Zero-support zoning excavation method for ultra-large and ultra-deep foundation pits in water areas

Abstract

The present invention provides a method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas, comprising: prefabricated piles for a construction platform, scissors braces, arched beams, an embedded construction platform, an outsourced construction platform, tie rods, main unit piles, equilateral sub-unit piles, isosceles sub-unit piles, water-stopping pins, reinforced concrete bottom plates, temporary sand cushion layers, steel caissons, and reinforced concrete retaining walls. Compared with commonly used rectangular foundation pits, the present invention uses a self-stabilizing geometric cofferdam composed of reusable unit piles of different models, so that soft soil foundation pits can achieve structural stability without support and have a water-stopping effect. Its zoning excavation method uses steel caissons to excavate different design depth areas of the foundation pit, saving the construction cost of ultra-large and ultra-deep foundation pits in water areas and improving construction efficiency.

Description

Technical field:

[0001] The present invention belongs to the field of soft soil foundation pit engineering, and in particular relates to a zero-support zoning excavation method for an ultra-large and ultra-deep foundation pit in a water area. Technical background:

[0002] Currently, rectangular foundation pits are often used in foundation pit construction. This makes it difficult for the pit slope to achieve self-stabilization without support, especially in soft soil foundation pits, where support is particularly critical. Consequently, simple support methods, trench support, inclined column support, anchor support, and wall support are often used, combined with internal support, significantly increasing construction costs and timelines. Examples include the foundation pit support methods disclosed in patents CN208009439U and CN208594559U. Furthermore, CO-type steel pipe piles are required for water-stopping. For example, the connection mechanism between the cofferdam support steel pipe piles and the steel pipe piles disclosed in patent CN218643402U further increases the number of construction steps and prolongs the construction period. Furthermore, these CO-type steel pipe piles are not self-stabilizing. Even though they can be flexibly assembled into various geometric shapes, they are constrained by the shape of the foundation pit support itself and cannot leverage the inherent self-stabilizing properties of the circular shape to improve foundation pit stability. Furthermore, these supports are often permanent and cannot be reused, significantly reducing their economic efficiency. Summary of the invention:

[0003] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and to provide a method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas.

[0004] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solution: a method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas, comprising the following specific steps:

[0005] S1: Drive precast piles for the construction platform in the designated waters; connect the precast piles of each construction platform with scissor braces; install an arched beam between two adjacent precast piles of the construction platform, and bolt both ends of the arched beam to the sides of the corbels of the precast piles of the construction platform; hoist the embedded construction platform and the outsourced construction platform to the top of the precast piles of the construction platform and secure them with bolts;

[0006] S2: Hoist the main unit pile to the set position where the arc transition is required and sink the pile to the designed depth; connect the main unit pile and the arch beam through the tie rod, and support the main unit pile through the arch beam and the tie rod;

[0007] S3: Hoisting and sinking the isosceles sub-unit piles and equilateral sub-unit piles. The isosceles sub-unit piles and equilateral sub-unit piles are hoisted between the main unit piles and sequentially hoisted along the designed arc. The isosceles sub-unit piles and equilateral sub-unit piles are sequentially spaced apart. Both sides of the isosceles sub-unit piles and equilateral sub-unit piles are provided with slots that match the water-stop pins. Adjacent isosceles sub-unit piles and equilateral sub-unit piles are closely connected. The isosceles sub-unit piles, equilateral sub-unit piles, and main unit piles together form a cofferdam with an arc-shaped structure that supports the entire side wall of the foundation pit.

[0008] S4: inserting the water-stop pins into the slots on the adjacent isosceles sub-unit piles and the equilateral sub-unit piles at the same time, so that the adjacent isosceles sub-unit piles and the equilateral sub-unit piles are sealed and connected by the water-stop pins;

[0009] S5: Pump out the water in the cofferdam to form a foundation pit, which is then excavated layer by layer until the set excavation depth is reached. After the excavation is completed, a reinforced concrete base plate is poured at the bottom of the foundation pit, and a partitioned excavation position is reserved, where a temporary sand cushion layer is laid.

[0010] S6: Hoist and sink the steel caisson at the partitioned excavation location; excavate in layers in the steel caisson to the set excavation depth, and pour a reinforced concrete bottom plate at the bottom of the excavation area in the steel caisson;

[0011] S7: Cast a reinforced concrete retaining wall along the inner side of the cofferdam. After the reinforced concrete retaining wall is cured, test its bearing capacity. Once the bearing capacity meets the standard, remove all equilateral and isosceles subunit piles.

[0012] S8: Remove the tie rods connecting the main unit piles and the arch beams, then lift and remove the main unit piles, and finally remove the embedded construction platform, outsourced construction platform, scissors braces and prefabricated piles of the construction platform one by one.

[0013] Preferably, the main unit pile is a pile with a regular triangular cross-section formed by welding a piece of slotless steel plate A and two pieces of three-slot steel plates A. The width and thickness of the three-slot steel plate A and the slotless steel plate A are equal. The three-slot steel plate A is provided with three slots for connecting waterstop pins; the slotless steel plate A is provided with a pull rod interface for connecting the pull rod.

[0014] Preferably, the pull rod includes a main rod, a rotatable fixed end and a connecting ball head. The rotatable fixed end is connected to the main rod through the connecting ball head, and the main rod is connected to the arch beam through bolts; the front end of the rotatable fixed end is provided with a connecting head, and the cross-sectional shape of the connecting head is the same as the pull rod interface on the slotless steel plate A; when the pull rod is connected to the main unit pile, the connecting head on the rotatable fixed end of the pull rod is aligned with the pull rod interface on the slotless steel plate A and then passed through the pull rod interface, and then the connecting head is rotated 90°, and finally the connecting head is fixed to the slotless steel plate A on the main unit pile by bolts.

[0015] Preferably, the isosceles sub-unit pile is a triangular cross-section pile welded by a three-groove steel plate B and two double-groove steel plates B; the three-groove steel plate B is provided with three slots for connecting waterstop pins, and the double-groove steel plate B is provided with two slots for connecting waterstop pins. The three-groove steel plate B on the isosceles sub-unit pile is the same length as the three-groove steel plate A on the main unit pile, and the slots on the three-groove steel plate A and the three-groove steel plate B correspond one to one.

[0016] Preferably, the equilateral sub-unit pile is an equilateral triangular cross-section pile welded from a slotless steel plate B and two double-slot steel plates A. The double-slot steel plates A and B have the same width, and the slots on the double-slot steel plates A and B correspond one to one.

[0017] Preferably, the main body of the waterstop plug is welded from two C-shaped steel pipes, the cross-section of the waterstop plug is in the shape of an "8", and the length of the waterstop plug is consistent with the height of the main unit pile; four waterstop rubber strips are inlaid on the outer wall of the waterstop plug; the two sides of the waterstop plug are respectively inserted into the slots on the adjacent isosceles sub-unit piles and equilateral sub-unit piles, and the waterstop rubber strips on the waterstop plug are in sealing contact with the inner wall of the slot.

[0018] The beneficial effects of this invention are: compared with conventional soft soil foundation pits that use a combination of supporting structures and CO-type steel pipe piles, the unit pile structure of this invention enables the foundation pit to be self-stabilized without support, while also providing water-stopping properties, eliminating the complex supporting structure process. The unit piles can be flexibly combined to accommodate soft soil foundation pits in different environments, and after construction is completed, they can be dismantled for reuse, making them more economical and environmentally friendly. Description of the drawings:

[0019] Figure 1 This is the plan view of construction steps S1-S3.

[0020] Figure 2 This is the plan view of construction steps S4-S5.

[0021] Figure 3 、 Figure 4 、 Figure 5 It is a plan view of construction steps S6-S7.

[0022] Figure 6 This is the plan view of construction step S8.

[0023] Figure 7 、 Figure 8 This is the plan view of construction step S9.

[0024] Figure 9 、 Figure 10 This is the plan view of construction step S10.

[0025] Figure 11 This is the plan view of construction step S11.

[0026] Figure 12 It is a cross-sectional view of the main unit pile.

[0027] Figure 13 It is a cross-sectional view of an isosceles subunit pile.

[0028] Figure 14 It is the cross section of the pile of equilateral subunit.

[0029] Figure 15 This is a cross-sectional view of a waterstop pin.

[0030] Figure 16 yes Figure 1 Elevation drawing of .

[0031] Figure 17 yes Figure 2 Elevation drawing of .

[0032] Figure 18 yes Figure 6 Middle BB section elevation.

[0033] Figure 19 yes Figure 7 Middle CC section elevation.

[0034] Figure 20 yes Figure 8 Middle DD section elevation.

[0035] Figure 21 yes Figure 9 Middle EE section elevation.

[0036] Figure 22 yes Figure 10 Elevation drawing of the middle GG section.

[0037] Figure 23 yes Figure 11 Middle HH section elevation.

[0038] Figure 24 It is a plan view of the main unit pile tie rod connection.

[0039] Figure 25 It is a schematic elevation diagram of the main unit pile tie rod connection.

[0040] Figure 26 This is a schematic diagram of the tie rod interface on the main unit pile.

[0041] Figure 27 It is a diagram of the pull rod.

[0042] Figure 28 It is a plan view of the embedded construction platform.

[0043] Figure 29This is the elevation drawing of the embedded construction platform.

[0044] Figure 30 It is a plan view of the outsourced construction platform.

[0045] Figure 31 It is a flow chart of the present invention.

[0046] In the figure: 1. Precast piles for construction platform; 2. Scissors brace; 3. Arch beam; 4. Embedded construction platform; 5. Outsourced construction platform; 6. Pull rod; 6-1. Main rod; 6-2. Rotatable fixed end; 6-3. Connecting ball head; 7. Main unit pile; 7-1. Slotless steel plate A; 7-2. Three-slot steel plate A; 8. Equilateral secondary unit pile; 8-1. Slotless steel plate B; 8-2. Double-slot steel plate A; 9. Isosceles secondary unit pile; 9-1. Three-slot steel plate B; 9-2. Double-slot steel plate B; 10. Waterstop pin; 10-1. C-type steel pipe; 10-2. Waterstop rubber strip; 11. Reinforced concrete bottom plate; 12. Temporary sand cushion layer; 13. Steel caisson; 14. Reinforced concrete retaining wall. Specific implementation method:

[0047] Combined with the drawings in the specification, Figures 1 to 31 The technical solution of the present invention is further described:

[0048] A method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas, such as Figure 8 、 Figure 28 、 Figure 29 、 Figure 30 As shown, it includes: prefabricated piles 1 of the construction platform, scissors struts 2, arched beams 3, embedded construction platform 4, outsourced construction platform 5, tie rods 6, main unit piles 7, equilateral sub-unit piles 8, isosceles sub-unit piles 9, water-stop pins 10, reinforced concrete base plate 11, temporary sand cushion layer 12, steel caisson 13 and reinforced concrete retaining wall 14.

[0049] The main unit piles 7, isosceles sub-unit piles 9 and equilateral sub-unit piles 8 are freely combined to form the arc-shaped structural cofferdam required by the design. The self-stabilizing characteristics of the arc-shaped frame are used to make the foundation pit stable without support.

[0050] The water-stopping pins 10 can be inserted into the slots between the main unit piles, the isosceles sub-unit piles and the equilateral sub-unit piles in the arc-shaped frame to achieve connection and water-stopping between the unit piles.

[0051] See also Figures 1-31 , the construction method of the present invention comprises the following steps:

[0052] S1: If Figure 1 、 Figure 16 As shown, a water operation equipment such as a ship is used to drive a construction platform prefabricated pile 1 to a designed depth in a predetermined water area.

[0053] S2: If Figure 1 、 Figure 16 As shown, the scissors brace 2 is installed and connected using a hoop, and the prefabricated piles of each construction platform are connected through the scissors brace 2 to prevent relative displacement between them.

[0054] S3: If Figure 1 、 Figure 16 As shown, an arched beam 3 is installed between two adjacent precast piles 1 of the construction platform, and both ends of the arched beam 3 are fixed to the side of the bracket of the precast pile 1 of the construction platform by bolts;

[0055] S4: As Figure 2 、 Figure 17 As shown, the embedded construction platform 4 and the outsourced construction platform 5 are respectively hoisted to the top of the precast pile 1 of the construction platform, and the interface positions on the embedded construction platform 4 and the outsourced construction platform 5 are aligned with the interface positions on the top of the precast pile 1 of the construction platform and fixed with bolts; after the embedded construction platform 4 and the outsourced construction platform 5 are installed, the materials required for the subsequent steps, such as the main unit pile 7, the water-stop pin 10, etc., and the equipment, such as the lifting device, can be transported and stored on the embedded construction platform 4 and the outsourced construction platform 5, and the operations of the construction personnel and equipment are also carried out on the embedded construction platform 4 and the outsourced construction platform 5.

[0056] S5: If Figure 2 、 Figure 17 As shown, according to the design, the main unit pile 7 is hoisted to the set position where the arc transition is required and the pile is sunk to the designed depth; the main unit pile 7 and the arched beam 3 are connected by the pull rod 6, and the main unit pile 7 is supported by the arched beam 3 and the pull rod 6 to make it stable and not fall over.

[0057] S6: As Figure 3 、 Figure 4 、 Figure 5 As shown, according to the design, the isosceles sub-unit piles 9 and the equilateral sub-unit piles 8 are hoisted and placed between the main unit piles 7 and are hoisted in sequence along the designed arc.

[0058] Among them, the isosceles sub-unit piles 9 and the equilateral sub-unit piles 8 are arranged in sequence, and slots matching the water-stop pins 10 are respectively provided on both sides of the isosceles sub-unit piles 9 and the equilateral sub-unit piles 8. The adjacent isosceles sub-unit piles 9 and the equilateral sub-unit piles 8 are closely connected with each other slot by slot. The isosceles sub-unit piles 9, the equilateral sub-unit piles 8 and the main unit piles 7 together form a cofferdam with an arc-shaped structure supporting the side wall of the entire foundation pit;

[0059] S7: As Figure 3 、 Figure 4 、 Figure 5As shown, the water-stop pins are simultaneously inserted into the slots on the adjacent isosceles sub-unit piles 9 and the equilateral sub-unit piles 8, and each unit pile is firmly connected by the water-stop pins 10. The adjacent isosceles sub-unit piles 9 and the equilateral sub-unit piles 8 are sealed by the water-stop pins 10;

[0060] S8: Figure 6 As shown, the water in the cofferdam is pumped out and discharged outside the cofferdam. After the water is pumped out, a foundation pit is formed. The foundation pit is then excavated layer by layer until the set excavation depth is reached. After excavation is completed, a reinforced concrete base plate 11 is poured at the bottom of the foundation pit, and locations for sub-divisional excavation are reserved. A temporary sand mattress layer 12 is laid on these sub-divisional excavation locations.

[0061] S9: As Figure 7 、 Figure 8 As shown, a steel caisson 13 is hoisted and sunk at the partitioned excavation position; layered excavation is continued in the steel caisson 13 to a set excavation depth, and a reinforced concrete bottom plate 11 is poured at the bottom of the excavation area in the steel caisson 13 .

[0062] S10: Figure 9 、 Figure 10 As shown, a reinforced concrete retaining wall 14 is cast along the inner side of the cofferdam. After the reinforced concrete retaining wall 14 is cured, its bearing capacity is tested. After the bearing capacity meets the standard, all the equilateral sub-unit piles 8 and isosceles sub-unit piles 9 are finally removed.

[0063] S11: If Figure 11 As shown, the tie rod 6 connecting the main unit pile 7 and the arch beam 3 is removed, and then the main unit pile 7 is lifted and removed, and finally the embedded construction platform 4, the outsourced construction platform 5, the scissors support 2 and the construction platform prefabricated pile 1 are removed one by one.

[0064] like Figure 12 As shown, the main unit pile 7 is a pile with a regular triangular cross-section, welded from a single slotless steel plate A7-1 and two triple-slot steel plates A7-2. The triple-slot steel plate A and the slotless steel plate A are of equal width and thickness. The triple-slot steel plate A is provided with three slots for connecting waterstop pins 10. The slotless steel plate A7-1 is provided with a tie rod interface for connecting the tie rod 6.

[0065] like Figure 24 、 Figure 25 、 Figure 26 、 Figure 27As shown, the tie rod 6 includes a main rod 6-1, a rotatable fixed end 6-2, and a connecting ball head 6-3. The rotatable fixed end 6-2 is connected to the main rod 6-1 through the connecting ball head 6-3, and can rotate relative to the main rod 6-1 through the connecting ball head 6-3. The main rod 6-1 is connected to the arch beam 3 by bolts, and the front end of the rotatable fixed end 6-2 is provided with a connector, the cross-sectional shape of the connector is the same as the tie rod interface on the slotless steel plate A; when the tie rod 6 is connected to the main unit pile 7, the connector on the rotatable fixed end 6-2 on the tie rod 6 is aligned with the tie rod interface on the slotless steel plate A and then passed through the tie rod interface, and then the connector is rotated 90 degrees, and finally the connector is fixed to the slotless steel plate A on the main unit pile 7 by bolts.

[0066] like Figure 13 As shown, the isosceles sub-unit pile 9 is a triangular pile formed by welding a single three-grooved steel plate B9-1 and two double-grooved steel plates B9-2. The three-grooved steel plate B9-1 forms the long side of the triangle, while the double-grooved steel plate B9-2 forms the waist. Three slots are provided on the three-grooved steel plate B, while two slots are provided on the double-grooved steel plate B, for receiving waterstop pins 10. The three-grooved steel plate B on the isosceles sub-unit pile 9 is the same length as the three-grooved steel plate A on the main unit pile 7, and the slots on the three-grooved steel plates A and B correspond one-to-one.

[0067] like Figure 14 As shown, the equilateral sub-unit pile 8 is an equilateral triangular cross-section pile formed by welding a single slotless steel plate B8-1 and two double-slot steel plates A8-2. The double-slot steel plates A8-2 and B9-2 have the same width, and the slots on the double-slot steel plates A and B correspond one to one.

[0068] like Figure 15 As shown, the main body of the waterstop bolt 10 is welded from two C-shaped steel pipes 10-1. The cross-section of the waterstop bolt 10 is shaped like an "8," and the length of the waterstop bolt 10 matches the height of the main unit pile 7. Four waterstop rubber strips 10-2 are embedded in the outer wall of the waterstop bolt 10. The two sides of the waterstop bolt 10 are respectively inserted into the slots of the adjacent isosceles sub-unit pile 9 and equilateral sub-unit pile 8. The waterstop rubber strips 10-2 on the waterstop bolt 10 are in sealing contact with the inner wall of the slots.

Claims

1. A method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas, characterized in that: The specific steps include: S1: Driving a construction platform precast pile (1) in a predetermined water area; connecting each construction platform precast pile (1) through a scissors brace (2); installing an arch beam (3) between two adjacent construction platform precast piles (1), and fixing both ends of the arch beam (3) to the side of the bracket of the construction platform precast pile (1) through bolts; hoisting an embedded construction platform (4) and an outsourced construction platform (5) to the top of the construction platform precast pile (1) and fixing them with bolts; S2: The main unit pile (7) is hoisted to a set position where a circular arc transition is required and the pile is sunk to a designed depth; the main unit pile (7) and the arch beam (3) are connected by a tie rod (6), and the main unit pile (7) is supported by the arch beam (3) and the tie rod (6); S3: The isosceles sub-unit piles (9) and the equilateral sub-unit piles (8) are hoisted and sunk between the main unit piles (7) and hoisted in sequence along the designed arc; the isosceles sub-unit piles (9) and the equilateral sub-unit piles (8) are arranged in sequence, and slots matching the water stop pins (10) are provided on both sides of the isosceles sub-unit piles (9) and the equilateral sub-unit piles (8), and the adjacent isosceles sub-unit piles (9) and the equilateral sub-unit piles (8) are closely connected. The isosceles sub-unit piles (9), the equilateral sub-unit piles (8) and the main unit piles (7) together form a cofferdam of an arc-shaped structure supporting the entire foundation pit side wall; S4: inserting the water-stop pins (10) into the slots on the adjacent isosceles sub-unit piles (9) and the equilateral sub-unit piles (8) at the same time, so that the adjacent isosceles sub-unit piles (9) and the equilateral sub-unit piles (8) are sealed and connected by the water-stop pins (10); S5: Pumping out the water in the cofferdam to form a foundation pit, which is then excavated layer by layer until the set excavation depth is reached; after the excavation is completed, a reinforced concrete base plate (11) is poured at the bottom of the foundation pit, and a partitioned excavation position is reserved, and a temporary sand cushion layer (12) is laid on the partitioned excavation position; S6: hoisting and sinking the steel caisson (13) at the partitioned excavation location; excavating in layers in the steel caisson (13) to a set excavation depth, and pouring a reinforced concrete bottom plate (11) at the bottom of the excavation area in the steel caisson (13); S7: Cast a reinforced concrete retaining wall (14) along the inner side of the cofferdam, and after the reinforced concrete retaining wall (14) is cured, test its bearing capacity. After the bearing capacity meets the standard, remove all equilateral sub-unit piles (8) and isosceles sub-unit piles (9); S8: Remove the tie rod (6) connecting the main unit pile (7) and the arch beam (3), then lift and remove the main unit pile (7), and finally remove the embedded construction platform (4), the outsourced construction platform (5), the scissors support (2) and the prefabricated pile (1) of the construction platform one by one.

2. The method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas according to claim 1 is characterized in that: The main unit pile (7) is a pile with a regular triangular cross-section formed by welding a piece of slotless steel plate A (7-1) and two pieces of three-slot steel plates A (7-2). The three-slot steel plate A and the slotless steel plate A have the same width and thickness. The three-slot steel plate A is provided with three slots for connecting water stop pins (10); the slotless steel plate A (7-1) is provided with a pull rod interface for connecting a pull rod (6).

3. The method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas according to claim 2 is characterized in that: The pull rod (6) comprises a main rod (6-1), a rotatable fixed end (6-2) and a connecting ball head (6-3); the rotatable fixed end (6-2) is connected to the main rod (6-1) through the connecting ball head (6-3), and the main rod (6-1) is connected to the arch beam (3) through bolts; a connecting head is provided at the front end of the rotatable fixed end (6-2), and the cross-sectional shape of the connecting head is the same as the pull rod interface on the slotless steel plate A; when the pull rod (6) is connected to the main unit pile (7), the connecting head on the rotatable fixed end (6-2) on the pull rod (6) is aligned with the pull rod interface on the slotless steel plate A and then passed through the pull rod interface, and then the connecting head is rotated 90 degrees, and finally the connecting head is fixed to the slotless steel plate A (7-1) on the main unit pile (7) by bolts.

4. The method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas according to claim 2 is characterized in that: The isosceles sub-unit pile (9) is a triangular cross-section pile formed by welding a three-groove steel plate B (9-1) and two double-groove steel plates B (9-2); the three-groove steel plate B (9-1) is provided with three slots for connecting a water stop pin (10), and the double-groove steel plate B (9-2) is provided with two slots for connecting a water stop pin (10); the three-groove steel plate B on the isosceles sub-unit pile (9) is the same length as the three-groove steel plate A on the main unit pile (7), and the slots on the three-groove steel plate A correspond one to one with the slots on the three-groove steel plate B.

5. The method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas according to claim 4 is characterized in that: The equilateral sub-unit pile (8) is an equilateral triangular cross-section pile formed by welding a non-slotted steel plate B (8-1) and two double-slotted steel plates A (8-2). The double-slotted steel plates A (8-2) and the double-slotted steel plates B (9-2) have the same width, and the slots on the double-slotted steel plates A and B correspond one to one.

6. The method for zero-support zoning excavation of ultra-large and ultra-deep foundation pits in water areas according to claim 1 is characterized in that: The main body of the water-stop plug (10) is formed by welding two C-shaped steel pipes (10-1). The cross section of the water-stop plug (10) is in the shape of an "8". The length of the water-stop plug (10) is consistent with the height of the main unit pile (7). Four water-stop rubber strips (10-2) are embedded on the outer wall of the water-stop plug (10). Both sides of the water-stop plug (10) are respectively inserted into the slots on the adjacent isosceles sub-unit piles (9) and the equilateral sub-unit piles (8). The water-stop rubber strips (10-2) on the water-stop plug (10) are in sealing contact with the inner wall of the slot.

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