Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1891-03-31
LIBBY HILLS SLIDE.
ApLeAsANr AND INTERESTING RIDE
WITH Clry-ENoINEeR cuTsKAW.
me Phenomenon Investigated and Ex-
plainsd-s.ong Cracks in chimbersso
Psrk-The Monament safe.

The article which appeared In the DIS
PATCH Of Sunday giving description OF
the sink that had taken place in Libby
Hill and tho consequent upheaval in Main
street Just below Twensy-eighth drew
thousands Of persons 10 these points during
tbeday.
The FIRST question that presented itself TO
evsry ones mind was whether the disturb
ance mad endangered the foundation OF
The Soldiers and Sailors monument.
The answer 20 this question is that 1t has
not. Moreover. IL IL not likely that tnat
structure will be endangered by any similar
disturbance that may take place IN the
future.
THE pHrnoMENoN EXPLAINED.
The explanation Of the phenomenon at
Libby Hill is simple but interesting. The
geological formation ct that point and in
ali the eastern portion Of the city consists OF
. heavy overburden stratum OF gravel and
red and yellow clay. under which Is a
stratum OF blue clay containing good deal
OF sulphate Of lime. Az long as the water
can End an outlet from or through this
CLAW the stratum remains firm and CO.
hesive, but when the contrary occurs. as ~
often does in excessively wet weather ana
the limit of percclation Is reached, the
lower layer dissolves 70 mushy consist
ency. The consequence is the superincum-
bent stratum sinks down and the musny
blue clay Is squeezed along the line OF It's
dip or levei until IL meets with an opsta-
Gle. and then ~ forced upwards. thus up
heaving whatever is above II, just in pro,
portion as the downward pressure OF
the sinking earth is greater than tne sur
face resistance over the mush.pocKet.
There Ia, of course, lateral as wen as yer
ticai movement of the overburden, put
the former is very slight, and owing 70 the
FRACTIONAL resistance OF this overburden or
upper stratum whatever may be upon IL
moves with il, and is not in danger unless
Il be too near the line OF clearage or =
slope that has not worn TO the natural
angle Of such formations.
DRIVE WITH COLONEL cUTsHAw.
Yesterday Colonel Cutshaw, City Engi-
peer. kindly invited q DISPATCH representa-
five TO drive with him over the western
part Of the city and pointed out number
OF places where similar phenomena had &C.
curred. Along the southern face OF Chim-
borazo- Hill terrace, and across the ROAD
inst under the terrace. are several woe
cracks. That on the slope is two or three
hundred wards long. When the blue-clay
LAYER shows itself in hill or a cut about
The level of road or street ii simply oozes
out on the surface of the street or road.
ONLY TWO REMEDIES.
There are only two remedies for these
xroubles. One is to underdrain the hills
and the other is to let the mush ooze out
and fill in the cracks with safe earth. Inc
former would involve infinite labor aud
expense, and the latter answers all the pur-
poses. ,,.,,
At the eastern end Of the Church-Hill
trAtshla aYnprlpnNpn
from these mush-pockets that retaining
walls were built along both sides OF the
track for some distance, but ON occasions
waves of the substance have rolled up on
and over the walls.
COVERED UP THE DAMS.
When the road 10 the Federal cemetery
was built the approaches TO the arch over
Gillie's creek were filed in at the bottom
with blue CLAY dug from the nelgbboring
hillsides. With the fret good soaking
spell. however. the foundation clay began
TO ooze out and even covered up the re-
tanning dams that were built to stop It,.
rather curious feature of this action is that
sometimes the upheaval puff" is higher
than the surface when the sink Is there
that produces 1t.
THE MONUMENT, AGAIN.
To recur TO the question Of the safety OF
fbo monument Colonel Cutshaw said
there was fully twenty feet of gravel and
red and yellow clay between the bottom
Of that structure and the blue clay. and
he inclined to the opinion that the dip OF
the latter here was towards Chimborazo
Park. The terracing here conforms to the
moInal angle of safety, and this, with the
FRACTIONAL resistance referred 10, renders
the site perfectly secure. But aside from
that the terrace around the monument Is
10 be extended, and running through the
oyerburden and above the line or the dis-
turbance is layer OF iron about on elghth
of an inch thick.
Yesterday force Of hands was engaged
ali day in repairing the break in Main
street. As for the cracks on Libby Hill
and along the road under the Chimohrazo
terrace. Colonel Cutshaw said that the
only thing TO be done was to ill them IN
with good gravel and clay.
THE DIspATcHs THEORY SUSTAINED.
Colonel Cutshaw's experience bore out
the theory advanced by the DISPATCH sun
dav that the irregular natural terracing on
the south side OF Libby Hill was due to O
series of such movements.
Colonel Cutshaw is the implacable foe of
blue clay, ard SAID during the drive that
about the worst fight he had ever had with
IL was on williamsburg avenue between
Main Cor Rocketts) street and the gas
works. Here, however, nature has rem
dered some compensation Cor the trouble
she has given the City Engineer by depoS--
iting several layers of good moulders'
sand.
As might have been expected the small
boy was very numerous" along the
cracks yesterday, and seemed to be INDUS
triously engaged in trying to get iimo
n A do "a lQndClf1n