Synchronous conversion construction method of super-thick variable cross-section outer wall formwork and support system in foundation pit

Abstract

The application discloses a kind of super-thick variable cross-section outer wall formwork and support system synchronous conversion construction method in foundation pit, this method divides outer wall into lower equal cross-section section and upper variable cross-section section, first construction equal cross-section section and retain its outside support system;The support is extended upwards and is tied with the stable structure outside foundation pit, forms transition support system, provides operation platform for variable cross-section section steel banding;Afterwards, by inserting conversion vertical rod in wall body, and is connected with original support system, conversion forms the final support system of variable cross-section section formwork;Finally, using from top to bottom segmented installation outside formwork, and the way of synchronous segmented removal internal temporary support cross bar carries out moulding and concrete pouring.This application solves the technical problems of traditional method in variable cross-section area support unstable, high-altitude operation surface missing and formwork removal difficult, significantly improves construction safety, efficiency and forming quality.

Description

Technical Field

[0001] This invention belongs to the field of construction of basement exterior walls with variable cross-sections in foundation pits, and in particular, it is a method for synchronous conversion of formwork and support system for ultra-thick variable cross-section exterior walls in foundation pits. Background Technology

[0002] With the rapid development of the construction industry, wall construction methods have undergone significant changes to adapt to increasingly complex and diverse structural design needs. In the past, basements within foundation pits generally used walls with uniform cross-sections; now, various variable cross-section wall forms have gradually emerged, such as tapered walls, stepped walls, and inclined curved walls. These new wall types have demonstrated significant advantages in enhancing architectural aesthetics, optimizing structural performance, and adapting to special functional requirements, and have become important design choices for modern high-rise buildings, large public facilities, and special projects. However, the construction challenges of these variable cross-section walls are also becoming increasingly prominent.

[0003] Traditional formwork installation systems are primarily designed for walls with uniform cross-sections. Their standardized and repetitive installation methods are ill-suited for walls with variable cross-sections that exhibit continuous changes in thickness, slope, or shape. Especially in the construction of ultra-thick variable cross-section walls, traditional formwork presents the following technical problems: First, standardized and repetitive templates and support systems are difficult to adapt to continuous changes in wall thickness, slope, or shape, resulting in difficulties in template assembly and difficulty in controlling molding quality.

[0004] Second, changes in the wall cross-section lead to complex stress states in the support. Traditional methods make it difficult to establish a stable and reliable support force transmission system in areas with variable cross-sections, which poses safety hazards.

[0005] Third, the construction of variable cross-section walls is usually located at a higher elevation. Traditional methods lack a safe and stable dedicated working surface, which affects the progress of processes such as rebar tying and formwork installation.

[0006] Fourth, the interweaving of variable cross-section structures and support systems makes traditional formwork removal methods prone to causing the formwork or support components to become stuck, making removal difficult and potentially damaging the structural concrete. Summary of the Invention

[0007] The purpose of this invention is to provide a construction method for the synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pits. This method aims to solve the technical problems of traditional formwork installation systems, which are mainly designed for walls with constant cross-sections and have difficulty adapting to walls with variable cross-sections, unstable support systems, lack of construction work surfaces, and difficulties in demolding.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for synchronously converting the formwork and support system of an ultra-thick variable cross-section external wall within a foundation pit, comprising the following construction steps: Step 1: Before construction, refine the formwork system for the variable cross-section underground exterior wall. Divide the underground exterior wall into a lower layer of constant cross-section wall and an upper layer of variable cross-section wall according to the location of the variable cross-section. The corresponding formwork systems are the constant cross-section outer formwork system, the constant cross-section inner formwork system, the variable cross-section outer formwork system, and the variable cross-section inner formwork system. Step two: Construct a stable structure located outside the foundation pit; Step 3: Construct the basement foundation slab within the excavation pit; Step 4: At the designed location of the formwork system on the basement foundation slab, construct the outer formwork system and the inner formwork system with equal cross-sections, tie the reinforcing bars of the wall with equal cross-sections and close the formwork components of both formwork systems, then pour the concrete of the wall with equal cross-sections and the concrete of the horizontal components near its inner side in one piece and cure it. Step 5: After the concrete of the uniform cross-section wall and horizontal members has initially set, remove the uniform cross-section inner formwork system and the formwork members of the uniform cross-section outer formwork system, while retaining its support system. Step 6: Extend the support system of the uniform cross-section outer formwork system upward to form an outer transition support system, and connect the outer transition support system to the outer stable structure through multi-level diagonal bracing. Step 7: Construct an internal transition support system separately on the horizontal member, and connect the external transition support system and the internal transition support system with horizontal through-wall rods to form a transition support system. Then, lay a transition operation platform plate on the horizontal through-wall rods. The elevation of the transition support system is higher than the elevation of the variable cross-section wall. Then, tie the reinforcing bars of the variable cross-section wall on the transition support system. Step 8: Remove the transition operation platform plate and horizontal through-wall rod from Step 7. Insert a row of conversion uprights along the inside of the variable cross-section wall. Place the bottom of the conversion uprights on the concrete surface of the uniform cross-section wall. Then, connect the conversion uprights and the outer transition support system by replacing the outer horizontal bar in situ at the horizontal through-wall rod position to form the support system of the variable cross-section outer formwork system. Lay the outer operation platform plate on the outer horizontal bar. Connect the inner transition support system by replacing the inner horizontal bar in situ at the horizontal through-wall rod position to form the support system of the variable cross-section inner formwork system. Lay the inner operation platform plate on the inner horizontal bar. Step 9: Construct the inner formwork of the variable cross-section formwork system on the support system of the variable cross-section inner formwork system and fix the through-wall bolts on one side. Step 10: Along the support system of the variable cross-section outer formwork system, construct the outer formwork of the variable cross-section formwork system into N+1 sections from top to bottom, corresponding to the number of layers N of the outer horizontal bars. The outer horizontal bar of the highest layer is the first outer horizontal bar. Construct the first section of the outer formwork on the inner operating platform plate corresponding to the first outer horizontal bar and fix it with the through-wall bolts of the corresponding section. After completing the first section of the outer formwork, remove the first outer horizontal bar and the inner operating platform plate. Continue in this manner to construct downwards. After removing the Nth outer horizontal bar and the inner operating platform plate, construct the N+1th section of the outer formwork on the support system of the equal cross-section outer formwork system and fix it with the through-wall bolts of the corresponding section. The mold closing of the two formwork systems is completed. Step 11: Remove the conversion pole; Step 12: Pour the concrete for the variable cross-section wall and cure it; Step 13: After the concrete of the variable cross-section wall has initially set, remove the support system and formwork components of all the formwork systems for the underground exterior wall, and remove the diagonal bracing.

[0009] The thickness of the variable cross-section wall gradually decreases from bottom to top; in step four, the reinforcing bars of the uniform cross-section wall and the concrete of the integrally cast uniform cross-section wall are both extended into the range of the variable cross-section wall, so that the construction joint of the two poured concretes is located within the range of the variable cross-section wall, avoiding the variable cross-section position of the wall.

[0010] In step two, the stable structures under construction include the site surface, the retaining structure within the foundation pit, and the slope protection formed between the site surface and the top of the retaining structure.

[0011] In step five, the support system of the uniform cross-section outer formwork system includes connected outer vertical poles and outer horizontal poles. The bottom end of the outer vertical pole is set on the surface of the basement foundation slab, and the outer horizontal pole is set in the trench, with its outer end supported on the inner wall of the enclosure structure.

[0012] In step six, the outer transition support system is formed by extending upward from the outer uprights; in step seven, the inner transition support system consists of separately installed inner uprights and inner horizontal bars, with the outer uprights and inner uprights connected by horizontal through-wall bars.

[0013] The diagonal bracing includes outriggers and top bracing. Outriggers are connected to the top of the retaining structure and between the slope surface and the outer uprights, respectively. Top bracing is connected between the ground surface and the top of the outer uprights. In step six, the position of the outriggers on the outer uprights corresponds to the position of the horizontal through-wall bracing. After the horizontal through-wall bracing is removed, in step eight, outriggers are added so that their positions on the outer uprights correspond one-to-one with the positions of each outer horizontal bar.

[0014] In step eight, the longitudinal distance between the conversion poles along the underground outer wall is the same as the longitudinal distance between the outer poles along the trench.

[0015] The horizontal members are the basement floor slabs, and the concrete elevation of the walls with uniform cross-sections is higher than that of the nearby horizontal members on the inside.

[0016] In step three, a section of wall with a uniform cross-section is constructed on the basement foundation slab in reverse order, and then the remaining walls with uniform cross-sections are constructed in step four.

[0017] Compared with the prior art, the present invention has the following characteristics and beneficial effects: I. This invention addresses the technical problem of insufficient adaptability of the formwork system by separately designing the external wall and formwork system into equal cross-section sections and variable cross-section sections, and by adopting a phased and regional construction process with synchronous conversion of the support system. This allows the formwork system to accurately adapt to the continuous changes in the wall cross-section, effectively ensuring the design line and forming quality of the variable cross-section wall.

[0018] Second, this invention proposes a transition mechanism between the transitional support system and the final support system during the construction of variable cross-section sections. By retaining and extending the original outer support of the constant cross-section section upwards, and reliably connecting it to the stable structure outside the foundation pit through multi-level diagonal bracing, while simultaneously connecting it to the independent inner support through horizontal bars, a stable and reliable aerial work support is formed during the variable cross-section reinforcement binding stage. Subsequently, it is converted into the final formwork support system composed of transitional uprights and horizontal bars, achieving a smooth transition and reliable transfer of support, greatly improving the structural safety of the entire construction process, and solving the technical problem of instability in the support system for variable cross-section areas.

[0019] Third, this invention includes transitional operating platform plates, external operating platform plates, and internal operating platform plates on the transitional support system and the final support system, respectively. These platforms are erected synchronously with the support system, providing a safe and stable working surface for high-altitude operations such as rebar tying, formwork installation, fixing, and dismantling of variable cross-section walls, improving construction efficiency, ensuring personnel safety, and solving the problem of lack of working surfaces in high-altitude variable cross-section areas.

[0020] IV. This invention proposes a construction method of "top-down segmented formwork assembly and simultaneous support dismantling." By inserting conversion uprights into the wall and connecting them to the original support system, a final support system for the variable cross-section formwork is formed. The formwork is assembled and concrete poured in segments, with the outer formwork installed from top to bottom and the internal temporary support crossbars removed simultaneously. Specifically, before pouring, the inner formwork is constructed and fixed to one side with through-wall bolts. Then, the outer formwork is installed in segments and fixed to one side with through-wall bolts. After each segment of the inner formwork is installed, the lower layer of temporary support crossbars and platform plates are removed. This method allows most of the support crossbars to be removed before concrete pouring, avoiding the dismantling difficulties caused by the formwork and support system interlocking after the variable cross-section concrete hardens. This achieves safe and efficient dismantling of variable cross-section wall formwork, reduces damage to the formwork and concrete, and solves the technical problem of difficult dismantling of variable cross-section wall formwork. Attached Figure Description

[0021] The present invention will now be described in further detail with reference to the accompanying drawings.

[0022] Figure 1 This is a schematic diagram of the design structure of the underground exterior wall of this invention.

[0023] Figure 2 This is a schematic diagram of the structure after step four of the construction method of the present invention.

[0024] Figure 3 This is a schematic diagram of the structure after step five of the construction method of the present invention.

[0025] Figure 4 This is a schematic diagram of the structure after step six of the construction method of the present invention.

[0026] Figure 5 This is a schematic diagram of the structure after step seven of the construction method of the present invention.

[0027] Figure 6 This is a structural schematic diagram showing the completion of step eight of the construction method of this invention.

[0028] Figure 7 This is a schematic diagram of the structure after step nine of the construction method of the present invention.

[0029] Figure 8 This is a schematic diagram of the structure after the completion of the first section of the outer formwork in step ten of the construction method of the present invention.

[0030] Figure 9 This is a schematic diagram of the structure after the completion of the second section of the outer formwork in step ten of the construction method of the present invention.

[0031] Figure 10 This is a schematic diagram of the structure after the completion of the outer formwork of the third section in the construction method of the present invention.

[0032] Figure 11 This is a schematic diagram of the structure after the completion of the fourth section of the outer formwork in the tenth step of the construction method of this invention.

[0033] Figure 12 This is a structural schematic diagram showing the completion of step eleven of the construction method of the present invention.

[0034] Figure 13 This is a schematic diagram of the structure after step twelf of the construction method of the present invention.

[0035] Figure 14 This is a schematic diagram of the structure after step thirteen of the construction method of the present invention.

[0036] Figure reference numerals: 1 – Constant cross-section wall; 101 – Reinforcement in constant cross-section wall; 2 – Variable cross-section wall; 201 – Reinforcement in variable cross-section wall; 3 – Constant cross-section outer formwork system; 31 – Support system; 311 – Outer vertical bar; 312 – Outer horizontal bar; 4 – Constant cross-section inner formwork system; 5 – Stable structure; 51 – Site surface; 52 – Enclosure structure; 53 – Slope protection; 6 – Basement foundation slab; 7 – Horizontal member; 8 – External transition support system; 9 – Diagonal brace. 91 - Outrigger, 92 - Top support, 10 - Inner transition support system, 11 - Groove, 12 - Horizontal through-wall rod, 13 - Conversion pole, 14 - Outer horizontal bar, 141 - First outer horizontal bar, 142 - Second outer horizontal bar, 143 - Third outer horizontal bar, 15 - Inner horizontal bar, 16 - Inner side formwork, 17 - Through-wall bolt, 18 - First section outer formwork, 19 - Second section outer formwork, 20 - Third section outer formwork, 21 - Fourth section outer formwork, 22 - Concrete construction joint. Detailed Implementation

[0037] See the examples. Figure 1 As shown, an ultra-thick variable cross-section underground wall to be constructed within the foundation pit of a certain project has a total height of 10,500 mm. The stabilizing structure 5 outside the foundation pit includes a site surface 51, a retaining structure 52 within the foundation pit, and a slope 53 formed between the site surface 51 and the top of the retaining structure 52. The retaining structure 52 is either a support pile with a capping beam at the top or a diaphragm wall.

[0038] This method of synchronously converting the formwork and support system for ultra-thick variable cross-section exterior walls within a foundation pit divides the exterior wall into a lower, uniform cross-section section and an upper, variable cross-section section. The uniform cross-section section is constructed first, retaining its outer support system. This support is then extended upwards and connected to the stable structure outside the foundation pit, forming a transitional support system that provides a working platform for the reinforcement binding of the variable cross-section section. Next, conversion uprights are inserted into the wall and connected to the original support system, transforming it into the final support system for the variable cross-section section formwork. Finally, the outer formwork is installed in sections from top to bottom, while the internal temporary support crossbars are simultaneously removed in sections for formwork assembly and concrete pouring. The specific construction steps are as follows: Step 1, see Figure 1 As shown, the underground exterior wall is divided into a lower layer of constant cross-section wall 1 and an upper layer of variable cross-section wall 2 according to the location of the variable cross-section of the thickness. Figure 1 The dotted line indicates the location of the variable cross-section wall. The bottom of the variable cross-section wall 2 has the same thickness as the constant cross-section wall 1, and the thickness of the variable cross-section wall 2 gradually decreases from bottom to top. The thickness of the lower constant cross-section wall 1 is 1500mm, and the top thickness of the variable cross-section wall 2 is 800mm. The top elevation of the basement foundation slab 6, i.e., the bottom elevation of the underground exterior wall, is -11.4m, the top elevation of the underground exterior wall is -0.9m, and the top elevation of the basement floor slab is -6.1m. Before construction, the formwork system for the variable cross-section underground exterior wall is detailed. The formwork systems corresponding to the lower constant cross-section wall 1 and the upper variable cross-section wall 2 are the constant cross-section outer formwork system 3, the constant cross-section inner formwork system 4, the variable cross-section outer formwork system, and the variable cross-section inner formwork system.

[0039] Step 2: Construct the stable structure 5 located outside the foundation pit.

[0040] Step 3: Construct the basement foundation slab 6 within the excavation pit.

[0041] Step 4: At the designed location of the formwork system on the basement foundation slab 6, construct the equal-section outer formwork system 3 and the equal-section inner formwork system 4, tie the reinforcing bars 101 of the equal-section wall, and close the formwork panels of the formwork components of both formwork systems. Then, pour the concrete of the equal-section wall 1 and the concrete of the nearby inner horizontal component 7 as a whole and cure it. The horizontal component 7 is the basement floor slab, and the elevation of the concrete of the equal-section wall 1 is higher than the elevation of the nearby inner horizontal component 7. In actual construction, the basement foundation slab 6 can also be constructed as a whole in step three, with a 300mm section of equal cross-section wall first, and then the remaining equal cross-section walls can be constructed in step four.

[0042] In step four, the reinforcing bars 101 of the uniform cross-section wall and the concrete of the integrally cast uniform cross-section wall 1 can be extended further into the variable cross-section wall 2, so that the construction joint 22 of the two poured concretes is located within the variable cross-section wall 2, avoiding the variable cross-section location of the wall. See [link / reference] for completion. Figure 2 As shown.

[0043] Step 5: After the concrete of the equal-section wall 1 and horizontal member 7 has initially set, or after 7 days, remove the equal-section inner formwork system 4 and the formwork components of the equal-section outer formwork system 3, retaining its support system. The formwork components refer to the formwork panels and tie bolts on both sides of the equal-section wall 1. The support system 31 includes connected outer vertical poles 311 and outer horizontal poles 312. The bottom end of the outer vertical pole 311 is set inside the trench 11 on the surface of the basement foundation slab 6, and the outer horizontal pole 312 is set inside the trench 11, with its outer end supported on the inner wall of the enclosure structure 52. See [link / reference]. Figure 3 As shown.

[0044] Step six: Extend the outer uprights 311 of the support system 31 of the uniform cross-section outer formwork system upward to form the outer transition support system 8. Connect the outer transition support system 8 to the outer stable structure 5 using multi-stage diagonal bracing rods 9. The diagonal bracing rods 9 include outriggers 91 and top bracing rods 92. Outriggers 91 are connected to the top of the retaining structure 52 and between the surface of the slope protection 53 and the outer uprights 311, respectively. Top bracing rods 92 are connected between the surface of the site ground 51 and the top of the outer uprights 311. See [link to relevant documentation]. Figure 4 As shown.

[0045] Step 7: Construct an internal transition support system 10 separately on the horizontal member 7. The internal transition support system 10 consists of separately installed inner vertical poles and inner horizontal poles. Connect the outer transition support system 8 to the internal transition support system 10 via horizontal through-wall rods 12 to form a transition support system. That is, connect the outer vertical pole 311 to the inner vertical pole via horizontal through-wall rods 12. Then, lay a transition operation platform plate on the horizontal through-wall rods 12. The elevation of the transition support system is higher than the elevation of the variable cross-section wall 2. Then, tie the reinforcing bars 201 of the variable cross-section wall to the transition support system. In this embodiment, three horizontal through-wall rods 12 are installed. The position of the outrigger 91 on the outer vertical pole 311 in Step 6 corresponds to the position of the horizontal through-wall rod 12 in Step 7. In this embodiment, two outriggers 91 are installed. See [link to relevant documentation]. Figure 5 As shown.

[0046] Step 8: Remove the transition platform plate and horizontal through-wall rod 12 from Step 7. Insert a row of conversion uprights 13, exceeding the height of the variable cross-section wall 2, along the interior of the variable cross-section wall. Place wooden blocks at the bottom of each conversion upright 13 on the concrete surface of the uniform cross-section wall 1. The conversion uprights 13 are arranged longitudinally along the underground exterior wall, with the same spacing as the outer uprights 311 along the longitudinal direction of the trench 11, both being 1.8m. (See [link / reference]). Figure 6 As shown.

[0047] Then, the conversion upright 13 and the outer transition support system 8 are connected by the outer horizontal bar 14, which is replaced in situ at the position of the horizontal through-wall bar 12, to form a support system for the variable cross-section outer template system, and an outer operating platform plate is laid on the outer horizontal bar 14; a bracing bar 91 is added so that its setting position on the outer upright 311 corresponds one-to-one with the setting position of each outer horizontal bar 14; the inner transition support system 10 is connected by the inner horizontal bar 15, which is replaced in situ at the position of the horizontal through-wall bar 12, to form a support system for the variable cross-section inner template system, and an inner operating platform plate is laid on the inner horizontal bar 15.

[0048] Step 9: Construct the inner formwork 16 of the variable cross-section formwork system on the support system of the inner formwork system and fix the through-wall bolts 17 on one side. See [link / reference]. Figure 7 As shown.

[0049] Step 10: Along the support system of the variable cross-section outer formwork system, from top to bottom, the number of layers of outer horizontal bars 14 is set. In this embodiment, N=3, so three layers are set. Correspondingly, the outer formwork of the variable cross-section formwork system is constructed in four sections, adopting a flow-line operation method that combines top-down, sectioned formwork assembly and support dismantling: The outer horizontal bar of the highest level is the first outer horizontal bar 141. The first section of outer formwork 18 is constructed on the inner operating platform plate corresponding to the first outer horizontal bar 141 and fixed with the corresponding section of through-wall bolts 17. After completing the first section of outer formwork 18, the first outer horizontal bar 141 and the inner operating platform plate are removed. See [link / reference]. Figure 8 As shown; construct the second section of outer template 19 on the inner operating platform plate corresponding to the second outer crossbar 142 and fix it with the corresponding section through-wall bolts 17. After completing the second section of outer template 19, remove the second outer crossbar 142 and the inner operating platform plate. See [link / reference]. Figure 9 As shown; construct the third section of outer formwork 20 on the inner operating platform plate corresponding to the third outer crossbar 143 and fix it with the corresponding section through-wall bolts 17. After completing the third section of outer formwork 20, remove the third outer crossbar 143 and the inner operating platform plate. See [link / reference]. Figure 10 As shown; the fourth section of outer formwork 21 is constructed on the uppermost support system 31 of the equal-section outer formwork system and fixed with the corresponding through-wall bolts 17. The formwork of both sides is completed. The through-wall bolts 17 are arranged strictly according to the construction plan requirements. See Figure 11 As shown.

[0050] Step 11, remove the conversion pole 13, see [link / reference] Figure 12 As shown.

[0051] Step 12: Pour the concrete for the variable cross-section wall 2 and cure it. See below. Figure 13 As shown.

[0052] Step 13: After the concrete of the variable cross-section wall 2 has initially set, remove all the support systems and formwork components of the underground exterior wall formwork system, and remove the diagonal bracing 9. (See below) Figure 14 As shown.

[0053] The support system in this invention uses material coupler-type scaffolding poles, which solves the technical problems of unstable support in variable cross-section areas, lack of high-altitude working surfaces, and difficulty in formwork removal in traditional methods, and significantly improves construction safety, efficiency and forming quality.

Claims

1. A method for synchronously converting formwork and support system for ultra-thick variable cross-section exterior walls within a foundation pit, characterized in that... The construction steps are as follows: Step 1: Before construction, refine the formwork system of the underground exterior wall with variable cross-section. Divide the underground exterior wall into a lower layer of constant cross-section wall (1) and an upper layer of variable cross-section wall (2) according to the position of the variable cross-section of the thickness. The corresponding formwork systems are constant cross-section outer formwork system (3), constant cross-section inner formwork system (4), variable cross-section outer formwork system, and variable cross-section inner formwork system. Step 2: Construct a stable structure (5) located outside the foundation pit; Step 3: Construct the basement foundation slab (6) within the foundation pit. Step 4: On the basement foundation slab (6), at the designed position of the formwork system, construct the equal cross-section outer formwork system (3) and the equal cross-section inner formwork system (4), tie the steel bars (101) of the equal cross-section wall and close the formwork components of the two side formwork systems, and then pour the concrete of the equal cross-section wall (1) and the concrete of the horizontal components (7) near its inner side as a whole and cure it. Step 5: After the concrete of the equal cross-section wall (1) and horizontal member (7) has initially set, remove the equal cross-section inner formwork system (4), remove the formwork members of the equal cross-section outer formwork system (3), and retain its support system. Step 6: Extend the support system (31) of the equal cross section outer template system upward to form an outer transition support system (8), and connect the outer transition support system (8) with the outer stable structure (5) through multi-level diagonal bracing rods (9); Step 7: Construct an inner transition support system (10) separately on the horizontal member (7), and connect the outer transition support system (8) and the inner transition support system (10) through the horizontal through-wall rod (12) to form a transition support system. Then, lay a transition operation platform plate on the horizontal through-wall rod (12). The elevation of the transition support system is higher than the elevation of the variable cross-section wall (2). Then, tie the steel bars (201) of the variable cross-section wall on the transition support system. Step 8: Remove the transition operation platform plate and horizontal through-wall rod (12) from Step 7. Insert a row of conversion uprights (13) along the inside of the variable cross-section wall. The bottom of the conversion uprights (13) rests on the concrete surface of the equal cross-section wall (1). Then, connect the conversion uprights (13) and the outer transition support system (8) by replacing the outer horizontal bar (14) in place at the horizontal through-wall rod position to form a support system for the variable cross-section outer template system. Lay the outer operation platform plate on the outer horizontal bar (14). Connect the inner transition support system (10) by replacing the inner horizontal bar (15) in place at the horizontal through-wall rod position to form a support system for the variable cross-section inner template system. Lay the inner operation platform plate on the inner horizontal bar (15). Step 9: Construct the inner formwork of the variable cross-section formwork system (16) on the support system of the variable cross-section inner formwork system and fix the through-wall bolts (17) on one side. Step 10: Along the support system of the variable cross-section outer formwork system, from top to bottom, the outer formwork of the variable cross-section formwork system is divided into N+1 sections according to the number of layers N set by the outer horizontal bar (14). The outer horizontal bar of the highest layer is the first outer horizontal bar (141). The first section of the outer formwork (18) is constructed on the inner operating platform plate corresponding to the first outer horizontal bar (141) and fixed with the through-wall bolt (17) of the corresponding section. After the first section of the outer formwork (18) is completed, the first outer horizontal bar (141) and the inner operating platform plate are removed. The construction is carried out step by step downward in this manner. After the Nth outer horizontal bar and the inner operating platform plate are removed, the N+1 section of the outer formwork is constructed on the support system of the equal cross-section outer formwork system and fixed with the through-wall bolt (17) of the corresponding section. The mold closing of the two formwork systems is completed. Step 11: Remove the conversion pole (13); Step 12: Pour concrete for the variable cross-section wall (2) and cure it; Step 13: After the concrete of the variable cross-section wall (2) has initially set, remove the support system and formwork components of all the formwork systems of the underground exterior wall, and remove the diagonal bracing (9).

2. The method for synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pit according to claim 1, characterized in that: The thickness of the variable cross-section wall (2) gradually decreases from bottom to top; the steel bars (101) of the equal cross-section wall tied in step four and the concrete of the integrally cast equal cross-section wall (1) are both extended into the range of the variable cross-section wall (2) so that the construction joint of the concrete poured twice is located within the range of the variable cross-section wall (2) and avoids the variable cross-section position of the wall.

3. The method for synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pit as described in claim 1, characterized in that: In step two, the stable structure for construction includes the site ground (51), the retaining structure (52) in the foundation pit, and the slope protection (53) formed between the site ground (51) and the top of the retaining structure (52).

4. The method for synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pit according to claim 3, characterized in that: In step five, the support system (31) of the equal cross section outer formwork system includes the connected outer vertical pole (311) and outer horizontal pole (312). The bottom end of the outer vertical pole (311) is set on the surface of the basement foundation slab (6), and the outer horizontal pole (312) is set in the trench (11), with its outer end supported on the inner wall of the enclosure structure (52).

5. The method for synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pit according to claim 4, characterized in that: In step six, the outer transition support system (8) is formed by extending upward from the outer upright (311); in step seven, the inner transition support system (10) consists of a separately installed inner upright and an inner horizontal bar, and the outer upright (311) and the inner upright are connected by a horizontal through-wall bar (12).

6. The method for synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pit according to claim 5, characterized in that: The diagonal bracing rod (9) includes a spur rod (91) and a top bracing rod (92). The spur rod (91) is connected to the top of the retaining structure (52) and between the surface of the slope protection (53) and the outer upright (311), respectively. The top bracing rod (92) is connected to the surface of the ground (51) and the top of the outer upright (311). In step six, the setting position of the spur rod (91) on the outer upright (311) corresponds to the setting position of the horizontal through-wall rod (12). After the horizontal through-wall rod (12) is removed, in step eight, a spur rod (91) is added so that its setting position on the outer upright (311) corresponds one-to-one with the setting position of each outer horizontal bar (14).

7. The method for synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pit according to claim 1, characterized in that: In step eight, the longitudinal distance of the conversion pole (13) along the underground outer wall is the same as the longitudinal distance of the outer pole (311) along the trench (11).

8. The method for synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pit according to claim 1, characterized in that: The horizontal member (7) is the basement floor slab, and the concrete elevation of the equal-section wall (1) is higher than the elevation of the nearby horizontal member (7).

9. The method for synchronous conversion of ultra-thick variable cross-section external wall formwork and support system in foundation pit according to claim 1, characterized in that: In step three, a section of equal-section wall is constructed on the basement foundation slab (6) as a whole, and then the remaining equal-section walls are constructed in step four.

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