Template support structure and construction method for enlarged and reconstructed part of gravity dam pier

Abstract

The application discloses a gravity dam pier expansion reconstruction part formwork supporting structure and a construction method, relates to the field of hydraulic engineering construction, and is installed on the outer side of an original pier dam body and comprises: a plurality of cantilever beams, the cantilever beams are arranged horizontally and at intervals along the outer contour of the original pier dam body, the first end part of the cantilever beam is fixed to the outer side of the original pier dam body, and the second end part of the cantilever beam extends outward to the outside of the contour line of an outer expansion dam body to be poured; a bottom formwork for supporting the outer expansion dam body to be poured, a supporting frame body is installed on the cantilever beam and used for supporting the bottom formwork; side formworks, the side formworks are located above the bottom formwork and used for enclosing the outer expansion dam body to be poured; and a plurality of side formwork reinforcing bars, the first end part of the side formwork reinforcing bar is fixedly connected with the original pier dam body, and the second end part of the side formwork reinforcing bar is connected with the side formwork. The construction quality of the expansion reconstruction part can be ensured, the construction cost and construction time can be saved, and the construction quality of the reconstruction part is ensured.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering construction. More specifically, this invention relates to a formwork support structure and construction method for the enlargement and renovation of a gravity dam gate pier. Background Technology

[0002] During the long-term operation of gravity dams, factors such as dam aging, lower-than-expected original design standards, and changes in hydrological conditions necessitate reinforcement and expansion of some gate pier structures. To meet new requirements for anti-sliding stability, stress distribution, and discharge capacity, it is typically necessary to add concrete structures downstream or laterally to the original gate pier dam body, forming an expanded dam body with a larger cross-sectional dimension. Since the original gate piers are mostly arc-shaped or curved, while the new structures are often square or rectangular in cross-section, the junction between the two forms a complex geometric shape transitioning from arc to square—the arc-to-square transition area. This area is not only a stress concentration zone but also a critical interface for the bonding of old and new concrete, and a challenging area for the layout of the formwork support system. Its construction plan directly affects the project cycle and cost.

[0003] Currently, for concrete construction of arc-shaped to square sections, the common practice is to use ground-mounted full-span scaffolding as the formwork support system. This method requires erecting uprights, horizontal bars, and scissor bracing layer by layer from the ground or dam foundation surface, forming a dense scaffolding structure covering the entire construction area. Due to the large cantilever span and irregular boundaries of the arc-shaped to square section, the support system cannot be locally optimized according to the structural outline; the only way to ensure overall stability is to increase the density of uprights and add multiple layers of horizontal bars. The erection and dismantling of full-span scaffolding is extremely labor-intensive. Before construction, the site must be leveled and hardened, and sufficient ground working space must be reserved; during the erection process, elevation control and verticality correction must be carried out layer by layer, and a single erection cycle usually takes 7 to 15 days; after the concrete is poured, dismantling can only begin after the expanded dam body reaches the design strength, and the dismantling work must be carried out layer by layer and section by section, and reverse construction is not allowed, resulting in a long occupation time and low turnover efficiency of the support system. Meanwhile, the dense array of uprights and horizontal bars severely encroached on the work space for rebar tying, formwork installation, and concrete vibration, making it impossible for each process to proceed in parallel and further lengthening the overall construction cycle.

[0004] Besides the time-consuming assembly and disassembly of the support system itself, traditional construction methods also involve a significant amount of on-site adjustments and rework at the curved-to-square section. The formwork needs to be assembled and trimmed piece by piece according to the measured contour, and the placement of tie rods and anchor bars often conflicts with the support members, requiring temporary cutting or relocation. Such adjustment work is highly dependent on manual experience and lacks standardized procedures, which not only prolongs the installation time per session but also increases the frequency of high-altitude work and safety hazards. In summary, the existing construction methods at this irregular node suffer from problems such as redundant support systems, slow material turnover, and poor process coordination, resulting in a longer construction cycle compared to conventional structural sections, becoming a key bottleneck restricting the overall progress of the gate pier renovation project. Summary of the Invention

[0005] One objective of this invention is to provide a formwork support structure and construction method for the enlarged and modified section of a gravity dam gate pier, which can effectively save construction costs and time while ensuring the construction quality of the enlarged and modified section.

[0006] To achieve these objectives and other advantages according to the invention, according to one aspect of the invention, a formwork support structure for the enlarged and modified section of a gravity dam pier is provided, installed on the outside of the original dam pier body, comprising: a plurality of cantilever beams, the cantilever beams being horizontally spaced along the outer contour of the original dam pier body, the first end of the cantilever beams being fixed to the outside of the original dam pier body, the second end of the cantilever beams extending outward in a horizontal direction, the projection of the second end of the cantilever beams on the horizontal plane being outside the contour line of the enlarged dam body to be poured; a bottom formwork for supporting the enlarged dam body to be poured, the bottom formwork being located above the cantilever beams, and a support frame being installed on the cantilever beams for supporting the bottom formwork; side formworks, the side formworks being located above the bottom formworks for enclosing the enlarged dam body to be poured; and a plurality of side formwork tie rods, the first end of the side formwork tie rods being fixedly connected to the original dam pier body, and the second end of the side formwork tie rods being connected to the side formworks.

[0007] Preferably, a new outer dam body is poured outside the original gate pier dam body located below the expanded dam body. The new outer dam body is formed by pouring an outer steel formwork. A steel support frame is set on the outside of the outer steel formwork. The first end of the cantilever beam is fixedly connected to the steel support frame. The edge of the bottom formwork is connected to the edge of the new outer dam body. A second support frame is also set between the bottom formwork and the steel support frame. The lower end of the second support frame is fixedly connected to the steel support frame, and the upper end of the second support frame is fixedly connected to or supports the bottom formwork.

[0008] Preferably, a diagonal bracing beam is also provided between the steel support frame and the cantilever beam, and the two ends of the diagonal bracing beam are fixedly connected to the steel support frame and the cantilever beam, respectively.

[0009] Preferably, a number of fixed steel pins are welded onto the cantilever beam, and the support frame includes a number of first longitudinal steel pipes. The first longitudinal steel pipes are sleeved on the outside of the fixed steel pins and fixedly connected to them. A number of transverse steel pipes are connected between the first longitudinal steel pipes on adjacent cantilever beams by fasteners. A number of second longitudinal steel pipes are connected to the body of the transverse steel pipes by fasteners. The tops of the first longitudinal steel pipes and the second longitudinal steel pipes are threaded with U-shaped supports. A number of bottom formwork support beams are fixed on the lower surface of the bottom formwork, and the bottom formwork support beams are supported by the second support frame and several U-shaped supports.

[0010] Preferably, the system also includes several bottom formwork tie bars, the first end of which is fixed to the outer wall of the original gate pier dam body, and the second end of which is fixedly connected to the bottom formwork.

[0011] Preferably, the second end of the bottom template tie rod is fixedly connected to the bottom template by a bottom template fastener. The bottom template fastener includes a fastener connecting rib and a fastening support portion. The lower end of the fastener connecting rib passes through the bottom template and is fixedly connected to the fastening support portion. The fastening support portion is fastened to the lower surface of the bottom template. The upper end of the fastener connecting rib passes through the bottom template and is welded and fixed to the second end of the bottom template tie rod.

[0012] Preferably, a side template support structure is provided on the outer side of the side template. The side template support structure includes a plurality of first back ribs and a plurality of second back ribs. The first back ribs are spaced apart and fit against the outer surface of the side template. The second back ribs are perpendicular to the first back ribs and are double-jointed steel pipes in pairs, which are attached to the outer side of the first back ribs. The second end of the side template tie rod passes through the gap between the double-jointed steel pipes of the second back ribs and the locking member in sequence. The second end of the side template tie rod is provided with threads, and the side template and the side template support structure are tightened and fixed by tightening the nuts.

[0013] Preferably, a number of anchor plates are fixed on the outer wall of the original gate pier dam body, and a first anchoring steel bar and a second anchoring steel bar are provided on the anchor plates. The first anchoring steel bar is welded and fixed to the first end of the bottom formwork tie bar, and the second anchoring steel bar is welded and fixed to the first end of the side formwork tie bar.

[0014] Preferably, the cantilever beam is fully covered with scaffold boards on the beam segment located outside the outline of the expanded dam body to form a construction platform, and the construction platform is surrounded by guardrails.

[0015] Secondly, the present invention provides a construction method for the enlarged and modified section of a gravity dam gate pier, employing the aforementioned template support structure for the enlarged and modified section of the gravity dam gate pier, comprising the following steps:

[0016] S1: Roughen and clean the outer part of the original gate pier dam body to be poured, and install reinforcing bars according to the design requirements;

[0017] S2: Several cantilever beams are fixedly installed at horizontal intervals on the outside of the original gate pier dam body, and the cantilever beams extend outward to the outside of the outline of the expanded dam body to be poured.

[0018] S3: Install the support frame on the cantilever beam and adjust the top elevation of the support frame to the design position;

[0019] S4: Lay the bottom template on top of the support frame, adjust the flatness and joints of the bottom template, and fix it to the support frame;

[0020] S5: Tie the reinforcing bars of the outer dam body above the bottom formwork and firmly connect the reinforcing bars to the embedded reinforcing bars on the outside of the original gate pier dam body;

[0021] S6: Install side formwork above the bottom formwork, and fix the side formwork to the outer wall of the original gate pier dam body by means of side formwork tie rods, and adjust the verticality and joints of the side formwork;

[0022] S7: Pour concrete into the formwork of the outward-expanding dam body, vibrate and compact it, and cure it to the design strength;

[0023] S8: After the concrete strength reaches the demolding requirements, remove the side formwork, bottom formwork, support frame and cantilever beam in sequence.

[0024] The present invention has at least the following beneficial effects:

[0025] First, this invention replaces traditional full-span scaffolding with a combination of cantilever beams and support frames, achieving a lightweight and suspended formwork support system. The cantilever beams are arranged horizontally at intervals along the original dam pier outline, with their second ends extending directly to the outer edge of the expanded dam body. This efficiently transfers the formwork load to the original dam pier through the steel support frame, diagonal bracing beams, and the second support frame, eliminating the need to start scaffolding from the ground. Compared to traditional methods, this solution significantly reduces the amount of support steel pipes used, shortens the construction period, and substantially reduces material turnover costs and labor input.

[0026] Secondly, this invention possesses strong flexibility and versatility. The spacing, overhang length, and erection height of the support frame can all be adjusted according to the arcuate contour of the original gate pier dam and the square cross-sectional dimensions of the expanded dam. The second support frame and diagonal bracing beams can be selected and matched according to the cantilever span and load conditions. The anchorage positions of the bottom formwork tie rods and side formwork tie rods can also be flexibly arranged in conjunction with the anchor plate layout scheme. Whether it is the partial reinforcement of small and medium-sized gravity dams or the large-section gate pier renovation of large water conservancy projects, the formwork support structure can be quickly adapted by adjusting the construction parameters to meet the construction requirements of different project scales and hydrogeological conditions.

[0027] Third, this invention features a dedicated formwork support structure designed for the arc-shaped to square section. A combination of cantilever beams and a support frame supports the bottom formwork, with bottom formwork tie bars fixed to it via fasteners, forming a two-way constraint system that effectively controls formwork deformation and joint misalignment. The side formwork is fixed by welding side formwork tie bars to the second anchoring steel bars anchored to the original dam body, and secured with multiple back braces in the side formwork support structure, ensuring the overall rigidity of the formwork system. The junction between the new outer dam body and the original dam body is smoothly connected via the edge of the bottom formwork, resulting in a dense and smooth interface between the old and new concrete, significantly improving the overall stability and durability of the structure.

[0028] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0029] Figure 1 This is a side cross-sectional view of the template support structure in one technical solution of the present invention;

[0030] Figure 2 This is a top view of the template support structure in one technical solution of the present invention;

[0031] Figure 3 This is a three-dimensional schematic diagram of the template support structure at slice A in one technical solution of the present invention;

[0032] Figure 4 This is a schematic diagram of the outer steel template at slice A in one technical solution of the present invention;

[0033] Figure 5 This is a schematic diagram of the support frame at slice A in one technical solution of the present invention;

[0034] Figure 6 This is a schematic diagram of the support frame installation at slice A in one technical solution of the present invention;

[0035] Figure 7 This is a schematic diagram of the installation of bottom formwork tie rods in one technical solution of the present invention;

[0036] Figure 8 This is a schematic diagram of the bottom template fastener in one technical solution of the present invention;

[0037] Figure 9 This is a schematic diagram of the installation of the side template support structure at slice A in one technical solution of the present invention.

[0038] Attached reference numerals: 1-Original dam body, 2-New outer dam body, 3-Expanded dam body, 4-Outer steel formwork, 41-Steel support frame, 42-Second support frame, 5-Cantilever beam, 51-Inclined brace beam, 52-Fixing steel stake, 53-Construction platform, 54-Guardrail, 6-Support frame, 61-First longitudinal steel pipe, 611-Second longitudinal steel pipe, 62-Transverse steel pipe, 63-U-shaped support, 7-Bottom formwork, 71-Bottom formwork tie bar, 72-Bottom formwork fastener, 721-Fastener connecting bar, 722-Fastening support part, 73-Bottom formwork support beam, 8-Side formwork, 81-Side formwork tie bar, 82-Side formwork support structure, 821-First back rib, 822-Second back rib, 83-Locking part, 9-Anchor plate, 91-First anchoring steel bar, 92-Second anchoring steel bar. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can implement it based on the description.

[0040] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0041] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are conventional methods, and the structures and components described are commercially available. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "setting" should be interpreted broadly. For example, they can refer to fixed connection or setting, detachable connection or setting, or integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The terms "lateral," "longitudinal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0042] like Figures 1-9As shown, this invention provides a formwork support structure for the enlarged and modified section of a gravity dam gate pier, installed on the outside of the original gate pier dam body 1. It is characterized by comprising: several cantilever beams 5, which are horizontally spaced along the outer contour of the original gate pier dam body 1; the first end of each cantilever beam 5 is fixed to the outside of the original gate pier dam body 1; the second end of each cantilever beam 5 extends outward in a horizontal direction; and the projection of the second end of each cantilever beam 5 on the horizontal plane is outside the contour line of the expanded dam body 3 to be poured; a bottom formwork 7, used to support the expanded dam body 3 to be poured, located above the cantilever beams 5; a support frame 6 installed on the cantilever beams 5 to support the bottom formwork 7; side formwork 8, located above the bottom formwork 7, used to enclose the expanded dam body 3 to be poured; and several side formwork tie rods 81, the first end of each side formwork tie rod 81 being fixedly connected to the original gate pier dam body 1; and the second end of each side formwork tie rod 81 being connected to the side formwork 8.

[0043] The cantilever beams 5 are the main load-bearing components of this support structure. They are made of steel sections, and I16 I-beams can be selected. Several cantilever beams 5 are arranged horizontally at intervals along the outer contour of the original gate dam body 1. The spacing between them is determined by calculation based on the load of the expanded dam body 3, and is typically controlled between 0.9m and 1.0m. Each cantilever beam 5 has a first end and a second end. The first end is fixedly connected to the outside of the original gate dam body 1, and the second end extends horizontally outward, with its endpoint located outside the contour line of the expanded dam body 3 to be poured. This arrangement creates a cantilever support system where the cantilever beams 5 transition from the arc-shaped outer edge of the original gate dam body 1 to the square boundary of the expanded dam body 3, providing a stable support foundation for subsequent formwork installation. The fixed connection between the first end of the cantilever beam 5 and the outside of the original gate dam body 1 can be achieved through anchor bolt insertion, welding of embedded parts, or transitional connection using existing structures.

[0044] The bottom formwork 7 is used to support the expanded dam body 3 to be poured, and it is located above the cantilever beam 5. The bottom formwork 7 is made of plate material with sufficient strength and rigidity, and can be made of film-coated plywood or combined steel formwork. Its plate size and splicing method are designed according to the bottom contour of the expanded dam body 3. The installation elevation, levelness and joint tightness of the bottom formwork 7 are precisely controlled by the support frame 6 below it.

[0045] The support frame 6 is installed above the cantilever beam 5 to support and fix the bottom formwork 7. The support frame 6 is a spatial rod structure, erected using a coupler-type steel pipe scaffolding or a disc-lock scaffolding system. The lower end of the support frame 6 is fixedly connected to the upper flange or upper surface of the cantilever beam 5, with specific connection methods including but not limited to welding positioning ribs, setting limiting bases, or locking with U-bolts. The upper end of the support frame 6 is equipped with an elevation adjustment mechanism, preferably an adjustable top support, to support the bottom formwork 7 and adjust its elevation. The erection height and member density of the support frame 6 are calculated and determined based on the thickness of the outer dam body 3 and the concrete pouring load.

[0046] The side formwork 8 is located above the bottom formwork 7 and is erected around the perimeter of the expanded dam body 3 to enclose the lateral outline of the expanded dam body 3 to be poured. The side formwork 8 also uses film-coated plywood or standardized steel formwork, with a smooth inner surface and good demolding performance. A back rib system is provided on the outer side of the side formwork 8, including vertical and horizontal back ribs. The back ribs are made of double steel pipes or rectangular steel sections and are tightly fitted to the side formwork 8 with locking devices to enhance the side formwork 8's ability to resist lateral concrete pressure.

[0047] The several side formwork tie bars 81 are used to tie and fix the side formwork 8 to the original gate pier dam body 1 to balance the lateral pressure generated during concrete pouring. Each side formwork tie bar 81 is made of round steel, and the two ends are pre-threaded. The first end of the side formwork tie bar 81 is fixedly connected to the original gate pier dam body 1. The connection method is as follows: an anchor point is set at the corresponding position of the original gate pier dam body 1. The anchor point can be formed by implanted chemical anchors, pre-embedded anchor bars, or by a combination of anchor plates 9 and expansion bolts. The first end of the side formwork tie bar 81 is welded or threaded to the anchor point. The second end of the side formwork tie bar 81 is connected to the side formwork 8. Specifically, the second end of the side formwork tie bar 81 passes through the side formwork 8 plate and the outer back rib in sequence, and is locked by a washer and double nuts to achieve the tying and verticality correction of the side formwork 8. The tension of the tie bar can be adjusted by turning the nuts, thereby controlling the flatness of the side formwork 8 plate surface and the tightness of the joints.

[0048] The formwork support structure for the enlarged and renovated gravity dam gate pier provided by this invention consists of cantilever beams 5 arranged horizontally at intervals along the outer contour of the original gate pier dam body 1 and extending outward to the outer contour of the enlarged dam body 3. These cantilever beams form an independent load-bearing frame that transitions from an arc-shaped boundary to a square boundary, completely replacing traditional full-span scaffolding. This eliminates material redundancy and construction time consumption caused by high-support formwork erection and dismantling from the structural root. The support frame 6 is fixed above the cantilever beams 5 and supports the bottom formwork 7. Together with the side formwork 8 and the side formwork tie bars 81 anchored to the original gate pier dam body 1, it forms a complete formwork support and tie system, ensuring a smooth and dense interface between the old and new concrete and a complete formwork system. The structural rigidity is significantly improved, effectively ensuring the forming quality and structural durability of the irregularly shaped node, which is transformed from an arc to a square shape. At the same time, all components of this structural system use common materials such as steel profiles, steel pipes, and fasteners. Through standardized processes such as welding, threaded connections, and fastener connections, rapid assembly and precise adjustment are achieved. The arrangement spacing and extension length of the cantilever beams 5 and the erection height of the support frame 6 can be flexibly adjusted according to different project scales and the original dam body 1 alignment. It is suitable for the rapid reinforcement of small and medium-sized dams and can also be extended to the large-section renovation of large water conservancy projects. It has significant construction efficiency, structural quality assurance capabilities, and wide adaptability to working conditions.

[0049] In another technical solution, a new outer dam body 2 is poured outside the original gate pier dam body 1 located below the outer dam body 3. The new outer dam body 2 is formed by pouring an outer steel formwork 4. A steel support frame 41 is set on the outside of the outer steel formwork 4. The first end of the cantilever beam 5 is fixedly connected to the steel support frame 41. The edge of the bottom formwork 7 is connected to the edge of the new outer dam body 2. A second support frame 42 is also set between the bottom formwork 7 and the steel support frame 41. The lower end of the second support frame 42 is fixedly connected to the steel support frame 41, and the upper end of the second support frame 42 is fixedly connected to or supports the bottom formwork 7.

[0050] First, a new outer dam body 2 is poured in the outer area below the extended dam body 3 of the original gate pier dam body 1. This new outer dam body 2 is a reinforced concrete structure encasing the original gate pier dam body 1. Its function is to repair surface defects, fill missing sections, and provide a reliable foundation for the subsequent installation of the cantilever beam 5. The new outer dam body 2 is poured using conventional reinforced concrete construction techniques, and its formwork system uses outer steel formwork 4. The outer steel formwork 4 is installed according to the design outline of the new outer dam body 2, and a steel support frame 41 is fixedly installed on the outer side of the outer steel formwork 4. The steel support frame 41 serves as the load-bearing foundation for the cantilever beam 5 and the second support frame 42. Its structural form is not limited to a triangular bracket welded from a single member; the steel support frame 41 can be composed of Bailey beams or prefabricated steel trusses. Bailey beams are composed of standardized chords, vertical members, and diagonal members connected by pins, featuring high load-bearing capacity, high rigidity, and the ability to be spliced ​​and extended. Steel support frames 41 are arranged horizontally at intervals along the outer contour of the original gate pier dam body 1. Each Bailey beam is installed vertically, with its lower end welded or bolted to the pre-embedded connecting seat or horizontal support beam on the outer side of the outer steel formwork 4. A transverse distribution beam is set at the upper end to support the cantilever beam 5. Adjacent Bailey beams are connected by adding horizontal bracing, vertical scissor bracing, and planar connections to form an integral spatial steel structure. This allows the structure to work together and deform together when bearing the vertical load transmitted by the cantilever beam 5 and the dynamic load during construction, avoiding lateral instability caused by the independent bearing of a single truss. This steel structure system has good integrity, fast installation speed, and can be reused in adjacent dam sections after dismantling, significantly reducing the amount of steel used in temporary support works.

[0051] The first end of the cantilever beam 5 is fixedly connected to the steel support frame 41. In specific implementation, the cantilever beam 5 is made of I16 I-beam, and its first end is cut into an inclined or right-angled surface that fits against the outer side of the steel support frame 41. It is then fully welded to the vertical members or transverse distribution beams of the steel support frame 41 on both sides. If necessary, triangular stiffening plates or node connection plates are added at the connection nodes to enhance the bending and shear bearing capacity of the nodes. The second end of the cantilever beam 5 extends outward to the outer contour line of the outer dam body 3 to be poured, and its extension length is determined based on the cantilever span of the outer dam body 3.

[0052] The edge of the bottom template 7 is connected to the edge of the new outer dam body 2. The bottom template 7 is cut and fitted according to the forming contour of the new outer dam body 2 on the side closest to the original gate pier dam body 1. During installation, the side edge of the bottom template 7 is tightly attached to the upper or side surface of the new outer dam body 2, and a sponge strip or sealant is applied at the joint to prevent grout leakage. At the same time, the elevation of the bottom template 7 should be smoothly connected to the top design elevation of the new outer dam body 2 to ensure that there are no misalignments or abrupt changes in cross-section at the junction of the outer dam body 3 and the new outer dam body 2.

[0053] To further enhance the support rigidity of the bottom formwork 7 and share part of the load borne by the cantilever beam 5, a second support frame 42 is provided between the bottom formwork 7 and the steel support frame 41. The second support frame 42 is made of φ48.3mm×3.6mm steel pipe or square steel pipe of the same specification, or a lightweight lattice steel frame. The lower end of the second support frame 42 is fixedly connected to the steel support frame 41. When the steel support frame 41 is a Bailey beam, the lower end of the second support frame 42 can be directly welded or bolted to the node plate of the upper chord of the Bailey beam, so that the force transmission path is clear and the node reliability is high; the upper end of the second support frame 42 is fixedly connected to or supports the lower surface of the bottom formwork 7. When a fixed connection is used, a connecting steel plate is welded to the top of the second support frame 42, and the steel plate is fixed to the back rib or plate surface of the bottom formwork 7 by bolts or nails. When a support is used, an adjustable top support is installed at the top of the second support frame 42. The top support directly supports the bottom formwork support beam 73 or timber at the bottom of the bottom formwork 7. The bottom formwork 7 is brought to the design elevation by adjusting the top support screw. The second support frame 42 is arranged at a certain interval along the span direction of the cantilever beam 5. The arrangement density is determined by calculation based on the load of the bottom formwork 7 and the cantilever span, and usually corresponds to the arrangement spacing of the cantilever beam 5, forming a multi-point support and coordinated force-bearing system. When the steel support frame 41 is constructed using Bailey beams and connecting systems to form an integral steel truss, the second support frame 42 can be flexibly arranged along the entire length of the truss, no longer limited to the location of the cantilever beam 5. This achieves denser support for the bottom formwork 7, effectively shortens the span of the bottom formwork 7, reduces formwork deflection deformation, and significantly reduces the peak bending moment of the cantilever beam 5. This makes the stress distribution of the entire formwork support structure more uniform and reasonable, and is especially suitable for the construction conditions of the outer expansion dam body 3 with large cantilever width and large cross-sectional thickness.

[0054] In another technical solution, a diagonal brace 51 is also provided between the steel support frame 41 and the cantilever beam 5. Both ends of the diagonal brace 51 are fixedly connected to the steel support frame 41 and the cantilever beam 5, respectively. The diagonal brace 51 is made of I-beams or channel steel of the same specifications as the cantilever beam 5, and its two ends are fixedly welded to the outer side of the steel support frame 41 and the corresponding positions of the lower flange or web of the cantilever beam 5 using double-sided full welding. To enhance the load-bearing capacity of the joint, triangular stiffening plates are added at the angles between the two ends of the diagonal brace 51 and the connecting components. The stiffening plates are not less than 10mm thick and are welded simultaneously with the base material. The inclination angle of the diagonal brace 51 is calculated and determined based on the cantilever length of the cantilever beam 5 and the load size, and is usually controlled between 30° and 60°. When the steel support frame 41 uses Bailey beams or prefabricated steel trusses, the upper end of the diagonal brace 51 can also be welded to the node plate or chord reinforcement area of ​​the Bailey beam, making the force transmission path clear and the joint reliability high. The diagonal bracing beam 51 diagonally transfers part of the vertical load borne by the cantilever beam 5 to the steel support frame 41, effectively reducing the calculated span and mid-span bending moment of the cantilever beam 5, while restraining the vertical deflection of the cantilever beam 5 during the concrete pouring process, significantly improving the overall stiffness and stability of the cantilever support system.

[0055] In another technical solution, several fixed steel rods 52 are welded onto the cantilever beam 5, and the support frame 6 includes several first longitudinal steel pipes 61. The first longitudinal steel pipes 61 are sleeved on the outside of the fixed steel rods 52 and fixedly connected to the fixed steel rods 52. Several transverse steel pipes 62 are connected between the first longitudinal steel pipes 61 on adjacent cantilever beams 5 by fasteners. Several second longitudinal steel pipes 611 are connected to the body of the transverse steel pipes 62 by fasteners. The top of the first longitudinal steel pipes 61 and the second longitudinal steel pipes 611 are threaded with U-shaped supports 63. Several bottom formwork support beams 73 are fixed on the lower surface of the bottom formwork 7. The bottom formwork support beams 73 are supported by the second support frame 42 and several U-shaped supports 63.

[0056] Several fixing steel rods 52 are welded to the upper flange surface of the cantilever beam 5 at the designed positions. The fixing steel rods 52 are made of φ25 round steel or φ48mm short steel pipe, with a length generally between 150mm and 200mm. They are fully welded on both sides perpendicular to the upper surface of the cantilever beam 5, with a weld leg height of not less than 6mm. The fixing steel rods 52 are set along the longitudinal direction of the cantilever beam 5 according to the spacing of the uprights of the support frame 6, typically with a spacing controlled between 0.3m and 1.0m, corresponding to the spacing of the cantilever beam 5.

[0057] The support frame 6 includes several first longitudinal steel pipes 61, which are scaffolding steel pipes with a specification of φ48.3mm×3.6mm. The lower end of the first longitudinal steel pipe 61 is sleeved on the outside of the fixed steel rod 52, so that the fixed steel rod 52 is inserted into the cavity of the first longitudinal steel pipe 61 to a depth of not less than 100mm. The first longitudinal steel pipe 61 and the fixed steel rod 52 are fixedly connected. The specific connection method is as follows: a through hole is drilled at the sleeve position of the lower end of the first longitudinal steel pipe 61 and the fixed steel rod 52, and a transverse through pin or bolt is used for locking; alternatively, circumferential welding can be directly performed around the sleeve position to form a rigid fixed connection between the first longitudinal steel pipe 61 and the fixed steel rod 52. This connection structure ensures that the first longitudinal steel pipe 61 can reliably transmit vertical and horizontal loads to the cantilever beam 5 without slippage or overturning.

[0058] Several transverse steel pipes 62 are connected to the first longitudinal steel pipes 61 on adjacent cantilever beams 5 via fasteners. The transverse steel pipes 62 are scaffolding steel pipes of the same specifications as the first longitudinal steel pipes 61, and their two ends are fastened to the body of the first longitudinal steel pipes 61 by right-angle fasteners or swivel fasteners. The transverse steel pipes 62 are arranged in layers along the height direction of the first longitudinal steel pipes 61 at intervals, typically 1.2m to 1.5m, forming a spatial frame that connects the longitudinal and transverse sides.

[0059] The transverse steel pipe 62 is connected to several second longitudinal steel pipes 611 via fasteners. The second longitudinal steel pipes 611 also use φ48.3mm×3.6mm scaffolding steel pipes, and their direction is parallel to the first longitudinal steel pipe 61. They are securely connected to the transverse steel pipe 62 via right-angle fasteners or swivel fasteners. The second longitudinal steel pipes 611 are arranged between two adjacent first longitudinal steel pipes 61, and their bottoms can be suspended or have additional pads added, without needing to be directly fixed to the cantilever beam 5. Through the fastener connection between the first longitudinal steel pipes 61, the transverse steel pipes 62, and the second longitudinal steel pipes 611, the supporting frame 6 forms a spatial truss structure with good overall integrity. Each upright works together to bear the force, significantly improving the overall rigidity.

[0060] Both the first longitudinal steel pipe 61 and the second longitudinal steel pipe 611 are threadedly connected to the top of a U-shaped support 63. The U-shaped support 63 consists of an adjustable screw, a support base, and a positioning nut. The screw diameter is not less than φ32mm, and the support base is made of stamped or cast steel plate. The width of the support base groove should be greater than the width of the bottom mold support beam 73. The lower end of the screw of the U-shaped support 63 is inserted into the cavity of the first longitudinal steel pipe 61 or the second longitudinal steel pipe 611. The elevation of the top surface of the support base is adjusted by rotating the positioning nut, with an adjustment range of not less than 200mm. After installation, all positioning nuts are tightened to the contact surface of the top of the steel pipe to prevent settlement during concrete pouring.

[0061] Several bottom formwork support beams 73 are fixed to the lower surface of the bottom formwork 7. The bottom formwork support beams 73 are made of square timber, I-beams, or rectangular steel pipes, and 50mm×100mm square timber or channel steel can be selected. The bottom formwork support beams 73 are arranged along the entire length of the cantilever beam 5, and their spacing is determined by calculation based on the thickness of the bottom formwork 7 and the concrete load, typically controlled between 300mm and 400mm. The bottom formwork support beams 73 are fixedly connected to the lower surface of the bottom formwork 7 using nails, self-tapping screws, or U-bolts to ensure that there is no relative displacement between them during concrete pouring.

[0062] The bottom formwork support beam 73 is supported by the second support frame 42 and several U-shaped supports 63. On the side closest to the original gate pier dam body 1, the bottom formwork support beam 73 is directly supported by the upper end of the second support frame 42. An adjustable top support is installed at the upper end of the second support frame 42, and the top support slot is inserted into the bottom of the bottom formwork support beam 73. The bottom formwork support beam 73 is adjusted to the design elevation by adjusting the screw rod. In the cantilevered area away from the original gate pier dam body 1, the bottom formwork support beam 73 is supported by the U-shaped supports 63 at the top of the support frame 6. The support base of the U-shaped supports 63 is directly inserted into the bottom of the bottom formwork support beam 73. Each bottom formwork support beam 73 is supported by at least two U-shaped supports 63, with a support spacing of no more than 1.2m. With the coordinated support of the second support frame 42 and the U-shaped support 63, the bottom formwork support beam 73 forms a multi-point continuous support system. The bottom formwork 7 is subjected to uniform stress, and the mid-span deflection is significantly reduced, effectively ensuring the flatness and geometric accuracy of the bottom surface of the expanded dam body 3.

[0063] In another technical solution, a plurality of bottom formwork tie bars 71 are also included. The first end of the bottom formwork tie bar 71 is fixed to the outer wall of the original gate dam body 1. The second end of the bottom formwork tie bar 71 is fixedly connected to the bottom formwork 7. The second end of the bottom formwork tie bar 71 is fixedly connected to the bottom formwork 7 through a bottom formwork fastener 72. The bottom formwork fastener 72 includes a fastener connecting bar 721 and a fastening support part 722. The lower end of the fastener connecting bar 721 passes through the bottom formwork 7 and is fixedly connected to the fastening support part 722. The fastening support part 722 is fastened to the lower surface of the bottom formwork 7. The upper end of the fastener connecting bar 721 passes through the bottom formwork 7 and is welded and fixed to the second end of the bottom formwork tie bar 71.

[0064] The bottom formwork tie rod 71 is made of φ16 or φ20 round steel. Its length is determined by on-site layout based on the distance from the outer wall of the original gate pier dam body 1 to the tie point of the bottom formwork 7. Threads are pre-processed or welded joints are reserved at both ends. The bottom formwork tie rod 71 is arranged at designed intervals along the longitudinal and transverse directions of the bottom formwork 7. Its arrangement density is determined by calculation based on the concrete thickness of the expanded dam body 3, the pouring speed, and the anti-buoyancy requirements of the bottom formwork 7. The longitudinal spacing is usually controlled between 0.8m and 1.2m, and the transverse spacing matches the arrangement spacing of the cantilever beam 5.

[0065] The first end of the bottom formwork tie bar 71 is fixed to the outer wall of the original gate pier dam body 1. For example, anchor holes can be drilled at corresponding positions on the outer wall of the original gate pier dam body 1, with a hole depth of not less than 150 mm and a hole diameter 4 mm to 6 mm larger than the tie bar diameter. After cleaning the anchor holes, inject anchoring adhesive or high-strength anchoring agent, insert the first end of the bottom formwork tie bar 71 into the anchor holes, and conduct a pull-out test after the anchoring material reaches the design strength. As another preferred connection method, the anchor plate 9 can also be fixed to the outer wall of the original gate pier dam body 1 by expansion bolts. The first anchoring steel bar 91 is pre-welded on the anchor plate 9, and the first end of the bottom formwork tie bar 71 is fixed to the first anchoring steel bar 91 by double-sided lap welding or bar welding, with a weld length of not less than 5 times the tie bar diameter.

[0066] The second end of the bottom formwork tie bar 71 is fixedly connected to the bottom formwork 7, specifically through a bottom formwork clamp 72. The bottom formwork clamp 72 is a dedicated connecting component, its function being to effectively transfer the tension force of the bottom formwork tie bar 71 to the bottom formwork 7, while simultaneously applying downward preload to the bottom formwork 7 to prevent floating or displacement of the bottom formwork 7 during concrete pouring. The bottom formwork clamp 72 includes a clamp connecting bar 721 and a clamping support part 722. The clamp connecting bar 721 is made of round steel of the same specifications as the bottom formwork tie bar 71, and its length is determined according to the thickness of the bottom formwork 7 and the installation space of the clamping support part 722, typically 120mm to 150mm. The lower end of the clamp connecting bar 721 passes through a pre-set hole in the bottom formwork 7 and is fixedly connected to the clamping support part 722. The connection between the clamp connecting bar 721 and the clamping support part 722 is achieved by double-sided full welding; the weld should be full, free of slag inclusions, and the weld leg height should be no less than 6mm. The retaining support part 722 is made of steel plate or short section steel with a thickness of not less than 8mm. Its shape can be a rectangular steel plate, a circular pad, or a channel-shaped bracket, with a planar dimension of not less than 80mm×80mm. The retaining support part 722 is clamped onto the lower surface of the bottom formwork 7, and its supporting surface is in close contact with the bottom of the bottom formwork 7, converting the tension force of the tie rod into downward compressive stress on the bottom formwork 7.

[0067] The upper end of the fastener connecting rib 721 also extends through the pre-set through hole in the bottom template 7 to the top of the bottom template 7. A through hole needs to be pre-drilled on the bottom template 7 at the position corresponding to the fastener connecting rib 721. The hole diameter should be 2mm to 3mm larger than the diameter of the fastener connecting rib 721, and the drilling position should be aligned with the arrangement axis of the bottom template tie rib 71. The upper end of the fastener connecting rib 721 should extend at least 50mm beyond the upper surface of the bottom template 7. This extended end is fixed to the second end of the bottom template tie rib 71 by double-sided lap welding or butt welding. Before welding, rust and oil stains at the connection points should be removed, and the weld should be coated with anti-rust paint after cooling for protection.

[0068] During installation, the following procedures should be followed: First, weld and assemble the fastener connecting rib 721 and the fastener support part 722 to form the bottom formwork fastener 72; then, pass the upper end of the fastener connecting rib 721 through the pre-set through hole from the bottom of the bottom formwork 7 upwards, so that the fastener support part 722 is tightly attached to the lower surface of the bottom formwork 7; subsequently, align the second end of the bottom formwork tie rib 71 with the upper end of the fastener connecting rib 721 and weld them; finally, after the first end of the bottom formwork tie rib 71 has been anchored, apply prestress to the tie rib by tightening the adjusting nut set in the middle of the bottom formwork tie rib 71, or by using a hand-operated hoist, jack, or other tools, so that the bottom formwork 7 is pressed tightly against the lower support frame 6 and the bottom formwork support beam 73. The prestress value should be determined by calculation based on the buoyancy load of the bottom formwork 7, and is usually controlled in the range of 5kN to 10kN.

[0069] Through the combined structure of the bottom formwork tie bar 71 and the bottom formwork fastener 72, when the bottom formwork 7 is subjected to an upward buoyancy during concrete pouring, this buoyancy is transmitted through the fastener support 722 to the fastener connecting bar 721, and then to the bottom formwork tie bar 71, ultimately borne by the first end anchored to the original gate pier dam body 1. This force-bearing system forms a complete anti-buoyancy force transmission path, effectively suppressing the upward deformation of the bottom formwork 7 under the action of concrete vibration and lateral pressure, ensuring that the flatness of the bottom surface and the cross-sectional height of the expanded dam body 3 meet the design requirements. At the same time, the bottom formwork tie bar 71, the cantilever beam 5, the support frame 6, and the second support frame 42 form a vertical multi-restraint system, significantly reducing the burden on the cantilever beam 5 to bear the load of the bottom formwork 7 alone, making the stress distribution of the overall support structure more uniform and the safety reserve higher.

[0070] In another technical solution, a side template support structure 82 is provided on the outer side of the side template 8. The side template support structure 82 includes a plurality of first back ribs 821 and a plurality of second back ribs 822. The first back ribs 821 are spaced apart and fit against the outer surface of the side template 8. The second back ribs 822 are perpendicular to the first back ribs 821 and are double-ply steel pipes in pairs, abutting against the outer side of the first back ribs 821. The second end of the side template tie rod 81 passes through the gap between the double-ply steel pipes of the second back ribs 822 and the locking member 83 in sequence. The second end of the side template tie rod 81 is provided with threads, and the side template 8 and the side template support structure 82 are tightened and fixed by tightening the nuts.

[0071] The side formwork support structure 82 includes several first back ribs 821 and several second back ribs 822. The first back ribs 821 are made of double-jointed φ48.3mm×3.6mm steel pipes or rectangular steel pipes, arranged vertically at intervals. The spacing is calculated based on the lateral pressure distribution of the newly poured concrete on the side formwork 8, and is usually controlled to be no greater than 300mm. The length direction of the first back ribs 821 is parallel to the long side direction of the side formwork 8, and their inner surfaces are in continuous contact with the outer surface of the side formwork 8, with no obvious gaps between them. The first back ribs 821 and the surface of the side formwork 8 can be temporarily fixed using short steel pipe clips or special pressure plates to ensure that the back ribs do not slip or tilt before the side formwork tie rods 81 are tensioned.

[0072] The second back rib 822 is perpendicular to the first back rib 821. The second back rib 822 is made of double-splittered steel pipes of the same specifications as the first back rib 821, and is arranged horizontally with a vertical spacing of 600mm to 900mm, corresponding to the arrangement height of the side formwork tie rods 81. This forms a grid-like support system with longitudinal and transverse back ribs for overall stress distribution.

[0073] The second end of the side formwork tie rod 81 passes sequentially through the gap between the double-jointed steel pipes of a set of second back ribs 822 and through the locking member 83. The width of the gap between the double-jointed steel pipes of the second back ribs 822 is determined by the arrangement spacing of the two steel pipes, and is usually controlled between 50mm and 80mm. This gap provides a through channel for the side formwork tie rod 81 and also serves as a guide for limiting the horizontal position of the tie rod. After the second end of the side formwork tie rod 81 passes through the side formwork plate 8, it first emerges from the gap between the double-jointed steel pipes of the first back rib 821, then passes through the gap between the double-jointed steel pipes of the second back rib 822, and finally passes through the central channel of the locking member 83. The locking member 83 adopts a conical cast iron lock head or a disc-shaped nut lock seat, with its front end abutting against the outer surface of the double-jointed steel pipe of the second back rib 822, and its rear end supporting the locking nut. As another embodiment, the locking member 83 can also be a locking plate made of a continuous steel plate or shaped steel. The locking plate is horizontally positioned, its length covering two or more adjacent side template tie rods 81 within the same floor height. The surface of the locking plate is attached to the outer surface of a set of second back ribs 822, and through holes are provided on the plate corresponding to the positions of each side template tie rod 81. The second ends of the two side template tie rods 81 respectively pass through the gap between the same set of second back ribs 822, and then simultaneously pass through the through holes at the corresponding positions on the locking plate, and are locked on the outside of the plate by nuts.

[0074] The second end of the side formwork tie bar 81 is provided with a continuous thread, the thread specification of which is determined according to the diameter of the tie bar, usually M16 or M20. After the side formwork tie bar 81 passes through the locking member 83, a flat washer, a spring washer, and a double nut are installed in sequence at its exposed end. During installation, the side formwork 8 is first hoisted into place and its verticality is initially adjusted. Then, the side formwork tie bar 81 is inserted into the design position to ensure that the first end of the tie bar is reliably connected to the anchor point of the original gate pier dam body 1. Subsequently, the first back rib 821, the second back rib 822, and the locking member 83 are installed in sequence on the outside of the side formwork 8. Finally, prestress is applied to the tie bar by tightening the outer nut.

[0075] In another technical solution, several anchor plates 9 are fixed to the outer wall of the original gate dam body 1. Each anchor plate 9 has a first anchoring steel bar 91 and a second anchoring steel bar 92. The first anchoring steel bar 91 is welded to the first end of the bottom formwork tie bar 71, and the second anchoring steel bar 92 is welded to the first end of the side formwork tie bar 81. The anchor plates 9 are made of Q235 steel plates with a thickness of not less than 12mm. Their planar dimensions are determined according to the tie bar design load, typically ranging from 150mm×150mm to 200mm×200mm. The anchor plates 9 are anchored to the outer wall of the original gate dam body 1 using M16 or M20 expansion bolts through installation holes drilled at the four corners. When the concrete strength of the original gate dam body 1 is high and rebar installation is feasible, chemical anchors can also be used to implant into the dam body, and the anchors are welded to the anchor plates 9. Before installing the anchor plate 9, the surface of the dam body should be leveled to ensure that the surface of the anchor plate 9 is perpendicular to the direction of force on the tie bar, thus avoiding eccentric tension. The anchor plate 9 is equipped with a first anchoring rebar 91 and a second anchoring rebar 92. Both the first anchoring rebar 91 and the second anchoring rebar 92 are made of round steel of the same specifications as the corresponding tie bars. Their lower ends are vertically welded to the outer surface of the anchor plate 9. The welding is a double-sided full weld, with a weld leg height of not less than 8mm. If necessary, a triangular stiffening plate is added at the root of the weld to enhance fatigue resistance. The first anchoring rebar 91 and the second anchoring rebar 92 can be arranged side-by-side or staggered vertically on the anchor plate 9. The specific positions are determined by layout based on the incident angles of the bottom formwork tie bar 71 and the side formwork tie bar 81. The first anchoring steel bar 91 is welded to the first end of the bottom formwork tie bar 71. The welding adopts double-sided lap welding or butt welding, with a lap length of not less than 5 times the tie bar diameter and a weld thickness of not less than 6mm. Before welding, the connection end face should be derusted and centered to ensure that the axes of the two bars coincide. The second anchoring steel bar 92 is welded to the first end of the side formwork tie bar 81, and its welding process and technical parameters are the same as those of the first anchoring steel bar 91. Through this anchor plate 9 combined anchoring structure, the bottom formwork tie bar 71 and the side formwork tie bar 81 can be concentratedly anchored at the same dam body position, reducing the number of dam body drillings and avoiding excessive weakening of the original structure. At the same time, the anchoring point position of the tie bar is precisely controllable and the force transmission path is direct and clear, which significantly improves the anchoring reliability and construction convenience of the tie bar system.

[0076] In another technical solution, the cantilever beam 5, located on the beam segment outside the outline of the outer dam body 3, is fully covered with scaffold boards to form a construction platform 53. A guardrail 54 is installed around the construction platform 53. The scaffold boards used on the construction platform 53 are high-quality wooden scaffold boards or standardized steel planks with a thickness of not less than 50mm, and the boards are flat, without cracks or severe deformation. The scaffold boards are laid continuously along the direction perpendicular to the axis of the cantilever beam 5, with tight joints between boards and a height difference of no more than 3mm between adjacent boards. Both ends of each scaffold board are overlapped on the upper flange surface of two adjacent cantilever beams 5, with an overlap length of not less than 100mm, ensuring that each scaffold board is supported by at least two cantilever beams 5, forming a stable multi-point support system. The construction platform 53 covers the entire beam segment area of ​​the cantilever beam 5 located outside the outline of the outer dam body 3. The width of the platform is the outward extension length of the cantilever beam 5. The length of the platform runs through the original gate pier dam body 1, forming a continuous working passage.

[0077] The construction platform 53 is surrounded by a guardrail 54. The guardrail 54 runs the entire length of the construction platform 53, and its specific construction is as follows: guardrail posts are welded or inserted at corresponding positions on the second end edge of the cantilever beam 5. The posts are made of φ48.3mm×3.6mm steel pipe, with a spacing of no more than 2.0m. The base of the posts is welded and fixed to the upper flange of the cantilever beam 5, or inserted into a special sleeve socket welded to the cantilever beam 5. The height of the posts is no less than 1.2m. Two horizontal crossbars are installed along the height of the posts, with the upper crossbar 1.2m above the platform surface and the lower crossbar 0.6m above the platform surface. The horizontal crossbars are fastened to the posts using right-angle couplers, with an overlap length of no less than 0.5m at the crossbar joints and at least two couplers at the overlap. The bottom of guardrail 54 is equipped with a toe board with a height of not less than 180mm. The toe board is made of wooden template or steel plate and is tied or clamped to the uprights and platform surface to prevent materials and tools from rolling off. The outer surface of the uprights and crossbars of guardrail 54 is painted with alternating red and white warning paint, and red warning lights are hung around the guardrail during nighttime construction.

[0078] The construction method for the enlarged and renovated section of the gravity dam gate pier, using the aforementioned formwork support structure for the enlarged and renovated section of the gravity dam gate pier, includes the following steps:

[0079] S1: Roughen and clean the outer part of the original gate dam body 1 to be poured, and install reinforcing bars according to the design requirements.

[0080] Specifically, the concrete surface of the outer area of ​​the original gate dam body 1, located below the extended dam body 3, was first roughened. An FC-803Z roughening machine or a YT-28 hand-held pneumatic drill was used as the main construction tools. During the roughening operation, the cutting depth was strictly controlled, with the standard being that 1 / 3 to 1 / 2 of the old concrete surface stones were exposed. The roughening depth was generally controlled within the range of 5cm to 10cm. After roughening, a high-pressure water gun and a wire brush were used alternately to clean the surface slag and loose aggregate, resulting in a clean, rough, saturated, and dry surface ready for bonding. For local depressions or defects, cement mortar of the same strength grade was used for leveling and repair to ensure the compactness and shear strength of the bonding surface between the new outer dam body 2 and the original gate dam body.

[0081] According to the design drawings, anchor bars are laid out and positioned on the outer wall of the original gate pier dam body 1. A YT-28 hand-held pneumatic drill or similar equipment is used for drilling. The drilling depth must not be less than the designed anchoring depth, and the hole position deviation should be controlled within ±50mm, with any excess depth not exceeding 100mm. After drilling, high-pressure airflow and a brush are used alternately to clean the holes, ensuring no dust or water accumulation. High-performance anchoring adhesive or micro-expansion cement-based anchoring material is used, with a grouting fullness of not less than 95%. Anchor bars of the designed specifications are then inserted, and the exposed length of the anchor bars should meet the requirements for subsequent rebar lap splicing. The anchoring system is cured at room temperature for no less than 72 hours. Pull-out force testing can only be conducted after the design strength is reached. The pull-out force of a single anchor bar should not be less than 40kN, and the sampling ratio should not be less than 5% of the total number of anchor bars.

[0082] Before binding the reinforcing bars of the new outer dam body 2, the embedded anchor bars are first derusted, straightened, and threaded. The binding of the reinforcing bars is strictly controlled according to the design spacing and protective layer thickness. The main bars and embedded anchor bars are firmly connected by double-sided lap welding or mechanical connection, with a lap length of not less than 5 times the diameter of the reinforcing bar. The outer steel formwork 4 uses large combined steel molds or custom-made arc-shaped steel molds. Before installation, a release agent is evenly applied, and double-sided tape or sponge strips are used to seal the joints. Steel support frames 41 are welded or bolted to the outside of the steel formwork at the design spacing. The steel support frames 41 can be welded triangular trusses using ∠75×8 angle steel, or assembled into an integral steel frame using Bailey beams. Horizontal braces, vertical scissor braces, and planar connections are added between adjacent steel support frames 41. All nodes are connected by double-sided full welding or high-strength bolts to form a spatial steel structure system with sufficient rigidity and overall stability. The concrete for the new outer dam body 2 is poured using a pumping process, with each layer controlled to a thickness of no more than 40cm. An immersion vibrator is used to compact each layer until it is completely compacted. After pouring, the concrete is covered with a geomembrane for moisture retention and curing for at least 7 days. The outer steel formwork 4 and steel support frame 41 are not removed after the concrete reaches its design strength, providing a reliable foundation for the subsequent installation of the cantilever beam 5.

[0083] S2: Several cantilever beams 5 are fixedly installed at horizontal intervals on the outside of the original gate dam body 1, and the cantilever beams 5 extend outward to the outside of the outline of the outer expansion dam body 3 to be poured.

[0084] Specifically, the layout parameters of the cantilever beam 5 are determined based on the design outline of the extended dam body 3, the cantilever span, and concrete load calculations. The cantilever beam 5 uses I16 I-beams, cut according to the on-site layout dimensions, with flat cut ends perpendicular to the axis and edges ground smooth to remove burrs. The spacing of the cantilever beams 5 is determined through structural stress analysis, typically controlled within the range of 0.9m to 1.0m to ensure the economy and safety of the support system. The first end of the cantilever beam 5 is aligned with the outer surface of the installed steel support frame 41, and fixed by double-sided full welding. The weld height is not less than 8mm, the weld width is uniform, and there are no slag inclusions or undercut. To enhance the bending and shear bearing capacity of the joint, a triangular stiffening plate is added at the angle between the first end of the cantilever beam 5 and the steel support frame 41. The stiffening plate is not less than 10mm thick and is welded simultaneously with the web of the cantilever beam 5 and the steel support frame 41. The second end of the cantilever beam 5 extends horizontally outward, and its extension endpoint should extend at least 300mm beyond the outline of the outer dam body 3 to be poured, so as to form a complete support boundary that transitions from the arc-shaped boundary of the original gate dam body 1 to the square boundary of the outer dam body 3.

[0085] A diagonal bracing beam 51 is added between the steel support frame 41 and the cantilever beam 5. The diagonal bracing beam 51 is made of I16 I-beams or [16 channel steel of the same specifications as the cantilever beam 5, and both ends are beveled according to the actual angle of the connection. The upper end of the diagonal bracing beam 51 is welded to the corresponding position of the lower flange or web of the cantilever beam 5, and the lower end is welded to the vertical member or node plate of the steel support frame 41. The inclination angle is determined by calculation based on the cantilever length and load size, and is usually controlled between 30° and 60°. All welds are double-sided full welds, with a weld leg height of not less than 8mm. Before welding, the weld joints are derusted and degreased. After welding, the weld slag is removed in time and a visual inspection is performed. If necessary, ultrasonic testing is used for spot checks. The installation of the diagonal bracing beam 51 transforms the cantilever beam 5 from a simply supported stress state to a diagonally tensioned-cantilever combined stress system, effectively reducing the calculated span and mid-span bending moment of the cantilever beam 5, while significantly constraining the vertical flexural deformation during concrete pouring, ensuring the overall stiffness and long-term stability of the cantilever support system.

[0086] S3: Install the support frame 6 on the cantilever beam 5, adjust the top elevation of the support frame 6 to the design position, and mark the positioning of the fixing steel rods 52 on the upper flange surface of the cantilever beam 5 according to the design position. The fixing steel rods 52 are made of φ25 round steel or φ48mm×3.6mm short steel pipes, with a single length controlled between 150mm and 200mm. The fixing steel rods 52 are perpendicular to the upper flange surface of the cantilever beam 5 and are fixed by double-sided full welding, with a weld leg height of not less than 6mm, and the perimeter weld of each fixing steel rod 52 is continuous and full. The fixing steel rods 52 are set along the longitudinal direction of the cantilever beam 5 according to the arrangement spacing of the uprights of the support frame 6, usually consistent with the arrangement spacing of the cantilever beam 5, controlled within the range of 0.9m to 1.0m.

[0087] The first longitudinal steel pipe 61 of the support frame 6 is a scaffolding steel pipe with a specification of φ48.3mm×3.6mm. Its lower end is sleeved on the outside of the fixed steel rod 52, with an insertion depth of not less than 100mm. To ensure the reliability of the connection between the first longitudinal steel pipe 61 and the fixed steel rod 52, one of the following two methods is used for fixing: First, drill a φ12mm through hole at the sleeve position and insert a matching pin or high-strength bolt for locking; Second, perform perimeter welding at the sleeve position, with a weld height of not less than 6mm. The verticality of the first longitudinal steel pipe 61 is corrected bidirectionally using a theodolite or plumb line, and the deviation is controlled within 5mm. The first longitudinal steel pipes 61 on adjacent cantilever beams 5 are connected to the transverse steel pipes 62 by right-angle couplers. The transverse steel pipes 62 are scaffolding steel pipes of the same specification and are set in layers along the height direction of the first longitudinal steel pipes 61 according to the step distance. The step distance is usually 1.2m to 1.5m, and the bottom step distance should not be greater than 1.2m. The fastener connection points between the two ends of the transverse steel pipe 62 and the first longitudinal steel pipe 61 should be close to the pole node, and the tightening torque of the fastener bolts should be controlled between 40 N·m and 65 N·m.

[0088] The transverse steel pipe 62 is connected to the second longitudinal steel pipe 611 via right-angle couplers or swivel couplers. The second longitudinal steel pipe 611 also uses φ48.3mm×3.6mm scaffolding steel pipe, and its arrangement direction is parallel to that of the first longitudinal steel pipe 61. The second longitudinal steel pipe 611 is set between two adjacent first longitudinal steel pipes 61, and its bottom can be suspended or equipped with an adjustable base, without needing to be directly fixed to the cantilever beam 5. Through the multi-directional coupler connection of the first longitudinal steel pipe 61, the transverse steel pipe 62, and the second longitudinal steel pipe 611, the support frame 6 forms a frame-truss combination structure with good spatial rigidity. Each upright works together to bear the force, and the overall stability is significantly improved. The top of both the first longitudinal steel pipe 61 and the second longitudinal steel pipe 611 are threadedly connected to U-shaped supports 63. The U-shaped supports 63 are composed of a φ32mm adjustable screw, a stamped steel support base and double positioning nuts. The adjustment range of the screw is not less than 200mm, and the width of the support base slot should be greater than the cross-sectional width of the bottom mold support beam 73.

[0089] Meanwhile, a second support frame 42 is installed between the bottom formwork 7 and the steel support frame 41. The second support frame 42 is made of φ48.3mm×3.6mm steel pipe or lightweight lattice steel column, and its lower end is welded and fixed to the crossbar, node plate or top chord of the steel support frame 41; when the steel support frame 41 is a Bailey beam, the lower end of the second support frame 42 should be welded to the node plate reinforcement area of ​​the Bailey beam. An adjustable top support is installed on the upper end of the second support frame 42, and the top support slot directly supports the bottom formwork support beam 73 or timber. The second support frame 42 is evenly arranged along the span direction of the cantilever beam 5 at the designed spacing (usually 0.9m to 1.2m), forming a staggered or corresponding layout with the cantilever beam 5, together forming a multi-point coordinated, bi-directional force transmission bottom formwork support system. After all the support frames were erected, a level was used to measure the elevation of the top surface of the U-shaped support 63 and the top support. Based on the measured deviation, the screw rod was rotated for fine adjustment to ensure that the elevation deviation of all support points was controlled within ±3mm.

[0090] S4: Lay the bottom template 7 on top of the support frame 6, adjust the flatness and joints of the bottom template 7, and fix it to the support frame 6.

[0091] Bottom formwork support beams 73 are erected on the U-shaped supports 63 of the supporting frame 6 and the adjustable top supports of the second supporting frame 42. The bottom formwork support beams 73 are made of 50mm×100mm square timber, channel steel, or 40mm×60mm rectangular steel pipes, and are arranged continuously along the length perpendicular to the axis of the cantilever beam 5. The spacing of the bottom formwork support beams 73 is determined by calculation based on the thickness of the bottom formwork 7, the concrete load, and the support span, and is usually controlled between 300mm and 400mm. Each bottom formwork support beam 73 is supported by at least two U-shaped supports 63 or top supports, and the distance between support points is no greater than 1.2m. There should be no gaps between the bottom formwork support beams 73 and the U-shaped supports 63; if necessary, wooden wedges should be used to tighten the gaps or adjusting screws should be used to eliminate them.

[0092] The bottom formwork 7 uses high-quality film-coated plywood or standardized steel formwork with a thickness of not less than 15mm. Upon arrival, each sheet is inspected for warpage and surface flatness. The formwork is designed and cut according to the bottom outline dimensions of the expanded dam body 3. Cut edges should be straight and smooth, and joints should use a toothed lap joint or a flat joint with added sponge strips. The bottom formwork 7 is laid on top of the bottom formwork support beam 73, with the formwork surface closely adhering to the top surface of the support beam, and the height difference between adjacent formwork surfaces not exceeding 2mm. The edges of the bottom formwork 7 smoothly connect to the upper or side surfaces of the original new outer dam body 2. Double sponge strips or polyurethane sealant are applied at the joints to prevent cement slurry leakage during pouring. The bottom formwork 7 is fixed to the bottom formwork support beam 73 using nails, self-tapping screws, or U-shaped clamps, with a nailing spacing not exceeding 300mm to ensure that the bottom formwork 7 does not experience localized floating or lateral displacement during concrete vibration.

[0093] Following this, the installation of the bottom formwork tie bar 71 is carried out. First, anchor bars are inserted at corresponding positions on the outer wall of the original gate pier dam body 1, or the first anchoring steel bar 91 is set through the anchor plate 9. The first anchoring steel bar 91 is made of round steel of the same specification as the bottom formwork tie bar 71, with an exposed length of not less than 150mm. The bottom formwork tie bar 71 is made of φ16 or φ20 round steel, cut according to the length laid out on site, with threads processed at both ends or pre-reserved for welding bevels. The first end of the bottom formwork tie bar 71 is fixed to the first anchoring steel bar 91 by double-sided lap welding, with a lap length of not less than 5 times the steel bar diameter and a weld thickness of not less than 6mm. Symmetrical segmented welding is used during welding to reduce thermal deformation.

[0094] The second end of the bottom formwork tie rod 71 is fixedly connected to the bottom formwork 7 via the bottom formwork fastener 72. The bottom formwork fastener 72 consists of a fastener connecting rib 721 and a fastening support part 722: the fastener connecting rib 721 is made of round steel of the same specification as the bottom formwork tie rod 71, and its length is determined according to the thickness of the bottom formwork 7 and the installation space, ranging from 120mm to 150mm. The fastening support part 722 is made of Q235 steel plate with a thickness of not less than 8mm, cut into 80mm×80mm square or φ80mm round pads. The lower end of the fastener connecting rib 721 passes through the pre-set through hole in the bottom formwork 7 and is fully welded to the center of the fastening support part 722 on both sides, with a weld leg height of not less than 6mm. The upper end of the fastener connecting rib 721 also passes through the pre-set through hole in the bottom formwork 7 and extends above the plate surface, with an extension length of not less than 50mm. The diameter of the through hole on the bottom template 7 corresponding to the fastener connecting rib 721 is 2mm to 3mm larger than the diameter of the connecting rib, and the hole position deviation is controlled within ±2mm.

[0095] After the second end of the bottom formwork tie bar 71 is aligned with the upper end of the fastener connecting bar 721, it is fixed by double-sided lap welding, with the weld length not less than 5 times the diameter of the reinforcing bar. After all welding operations are completed and the weld has cooled, an adjusting nut and matching washer are installed in the middle of the bottom formwork tie bar 71. By tightening the adjusting nut or using a manual hoist to assist tensioning, a prestress of 5kN to 10kN is applied to the bottom formwork tie bar 71, so that the bottom formwork 7 is pressed tightly against the bottom formwork support beam 73 and the upper surface of the support frame 6. During the tensioning process, a level is used to monitor the elevation change of the bottom formwork 7 plate surface to ensure that excessive arching or depression does not occur. After all the bottom formwork tie bars 71 are tensioned, the adjusting nut is tightened a second time, and anti-loosening treatment is spot welded at the threaded connection between the nut and the tie bar.

[0096] S5: Tie the reinforcing bars of the outer dam body 3 above the bottom formwork 7, and firmly connect the reinforcing bars to the embedded reinforcing bars on the outside of the original gate pier dam body 1.

[0097] Specifically, the reinforcement binding work for the outer dam body 3 is carried out above the bottom formwork 7. After the reinforcement arrives on site, it is sorted and stacked according to specifications and batch numbers, and samples are taken for mechanical property retesting. The surface of the reinforcement should be clean and undamaged. Oil stains, paint, and loose rust should be removed with a wire brush or sandblasting. Reinforcement with granular or flaky old rust is strictly prohibited. The cutting length of the reinforcement is accurately calculated according to the construction drawings and the thickness of the protective layer, and is cut using a mechanical cutting machine, with flat ends and no horseshoe deformation. The reinforcement is bent using a reinforcement bending machine for cold bending, and the bending mandrel diameter and bending angle comply with the relevant provisions of the "Code for Construction of Concrete Structures".

[0098] The order of rebar tying follows the principle of main bars first, then distribution bars, and bottom layer first, then lateral bars. Before laying the bottom layer of rebar, mark the rebar position lines on the upper surface of the bottom formwork 7 according to the design spacing, and place precast concrete spacers or plastic protective layer clips. The strength grade of the spacers should not be lower than the design strength of the concrete of the outer dam body 3, and the thickness deviation of the protective layer should be controlled within ±5mm. The main bars are connected by straight threaded sleeves or double-sided lap welding, with the joint positions staggered and the joint area percentage of the same section not exceeding 50%. The intersection of the stirrups and the main bars is tied point by point with double-strand No. 20 galvanized iron wire, with the tying buckles distributed in a figure-eight shape and the thread ends bent inward to avoid exposure and rust. The rebar skeleton of the outer dam body 3 should be effectively connected to the embedded rebar on the outside of the original gate pier dam body 1. The connection method is mainly double-sided lap welding, with a lap length of not less than 5 times the diameter of the rebar, and the weld is full and free of slag.

[0099] Meanwhile, anchor plates 9 are installed on the outer wall of the original dam body 1 at the designed locations. Anchor plates 9 are made of Q235 steel plates with a thickness of not less than 12mm, with planar dimensions of 150mm×150mm to 200mm×200mm, and φ18mm installation holes drilled at the four corners. Before installation, the surface of the dam body is partially leveled to ensure that the plate surface is perpendicular to the direction of the tension reinforcement. M16×150mm expansion bolts are used to anchor the anchor plates 9 to the dam body, with an insertion depth of not less than 100mm and a tightening torque controlled between 80N·m and 100N·m. When the concrete strength of the original dam body 1 is high, chemical anchors can also be used, with a diameter of not less than 16mm and an insertion depth of not less than 150mm. There should be no gaps between the surface of the anchor plates 9 and the outer wall of the dam body; if necessary, high-strength epoxy resin mortar should be injected to fill the gaps.

[0100] The first anchoring rebar 91 and the second anchoring rebar 92 are vertically welded onto the anchor plate 9. The first anchoring rebar 91 is used to connect the bottom formwork tie bar 71, and the second anchoring rebar 92 is used to connect the side formwork tie bar 81. Both anchoring rebars are made of round steel of the same specification as the corresponding tie bars, and their lower ends are fully welded to the surface of the anchor plate 9 on both sides. The weld height is not less than 8mm. If necessary, triangular stiffening plates with a spacing of 45° are added around the root of the weld. The first anchoring rebar 91 and the second anchoring rebar 92 can be arranged side by side or staggered vertically by 200mm, depending on the incident angle of the tie bars and the site layout. After welding, all welded joints are cleaned of weld slag and coated with two coats of inorganic zinc-rich anti-rust paint, with a paint film thickness of not less than 80μm.

[0101] S6: Install side formwork 8 above bottom formwork 7, and fix side formwork 8 to the outer wall of the original gate dam body 1 by side formwork tie rod 81, and adjust the verticality and joint of side formwork 8.

[0102] Specifically, the side formwork 8 is installed above the bottom formwork 7. The side formwork 8 uses high-quality film-coated plywood or custom-made combined steel formwork with a thickness of not less than 18mm, ensuring a flat surface free from warping or deformation. The formwork is designed according to the cross-sectional dimensions of the expanded dam body 3, prioritizing the use of large formwork panels to reduce the number of joints. After cutting, the edges of the formwork are coated with edge sealant to prevent water absorption and deformation. Joints are constructed using tongue-and-groove overlaps or flat joints with added sponge strips, and the height difference between adjacent formwork surfaces is no more than 2mm. A continuous sealing sponge strip is installed at the junction of the bottom of the side formwork 8 and the bottom formwork 7, and cement mortar is used to seal the outside of the formwork to prevent grout leakage at the root, which could lead to root rot.

[0103] Side formwork support structures 82 are installed on the outer side of the side formwork 8. The first vertical back rib 821 is made of double-ply φ48.3mm×3.6mm steel pipe, evenly arranged along the height direction of the side formwork 8 at intervals not exceeding 300mm. The inner surface of the first back rib 821 is in continuous contact with the outer surface of the side formwork 8, temporarily fixed using steel pipe clips or special pressure plates. The second horizontal back rib 822 is made of double-ply steel pipe of the same specification, perpendicularly intersecting the first back rib 821, with a vertical spacing controlled between 600mm and 900mm, corresponding to the arrangement height of the side formwork tie rods 81. The second back rib 822 uses double-ply steel pipes arranged in pairs, with the inner surface of the double-ply steel pipes of the second back rib 822 tightly fitted with the outer surface of the first back rib 821. Each intersection of the first back rib 821 and the second back rib 822 is locked in both directions by right-angle fasteners. The tightening torque of the fastener bolts is controlled between 45 N·m and 60 N·m, so that the longitudinal and transverse back ribs form a grid-like support frame that bears the overall force.

[0104] The side formwork tie bar 81 is made of φ16 or φ20 round steel, and its length is 200mm longer than the distance from the outer wall of the original gate pier dam body 1 to the outer back rib of the side formwork 8. Both ends are rolled with continuous threads, and the thread length is not less than 100mm. The first end of the side formwork tie bar 81 is fixed to the second anchoring steel bar 92 of the outer wall of the original gate pier dam body 1 by double-sided lap welding. The welding process and quality requirements are the same as those for the bottom formwork tie bar 71. The second end of the side formwork tie bar 81 passes through the pre-set hole in the side formwork 8, the gap between the double-jointed steel pipes of the first back rib 821 and the second back rib 822, and finally passes through the central channel of the locking member 83.

[0105] The locking component 83 has two implementation methods: When the spacing between the tie rods is large and requires independent adjustment, the locking component 83 uses a conical cast iron lock head or a disc-shaped nut lock seat, with each tie rod passing through and locking independently; when the spacing between the tie rods is close and requires overall force bearing, the locking component 83 uses a continuous locking steel plate with a thickness of not less than 12mm, a width of 80mm to 100mm, and a length covering two or more adjacent side formwork tie rods 81 at the same floor height. Through holes are made on the surface of the continuous locking steel plate at the corresponding tie rod positions. The second ends of the two side formwork tie rods 81 simultaneously pass through the gap between the double-jointed steel pipes of the second back rib 822, and then pass through the corresponding holes on the locking steel plate. Washers and double nuts are installed on the outside of the steel plate for locking.

[0106] After the second end of the side formwork tie bar 81 passes through the locking member 83, a flat washer, a spring washer, and a double nut are sequentially fitted on it. A torque wrench is used to tighten the nuts symmetrically and gradually in stages, with the nut on each tie bar on the same locking steel plate tightened alternately to ensure that the locking steel plate is evenly stressed and does not deflect. As the nuts are tightened, the locking member 83 pushes the second back rib 822 inward, and the second back rib 822 transmits the thrust to the first back rib 821, thereby pressing the side formwork 8 tightly against the outside of the steel reinforcement skeleton of the outward-expanding dam body 3. During the tensioning of the tie bars, a 2m straightedge and feeler gauge are used simultaneously to check the flatness of the side formwork 8, and a theodolite or plumb bob is used to correct the verticality in both directions, ultimately ensuring that the flatness deviation is no greater than 3mm and the verticality deviation is no greater than 3mm.

[0107] Meanwhile, a construction platform 53 is formed by fully laying scaffold boards on the beam segment of the cantilever beam 5 located outside the outline of the outer dam body 3. The scaffold boards are made of high-quality wooden scaffold boards or shaped steel planks with a thickness of not less than 50mm, and are laid continuously along the direction perpendicular to the axis of the cantilever beam 5. Each scaffold board is overlapped at both ends on the upper flange surface of the two adjacent cantilever beams 5, with an overlap length of not less than 100mm and a joint between boards not greater than 5mm. The scaffold boards are tied to the cantilever beam 5 with double strands of No. 12 galvanized iron wire, and each board is tied at each end with no less than two bindings. A continuous guardrail 54 is installed around the perimeter of construction platform 53. The guardrail posts are made of φ48.3mm steel pipes, spaced no more than 2.0m apart, and are welded to the upper flange of cantilever beam 5 or inserted into a special sleeve socket. The posts are 1.2m high, with two horizontal bars and a 180mm high toe board at the bottom. The outer surface of the guardrail posts is painted with alternating red and white warning paint, and a red warning light is hung during nighttime construction. Construction platform 53 serves as the main operating platform for formwork installation, rebar tying, concrete pouring, and vibration operations. The platform surface is located 1.5m to 1.8m below the elevation of the bottom formwork 7, ensuring convenient and safe personnel passage and material transfer.

[0108] S7: Pour concrete into the formwork of the outward-expanding dam body 3, vibrate to compact, and cure to the design strength.

[0109] Specifically, the concrete for the outer dam body 3 uses pre-mixed commercial concrete, with strength and impermeability grades strictly adhering to design requirements. During transport, the concrete mixer trucks maintain a slow drum rotation speed of 3-6 r / min to prevent segregation and slump loss. Upon arrival at the site, the slump of each truck is checked and controlled between 180mm and 200mm; any substandard slump is strictly prohibited from being placed in the formwork. After the concrete pump truck is in position, the pump pipe is first moistened with cement mortar, which is evenly distributed on the formwork surface and not piled up. Concrete pumping should be continuous. If the pumping interval exceeds 20 minutes and the pipeline is long, the pump should be started every 5 minutes, pumping a small amount of concrete to prevent pipe blockage. If the interval exceeds 45 minutes or the temperature is above 30℃, the concrete in the pump pipe must be removed and the pipeline cleaned.

[0110] Concrete pouring employs a flat-laying method, proceeding sequentially from one end of the outer dam body 3 to the other, with each layer's thickness strictly controlled within the range of 300mm to 500mm. During pouring, the concrete is evenly distributed, and excessive accumulation that could overload the side formwork 8 is strictly prohibited. Concrete vibration utilizes a φ50mm immersion high-frequency vibrator, with vibration points arranged in a quincunx pattern. The moving interval is controlled at approximately 400mm, and the vibration time is controlled between 15s and 30s, determined by the concrete surface showing a slurry sheen, no further significant settling, and no air bubbles escaping. After each layer of concrete is vibrated, a second vibration is performed after a 20-30 minute interval, penetrating 50mm to 100mm into the lower layer of concrete. This effectively removes any bleed water and residual air bubbles accumulated after the initial vibration, significantly improving the concrete's density and interfacial bonding strength.

[0111] Thin-walled steel cooling water pipes, using φ32mm×1.5mm black iron pipes, are installed at the designed locations along the thicker sections of the concrete (thickness greater than 800mm). These pipes are arranged in layers along the height of the outward-expanding dam body, with a layer spacing of 1.0m to 1.5m. The cooling water pipes are tied and fixed to the reinforcing steel frame during installation, and the joints are sealed by welding with sleeves. After installation, a water pressure test is conducted at 0.6MPa, with no leakage observed after 15 minutes of pressure stabilization. Cooling water is supplied during concrete pouring, with the flow rate controlled at 0.6m / s to 0.7m / s. The water flow direction is reversed daily to ensure a uniform temperature drop within the concrete. During water supply, the inlet and outlet water temperatures, as well as the internal concrete temperature, are monitored every 2 hours. The difference between the highest concrete temperature and the water temperature is controlled to not exceed 25℃, and the daily temperature drop is limited to no more than 1℃ to prevent excessively rapid cooling and the resulting temperature cracks.

[0112] Curing should begin immediately after the concrete has set. A φ25mm perforated plastic pipe is suspended from a cantilever formwork tripod and connected to pressurized water to create a continuous water curtain, ensuring the exposed concrete surface is always under continuous water curing. The water flow should be gentle, avoiding splashing. Continuous water curing should last at least 7 days. After 7 days, intermittent watering should be used, and a composite geomembrane should be used for coverage. Sandbags should be used to secure the geomembrane seams to prevent them from being blown away by the wind. When the average daily temperature is below 5℃, watering should be suspended and an insulating straw mat should be laid on the outside of the geomembrane. When the average daily temperature is above 25℃, the frequency of nighttime watering should be increased to prevent excessive water loss and shrinkage cracks on the concrete surface. The curing period should be at least 14 days, with critical load-bearing areas requiring at least 21 days of curing.

[0113] S8: After the concrete strength reaches the demolding requirements, remove the side formwork 8, bottom formwork 7, support frame 6 and cantilever beam 5 in sequence.

[0114] Specifically, the formwork support system can only be removed after the concrete specimens of the expanded dam body 3, cured under the same conditions, have reached 75% of the design strength and are not less than the demolding strength requirement. The demolding sequence should follow the principles of top to bottom, sides to bottom, and non-load-bearing to load-bearing, and rough construction that disturbs the concrete structure is strictly prohibited.

[0115] First, remove the side formwork 8 and its supporting structure 82. Workers stand on the construction platform 53 and use a torque wrench to loosen the outer locking nuts of each side formwork tie rod 81, removing the washers and locking parts 83. For forms using continuous locking steel plates, the tie rod nuts at both ends should be removed first, followed by the middle tie rod nuts. After all nuts are removed, use a pry bar to gently pry at the formwork joints to separate the side formwork 8 from the concrete surface; do not use a sledgehammer to strike it violently. After the side formwork 8 is lifted off in sections, promptly clean any residual concrete slurry from the surface and check the flatness. Formwork with excessive deformation should be sent to the processing area for reshaping and repair. After the first back rib 821 and the second back rib 822 are removed, they are sorted and stacked according to specifications. Fasteners are centrally soaked, cleaned, and oiled for maintenance.

[0116] Next, dismantle the bottom formwork 7 and the bottom formwork support beam 73. Before dismantling the bottom formwork 7, release the prestress of the bottom formwork tie rod 71: use an oxy-acetylene torch to cut the weld between the second end of the bottom formwork tie rod 71 and the fastener connecting rod 721, or loosen the adjusting nut to release the tension. The fastener connecting rod 721 and the fastening support part 722 can be left on the concrete structure surface, or they can be ground smooth with an angle grinder. Use a pry bar to apply force evenly from the edge of the bottom formwork 7 to separate the surface of the board from the concrete bottom surface. It is strictly forbidden to pry hard at a single point and damage the concrete edges. After the bottom formwork 7 is hoisted to the ground piece by piece, clean the residual slurry on the board surface, replace the damaged sponge strips, and apply release agent for later use. The bottom formwork support beam 73, U-shaped support 63, adjustable top support and other accessories are dismantled simultaneously. Check whether the screw rod is bent or deformed, apply oil for maintenance, and then put them into storage according to their categories.

[0117] Then dismantle the support frame 6. The dismantling sequence is from top to bottom: first, remove the U-shaped bracket 63 and the second longitudinal steel pipe 611; second, remove the transverse steel pipe 62; and finally, remove the first longitudinal steel pipe 61. Use a special wrench to remove the fasteners; never use a hammer or pry bar. The connection between the first longitudinal steel pipe 61 and the fixing steel rod 52 can be achieved by cutting the locking pin with an oxy-acetylene torch or by welding, or the fixing steel rod 52 can be retained for future reuse. After dismantling, reclassify the steel pipes by length; straighten and repair any bent or deformed pipes; and replace any missing fasteners.

[0118] Finally, the cantilever beam 5 and the diagonal bracing beam 51 were cut in sections using gas cutting. Before the cutting operation, temporary suspending steel wire ropes were set up under the cantilever beam 5 to prevent the beam from falling at the moment of cutting. The cutting point was selected 100mm to 200mm from the outer edge of the steel support frame 41, and oxy-acetylene flame cutting was used. The cut should be straight and neat. The cut cantilever beam 5 sections were promptly lifted to the ground storage area by tower crane or truck crane, and it was strictly forbidden to stack them on the construction platform 53. The first end of the cantilever beam 5 could be left on the steel support frame 41 and coated with anti-rust paint, or it could be cut off and recycled together. The diagonal bracing beam 51 was cut off simultaneously with the cantilever beam 5. After cutting, the residual weld scars on the steel support frame 41 were ground off and coated with two coats of anti-rust primer and topcoat.

[0119] After all dismantled components are inspected, repaired, and painted, they are neatly categorized and stacked, and an inbound / outbound log is established for future reuse. The scaffolding boards and guardrails 54 on construction platform 53 are dismantled simultaneously with the removal of cantilever beam 5. Temporary guardrails or warning tapes are promptly installed at the edges of the work surfaces after dismantling to ensure the safety of subsequent workers. After all dismantling work is completed, a comprehensive visual inspection of the external dam body 3 is conducted, measuring cross-sectional dimensions, flatness, verticality, and protective layer thickness, and a demolding inspection record is created and archived.

[0120] It should be noted that although the steps are described in a specific order above, this does not mean that they must be performed in that order. In fact, some of these steps can be executed concurrently, or even in a different order, as long as the required functionality is achieved. The number of devices and processing scale described herein are for simplification of the invention; applications, modifications, and variations of this invention will be readily apparent to those skilled in the art.

[0121] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A template support structure for the enlarged and renovated section of a gravity dam gate pier, installed on the outside of the original gate pier dam body (1), characterized in that, include: Several cantilever beams (5) are arranged horizontally at intervals along the outer contour of the original gate dam body (1). The first end of the cantilever beam (5) is fixed to the outside of the original gate dam body (1), and the second end of the cantilever beam (5) extends outward in the horizontal direction. The projection of the second end of the cantilever beam (5) on the horizontal plane is located outside the contour line of the outer expansion dam body (3) to be poured. The bottom formwork (7) is used to support the outer expansion dam body (3) to be poured. The bottom formwork (7) is located above the cantilever beam (5). A support frame (6) is installed on the cantilever beam (5) to support the bottom formwork (7). Side formwork (8), which is located above the bottom formwork (7), is used to enclose the outer expansion dam body (3) to be poured; Several side formwork tie bars (81) are provided, the first end of which is fixedly connected to the original gate pier dam body (1), and the second end of which is connected to the side formwork (8). A new outer dam body (2) is poured outside the original gate pier dam body (1) located below the outer dam body (3). The new outer dam body (2) is formed by pouring the outer steel formwork (4). A steel support frame (41) is set on the outside of the outer steel formwork (4). The first end of the cantilever beam (5) is fixedly connected to the steel support frame (41). The edge of the bottom formwork (7) is connected to the edge of the new outer dam body (2). A second support frame (42) is also set between the bottom formwork (7) and the steel support frame (41). The lower end of the second support frame (42) is fixedly connected to the steel support frame (41). The upper end of the second support frame (42) is fixedly connected to or supports the bottom formwork (7). It also includes several bottom formwork tie bars (71), the first end of which is fixed to the outer wall of the original gate dam body (1), and the second end of which is fixedly connected to the bottom formwork (7).

2. The template support structure for the enlarged and renovated section of the gravity dam gate pier as described in claim 1, characterized in that, An inclined bracing beam (51) is also provided between the steel support frame (41) and the cantilever beam (5), and the two ends of the inclined bracing beam (51) are fixedly connected to the steel support frame (41) and the cantilever beam (5) respectively.

3. The template support structure for the enlarged and renovated section of the gravity dam gate pier as described in claim 1, characterized in that, The cantilever beam (5) is welded with several fixed steel rods (52), and the support frame (6) includes several first longitudinal steel pipes (61). The first longitudinal steel pipes (61) are sleeved on the outside of the fixed steel rods (52) and fixedly connected to the fixed steel rods (52). Several transverse steel pipes (62) are connected between the first longitudinal steel pipes (61) on adjacent cantilever beams (5) by fasteners. Several second longitudinal steel pipes (611) are connected to the body of the transverse steel pipes (62) by fasteners. The top of the first longitudinal steel pipes (61) and the second longitudinal steel pipes (611) are threaded with U-shaped brackets (63). The bottom template (7) has several bottom template support beams (73) fixed on its lower surface. The bottom template support beams (73) are supported by the second support frame (42) and several U-shaped brackets (63).

4. The template support structure for the enlarged and modified section of the gravity dam gate pier as described in claim 1, characterized in that, The second end of the bottom template tie rod (71) is fixedly connected to the bottom template (7) through the bottom template fastener (72). The bottom template fastener (72) includes a fastener connecting rib (721) and a fastening support part (722). The lower end of the fastener connecting rib (721) passes through the bottom template (7) and is fixedly connected to the fastening support part (722). The fastening support part (722) is fastened to the lower surface of the bottom template (7). The upper end of the fastener connecting rib (721) passes through the bottom template (7) and is welded and fixed to the second end of the bottom template tie rod (71).

5. The template support structure for the enlarged and modified section of the gravity dam gate pier as described in claim 1, characterized in that, A side template support structure (82) is provided on the outside of the side template (8). The side template support structure (82) includes a plurality of first back ribs (821) and a plurality of second back ribs (822). The first back ribs (821) are spaced apart and fit against the outer surface of the side template (8). The second back ribs (822) are perpendicular to the first back ribs (821) and the second back ribs (822) are double-ply steel pipes in pairs, which are attached to the outside of the first back ribs (821). The second end of the side template tie rod (81) passes through the gap between the double-ply steel pipes of the second back ribs (822) and the locking member (83) in sequence. The second end of the side template tie rod (81) is provided with threads, and the side template (8) and the side template support structure (82) are tightened and fixed by tightening the nuts.

6. The template support structure for the enlarged and modified section of the gravity dam gate pier as described in claim 1, characterized in that, Several anchor plates (9) are fixed on the outer wall of the original gate dam body (1). The anchor plates (9) are provided with a first anchoring steel bar (91) and a second anchoring steel bar (92). The first anchoring steel bar (91) is welded and fixed to the first end of the bottom formwork tie bar (71), and the second anchoring steel bar (92) is welded and fixed to the first end of the side formwork tie bar (81).

7. The template support structure for the enlarged and modified section of the gravity dam gate pier as described in claim 1, characterized in that, The cantilever beam (5) is located on the beam segment outside the outline of the outer dam body (3) and is fully covered with scaffold boards to form a construction platform (53). The construction platform (53) is surrounded by guardrails (54).

8. A construction method for expanding and modifying a gravity dam gate pier, characterized in that, The formwork support structure for the enlarged and modified section of the gravity dam gate pier as described in any one of claims 1 to 7 includes the following steps: S1: Roughen and clean the outer part of the original gate dam body (1) to be poured, and install reinforcing bars according to the design requirements; S2: Several cantilever beams (5) are fixedly installed at horizontal intervals on the outside of the original gate dam body (1), and the cantilever beams (5) extend outward to the outside of the outline of the outer expansion dam body (3) to be poured. S3: Install the support frame (6) on the cantilever beam (5) and adjust the top elevation of the support frame (6) to the design position; S4: Lay the bottom template (7) above the support frame (6), adjust the flatness and joints of the bottom template (7), and fix it to the support frame (6); S5: Tie the reinforcing bars of the outer dam body (3) above the bottom formwork (7), and firmly connect the reinforcing bars with the embedded reinforcing bars on the outside of the original gate pier dam body (1); S6: Install side formwork (8) above bottom formwork (7), and fix side formwork (8) to the outer wall of the original gate dam body (1) by side formwork tie rod (81), and adjust the verticality and joint of side formwork (8); S7: Pour concrete into the formwork of the outward expansion dam body (3), vibrate to compact, and cure to the design strength; S8: After the concrete strength reaches the demolding requirements, remove the side formwork (8), bottom formwork (7), support frame (6) and cantilever beam (5) in sequence.

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