The Portland daily press., 1897-04-09

through the screw in the order In which
they are encountered. A perfect record
of the condition OF the ground, with THE
| depths of the various substances nm
| ehrthed, Is obtained. For very large
steel buildings, however, 1t lis necessary
and safer to rest the foundations on solid
rocks.
This is done by sinking caisson hollow
| tn hes, which are forced or screwed down
through the various clays and gravel to
hardsspan. When these hollow steel tubes
strike the rock they are firmly secured to
| it. Then they are filed with concrete.
The concrete hardens into rock, which is
rendered all the stronger by Its steel coat
ing, and the whole affair becomes pill
lar of rock, sheathed with steel and ex-
| tending from the immovaple backbone OF
the earth itself to the surface. Inc mod
ern sky-scraper may then De salo n
many cases to. stand upon stills. Nothing
| can alter perceptibly it's sol1dlty mot
| even the winds, the swaying power OF
which cannot prevail against the Ifuss
formation of the structure itself. Ihere
| Is one power whion does at times arrest
the sta bility Of the sky-scraper. This Is
she sun. The 1mmense amount OF iron
| In the structure lie acted upon, and to
certain extent expanded and contracted
as the rays change their direction but not
enough to cause any fear Of disaster. In
bridges. showever. this expansion and
contracting Is very kmarked. In con-
crete fioored bridge the whole structure
VIII bend backward and forward as the
| DAY passes to the extent of one-Quarter OF
an inch, but in iron bridges, suoh az
are used by railroads, the "'draw" may
go several inches out of plumb. This il
| the reason why on drawbridges the rail.
| road tracks are conn ected by haring
! tracks or what is technically known as
a Y.
In tall buildings the greatest amount
OF engineering skill Is required in the
foundations. The building itself is after
all superstructure. 1t Is the foundation
| that requires the:engineer's greatest skill
for sometimes the conditions are most
adverse. For instance, in lower New
YORK water is encountered at very shall.
low depths, and 1t is in this lower section
| that most of the Sky-scrapers ara built.
The Commercial Gable building is eigh-
teen stories high. Its foundation floor
Is eighteensfee below the ssurfaee water
level and at least ten feet below river
| level. Yet the lowest sub cellars are as
dry as punk. They were made SO by
means OF the intricate and extended Gals
son system. The water is entirely ex-
cluded. When such low levels are reached
the contractor has really US much to no
| ind preserving the integrity of..the sur
rounding buildings and streets as he has
| ia economically carrying on his excava-
tions. The laws are very stringent in
| regard to a cave-in, and municipal law
suits are sure to drain ones pockets In
some places, however, in spite of the most
extended Snoring up" there is sure to
be curve in the nearby strait liDes.
Recentlyfin thisscity at deep excavation
person could, by going some distance
up, gaze along the car tracks and discern
part of an immense quadrant, formed by
the tracks where they had followed the
sinking of the ground toward the exca-
walton,