rerroll &!l� Prn

J.�e• '!..o •�•·t>!l. Mer:-• ' t f-I!U"t.U:::!. c:' H!e . , " :;,.e:-,....l.e !t.g el.t) ... t.f"'e " •

.g "'Xf :-tos&'-•Y :a 1: �:"11�!1� ll:lk .t. • th: cc:rJth1

;.=; !. S:o�t ICLB1 r..nckcr�".!f,

I

I

I I I I I I I I I

I I

I I I I I I I • I I I I I I I I I I I

.. . . . t � · ---

-

-.. _::_ .. --::�� ... __.;!'""

- 25 -

w r• .. 1 r f1 ' • ... t ,..ILl:; •• •

p t 11. E.. .. ; -; • :. " !:\."! .. • • :::e _

Jf\'" :--: a

� • • . ... "-• .. t

..... ....1: la ..... : .c ";..! t\,;

t.••s .. r .. :- , tc t

.= r -!r.;. . ... : ... ..... : ..

· -1!': '

IL o

I � l

--

: "t.- -.... , .

' . , . . ·- a ... - .•.

- 26 -

' -· ·

, �i'.c • ..

. � •

.. • l'� •!.:" :!'J. •• c . ' J ... !:. �·"') c r..l!.:.t.:.

.. 1: -. ,. ... . .. .. .

� -·J. • ' I ... .

. ...

I I I I I I I I I I I I I I

I I I I I I I I I I I I I I I I I I I

(";! .:UI:ztt. :t)C�: Ot. � !u toea! 1.!:.:- c� bot.�:::o eo: .:--e-"lr,:�. l:T"'" : • • : .. �c: • we:c c•. �«:-! :.:.t:,e��er 't:J :!.! ·C'� a.:-...! :e..:A!Jil::.i 1po.c� be!..,.e-.: !.:a11tr 1.: -: a: • t'.. �:.� .... t; -�• �.::I!'! or!.-; c.:�.c:e::.c. !:c,.• , £ - ! . : !.::e: c.:- ::. :-' • :-e t-1�':. f\:'t-...: • .! a- t•c.: " 0" •• ,.:- Jo! ' 11 a: ! -..· .. · � -c:" \:' '\''!'("! .!-;!': n :·.:.· ...... :·c.:• .. '" .. 11:'".1."":0 :: :•s.: • . J\-.. .. :, � .. 3 e:.'t" t ... ll!.rlL.!s �C'• -er-:: re ��':!.!J ...-.... � t' .;:ocsa ·'�·• ��.-:. · �.:,..·.....,. . • .,e!:.t •C:"C" • !,.! ': ... .. ::: -: :.!1• •co .. : -. -!:.t 11.. : .!""!"' :-!· .: : � !.�! • 'n�· ' - :. ... ...� .. :,. ! ..... 1"':�! 'l":. :.r.!:s 1 • • •

'1 . .. :- � t ..;• • \

• .1 ;12A.,,.e:, - u . • -· ty t .. 0 .L

- 27 -

· -" -

...

PROBLrMS OF CONSTR UCTING 1!\TT ERSTATE ROUTE 64 ALONG WILLOUG HBY SPIT (STOP NO. 6)

A feasJbil ny study for constructmg Interst ate Route 6 4 totally on l and tlu·ough the W1lloughby area was made in 1 9 5 7 . howe\· er , the w1dth of t he roadway badly dam aged pri,·ate property. Consequently , a long trestle was bu 1 l t across Wi l l oughby Bay. Tlu s site also i n" ol v ed t he cross1ng of t.be waste tJ1at was dredged fo1· the sea pl ane base for the Na1 y . The ftJ l s were surcharged, and se\·era.l mud waves de\ eloped Or1gmall) . the design called for about 1 5 feet of O\ ste1· shel l s t o be placed at. the bot tom of each em bankment to act. as a pl atJorm for the roadway . Unfortunately, t·he shells were not· a\·atlable at the t i me of eont ract. One hr1dge had to be mo, ed because met hane gas (marsh gasl was encountered abou t 50 feet down under pressure. A n attempt t o burn t h e gas off was made for 3 months , howe\ er , the d ifferenr:-c in pressure was hard]\' noti t'eable The construcuon area 1s shown 111 Ftgure 9 ,

• ' . ... • • 10 ,. · • ·� ...... 13 13 _.; -' . .> .. ·.� , . . �. Fort V."ool • f . 13 13 -• � 10 ,• . - y - ·ii - - - - - - 14 -�• ·· ·lo ' • !• · J ·- -

•.. 1i t _i 13 - _..il- --;- - IS , '"' . ..r s - -.-' .: -., 13 � fs�· '· - Vl- - - ··'1 s !Jt 14 "" 14 -t 16 7UN,.(L • � tt . -- -� -··...... 13 .,' ,' 1 w '··· ··.. "oust \ ..... .' ' .... .. • 13

' . ' . 7 . 14 · .. 15 -- lh .. '

-. ..,.. ··... . ,., .. .... ·: ���·:: 12 12� � . .. .��- - ... _ _ _ .. . __ .. _ _ B ·· •. , II 14 \ 11 ' 13

I \ 1 .l ,j

I� 17

22

t3

13 13 IS

17

·--

9

- - -I

IS 6

18 II

18

::1.1 1 4 13 1 �� 8 • /rl I ',

�� 5 3 / . .. _ _ \ ... 17 Ill .. ... ... .. 20 17 20 � ... - � �: -� '\�.. e

e �- \ · · .. ;�-.. - .. .. 13

'\;\' II' r: l ... � .... .... (

.. ' r ... ,.• 12 • . 16

: ��\ ,)·� / / ;'h ' ·: �-.:�0,, :;- ·- - ',' >·c

.... ,

,},%\ tz ' ,..,...·· .··: z\ ·, \ 2 lrl �c-� <- �;:: ,�, � ! \"" \ ·,o ! z ' �-

\i. \ > . . ,.,.. . \ \ 11 tJ \"' \. .. · �e i , : ·

•

.\ , 7· •··

.. •

• ( 7 I .... 2 •• ·k::��-J-.;...;.�.,.);�7-1_.';1, R::"'' , ; .. . , �'· � '':.'.. ; : " " 1 A ' ., ' I \ 4 f

10

I ' ' ' ·... 7 :

17

.. I I

16

·� - . _ ' -

··· .... ) I -

F1gurl' 9 . W i l 1 oughby Sp!l. t :onsr.ruct 1011 area.

16

'·.1:

17

•• 7

\! 17

" ,; - -

--- . 13

16

17

""' 18

16

'

i l

.. I

\ •

.,

N

ep . -----.... - .I l l f l

0 w o wrt.zr• (?) J W ... JO"" A C&AA (') Nf!'..l lf\UU..w Y • " S <•) � ' ' " "'" \.') ttAllAHD f"IStt..., O'Slftf£0 @ UOAA1TCO �AC.,.frfG CO {!) lUUO O'fSf(A GAOUNO ® J R \llOA[,JR - Gt:CI!Gt S rQARtsT @ @)

:.

'

,, � . '·

... . . . · -. . - ��

. :•j . � 't � • ..

,.. .

•

• •'to' • .•

. .

., ·,) �­

o-� ·. I

. :. ·· .. , . . •' . . . .,

... . .. .. .

.• .·

, •, .. I "

, '• . . � . ,, .. .

,: :- • . .. : ::'i - . . •

-�;;:- . �· - . : :::· . - .

J ·.: ..... · . .. �. ,"; . . _ . .

/ .. : ' • - /.·/ · ; 1. ,�; . ·b: • '-._· ./.' - , . _ _.,." I \. ....

· _..._,-..;'- -�'ir i . .• ; .... ��� •• •',7·' .._.·f:·: . : � - ���-){-f. . ; : 1 • "-'J I

,,"! ... -- .::.-: .• .-

.... --�r:,:�� .. · � : ! -/!?;�:� �· .= 1 i tJ'.:1·

··;::{�·-. i�-�- :�

. . . . . � ·�) .

• • r t) • . . ·· . .. • I .. .. • • • • ... • • • r • • • • • , f • I * ., • a "' • ., ••• •

... . . :, . :.:::".;-�· . . . . 1 . . .

. ''\to • ..

- · .. "

. .... " •.t::

��···

:�

'tiil• (�

, . . • .. ;.� ... .. \�

..•

• •· ... .... t� ... . ::;i. .�- i� ... .

.:.�.-.. -·�·-. ; -� .... . ' s�-... -l:;�� �� . . _:; . . ..

t.;..._ . ,·

·';,· -- .. ,� -·

.. . . ....... \.L ....

.. . :-:: .·�::.....:. ..

'.::· ...

.. . -:. .. .... . .

.. ·.

-·

· ' .

'-·-

·-

- · "' - --;:.�··::·� . -... · -· ···· ··-·

r " .. N . . . . J ':0

·--.. �.:-.j • . 1

I : r - -' • : .-.:' . - I - .

- - :.·

I. - ·· ..

-.... , .·• (,. '"•! ·•. �· ;�·.;--�.�.: ·-··

... . ,., . •• )o ·- .

·�, .• \ ..... f

Jl j .r . . : · .rj

_ _ _ .. . , .. . - • . �;.�f

.� ' . . . . · .

: . . . . . · .. �.

.•.-

. .. 1,11 · =:S:;+­r�: . . ·-· .. _ .. , , , . .... . , .... ...... . .... . . ,i) .. , .. i: .,

·�= = = =

. :

:F':lgure 6 . Site conditions at secooo Hampton Roads bridge-tunnel crossing.

= = � !! !! !! !! � e e � e � �

� � ' �

- • !I

I t f{ ,· -l, i � -. :.

-. - ct: � . � � �· _ -- - - ---· -- - ·- - . . · ---- --.-----------..._..____ . , .:..t.."' I

• ••

• I

0

�· •• ·: • I ! •

E� 8 I

� ·. � .· . ' -

. •! • • 0 •

.. .... · . ... � ·-· 0 0 • '� •

·��,\ ................. :- - .... �t: .... 0 - 0 .. 0 • -

• ,-\

: 0 �f� ' _ ': . : :{ : ' ·:: .) _ tij' . " '-c- 'I '

. .:: : ' .. .. . . ·:. " :• � .1 •

-�-·.••:r . . ·- - . \._J .-... o �- •

I '1"\.1?! .. . l fi'Pt.O'X lf""'K1 • · - '" a.

. .. . - ' .. . - I �·. '

<t;'§.r � : :·

liD p WH WR •.

- · . -fi ._. ... . .. � ' H

A Ba;EVTA TICN Undish.rte� Som�::e Pu•h . We·;� o! �J-:>mer

.. -We:g�l o� R�� · . .

.. ... . . : .. ·· "' ·

: · ·

• .,-: • • • •• • • •

• !.� ••

•

•

... :-;.,_;: ':-;: .

. :. :I: ';. :

... •. •; : .;, ';' · . . ·.· :.

·:: � . . _; ·.: .. �-... ·: . ,

. . . .:.

I I ' • : . i i. . � : . , . I ;'

' . .. � ' • I • , , ;. ' •I : � . :::� --.::; ��-: 1:�·-r�: -.

. · ·

.

- -�- ,- : · � i .. • .i ' • . � • .- I . . ' • • - I

• • T .. I ' o ... . ' • · ' ; I I 0 I ·

0 t�· � . . 1

; . I !

[illJ �� · J l l GEI\�L NOTES - -� • • • : :! - !

• .. . . . - ; · • . .: . I L Nwr.tor- o:::f!o=��t '�� lx:.r�t tf;t'��nt t::�,,3 en o 1..:.0 :b...:._ · J ; - S:..T •

•

I . ' .

��:, .. �>� - . �-.& - - .. ,

ti/2.!; : � � CI.AY • I'/ .:;_!_l ·_ : / _,1 �� _; � ["''l S· : : � - ::: :·.; �:.:-....:::. I • ··::: !2.1.. .._ :

•• i- ....... i

:n:'�� � •.·__1- J � \t:s-.:.::i' --·

­

lt�,·�n--� :. . . !f :3 VATER-��� ·

g:a 1

-o

} j

I ·. � '.

homtniJ:- !.aJ·,�� 3J ��! ' ·:t .. c.f ""--=!"'�fr.j,:l,:l ��r o !:: r ., : �1 !C:::;>!er. (2' Oil. 1-:/3 LO.) _, • • ' '/·' l.-.4 2.- Soils $)"T.!xl's r�e�ew1 o cor�·JI zc:l Ci.Jio! ':41;, Sra �-:-J • · :

loC$ for mc<iJ c.·c,._; ''�<•·' ;c!�i\ . . • . f .,_ ,..:..:.... _, .·. - • ,. • l ; I ... --- ��..., ;rcur.....

• ., ::: ._. ....... . -� :: :� ·• �r. --,-.

. - ·

· .

�··

0 -!. . � , . .-._ I I .. .. . .... . . ( . ·. .. . , . ..

: .. · - · .. · :::�-· . . . - r

ROADS ?ROJECT 1 i I • SECOIIO BR'OCE TU�·-·•::L c;;::.H;�.::; • I HAM ?TON

BORING PP.OF t:.t:: SC-.ITH ISLAND

--=------I �-.,

..... I

- · ...._ ·-·

·-·· " :M : :. . -1 �va

.. I .,,., ,:_.u:_, I '! ,.

. ; - ·

- I .... . . , . -� -

. " - :-:

: .

·- - - l j ' - -, -l �

. . �· .:;_,

. - - .

' .

. ·4--� . . .

. !

. -.

' - · -

.

. I

- t . ' ...

.. .. . .. .

.

I I

-

.

. - - -

I

:-,

'

I t· � � 1·: I I

I , . i I · I

,• I

.. -t . � .

. · . · · . .

,.

. . '

' 0 .. 0 ,1 . i . . . . . . . ' - ' . . . ; ' ' . \

. . · . . . : ·:�· ·; > :: . .. .

. , .

. ··• • t •

. . � .. ,.

·.

' .

. . . · . • , .·.· · ,� ='· •• ; ,

' I · . .

'\ I . I

' •

' I

' ·

t , ,

; : � .,· I , '

.. � '· . . -�· \ . ··. I ' \ ,

.· ·

q �-:-(

, ·

. ..

.•

- - ..

i' . .

'

/ ·I

/ • t'

' • � • : . • • ' ; �.··· • • ., • • t ,... .,.._ ..,. ..,...... ,_._..,..,._......� .,.,..... : --• .,_ .....,_. - --,.-....,. .... a..: .. -..;...,._,_.,......,.,.....,.._ •-w ..... ' � ...- I'"W• ��-•-;

· ·----.... -................ ,, ____ �·-·.-.......· � --.-..-� .. ..,__. --...... ___ �_ ------------