TIMBER PILES. PILE-DRIVING.
General Consideration.
"Now, as promised, I will tell you of a little bit of free trade with
some timber pilework."
"That's it. I am waiting for it."
"Well, they let me have 400 feet run of pile-driving. Double row of 16
to 12 inch piles, and there were some fine sticks nearly 55 feet long,
and that is a long length for a sound pile, and you have to pay for
them."
"Before you begin to tell me how you scamped it, give me a hint or two
about piling, and say what you have learned from experience."
"All right. First, when a pile is some distance below the bottom
waling, which should be fixed as low as possible, a lot must be taken
for granted, and it cannot be controlled much. I know this from drawing
many piles; hundreds, I may say. After they are down about 5 or 6 feet
they begin to do as they like, and take to irregular habits, and you
cannot be certain the points are straight unless the ground is the same
throughout, and it hardly ever is. In fact, the resistance they meet
with varies, and then they accommodate themselves to circumstances; and
even when the ground is very soft they turn to the line of least
resistance, and if they have to be driven through several feet of soft
earth to reach the solid, they may play tricks and bend about in the
soft soil in go-as-you-please style, yet seem to be driving nicely; or
they may stick between boulders and can't be driven further and appear
to be firm as a rock, and so they may be as long as the boulders do not
move, but they often do after a time, should the ground become wet, and
sometimes when the next pile is being driven.
"Always be careful to see that the shoe has as large a bearing as
possible for the end of the pile, and is long in the point, and more
pointed as the soil is harder. Take a 12-inch pile with a 4-inch or so
seat in the shoe for the stick. Well, 12 by 12 is 144, and 4 by 4 is
16, and therefore the pile end has a bearing area upon the pile shoe of
one-ninth of the area of the pile. No wonder the bottom often becomes
ragged and the pile shifts. The shoe should have a good hold of the
timber, and be put on true to a hair, so that the point is in the exact
centre line of the pile, or look out for squalls. Now high falls and
light monkeys are out of fashion, and short falls and heavy monkeys are
the thing, not so many piles are injured. Pushing them down is better
than breaking them to bits. You should have the monkey so that its
centre falls upon the centre line of the pile. The average centre of
the pile should be marked on as exact as possible, and the end of the
pile be cut to a template, so as to make it fit tightly to the shoe, or
it may not drive straightly. I always take a lot of trouble that way
and seldom have to draw a ragged one, and believe they used to drive
straight. I mean from start to finish about the same number of blows
and to the same depth and vertically.
"When hand-driving in soft earth--it's slow business at the
best--weight the pile when the monkey is being lifted so as to stop the
quivering and press it down and keep it from springing. Provided the
work was of importance, and I was the Caesar of it, before any pile was
pitched ready for driving it should be inspected, its dimensions taken,
it should be numbered, numbers be burnt in, and every foot from top to
bottom should be marked on by a brand; and perhaps the numbers should
begin at the bottom and work up, as there is not so much chance to
tamper with two figures as with one, &c.
"Pile-driving is fickle work, for sometimes the piles stick because the
points can't pierce the earth, and at others because they are held by
friction on the surface of the piles. I have known the shoe to be cast,
and the pile end look like a bass broom, and to be all in shreds. When
piles split a great deal and they must be driven, the best thing to do
is to get harder wood, lessen the fall and increase the weight of the
monkey; same as in tunnel lining, when stock bricks are crushed, blue
bricks have to be put in. The nature of the ground should govern the
hardness of the wood for piles. I always pick out darkish even-coloured
wood, and sniff for the resin, and the more in it the better for me.
You don't catch me driving many white wood piles, for they become dry
and break off short, and are not the timber for piles. Once a bother
arose about some piles. There was a layer of hard gravel, and by the
way the piles were driving I knew they would split, so I gave the word
that Memel piles were not hard enough for such gravel; and I worked it
humble like, and said to the engineer, 'I think you will agree, sir,
you can't expect me to be answerable for smashing them until we get
into the soft ground again. It wants rock elm or as strong timber for
this soil.' After smashing a few to shreds, they supplied us with rock
elm piles, and then we managed. It is true to say in the same soil the
harder the pile the better it will drive, and therefore with less
trouble and expense. The monkey should have an even widened-out base
where it touches the pile head, so as to get the weight as near the
head of the pile as possible; it also falls straighter than the long
thin rams of nearly the same width throughout. Grease the ways well,
and take care they are as straight as a die, and exactly vertical if it
is upright pile-driving, and you'll save money. Make the blows quickly
in fine-grained soil, so that it has not time to settle round the pile.
In clay there is no occasion for such quick-driving, but take care to
prevent the piles rebounding. Remember the same system does not do for
every soil, for quick driving in hard soil sometimes smashes the piles;
perhaps the earth has not had time to become displaced nicely and
settle before being jammed again, and then the pile point turns and
quivers and soon shreds, and cannot be driven down properly. Anyone
that says piles make the ground itself firmer when they are driven into
it, and so cause it to support a heavier load, will have to prove it
before that can be swallowed. It is the friction on the sides of the
piles that principally sustains them and not the bearing of the points.
In hard soils drive slowly, for it is like chipping up a stone with a
hammer. You must do it gently, or it will break the tool; and as you
can't clear out the hole in driving piles, it seems to me time is
required instead, so that the pressed out soil may settle away and take
a bearing. I tricked a chap once pile-driving from a barge."
"How did you do it?"
"Well, it was bound to be driving from a barge or nothing, and there
were three pile-drivers for us, almost as many as we could work, as the
driving had to be done by degrees. Some of the work was let to a chap I
did not like too much, and the rest to me. They gave me the choice of
plant, so I said to the engineer, 'May I have two of the pile-drivers
upon my barge, as Faggitts'--that was the other chap's name--'only
wants one.' I got the two. Now Faggitts knew about driving piles on
land, but had never done any driving from a barge, so I had a bit in
hand of him. If you take any pile-driving and it has to be done from a
barge, have more than one pile-driver on it if you have the chance; but
don't place them close together, make one steady the other, and have as
many as you can conveniently work at once; because, in my experience,
the more you have the less the swaying, and the piles drive more
regularly and the barge is steadier, and you don't have so much bother
with the moorings. Of course, if the monkey does not fall flat upon the
pile head the pile does not receive the full force of the blow in the
right direction, the pile may be driven slightly crooked and it does
not get properly treated and won't penetrate so easily, and therefore
you lose money. Old Faggitts found that out in the soft soil we were
driving them into. I said nothing to him, but he did to me. I never
told him.
"I have read somewhere that it is wearying work going into details, but
when you have to do the work yourself, unless you take care of the
details you'll find they will make it hot for you; and after all, any
one can speak generally, but when they have to explain in detail what
they think they mean, and have to do the work themselves, they will
soon find out that unless you know the details and attend to them
carefully, that you won't make a profit nor anyone else. Anybody can
talk tallish after about a fortnight's training, but then they have to
pull up or they will fall at the next fence, which I label 'details
wanted.' That's by the way, and I may have made it too strong, but it
is as well to sound your engineer. No general is successful unless he
knows the strength of his enemy and as much more about him as he can,
and acts accordingly, and chooses his own time and place for a battle.
"Driving piles in groups, especially if the ground is soft, and not
singly, is good. They go down more regularly and fit tighter, and they
seem to drive quicker. I have driven cheap fir piles between elm piles
that way, and a good many of the soft ones split when we had to drive
them singly. Have as few key piles as possible, because they are liable
to be jammed before they are down to the right depth, and then, if it
is a cofferdam, it is probable a leak will occur under the key pile,
because it is the easiest place for the water to soak through, and the
other piles being down below it, stop the flow, and it soon finds out
the short-driven key pile. When I notice a spot in a cofferdam at which
water leaks through the bottom, unless it is an old stream bed, it
occurs to me that the piles have not gone down properly, have got
bruised, bent, turned up, or broken off, and I have found out that was
the case on drawing them when the cofferdam was of no further use. Once
I was ordered to drive some three-cornered piles at the turns in a
cofferdam on a river front, but said, 'Square or circular shall be
driven, but any other shape I will try to get down properly, provided
they are carefully fitted and bevelled, but you really can't expect me
to be answerable.' They deducted a fixed amount if after the piles were
pitched there were more than a certain number visibly damaged or
smashed, so you may depend I had a good look at the sticks before they
were driven.
"I have driven piles 60 feet in length, kind of giant sticks, but 45 to
50 feet is long enough for good sound piles. Socket pile driving
piecework I avoid, for the joints are ticklish business; and if a pile
of ordinary length will not do, I throw out a mild hint whether the
better system to use would not be Indian brick or concrete wells, or to
spread out the foundations so as to get a sufficiently large bearing,
or have a fascine platform, and sink it till it is firm, and test its
stability properly by a load.
"There is a great deal in starting the driving correctly. I always am
very careful at the start, and experiment and watch how the piles
drive, and vary the fall a little until the best is known. Few
considerable stretches of ground are of the same kind, and to fix a
certain fall throughout is not the thing, it generally wants varying. I
have easily driven piles in fine sand by having two small pipes, one
each back and front, reaching a few inches below the point of the pile,
and sending water down them under pressure, and by keeping the pipes on
the move so that they can't be gripped. I worked out with the pipes the
place where the pile had to be pitched and made a profit that way,
because not only did the piles go down much quicker, and a lot of blows
were therefore saved, but the piles were easier to start right. I used
to call my two pipes the two bobbies, because they steered straight for
their station, and these two did the same office for the piles.
"Now a word as to systems of driving; the method must suit the ground.
I knew a man that believed in nothing but driving by gunpowder; he must
have been going in strong for gunpowder tea, or have been in the
militia, for the soil he had to do with was not homogeneous, and had
boulders and other hard obstructions in it. It was not like soft sand
and clay, consequently many of the piles were broken. The noise also
was a nuisance in the dock, and cattle that had to be unshipped from
the steamers were so unruly that they had to stop the gunpowder
pile-drivers; besides, to do much good with them, a large charge is
required, or it costs too much. The power necessary to work the
machines is better obtained by other means, and can be without so much
noise or shock.
"I have used all sorts and sizes of monkeys, from half a hundredweight
to four tons, but heavy rams and short falls are the best, and steam
for the power if the contract is considerable and will pay for such
plant; otherwise hand, unless the piles are large and have to be driven
a long way. A sixteen hundredweight monkey is about heavy enough to
work nicely by hand, but it is not sufficiently heavy for a 12-inch
pile, except in soft ground. For sheet piles a hand machine is good
enough, for it can be moved easily, and six to eight tons weight, being
about that of a steam pile-driver, costs something to shift, unless
there are rails and tackle handy. Of course the blows are quicker with
a steam pile-driver, and in sand that is a great point as the ground
has no time to settle round a pile; but should the soil vary and be
hard and soft, it is well to slow down the machine at first to lessen
the fear of smashing the piles and shaking them till they tremble to
destruction. I have worked a lot of different kinds of plant, and
driven many piles at once, and the power was obtained from one engine
giving the motion by driving bands, and in another case with drums
fixed on the engine shafts, the chains being carried over sheaves to
the different pile engines.
"This is my idea of pile-driving:--
"1. Steam driving. 2. Hand driving, if the piles must be driven very
slowly, and there are not many to drive. 3. Never use gunpowder
pile-drivers, always prefer steam, hydraulic, atmospheric, or some
other motive power.
"Gunpowder is more for blowing up than anything else, in my opinion,
and I know the pile shoes often shed in driving with it; that is, they
loose their hold of the piles and become detached.
"A pile should penetrate regularly, and after the first few blows drive
less and less, as then you have a good idea it is all right and
uninjured. Uneven penetration is a proof that piles are not all right,
and when they sink suddenly there is almost sure to be something wrong,
and they are most likely being over-driven, shredded, frayed,
shoe-cast, or split up. The rate of descent should be noted. It may be
considered they are driving properly if they sink about a foot at a
blow for the first one or more, and then 8 or 6 inches, and when they
get down to one-eighth, one-fourth, or half-an-inch a blow for some
successive blows it is time to stop and consider. I have driven piles
with as few as ten blows in sand with the aid of two water pipes at
work fore and aft, as mentioned before, and have had to give a pile as
many as 300 blows, and when they want as many as that, with all due
deference to everyone, the ground is firm enough to build upon for
permanent foundations without piles. My experience goes to show that
piles are often driven further than they need be, if only for use as a
cofferdam, and that back struts and counterforts are better than extra
depth in the ground, provided leakage is prevented. 8 to 10 feet down
for solid clay, 10 to 12 feet in gravel, and about 15 feet for ordinary
soils, and more care taken to ascertain the piles are where they should
be, and that they are sound and whole, and not turned aside, bulged,
and injured, would be my practice. In boulder ground, in my opinion,
piles should not be adopted; for broken, crushed, and twisted fibre
bass-broom shreds are not piles; they are out of place and should be
used for clearing leaves from garden walks. The longer the piles the
softer should be the ground they have to be driven into, or they shake
so much, and cost more to drive.
"Unless always well buried and at such a depth that neither the
moistness nor condition of the earth vary, I scarcely believe in timber
pile foundations at all, except in very peculiar cases, and as a kind
of aid to the main support or to help to prevent the toe of a wall from
being thrust forward, but for cofferdams, jetties, piers, and such
structures, of course they are useful. In hard and most gravelly soil
avoid them, and also in sharp sand, if you cannot use the
previously-mentioned water-pipe arrangement fore and aft; and although
in ordinary clays they drive nicely, and you make a bigger profit than
in sand, it puzzles me to discern what is the use of them for permanent
foundations, except to help to prevent a wall sliding forward, because
when a pile is driven into most clays the clay becomes tempered and
softer, and a layer of concrete put in a proper distance down is better
and much more certain, and distributes the load more equally. Elastic
soil is bad in which to drive piles, for it yields and then rebounds. A
pile will sometimes spring back almost as much as it is driven, and in
such a case it is well to let the ram or monkey rest on the pile
immediately after the blow is given, if you are hand-driving, or have
an arrangement so that it is weighted directly each blow is delivered,
and perhaps the best way is to hang heavy weights on the pile. In
driving in firm sand the ground at the surface becomes considerably
displaced, in clay about half as much as in sand.
"Pile-driving is different to masonry, and I always read the
specification for pile work, and then judge whether and how a bit
'extra' is to be obtained, and guess as to the knowledge of those I
have to deal with, and act accordingly. Sometimes a specification
simply says all the piles are to be driven to the same depth or as
shown on the drawings. That may be right should the ground have been
tested by experimental driving, or the nature of it be known; but if
not, I don't take much notice of the specification, because I hate
waste, and can't afford the luxury; and it stands to reason that simply
because a lot of piles are driven to the same depth they are not
equally firm, nor will they support the same load unless the soil is
exactly the same, and they drive well and regularly to the same depth
and all nearly alike inches by inches, and this seldom occurs. Often
'extra' profit is to be had, as you will soon hear described, for when
piles will not drive further than half or a quarter of an inch a blow
they satisfy me they are tight enough for the purpose intended if they
are at a fair depth and not wedged by boulders; but between ourselves,
should a building of any kind have to be erected on piles, and anyone I
really cared about had to live in it, I should always weight the piles
for as long a time as possible after finishing the driving and
reasonably more than the permanent load, watch the effects, and act
accordingly, particularly in elastic soil.
"Remember a pile sinks less after it has rested than if it be driven
continuously, therefore always take note of the set when the driving is
proceeding, and not just at the start, or after an interval, although
one does that for one's own benefit, and with a view to 'extras'; and
no one wants to drive a pile an inch more than can be helped--at least
I don't, nor have I, and it is certain never shall.
"You want to know when to stop driving. The time has arrived when a
pile penetrates very little, and nearly equal for several successive
blows of the heaviest ram by which it has been driven at the usual
fall.
"A word as to tie and sheet piles before referring to the way I have
worked piles for 'extra' profit. It is difficult to make a main pile
and a tie act together, one or the other is nearly sure to have to bear
more than its proper strain, and the tie rod becomes eaten by rust,
bent, and loose in the piles. In taking down old banks and quays you
will generally find the main pile and the tie pile are not held tightly
by the tie rod, the tie pile is loose or pulled over, perhaps when
first strained, and then becomes disengaged when the main pile has set
to the strain. The tie rods want to be very carefully and frequently
adjusted, if possible, and big washers and cleats on them are required.
They hold best in firm sand, not so well in clay, and in large light
loose soil, such as ashes, they are not much good. It is an impotent
arrangement and it is always uncertain whether they will act together.
Don't undertake to tighten up the rods. Fix the piles, and let the
engineer see to the tightening up, as you may injure the piles.
"When I have to drive a lot of sheet piles, of course the piles are
supplied to me, and I only take the driving. You may be sure the timber
is right, and that the edges are sawn square so as to drive tightly
together, and that the point is in order. I find it always pays well to
temporarily place a baulk at the ground line like a waling, but not
fixed to the sheet piling, as it guides the piles, lessens the shaking,
and they drive easier and better. It appears to me piles cannot vibrate
without force, and that is not where it is wanted, so it is wasted
motion. Agitation when drawing piles is all right, but when you are
driving you want it in the ground itself, and not in the piles. Once
when I had to drive some thin sheet piles, I made a movable guide
frame, the side against the sheet piling being planed and greased. It
was like one bay of a timber-lattice bridge, and it well paid for
itself as it steadied the piles.
"In taking a contract for drawing piles always find out how long the
piles have been driven, for if they have been down many years they will
be much harder to draw than if they have only been fixed a few months.
They can be drawn by lever, hydraulic jack, and chains, and pontoons in
a tide way."