Tail Seal For A Shield Type Tunneling Machine

Abstract

A tail seal mechanism in a shield type tunneling machine, said tail seal mechanism comprising an L-type annular seal of an elastic material installed to the inner periphery of the tail such that the tongue portion of the seal faces rearwardly and a U-type annular seal of an elastic material installed to the inner periphery of said tail rearwardly of and parallel to said L-type annular seal, said U-type seal being adapted such that it can be inflated by an internal fluid, as required.

Description

This invention relates to a tail seal mechanism of a shield type tunneling machine.

The tail seal mechanism in the conventional shield type tunneling machine is in most cases an arrangement consisting of an L-type annular seal of an elastic material such as natural or synthetic rubber, which is installed at the rearmost end of the tail plate, the installation being made, if necessary, with the supplemental use of steel plates. However, this type of seal is frequently susceptible to troubles or accidents such as curling up of the inner peripheral portion of the seal due to a change in pressure, breakage due to a deviation of the segments from their central position or sinking of the segments due to their weight, or the seal becoming worn out due to the roughness of the segment surface resulting from the step-wise unevenness in assembling the segment.

An object of the present invention is to provide a seal mechanism by which water can be stopped exigently when troubles, such as noted above, have occurred in the L-type annular seal. Another object is to provide a seal mechanism by which the operation of exchange of the L-type annular seal can be facilitated when these troubles have occurred.

We found that the foregoing objects of the invention could be achieved by a tail seal mechanism which is formed by installing rearwardly of and parallel to the L-type annular seal of an elastic material installed at the inner periphery of the tail of the shield type tunneling machine with its tongue facing rearwardly, a U-type annular seal of an elastic material, which can be inflated, as required, with an inner fluid.

A preferred embodiment of the invention will be described below with reference to the accompanying drawings, wherein the invention tail seal mechanism is specifically illustrated.

FIG. 1 is a view in section showing the relationship between the tail seal and the segments being assembled in the shield type tunneling machine;

FIG. 2 is a sectional view on an enlarged scale of the tail seal shown in FIG. 1; and

FIG. 3 is a sectional view taken along line III -- III of FIG. 2.

As shown in FIG. 1, according to the tail seal mechanism of the present invention there are provided two types of seals disposed annularly in the clearance 8 between that tail plate 2 of the shield type tunneling machine 1 and the segment 3. The first seal 4 is an L-type annular seal of the same form as that conventionally used. This is installed to the inner periphery of the tail at a point forward of the rear end of the tail plate 2 with its tongue facing rearwardly. The second seal 5 is a U-type annular seal of the type that can be inflated by filling its interior with a fluid, i.e., it is a seal of the type similar to a tire tube. This latter seal is installed to the inner periphery of the tail, as shown in the drawing, in parallel to and rearwardly of the first seal at a point near the rear end of the tail plate 2.

From the very nature of obtaining an effective sealing effect, the L-type annular seal is made with an outer diameter somewhat larger than the inside diameter of the tail plate 2, while the inner diameter of the seal is made somewhat smaller than the outside diameter of the segment 3. As shown on an enlarged scale in FIGS. 2 and 3, the outer edge portion of the seal is secured to the inner periphery of the tail plate 2 with screws, and the inner edge portion of the seal comes into intimate contact with the outer periphery of the segment 3. The magnitude of the tongue portion of the seal to be brought into contact with the segment is suitably determined by calculation and experimentation.

On the other hand, the U-type annular seal 5, as shown in FIG. 2, has its base portion secured to the inner periphery of the tail plate 2 with screws. This U-type seal is so adapted that the interior of tube 9 can be inflated by feeding air or water from a pipe 6, as required, thus making it possible to achieve an intimate contact of the outer surface of the tube 9 with the outer surface of the segment 3 only at those times necessary, as hereinafter indicated. That is to say, in the present invention the U-type annular seal 5 is normally kept in a collapsed state (e.g. as shown by the dotted lines in the drawing), and the closure against the access of water is allowed to be taken care of solely by the L-type annular seal 4. Only when there is a great leakage due to an unevenness of the segment or when the L-type seal 4 must be replaced due to wear and tear, the U-type annular seal 5 is used by inflation to a desired degree.

In a preferred embodiment of the invention, for example, the diameter of the tail plate is 3 meters, and the magnitude of the contact of the tongue portion of the L-type annular seal 4 with the outer surface of the segment 3 is 25 - 35 centimeters when the pressure is 2 kg/cm.sup.2. On the other hand, the internal pressure of the U-type annular seal 5 is higher by 0.5 - 1.0 kg/cm.sup.2 than the external pressure. Both seals are made of natural rubber having a thickness of 20 - 22 millimeters.

In the shield type tunneling machine provided with only the L-type annular seal, when the seal became impaired by wear and tear in the past, the diminution of the sealing effect was prevented by the supplemental use of steel plates at the rubber contact surface. However, this method had the shortcoming that because the seal does not make sufficiently close contact with the small unevennesses in the external surface of the segment, troubles were frequently experienced in that the seal would turnup towards the shield side as result of the hydrostatic pressure or pressure resulting from pumping in water. Again, when only the L-type annular seal was used, there were other troubles as well. The normal functioning of the seal could not be achieved in numerous instances. At times, the compression of the seal would occur only at the bottom of the segment because the weight of the segment would cause it to say or, when the shield takes a meandering course, the seal would be compressed against a specific direction only. On the other hand, in accordance with the present invention, the U-type annular seal 5 can be brought into operation in these cases, and thus the tightness of the seal can be maintained without the use of steel plates, the biased compression of the seal can be prevented, and the closure against access by water can be maintained even though there is a variation in pressure. Thus, in accordance with the present invention, it becomes possible to conduct operations behind the shield with ease.

Claims

We claim:

1. A tail seal mechanism in a shield type tunneling machine, said tail seal mechanism comprising an L-type annular seal of an elastic material installed to the inner periphery of the tail such that the tongue portion of the seal faces rearwardly and a U-type annular seal of an elastic material installed to the inner periphery of said tail rearwardly of and parallel to said L-type annular seal, said U-type seal being adapted such that it can be inflated by an internal fluid, as required.