The Washington weekly post., 1899-06-06
CARRYING RAILROADS OVER MARSHES.
Devices Which Engineers Have Adopted
TO Subdue Mud Foundations

TrClu ths saz FFarcisco CsrgaicIs.
The sinking OF a section Of the main Inc
OF the South Pacific Coast marrow gauge
Railroad a short distance south Of tho
bridge across the entrance to San Lean
dro bay opens up new problem in rail-
road engineering "a be solved. The road
bed trayerses the salt marshes bordering
the bag almost al the way from Alame-
da 20 Alyiso. ard In some parts these
marshes are very soft and cut in every
direction BY sioJghs- In many parts the
roadbed lies OF a foundation Of mud, 10
which there f. apparently no bottom;
but so long as there Is no room for the
mud 10 shift or no agent at work un-
dermining It the roadbed stays In place.
The company has had much trouble, aow-
ever. where the recent subsistence oc-
CURED. II has subsided on more than one
occasion before and IL has taken a lot
Of new material each time 10 bring II up
10 grade The difficulty grows out % the
fact that ;he road embankment at that
particular point l. swept al its base by
swift tidal current, which undermines the
soft mud stratum and causes the road
bed TO slip In a body out OF sight. leav-
INK the rails and ties hanging IN the air.
The Troublesome current Is said 10 have
a velocity Of fifteen or sixteen miles an
hour. Il i intended 10 control II b.
damning the source. thus holding the
water brought BY the rising tide into The
depressed marsh land in the lieignbOr
hood BY preventing its outflow.
TIE marshes in the EeighboThood Of
San Francisco and adjacent bays have
perpleXed railroad builders since early
days. In spots TIE mud j. so deep that
attempts to sound il have resulted in the
discovery OF no bottom. Al those points
on the north arm OF the estuary OF San
AHtoniO-that is, the arm connecting OAK
! land Greek with Lake Aerrtt-where the
steam railroads serving Oakland cross.
there is at least ll0 feet of soft mud
There the engineers We're forced 10 rely
on suction 10 support the trestling, and
the spliced piles In the middle of the First
street railroad crossing are said TO be 10
feet in length and are held solely by rhe
suction OF the mud itself.
All the pilng constituting the fOunda-
tiOn OF the ferry building at the foot of
Market street and much of the piling
driven into the made land on which the
| foundations Of most of the dig buildings
/ in the lower Market street building rest
are held in place by suction. So powerful
/ is this suction Of the soft mud that a pile
/ driven into it so far cannot be tudged by
| the strokes of the heaviest trip-namElers
used in pie-driVinE and the end of il will
| broom under the blows.
! The builders OF the California Pacific
| Railroad encountered much trouble with
| a section OF soft marsh land adjacent 10
| SuiSun Time after time the entire road
| bed sunk not only out of sight but out Of
| SOunGingS also. and a stable foundation
| was only acquired after repeated filling in
| the lower stratum of material being held
| iE suspension. IL is believed, In the body Of
/ the mud, suction preventing il from sub
| siding farther.
| The engineer Of the Valley Railroad
/ has made a mattress fOundat tion for the
| rCadbcd over the Martinez and San JOa-
| QUin marshes like the mattress fOunda-
/ tiOn which Capt. Eads adopted for the
| levees constructed by him at the mouth
| OF the Mississippi River. These mattresses
! are made OF brush bound together with
wire. and laid on the surface OF the
| marsh. Dredgers then lift the mud cut
| out OF trenches on either side and de-
| pOsit il on these mattresses. thus forming
| an en- bankment that will carry. when
| thoroughly settled. many times the weight
| IL will ever be required to carry. These
| mattresses distribute the weight evenly
| over so large an area of the soft mud un-
| deriving the marsh that ii does not per
ceptibly affect it. and the embankment Is
| practically as secure and permanent as II
| were built on A foundation OF rock.