The daily union. [volume] (Washington [D.C.]) 1845-1857, 1857-02-12

,,. AT the site of the Long Bridge, the proposed plan
oud diminish its cost by nearly one-hal large por-
ION OF the structure may be simply causeway If there is
20 be no bridge at this location the citizens of
Washington should possess at least the facilities afforded
nv ferry In the actual state of the river that privilege
denied ordinary low water to the lghtes row. boat
TO pass from Washington to Georgetown by water, 1t is
nessary to the point OF auvsl deposit below the
arsenal in order to ascend the Virginia channea dis
lance OF two miles being thus drawn out to six.
4 BY the proposed modification Of the dam connecting
Masons island with the Virginia shore should
All Of its advantages without experiencing any OF its evil
effects In all ordinary stages OF the river ii would force
the whole around by Georgetown thus keeping its
channel Free In times of dangerous reshes II would act
as saeyyalve by largely increasing the waterway thus
depressing the level OF the river Its passage by the
neghborng cities and greatly diminishing the injurious
effects of nundations especially in Georgetown At
the same time the formation OF marshes along the Virginia
shore would be prevented II would OF course be
sary leave permanent and suitable passage for the
fer through any causeway that might be constructed the
site Of the Long Bridge. BY means of the modification
here recommended the dam at the head of Masons island
would become immense waste weir OF great stability I;
lis soping surface would lex breaker while its
ened height would preserve it from the angry violence
of swollen waters of the Potomac which, previous
occasion, effected its destruction.
9TH The expenditures necessary to the advanta
geB enumerated above will not amount to onesxh part of
the value of the land reclaimed the greater portion of
which, presume will belong to the United States three
reservations and one street front on BY referring to the
the cost of removing portion Of the Long Bridge cause
way, replacing 1t temporarily by wooden structure de-
pressing the dam at Masons island, dredging chan
mel and building breakwater from the island, amounts
o$l08367 IT. in addition, construct guard-lock at
the mouth of the Tbe and reclaim 1865 acres OF land by
raising the level of the flats six feet and facing them with
more elevated dixie the total expenditure will amount TO
$oO277 equal to al0 cents per superficial foot This
sum could be very considerably diminished by making
rangemen,s retain the alluval deposit 1t would
que however series of years 70 realize very material
suits from such system. Should expeditions
be thought advisable the earth required could be procured
by grading the contiguous portions Of the city thus
inc double benefit The value of this land at reason
able estimate possessing it would great commercial ia
ee be less than fifty cents per superficial foot
or the aggregate $36l5 480 which, before stated is
six times the expenditure in question.
For each and all of these feel hesitation In
recommending prompt and efficient measures for the inn
poy0ment of the river in the manner herein indicated
knowing the possible doubts which might exist in
quarters to the efficacy OF the plan proposed, however
clear my convictions Of its certain success have felt
it my duty to consult with of the highest engi
neerng authorities Of the country the subject and they
in the opinion that the plan SAFE feasible eligible
in ITSELF and what also t portant susceptible of rapid
realization without interfering in any way at any time
with the general interests of navigation with the
venience Of the travelling public
PLANS FOR THE SITE or THE LONG BRIDGE.
From the Improvement of the river, pass to the
consideration Of plan for bridging the Potomac at the
site of the Long Brdgethe the most influencing and
the most influenced by navigation. The resolution Of
Congress calls for both stone arch and iron suspension
bridge First them supposing he river to have been mod
flied in the proposed the arch bridge
according to The plan have prepared and herewith sub
nit (seeaccompanying drawings) will commence with
abutnent the Washington Shore having an entrance
from both Maryland and Fourteenth street 1t will
be pierced by four arches Of 20 feet span de
tined to afford passage vehicles along the rivers bank
quay 20 feet wide will be reserved Immediately in front
Of the abument Three arches of 100 feet with their
accompanying PIERS reach draw presenting two open
ngs OF 10 feet EACH next nine arches attain causeway
$500 feet in length surmounted by a brick viaduct
formed of arches of 20 feet span ghtened to
the utmost extent the side walls to be faced with stone
Finally three 40 feet arches span the reserved Virginia
channel and with their abutment terminate the bridge
Every third arch will rest abutment or abutmen
peran indispensable precauon and greatly facilitating
the erection Of the bridge it may be completed in
ons The supporting pers are fourteen, and the abut
ment piers twenty-five feet thick, at the spriDgng line
The accompanying estimates show that economy OF
may be realized by dispensing with the brick via
duct across the causeway together with the stone arches
the Virginia channel 1t b proposed in that case to
make solid earthen causeway with descending grade
and span the Virginia channel by single suspension arch
Of 400 feet chord
HEIGHT BRIDGE ...r .. T
The surface Of the roadway is elevated 40 feet above
low tide and corresponds with the summit of the ele
waited ground the Washington SIDE both in Maryland
and Fourteenth street higher level than this
increase the expenditures the proposed causeway would
be less suitable for railroad PURPOSES and very heavy
pressure the foundations less height however would
highly Objectionable 1t would diminish the spans
the free passage OF small craft.
PROPORTIONS ARCH saaa
The spans the arches before stated have been taken
at 100 feet while the 80 feet oneourh the span
This is limiting ratio fixed by high authority and cele-
brated examples. Wider spans and hatter arches give
greatly increased thrust and consequently require much
heavier abntmen piers four of which to be construct
ed may be the accompanying plan The warped
so has been employed giving appearance of great
ghtness and elegance and dispensing with or at least
greatly diminishing the necessity of icebreakers The d.
mensons and dispositions adopted to combine every
requisite and enable at the time to take advan-
ge of the natural features of the ground exhibited in
Colonel Kearneys report,
FOUNDATIONS.
The bed Of the river towards the Washington shore is
composed of thick layer of mud and sand resting firm
ground-eher compact sand and gravel gravel alone
clay mxed with either OF the preceding AT the point
where the draw is be placed The alluval deposit at
ans depth Of 60 to 10 feet through which we must pen
citrate to secure firm foundation A large proportion of
the remaining piers reach the natural soil at very much
less depth The system of foundations proposed for the
most difficult piers is analogous TO thatapped on large
scale and with eminent the celebrated naval de-
pots at Touon It consists in driving sheet plng around
the space reserved for the pier dredging out the interior to
depth of 30 feet driving the whole piles feet
inches from centre centre surrounding the outer row
by strong vale pieces ramming home broken stone be-
thus prepared depth of 10 feet with the best hydraulic
concrete and finally founding as solid rock The di-
Vngbe is then used to bring the masonry up to the level
OF low water Where uDyieldng soil can be reached
without ping it Is proposed to found simply BY driving
sheet pling, dredging the interior down to firm ground
pier by stone thrown around and erecting the submerged
portion before by dvingbe The current can annoy
but little owing to the protection afforded by the sheet
Piing.