Autobiography of Sir John Rennie, F.R.S 64
Fresh water should be laid round all the quays and warehouses, through
iron or glazed earthen pipes, and there should always be an ample supply,
either for vessels frequenting the docks, or for extinguishing fires;
and for this purpose capacious tanks or reservoirs should be established
at the most convenient places; and if these reservoirs cannot be made at
a sufficient height so as to command the highest warehouses, then the
water should be forced through the hose attached to the supply-pipes
by steam or other power, as shall be found most advisable. Gas, also,
in properly fitted pipes, should be distributed over the quays and
warehouses, and the movable lights should be as few as possible; those
that are used should be properly guarded, so that all risk of fire from
them may be avoided. No lucifer-matches should be permitted in any part
of the establishment, nor should smoking be allowed. By these means the
probabilities of fire will be reduced; and if, notwithstanding these
precautions, a fire should break out, there will be the most ample
provision for extinguishing it in the shortest possible time, and with
the least damage to the property.
With regard to architecture, that strictly belonging to the office of the
civil engineer is of the most simple character. The buildings should be
laid out in the best manner, and the most convenient for their respective
purposes, and thoroughly substantial. At the same time, their exterior
appearance should possess a certain degree of symmetry and dignity, so as
to impress upon the spectator the idea that they are thoroughly adapted
for their purpose. The materials should be chiefly iron, stone, and
brick; and timber should only be used when absolutely necessary. At the
same time, although it is not altogether necessary, the civil engineer
should have a thorough knowledge of the five orders of architecture,
and the mode of applying them; the principles of constructing and
equilibrating arches of all kinds must be thoroughly understood; and if
he intends to combine the practice of domestic and public architecture
with that which is only strictly necessary for civil engineering, then he
must enter more largely into the subject, and study the different ancient
and modern styles of building.
Surveying and levelling will also form an important part of his
duties. In order to understand them it is necessary that he should
know thoroughly plane and spherical trigonometry, and the calculations
necessarily connected with them. He should also have a certain knowledge
of astronomy, to enable him to calculate the tides and other phenomena
connected therewith, and to be able to lay down correct charts of any
harbour or sea coast, with the soundings, currents, and winds prevailing
there.
Geology will form another important department of study, without which he
cannot understand the nature of the materials that he will have to deal
with, such as stone, lime, cements, earths, &c.; the angles at which they
will stand in making deep cuttings and embankments; the best and most
durable kind to be employed in any particular work, the proper mode of
working it, and how to place it in the best position so as to resist the
effects of the atmosphere or running water, the concussion of waves, &c.,
in the most effectual manner. The study of geology will further enable
him to account for the formation of shoals and any given line of coast,
together with the operation of the currents upon them, and the best mode
of remedying their disastrous effects; also the best plan for designing
and constructing harbours on each particular coast or situation.
Again, by having a thorough knowledge of the strata and formation of any
given district of country, he will be enabled to ascertain where water
may be found, and in what quantity; and if he practises mining, he will
be able to predict with tolerable certainty where different kinds of
minerals may be obtained, such as coal, iron, lead, copper, tin, gold,
silver, &c., and the mode of working them to the greatest advantage.
In fact, geology combined with mineralogy he will find to be of most
essential service in almost every department of civil engineering.
_Embankments._--This is another department of engineering which requires
a good deal of skill and judgment, particularly along an exposed open
coast, where lowlands are to be protected against the encroachments of
the sea. The first point is to select the line of embankment in such a
manner that there shall always be in front of it a good foreshore, so
that the force of the sea may be broken before it reaches the embankment;
that is to say, where practicable, to have a certain extent of green or
outlying marsh in front of it, so that the embankment when completed
will seldom have a head of water to contend with at high tide of above
six or seven feet. And even with this moderate depth at high water, when
exposed to the action of a heavy gale of wind, there will for three or
four hours be a considerable broken sea, calculated to do a great deal
of damage, if the embankment be not properly constructed. Now, if the
embankment have a good green foreshore in front, with sea slope of about
5 or 6 to 1, well sodded up, a facing of clay about 18 inches thick, 6
feet above the highest level of spring tides, the top being 6 feet wide,
with back slopes of 2 to 1, with a back ditch 10 feet from the foot
of the inner slope, the interior of the embankment being composed of
sound earth well rammed or pressed together, so as to make it solid--an
embankment of this kind will be able to resist such a pressure as we may
ordinarily expect it to be exposed to.
There may be extraordinary cases where this will not be sufficient. When
these occur it will be necessary to pave the surface with stone, about 9
inches thick, or with fagots. The former is, however, decidedly the best
plan, as it will be permanent, whereas fagots are constantly rotting, and
require renewal.
If the sea shows a tendency to carry away the foreshore, it must be
prevented, by means of jetties so disposed as to collect the alluvial
matter held by the sea water in suspension. These, if properly designed
and constructed, will generally have the desired effect.
In cases where the water outside is deep and the sea face of the
embankment may be exposed to a head of water of 12 feet and upwards,
much greater precautions must be taken to guard against accident. The
sea slopes of the embankment must be increased to 7 or 9 to 1, well
faced with clay and paved with stone, having the foreshore in front well
protected with jetties. In fact, no two cases will be alike: each must
be treated separately according to the particular local circumstances,
and therefore it is impossible to design a proper plan for any embankment
without knowing all the local circumstances. The general principle is
that the sea face of the embankment should never be less than from 4
or 5 to 1. In some particular cases a less slope will do, say 3 to 1.
This, however, certainly depends upon local circumstances. The base of
the outer slope should be particularly watched, and if any crack appears
to be forming, it should be immediately stopped by jetties carried out
as far as necessary. In forming embankments it is usual, when it can
be done, to take the earth from the outside of the sea slope, but this
should never be done within less than 10 yards from the base of the
slope, and these “_floor pits_,” as they are termed, should generally not
exceed 12 to 18 inches in depth, and be increased in width in proportion
to the quantity of earth required for the bank; at every 10 or 15 yards,
in the longitudinal direction, the earth should not be removed, but left
to form small cross banks between the floor pits, so as to prevent any
current being formed in them; thus these floor pits will soon be filled
up by the alluvial matter brought in by the tide, when the outside slopes
of the bank are neither exposed to the heavy lash of the waves nor to
strong currents. Then if they are covered with good grass sods properly
laid on and beaten into the face of the bank it may suffice, but not
otherwise. If this should not answer the slope must be increased and, if
necessary, paved with stone as above mentioned. When good clay cannot be
obtained to face the bank, then the best of the earth that can be got
must be employed, mixed with straw, well puddled with water, and laid
upon the surface of the bank in a moist state about 18 inches thick, and
then faced with stone about 9 inches thick, well rammed edgeways into it.
In cases where it is necessary to protect any line of coast against the
ravages of the ocean, the measures to be adopted will depend upon the
form and geological character of the coast to be so protected, whether
low flats and alluvial, or cliffs composed of rocks more or less hard,
and easily acted upon by the waves, rain, and atmosphere. In the former
case it will generally be found that the coast is surrounded by extensive
flat sands, and that the water holds a large quantity of alluvial matter
in suspension. The great object, therefore, should be to cause this
alluvial matter to be deposited in such form and in such places as are
best adapted to our purpose. Now this may generally be effected in an
inexpensive manner, considering the object to be attained, by a series
of jetties, either composed of stakes wattled together with fagots, or
lines of loose stones disposed in such a manner that they shall break the
rising and falling waters, and make them stagnant between the jetties,
so that they may deposit their alluvial matter. In the first instance
these jetties need not be raised more than two feet above the level of
the sand, and when the sand or alluvial soil has accumulated up to the
top, they may be again raised to a similar height, and so on until the
soil in front of the coast has been converted into a green marsh; thus
there will not only be formed a protection to the coast invaded by the
sea, but fresh land may be gained in front of it and embanked from the
sea. It is impossible to explain the precise disposition and direction
of these jetties and works without a thorough knowledge of the locality,
and such circumstances as its exposure to winds, tides, and currents.
The principle however is to check the currents gradually, and in such a
way as to prevent any strong current from being formed; for if a new and
strong current should be created, not only will the alluvial matter not
be deposited, but the works themselves will be carried away, and all the
labour and expense will be wasted. It is generally advisable that such
works should be commenced near the shore, and worked downwards towards
the sea; thus, if they are properly managed, no deep pools or strong
currents will be formed behind them; and the required process of filling
or silting up will proceed regularly seaward, always increasing the
protection required, and obtaining additional land as they proceed.
In some cases, where the sea is heavy, it may be necessary to have
stronger jetties or works to relieve and protect the minor ones above
described; but these should only be resorted to in places where the
others are insufficient, or in greatly exposed situations; wherever the
minor works will suffice, as they will in most cases if properly applied
and constructed, the less heavy works are resorted to the better, as
the great object is to lead not drive Nature; that is, to work with her
instead of against her. By this means a few bricks and stakes will do
a great deal more than far greater and more expensive works. So far as
regards low alluvial coasts, these, if properly managed, will be found
comparatively easy to deal with.
When we come to rocky coasts that are wearing away by the combined action
of the sea below and the rains and atmosphere above, and where there is
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