Cliff deep water area cofferdam stand column steel pipe positioning construction method

Abstract

The invention relates to the technical field of cofferdam construction, and particularly discloses a cliff deepwater area cofferdam stand column steel pipe positioning construction method which comprises the steps that a, four sensors are arranged to serve as reference sensors, and three of the reference sensors are adjusted to be located on the same horizontal plane through a Beidou system; b, the stand column is hoisted in place through a crane, the stand column makes contact with the base covering bed rock, a sensor is installed at the upper end of the stand column to serve as a positioning sensor, and the positioning sensor is adjusted to be located on the datum plane; c, a sensor is installed at the lower end of the stand column to serve as an inclination sensor, and it is ensured that the stand column is vertical through the distance among the positioning sensor, the inclination sensor and the reference sensor; and d, after all the stand columns are installed, the bottoms of the stand columns are fixed to the bed rock through concrete. The technical problem that in the prior art, in the deep water construction environment facing cliff, after the cofferdam is thinned to make room for construction work, the stand columns of an internal frame supporting structure cannot be guaranteed to be vertical is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of cofferdam construction, and specifically to a construction method for positioning steel pipes of cofferdam columns in a deep water area near a cliff. Background Art

[0002] An arch bridge is a type of bridge with an arched structure as the core load-bearing member. It efficiently distributes and bears forces by converting vertical loads into axial pressures transmitted along the arch axis. From ancient stone arch bridges to modern steel-concrete composite structures, arch bridges have become an important type in bridge engineering due to their beautiful shapes and strong spanning capabilities. The arch seat is located at the arch foot of the arch bridge and is the key connection point between the main arch ring and the pier / abutment. Since an arch bridge is a structure that thrusts towards both ends, the arch seat is an important member for transmitting the huge horizontal thrust and vertical load generated by the arch ring to the foundation.

[0003] Arch bridges usually span mountains and large rivers. Therefore, during the construction of the arch seat, it is often in a wading state and a cofferdam needs to be built to block water. A cofferdam refers to a temporary impervious structure built around a foundation pit or construction area. By intercepting water flow and blocking soil from entering the construction area, it creates a dry and safe working environment, facilitating drainage, foundation pit excavation, and building construction. The construction of ordinary arch bridges can usually be completed using general concrete cofferdams or steel cofferdams. However, with the development of infrastructure and the laying of the national highway network, the locations where arch bridges need to be built are becoming more and more remote, and the construction environment is becoming more and more complex. For example, construction in a deep water area near a cliff; this poses a huge challenge to the construction of the arch seat of the arch bridge. Deep water means great water depth and large hydrostatic pressure, and the cliff makes the drop large, the water flow speed fast, the impact strong, and the construction environment near the cliff also causes the ground in front of the arch seat to be a steep slope and cliff, further compressing and narrowing the construction space, and basically there is no construction space.

[0004] In order to construct the arch seat in such a construction environment of deep water near a cliff, the present application innovatively thins the width of the cofferdam to squeeze space for construction operations. However, after the cofferdam is thinned, its anti-overturning ability becomes weaker and the cofferdam needs to be supported. In order to have construction operation space inside, the support structure can only adopt a frame structure that can carry out construction operations inside. A frame structure is usually a building skeleton formed by combining cross beams and columns layer by layer. The support strength of this structure requires the verticality of the columns. If the columns are not vertical, the interior of the formed frame is composed of several parallelogram structures. When a parallelogram structure is subjected to lateral pressure, it is prone to deformation; the overall support strength of its internal support is insufficient and cannot provide reliable support for the cofferdam. Therefore, a construction method for ensuring the verticality of the columns is needed. Summary of the Invention

[0005] The object of the present invention is to provide a construction method for positioning steel pipes of cofferdam columns in deep waters near cliffs, so as to solve the technical problem in the above-mentioned existing technology that when the cofferdam is thinned to create space for construction operations in the construction environment of deep waters near cliffs, the columns of the internal frame support structure cannot be guaranteed to be vertical.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows: A construction method for positioning steel pipes of cofferdam columns in deep waters near cliffs, characterized by comprising the following steps:

[0007] Step a: Set four sensors on the cofferdam as reference sensors, and adjust 3 of the reference sensors to be on the same horizontal plane as the reference plane;

[0008] Step b: Use a crane to hoist the column into place so that the column contacts the underlying bedrock, install a sensor at the upper end of the column as a positioning sensor, and adjust the positioning sensor to be on the reference plane;

[0009] Step c: Install a sensor at the lower end of the column along the vertical line of the column as an inclination sensor, determine the verticality of the column using the distances between the positioning sensor, the inclination sensor, and the four reference sensors, and after the verticality is achieved, use connecting members to fix the column to the cofferdam or other adjacent columns to ensure that the column remains vertical;

[0010] Step d: After all the columns in the cofferdam are vertically installed using Step c, use underwater concrete to fix the bottom of the column to the bedrock and form a flat foundation at the bottom of the foundation pit.

[0011] The beneficial effects of this implementation scheme are as follows:

[0012] 1. In the prior art, the construction of ensuring the verticality of columns generally uses equipment such as spirit levels, theodolites, total stations, etc. After keeping the columns vertical, leveling concrete is poured at the bottom of the columns to achieve the vertical installation of the columns. However, if it is underwater operation, using these equipment for leveling requires divers to repeatedly adjust the equipment, which is rather troublesome. And for each column to be pressure-adjusted, a pouring of leveling concrete is required, which is extremely cumbersome, with low construction efficiency. In this application, sensors are set on the cofferdam. A plane is formed by the reference sensors on the reference plane of the cofferdam, and a space coordinate system is formed in cooperation with the fourth sensor on the cofferdam. Positioning sensors and inclination sensors are respectively set at the upper and lower ends of the column. Three reference sensors are used to determine a plane, and a coordinate system is established in cooperation with the fourth sensor. The distance between the positioning sensor and the reference sensors can be directly measured to obtain the coordinates of the positioning sensor, and the coordinates of the positioning sensor are utilized. Through the plane equation Ax + By + Cz + D = 0, it is ensured that the positioning sensor is on the reference plane, and the position coordinates of the column hoisted into the cofferdam are made consistent with the designed position coordinates by using the plane coordinates. After the positioning sensor is on the reference plane, only by using the positioning sensor, the inclination sensor, and the three reference sensors on the reference plane, the distance a between the inclination sensor and the positioning sensor, the distances b1, b2, b3 between the positioning sensor and the three reference sensors, and the distances c1, c2, c3 between the inclination sensor and the reference sensors can be obtained; as long as a, b1, c1, a, b2, c2, and a, b3, c2 are all Pythagorean triples, then it can be ensured that the column is vertical.

[0013] 2. After the verticality of the columns is adjusted, instead of constructing the leveling concrete for each column separately, connecting members are used to simply fix them. When all the columns are adjusted, the bottom-sealing concrete is used for fixation at the same time. Compared with the prior art of pouring leveling concrete for each single column, this method is simpler in construction, has higher efficiency, and is more obvious in underwater construction.

[0014] 3. Since the columns in this application are applied to the cofferdam, the cofferdam needs to be bottom-sealed. Without pouring the leveling concrete for the columns, the bottom-sealing concrete is directly used to fix the columns, which makes the bottom-sealing concrete serve two purposes, both completing the bottom-sealing of the cofferdam and fixing the columns, with lower cost.

[0015] Further, in step a, a spirit level or the Beidou system can be used to ensure that three of the reference sensors are on the same horizontal plane as the reference plane. Since most of the arch bridge construction is in the deep mountains and is affected by the power grid and the environment, the models of the Beidou system are not stable. Using the spirit level and the Beidou for positioning and ranging at the same time can correct each other, with better effects.

[0016] Further, in step 1, the cofferdam is a steel-concrete composite cofferdam including a steel structure and a concrete structure.

[0017] Furthermore, the construction method of the steel-concrete composite cofferdam in the above steps includes the following steps:

[0018] Step 1, Cofferdam foundation pit construction: Use the survey control points and encrypted points to loft the position of the cofferdam construction, determine the foundation pit boundary of the cofferdam, and reserve a construction space of 1-2m to excavate the cofferdam foundation pit; Step 2, Formwork installation and embedding: Use the earth cofferdam as the outer formwork to install the mold for pouring the concrete cofferdam, and embed the embedded parts of the steel cofferdam in the mold; Step 3, Pour the concrete cofferdam: Pour the concrete cofferdam in the mold installed in Step 2; Step 4, Setting of the steel cofferdam: Weld the steel cofferdam to the embedded parts in Step 2, and set up a cofferdam support behind the steel cofferdam to complete the construction of the cofferdam.

[0019] Furthermore, the built cofferdam in Step 4 also needs to be provided with an internal support of a frame structure.

[0020] Furthermore, the internal support is formed by laying the cross beams and columns layer by layer to form a frame structure.

[0021] Furthermore, the internal support can be used as a construction passage for the subsequent construction of the arch seat. Brief Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of the arch seat construction of the present invention.

[0023] Figure 2 It is a schematic structural diagram of the front wall of the cofferdam of the present invention.

[0024] Figure 3 It is a schematic diagram of the slipform pouring of the present invention.

[0025] Figure 4 It is a schematic structural diagram of the connection structure between the cross beam and the cofferdam of the present invention.

[0026] Figure 5 It is a schematic structural diagram of the connection structure between the column and the bedrock of the present invention. Detailed Description of the Invention

[0027] The following is a more detailed description through specific embodiments:

[0028] The reference numerals in the drawings of the specification include: arch seat 1, cofferdam 2, front wall 21, side wall 22, back wall 23, internal support 3, column 31, connecting member 32, angle iron 33, bedrock 4, and bottom-sealing concrete 5.

[0029] Example 1

[0030] The construction method for positioning the steel pipe of the cofferdam column in the deep water area near the cliff is as follows:

[0031] A construction method for the arch seat of a cantilever cast-in-place arch bridge in a deep water area near a cliff includes the following steps:

[0032] Step S1, building a cofferdam: Build a cofferdam extending outward from the designed construction position of the arch seat. The cofferdam is a steel-concrete structure with a steel cofferdam for the front wall;

[0033] This application is mainly applied to the construction of the arch seat of an arch bridge in a deep water area near a cliff beside a river or a lake. As Figure 1 shown, due to the limitation of the deep water near the cliff, not far from the front side of the arch seat 1 is a cliff, and the constructible 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, without enough space for construction operations and without enough width space to build the cofferdam. Moreover, there is a high water level period in the reservoir. Since all construction cannot be completed in a low water level period, the height of the cofferdam is forced to be raised above the water level line in the high water level period. However, when the arch ring needs to be constructed on the arch seat later, the 1# segment of the arch ring will collide with the front wall of the cofferdam. Therefore, direct construction is impossible, and the front wall needs to be demolished to construct the 1# segment of the arch ring. Therefore, this application develops a construction method for the cofferdam of the arch seat in a deep water area near a cliff, and the specific construction steps are introduced in detail:

[0034] The cofferdam 2 of this application is designed as a steel-concrete composite cofferdam, and its structure is as Figure 1 shown. The main part of the cofferdam 2 is composed of a front wall 21 (near the water flow side), side walls 22, and a back wall 23. The main structures of the side walls 22 and the back wall 23 are concrete structures, and the front wall 21 is arranged in front of the arch seat. The front wall of the cofferdam in this application adopts a composite structure of a concrete foundation combined with a steel cofferdam. As Figure 2 shown, it includes a front wall I and a front wall II. Among them, the front wall I is a concrete cofferdam, and the front wall II is a steel cofferdam. When constructing the 1# segment of the arch ring, the steel-structured front wall II can be directly cut and demolished quickly, so it does not affect the construction of the 1# segment of the arch ring. The construction method is as follows:

[0035] Step 1, cofferdam foundation pit construction: Use survey control points and densified points to set out the construction position of the cofferdam in a low water level period before the target low water level period, determine the foundation pit boundary of the cofferdam, and reserve a construction space of 1 - 2 m to excavate the cofferdam foundation pit;

[0036] Use survey control points and densified points to set out the designed foundation position of the cofferdam in a low water level period before the target low water level period. The setting out is carried out using a total station to ensure that the construction area of the cofferdam foundation pit is consistent with the design. When constructing the cofferdam in the low water level period, the water level is relatively low during construction, which is convenient for use. The anti-overturning ability of the steel-built cofferdam is relatively weak, and the water pressure in the low water level period is relatively small, avoiding damage to the cofferdam during the construction period.

[0037] When starting construction, the construction method of excavation needs to be adjusted according to the water level line, which is divided into two parts. First, when the elevation of the excavation site is higher than the water level line, the construction no longer considers the water level changes in the morning and evening of a day. It is the same as land construction, and conventional methods such as excavators and blasting are directly used for excavation. Second, when the elevation of the excavation site is lower than the water level line, the construction is carried out by setting up an earth cofferdam. Use an excavator to excavate the foundation pit until the bedrock surface is reached. Blasting construction is not carried out, and the loose rock in the foundation pit is promptly cleaned up to ensure that the base has no mud, stone slag and various construction wastes. If the foundation pit has been placed for a long time after excavation due to other external factors and there is sediment at the bottom, a large-power mud suction device needs to be used to clean it up to ensure that the base is a large-area bedrock surface. The construction of the cofferdam foundation pit needs to construct the base inside the cofferdam together.

[0038] When the elevation of the excavation site is lower than the water level line, set up an earth cofferdam according to the water level change. The earth cofferdam mainly uses soil bags, and the size of the filled soil bags is about 60x15cm. When the water depth in the foundation pit is less than 2m, set up a double-row soil bag cofferdam (about 1.2m wide). When the water depth in the foundation pit is between 2 - 4m, set up a four-row soil bag cofferdam (about 2.4m wide). Since the earth cofferdam leaks water severely, try to choose red clay when selecting soil, and use special waterproof materials such as leak repair agents to seal the gaps between the soil bags to reduce the water leakage. The foundation pit is constructed by excavating layer by layer downward.

[0039] After the excavation of the foundation pit is completed, quality inspection of the plane position, size and base elevation of the base needs to be carried out to ensure that the plane position should meet the design requirements and should meet the needs of foundation construction operations. The allowable deviation of the base elevation is based on the geological conditions of the base. All reach the bedrock surface, and it is only necessary to ensure that the geological conditions and bearing capacity of the base are consistent with the design.

[0040] Step 2: Formwork installation and embedding: Use the earth cofferdam as the outer formwork to install the mold for pouring the concrete cofferdam, and embed the embedded parts of the steel cofferdam in the mold;

[0041] 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 template uses a large-area steel template and is constructed according to the ordinary concrete construction method. 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 template on the outer edge of the water for construction. The steel-concrete composite cofferdam of the present application only installs the back wall, side wall and front wall in the template, and the front wall I. After the installation is completed, the embedded parts of the steel cofferdam need to be embedded at the end surface where the front wall II and the front wall I are connected, ensuring that part of the embedded parts are poured into the front wall I, and part of them leak 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 template, and the embedded parts of the steel cofferdam are completely consistent with the material and thickness of the front wall II steel cofferdam.

[0042] Step 3, pouring concrete cofferdam: pouring concrete cofferdam in the mold installed in step 2;

[0043] 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 3 As shown, first use the 2m formwork to pour the three-layer standard section cofferdam concrete. When the three-layer standard section cofferdam concrete is poured, and the concrete strength and curing period meet 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 not removed, as the basic formwork for the second pouring of the cofferdam wall formwork. The removed formwork is used to continue pouring the cofferdam wall upwards. It must be removed individually 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 to the location 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 in this application is poured. During the whole process, the water in the cofferdam is not pumped out, and only the water in the cofferdam wall pouring formwork is pumped out to pour concrete.

[0044] Step 4, setting of steel cofferdam: welding the steel cofferdam to the embedded parts in step 2, and setting cofferdam supports behind the steel cofferdam to complete the construction of the cofferdam;

[0045] After pouring is completed, weld the steel plates of the steel cofferdam to the exposed ends of the embedded parts in the front wall I. The weld strength shall meet the requirements of compressive resistance and impermeability in the construction environment. After welding, channel steels shall be equidistantly arranged on the rear 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 compressive capacity. To ensure that there is no water seepage accident at the welding position of the embedded part and the steel plate, when arranging the channel steel as the rear support of the steel plate, it is necessary to ensure that there is a channel steel covering the weld at the weld position. After covering, the contact edge between the channel steel and the steel plate is also sealed by full welding to ensure that the weld quality can withstand sufficient water pressure, and other channel steels and the steel plate are also fixed by welding. After all the construction of the channel steel and the steel plate is completed, the front wall II is formed.

[0046] In this embodiment, to ensure the stability of the cofferdam, the structural form of the front wall II steel cofferdam is composed of 20 mm steel plates + 20a channel steels. The channel steels are equidistantly arranged, and the equidistant arrangement spacing of the channel steels is 1 m.

[0047] Step S2: Set the internal support: Synchronously carry out the internal support construction and pump out the water inside the cofferdam within the constructed cofferdam. When the internal support construction is completed, just pump out the river water inside the cofferdam;

[0048] Due to the characteristics of this application being adjacent to a cliff and in deep water, the original ground at the front edge of the arch seat is a steep slope and a cliff, resulting in insufficient width of the cofferdam foundation. Furthermore, the anti-overturning ability of the cofferdam wall itself is insufficient. Under the static pressure of high water level, there is a risk of crushing the cofferdam. Therefore, it is necessary to add internal supports inside the cofferdam to support the cofferdam. The internal support adopts a frame structure, which includes several cross beams and columns. The columns adopt a steel pipe structure, and the cross beams adopt an I-beam steel structure. An integral frame is formed inside the cofferdam by using the I-beam steel and the columns to support the cofferdam. The inside of the cofferdam is fully paved, so that the static pressure received by the front wall can be transmitted to the back wall through the frame, and the static pressure of the upper side wall and the static pressure of the lower side wall cancel each other out through the frame, making it impossible for the front wall and the side walls to be crushed by the static pressure of deep water.

[0049] The construction method of the internal support inside the cofferdam is specifically as follows:

[0050] N1: Column construction: Hoist the columns in place at the designed positions inside the cofferdam. After all are in place, fix the columns to the base with anti-dispersive concrete underwater;

[0051] Since the bottom of the foundation pit is not sealed with concrete during the construction of the steel-concrete composite cofferdam of the present application, the bottom of the foundation pit is an uneven bedrock surface at this time. When the column is directly hoisted into the foundation pit and installed on the bedrock, it is impossible to make it vertical. If the column is not vertical, the interior of the formed framework is composed of several parallelogram structures. When the parallelogram structure is subjected to lateral pressure, it is prone to deformation. As a result, the overall support strength of the internal support is insufficient and cannot provide reliable support for the cofferdam. In order to ensure that the formed internal support can provide reliable support strength, the column needs to be vertical. The present application uses the construction method for positioning the steel pipe of the cofferdam column to ensure the vertical installation of the column. The specific construction method is as follows:

[0052] Step a: Set four sensors on the cofferdam as reference sensors, and use the Beidou system to adjust 3 of the reference sensors to be on the same horizontal plane as the reference plane;

[0053] After the cofferdam is built, draw a circle with the center of the cofferdam as the center. At the points where the arc intersects the cofferdam, select any three points to set sensors as reference sensors. When installing the reference sensors, a level can be used to make these three sensors on the same plane. The level can be a laser level. The reference sensors need to be able to measure the distance between each other independently and can also be connected to the Beidou system to directly use the Beidou system to adjust the three sensors to be on the same plane. Therefore, the reference sensors need to achieve two functions. One is to measure the distance between each other, and the other is to be able to communicate with the Beidou system. It can choose a combined solution: Beidou positioning module + distance measurement sensor, such as the combination of SinoGNSS T300 Beidou module + SICK DL100 laser distance measurement sensor, or directly choose an integrated device (directly built-in distance measurement and Beidou positioning), such as Huace Navigation i70 Pro. Using a level and the Beidou system, 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, set the fourth reference sensor directly above any one of the sensors. Use this fourth reference sensor to cooperate with the reference plane to establish a coordinate system inside the cofferdam.

[0054] Step b: Use a crane to hoist the column into place so that the column contacts the underlying bedrock, and install a sensor on the upper end of the column as a positioning sensor, and adjust the positioning sensor to be on the reference plane;

[0055] The column is installed underwater. Before hoisting the column, it is necessary to use dredging equipment to clean the sediment in the foundation pit, so that the bedrock surface is exposed. When the column is hoisted into the foundation pit, the bottom of the column can contact the bedrock surface at the bottom of the foundation pit. After hoisting the column in place, install a sensor at the upper end of the column as a positioning sensor. The selection of the positioning sensor needs to be consistent with the reference sensor. Therefore, the distance between the positioning sensor and the reference sensor can be directly measured with each other, or it can be completed through the Beidou system. Use three reference sensors on the reference plane to determine a plane, and jointly establish a coordinate system with the fourth reference sensor. The distance between the positioning sensor and the reference sensor can be directly measured with each other to obtain the coordinates of the positioning sensor. Use the coordinates of the positioning sensor. The equation of the plane is Ax + By + Cz + D = 0, ensuring that the positioning sensor is on the reference plane, and the position coordinates from the hoisting position to the position within the cofferdam are consistent with the designed position coordinates. Of course, the Beidou system can also be used to directly determine that the positioning sensor is on the reference plane and is accurately positioned.

[0056] Step c: Install a sensor at the lower end of the column along the vertical line of the column as an inclination sensor. Use the distances between the positioning sensor, the inclination sensor, and three reference sensors on the reference plane to determine the verticality of the column. After it is vertical, use connecting rods to fix the column to the cofferdam or other adjacent columns to ensure that the column remains vertical.

[0057] When installing the inclination sensor, it is necessary to ensure that the line connecting the inclination sensor and the positioning sensor is a vertical line perpendicular to the central axis of the column. During actual construction, before hoisting the column, draw a straight line perpendicular to the central axis of the column on the column, and directly install the positioning sensor and the inclination sensor at both ends of the straight line. When the lower end of the column contacts the bedrock, due to the unevenness of the bedrock surface, the column may be completely submerged underwater. Angle irons can be welded along the straight line perpendicular to the central axis of the column, and the positioning sensor can be installed on the angle irons.

[0058] The model of the inclination sensor is the same as that of the reference sensor. Therefore, the distances between the inclination sensor, the reference sensor, and the positioning sensor can all be measured, or they can be connected to the Beidou system to determine the position.

[0059] Using a positioning sensor, an inclination sensor, and three reference sensors on a reference plane, the distance a between the inclination 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 inclination sensor and the reference sensors can be obtained. As long as a, b1, c1; a, b2, c2; and a, b3, c2 are all Pythagorean triples, the upright post can be ensured to be vertical. The Beidou system positioning can also be used to connect with each sensor for distance measurement to determine the values of a, b, and c, ensuring the upright post is vertical. After ensuring the upright post is vertical, connecting members are used to fix the upright post to the cofferdam. The installation sequence of the upright posts is as follows: First, install the circle of upright posts close to the cofferdam. After the installation of the circle of upright posts close to the cofferdam is completed, install them in a circular manner and push towards the center of the cofferdam. The outermost upright posts are fixed to the cofferdam, and the inner upright posts are fixed to the adjacent upright posts until the installation is completed.

[0060] Step d: After all the upright posts in the cofferdam are vertically installed using Step c, use underwater sealed concrete to fix the bottom of the upright posts to the bedrock and form a flat foundation at the bottom of the foundation pit.

[0061] Before the underwater sealed concrete construction, it is necessary to determine again that the upright posts are vertical. The underwater sealed concrete uses C40 underwater anti-dispersion concrete for underwater construction. Before construction, clean the bottom sediment and mud again to ensure that the thickness of the sediment at the bottom of the arch seat is not greater than 1 cm before pouring the concrete. The concrete pouring should 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 move in the water. When the conduit is lowered, it must first be inserted into the bottom of the foundation pit and then lifted 30 - 50 cm as the concrete construction space. Divers roughly control the elevation of the concrete to ensure that the pouring elevation of the concrete is basically the same. After pouring, the upright posts and the bedrock form a fixed structure, and its stability is enhanced, meeting the requirements for the installation of internal supports.

[0062] During the positioning construction of the entire upright post, the coordinates provided mainly by the distance measurement between the sensors, and the data transmitted by the Beidou system are used as an early warning aid.

[0063] N2. Crossbeam support construction: After the upright posts are fixed, lay crossbeams between the upright posts to form a frame structure. Both ends of the crossbeams are fixedly connected to the adjacent upright posts. The laying sequence is from top to bottom. For each layer of crossbeams laid, pump out a layer of accumulated water in the cofferdam, and repeat alternately until the water is finally pumped to the bottom of the foundation pit to complete the construction of all crossbeams. The outermost crossbeams are directly fixed to the cofferdam.

[0064] After the columns are fixed by the concrete with a sealed bottom, I-beams are used as crossbeams between the columns to form an integral frame structure. The construction follows the sequence of from top to bottom, from the middle to both sides, first longitudinally and then transversely. Since there is water in the foundation pit, the construction method of pumping water while setting the I-beams can be adopted. For the first pumping, install the first layer of I-beams. After the installation of the first layer of I-beams is completed, pump water again and install the second layer of I-beams. Repeat this process until the water is finally pumped to the bottom of the foundation pit and all the I-beams are constructed. When all the crossbeams are completely laid, the internal support will completely cover the space of the cofferdam.

[0065] Step S3: Pour the arch seat: After the internal support is set up, complete the pouring of the arch seat before the target low water level period.

[0066] Since all the construction of the 1# segment needs to be completed within the window time of the target low water level period, during the high water level period, the pouring construction of the arch seat should be completed, and at the latest, it should be completed before the high water level drops to the low water level period. Pouring construction of the arch seat: Determine the construction position of the arch seat within the cofferdam of the internal support structure in S2, and use the frame structure of the internal support as the construction passage to pour the arch seat. For the overlapping part between the arch seat and the internal support, directly pour the internal support into the arch seat;

[0067] According to the designed position of the arch seat, determine the construction position of the arch seat for pouring construction. The pouring construction of the arch seat includes steps such as steel bar construction, laying of cooling pipes, formwork installation, concrete pouring, formwork removal and concrete curing. Since 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 crossbeams of the internal support to form construction platforms layer by layer, and construction can be carried out through the construction platforms.

[0068] Steel bar construction and laying of cooling pipes: Set the arch seat steel bars in the arch seat foundation pit after the bottom is sealed, and install the cooling pipes. When the cooling pipes conflict with the arch seat steel bars, move the positions of the cooling pipes to ensure the shape of the arch seat steel bars;

[0069] The arch seat steel bars are tied into shape at one time. During the process of steel bar tying, the stiffening skeleton must be installed first, and some temporary supports should be added as needed to ensure that the steel bar tying can be smooth and straight without deformation. The steel bar tying is carried out in blocks from one end to the other to ensure that personnel can construct during the three-way tying of the steel bars. During the process of steel bar tying, some positioning steel bars must be spot-welded firmly to avoid large deformation of the lower steel bars when constructing the upper steel bars. For the embedded steel bars of the boundary piers and arch rings, positioning frames should be used to ensure the accurate position of the embedded steel bars;

[0070] To reduce the hydration heat generated during the construction of the arch seat concrete and prevent temperature difference cracks in the concrete, circulating cooling water pipes are installed in the arch seat. The circulating cooling pipes are made of ordinary welded steel pipes with good heat conduction performance and certain strength. The steel pipes themselves have relatively high strength and stiffness. During installation, they are welded to the arch seat steel bars (including the stiffening skeleton). When necessary, erection steel bars are used to assist in ensuring the forming effect of the cooling pipes, but the arch seat steel bars shall not be moved. When there is a conflict, the position of the cooling pipes shall be moved to ensure the shape of the arch seat steel bars. The arch seat cooling pipes are arranged in layers at intervals of 0.8 m, and the distance between the cooling pipes in the same layer is 60 cm. The directions of the cooling pipes in adjacent layers are perpendicular to each other.

[0071] Formwork installation: Use lifting equipment to hoist the arch seat casting formwork to the arch seat installation position, place it between the crossbeams, fix the formwork to the columns, and use the internal support as the fixing structure of the formwork to facilitate the installation of the formwork. The formwork needs to be customized to perfectly fit the space of the internal support frame.

[0072] Concrete pouring: Use a concrete pump to pour the arch seat concrete. The strength of the poured concrete shall meet the requirements of C40 mass concrete. The designed slump of the concrete mix is between 16 cm and 20 cm, the initial setting time of the concrete is 5 - 6 hours, and the final setting time is 13 - 14 hours.

[0073] Formwork removal and concrete curing: After the concrete in S5 is poured, when the concrete strength reaches 4 - 5 Mpa, the formwork can be removed using a crane, and after the formwork is removed, the concrete surface is sprinkled with water for curing.

[0074] During the whole process, the temperature control standard for mass concrete shall be followed. The cooling pipes are used to ensure that the hydration heat is released well, and the poured arch seat meets the design standards.

[0075] Step S4, construction of the 1# segment arch joint: Demolish the steel structure during the target low water level period and complete the construction of the 1# segment.

[0076] 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 during the high water level period gradually drops, the steel structure exposed above the water level line of the front wall of the cofferdam can be quickly cut using a cutting machine. When the water level line reaches the low water level period, the demolition of the front wall of the cofferdam is just completed, creating the construction space for the 1# segment. It is also possible to use a cutting machine to quickly cut the front wall of the cofferdam after reaching the low water level period. The construction of the 1# segment is the same as the existing technology, and it is quickly poured by building a formwork. It should be noted that the construction of the 1# segment needs to be completed before the arrival of the high water level period to avoid water rising and flowing back into the cofferdam, resulting in the underwater construction of the 1# segment and thus interrupting the construction.

[0077] The above are only embodiments of the present invention, and common knowledge such as specific structures and characteristics known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application shall be subject to the content of its claims, and the specific implementation manners and the like recorded in the specification can be used to interpret the content of the claims.

Claims

1. The method for positioning steel pipes for cofferdam columns in deep water areas near cliffs is characterized by: The following steps are involved: Step a: four sensors are set on the cofferdam as reference sensors, and three of the reference sensors are adjusted to be on 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, installing a sensor as an inclination sensor at the lower end of the column along the vertical line of the column, and using 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 the column is vertical, the column is fixed to the cofferdam or other adjacent columns using a connecting rod to ensure that the column remains vertical; Step d: After all the columns in the cofferdam are vertically installed in step c, the bottom of the columns is fixed to the bedrock using bottom sealing concrete to form a flat foundation pit bottom foundation.

2. The method for positioning steel pipes for cofferdam columns in deep water areas near cliffs according to claim 1 is characterized by: In step a, a level meter or a BeiDou system can be used to ensure that the three reference sensors are on the same horizontal plane as the reference plane.

3. The method for positioning steel pipes for cofferdam columns in deep water areas near cliffs according to claim 2 is characterized in that: The cofferdam in step 1 is a steel-concrete composite cofferdam including a steel structure and a concrete structure.

4. The method for positioning steel pipes for cofferdam columns in deep water areas near cliffs according to claim 3 is characterized by: The construction method of the steel concrete composite cofferdam in the steps comprises the following steps: Step 1: Construction of cofferdam foundation pit: Use the measurement control points and encryption points to stake out the location of the cofferdam construction, determine the boundary of the cofferdam foundation pit, and reserve 1-2m of construction space to excavate 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, pouring concrete cofferdam: pouring concrete cofferdam in the mold installed in step 2; Step 4, setting of steel cofferdam: weld the steel cofferdam to the embedded parts in step 2, and set cofferdam supports behind the steel cofferdam to complete the construction of the cofferdam.

5. The method for positioning steel pipes for cofferdam columns in deep water areas near cliffs according to claim 4 is characterized by: The cofferdam constructed in step 4 also needs to be provided with internal supports of the frame structure.

6. The method for positioning steel pipes for cofferdam columns in deep water areas near cliffs according to claim 5 is characterized by: The inner support is a frame structure formed by laying beams and columns layer by layer.

7. The method for positioning steel pipes for cofferdam columns in deep water areas near cliffs according to claim 6 is characterized by: The inner support can be used as a construction channel for subsequent arch seat construction.

Images