JP2008240459A - Shield machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shield machine capable of preventing the occurrence of the problem of insufficient thrust likely to occur in a part of a deformed excavation cross section of a cutting edge even if the excavation cross section for the cutting edge is the deformed excavation cross section being unsymmetrical in upper and lower parts and/or right and left parts and an interval of arrangement of shield jacks is made equal along a peripheral fringe of the deformed excavation cross section. <P>SOLUTION: A plurality of shield jacks 7 for letting a shield machine main body 3 advance by making use of reaction force of an existing segment 6 are arranged at an equal interval along the peripheral fringe of the deformed excavation cross section in the main body 3 of the shield machine 1. The deformed excavation cross section is virtually divided into two parts, namely, a large area part B and a small area part A by a virtual line X passing through the center G of the Figure showing the deformed excavation cross section and extended in the direction crossing the direction of advance of the machine main body 3 orthogonally. The large area part shield jacks 7b arranged in the large area part B among the shield jacks 7 include the shield jacks having larger jack thrust than jack thrust of the small area part shield jacks 7a arranged in the small area part A. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a shield machine in which an excavation cross section with respect to a face is an asymmetrical excavation cross section that is asymmetric in vertical and / or left and right directions.

  The shield machine has a main body having a cylindrical shield frame, a cutter disposed to cut the face at the front of the machine, and earth and sand cut by the cutter inside the machine. Take the reaction force to the earth removing device for taking in, the erector provided inside the excavator body to assemble the segment in a ring shape along the inner peripheral surface of the shield frame, and the segment assembled in the ring shape In order to advance the main body of the excavator, a plurality of shield jacks are provided on the inner peripheral surface of the shield frame at intervals in the circumferential direction.

  Such shield machine extends the shield jack, presses the cutter against the face, rotates the cutter around an axis parallel to the direction of excavation, etc., cuts the face with the cutter, and removes the excavated earth and sand ( It is taken into the inside of the excavator main body by a screw conveyor, etc., and the excavator main body is moved forward (excavated) according to the extension stroke of the shield jack. After dredging, the shield jack is contracted to provide a space between the existing segment and the shield jack. Is formed, and the segments are assembled in a ring shape by an erector in the space to construct a tunnel.

  The conventional shield machine generally has a digging cross section with respect to the face that is symmetrical in the vertical and / or left and right directions. Therefore, each shield jack has the same jack thrust at equal intervals in the circumferential direction of the shield frame. Had been placed. In other words, if the excavation cross section with respect to the face is symmetrical vertically and / or left and right, even if shield jacks having the same jack thrust are arranged at equal intervals in the circumferential direction of the shield frame, the pressing force of the cutter against the face will be There is no imbalance between the top and bottom and / or left and right.

JP 2002-47883 A

  However, in recent years, shield machines have been developed in which the excavation cross-section is an atypical excavation cross-section that is asymmetric in the vertical and / or left-right direction. For example, in the field of road tunnels in which a plurality of lanes are arranged side by side, there is a demand for the development of an asymmetric shield shield machine having an excavating cross-sectional shape that is a horseshoe shape. In the horseshoe-shaped tunnel, a plurality of lanes are juxtaposed at the widest portion thereof. However, when compared with a tunnel having a circular cross section having the widest portion as a diameter, a waste digging region is reduced.

  In such a shield machine with a horseshoe-shaped excavation cross-section, the portion below the centroid (center of gravity) of the excavation cross-section (horse-shoe shape) (the portion below the virtual line extending in the left-right direction through the centroid) is The area is larger than the part above the centroid (the part above the virtual line). For this reason, if shield jacks with the same jack thrust are arranged at equal intervals along the periphery of the horseshoe-shaped excavation cross section inside the main body of the excavator, the thrust below the centroid is insufficient in the excavation cross section with respect to the face Resulting in.

  As a countermeasure against this, if the arrangement interval of the shield jacks in the portion below the centroid is narrower than the arrangement interval of the shield jacks in the portion above the centroid to increase the arrangement density of the jacks, the above-mentioned thrust is insufficient. Although the problem is solved, if the interval between the shield jacks is reduced, the shoes of the adjacent shield jacks (portions that abut against the existing segments) interfere with each other, and it is difficult to actually establish it.

  Patent Document 1 describes a shield machine that constructs a circular tunnel with a floor using a thick invert segment with a floor integrally formed and a normal arch segment. In this shield machine, the point of action of the invert segment shield jack that presses the invert segment is closer to the center of the shield frame than the point of action of the arch segment shield jack that presses the arch segment, The thrust of the shield jack for the invert segment is set larger than the thrust of the shield jack for the arch segment.

  In the shield machine described in Patent Document 1, the shield arm for the invert segment having a large thrust has a short arm arm length acting on the machine body, and the shield jack for the arch segment having a small thrust is provided in the machine. Because the arm of the moment that acts is long, the shield jack for the invert segment with a large thrust presses the segment and the shield jack for the arch segment with a small thrust presses the segment. It is possible to balance the moment generated in the excavator body.

  However, Patent Document 1 only describes a shield machine having a circular excavation cross section, and is an irregular excavation cross section in which the excavation cross section with respect to the face is asymmetrical in the vertical and / or left and right directions, which is the premise of the present invention. The shield machine is not disclosed or suggested. In addition, since it is not described about the shield excavator of the irregular excavation cross section, the irregular excavation cross section is a virtual line extending through the centroid of the irregular excavation cross section in the direction orthogonal to the forward direction of the excavator main body, A large area shield jack that is virtually divided into a large area part and a narrow area part and is placed in the wide area part has a larger jack thrust than a narrow area shield jack placed in the narrow area part The technical idea of the present invention, including that of course, is not disclosed or suggested.

  The object of the present invention, which was created in view of the above circumstances, is to provide a shielded excavator having an atypical excavation cross section with an asymmetrical vertical and / or left and right excavation cross section with respect to the face. An object of the present invention is to provide a shield machine capable of avoiding the problem of insufficient thrust generated in a part of the deformed excavation cross section at the face even at equal intervals along the periphery.

  In order to achieve the above object, the present invention provides a shield machine having a deformed cross section with an asymmetrical vertical and / or left and right asymmetrical excavation sections with respect to the working face, wherein a reaction force is applied to an existing segment in the excavator body. A plurality of shield jacks for advancing the main body of the excavator are arranged at equal intervals along the periphery of the irregular excavation section, and the irregular excavation section is passed through the centroid of the irregular excavation section. A virtual line extending in a direction orthogonal to the forward direction of the machine body, virtually divided into a large area part and a narrow area part, and a wide area arranged in the wide area part of the shield jack The partial shield jack includes one having a larger jack thrust than the narrow area shield jack disposed in the narrow area portion of the shield jack.

  The deformed excavation section is a horseshoe excavation section with the lower part bulging in the left-right direction compared to the upper part, and the virtual line passes in the left-right direction through the centroid of the horseshoe excavation section. The horseshoe-shaped excavation section is divided into two parts up and down, and the wide area part is a lower part of the horseshoe-shaped excavation section vertically divided by the virtual line, and the narrow area part is It is preferable that the upper portion of the horseshoe-shaped excavation cross section divided into two vertically by a virtual line.

  The lower wide area pressing force value obtained by dividing the jack thrust of all jacks of the large area shield jack by the area of the large area section is the jack thrust of all jacks of the narrow area shield jack of the narrow area section. It is preferable that it is larger than the pressing value of the upper narrow area divided by the area.

  The difference between the pressing force value of the lower wide area portion and the pressing force value of the upper narrow area portion is determined based on the difference in earth load that the narrow area portion and the lower wide area portion below receive from the face. It is preferred that

  According to the present invention, in a shield machine having a modified excavation cross-section in which the excavation cross section with respect to the face is asymmetrical in the vertical and / or left and right directions, even if the interval between the shield jacks is equal along the periphery of the irregular excavation cross-section, The problem of insufficient thrust generated in a part of the deformed excavation section in FIG.

  A preferred embodiment of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, a shield machine 1 provided with a propulsion device according to the present embodiment cuts a face into a machine body 3 having a cylindrical shield frame 2 and a front portion of the machine body 3. , A soil removal device 5 for taking the earth and sand cut by the cutter 4 into the inside of the excavator body 3, and a segment 6 provided inside the excavator body 3 within the shield frame 2. A plurality of erectors (not shown) assembled in a ring shape along the peripheral surface and a plurality of spacers 6 provided on the inner peripheral surface of the shield frame 2 at intervals in the circumferential direction. And a shield jack 7 for advancing the excavator main body 3.

  The shield frame 2 is provided with a partition wall 8 that divides the interior of the shield frame 2 into the front and rear in the digging direction. The cutter 4 is rotatable about an axis parallel to the axis (rotation axis) along the digging direction. It is supported by. Specifically, a plurality of intermediate beams 9 extending rearward in the axial direction are provided on the surface of the cutter 4 on the side opposite to the face, with an interval in the circumferential direction. Are mounted on a rotating ring 10 supported so as to be rotatable around the rotation shaft. That is, the cutter 4 is rotatably supported by the partition wall 8 via the intermediate beam 9 and the rotating ring 10. Therefore, by rotating the rotating ring 10 via the motor 11 and the gear 12, the cutter 4 is rotationally driven around the rotating shaft. The earth and sand cut by the cutter 4 is once taken into the cutter chamber 13 in front of the partition wall 8 and then transported into the mine behind the partition wall 8 by a soil removal device 5 (screw conveyor) penetrating the partition wall 8.

  The shield frame 2 includes a cylindrical front cylinder 2f and a rear cylinder 2r. The front cylinder 2f and the rear cylinder 2r are connected via a spherical joint 14 so as to be bent in all directions, and the front cylinder 2f and the rear cylinder 2r. And are connected via a jack 15 that is bent halfway. By bending the front cylinder 2f and the rear cylinder 2r, a sharp curve can be excavated. A plurality of the middle folding jacks 15 are arranged at equal intervals in the circumferential direction of the shield frame 2, and the sizes of the upper middle folding jack 15a and the lower middle folding jack 15b in FIG. 1 are different. This will be described later.

  The rear cylinder 2r is provided with an erector (not shown) for assembling the segment 6 in a ring shape along the inner peripheral surface of the rear cylinder 2r, and the reaction force is applied to the segment 6 assembled in the ring shape. A shield jack 7 is provided for moving the excavator main body 3 forward. A plurality of shield jacks 7 are arranged at equal intervals in the circumferential direction of the shield frame 2, and the size of the upper shield jack 7a and the lower shield jack 7b in FIG. 1 is different. It will be described later.

  As shown in FIGS. 2 to 4, the shield frame 2 (the front trunk 2 f and the rear trunk 2 r) is formed in a horseshoe shape with a lower portion bulging in the left-right direction as compared with the upper portion. This is because the tunnel has a horseshoe shape in cross section and a plurality of lanes are juxtaposed in the widest part of the tunnel. The cutter 4 has a function of cutting the face into a cross-section horseshoe according to the cross-sectional shape of the shield frame 2. In other words, the shield machine 1 has an irregularly shaped excavation section in which the excavation section with respect to the face is asymmetrical in the vertical direction.

  As shown in FIGS. 2 and 3, the cutter 4 includes a center portion 16 arranged at the center of rotation C thereof, a plurality of first cutter spokes 17 attached to the center portion 16, and a first cutter spoke 17. A plurality of second cutter spokes 19 attached to the first cutter pork 17 via a connecting member 18 and a beam cutter 20 (trademark registration pending) attached to the first cutter pork 17. The connecting member 18 is interposed not only between the first cutter pork 17 and the second cutter pork 19 but also between the first cutter porks 17 and between the second cutter porks 19. , 19 are connected. The tips of adjacent first cutter porks 17 are connected by an arc-shaped connecting member 21, and the tips of adjacent second cutter porks 19 are connected by an arc-shaped connecting member 22. Further, the intermediate beam 9 (see FIG. 1) described above is attached to the surfaces of the first cutter spoke 17 and the second cutter spoke 19 on the side opposite to the face.

  The first cutter spoke 17 and the second cutter spoke 19 are arranged radially with respect to the rotation center C of the cutter 4 in the same plane parallel to the face. The rotation center C is located at the midpoint between the upper end and the lower end of the shield frame 2, and the distance from the rotation center C to the tip of the first cutter pork 17 and the tip of the second cutter pork 19. Are equal to the distance from the rotation center C to the upper end (or lower end) of the shield frame 2. Therefore, when the first and second cutter spokes 17 and 19 are integrally rotated around the rotation center C, the face is excavated in a circular shape as indicated by an imaginary line L. The face between the circular imaginary line L and the shield frame 2 having a horseshoe cross section is excavated by the beam cutter 20 described above.

  The beam cutter 20 is formed in a substantially arcuate shape, and the portions inside the longitudinal ends of the beam cutter 20 are accommodated in the two first cutter spokes 17 spaced apart from each other in the circumferential direction. A pin is coupled to the expansion / contraction portion 23 a of the drive jack 23. The drive jack 23 (hydraulic jack) includes a fixing portion 23b and an expansion / contraction portion 23a that expands and contracts with respect to the fixing portion 23b. The fixing portion 23b is pin-coupled to the central portion 16 of the cutter 4, and the expansion / contraction portion 23a is the portion of the beam cutter 20 It is pin-coupled to. A hydraulic line is connected to each drive jack 23, and these hydraulic lines pass through the inside of a shaft body 24 (see FIG. 1) provided on the surface opposite to the face of the central portion 16 of the cutter 4, and the partition wall 8. It is pulled out behind the partition wall 8, that is, into a pit, through a rotary joint 25 provided in the, and connected to a hydraulic circuit (not shown).

  The hydraulic circuit controls the expansion and contraction of each drive jack 23 such that both end portions of the beam cutter 21 excavate the face between the virtual line L and the shield frame 2. In other words, the rotary joint 25 is provided with a rotation angle sensor for detecting the rotation angle of the cutter 4, and the expansion / contraction amount of each drive jack 23 is controlled by a controller incorporated in the hydraulic circuit according to the output value of the rotation angle sensor. By doing so, both side portions of the beam cutter 20 appropriately protrude radially outward from the imaginary line L, and the face between the imaginary line L and the shield frame 2 is appropriately excavated.

  As shown in FIG. 4, a plurality of shield jacks 7 (7a, 7b) are arranged at equal intervals in the circumferential direction on the inner peripheral surface of the shield frame 2 (rear barrel 2r). That is, a plurality of shield jacks 7 are arranged at equal intervals along the peripheral edge of the irregular excavation section (horse-shoe excavation section). These shield jacks 7 have different jack thrusts for the upper side 7a and the lower side 7b, and the jack thrust of the lower side 7b is larger than the jack thrust of the upper side 7a. This point will be described in detail below.

  A plurality of shield jacks 7 cross the shield frame 2 in the direction perpendicular to the forward direction of the excavator body 3 through the centroid G of the modified excavation section (in a plane parallel to the face). The narrow area shield jack 7a disposed in the upper narrow area portion A is virtually divided into the narrow area portion A and the wide area portion B by the virtual line X extending in the horizontal direction). And a large area shield jack 7b arranged in the lower large area B. The virtual line X may extend in the left-right direction so as to cross the deformed excavation section (horse-shoe excavation section) through the rotation center C instead of the centroid G, and may divide the horseshoe excavation section into two.

  The large area shield jack 7b includes a jack having a larger jack thrust than the narrow area shield jack 7a. Specifically, the narrow area shield jack 7a is composed of only a small shield jack 7s having a small jack thrust, and the wide area shield jack 7b is composed of a small shield jack 7s and a large shield jack 7L having a larger jack thrust. The segment 6 pressed by the small shield jack 7s is a thin segment 6s, and the segment 6 pressed by the large shield jack 7L is a thick segment 6L thicker than the thin segment 6s.

  D in FIG. 4 is a dividing line of each segment 6. As the radius of curvature of the segment 6 is larger, that is, as the curvature is closer to flat, the strength against a load (earth pressure, water pressure) applied from the outside decreases, so the thickness needs to be increased. The axis of the small shield jack 7s is disposed on the neutral axis Ns (neutral line) of the thin segment 6s, and the axis of the large shield jack 7L is disposed on the neutral axis NL of the thick segment 6L. .

The value obtained by dividing the jack thrust of all jacks of the large area shield jack 7b by the area of the large area portion B (lower large area portion pressing force value: Ton / m ² ) is the value of all jacks of the narrow area shield jack 7a. It is larger by a predetermined value than the value obtained by dividing the jack thrust by the area of the narrow area part A (upper narrow area part pressing force value: Ton / m ² ). This predetermined value is a correction value determined based on the difference in earth load that the upper narrow area part A and the lower wide area part B below receive from the face. In the case of a small-diameter tunnel in which the length (height) between the upper end and the lower end of the shield frame 2 is small, the upper narrow area portion A and the lower wide area portion B are respectively received from the face. Since the earth load difference is small, the correction value (predetermined value) is set to zero, and the lower wide area pressing force value (Ton / m ² ) and the upper narrow area pressing force value (Ton / m ² ) It can be considered to be equal.

  As shown in FIG. 1, a plurality of bent jacks 15 (15 a, 15 b) that connect the front barrel 2 f and the rear barrel 2 r are arranged at equal intervals in the circumferential direction of the shield frame 2. These middle folding jacks 15 are divided into upper and lower parts along a virtual line X shown in FIG. 4, and a wide area part middle folding jack 15b arranged in a wide area part B below the virtual line X and the virtual line X. It is divided into a narrow-area portion folding jack 15a arranged in the upper narrow-area portion A. The wide area portion bent jack 15b includes a jack having a larger jack thrust than the narrow area portion bent jack 15a.

  Specifically, the narrow area jack 15a is composed of only a small middle jack 15s with a small jack thrust, and the wide area jack 15b is a small middle jack 15s and a large middle jack with a larger jack thrust. 15L. The large / medium fold jack 15L corresponds to the large shield jack 7L in FIG. 4 and is arranged on the radially inner side of the shield frame 2 with respect to the jack 7L. The small / medium fold jack 15s corresponds to the small shield jack 7s in FIG. Correspondingly, the shield frame 2 is disposed radially inward of the jack 7s.

  The operation of this embodiment will be described.

  According to the shield machine according to the present embodiment, as shown in FIG. 4, the shield machine corresponds to the wide area portion B below the virtual line X extending in the horizontal direction through the centroid G of the horseshoe excavation section. Since the wide area shield jack 7b includes a jack having a larger jack thrust than the narrow area shield jack 7a corresponding to the narrow area A above the virtual line X, the lack of thrust in the wide area B of the face is avoided. can do.

The value obtained by dividing the jack thrust of all jacks of the large area shield jack 7b by the area of the wide area portion B (lower wide area portion pressing force value: Ton / m ² ) is the value of all jacks of the narrow area shield jack 7a. The upper narrow area part A and the lower wide area part B are received from the face than the value obtained by dividing the jack thrust by the area of the narrow area part (upper narrow area part pressing force value: Ton / m ² ). Since it is large by the correction value determined based on the difference in earth load, the face pressing force per unit area in the large area part B of the face and the face pressing force per unit area in the narrow area part A of the face are: It is equal after taking into account the area difference between the narrow area part A and the wide area part B and the earth load difference due to the vertical position. For this reason, when each shield jack 7 (7a, 7b) is unintentionally extended with the thrust of a predetermined design value, the shield machine 1 goes straight, and direction control in all directions of the excavation direction is easy. Become.

  Since the large area shield jack 7b and the narrow area shield jack 7a are arranged at equal intervals in the circumferential direction of the shield frame 2, the shoe 71 (71a) of the adjacent shield jack 7 (7a, 7b) is disposed. 71b) do not interfere with each other. In addition, if the space | interval of the lower wide area part shield jack 7b is made narrower than the upper narrow area part shield jack 7a, the thrust of the large area part shield jack 7b shall be made larger than the thrust of the narrow area part shield jack 7a. However, the problem of insufficient thrust in the large area B of the horseshoe-shaped excavation cross section of the face is solved, but if the arrangement interval of the shield jack 7b is reduced, the shoe 71b (segment 6L of the adjacent large area shield jack 7b is damaged). Since a predetermined pressing area is necessary for pressing without any interference), it is difficult to actually establish it.

  The shoe 71L of the large shield jack 7L of the large area shield jack 7b has a smaller circumferential dimension than the shoes 71s of the other small shield jacks 7s, but the radial thickness is obtained by utilizing the plate thickness of the thick segment 6L. Since the dimensions are increased, it is possible to secure a pressing area for pressing the segment 6L (made of concrete) without damaging it.

  Since the shaft centers of the shield jacks 7a and 7b are respectively arranged on the neutral axes Ns and NL of the segments 6a and 6L, the shoes 71a and 71b of the shield jacks 7a and 7b press the corresponding segments 6a and 6L. Then, the segments 6a and 6L only receive a compressive force in the axial direction, and no moment that causes a change in posture of the segments 6a and 6L does not occur.

  With respect to the bent jack 15, the wide area portion bent jack 15b corresponding to the wide area portion B includes a jack having a larger jack thrust than the narrow area portion bent jack 15a corresponding to the narrow area portion A. For the same reason as 7 (7a, 7b), it is possible to avoid shortage of the middle-turn thrust in the wide area B of the horseshoe excavation cross section of the face.

  The present invention is not limited to the above embodiment.

  For example, the above-described horseshoe excavation section may be turned upside down so as to be an asymmetrical irregular excavation section having a wide area B on the upper side and a narrow area A on the lower side. Around (rotation center C), for example, it may be rotated 90 degrees to form an asymmetrical excavation section that is asymmetrical to the left or right, or may be rotated at an angle of less than 90 degrees to form an asymmetrical excavation section that is asymmetrical.

  In addition, the virtual line extends through the centroid of the irregular excavation section in a direction orthogonal to the forward direction of the excavator body and crosses the excavator body to divide the irregular excavation section into a wide area portion and a narrow area portion. If it is a thing, it is not restricted to the virtual line X of FIG.

  The irregular excavation cross section is not limited to the horseshoe excavation cross section, and various irregular excavation cross sections (for example, deformed elliptical cross section, deformed spectacle-shaped cross section, etc.) that are asymmetrical in the vertical and / or left and right directions are conceivable. FIGS. 5A and 5B show the arrangement of the shield jacks (the narrow area portion shield jack 7a and the wide area portion shield jack 7b) in the case of the modified elliptical cross section and the modified spectacle-shaped cross section. In the figure, the intervals between adjacent jacks are all equal.

It is a sectional side view of the shield machine based on one Embodiment of this invention. It is the II-II sectional view taken on the line of FIG. It is the III-III sectional view taken on the line of FIG. It is the IV-IV sectional view taken on the line of FIG. It is a rear view of the shield machine which concerns on the deformation | transformation embodiment of this invention, (a) is excavation cross-section a deformation | transformation elliptical cross-section type, (b) is explanatory drawing of a excavation cross-section a deformation | transformation spectacle-shaped cross-section type.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shield engraving machine 3 Engraver main body 6 Segment 7 Shield jack 7a Narrow area part shield jack 7b Wide area part shield jack A A narrow area part B Wide area part G Centric X Virtual line

Claims (4)

A shield machine in which the excavation cross-section with respect to the face is an asymmetrical excavation cross-section that is asymmetric in vertical and / or left and right directions,
In the excavator main body, a plurality of shield jacks for advancing the excavator main body by taking a reaction force on an existing segment are arranged at equal intervals along the periphery of the irregular excavation cross section,
The irregular excavation cross section is virtually divided into a wide area portion and a narrow area portion by a virtual line extending in a direction orthogonal to the forward direction of the excavator body through the centroid of the irregular excavation cross section. And
The large-area shield jack arranged in the wide-area portion of the shield jack includes a jack having a larger jack thrust than the narrow-area shield jack arranged in the narrow-area portion of the shield jack. A shield machine characterized by that. The deformed excavation section is a horseshoe-shaped excavation section with the lower part bulging in the left-right direction compared to the upper part, and the virtual line passes in the left-right direction through the centroid of the horseshoe-shaped excavation section. The horseshoe-shaped excavation section is divided into two parts up and down,
The wide area portion is a lower portion of the horseshoe-shaped excavation cross-section divided into two vertically on the virtual line,
2. The shield machine according to claim 1, wherein the narrow area portion is an upper portion of the horseshoe-shaped excavation cross section that is vertically divided into two along the virtual line.   The lower wide area pressing force value obtained by dividing the jack thrust of all jacks of the large area shield jack by the area of the large area section is the jack thrust of all jacks of the narrow area shield jack of the narrow area section. The shield machine according to claim 2, wherein the shield excavator is larger than the pressing force value of the upper narrow area divided by the area.   The difference between the pressing force value of the lower wide area portion and the pressing force value of the upper narrow area portion is determined based on the difference in earth load that the narrow area portion and the lower wide area portion below receive from the face. The shield machine according to claim 3.

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