Autobiography of Sir John Rennie, F.R.S 65

Autobiography of Sir John Rennie, F.R.S 65

There is another point to be attended to. The base being secured, we

must look to the cliff above. Here, from the effect of rains, the water

frequently cannot get away, accumulates behind at the top, and sinks

through the fissures, when partly by hydraulic pressure and partly by

the effects of frost, large masses are detached and fall below; and as

this is continually occurring, the progress of decay goes on increasing.

Having secured the base, the next thing, where practicable, is to slope

off the upper surface of the cliff, so as to prevent it from overhanging,

and then to make a drain at the back to carry off any water that may

lodge there. By these means, if properly carried into effect, the base

of the cliff being protected against the sea from below and rainwater

from above, there is every probability that it will be preserved, in all

ordinary cases. In extraordinary cases additional measures must be taken

to meet them upon the same principles. With regard to retaining walls

of brickwork or masonry, these should be always in excess of strength

beyond the pressure, whether vertical or lateral, that they may have to

resist. When the pressure is simply lateral, then the mean thickness

of wall built of masonry and brickwork--the mean thickness, generally

speaking, of the main body of the wall--should be about one-fourth of

the height, besides counterforts at the back at certain distances from

each other, regulated according to the particular circumstances. These,

upon the average, including the thickness of the main wall, will make the

total mass to be equal to nearly one-third of the total height. My father

frequently made these walls curved in the front as well as at the back,

the front being struck from a radius whose centre was level with the top

of the wall, and of such a length that the face of the wall should batter

one-fifth of the total height; the back of the wall should be struck from

a centre at the same level as the other, but a little longer, so that

at the base the wall might be about 2 feet thicker than at the top, in

addition to two or three footings of 6 inches each; and the base of the

wall was made to incline backwards, according to the radius from whence

it was struck.

 

These walls, when they are to rest upon alluvial soil, must be founded

upon a platform composed of piles of a sufficient length and thickness,

driven at right angles to the line of the foundation, until with the

blow of a ram weighing 15 cwt. and falling 20 feet they will not move

one-eighth of an inch. These piles should be driven in regular rows,

longitudinally and transversely, about 3 feet apart, and hooped and shod

with wrought-iron hoops and shoes. At the front, immediately under the

tie of the wall, there should be a row of grooved and tongued sheeting

piles driven close together, and to the same depth as the others, about

6 inches thick, having a waleing or longitudinal brace 6 inches thick

and 12 inches wide, well bolted in each side of the top of the sheeting

piles. The loose earth should be taken out to about a foot in depth, and

the space filled in with stone or brickwork to the level of the pile

heads, which should be carefully trimmed, then covered with sills about

12 inches square, well spiked down to them. The spaces between the sills

should be well faced with brickwork, and the whole surface should then be

covered with 6-inch plank, properly spiked down to the sills below. Upon

this platform the masonry and brickwork of the wall should be built. The

wall should be carefully backed up as it proceeds with sound earth or

clay, or clay mixed with one-sixth of gravel or concrete, as shall be

deemed most advisable. These curved walls, if properly constructed, are

stronger and more economical than the ordinary walls.

 

In some cases, as in that of Sheerness, for example, the foundation is so

bad that a totally different plan must be adopted. At Sheerness it was

necessary that the base of the walls should be increased, distributing

the weight over a wider area, so that each superficial foot of the

superincumbent mass should have a larger bearing, thus greatly relieving

the pressure over every part.

 

The foundation upon which the walls were built was as bad as possible,

being composed of nothing but loose running silt and sand. Upon such a

foundation walls of the ordinary kind would not have stood; my father

therefore saw the necessity of designing some new construction, upon the

principles above mentioned. He had previously adopted something similar

for the docks at Great Grimsby, in Lincolnshire, in 1786, which design

was carried into effect with great success. The walls at Sheerness and at

Great Grimsby were built both upon the same principle, modified according

to local circumstances. Sheerness docks were finished altogether in the

year 1826, and they have stood ever since.

 

I believe that I have now enumerated all the chief points to which the

education of a civil engineer should be directed. Whilst he continues in

an engineer’s office, whatever business is brought before him, he should

always endeavour to thoroughly understand the reasons for which such and

such a work is proposed to be made, and the principles upon which it is

to be constructed; and if he finds, according to his previous education,

difficulties either in the principle or construction, he should modestly

state his doubts to his superior; if no explanation is given, he has

simply to do as he is ordered, making notes of his doubts, and when the

work is carried into effect he will then be able to ascertain how far he

was right or wrong. If the work turns out to be a failure, his previous

calculations will show him that he was right; but if the work succeeds,

his calculations were wrong, and he should carefully go over them again

to ascertain his error. He should follow the same process when he has

to design and carry into effect any work upon his own responsibility,

and if he is in doubt as to any point, let him consult some one of his

professional brethren in whom he has confidence. When he is consulted

on similar occasions by another engineer, let him give his advice and

opinion to the best of his power; by this means he will gain the respect

of his colleagues, and every one will be ready to help him when required.

 

Let him be particularly careful about his estimates; and after he has

estimated _fully_ the probable cost of a work, let him add an allowance

of quite 15 per cent. for contingencies, which in all engineering works

are so numerous and varied that it is almost impossible to foresee them.

 

We should always recollect that the great object of all engineering works

is to produce a fair return for the capital expended upon them, or, in

other words, that they should pay. If, after due calculation, it is found

there is no chance of that, they should not be undertaken; for although

it may be very gratifying to the professional reputation of an engineer

to have executed a great work, it is but a poor consolation to his

subscribers to find that their money has been comparatively thrown away

without any adequate return.

 

Upon these grounds, therefore, I think it is better that the engineer

should confine himself strictly to his business, that is, of designing

and estimating any proposed work in the best possible manner to ensure

the object intended. Let those who are most competent ascertain whether

there is a sufficient prospect of traffic to pay a good return for the

required capital; and so long as the engineer executes the work for his

estimate, he cannot be blamed if the work does not pay a sufficient

return. In fact, the whole commercial value of a work depends upon its

cost, and therefore it is so important that the estimate should be

adhered to as closely as possible, for if this be much exceeded the

commercial calculation falls to the ground, and then the subscribers

have just reason to complain. Against this I have heard it argued that

if correct estimates were always made, and the ultimate cost of many

works was known beforehand, they would never have been carried out,

although notwithstanding the increased cost they have finally proved to

be very valuable. This is certainly to some extent true; many inventions

and discoveries have ruined the original promoters, yet have ultimately

conferred the greatest benefits upon mankind; and many enterprises

that have ruined the original undertakers have greatly enriched their

successors. Still there can be no excuse for an engineer knowingly

underestimating the cost of a work; he is undoubtedly bound to make a

fair, honest estimate of every work committed to his charge, so far as

his judgment goes; having done that his duty is discharged; nothing

further can be expected of him than to see that the work entrusted to his

care is strictly carried into effect according to that estimate.

 

* * * * *

 

Since the summer of 1866 I have done scarcely anything. The great crisis

and subsequent panic that occurred at that time paralysed the commercial

world. I considered my advancing years (I was then seventy-two), and

the great hazard and uncertainty of carrying on business, and thought

it most prudent to retire. After the harassing and anxious life that I

had led for so many years, I felt my health so shaken as to require

complete repose. But I hope, if God spares me, to be still useful to the

profession and my country, by completing a work on the drainage of the

fens and lowlands of Great Britain, and hydraulics generally. I also

design to write a history of engineering, enlarged from my Address to

the Institution of Civil Engineers, and a life of my revered father. All

these I have already sketched out, and I hope to complete them, if it

please God to spare my life a few years longer.

 

My apology for the present work is this: I think it is the duty of

everyone who has led an active professional life faithfully to record

the various works in which he has been engaged, the failures as well as

the successes, detailing the causes of both; for we frequently learn

more from the former than from the latter. I believe I have in this

book faithfully done this. From unavoidable circumstances I have been

obliged to trust entirely to memory while writing these pages, having

been totally precluded from consulting notes or memoranda of any kind; I

hope, therefore, that any inaccuracies that may be detected by the reader

will be pardoned, though I believe that in the main my statements will be

found correct.

 

Like others, I have had to contend with professional jealousy; but I

believe I have on all occasions done justice to my rivals, and I have

never wilfully attempted to injure anyone. Naturally of a very sanguine

temperament, I am but too apt to view things in a favourable light, and

to judge well of those with whom I come in contact; as a consequence

of this I have often been deceived by those in whom I have placed the

greatest confidence. This sanguine disposition has been the cause of

many disappointments; but it has also enabled me to bear up successfully

against failure, and still to look forward with hope to the future.

Whenever a misfortune has occurred I have endeavoured to forget it as

soon as possible; I always called to mind the words of the great Duke of

Wellington, who said, _There is no use in looking back and brooding over

the past; forget it, and apply your energies to the future, and do better

next time_. This many people either cannot or will not do; hence they

succumb. Doubtless everyone has his trials, and some are much better able

to get through them than others; nevertheless, a very little reflection

will show that what is past cannot be helped, and that by brooding over

misfortune we do no good, but only waste our energies and invite failure

in everything else.