The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1893-04-22
THE SEWER TUNNELS.
Progress Made at Lake Union
and the South End.
CURIOUS EXPERIENCES HAD
EDofescence On the Brick and Aeidity
Of water-DiMealsies Eneo1n.
tered and Overcome.

now In view OF the proposed issue OF Oonds
to complete the Lake Union tunnel. The
amount already provided for the south
sewer tunnel will probably not be ex-
ceeded. Yesterday Posr-INTELLrGEycER
reporter questioned City Engineer Thorn
son as to the Roadway made and the pros
poets of completion.
How are we getting alongf Well, by
hard work and patience, we are progressing
favorably in both tunnels" he replied.
For bad ground. our Lake Union tunnel
has scarce had an equal in the annals of
the works of any American city. During
the past week or two We have had pretty
good ground, however, and it looks as
though her last days were to be her best.
There remains about ninety feet of excava-
ton between faces and about 1000 feet of
masonry to be put IN.
The most interesting chemical studies
In our work have been the action of GER
tain veins of water struck. and the effior-
escence of some of our brick work. Early
in the construction of the tunnel. Mr..
Aibro Gardner, my predecessor, found
several veins of very acid water. So acid
was one of them that new shovel having
been accidentally thrust into the soil be-
side 1t. the workman removing il from the
soil a few days later found the steel eaten
through in several places. Another work
man having accidentally taken drink of
the water, was made deathiy sick. These
springs still run little.
1.-THE efflorescence on our brick work has
afforded us some interesting study. A few
weeks after the completion of any section
of our brick lining it would appear to
sweat. In some places, generally under
very wet ground, the sweating was heavy;
in other places, generally under dry
ground, it was much lighter. As this
sweat went of there was found upon the
surface of the brick work an effloresence
having the appearance of a very delicate
hoar frost. In the dryer portions there
has been but one sweat, but in the wetter
portions there have occurred two of them.
the second swea: tending to melt down
and render shiney the first deposit. and in
extremely wet ground sight moisture
seems to be present upon the face of the
masonry continuously. In our mortar We
have used four brands of cement, and have
used proportions of sand and cement vary
ing from Hto.1 to 2H to 1, but neither
the brand Of the cement nor the proper
tons of the mortar seems to make any
perceptible difference, the amount of
water in the surrounding soil appearing to
govern.
II have called the attention of a number
of masons. engineers and scientific gentle
men to its characteristics, bat none of
them had personal knowledge of just such
behavior. Editor Goodell, of the Engineer
eng Record, in letter to me under date
April II. 1893, said: your experience is
the most remarkable on record. have
asked several engineers of long experience
in masonry construction if they have heard
Of any case at all equaling that of the
Lake Union tunnel. and the answer was
invariably negative In the course of
his letter he refers to q high authority who
states that such effiorescence is produced
when the brick are burned with sulphurous
coal, and as all our brick are burned with
such Goals. am inclined to attribute the
result to the sulphur. l am having care.
full analysis of the effiorescence made, and
propose to thoroughly examine the prog
ress and result.
"How are we doing at the southf Well.
We hammer away there night and day, and
hope to show a record of about twelve feet
Roadway per day. So far the entire exca-
walton has been made in dry blue clay.
Some of the way the clay has been COM
pacted almost like hard pan, and in few
places it has been Jointly and treacherous,
but generally it has been firm clay.
always favored carrying the masonry for.
ward with the face of the excavation, but
at the date of beginning work the
way was not clear enough to do so.
but after about 500 feet had been driven
the way was opened for the use of masonry.
These first 500 feet have been timbered
throughout with heavy timbers and We
had hoped to draw them when the
masonry was laid in, but we found that
the clay had SO air-slaked rs to render
withdrawal very unsafe. We therefore
left our timber and built our masonry in
side OF il. As there is always certain fixed
expense running with all work, and as we
desired to complete the work at the earli-
est possible date, We began on masonry at
what was then the face and carried it both
east and west from that point.
''ln order to do this We were compelled
to have our little air box running from
near the portal, up in the spandrel be-
tween the curve Of our arch and the tim
Der lining. all the other space being
tamped with backflling. As soon as pos
the masonry, and when we get through
We shall pump that portion of the air box
behind the masonry full OF grout.
''The shape of our finished lining is owl
form and consists of two 'row-locks' of
brick laid in cement mortar. The great
est vertical height is six feet and the great
est horizontal width is four feet. We
carry our little railroad in this on ties sus-
pended in the bottom or point of the egg
To get the width necessary for our track
We have to set the top of our ties foot
above the bottom OF the invert. and on
these ties We have walkway laid. This
leaves our headroom rather low and en-
forces considerable humidity upon the
traveller. but it provides Us a most liberal
drainage space. For instance, if we
should strike a pocket of water we have in
the bottom of our lining and below our
waIkway and ties a space nine inches deep
and at the top twenty inches wide. which
would carry an enormous stream of water
nope, however. never to see water run
ming there until We are ready for sewage.
we have to exercise our greatest care
IN the places where We encounter 1oiuty
clay. In such places We fill all space with
either masonry or sand. Under hardpan
and through the usual firm blue CLAY We
hi all space 10 above the spring of the
arch with masonry or tanned sand.
Above that, If the roof of our excavation
Is but few inches above the masonry, the
space Is ntsed with mortar or sand. but if,
as often happens, our miners have made q
httIe too much headroom, and instead of