Tail structure of shield driving machine

The present invention relates to a tail structure of a shield driving machine, and in particular relates to an improvement technique of the tail sealing portion of this type of shield driving machine, in order to eliminate wearing of the tail seal. The tail structure has a first tail seal 12 and a second tail seal 14. The first tail seal 12 is provided with a tail ring 12a, a seal tube 12b and packing 12c, and the tail ring 12a is secured movably in the axial direction of a skin plate 10. The packing 12c is pressure-fitted to segments 11 in line with enlargement of the seal tube 12b and is spaced from the segments 11 in line with reduction of the seal tube 12b. The second tail seal 14 is provided with a seal tube 14a and packing 14b, wherein the packing 14b is pressure-fitted to the segments 11 in line with enlargement of the seal tube 14a and is spaced from the segments 11 in line with reduction of the seal tube 14b. When excavating, the packing 14b causes the first tail seal 12 to be pressure-fitted to the segments 11 without moving the first tail seal 12, and causes the second tail seal 14 to be spaced from the segments 11.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
The present invention relates to a tail structure of a shield driving 
machine, and in particular relates to an improvement technique of the tail 
sealing portion of this type of shield driving machine. 
2. Description of Prior Arts 
In a shield construction applied to building of a subway tunnel in a city 
zone, recently, reduction of the construction costs and shortening of the 
construction term are of importance. In order to meet these requests, it 
is attempted that the excavation distance per shield driving machine is 
lengthened. 
Furthermore, in shaft building work in a shield construction, since it 
becomes very difficult to secure a site in line with recent overcrowding 
of a city zone, and the installation level of a shield tunnel is even 
deepening, the costs and term required for building a shaft has been 
increased, wherein lengthening of the excavation distance of a shield 
driving machine is further accelerated. 
Although various problems arise in line with a lengthening of the 
excavation distance of a shield driving machine, the durability of the 
tail seal portion of a shield driving machine is an important theme. The 
tail seal portion which prevents peripheral water, earth and sand, and 
back-filling materials from flowing into the shield driving machine body 
is usually constructed as shown in FIG. 13. 
The tail seal portion "a" illustrated in the drawing prevented peripheral 
water, etc., from flowing into the machine body by providing a plurality 
of flutes of tail brush "d", which is slidably brought into contact with 
the outer circumferential surface of segments "c", on the inner 
circumferential surface of a skin plate "b" at the tail side, and by 
filling a semi-solid filling material "e" such as grease between the tail 
brushes "d". 
However, with such a conventional structure of the tail seal portion "a", 
especially, in line with a lengthening of the excavation distance of a 
shield driving machine, there were technical problems as described below; 
That is, at the tail seal portion "a" illustrated in FIG. 13, since the 
tail brushes "d" are brought into contact with segments "c" while the 
shield driving machine is excavating, they slidably move in line with the 
excavation. Therefore, the tail brushes "d" are worn by frictions with the 
segments "c", whereby peripheral water invades the tail portion of the 
shield driving machine while driving a long distance. 
Furthermore, a back-filling material invades the tail brushes "d" and is 
adhered thereto gradually, wherein the adhered back-filling material is 
solidified. The resiliency of the tail brushes "d" is gradually spoiled, 
and it becomes difficult to follow a change of the clearance between the 
skin plate "b" and segments "c", wherein when driving and excavating a 
long distance, peripheral water, etc., invades the tail portion of the 
shield driving machine. 
However, construction of tunnels by a shield driving machine is not limited 
to construction of tunnels for subways and roads for transport facilities. 
For example, the inventors disclosed utilization of the present invention 
in construction of water-intake tunnels to intake sea water for a plant 
producing fresh water by using sea water in Japanese Patent Application 
No. 218492 of 1997. 
That is, in order to secure drinking water on islands where it scarcely 
rains or in desert areas, a plant producing fresh water is installed in 
the vicinity of a sea shore. Furthermore, sea water is prime water for 
treatment in salt production plants, wherein in these types of sea water 
treatment facilities, it is necessary to introduce sea water into a plant 
producing fresh water. 
Therefore, in such a sea water treatment facility, conventionally, sea 
water was introduced through a water-intake tunnel in which vinyl chloride 
tube covered with unwoven cloth, having a number of penetrated 
water-intake pores formed thereon, and porous Hume pipes are laid, 
However, since a water-intake tunnel of such construction is buried by an 
excavation construction method or a sinking and laying method, the site on 
the ground right above the laying position and/or its surrounding are 
exclusively occupied for the sinking and laying work. Therefore, from this 
viewpoint, there are various limitations in the construction work 
resulting therefrom. 
Therefore, the inventors developed a technique for building these types of 
water-intake tunnels by a shield driving method. Segments used to build 
such water-intake tunnels are, as shown in FIG. 14, such that a permeable 
member 2 is attached to the outside of a body plate 1 such as steel 
segments and ductile segments conventionally used for a usual shield 
construction method. 
The permeable member 2 is made of porous concrete, etc., and is so 
constructed that underground water passing through the permeable member 2 
is positively taken into the inside through water-intake openings (not 
illustrated) which are openable and closable, and secured at the body 
plate 1. 
However, when building a water-intake tunnel by a shield driving machine, 
using such water-intake segments 3, particularly, there were such 
technical problems as described below as regards the tail portion of a 
shield driving machine. 
That is, as described above, the tail structure of a shield driving machine 
used for a usual shield construction method, plural flutes of tail brushes 
"d" which are slidably brought into contact with the outer circumferential 
surface of segments "c" were disposed on the inner circumferential surface 
of the skin plate "b" at the tail side, and a filling material "e" was 
filled in between the tail brushes "d", wherein peripheral water was 
prevented from invading inside. 
However, if the tail structure of such a construction is applied to the 
abovementioned water-intake segments 3, it is impossible to cover the 
entirety of the permeable member 2 even in a case where, as shown in FIG. 
14, the tail brushes "d" are slidably brought into contact with the outer 
circumferential surface of the water-intake segments 3. Therefore, 
peripheral water invades in a channel indicated by the arrow depicted by a 
solid line, and the tail structure does not function as a tail seal. 
Furthermore, if a filling material "e" is filled in between the tail 
brushes "d" even though the entirety of the permeable portion 2 can be 
covered by the tail brushes "d", grease clogs pores of the permeable 
member 2 and reduces the permeability of the permeable member 2. 
Therefore, the filling material "e" can not be used. Unless the filling 
material "e" is used, peripheral water invades through the clearance of 
the tail brushes "d", wherein the tail brushes "d" can not function as a 
tale seal. 
SUMMARY OF THE INVENTION 
The present invention was developed in order to solve the abovementioned 
problems, and it is therefore the first object of the invention to provide 
a tail structure of a shield driving machine, by which the durability 
thereof can be improved by getting rid of the friction at the tail seal 
portion. 
Furthermore, it is the second object of the invention to provide a tail 
structure of a shield driving machine, which is able to prevent peripheral 
water from invading in a case where a water-intake tunnel is built by 
using water-intake segments. 
In order to achieve the abovementioned objects, the invention is 
characterized in that, in a shield driving machine provided with a tail 
sealing portion which intervenes between the outer circumferential surface 
of segments installed on the excavation wall surface and the inner 
circumferential surface of a skin plate at the tail side and prevents 
peripheral water, earth and sand, and back-filling material from flowing 
into the skin plate; the tail sealing portion is a first tail seal and a 
second tail seal which are disposed in the axial direction of the 
abovementioned skin plate; the first and second tail seals are constructed 
so that they are able to be pressure-fitted to the abovementioned segments 
and spaced therefrom; the first tail seal is secured movably in the axial 
direction of the abovementioned skin plate, and concurrently, the 
abovementioned second tail seal is fixed at the abovementioned skin plate; 
any one of the abovementioned first and second tail seals is 
pressure-fitted to the abovementioned segments when the abovementioned 
shield driving machine stops excavation; and when the abovementioned 
shield driving machine is excavating, the abovementioned first tail seal 
is pressure-fitted to the abovementioned segments without being moved, and 
concurrently the abovementioned second tail seal is spaced from the 
abovementioned segments. 
According to the tail structure of a shield driving machine constructed as 
described above, since either one of the first tail seal and the second 
tail seal is always pressure-fitted to segments when the shield driving 
machine is excavating or the segments are assembled, it is possible to 
prevent peripheral water, earth and sand, back-filling materials, etc., 
from invading. 
Furthermore, since, when the shield driving machine is excavating, the 
first tail seal is pressure-fitted to the segments without being moved and 
the second tail seal is spaced from the segments, the first and second 
tail seals are not moved while being slidably brought into contact with 
the segments, no friction is produced between the respective tail seals 
and the segments, the durability of the tail seals is further improved, 
even in a long distance excavation, and the number of times of replacement 
of the tail seals is reduced. 
A tail structure of a shield driving machine; wherein the abovementioned 
first tail seal is disposed frontward of the abovementioned second tail 
seal in the direction of excavation; and 
a tail ring movably disposed along the axial direction of the 
abovementioned skin plate; is provided with a seal tube secured and fixed 
at the abovementioned tail ring, the diameter of which is enlargeable and 
reduceable; and packing which is pressure-fitted to the abovementioned 
segments in line with enlargement of the abovementioned seal tube and is 
spaced from the abovementioned segments in line with reduction of the 
abovementioned seal tube. 
According to the construction, since the first tail seal is disposed 
frontward of the second tail seal in the direction of excavation and the 
tail ring is made movable, it is possible to easily replace the seal tube 
and packing of the first tail seal by drawing out the tail ring to the 
shield driving machine side. 
Furthermore, in order to achieve the abovementioned object, the invention 
is characterized in that, in a shield driving machine used for building a 
water-intake tunnel, which intervenes between the outer circumferential 
surface of water-intake segments secured on the excavation wall surface 
and the inner circumferential surface of a skin plate at the tail side and 
prevents inflow of peripheral water into the abovementioned skin plate; 
the abovementioned tail structure is provided with a first tail seal and a 
second tail seal, which are disposed along the axial direction of the 
abovementioned skin plate, either one of the abovementioned first or 
second tail seals is always pressure-fitted to a non-permeable portion of 
the abovementioned water-intake segments when the abovementioned shield 
driving machine is excavating or the abovementioned water-intake segments 
are assembled. 
According to the tail structure of a shield driving machine construction as 
described above, since, when the shield driving machine is excavating or 
water-intake segments are assembled, either one of the first tail seal or 
second tail seal is always pressure-fitted to the non-permeable portion of 
water-intake segments, it is possible to prevent peripheral water from 
invading. 
The abovementioned first tail seal is secured movably along the axial 
direction of the abovementioned skin plate; the abovementioned first and 
second tail seals are constructed so that they are able to be 
pressure-fitted to the abovementioned non-permeable portion and spaced 
therefrom; and when the abovementioned shield driving machine is 
excavating, the abovementioned first tail seal is pressure-fitted to the 
abovementioned non-permeable portion without being moved, and the 
abovementioned second tail seal is spaced from the non-permeable portion. 
According to the construction, since, when the shield driving machine is 
excavating, the first tail seal is pressure-fitted to the non-permeable 
portion in a state where the first tail seal does not move, and 
concurrently, since the second tail seal is spaced from the non-permeable 
portion, the first and second tail seals do not move while sliding on the 
water-intake segments, in line with excavation of the shield driving 
machine, and no friction is produced between the respective tail seals and 
segments. Therefore, the durability of the tail seals is further improved, 
and it is possible to attempt to reduce the number of times of replacement 
of the tail seals in a long distance excavation. 
The abovementioned first tail seal is constructed so as to be provided with 
a tail ring disposed movably along the axial direction of the 
abovementioned skin plate; a seal tube secured and fixed at the 
abovementioned tail ring, the diameter of which is enlargeable and 
reduceable; and packing which is pressure-fitted to the abovementioned 
non-permeable portion in line with enlargement of the abovementioned seal 
tube and is spaced from the abovementioned non-permeable portion in line 
with reduction of the abovementioned seal tube. 
According to the construction, since the tail rings are made movable, it is 
possible to easily replace the seal tubes and packing of the first tail 
seal by drawing out the tail rings toward the shield driving machine side. 
The abovementioned water-intake segments are assembled to be annular at the 
tail portion side of the abovementioned shield driving machine. 
Furthermore, the water-intake segment is constructed of a non-permeable 
body plate on which openable and closable water-intake pores are provided, 
and a permeable member integrated with the outside of the abovementioned 
body plate. 
As described in detail in the preferred embodiments, according to the tail 
structure of a shield driving machine, since it is possible to improve the 
durability while securely preventing peripheral water, etc., from 
invading, it is possible to lengthen the excavation length of a shield 
driving machine. 
Furthermore, by the tail structure of a shield driving machine according to 
the invention, in a case where a water-intake tunnel is built, using 
water-intake segments, it is possible to prevent peripheral water, etc., 
from invading.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, a detailed description is given of a preferred embodiment of 
the invention with reference to the accompanying drawings. FIG. 1 through 
FIG. 6 shows one preferred embodiment of a tail structure of a shield 
driving machine according to the invention. 
FIG. 1 is a sectional view of the tail portion of a shield driving machine, 
a skin plate 10 illustrated in the drawing is formed to be cylindrical in 
the shield driving machine, and reference number 11 is segments. 
The segments 11 are generally used for shield construction. The segments 11 
are assembled to be annular one after another at the tail portion side in 
line with advance of excavation of a shield driving machine, wherein steel 
segments and ductile segments are used as segments 11. 
A filling opening (not illustrated) of a back-filling material, which is 
closed by a cover body during construction and is opened after a tunnel is 
constructed, is secured at the respective segments 11. 
In the structure illustrated in FIG. 1, the first tail seal 12 and the 
second tail seals 14 are secured along the axial direction of a skin plate 
10 of the shield driving machine, and the third tail seal 16 is provided 
at the rear end of the skin plate 10. 
The first tail seal 12 consists of an annular tail ring 12a along the inner 
circumferential surface of the skin plate 10 at the tail side, a seal tube 
12b secured and fixed on the inner side of the tail ring 12a, and packing 
12c provided in the vicinity of the seal tube 12b. 
The tail ring 12a is in contact with the inner circumferential surface of 
the skin plate 10 and movably provided along the axial direction (forward 
and backward direction in FIG. 1) of the skin plate 10, wherein for 
example, it is moved by an actuator such as a jack outside the drawing. 
The seal tube 12b is composed of rubber which is hollow and is annularly 
provided on the entire circumference along the inner circumferential 
surface of the tail ring 12a, one end of which is secured and fixed at the 
inner circumferential surface of the tail ring 12a. 
The seal tube 12b is connected to a compressor or an oil hydraulic power 
unit outside the drawing via a switching valve, and the seal tube 12b is 
enlarged in diameter by supplying compressed fluid such as compressed air 
or oil thereto, and concurrently, is reduced in diameter by discharging 
the compressed fluid therefrom. 
The packing 12c is composed of a rubber plate, etc., and is annularly 
provided on the entire circumference along the inner circumferential 
surface of the tail ring 12a. 
The packing 12c is such that only one end thereof is secured and fixed on 
the inner circumferential surface of the tail ring 12a, and the other end 
thereof is a free end, wherein the free end side is adhered to the outside 
of the seal tube 12b. 
If the seal tube 12b is enlarged in diameter at the first tail seal 12 thus 
constructed, the free end side of the packing 12c is pushed inwardly in 
line with the enlargement, and the tip end side of the packing 12c is 
pressure-fitted to the outer circumferential surface of the segments 11. 
Furthermore, if the seal tube is reduced in diameter, the free end side of 
the packing 12c is moved to the seal tube 12b side in line with the 
reduction, and the tip end of the packing 12c is spaced from the outer 
circumferential surface of the segments 11. 
The second tail seal 14 is disposed rearward of the first tail seal 12 in 
the direction of excavation, and it is provided with a seal tube 14a 
secured and fixed on the inner circumferential surface of the skin plate 
10, and packing 14b. 
The seal tube 14a is annularly disposed so as to turn around along the 
inner surface of the skin plate 10 as well as the seal tube 12a of the 
first tail seal 12. 
The seal tube 14a is connected to a compressor or an oil hydraulic power 
unit outside the drawing via a switching valve, wherein the seal tube 14a 
is enlarged in diameter by supplying compressed fluid such as compressed 
air or oil thereto, and is reduced in diameter by discharging the 
compressed fluid therefrom. 
Packing 14b is composed of a rubber plate, etc., and is disposed so as to 
turn around along the inner surface of the skin plate 10. 
The packing 14b is such that only one end side thereof is secured and fixed 
at the inner circumferential surface of the skin plate 10, and the other 
end side is made a free end, wherein the free end side is adhered to the 
outer surface of the seal tube 14a. 
In the second tail seal 14 thus constructed, the free end side of the 
packing 14b is moved inwardly or outwardly, as in the first tail seal 12, 
in line with the enlargement or reduction of the seal tube 14a in 
diameter, and the tip end side of the packing 14b is pressure-fitted to 
the first tail seal 12 and the outer circumferential surface of the 
segments or spaced from the outer circumferential surface thereof. 
The third tail seal 16 is composed of an annular tail brush, one end of 
which is secured and fixed on the inner surface at the rear end side of 
the skin plate 10 and is constructed so as to be slidably brought into 
contact with the outer circumferential surface of the segments 11. 
Furthermore, the third tail seal 16 has the same functions as those of a 
general earth and sand seal, which prevents earth and sand, and 
back-filling material from flowing inwardly. Furthermore, the third tail 
seal 16 may be provided in multiple flutes. 
Next, a description is given of actions of a tail structure constructed as 
described above. FIG. 1 through FIG. 7 show operating states of the tail 
structure when causing the shield driving machine to excavate or 
assembling the segments 11. 
FIG. 1 shows a state before the shield driving machine begins excavating, 
wherein segments 11 equivalent to three rings are coupled, the first tail 
seal 12 is located at the end edge, in the direction of excavation, of the 
left side segments 11 assembled immediately before, and the second tail 
seal 14 is located right above the coupled portion of the middle segment 
3. 
Furthermore, the third tail seal 16 is slidably in contact with the outer 
circumferential surface of the right end segment 11. In this state before 
excavation, the seal tube 12b of the first tail seal 12 is enlarged in 
diameter and the packing 12c is pressure-fitted to the outer 
circumferential surface of the left end segment 11, whereby peripheral 
water is prevented from invading. 
On the other hand, the second tail seal 14 and seal tube 14a are reduced in 
diameter, and the packing 14b is spaced upward from the outer 
circumferential surface of the segment 11. 
As the excavation of the shield driving machine is commenced from the state 
shown in FIG. 1, the first tail seal 12 does not cause the tail ring 12a 
to move and leaves it as it is, wherein only the skin plate 10 is 
permitted to advance. 
And until the excavation equivalent to one ring length corresponding to the 
axial length of the segments 11 is finished, the operating state of the 
first tail seal 12 and the second tail seal 14 are maintained as they are. 
At this time, the operating states of the first tail seal 12 and the second 
tail seal 14, and the mutual positional relationship are illustrated in 
FIG. 2, wherein in this state, the second tail seal 14 is drawn near the 
first tail seal 12 by only the distance equivalent to one ring. 
Next, as shown in FIG. 3, a new segment 11a is assembled at the left side 
of the third ring. Until the new segment 11a is assembled, the operating 
states of the first tail seal 12 and second tail seal 14 are maintained as 
described above. 
As the assembling and connection of the new segment 11a are completed, as 
shown in FIG. 4, first, the seal tube 14a of the second tail seal 14 is 
enlarged in diameter to cause the packing 14b to be pressure-fitted to the 
outer circumferential surface of the segments 11, wherein peripheral water 
is prevented from invading inwardly by operation of the second tail seal 
14. 
Next, the seal tube 12b of the first tail seal 12 is reduced in diameter, 
the packing 12c is caused to be spaced upward from the outer 
circumferential surface of the segments 11, and the tail ring 12a is moved 
forward by only the distance equivalent to one ring length. 
FIG. 5 shows a state where the abovementioned operation is completed. The 
seal tube 14a of the second tail seal 14 is maintained at its enlarged 
state until the movement of the tail ring 12a is completed, and the 
packing 14 is pressure-fitted to the outer circumferential surface of the 
segment 11, whereby peripheral water, etc. can be prevented from invading. 
Subsequently, as the movement of the tail ring 12a is completed, as shown 
in FIG. 6, the seal tube 12b of the first tail seal 12 is enlarged in 
diameter, the packing 12c is pressure-fitted to the outer circumferential 
surface of the segment 11a, and peripheral water is prevented from 
invading. Thereafter, the seal tube 14a of the second tail seal 14 is 
reduced in diameter, and the packing 14b is spaced from the outer 
circumferential surface of the segments 11. After that, operating states 
similar to those described above are repeated in line with advancement of 
the excavation by the shield driving machine. 
Herein, according to the seal structure constructed as described above, 
since any one of the first tail seal 12 and the second tail seal 14 is 
always pressure-fitted to the outer circumferential surface of the segment 
11 when causing the shield driving machine to excavate or assembling the 
segments, it is possible to prevent peripheral water, etc., from invading. 
Furthermore, in the case of the preferred embodiment, since, when the 
shield driving machine is excavating, the first tail seal 12 is 
pressure-fitted to the outer circumferential surface of the segments 11 
without moving the first tail seal 12, and concurrently, the second tail 
seal 14 is spaced from the outer circumferential surface of the segments 
11, the first tail seal 12 and second tail seal 14 do not move slidably in 
contact with the segments 11 in line with the excavation by the shield 
driving machine, no friction is produced between the respective tail seals 
12 and 14, and the segments 3, and the durability of the tail seals 12 and 
14 is further improved, wherein that the number of times of replacement of 
tail seals 12 and 14 is reduced even in a long distance excavation. 
Furthermore, in the case of the preferred embodiment, since the first tail 
seal 12 is disposed frontward of the second tail seal 14 in the direction 
of excavation, and the tail ring 12a is made movable, the seal tube 12b 
and packing 12c of the first tail seal 12 can be easily replaced by 
drawing them out toward the shield driving machine side. 
FIG. 7 through FIG. 12 show another preferred embodiment of a tail 
structure of a shield driving machine according to the invention. The 
preferred embodiment illustrated in these drawings is an example which is 
applied to the building of a water-intake tunnel. The parts which are 
identical to those of the abovementioned embodiment are given the same 
reference numbers. 
FIG. 7 is a sectional view of the tail portion of the shield driving 
machine. A skin plate 10 illustrated in the drawings is formed to be 
cylindrical in the shield driving machine. A water-intake segment 3 is as 
described in the Background section of this specification. 
Similar to usual segments, water-intake segments are assembled to be 
annular at the tail portion side one after another in line with 
advancement of the excavation of the shield driving machine, and are such 
that a permeable member 2 is attached to the outside of the body plate 1 
such as steel segments and ductile segments. 
A water-intake opening (not illustrated), which is closed during 
construction of a water-intake tunnel and is opened after the tunnel is 
completed, is provided in the body plate 1 of each of the respective 
water-intake segments 3, and concurrently, one part of the body plate 1 is 
exposed to both ends of the permeable member 2, wherein the exposed 
portion forms a non-permeable portion 1a. 
In the tail structure illustrated in FIG. 7, the first tail seal 12 and 
second tail seal 14 are provided along the axial direction of the skin 
plate 10 of the shield driving machine, and the third tail seal 16 is 
provided at the rear end of the skin plate 10. 
The first tail seal 12 consists of an annular tail ring 12a along the inner 
circumferential surface of the skin plate 12 at the tail side, a seal tube 
12b secured and fixed at the inner circumferential side of the tail ring 
12a, and packing 12c provided in the vicinity of the seal tube 12b. 
The tail ring 12a is made in contact with the inner circumferential surface 
of the skin plate 10 and is provided so as to be movable along the axial 
direction (forward and backward direction in FIG. 7) of the skin plate 10, 
wherein, for example, the tail ring 12a is moved by an actuator such as a 
jack outside the drawing. 
The seal tube 12b is composed of rubber whose section is hollow, and is 
provided to be annular on the entire circumference along the inner 
circumferential surface of the tail ring 12a, one end of which is secured 
and fixed on the inner circumferential surface of the tail ring 12a. 
The seal tube 12b is connected to a compressor or an oil hydraulic power 
unit outside the drawings, via a switching valve, and the seal ring 12a is 
enlarged in diameter by supplying compressed fluid such as compressed air 
or oil thereto, and is reduced in diameter by discharging the compressed 
fluid therefrom. 
The packing 12c is composed of a rubber plate, etc., and is provided to be 
annular on the entirety of the circumference along the inner 
circumferential surface of the tail ring 12a. 
The packing 12c is such that only one end thereof is secured and fixed on 
the inner circumferential surface of the tail ring 12a, and the other end 
thereof is made a free end, wherein the free end side is adhered to the 
outer surface of the seal tube 12b. 
In the first tail seal 12 thus constructed, if the seal tube 12b is 
enlarged in diameter, the free end side of the packing 12c is pushed 
inwardly in line with the enlargement, and the tip end side of the packing 
12c is pressure-fitted to the non-permeable portion 1a of the water-intake 
segments 3. 
If the seal tube 12b is reduced in diameter, the free end side of the 
packing 12c is moved to the seal tube 12b side in line with the reduction, 
and the tip end side of the packing 12c is spaced from the non-permeable 
portion 1a of the water-intake segments 3. 
The second tail seal 14 is disposed rearward of the first tail seal portion 
12, and is provided with a seal tube 14a secured and fixed on the inner 
circumferential surface of the skin plate 10, and packing 14b. 
The seal tube 14a is annularly disposed so as to turn around along the 
inner surface of the skin plate 10 as in the seal tube 12a of the first 
tail seal 12. The seal tube 14a is connected to a compressor or an oil 
hydraulic power unit outside the drawings, via a switching valve, wherein 
by supplying compressed fluid such as compressed air or oil thereto, the 
seal tube 14a is enlarged in diameter, and, by discharging the same 
therefrom, the seal tube 14a is reduced in diameter. 
The packing 14b is composed of a rubber plate, etc., and is annularly 
disposed so as to turn around along the inner surface of the skin plate 
10. 
The packing 14b is such that only one end thereof is secured and fixed at 
the inner circumferential surface of the skin plate 10, and the other end 
thereof is made a free end, and the free end side is adhered to the outer 
surface of the seal tube 14a. 
In the second tail seal 14 thus constructed, as in the first tail seal 12, 
if the seal tube 14a is enlarged in diameter, the free end side of the 
packing 14b is pushed inwardly in line with the enlargement thereof, and 
the tip end side of the packing 14b is pressure-fitted to the first tail 
seal 12 and the non-permeable portion 1a of another water-intake segment 
3. 
The third tail seal 16 is composed of an annular tail brush, one end of 
which is secured and fixed on the inner surface at the rear end side of 
the skin plate 10, and it is slidably brought into contact with the outer 
surface of the water-intake segment 3. 
Furthermore, the third tail seal 16 functions, as well, as a general earth 
and sand seal, and it is able to prevent earth and sand, and a 
back-filling material from flowing thereinto. 
Next, a description is given of actions of the tail structure according to 
the above construction. FIG. 7 through FIG. 12 show operating states of 
the tail structure when causing the shield driving machine to excavate and 
assembling water-intake segments 3. 
FIG. 7 shows a state before the shield driving machine begins excavating. 
In this state, the water-intake segments 3 equivalent to three rings are 
connected to each other, the first tail seal 12 is located right above the 
non-permeable portion 1a of the left end side water-intake segment 3 
assembled immediately before, and the second tail seal 14 is located right 
above the connection portion of the middle water-intake segment 3. 
Furthermore, the third tail seal 16 is slidably brought into contact with 
the permeable member 2 of the right end water-intake segment 3. In the 
state before excavation, the seal tube 12b of the first tail seal 12 is 
enlarged in diameter, and the packing 12c is pressure-fitted to the 
non-permeable portion 1a of the left end water-intake segment 3, whereby 
it is possible to prevent peripheral water from invading. 
On the other hand, the second tail seal 14 and seal tube 14a are reduced in 
diameter, and the packing 14b is spaced upward from the non-permeable 
portion 1a of the water-intake segment 3. 
As the shield driving machine begins excavating from the state shown in 
FIG. 7, the first tail seal 12 does not cause the tail ring 12a to move 
and leaves it as it is, wherein only the skin plate 10 is permitted to 
advance. 
Subsequently, the operating states of the first tail seal 12 and second 
tail seal 14 remain unchanged until the excavation equivalent to one ring 
corresponding to the axial length of the water-intake segment 3 is 
finished. FIG. 8 shows the operating states of the first tail seal 12 and 
second tail seal 14 at this time and the mutual positional relationship 
therebetween. In this state, the second tail seal 14 is drawn near to the 
first tail seal 12 by only the distance equivalent to one ring. 
Next, as shown in FIG. 9, a new water-intake segment 3 is assembled at the 
left side of the third ring. The operating states of the first and second 
tail seals 12 and 14 are maintained as in the state described above until 
the newly secured water-intake segment 3 is completely assembled. 
As the assembling and connection of the newly secured water-intake segment 
3 are completed, as shown in FIG. 10, first, the seal tube 14a of the 
second tail seal 14 is enlarged in diameter, the packing 14b is 
pressure-fitted to the non-permeable portion 1a of the water-intake 
segment 3, and peripheral water is able to be prevented from invading by 
operation of the second tail seal 14. 
Next, the seal tube 12b of the first tail seal 12 is reduced in diameter, 
and the packing 12c is spaced upward from the non-permeable portion 1a, 
wherein the tail ring 12a is moved forward by only a distance equivalent 
to one ring. 
FIG. 11 shows the state where the movement is completed. The seal tube 14a 
of the second tail seal 14 is maintained in its enlarged state until the 
movement of the tail ring 12a is completed, and the packing 14b is 
pressure-fitted to the non-permeable portion 1a, whereby peripheral water 
can be prevented from invading. 
And as the movement of the tail ring 12a is completed, the seal tube 12b of 
the first tail seal 12 is enlarged in diameter, and the packing 12c is 
pressure-fitted to the non-permeable portion 1a of the water-intake 
segment 3, wherein after preventing the peripheral water from invading, 
the seal tube 14a of the second tail seal 14 is reduced in diameter, and 
the packing 14b is spaced from the non-permeable portion 1a. Thereafter, 
operations similar thereto are repeated in line with excavation of the 
shield driving machine. 
According to the seal structure constructed as described above, since 
either one of the first tail seal 12 and second tail seal 14 is always 
pressure-fitted to the non-permeable portion 1a of the water-intake 
segment 3 when causing the shield driving machine to excavate or 
assembling the water-intake segments, it is possible to prevent peripheral 
water from invading. 
Furthermore, in the case of the preferred embodiment, since the first tail 
seal 12 is pressure-fitted to the non-permeable portion 1a without moving 
the first tail seal 12, and concurrently, the second tail seal 14 is 
spaced from the non-permeable portion 1a, the first and second tail seals 
12 and 14 do not move while slidably being brought into contact with the 
water-intake segment 3 in line with the excavation of the shield driving 
machine, wherein no friction is produced between the respective tail seals 
12 and 14, and the segment 3, the durability of the tail seals 12 and 14 
is further improved, and it is possible to reduce the number of times of 
replacing the tail seals 12 and 14 in a long distance excavation. 
Furthermore, in the case of the preferred embodiment, since the tail ring 
12a is made movable, it is possible to easily replace the seal tube 12b 
and packing of the first tail seal 12 by drawing out the tail ring 12a to 
the shield driving machine side. 
Furthermore, although, in the abovementioned preferred embodiment, a 
description is given of a case where one seal tube 12b and packing 12c are 
disposed at the tail ring 12a of the first tail seal 12, the present 
invention is not limited to the abovementioned case, for example, a 
plurality of seal tubes 12b and packing 12c may be disposed at the tail 
ring 12c, and they may be operated at the same time.