The Sun.
London, England, 1864-03-23 00:00:00

THE BRADFIELD RESERVOIR,

(From the Mechanics' Magazine.)
The first essential to the construction of a good embank-
ment is excellence of material, Unfortunately the Loxley
valley, whatever its other advantage, in this respect was
lamentably deficient; clay for puddling was scarce and bad.
The hills at either side consist for the most part of a loose
blue shale, which no care can render impervious to moisture,
or lapse of time feirly consolidate. Nevertheless, nothing
else was to be had, and, such as it was, it must be used,
The works were tmdertaken by Messrs. Craven Brothers,

under terms of which we as yet know nothing. The engi-
neering difficulties involved were very moderate. No springs
were encountered, no slips of any magnitude took place.
Dykes have been made before now of poorer stuff than shale.
Sand, loose earth, even shin'le, has served a good purpose
in the time of need, and as the dam was not called on to

sustain any pressure due to water, until its constructors
thought fit, the practical details of its formation involved
none of those troubles met with in the building of sea walls,
or the rearing up, tide by tide, of embankments intended to
rescue land from the sea. Even after its completion,
when in actual use, it was exempt from the action of
waves, as nothing worthy the name could be formed on a
narrow land-locked pond of a few score acres. Like
all similiar structures, it consisted of a central wall of clay
puddle, supported on either side by retaining banks, in
the present case formed of the shale or earth dug from the
bottom and sides of the valley. In length the embankment
extended about 400 yards, with a height of nearly 90ft. The
_ _

top, we are told, was extremely narrow. The width of the
base is variously stated. The Times, with its usual disre-
gard for scientific accuracy, sots it down at but 40ft, From
more reliable resources we are inclined to estimate it at
about 2701 t. or 300 ft. Inasmuch as the embankment was
not destroyed from below, was not " blown up," in fact,
this is a matter of minor consequence--at present, at least.
The Sheffield Waterworks Company has, it appears, of late
found full employment for its capital, and from this reason
no doubt economy became a matter of paramount impor-
tance. Now, bad the embankment been formed of much
better material than loose shale, its proper width at the
bottom should have been, at the very least 400 ft. As it
was, the course to be pursued was clear. The shale was in
itself wholly unreliable. It only remained to make the
puddle-wall strong and thick, carefully rammed and solidly
beaten together foot by foot, and inch by inch ; using the
shale merely as a retaining wall, in quantity on the outside,
and as a protecting covering to prevent attrition within. We
fail to discover that any such course was pursued. Most of
the evidence goes to show that the puddle-wall was inferior,
both in workmanship and material, while the embankment
when finished wanted breadth of base—in a word, it was too
weak. The inner side was protected by a thin pavement,
of small sandstone blocks laid without cement. We pre-
sume the slopes were concave on both sides, as they usu-
ally are in such structures. Now the formation of a mound,
for such we may call it, 1,200 feet long, 90 feet high, and
400 feet broad at the base, is a rather expensive undertak-
ing, and we have every reason to believe that the deposit of
shale was curtailed as touch as possible. The pressure on
the embankment when the reservoir was full must have
equalled more than the seventh part of the weight of the
dam. Nothing retained it in its place and prevented it from
sliding down the valley save the friction—due to its weight
en the surface which supported it. We cannot estimate the
co-efficient of this friction at more than half the insistent
I weight, and we therefore find •hat the margin of safety al-
lowed, even while the soil of which the dam was composed
remained free, or nearly free, from moisture, was run very
fine indeed. It is the fashion unhappily just now to leave
little margin of safety in any of our structures, and it would
not be difficult to find embankments held to be good, re-
garded as models, and thought worthy of every confidence,
where the line of safety is quite as nearly approached, when-
ever the reservoirs of which they form a part are full, as it
was in the Bradfield bank. When we consider the Bradfield
dam was afflicced with congenital weakness, that it was a new
structure, not firmly consolidated—if shale ever can coneoli-
date—it is not difficult to comprehend how the accident, so
called, occurred. The thickness of the bank at a distance
of some 12 or 15 feat from the top, must have been com-
paratively insignificant. The reservoir had never been full
before. However carefully the first part of the work had
been executed, it was natural enough that this, the upper
portion, exposed to a comparatively trifling strain, would
receive less attention, less labour. As a result of all these
circumstances, tending to the one point, water foUnd its
way into the very heart and substance of the dam ; there,
acting as it always does in such cases, it dissolved the sole
bond which held the upper sections of the dam to those
which were lower. It reduced the co• efficient of friction
to such an extent that the upper portion of the embank-
ment seems to have been pushed fairly off the lower por-
tions on which it rested, to which it never adhered. The
water found a vent at once through a wide chasm, and
quickly wreaked its fury on the external slope of the em-
bankment, down which it poured, tearing it up al though
it had been so much running sand. The total destruction of
a vast section of the embankment followed in a moment,
and then commenced those horrors which England will not
Soon forget. It has been urged in defence of those who are
responsible, that the event must be attributed to the pre-
sence of an unusual quantity of water in the reservoir ;
to the recent formation, and almost incomplete state
of the embankment ; and to the inclemency of the
weather. The reply to all these arguments is clear. if the
embankment was not intended to sustain the strain, why
was it piled up to a height of 90 feet ? If it was not in a
fit state to receive the pressure due to this immense depth of
water, why was the water suffered to accumulate ? We are
told that up to the last the engineer in charge was reluc•
taut to draw off the water, as by doing so he ran the risk of
being unable to fill the reservoir again during the spring.
Every cubic foot stored up represented so much pecuniary
value, which he was unwilling to waste. We trust that
this assertion is unfounded. At the eleventh hour we find
him endeavouring to blow up part of the embankment with
gunpowder. Alas! all power in the matter had by that
time been taken out of the hands of man. A Government
inspector hoe bem sent down to investigate every particular