It plays the role of waterproof and soil retaining in the process of foundation construction, does not participate in the stress of the main structure, and there is no partition wall inside the cofferdam.
Especially the flat rock riverbed with thin overburden (O.5 ~ 2m).
7.1 double wall steel cofferdam double wall steel cofferdam is a cylindrical double wall watertight steel structure with inclined plane and double edge feet.
When the cofferdam needs to sink to the rock surface, it can be made into equal height or unequal height cutting feet with the same inclination as the rock surface according to the rock surface and weathered layer.
The inner and outer walls of the cofferdam shall be welded with full joints without scars, missing welding and sand holes.
In the inner cavity of the weir wall, it is symmetrically divided into several sealed compartments by compartment plates to facilitate unbalanced irrigation to control its inclination during sinking.
During construction, the assembled bottom section cofferdam shall be floated to the pier, lifted into the water, then raised and filled with water to sink in the cofferdam.
10.2 cofferdam fabrication and processing the fabrication of double wall steel cofferdam should be made into blocks in the factory according to the method of exchanging parts or seating according to the number.
8.2 formulate the cofferdam assembly and hoisting scheme.
During the whole sinking process of the cofferdam, there is no need for steel air cylinder, air supply system, inflatable machinery, etc.
If necessary, conduct a hydrostatic test, and eliminate the welding seam leakage and re weld.
Double wall steel cofferdam has larger stiffness and larger working space, so it is more convenient for construction and can adapt to greater water depth.
Before leaving the factory, check and recheck the structural size of the block according to the construction drawing, and check the welding quality of the block with appropriate methods.
In case of infringement, please contact delete 1.0.
When manufacturing the double wall steel cofferdam, the facade is divided into several layers and the plane is divided into several blocks.
The double wall steel cofferdam has the characteristics of light weight and high buoyancy.
The top surface of the cofferdam can be used as the construction platform of the bearing platform.
Its size can be determined according to the manufacturing equipment, transportation conditions and installation and lifting capacity.
8.0 construction preparation 8.1 determination of cofferdam size and height according to river hydrogeology and engineering needs.
When conditions permit, blocks should be large to reduce site welding, improve quality and speed up progress.
Double wall steel cofferdams are often circular, and some are made into special shapes to adapt to the shape of the foundation.
Waterproof rubber strips must be installed between sections and blocks.
For general large and medium-sized cofferdams, if the water flow conditions at the pier position allow, they can be assembled at the pier position and on the assembly ship; The height of each section is generally no more than 5m and the total weight is no more than 10ot.
(3) when the double wall steel cofferdam falls to the bedrock surface or the stratum that is not scoured to build the bored pile foundation with low bearing platform, the cofferdam floating, positioning, heightening, sinking in water, sinking in soil and foundation clearing shall not only comply with the relevant provisions of relevant construction technical standards, but also ensure that the main structure of the bridge inside the cofferdam meets the requirements of the design drawings, The top surface of the steel cofferdam meets the needs of the construction platform.
After assembly, the cofferdam size, height, inclination angle and welding quality shall be inspected and accepted.
After the cofferdam falls into the riverbed, concrete (or water) shall be poured into the cofferdam as necessary to increase the weight of the cofferdam and suck mud in the cofferdam to make it sink gradually and evenly to the design elevation.
The welding between angle steel frames shall be fully welded, and the lifting ring shall be welded on the outer wall plate of the frame block.
Vertical welding or overhead welding shall be avoided as far as possible to ensure the welding quality.
When the underlying layer is dense boulder or rock stratum, steel sheet pile cofferdam cannot be used, and due to engineering requirements, support should not be set during blasting operation in the pit.
(2) the double wall steel cofferdam should be manufactured in the factory in sections and blocks, and the size of the blocks can be determined according to the manufacturing equipment, transportation conditions, site installation, lifting and moving capacity.
The bottom end of the weir wall is provided with a blade foot to facilitate soil cutting and sinking.
According to the construction conditions, the full height of the cofferdam can be manufactured in sections, and each section can be symmetrically divided into units to make a unit body.
The size, strength, stiffness, structural stability and anchorage method of the cofferdam shall meet the construction drawings and construction requirements.
5.0 operation contents: the construction of double wall steel cofferdam bridge foundation includes the assembly of double wall steel cofferdam on the shore or assembly ship, floating in place, lifting and sinking, steel wall heightening and pouring water or concrete in the shell, bed sinking to the bedrock surface, foundation cleaning and bottom sealing, foundation concrete pouring, cofferdam removal, etc.
The cofferdam blocks shall be manufactured in the form of lying flat on the jig frame in the factory or site workshop, and turn over after assembly.
6 watertight test does not allow water seepage and water inspection: 7.0 construction machinery and process equipment in each section.
Fixing Socket Cross Hole Nail Plate
All welds for manufacturing, assembling and heightening of double wall steel cofferdam shall have high quality requirements.
When the single wall steel boxed cofferdam does not have sufficient stiffness, it shows the advantages of double wall steel cofferdam.
For the super large double wall steel cofferdam, the section height must be reasonably determined, and the sinking height must be spliced in sections and blocks.
It has good stiffness and watertight performance, so it has been applied in deep-water construction.
The steel shell of the weir wall is composed of inner and outer wall plates with stiffeners and multi-layer horizontal trusses.
4.0 process overview steel cofferdam is not only a temporary structure for water and soil retaining, but also a platform for underwater construction.
Ultrasonic: spot check 50% of horizontal and vertical welds respectively.
The plane of double wall steel cofferdam is a circular steel ring structure with good stiffness and convenient construction.
In addition, bored cast-in-place piles can also be constructed in the double wall steel cofferdam.
The cofferdam height shall be determined according to the sinking depth, the highest water surface elevation and wave height that may occur during construction.
9.0 process and quality control process the construction process and quality control process of double wall steel cofferdam are shown in Figure 9-1 below.
It is applicable to the deep-water foundation of large rivers of highway bridges, which can bear large water pressure and ensure the safe flood crossing of foundation construction throughout the year.
The double wall steel cofferdam can be welded or partially bolted by channel steel, angle steel and flat steel to form a rectangular or circular Double-layer framework, and the blade foot is set at the bottom; The inner and outer wall basic plates and bulkhead plates are made of angle steel, flat steel and steel plate, and then assembled into a double wall steel cofferdam that can meet the requirements of water depth and stress.
It is a rigid and reliable waterproof structure.
After determining the block size and section height, in order to ensure the block manufacturing accuracy and improve the efficiency, high-precision setting molds, especially arc formwork, should be made in advance..
6.0 quality standards and inspection methods the quality inspection standards and methods for the fabrication and assembly of double wall steel cofferdam are shown in the table below: quality inspection and quality standard item inspection of double wall steel cofferdam check term Inspection method and frequency of the specified value or allowable deviation of the project 1.
In addition to meeting the requirements of the construction drawing, all welds must also undergo water tightness test to ensure no water leakage.
7.2 main construction machinery and equipment include tugboat, floating crane, flat head barge, lifeboat, mast crane, electric air compressor, diesel generator, high-pressure water pump, concrete mixer, electric winch, AC and DC welding machine, decompression chamber, plate bending machine, plate shearer, mud suction machine, total station, current meter, depth sounder, universal rod, etc.
After the steel cofferdam is floated in place and lifted into the water, it can float on the water surface at the pier position stably and vertically like the ship hull.
The center deviation of the top surface (mm) 20 along the bridge direction, the plane size of the total station or theodolite 202 cofferdam in the transverse bridge direction (mm) diameter / 500 and 30, and the diameter difference perpendicular to each other < 20 feet: 4 places and 3 heights shall be inspected in each section Degree (mm) ± 10 feet measurement: check 2 places in each section, 4 staggered platforms between sections (mm) 2 feet measurement: check 4 places in each section, 5 weld quality meets the design requirements.
The purpose of preparation is to clarify the process flow, operation points and corresponding process standards of double wall steel cofferdam construction, and guide and standardize the construction of double wall steel cofferdam.
Figure 9-1 Construction process and quality control process of double wall steel cofferdam 10.0 description of process steps 10.1 construction of double wall steel cofferdam ⑴ double wall steel cofferdam shall be specially designed.
The weld length between steel plate and angle steel horizontal bar should be greater than 100mm, and the spacing should be ≤ 80mm.
2.0 it is prepared according to 3.0 of technical code for construction of highway bridges and culverts and standard for quality inspection and evaluation of highway engineering.
