Construction method for cantilever casting arch bridge skewback in cliff deep water area

Abstract

The invention relates to the technical field of bridge construction, and particularly discloses a cliff-near deep water area cantilever casting arch bridge skewback construction method which comprises the following steps: S1, building a cofferdam: outwards extending at a designed skewback construction position to build the cofferdam which is a steel-concrete structure with a front wall adopting a steel cofferdam; step S2, arranging an inner support: synchronously performing inner support construction and water pumping in the cofferdam in the built cofferdam, and just evacuating river water in the cofferdam when the inner support construction is completed; s3, arch support pouring is conducted, specifically, after the inner supports are arranged, arch support pouring is completed before the target low water level period; and S4, 1 # section arch section construction is conducted, specifically, the steel structure is dismantled in the target low water level period, and 1 # section building is completed. The technical problems that in the prior art, the size of the skewback becomes large, in the construction environment of deep water near the cliff, the construction space is forced to become small near the cliff, a cofferdam needs to be built firstly due to the deep water, the construction space is further compressed, and construction is difficult to complete through a construction scheme in the prior art are solved.

Description

Technical Field

[0001] The invention relates to the technical field of bridge construction, in particular to a method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep water area. Background Art

[0002] An arch bridge is a type of bridge with an arch structure as its core load-bearing component. It efficiently distributes and carries loads by converting vertical loads into axial pressure along the arch axis. It is a crucial type of bridge in bridge engineering. The arch abutment, located at the foot of an arch bridge, is the key connection point between the main arch ring and the piers / abutments. Because an arch bridge is a structure that thrusts in both directions, the abutment is a crucial component that transmits the enormous horizontal thrust and vertical loads generated by the arch ring to the foundation.

[0003] Although the force borne by the arch ring will be transferred to the arch seat first, the load will eventually be transferred to the foundation of the arch seat. This places certain requirements on the geological conditions of the arch seat. The basic bearing capacity of the bedrock at the arch seat must be able to meet the bearing capacity requirements of the entire bridge, otherwise the foundation will be crushed, which will affect the safety of the arch bridge. Therefore, at the beginning of the design of the arch bridge, the geology will be explored along the linear direction of the arch to see which hard bedrock on both sides is suitable for the construction of the arch seat. The arch bridge is then designed by comprehensively considering factors such as the span, cost, and construction conditions of the arch bridge. Generally speaking, the farther the location that meets the conditions is from the shore, the larger its span, the higher the overall arch structure is, and the cost increases. Therefore, a location closer to the shore is generally chosen.

[0004] Sometimes, the geologically suitable location is either too far from shore or involves fording water. In this case, due to span and cost considerations, the arch abutment is designed at a fording location. Because reservoirs are also built into river channels, the geological conditions for the arch abutment are generally found near cliffs. However, the construction of reservoirs often causes the river water level to rise to the cliff edge. Therefore, the designed arch abutment location would be completely underwater, requiring construction to be carried out underwater. Typically, any underwater construction requires the construction of a cofferdam to provide a relatively dry environment. Water level fluctuations must also be considered. Water bodies experience periods of high and low water levels, and these periods of high and low water levels are seasonal and cyclical. In river channels with reservoirs, these fluctuations are even more pronounced, so reservoir water level control is seasonal and cyclical (water is stored during the flood season to prevent flooding downstream; water is released during the dry season to replenish the water supply downstream). Low water levels are the best time to start construction, as low water levels only require relatively low cofferdams, or even no cofferdams at all. However, there is a time window during low water levels. If the abutment foundation cannot be completed within this time window, construction will have to be carried out during high water levels.

[0005] During high water levels, the underwater arch abutment construction required the cofferdam elevation to take into account the highest water mark during high water levels, necessitating a higher cofferdam height. This elevation created a design collision between Section 1 of the arch bridge and the front wall of the cofferdam. This necessitated the removal of the front wall to clear space for Section 1. However, this removal would cause water to flow back into the cofferdam, making Section 1 impossible to construct during high water levels. Therefore, Section 1 could either be constructed during low water levels or within the cofferdam. If Section 1 were constructed within the cofferdam, the cofferdam would have to be expanded. However, as the front wall of the cofferdam abutted a cliff, expanding the cofferdam would increase the construction time and complexity. If construction were to take place during low water levels, it would be necessary to seize the opportunity to complete Section 1 during this low water window. If construction cannot be completed during a low water window, river water will backflow into the cofferdam, not only causing erosion of the unfinished 1# section, but also requiring a second low water window before construction can resume, significantly extending the construction period. Therefore, there is an urgent need for a construction method that can ensure that each section is constructed within a reasonable time window, thereby shortening the construction period and reducing construction costs. Summary of the Invention

[0006] The purpose of the present invention is to provide a cantilever cast arch bridge arch seat construction method in deep water areas near cliffs, so as to solve the technical problem mentioned above that the existing technology urgently needs a construction method to control the construction of each segment within a reasonable time window, thereby shortening the construction period and reducing construction costs.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is as follows: a method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep water area, characterized by comprising the following steps:

[0008] Step S1, constructing a cofferdam: extending outward from the designed arch seat construction position to construct a cofferdam, the cofferdam being a steel-concrete structure with a steel cofferdam as the front wall;

[0009] Step S2, setting up internal supports: carrying out internal support construction and pumping water inside the cofferdam simultaneously in the built cofferdam. When the internal support construction is completed, the river water inside the cofferdam is just pumped out;

[0010] Step S3, casting the arch seat: after the internal support is set, the arch seat is cast before the target low water level period;

[0011] Step S4, 1# segment arch construction: During the target low water level period, the steel cofferdam of the front wall is removed and the 1# segment construction is completed.

[0012] The beneficial effects of this embodiment are:

[0013] When constructing arch abutments on rivers with reservoirs, the reservoir raises the water level to the cliff face. Due to geological requirements, the abutments are often built on the cliff face. This results in the abutments being constructed underwater, necessitating the construction of a cofferdam to create a relatively dry construction environment. Rivers with reservoirs exhibit two distinct characteristics: 1. Large variations in high and low water levels. The water level in the river is the result of intentional water storage by the reservoir, which controls the water level seasonally (reservoir storage during the flood season to prevent downstream flooding and release water during the dry season to replenish the water supply). Therefore, compared to typical rivers, the water level naturally rises during the flood season, and the reservoir's intentional water storage further contributes to the significant rise. During the dry season, the water level is relatively low, and after water release, the water level drops significantly. Consequently, the difference between high and low water levels is significant. Second, the periodicity is significant. Due to the intentional storage and release of water, the periodicity is significant. Given these two characteristics, effectively utilizing the windows of high and low water levels can significantly reduce the difficulty of construction. The optimal approach is to complete all construction during the low water window (construction during this window requires lower cofferdam heights, resulting in faster construction and lower costs). However, the reservoir's primary function is to store water, and the window for release of water at low water levels is relatively short. It is impossible to complete the cofferdam construction, arch seat casting, and construction of Section 1 within a single window. Therefore, construction of some sections must be completed during the high water period. During this period, the cofferdam elevation must take into account the highest water level during the high water period, requiring the cofferdam to be raised. This elevated cofferdam design creates a collision between Section 1 of the arch bridge and the front wall of the cofferdam. Consequently, the front wall of the cofferdam must be demolished before construction of Section 1 to clear space. However, after the front wall is demolished, the river water during the high water level period will flow back into the cofferdam, and the 1# section will wade through water during the high water level period and construction cannot be carried out. Therefore, this application will place the cofferdam construction and arch seat casting before the target low water level period, and the construction of the 1# section will be placed during the target low water level period. Therefore, after the front wall of the cofferdam is demolished, no river water will flow back into the cofferdam, which will not affect the 1# section, so that the construction of the 1# section can be completed smoothly.

[0014] 2. Although the construction of the 1# segment is carried out during the target low water level period, the impact of river water backflow after the cofferdam is removed can be avoided, but the window time of the target low water level period is relatively short, and the construction needs to be accelerated as much as possible. If a low water level period cannot be completed, the river water will backflow into the cofferdam, which will not only cause erosion to the unfinished 1# segment, but also require waiting for the second low water level period before the 1# segment can be constructed again, which greatly prolongs the construction period. The construction of the 1# segment requires the removal of the front wall of the cofferdam first. In the prior art, the cofferdam includes two types of concrete cofferdams and steel cofferdams. The removal time of the concrete cofferdam is relatively long, which is not conducive to grasping the time window; and although the steel cofferdam has a short removal time, it requires a lot of cost to meet the anti-overturning requirements of high water levels, and its cost is too high. Therefore, the present application designs the cofferdam as a steel-concrete structure with a steel cofferdam as the front wall. While reducing costs, it speeds up the time for removing the front wall of the cofferdam, and thus reasonably completes the 1# segment during the low water level period.

[0015] Further, in the step 2, the inner supporting structure needs to be paved over the entire cofferdam, and the opposite wall is connected. Its main structure includes columns and beams, and its construction comprises the following steps: N1, column construction: the columns are hoisted into place in the cofferdam according to the design position. After all are in place, the columns are fixed to the base underwater using anti-dispersion concrete; N2, beam support construction: after the columns are fixed, beams are laid between the columns to form a frame structure. The two ends of the beams are fixedly connected to the adjacent columns. The laying order is laid from top to bottom. Each layer of beams is drawn out of a layer of accumulated water in the cofferdam. The process is repeated alternately until the water is finally pumped to the bottom of the foundation pit. The construction of all beams is completed, and the outermost beam is directly fixed to the cofferdam. The method of laying beams layer by layer and pumping water layer by layer makes the internal support of the cofferdam smoothly transition, and the whole process has little change in strength, and its construction safety is higher.

[0016] Furthermore, the outermost beam in N2 is connected to the cofferdam by pre-buried anchor bars and the beams, and epoxy resin concrete is poured to seal the connection after anchoring to avoid water seepage.

[0017] Furthermore, when the arch seat is cast in S3, a steel plate can be laid on the crossbeam to form a construction platform. By laying the steel plate on the crossbeam, the inner support can be used as a scaffold for casting the arch seat, which reduces the laying of scaffolding and reduces the cost of building the inner support.

[0018] Furthermore, the cofferdam in step 2 is a steel-concrete composite cofferdam comprising a steel structure and a concrete structure.

[0019] Furthermore, the steel-concrete composite cofferdam includes a front wall, side walls, and a back wall. The front wall is a composite wall structure combining concrete and steel cofferdam structures. Due to the deep water near the cliff, the ground at the front edge of the arch seat is a steep slope and cliff, and the area available for cofferdam construction is small. The size of the cofferdam can only be reduced, resulting in a shorter distance between the cofferdam and the arch seat. When the arch ring is constructed on the arch seat later, its 1# segment will collide with the front wall of the cofferdam, and the construction of the 1# segment cannot be completed. In this application, a steel cofferdam is set in the front wall. When the 1# segment is under construction, the steel cofferdam can be quickly removed by cutting without affecting the construction of the 1# segment.

[0020] Furthermore, the construction method of the steel-concrete composite cofferdam in step 2 includes the following steps: step 1, cofferdam foundation pit construction: use measurement control points and encryption points to stake out the position of the cofferdam construction, determine the foundation pit boundary of the cofferdam, and reserve 1-2m of construction space to excavate the cofferdam foundation pit; step 2, pouring concrete cofferdam: after the foundation pit excavation is completed, use earth cofferdam to pour concrete cofferdam; step 3, setting up steel cofferdam: use the combination of steel cofferdam embedded parts and concrete cofferdam.

[0021] Furthermore, the inner support frame structure is provided with a plurality of columns fixed vertically to the bedrock surface.

[0022] Furthermore, the positioning construction method of the column includes the following steps: step a, setting three sensors on the top corners of the cofferdam, and also setting sensors on the upper and lower end faces of the column; step b, using a crane to hoist the column with the sensors into place, and using the Beidou system to ensure that the column is vertical, and then using connecting rods to fix the column to the cofferdam or other adjacent columns to ensure the stability of the column; step c, after all the columns in the cofferdam are installed vertically, use bottom sealing concrete to fix the bottom of the column to the bedrock, and form a flat foundation pit bottom foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the construction flow chart of the arch seat of the present invention.

[0024] Figure 2 This is the bridge layout diagram in the construction environment of the present invention

[0025] Figure 3 This is a schematic structural diagram of the cofferdam of the present invention.

[0026] Figure 4 This is a schematic structural diagram of the front wall of the cofferdam of the present invention.

[0027] Figure 5 This is a schematic diagram of the mold casting of the present invention.

[0028] Figure 6 This is a schematic diagram of the connection structure between the beam and the cofferdam of the present invention.

[0029] Figure 7This is a schematic diagram of the connection structure between the column and the bedrock of the present invention. DETAILED DESCRIPTION

[0030] The following is further described in detail through specific implementation methods:

[0031] The reference numerals in the drawings of the specification include: arch seat 1, cofferdam 2, front wall 21, side wall 22, back wall 23, inner support 3, column 31, connecting rod 32, angle iron 33, bedrock 4, bottom concrete 5.

[0032] Implementation example Figure 1-7 As shown:

[0033] A method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep water area comprises the following steps:

[0034] Step S1, constructing a cofferdam: extending outward from the designed arch seat construction position to construct a cofferdam, the cofferdam being a steel-concrete structure with a steel cofferdam as the front wall;

[0035] This application is mainly used to build arch abutments of arch bridges in deep water areas near cliffs beside rivers, such as Figure 3 As shown, due to the limitation of the deep water near the cliff, there is a cliff not far from the front side of the arch seat 1, and the construction space is small. Therefore, the width of the cofferdam 2 that can be built is limited, and the distance between the arch seat 1 and the cofferdam 2 is very short. There is not enough space for construction work, and there is not enough width space to build the cofferdam. In addition, the water level of the reservoir has a high water level period. Since it is impossible to complete all construction in a low water level period, the height of the cofferdam is forced to be raised to above the water level line of the high water level period. However, when it is necessary to construct an arch ring on the arch seat in the later stage, the 1# segment of the arch ring will collide with the front wall of the cofferdam. Therefore, it is impossible to construct directly, and the front wall needs to be demolished to construct the 1# segment of the arch ring. Therefore, the present application has developed a construction method for an arch seat cofferdam in a deep water area near a cliff, and its specific construction steps are introduced in detail:

[0036] The cofferdam 2 of this application is designed as a steel-concrete composite cofferdam, and its structure is as follows Figure 3 As shown, the main part of the cofferdam 2 is composed of a front wall 21 (close to the water flow side), a side wall 22, and a back wall 23. The main structure of the side wall 22 and the back wall 23 is a concrete structure, and the front wall 21 is set in front of the arch seat. The front wall of the cofferdam of this application adopts a composite structure of a concrete foundation combined with a steel cofferdam, such as Figure 4 As shown, it includes front wall I and front wall II, of which front wall I is a concrete cofferdam and front wall II is a steel cofferdam. The steel structure of front wall II can be directly cut and removed during the construction of arch ring 1# segment, and the removal is quick, so it does not affect the construction of arch ring 1# segment. Its construction method is as follows:

[0037] Step 1: Cofferdam foundation pit construction: During a low water level period before the target low water level period, use survey control points and infill points to stake out the cofferdam construction location, determine the cofferdam foundation pit boundary, and reserve 1-2m of construction space for excavating the cofferdam foundation pit;

[0038] During a low water period prior to the target low water period, the cofferdam design foundation position was staked out using survey control points and infill points. This was performed using a total station to confirm that the cofferdam foundation pit construction area was consistent with the design. During the low water period, the cofferdam was constructed when the water level was relatively low, making it easier to construct. Steel cofferdams have relatively weaker anti-overturning capabilities, and the water pressure during the low water period was relatively low, preventing damage to the cofferdam during the construction period.

[0039] When construction begins, the excavation method needs to be adjusted according to the water level, which is divided into two parts. First, when the elevation of the excavation is above the water level, the construction no longer considers the water level changes in the morning and evening of the day. It is consistent with land construction and directly uses conventional methods such as excavators and blasting for excavation. Second, when the elevation of the excavation is lower than the water level, construction is carried out by setting up an earth cofferdam. Use an excavator to excavate the foundation pit until the bedrock surface is reached. No blasting is performed, and the loose stones in the foundation pit are cleaned up in time to ensure that the base is free of mud, slag and various construction waste. If the foundation pit is left for a long time after excavation due to other external factors, mud and sand will remain at the bottom. A high-power mud suction device needs to be used to clean it to ensure that the base is a large area of bedrock surface. The cofferdam foundation pit construction requires the base inside the cofferdam to be constructed at the same time.

[0040] When the excavation elevation is below the water level, an earthen cofferdam is set up according to the water level changes. The earthen cofferdam is mainly made of earthbags, and the size of the filled earthbags is approximately 60x15cm. When the water depth of the foundation pit is less than 2m, a double row of earthbag cofferdams (approximately 1.2m wide) is set up. When the water depth of the foundation pit is between 2-4m, a four row of earthbag cofferdams (approximately 2.4m wide) is set up. Due to the severe water seepage in the earthen cofferdam, red clay is selected as much as possible, and special waterproof materials such as leak-proof agents are used to seal the gaps between the earthbag layers to reduce water seepage. The foundation pit adopts a layer-by-layer excavation construction method.

[0041] After the excavation of the foundation pit is completed, the plane position, size and base elevation of the base need to be quality inspected to ensure that the plane position meets the design requirements and meets the needs of foundation construction operations; the base elevation is allowed to deviate, and the deviation is based on the geological conditions of the base, and all reach the bedrock surface, and ensure that the geological conditions and bearing capacity of the base are consistent with the design.

[0042] Step 2: Formwork installation and pre-embedding: Use the earth cofferdam as the outer formwork to install the mold for pouring the concrete cofferdam, and pre-embed the embedded parts of the steel cofferdam in the mold;

[0043] Since the cofferdam structure of the present application is a steel-concrete composite cofferdam, its concrete cofferdam includes its side walls, back walls and part of the front wall. The pouring of the concrete cofferdam is divided into two parts. First, when pouring on land (such as the back wall), the formwork uses a large-area steel formwork and is constructed according to ordinary concrete construction methods. Second, when pouring underwater, when the foundation of the cofferdam is below the water level, the earth cofferdam in step 1 is used as the outer water-facing side formwork for construction. The steel-concrete composite cofferdam of the present application only installs the back wall, side wall and front wall of the front wall I in the formwork. After installation, it is necessary to embed the embedded parts of the steel cofferdam at the connecting end face of the front wall II and the front wall I to ensure that part of the embedded parts is cast in the front wall I and part leaks out of the front wall I to form an end that can be connected to the front wall II. It is worth noting that the embedded parts need to be firmly fixed and will not tilt during the pouring process. The embedded parts can be fixed to the bottom of the base or to the formwork. The material and thickness of the steel cofferdam embedded parts are exactly the same as those of the front wall II steel cofferdam.

[0044] Step 3: Pour concrete cofferdam: Pour concrete cofferdam in the mold installed in step 2;

[0045] The concrete cofferdam is poured in layers as a whole, and the thickness of each pouring shall not exceed 2m to prevent the earth cofferdam template on the water side from collapsing. The template for layered pouring is constructed by flipping the mold. The construction method of flipping the mold is as follows: Figure 6 As shown, first use a 2m formwork to cast three layers of standard section cofferdam concrete. When the three layers of standard section cofferdam concrete are cast, and the concrete strength and curing period reach the conditions for removing the formwork, only the formwork of the lower two standard section cofferdam concrete is removed, and the 2m formwork of the top standard section is left on the wall and is not removed, serving as the basic formwork for the second casting of the cofferdam wall formwork. The removed formwork is used to continue casting the cofferdam wall upwards. It must be removed in pieces during removal, and each removal must ensure that the removed formwork is the lowest layer of formwork. After the surface of the removed formwork is cleaned and coated with a release agent, it is lifted by a crane and installed in the position to be installed. After the installation is completed and the bottom is cleaned, the next layer of concrete is poured until the wall of the concrete cofferdam of this application is poured. During the entire process, the water in the cofferdam is not pumped out, and only the water in the cofferdam wall casting formwork is pumped out to pour the concrete.

[0046] Step 4: Setting up the steel cofferdam: Weld the steel cofferdam to the embedded parts in step 2, and set up cofferdam supports behind the steel cofferdam to complete the cofferdam construction;

[0047] After pouring is completed, the steel plate of the steel cofferdam is welded to the leaked end of the embedded parts in the front wall I. The strength of the weld must meet the pressure resistance and anti-seepage requirements in the construction environment. After welding is completed, channel steels must be set at equal intervals on the back side of the steel plate (the side away from the water body) as the rear support of the steel plate to ensure that the steel plate can provide sufficient pressure resistance. In order to ensure that there is no water seepage accident at the welding position of the embedded parts and the steel plate, when setting the channel steel as the rear support of the steel plate, it is necessary to ensure that a channel steel must be set at the weld position to cover the weld. After covering, the contact edge of the channel steel and the steel plate is also sealed by dense welding to ensure that the quality of the weld can withstand sufficient water pressure. Other channel steels and steel plates are also fixed by welding. After the construction of the channel steel and steel plates is completed, the front wall II is formed.

[0048] In this embodiment, in order to ensure the stability of the cofferdam, the structure of the front wall II steel cofferdam is composed of 20mm steel plate + 20a channel steel, the channel steels are evenly spaced, and the spacing of the evenly spaced channel steels is 1m.

[0049] Step S2, setting up internal supports: carrying out internal support construction and pumping water inside the cofferdam simultaneously in the built cofferdam. When the internal support construction is completed, the river water inside the cofferdam is just pumped out;

[0050] Due to the characteristics of this application being close to a cliff and deep water, the original ground at the front edge of the arch seat is a steep slope and cliff, resulting in insufficient width of the cofferdam foundation, and thus insufficient anti-overturning capacity of the cofferdam wall itself. Under the static pressure of high water levels, there is a risk of crushing the cofferdam. Therefore, internal supports must be added inside the cofferdam to support the cofferdam. The internal support adopts a frame structure, which includes a number of beams and columns. The columns are made of steel pipe structure, and the beams are made of I-beam structure. The I-beams and columns are used to form an integral frame inside the cofferdam to support the cofferdam. The cofferdam is fully paved so that the static pressure on the front wall can be transmitted to the back wall through the frame. The static pressure of the upper side wall and the static pressure of the lower side wall are offset by each other through the frame, making it impossible for the front wall and the side wall to be crushed by the static pressure of deep water.

[0051] The construction method of the internal support of the cofferdam is as follows:

[0052] N1. Column construction: hoist the columns into place according to the designed position within the cofferdam. Once all are in place, use anti-dispersion concrete to fix the columns to the base underwater.

[0053] Since the steel-concrete composite cofferdam of this application does not use concrete for bottom sealing during its construction, the bottom of the foundation pit is an uneven bedrock surface. When the columns are directly hoisted into the foundation pit and installed on the bedrock, they cannot be vertical. If the columns are not vertical, the internal structure of the frame formed will be a number of parallelogram structures. When the parallelogram structure is subjected to lateral pressure, it is easy to deform. This makes the overall support strength of the internal support insufficient and unable to provide reliable support for the cofferdam. In order to ensure that the formed internal support can provide reliable support strength, it is necessary to ensure that the columns are vertical. This application uses a steel pipe positioning construction method for the cofferdam columns to ensure the vertical installation of the columns. The specific construction method is as follows:

[0054] Step a: Set four sensors on the cofferdam as reference sensors, and use the BeiDou system to adjust three of the reference sensors to the same horizontal plane as the reference plane;

[0055] After the cofferdam is constructed, a circle is constructed with the center of the cofferdam as the center. At the intersection of the arc and the cofferdam, sensors are installed at any three points as reference sensors. When installing the reference sensors, a level (a laser level) can be used to align the three sensors. The reference sensors must be able to independently measure distances between each other or connect to the Beidou system, using the system to align the three sensors. Therefore, the reference sensors need to perform two functions: first, measure distances between each other, and second, communicate with the Beidou system. A combination solution is available: a Beidou positioning module + a ranging sensor, such as the Sinan T300 Beidou module + the SICK DL100 laser ranging sensor. Alternatively, an integrated device (with built-in ranging and Beidou positioning) can be used, such as the Huace Navigation i70 Pro. Use a level and Beidou system to ensure that the three reference sensors are on the same horizontal plane, and use this horizontal plane as the reference plane. After the three sensors on the reference plane are set up, set the fourth reference sensor vertically above any sensor. Use this fourth reference sensor to cooperate with the reference plane to establish a coordinate system inside the cofferdam.

[0056] Step b: using a crane to hoist the column into place so that the column contacts the base bedrock, and installing a sensor as a positioning sensor on the upper end of the column, and adjusting the positioning sensor so that it is on the reference plane;

[0057] The columns are installed underwater. Before hoisting the columns, sediment removal equipment is used to clear the foundation pit, exposing the bedrock surface. This ensures that the bottom of the columns will contact the bedrock surface at the bottom of the pit when hoisted into position. After the columns are hoisted into position, sensors are installed at their upper ends as positioning sensors. The positioning sensors must be selected in the same manner as the reference sensors. Therefore, the positioning sensors can directly measure distances with the reference sensors, or they can use the BeiDou system. Using three reference sensors on the reference surface to define a plane, a coordinate system is established with a fourth reference sensor. Direct distance measurements can be made between the positioning sensors to obtain the positioning sensor's coordinates. Using the plane equation Ax + By + Cz + D = 0, the positioning sensor is ensured to be on the reference surface, and the coordinates of the hoisted position within the cofferdam are consistent with the designed position coordinates. Alternatively, the BeiDou system can be used to directly confirm that the positioning sensor is on the reference surface and accurately positioned.

[0058] Step c: Install a sensor as an inclination sensor at the lower end of the column along the vertical line of the column, and use the distance between the positioning sensor, the inclination sensor, and the three reference sensors on the reference surface to determine whether the column is vertical. After verticalization, use a connecting rod to fix the column to the cofferdam or other adjacent columns to ensure that the column remains vertical;

[0059] When installing the tilt sensor, ensure that the line connecting the tilt sensor and the positioning sensor is perpendicular to the column's centerline. During actual installation, before hoisting the column, draw a straight line perpendicular to the column's centerline and install the positioning sensor and tilt sensor directly on either end of the line. When the lower end of the column contacts the bedrock, the column may be completely submerged due to the unevenness of the bedrock surface. To do this, weld angle iron along a line perpendicular to the column's centerline and install the positioning sensor on the angle iron.

[0060] The tilt sensor and the reference sensor have the same model. Therefore, the distance between the tilt sensor, the reference sensor and the positioning sensor can be tested, and they can also be connected to the Beidou system to determine the position.

[0061] Using the positioning sensor, tilt sensor, and three reference sensors on the reference surface, we can determine the distance a between the tilt sensor and the positioning sensor; the distances b1, b2, and b3 between the positioning sensor and the four reference sensors; and the distances c1, c2, and c3 between the tilt sensor and the reference sensors. As long as a, b1, and c1, a, b2, and c2 are all Pythagorean trigonometric, the columns will be vertical. Beidou positioning can also be used to connect to each sensor to perform distance calculations and determine the values of a, b, and c. Ensure the columns are vertical. After ensuring the columns are vertical, use connecting rods to secure them to the cofferdam. The column installation sequence is as follows: first install the circle of columns closest to the cofferdam. After this circle of columns is installed, proceed in a circular pattern toward the center of the cofferdam. Secure the outermost circle of columns to the cofferdam, and then secure the inner circle of columns to the adjacent columns until installation is complete.

[0062] Step d: After all the columns in the cofferdam are vertically installed using step c, the bottom of the columns are fixed to the bedrock using bottom sealing concrete to form a flat foundation pit bottom foundation.

[0063] Before using concrete bottom seal construction, it is necessary to confirm that the columns are vertical again. The bottom seal concrete is constructed underwater using C40 underwater anti-dispersion concrete. During construction, the bottom sediment and mud are cleaned again to ensure that the thickness of the sediment at the bottom of the arch seat is not greater than 1cm before pouring concrete. Concrete pouring must be carried out in a timely manner to avoid mud sedimentation. During construction, a boom pump is used for pouring, and a crane is used to lift the conduit and hopper. The conduit and hopper can be moved in water. When lowering the conduit, it must first be inserted into the bottom of the foundation pit, and then raised 30-50cm as concrete construction space. Divers roughly control the elevation of the concrete to ensure that the concrete pouring elevation is basically consistent. After pouring is completed, the column and the bedrock form a fixed structure, its stability is enhanced, and it meets the requirements for internal support settings.

[0064] During the entire column positioning construction, the coordinates are mainly provided by distance measurement between sensors, and the data transmitted by the Beidou system is used as an early warning aid.

[0065] N2. Beam support construction: After the columns are fixed, beams are laid between the columns to form a frame structure. The two ends of the beams are fixedly connected to the adjacent columns. The laying order is from top to bottom. Each time a layer of beams is laid, a layer of accumulated water in the cofferdam is pumped out. This is repeated alternately until the water is finally pumped to the bottom of the foundation pit. The construction of all beams is completed, and the outermost layer of beams is directly fixed to the cofferdam.

[0066] After the columns are secured with concrete at the bottom, I-beams are used as crossbeams between them to form the overall frame structure. Construction proceeds from top to bottom, from the center outward to the sides, first vertically and then horizontally. Because there is water in the foundation pit, the I-beams can be installed while pumping water. During the first pumping, the first layer of I-beams is installed. Once the first layer is installed, the water is pumped again and the second layer is installed. This cycle is repeated until the water is pumped down to the bottom of the pit, completing the installation of all I-beams. Once all crossbeams are installed, the internal supports will completely fill the cofferdam space.

[0067] Step S3, casting the arch seat: after the internal support is set up, the arch seat casting is completed before the target low water level period.

[0068] Since all construction work on Section 1# needs to be completed within the target low water level window, the arch seat casting construction must be completed during the high water level period, and at the latest before the high water level drops to the low water level period. Arch seat casting construction: Determine the arch seat construction position within the cofferdam where the internal support structure is completed in S2. Use the internal support frame structure as a construction channel to cast the arch seat. Cast the internal support directly into the arch seat where the arch seat and the internal support overlap.

[0069] Based on the designed arch seat position, the arch seat construction location is determined and the arch seat casting construction is carried out. The arch seat casting construction includes the steps of reinforcing steel and cooling pipe laying, formwork installation, concrete pouring, formwork removal, and concrete curing. Because the internal support is a frame structure, the space between the frames can be used for construction. Therefore, steel plates can be laid on the internal support beams to form a layered construction platform, through which construction can be carried out.

[0070] Rebar construction and cooling pipe laying: After the bottom is sealed, the arch seat reinforcement is set in the foundation pit, and the cooling pipe is installed. If the cooling pipe conflicts with the arch seat reinforcement, the cooling pipe is moved to ensure the shape of the arch seat reinforcement.

[0071] The arch seat reinforcement is formed by one-time binding. During the reinforcement binding process, a rigid skeleton must be installed first, and some temporary supports must be added as needed to ensure that the reinforcement binding can be straight and straight without deformation. The reinforcement binding is divided into blocks and bound from one end to the other to ensure that personnel can construct in the three-way reinforcement binding. During the reinforcement binding process, some positioning reinforcements must be spot welded firmly to avoid large deformation of the lower reinforcement when constructing the upper reinforcement. For the embedded reinforcement of the junction pier and arch ring, a positioning frame should be used to ensure the accurate position of the embedded reinforcement.

[0072] In order to reduce the hydration heat generated during the construction of the arch seat concrete and prevent temperature difference cracks in the concrete, a circulating cooling water pipe is installed in the arch seat. The circulating cooling pipe uses an ordinary welded steel pipe with good thermal conductivity and a certain strength. The steel pipe itself has great strength and rigidity. It is welded to the arch seat steel bar (including the rigid skeleton) during installation. If necessary, it is assisted by erection steel bars to ensure the forming effect of the cooling pipe, but the arch seat steel bar must not be moved. In case of conflict, the cooling pipe position must be moved to ensure the shape of the arch seat steel bar. The arch seat cooling pipe is set at every 0.8m, and the spacing between the cooling pipes on the same layer is 60cm. The cooling pipes of the two adjacent layers are set vertically.

[0073] Formwork installation: Use lifting equipment to lift the arch seat casting formwork to the arch seat installation position, insert it between the beams, fix the formwork to the columns, and use the internal support as the fixed structure of the formwork to facilitate the installation of the formwork. The formwork needs to be customized so that it can perfectly fit into the space of the internal support frame.

[0074] Concrete pouring: Use a concrete pump to pour the arch seat concrete. The strength of the poured concrete must meet the requirements of C40 large-volume concrete. The slump of the concrete mix ratio should be designed to be between 16cm-20cm. The initial setting time of the concrete is 5-6 hours, and the final setting time is 13-14 hours.

[0075] Formwork removal and concrete curing: After pouring the concrete in S5, when the concrete strength reaches 4-5Mpa, the formwork can be removed by crane. After the formwork is removed, water should be sprinkled on the concrete surface for curing.

[0076] The entire process should follow the temperature control standards for large-volume concrete, and cooling pipes should be used to ensure that the hydration heat is well released and that the cast arch seat meets the design standards.

[0077] Step S4, 1# segment arch construction: dismantle the steel structure and complete the 1# segment construction during the target low water level period.

[0078] After the construction of the arch seat is completed, wait for the arrival of the target low water level period. When the water level line of the high water level period gradually drops, the steel structure of the front wall of the cofferdam exposed above the water level line can be quickly cut with a cutting machine. When the water level line reaches the low water level period, the removal of the front wall of the cofferdam is just completed, freeing up construction space for the 1# section. It is also possible to use a cutting machine to quickly cut off the front wall of the cofferdam after the low water level period is reached. The construction of the 1# section is consistent with the existing technology, and the construction is quickly poured by setting up a template. It is worth noting that the construction of the 1# section needs to be completed before the high water level period arrives to avoid the water level rising and flowing back into the cofferdam, causing the construction of the 1# section to be underwater and then interrupted. During the construction of the 1# section, if the concrete cofferdam needs to be removed, it can be completed simultaneously.

[0079] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep water area, characterized by: The following steps are involved: Step S1, constructing a cofferdam: extending the cofferdam outward from the designed arch seat construction position, wherein the cofferdam is a steel cofferdam for the front wall and a steel-concrete composite cofferdam for the other walls; Step S2, setting up internal supports: carrying out internal support construction and pumping water inside the cofferdam simultaneously in the built cofferdam. When the internal support construction is completed, the river water inside the cofferdam is just pumped out; Step S3, casting the arch seat: after the internal support is set, the arch seat is cast before the target low water level period; Step S4, 1# segment arch construction: dismantle the steel structure and complete the 1# segment construction during the target low water level period.

2. The method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep-water area according to claim 1 is characterized by: In step S2, the internal support structure needs to be laid throughout the entire cofferdam, connecting the opposite walls. Its main structure includes columns and beams, and its construction includes the following steps: N1. Column construction: hoist the columns into place according to the designed position in the cofferdam. After all are in place, use anti-dispersion concrete to fix the columns to the base underwater; N2. Beam support construction: After the columns are fixed, beams are laid between the columns to form a frame structure. The two ends of the beams are fixedly connected to the adjacent columns. The laying order is from top to bottom. Each time a layer of beams is laid, a layer of accumulated water in the cofferdam is pumped out. This is repeated alternately until the water is finally pumped to the bottom of the foundation pit. The construction of all beams is completed, and the outermost layer of beams is directly fixed to the cofferdam.

3. The method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep-water area according to claim 2 is characterized by: The outermost crossbeam in N2 is connected to the cofferdam by pre-buried anchor bars and crossbeam anchoring, and epoxy resin concrete is poured to seal the connection after anchoring.

4. The method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep-water area according to claim 2, characterized in that: When the arch seat is cast in step S3, a steel plate may be laid on the inner supporting beam to form a construction platform.

5. The method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep-water area according to claim 1 is characterized by: The construction of the cofferdam in step S1 may be carried out during a low water level period preceding the target low water level period.

6. The method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep-water area according to claim 1 is characterized by: The steel-concrete composite cofferdam comprises a front wall, side walls and a back wall, wherein the front wall is a composite wall body combining concrete and steel cofferdam structures.

7. The method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep-water area according to claim 6 is characterized by: The construction method of the steel concrete composite cofferdam in step S1 comprises the following steps: Step 1: Cofferdam foundation pit construction: Use survey control points and infill points to stake out the cofferdam construction location, determine the cofferdam foundation pit boundary, and reserve 1-2m of construction space for excavating the cofferdam foundation pit; Step 2: Formwork installation and pre-embedding: Use the earth cofferdam as the outer formwork to install the mold for pouring the concrete cofferdam, and pre-embed the embedded parts of the steel cofferdam in the mold; Step 3: Pour concrete cofferdam: Pour concrete cofferdam in the mold installed in step 2; Step 4. Setting up the steel cofferdam: Weld the steel cofferdam to the embedded parts in step 2, and set up cofferdam supports behind the steel cofferdam to complete the construction of the cofferdam.

8. The method for constructing a cantilever cast arch bridge abutment in a cliff-side deep-water area according to claim 1 is characterized by: The inner support frame structure is provided with a plurality of columns which are vertically fixed to the bedrock surface.

9. The method for constructing a cantilever cast arch bridge arch seat in a cliff-side deep-water area according to claim 8, characterized in that: The column positioning construction method comprises the following steps: Step a: Set four sensors on the cofferdam as reference sensors, and use the Beidou system to adjust three of the reference sensors to the same horizontal plane as the reference plane; Step b: using a crane to hoist the column into place so that the column contacts the base bedrock, and installing a sensor as a positioning sensor on the upper end of the column, and adjusting the positioning sensor so that it is on the reference plane; Step c: Install a sensor as an inclination sensor at the lower end of the column along the vertical line of the column, and use the distance between the positioning sensor, the inclination sensor, and the three reference sensors on the reference surface to determine whether the column is vertical. After verticalization, use a connecting rod to fix the column to the cofferdam or other adjacent columns to ensure that the column remains vertical; Step d: After all the columns in the cofferdam are vertically installed using step c, the bottom of the columns are fixed to the bedrock using bottom sealing concrete to form a flat foundation pit bottom foundation.

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