The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1894-07-24
DUE TO PERCUSSION.
Engineer Thomson's Opinion on
the Broken Sewers.
NATURE OF THE FRACTURES.
The Theory OF Explosion Rejected on
Close Standardization the
Breaks Occurred.

While he will not report for several
days. City Engineer Thomson has come
10 the conclusion from the investigation
he has SO far made of the broken sewer
pipe, that the breakage is due
not to explosion from within, as
was supposed at first. but to per-
cussion from without, due to lack
of care in back filling and to the use of
some lengths of soft-burned pipe in wet
ground. Mr.. Thomson not only explained
the grounds for this belief regarding all
the broken pipes he had seen so far In his
examination, but took Posr-ISTELI-
GEscER reporter to the sewer he has
opened on Kenny street, south of REM
ington avenue. and showed him the nature
of the breaks.
AT that point there are two groups OF
broken pipes separated by stretch OF
sound pipe running through place where
il was run through tunnel instead of
being laid in an open trench. In one OF
these groups there were twenty-eight
lengths, OF which three are broken
| into small pieces, and were
taken out without difficulty,
while twenty of the remaining
twenty-five we apparently soft burnt and
are generally broken lengthwise in three
or four places. One break runs in almost
a straight line along the bottom of
the group, another runs along each
side and another along the top, though
occasionally one cuts across the length
of the sewer and sets free a triangular
piece. In the more southerly group the
pipes are not so much broken. In both
groups the circular form of the pipe has
caused the broken pieces to form an
arch and thus has prevented cavern.
The ground in both places is wet and
ciayey and in such weather as prevailed
when the sewers were built il would form
in grS=s sticky clods.
These are the facts as observed by the
reporter. and Mr. Thomson. in drawing his
conclusions from them, said:
81 have found nothing to support the
theory that the pipes were broken by ex-
| piosion from within, and have seen no
breaks so far which do not attribute to
percussion. Some persons have been in
| elined To ridicule this percussion theory,
rs they cannot see how shoyeifuf of
earth thrown on q pipe can break pipe
which will stand strain of 6000 to TO-
/ 600 pounds, but the principle OF percas-
sion is used in practice every day. If you
rest tack hammer on the head OF
tack II Is pressing on the tack in the
Stitc way tidt vic dlTCSL pressure Is
brought to bear on the pipes IN testing
them and will never drive it into
| the wood. but if child lifts
| the hammer and strikes the tack
| With 1t he will soon drive it In.
That is the principle We use IN
| driving piles, for We simply let hammer
drop on the pile and not only drive it
! into the earth but smash the head In
| like manner. If you take a ciod of wet
| clay and drop IL twelve feet on one of
these pipes, it will strike with many
times its weight. 1t will strike with
| the force of the square of the velocity per
second multiplied by its own weight,
| which will often exceed the breaking
| pressure to which the pipe has been sub
| jected.
In every place / have seen yet where
| these pipes are broken they are in wet
elayey earth. Before being laid in the
! trench each pipe was tested for
/ soundness by being struck with
/ mallet, having already been tested
with breaking pressure, and all
which did not give clear ring were re-
! jeeted. Some pipes were burned softer
than others, though all stood the test, and
| this caused slight variation in size. In
| order 70 make them fit as well as possible,
| the pipes of the same size are punched to-
! gether. and thus the soft lengths
/ are in groups. Where these groups have
1 occurred in wet ground the breakages have
! occurred. The pipes were first covered
with about six inches of earth. and then
/ the back filling Was put in, the men
| having orders to throw small shovelfuls
/ lightly and to send them against the bank
and not directly on the pipe. But this wet
| clay forms in great clods and sticks 10
| the shovel SO that while the foreman's
back was turned q workman would
| be apt to take a large shovelful
| and. IL il stuck to his shovel, would shake
ii off with some force, or he might kick a
| large clod weighing as much as fifty
pounds into the ditch. Try how heavy
this wet earth is. (Mr. Thomson here
| handed the reporter shovelful of earth
which must have weighed at least twenty
pounds.)
The repeated strokes of heavy earth
falling from height of from seven To six
| teen feet would be very likely to break
| pipe that was ordinarily sound. as
| the experiments made by Sir Joseph
| BaZalgette near London would show.
He took i2-inch pine which had
| stood pressure of nearly 1900 pounds
and dropped an iron bail weighing four
teen pounds on it from heights of tive to
| seven inches and broke it TO pieces At the
! forty-ninth blow, while some pipes broke
with very few blows"
Mr. Thomson will continue his exami-
| nation all through this week. and will not
| conhne himself TO the sewers laid in this
city. lie intends TO extend them 10 some
| pipe sewers laid in Ballard and Olympia
aad will present an exhaustive report on
the subject 70 the board OF public works
| next Monday.