The daily union., 1852-04-08

SIR On the subject oil the resolution oil the Senate oil the
10th instant relating 10 the foundations oil the extension
Of the Capitol, referred by you TO on the 22d with
request tor opinion, have The honor 10 state that,
after examination sufficiently minute to satisfy our
minds, we have come TO the following conclusions on
the different points presented.
81. As the uniformity of that strata upon which the
walls rest"
Excavations were made under our direction the four
OF the worklhat is, at the northeast and
northwest of the north wing and the southeast
and southwest corners Of the south wing These
yatons extended from six 10 ten feet below the bottom
of the foundations, except the latter point where it
went only the actual level of the bottom of the oun-
daton. The ground on which the foundations laid
thus examined, as well as the underlying stratum,
at three poAts and enabled TO express conf
dent opinion that the stratum OF gravel several feet
thick (overying stratum OF hard sand,) on which the
foundations rest throughout is OF uniform incompress
bilty and that there reason to appehend settle
ment OF the walls from giving way.
-. A, to the quality and the dimensions of the stone
and quality OF tho mortar used
The quality OF the stone (gneiss. commonly called blue
rock) is excellentprobaby better could be obtained
for foundations As general rule, the stones are OF
decidedly large Dimensions. In some few places, the
small stones generally used in construction TO ill up
in larger quantities than would consider desirable,
but nowhere TO excite apprehension TO the sta
bility OF the structure.
The mortar used for the bedding or lower part of the
foundation, resting directly on the ground is throughout
of hydraulic cement and sand as il should be- In
other parts mixture OF cement and lime with the sand
was used in good proportions In other portions-say
about one bali OF the whole above the beddng-no hy
drauc cement used in the mortar This we con-
sder error, pure lime mortar OF the common fat
mes without cement. will never set in the interior of
thick walls
The best illustration of the truth Of this will be found
inspection OF the specimens of mortar submitted here
with 10 the committee. Specimen was taken from the
foundations OF The northwest corner OF the main bu ding
Of the present Capltolaken from about foot inside
the face OF the wall II laid nearly fifty years ago,
and is now soft and without cohesive power Specimen
B was taken from the foundations OF the southern
wal Of ma ding pf CaDit laid
some seven or eight years ago in making repairs This
mortar is similar IN character 10 the first. Specimen
was found on certain stones cut out years ago. OF
the cellar walls under the rotundo where the furnaces
were put in. This specimen is much drer than the
others, owing to its exposure to the dry and hot air Of the
but il will be perceived that is nearly
as destitute Of cohesive power the other.
IL is by means 10 be understood, however, that The
stability OF wall is to be considered dependent upon
the OF cement The Introduction OF cement into gen
ep has been Of quite date in this country and
in many large and substantial structures particle
has been employed.
80 As to the character Of the work the mode Of It's
suucton, and its power Of resistance"
The character OF the work and the mode OF construc-
lion consider excellent, with the exceptions alluded
and in part do perceive DEFICIENCIES warrant
in US apprehension as TO the power OF these lounda-
tons to resist The pressure OF the superstructure
tmay be proper under this head TO notice feature Of
the construction proposed by the accomplished architect
in charge. Immediately upon the foundation walls, as
existing, he proposes to lay two courses OF
sonry-making depth of four ieet--composed of the
largest sized blocks, carefully laid in cement mortar
without lime this 10 equalize the pressue OF the su-
pesiructure the whole thickness of the wa--an
excellent arrangement, which TO TO promise full
security against any anticipated danger
aih inieHogaory. Under this general head we have
perceived nothing calling for further remark
We respectfully, therefore, submit II as our opinion
that the existing foundations sufficient for their pur-
pose.
Respectfully submitted
FRED A. SMITH,
Captain Engineers.
J. l.. MASON,
Captain Engneers Brevet Lieutenant Colonel
Hon. r. M. 4. HUNTER
Chairman OF the Committee on Public Buildings,
II. s. Senate