U.S. patent number 3,885,832 [Application Number 05/436,401] was granted by the patent office on 1975-05-27 for apparatus and method for large tunnel excavation in hard rock.
This patent grant is currently assigned to The United States of America as represented by the United States Energy. Invention is credited to John H. Altseimer, Robert J. Hanold.
United States Patent |
3,885,832 |
Altseimer , et al. |
May 27, 1975 |
Apparatus and method for large tunnel excavation in hard rock
Abstract
A tunneling machine for producing large tunnels in rock by
progressive detachment of the tunnel core by thermal melting a
boundary kerf into the tunnel face and simultaneously forming an
initial tunnel wall support by deflecting the molten materials
against the tunnel walls to provide, when solidified, a continuous
liner; and fragmenting the tunnel core circumscribed by the kerf by
thermal stress fracturing and in which the heat required for such
operations is supplied by a compact nuclear reactor.
Inventors: |
Altseimer; John H. (Los Alamos,
NM), Hanold; Robert J. (Los Alamos, NM) |
Assignee: |
The United States of America as
represented by the United States Energy (Washington,
DC)
|
Family
ID: |
23732246 |
Appl.
No.: |
05/436,401 |
Filed: |
January 25, 1974 |
Current U.S.
Class: |
299/14; 175/11;
299/33 |
Current CPC
Class: |
E21D
9/1073 (20130101) |
Current International
Class: |
E21D
9/10 (20060101); E21d 009/00 () |
Field of
Search: |
;299/33,14 ;175/11,16
;61/45R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Abbott; Frank L.
Assistant Examiner: Pate, III; William F.
Attorney, Agent or Firm: Carlson; Dean E. Heyman; Henry
Claims
What we claim is:
1. An earth drilling machine for excavating tunnels comprising an
elongated hollow hull having a frontal portion with cross section
equal to the cross section of the final tunnel prior to
installation of final tunnel wall lining and a rearward portion
reduced in cross-section relative to the frontal portion, a rock
melting kerf penetrator affixed to and projecting longitudinally
forward of the front end of the hull and having a peripheral shape
similar in configuration with the front portion of the hull, a hull
closure face plate affixed to the interior of the hull at the front
end thereof, a plurality of rod-shaped thermal stress fracturing
penetrators supported in said hull closure face plate with their
direction of elongation parallel to the direction of elongation of
the hull, and projecting forward of the front surface of the hull
closure plate, rock debris removal means supported in a peripheral
portion of the hull closure plate, a nuclear reactor supported
within the hull of the machine, heat pipe heat conduction means
coupled to the reactor core at one end and to the kerf melter and
thermal stress fracturing penetrators at the other end; the rear
end of the kerf melting penetrator skirt and the front end of the
hull being smoothly joined together, thermal cooling means coupled
to the front end of the hull whereby said front end of the hull
supports the molten rock against the excavation walls and
simultaneously solidifies said molten rock into a tunnel wall
initial supporting liner.
2. The earth tunneling machine of claim 1 in which the
cross-sectional shape of the hull is cylindrical, and said rock
kerf melting penetrator segments form a cylindrical projection on
said hull.
3. The earth tunneling machine of claim 2 in which the rock kerf
melting penetrator is a single segmental cylindrical array heated
to a temperature above about 1470.degree.K whereby a narrow kerf is
melted in the tunnel rock face and the thickness of the molten zone
in the excavation wall increases, as the rock kerf melting
penetrator is propelled forwardly, due to heating by the body of
the penetrator.
Description
BACKGROUND OF THE INVENTION
The need for fast economical methods and machines for producing
large tunnels and other excavations has considerably increased in
importance with the increase in population, industrial congestion
and environmental pollution. The production of large tunnels such
as are needed, for example, for subway systems in and between
cities presents formidable tasks in excavating and removing the
tunnel core and supporting the tunnel walls, particularly the roof,
against collapse. Although progress has been made in increasing the
rate of tunnel excavation by the use of large mechanical tunnel
boring machines such as the "MOLE," many problems are encountered
in the use of such machines due to the extreme variations in earth
through which the tunnel penetrates. For example, in abrasive hard
rock the advance rate of the mechanical machine is slow because the
cutting rate is low, and progress is impeded by the frequent need
to replace the cutters, particularly the gage cutters. The
down-time of the machine and the cost of the cutters significantly
increases the cost of the project. In addition, the inaccessibility
of the tunnel wall immediately adjacent the tunnel face and
alongside the tunneling machine prevents the installation of tunnel
support where it is indispensable to prevent possible cave-in and
possible burial of the machine and crews. When very hard rock is
encountered, the MOLEs are discarded in favor of drill and blast
techniques. In this case the mechanical forces and vibration
transmitted into the surrounding earth by the excavation process
results in loosening and breaking loose excess tunnel wall material
with attendant increased expense in removal and rehabilitating the
tunnel wall as well as the dangerous reduction in the integrity of
the tunnel walls, particularly the tunnel roof.
It is a primary objective of the present invention to provide a
tunneling machine which is capable of economical excavating in rock
and which simultaneously with detachment of the tunnel core at the
tunnel face installs an initial supporting liner on the tunnel
walls.
Another object is to provide a machine and method capable of an
economical excavation rate in hard abrasive rock through the use of
a peripheral kerf melter to define the tunnel bore thereby
eliminating the short duty cycle and expensive mechanical "gage"
cutters.
Still another object is to eliminate the short-life mechanical face
cutters by incorporating in the face of the present invention
device, arrays of small diameter melting penetrators to detach and
fracture the tunnel-face rock by thermal stress fracturing.
Another object of the present invention is to provide a machine and
method for tunneling which eliminates the excessive dust, ground
shock and fumes incident to the use of the mechanical tunneling
machine or drilling and explosive practices by using the melting
process.
The above and other objectives and advantages afforded by the
present invention will become apparent with reading the following
specification taken with the drawings made a part of this
specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a horizontal isometric view, partly in section, of a
preferred embodiment of the invention.
FIG. 2 is a vertical cross-sectional diagrammatical view of the
forward part of a tunneling machine in accordance with the present
invention.
FIG. 3 is a vertical cross section of one form of kerf melting
penetrator and melt deflector.
FIG. 4 is a vertical cross-sectional view of an alternative form of
melt penetrator and melt deflector.
FIG. 5 is a diametric cross section of the hull showing cooling
details.
DESCRIPTION OF THE PRIOR ART
The utilization of the basic concept of melting earth materials to
dig a hole or small tunnel is taught in the prior art. For example,
U.S. Pat. No. 3,357,505 issued to Armstrong et al. in 1967,
disclosed an electrically heated rock drill. U.S. Pat. No.
3,396,806 issued August 1968 to Benson disclosed a unitized machine
for thermal earth drilling utilizing a nuclear reactor for
supplying the melting energy requirements. This patent also
suggests that the hole could be melted to a larger diameter than
required for the finished hole so that melt material would provide
the hole casing.
U.S. Pat. No. 3,693,731 issued Sept. 1972 to Armstrong et al. also
discloses a nuclear reactor powered earth boring machine and melt
material is used as structural hole lining material. However, this
patent, like others that disclose machines for drilling tunnels by
melting the earth, is a solid front machine which creates an amount
of melt equal to the tunnel cross section.
The machine of the present invention is particularly adapted to
excavate large tunnels, that is, having a cross-sectional
measurement in the range of 2 to 12 metres and larger. The melting
of the entire cross section of such large tunnels requires large
heat flow rates and creates excessive costs of the heat generating
and supply system. The most economical method is for the machine to
thermally melt just enough material to detach the core, and to
provide adequate tunnel lining material. The core materials can be
machanically fractured for disposal. However, in hard rock the
disintegration of the core material is best done by heated thermal
stress fracturing penetrators.
SUMMARY OF THE INVENTION
Briefly stated, the tunneling machine of the present invention is a
self-propelling vehicle carrying on its front face a cylindrical
segmented heated ring for melting a kerf in rock. Rearward of the
heated ring, hereafter termed "kerf melting penetrator," is a heat
dissipating annular cylinder for solidifying the melt into an
initial tunnel wall supporting liner. On the front end of the
vehicle, set back from the front end of the kerf melting
penetrator, is a front end closure plate in which are supported in
uniformly spaced arrays forward projecting heated rods for
fracturing the core rock by thermal stress. These heated rods,
hereinafter termed "thermal stress fracturing penetrators" are
heated to a temperature above the melting temperature of the rock
in order to provide penetration of the rock. Also, heat is
transferred from the penetrators into the solid rock to thermally
expand and stress the surface rock which separates or spalls from
deeper rock because of shear and tensile stress failures. The heat
supply demand for the kerf melting penetrator and the thermal
stress fracturing penetrators is in the megawatts range and is
supplied by a compact nuclear reactor.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2 of the drawing, the tunneling machine of
the present invention includes a structural shell or hull 11 in and
on which the machine parts are assembled. Peripheral segmented kerf
melting penetrator 13 is mounted on the front end of the machine.
The peripheral rock melting penetrator is of a shape to melt a kerf
in the rock. The kerf outlines the cross-sectional shape and is
either configured as shown in FIG. 4 or is provided with an
outwardly flaring skirt shown in FIG. 3 to trowel outwardly the
melt to form initial glass liner. The kerf penetrator may be a
single annular shaped segmented elongated band such as shown in
cross section in FIG. 4 but can also be of the dual type shown in
cross section in FIG. 3. The dual type kerf penetrator comprises a
pair of thermal rock melting bands supported in spaced telescoped
relationship. The melting function of spacially separated plates is
enhanced as a result of the concentrated hot region generated
therebetween. For competent rock strata requiring a minimal tunnel
support liner the single band type of FIG. 4 is preferable.
A front end closure face plate 15 is attached to the front end of
the structural shell within the circumferential boundary of rock
penetrator 13 and is set back a fraction of a metre from the
leading edge of the kerf melting penetrator.
Rock fracturing penetrators 17 are supported on face plate 15.
Penetrators 17 transmit high temperature to localized areas of the
rock face of the tunnel. The coefficient of expansion of rock is
such that the localized heated portions spall or break loose from
the core by failure in shear and tension.
The thermal stress fracturing penetrators are set back with their
penetrating ends in a cross-sectional plane rearward of the plane
of the front end of the peripheral penetrators 13. The spall
loosened by the thermal stress fracturing penetrators falls to the
lower portion of the machine face and is transported rearwardly of
the tunneling machine by any state-of-the-art device such as auger
28 and auger tube 29. In order to provide adequate clearance for
the rock debris to fall to the mouth of the auger, a rock melting
nose cone 31 is supported in front of the auger opening. In the
event that large fragments of rock become detached from the rock
face and become suspended in the arrays of fracturing penetrators,
a clearing plate 33 is slidably supported on face plate 15 and is
reciprocated as necessary by hydraulic cylinder 21 to clear the
fracturing penetrators. This is one way to provide clearance.
Another arrangement would provide for retraction of the fracturing
penetrators into face 15. Each penetrator would be made to slide
axially to prevent excessive axial loading on any individual
penetrator.
The heat source for the penetrators is nuclear reactor 23 as shown
in FIG. 2. The nuclear reactor is of the compact type such as
developed for space propulsion. One form of suitable reactor is
shown in U.S. Pat. No. 3,693,731. As shown in the referenced
patent, the heat energy generated in the reactor is transferred to
the rock melting and fracturing penetrators by a liquid metal heat
exchanger 25 and heat pipes 27.
The thermal power requirements for any desired size nuclear system
tunneling machine are determined in accordance with well known heat
transfer and nuclear reactor design data. The melting temperature
of basalt is about 1420.degree.K and of tuff, it is about
1470.degree.K. The ambient temperature of the rock is assumed to be
about 290.degree.K. To assure fluidity of the melt necessary to
form the tunnel liner, the rock is heated to an average melt
temperature of 1570.degree.K. The glass liner thickness needed to
provide safe interim support depends on the integrity of the earth
in which the tunnel is being constructed. Considerations of liner
thickness may include such variables as overburden pressure, type
of ground, water flow, geologic consistency and tendency to swell.
Due to these imponderables, tunnel designers have used empirical
rules which have proved to be safe and practical. According to one
such rule, the permanent concrete lining should have a thickness
equal to approximately 8 percent of tunnel diameter. From a
comparison of glass or solid rock lava strength in compression to
that of concrete, it is deduced that interim adequate tunnel
support is afforded by a glass liner thickness equal to 4 percent
of tunnel diameter in unfavorable ground and 2 percent of tunnel
diameter in rock of favorable quality. Typical values of the heat
of fusion in joules per kilogram of rock is 418 .times. 10.sup.3
and the specific heat is 1000 joules per kilogram-kelvin. From this
data and allowing about 40 percent loss of heat, not available for
rock melting, and selecting an advance boring rate of about 1.5
metre per hour, calculations show that a nuclear reactor power
output capability of 25 MW is more than adequate for any earth
material to be encountered for a tunnel of 7.3 metre diameter. The
energy requirement for other size tunnels can be readily
extrapolated.
FIG. 5 shows a fragmentary cross section of liner forming band 37.
Band 37 is provided with water conducting bores 39 which in turn
are connected to water inlet manifold 41 and water outlet port 43.
In order to reduce thermal shock to the solidifying glass and make
use of well known counterflow heat exchanger principles, the water
circulation system is provided in the rearward portion of the liner
forming band 37. The molten rock is actually cooled to
solidification in two ways. The heat is dissipated radially outward
into the surrounding rock and by inward flow into the water cooling
system in the liner forming band 37. The structural characteristics
of the liner are determined by the rate of solidification cooling
from about 1570.degree. to about 900.degree.K. The solid glass is
further cooled by forced air passing between the hull of the
machine and the glass liner. In order to minimize low density
utility air flow to the machine from the tunnel portal, water is
used in heat exchanger 77 to cool both the tunnel air and the liner
to acceptable life support level. Heat exchanger 77 is provided
with cold water entering duct 79 to cool hot air which has
circulated in contact with the solidified tunnel liner. The cooled
air is pressure forced through duct 83 to port 85 through the hull
wall. Exit water from the heat exchanger has been warmed somewhat
by the tunnel air and is conducted by duct 87 to duct 39 in glass
liner forming band 37. The hot water circulated out of manifold 43
is transferred to appropriate heat extraction equipment for heat
conservation purposes, e.g., the generation of auxiliary electric
power. The hull is reduced in cross-sectional diameter rearwardly
of the liner forming band 37 by means of relatively short
rearwardly converging hull portion 45. An elongated reduced
cross-section hull portion 47 extends from the converging hull
portion 45 to the rear end of the machine. The reduced cross
section of the rearward portion of the hull admits of the external
coolant air passage and steerability of the machine.
Nuclear reactor 23 is rigidly supported in the hull by affixing
means such as brackets 49 and stanchions 51. Liquid metal heat
exchanger 25 thermally couples the nuclear reactor core to heat
pipes 27. The working ends of the heat pipes are closely coupled
thermally to kerf penetrators 13 and fracturing penetrators 17. The
output control mechanism and fail-safe scram control for the
reactor are housed in reactor control housing 53 and are similar to
the mechanism shown in FIG. 4 of U.S. Pat. No. 3,693,731.
Crawler mechanism for propelling the tunneling machine is shown in
FIG. 1 and is similar to the art MOLE-TYPE machines. Two sets of
radially arranged hydraulic wall gripping ram arrays are used. The
most forward set consists of 55 and 65. The aft set is identical
and not illustrated. Array 65 is slidably supported in hull 11 for
axial reciprocation. Ram array 55 is provided with radially
extensible liner gripping pads 57 and is supported in the hull with
restraint against movement in the direction of elongation of the
hull. Ram array 65 is provided with tunnel wall gripping pads 73.
Propulsion ram 69 is supported in an axial position in associated
relation with ram arrays 55 and 65 to controllably reciprocate ram
array 65 or, when 65 is stationary due to the gripping pad actions,
the remaining machine is reciprocated. Operation of the propulsion
and gripping mechanism either for forward or backward motion and
for machine axial orientation is self obvious. Selective extension
of the ram array pistons permits controllable guidance of the
machine.
Utility services such as electricity, cooling water, and debris
removal are connected to the tunneling machine from the earth's
surface by conduits, cables, etc. through the rearward open hull of
the machine.
Although the illustrative embodiment of the kerf melting and tunnel
face removal machine has been described as cylindrical, there is an
advantage inherent in this type of tunneling which is that it need
not be cylindrical, but can be any shape most economical with
respect to the desired cross section of the tunnel being bored.
From the foregoing it is seen that the present invention provides a
tunneling or excavation machine that is capable of rapid
penetration and disintegration of rock in the way of construction
of any desired size. The combination of a nuclear reactor heat
source, rock melting kerf penetrator, tunnel wall glass liner and
thermal stress tunnel face rock fracturing penetrators provides an
economically advantageous mechanism which is capable of achievement
with various modifications of the component parts. Therefore,
although an exemplary embodiment of the invention has been shown
and described, it will be obvious that modifications and
adaptations can be made without departing from the spirit of the
invention.
* * * * *