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are due more to the unusually favorable conditions — as far as material
penetrated, absence of rock pressure, small quantity of water under-
ground, and low rock temperatures are concerned — than to the driving
methods adopted by the contractors.

In preparing their bids, those interested in this work, had to assume
that there would be a reasonable amount of difficulty, and this, no
doubt, accounts for their selection of the bottom-heading method of
tunneling, the only method known to-day, which insures absolute suc-
cess, both under favorable and unfavorable conditions. Now, as just
mentioned, there was no information available of a nature to cause
bidders to select a driving method, practicable under ideal conditions
only, and no experienced tunnel contractor could afford to gamble on
an undertaking of this magnitude.

The driving method actually adopted based its greatest expectations
on the enlargement of the tunnel, and necessitated an auxiliary or
pioneer tunnel. Ventilation alone did not call for an exceptional
ventilation system, as has been proved during past years, in connection
with the driving of tunnels from 5 to 9 miles long, driven under far
less favorable conditions than those at Rogers Pass.

Had an intense ground pressure developed over a long section, or
over several short sections, then in order to keep within the schedule of
progress, the method of enlarging the bore at one point only would
have necessitated such radical changes as to jeopardize the success
of the enterprise. In Rogers Pass Tunnel it was possible to enlarge

* New York City.



472 DISCUSSION ON TUNNEL CONSTKUCTION METHODS

Mr the tunnel at one point only, and an obstacle, such as intense ground

^^^ '■ pressure at the enlargement point, would have necessitated keeping

the timbering, and probably also the masonry lining, close to the

enlargement ; and thus the blasting and mucking operations would have

been greatly hampered.

On the other hand, the method of enlarging the bore to full section
from several working points, as used for instance in the Loetschberg,
Hauenstein, and Grangs Tunnels, in Switzerland, possesses the advan-
tage of being adaptable both in light and heavy ground, and, under
favorable conditions, such as met in Rogers Pass Tunnel, the drilling
and blasting operations are at least as economical as those used in
the last bore referred to, the only differences being the temporary
heading timbering and the removal of the two side benches adjacent
to the heading.

It may be useless to point out here that the removal of the benches
could have been done with air-operated shovels. It is questionable,
also, whether the total cost of driving this tunnel by the method
actually adopted was less than it would have been by using the
bottom-heading method. In the first place, the pioneer or auxiliary
tunnel method involves practically two headings instead of only one,
as used in connection with the European method; for, in this case,
the length of the pioneer tunnel, together with the cross-cuts, is a
little more than 20 000 ft., and, of course, this auxiliary tunnel is
chargeable to the main bore. Then, also, it is questionable whether
the weathering or ground pressure will not incur maintenance charges
in connection with the pioneer tunnel and the cross-cuts, in order to
avoid disturbances of the rock surrounding the main bore. The
practice, also, of not lining the main bore at the very outset is open
to criticism, as it is always desirable to prevent initial disturbances
from taking place in the overlying strata, especially in deeply overlaid
tunnels, rather than to check these later, perhaps under operating con-
ditions in the tunnel.

The speaker, who made a careful study of the proposition, figured
that, on the assumption of a daily progress of 20 ft. from each portal,
and assuming that one-third of the tunnel would necessitate temporary
timbering, also that the masonry lining would follow close to the
excavation, the cost of driving this bore, with a bottom heading,
would be $5 per cu. yd., exclusive of contractor's profit. Mr. J. G.
Sullivan has stated* that the cost of driving the tunnel through rock,
including the cost of driving the pioneer tunnel and the cross-cuts,
'^will amount to a little less than $5 per cu. yd. for excavation in
the tunnel proper."

In comparing the costs of different methods, the mistake has often
been made of comparing short tunnels with long ones, such as the

* Engineering Nmos, February 24th, 1916.



DISCUSSION ON TUNNEL CONSTKUCTION METHODS 473

Simplon or the Loetschberg; for, it is a well-known fact, that the Mr.
cost per linear foot of long tunnels is higher than that of short ones. ^"^ *'
For instance: for the first kilometer of the Loetschberg Tunnel, the
cost was $160 per lin. ft. including lining; the cost for the seventh
kilometer (center of tunnel) was $224 per lin. ft., the average for the
whole bore being $201.65 per lin. ft.

On the other hand, the cost of Rogers Pass Tunnel can be compared
favorably with that of the more recently completed Hauenstein Tunnel,
26 680 ft. long, driven under conditions very similar to those encoun-
tered in Rogers Pass Tunnel, although less favorable. The wages paid
in connection with the Hauenstein Tunnel were higher than in the
case of the Loetschberg Tunnel, being about half as much as those ^
paid at Rogers Pass Tunnel.

On the other hand, the tunnel was driven 20 000 ft. from the south
portal, the remaining 6 680 ft. being driven from the north portal, and
this alone increased the cost. Another feature of material importance
is the fact that the bore was lined throughout, the masonry lining being
kept close to the excavation. This feature also complicates driving
operations, and increases the cost of excavation by about 50 cents
per cu. yd.

Finally, the mining operations had to be carried on very carefully
on accoimt of swelling ground, and at several points masonry inverts
had to be provided; yet the cost of excavation was less than $2.70 per
cu. yd. Had it been possible to line this tunnel after the completion
of the excavation, and, also, had the tunnel been taken out equally
from each end, there is no doubt that the cost for excavation would
not have been more than $2.25 per cu. yd.

This bore was driven at an average speed of 750 ft. per month
for the heading, for a whole year (maximum 1 030 ft.), and at the
rate of 658 ft. per month for stoping (maximum 870 ft.), also at a
rate of 656 ft. per month for enlarging to full section (maximum 850
ft.) ; and the masonry lining was carried on at the rate of 650 ft.
per month.

Robert A. Shailer,* M. Am. Soc. C. E. — The speaker is of the Mr.
opinion that the pioneer heading, entirely outside the main tunnel
section, is a new feature in timnel construction.

Apparently, the time of completion was vital, and the fact that the
contract was completed more than 11 months ahead of the specified
time surely shows that the adoption of the pioneer heading was
justified economically.

To the advantages which Mr. Dennis claims for this heading there
might be added: that it enabled the work on the long rock tunnel to
be well under way before the earth and soft ground approaches on the

• New York City.



474 DISCUSSION ON TUNNEL CONSTRUCTION METHODS

Mr. east and west ends were commenced; also, that the pioneer heading

Shaiier. ggj-yg^j ^-^q purpose of a pilot tunnel to inform the contractor as to the

character of the rock through which the main tunnel was to be driven.

Had the speaker's opinion been asked as to the plant layout before
the work was commenced, he would have said that five boilers, each
of 150 h. p., would prove inadequate to fulfill the requirements at each
end of the tunnel, namely : 4 000 ft. of free air compressed to 100 to 125
lb., and 1 500 ft. of free air compressed to 1 000 to 1 100 lb., as well as
power for the lighting, ventilating, and pumping plants; and appar-
ently, that opinion would have been — in some degree, at least — correct,
for, the author says: "The boilers were run generally much beyond
their nominal rating", and this, as all know, is not good for the boilers
or for the contractor's pocketbook.

It is noted that there was a drop of approximately 15% from the
power-house pressure to the drills, and of 25% to the high-pressure
charging station, due probably to the pipe lines being of too small
diameter. This loss seems excessive, and must have proved expensive.

The descriptions of the various tunnel operations are clear and
concise, and the speaker thinks the members of the Society are indebted
to Mr. Dennis for this paper.

Mr. E. H. Keays,* Assoc. M. Am. Soc. C. E. (by letter). — This is a

^^^^' very interesting paper, as it explains new methods for obtaining speed
in driving long tunnels in rock.

Some years ago it was generally stated that the art of tunnel driving
in Europe was much further advanced than in America, as was shown
by the great progress in the various tunnels through the Alps as com-
pared with America's much more modest attainments. The proper
reply was to argue that the reason American engineers did not specialize
in speed was that they had no long tunnels to drive, and when, for
financial reasons, they found it necessary to speed up their work they
would soon find a way to do so. Certainly, some of their records of
late years have been very creditable.

In the writer's opinion, a large part of the credit for the great
progress should be given to the improved types of drills developed
during the last few years. Where it used to be agreed that the con-
trolling feature of speed was the time taken to drill the heading, it
is now considered that tunnel driving is a mucking proposition, and
the feature to which most attention should be devoted is the cleaning
away of the muck.

In explaining why the pioneer tunnel method was used for the
Rogers Pass Tunnel, the author states that the usual "top heading and

* Jersey City, N. J.



DISCUSSION" ON- TUNNEL CONSTEUCTION METHODS 475

bench" method was considered too slow and the "bottom heading" Mr.
method too expensive. ^^^^'

As to the "top heading and bench" method, the writer is of the
impression that it has not yet shown its capabilities as to speed, no
tunnel driving with modern drills having as yet been attempted where
speed was the primary object and where the conditions were so nearly
ideal for fast work as in the Rogers Pass Tunnel. The writer has
never used the bottom heading method, but has always heard it recom-
mended for its economy. Substantiating this claim, the writer knows
of several tunnels where it was used, but they were of such short length
that speed was of minor importance.

From a careful reading of the paper, the writer is of the opinion that
the author has not demonstrated that the pioneer heading has enough
advantages to justify its use as a standard method.

The author gives a list of reasons for using the pioneer heading,
showing various advantages which no doubt would expedite work in the
main tunnel ; but, in the writer's opinion, it would be very little. The
paragraphs explaining the location of the portals of the pioneer head-
ings, however, would indicate that, on accoimt of avoiding a lot of
soft ground work, the pioneer heading could be driven far in advance
of the main heading, but as no heading was driven in the main tunnel,
using the pioneer heading to work from, the writer does not under-
stand how greater speed was made in the main tunnel on this account.
It merely cheapened the cost of driving the pioneer heading and pro-
vided better dumping ground.

The writer assumes that the main heading was being excavated at
one face only at any one time, and also that enlargement operations
were being carried on at one place only.

Of the reasons given by the author for adopting the pioneer head-
ing, No. 2 is the only one that could tend to expedite work in the main
tunnel. Reason No. 1, treating of ventilation, should have no influence
on the speed, as the matter of ventilation at the working face can be
taken care of very well in the "top heading and bench" method, and
ventilation between the heading and portal is not important.

No. 3, of course, would not be an advantage in the "top heading
and bench method", for the enlargement operations would be close to
the heading.

No. 4 could hardly be called an advantage, for the rate of speed
depends on the enlargement operations.

No. 5 is rather unimportant.

No. 6 would also be of no advantage, as the enlargement operations
are close to the heading.

Ventilating systems, as usually put in, are disappointing. There
is no agreement as to the relative advantages of the pressure and sue-



476 DISCUSSION ox TUNNEL CONSTEUCTION METHODS

Mr. tion systems, the size of pipe to be used, the pressures, or the quantity
' of air necessary.

It may be said that much larger pipes are required with suction
than with pressure systems in order to handle the same quantity of air.
The suction system keeps the air of the whole timnel in relatively good
condition, but, at the heading itself, where the men are working, it has
the least effect. This trouble is augmented, generally, by the fact that
the pipe used is of very light weight and is leaky at the joints, so that
there may be very little air taken in at the end.

The pressure system, on the other hand, clears out the heading first,
so that the men can go back to work immediately, and ventilation
between the working fac6 and the portal is not important.

The pressures generated at the fan are usually so low that a very
large pipe is needed in order to get the volume. For economical rea-
sons, a large pipe is always made of light material, which is not
satisfactory.

The writer, therefore, on accoiuit of the foregoing considerations,
believes that a medium pressure system, using a relatively small, screw-
joint, standard steel pipe for delivering air to the heading, is the best.

On a recent job he used a Connersville blower, good for a pressure
of 10 lb., delivering 750 ft. of air per min. to a heading somewhat more
than a mile distant. The pipe was of steel, 6 in. in diameter, and the
maximum pressure was about 7 lb. The condition of the air at the
heading was always good. The heading and bench were always shot
at the same time, every 8 hours, and the blower was usually run for
about 2 hours each time.

Mr. F. La VIS,* M. Am. Soc. 0. E. (by letter). — This account of the

most successful tunneling operation in North America — and this is
said with, it is believed, due appreciation of all the work of this kind
which has been done in recent years — is a tribute to the advent of
the engineer as a director of a type of construction which requires
the planning and organizing ability of which usually only the trained
engineer is capable.

Confronted with the problems of organization required for the
successful economical completion of the long Alpine tunnels,
Europeans long ago realized that these were problems for the engineer,
and were not of the kind which could be put through solely by "pick,
shovel, and pluck," or mere driving power, unaided by a trained mind
to plan and execute.

The writer fully recognizes the value of the qualities of the con-
tractor, especially those of the railway contractor, which are very
necessary, and which engineers seldom possess. The need of planning,

* New York City.



Lavis



DISCUSSION" ON TUNNEL CONSTEUCTIOX METHODS 477

of co-ordinating the work of the organization with the plans, the Mr.
successful modification of the plans to fit both the conditions and
the organization as they develop, are, however, essentially qualifica-
tions which the properly trained engineer alone possesses.

Though this is not the first tunnel driven in North America which
has demonstrated the ability of the engineer as an organizer along
lines which require this necessary co-ordination of planning with
execution, it is the latest and most successful, and the writer believes
that the realization of this phase, of the conduct of the operations
which have resulted so successfully, is of quite as great importance
as the recognition of the successful application and improvement in
the "pioneer heading" method, important as this latter is as a demon-
stration of efficiency.

There is little opportunity for comment in regard to the methods
used. Figures are not given, though it is hoped they may be supplied
later, either by the author or by the officials of the railroad company,
showing the value of the time saved and the economy of the extra
expense involved in the speed of driving. The writer has no doubt the
expense was justified, but the author's comments would be of great value,
if he would indicate his views on the economical speed from the stand-
point of construction alone without regard to operating losses to the
railway, and on the value of the saving to the railroad company.

There is a growing tendency to give, in connection with the
description of works of this kind, either exact or approximate costs,
and it is rather to be regretted that they have not been stated in this
case, as such information has a distinct value, and its suppression is of
doubtful utility to the railroad company or the contractors.

The paper is filled with instances which show the careful continuous
study of conditions and improvements in details as the work pro-
gressed. Many of these latter are not altogether new; some of them
have been advocated by the writer and others; but as their general
application to tunneling is by no means common, even yet, it seems
permissible, even at the risk of repetition, to refer briefly to some of
them :

Ventilation is a sine qua non.

Bonus system used.

Hammer drills used entirely, columns carefully set with relation

to line and grade, holes pointed by clinometer.
Three helpers were used for each two drills.
Fuse was used instead of batteries for blasting.
Water was used to wet down the muck pile and wash the dirt from

the sides, roof, and face.
Muckers have brief rest between each carload.
Mucking sheets were used.



Sanborn



White



478 Discussiox ON tunnel consteuction methods

Mr. There is also one statement full of significance to those who have

^*^'^' had much timnel experience, namely, that "The plant was properly-
put in and properly looked after, and caused practically no delay".
This epitomizes the attitude of those responsible for the conduct of
the work, and indicates one of the most important reasons for the
success attained.

Mr. James F. Sanborn,* Assoc. M. Am. Soc. C. E. — The speaker has

been asked to call attention to a volume, now being prepared regarding
the tunnels of the Catskill Aqueduct, recently completed. Dr. Charles
P. Berkey, of Columbia University, the Geologist of the Board of
Water Supply, is imdertaking to collect, as far as possible, information
for a comprehensive history of the geological features which had an
important bearing on the tunnel design and construction of the
several long siphons and other structures of the Catskill Aqueduct.

It is hoped that this voltune will bring out some of the finer points
of tiuineling. Usually, a tunnel is driven, and one never hears any-
thing more about it, unless, like Mr. Dennis, somebody has the courage
to describe it in a paper.

Mr. Lazarus White,* Assoc. M. Am. Soc. C. E. — The speaker visited

Eogers Pass Tvmnel in September, 1915, when it was being driven
at about its most rapid rate. The profile (Fig. 1), shows that the
mountains are only 9 000 ft. high, but, to the speaker, they looked as
though they might be 19 000 ft. It was raining at the time ; the moun-
tains were covered with snow and ice ; and there was snow in the woods ;
but the tunnel was dry. The work had then been advanced more than
2 miles from the west end and there was just a little trickle of water
coming out of the entrance.

The rock was "made to order". It was one solid block, as far as
could be seen, practically without faults or the disturbances usually
found in rock, and, to the speaker's unpracticed eye, it appeared to
be a hard shale or slate. He would hardly classify it as a hard
quartzite, as Mr. Dennis does; but he probably knows.

The pioneer heading method appeared to be a very good one for
that place, and the whole scheme of the tunnel and its execution a
very good piece of work. In the speaker's opinion, it was the first
successful combination of the Swiss and the American . methods of
tunneling. Other attempts have been made to combine the two
systems, but they have not been successful, either financially or other-
wise. This project, however, was successful in all respects.

The pioneer tunnel was of quite a small bore, and, as Mr. Dennis
has stated, it served primarily for ventilation, because through it
any quantity of air was sent around the heading, and blew out the
smoke. The tiuinel was both the driest and the best ventilated of

• New York City.



DISCUSSION" ON TUNNEL CONSTRUCTION' METHODS 479

any the speaker has visited. On account of the extensive blasting Mr.
that was done, it must be realized that the ventilation had to be well
nigh perfect, because from fifteen to twenty rounds were set off in
succession in order to break up the rock ahead of the steam shovel.

In any ordinary method of tunnel ventilation, this would have
made the work difficult, if not impracticable, but, with this pioneer
tunnel, the air was sent around and blown through the main tunnel.
There was an immense fan in the pioneer heading through which there
was always a strong wind blowing.

The most original part of the pioneer heading has a strong resem-
blance to the double tunnel of the Simplon. The main heading was
more of a center heading than a bottom heading, and, by working
within it, the men had plenty of time to do their drilling in the face,
which previously had always limited the progress. In this case it
did not; the blasting was done as rapidly as the shovel could take
the muck. That shovel, of about 40 tons capacity, was worked just
as hard as any shovel in the open. It loaded full-sized, 12-yd. cars,
and there was continuous and very good service rendered to the
shovel, with no interruption.

The speaker believes this progress could not have been made if
the rock had not been so exceptionally good, because timbering would
have delayed the work, and probably the method would not have been
successful if much timbering had been required. Eventually, it will
be necessary to concrete more of this tunnel than has yet been done,
because the rock may weather.

Another feature, not brought out very strongly in the paper, which
contributed very largely to the success of this tunnel, was the drills
used. The speaker believes they were little water-fed drills. With
these it was possible to maintain the high rate of progress in the
heading, and they contributed very largely to the success of the work.

The camp was very well kept, but the speaker was surprised to
note that the power plant was of such small capacity. The working
organization was very effective, and, without intermission, sustained
the undoubted record-breaking progress with which this tunnel must
be credited. This organization, the speaker is informed, was brought
from the United States, where the men had done some very rapid
work on the Gunnison and Laramie-Poudre Tunnels.

The wooden water pipe, used for ventilation, served its purpose
well, and was much superior to the ordinary iron pipe. It was well
laid, and the joints were so tight that the exhaust could be conducted
through it.

T. Kennard Thomson,* M. Am. Soc. C. E. — Mr. Dennis deserves Mr.
the thanks of the Society for his very interesting paper, but it is to be
hoped that he will add many details before its final publication.

• New York City.



Thomson.



480 DISCUSSION ON TUNNEL CONSTHUCTION METHODS

Mr. The speaker understands that the report of the late Virgil G.

Bogue, M. Am. Soc. C. E., is a masterpiece of one of the foremost of
old-time railroad engineers, and it would seem that its publication
in full, in connection with this paper, would be of great value to other
engineers and students. For that reason it is hoped that the author
will prevail on the Canadian Pacific Railway Company to allow its
publication in full.

Mr. Dennis' paper is of special interest to the speaker because he
was engaged on the location and construction of the Canadian Pacific
Railway from Medicine Hat to the west slope of the Selkirks in
1883-84-85. Haste, the key-note then, as it seems to be still, resulted



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