Structural characteristics of high-piled wharf
High-piled wharf is widely used in port engineering in China, which is mainly composed of pile foundation, superstructure and shore-connected structure. ① The general forms of pile foundation include large pipe pile, steel pipe pile, PHC pile, prestressed concrete square pile, non-prestressed concrete square pile, rock-socketed pile and cast-in-place pile. In hydraulic structures, the mixed arrangement structure of fork piles and straight piles often appears. Diesel piling hammer is mainly used in pile foundation construction, but hydraulic hammer piling is used in some projects. In some projects, the pile foundation treatment is to embed rocks in the pile after sinking, or to carry out anchor construction in the pile; (2) the superstructure is generally divided into plate structure, beam-slab structure or pier structure. According to the different prestress conditions, it can be divided into prestressed structure and non-prestressed structure; According to the different installation and pouring techniques, it can be divided into prefabricated installation structure, laminated structure and cast-in-place structure; According to different materials, it can be divided into ordinary concrete structure and high performance concrete structure; ⑧ Slope is the most common form of shore connection structure, which is mainly suitable for the soft foundation of high-piled wharf, and can avoid problems such as pile foundation damage and wharf displacement caused by large slope. In addition, sheet piles can also be used to unload platforms and gravity structures. Under normal circumstances, the foundation will be excavated and replaced, or the sand-throwing cushion will be adopted, and the drainage plate will be used to strengthen the stress of soft soil and improve the unfavorable conditions of the foundation; On the slope, artificial face protection blocks or stones should be used to protect the face, and small vertical retaining structures should be used on the upper part to realize the transition with the wharf. According to the actual application of high-piled wharf at present, the settlement between wharf and shore should be fully considered in the design process, and rubber bearings should be set under the simply supported slab.
High-piled wharf generally adopts permeable structure, which is light in structure and suitable for soft foundation. The displacement and settlement of high-piled wharf are relatively small, which has the advantages of low cost and good use effect. Especially in container terminals with high requirements for use, or oil and gas chemical terminals with small operating area and small vertical load, or terminals in open areas in the open sea. Under the guarantee of various conditions, through the application of high-piled wharf, the economic and reasonable engineering goal can be realized.
In addition, the structure of high-piled wharf is relatively weak, sensitive to external load and poor in durability. In addition, the wharf structure is complex, and there are many construction procedures, which have certain restrictions on construction conditions and equipment, and the construction period is long. Therefore, it is necessary to carry out quality control and post-maintenance on the durability of high-piled wharf. In view of the problems such as stability and settlement of wharf backfill that often appear in construction and use, if it is not handled properly, it may also cause displacement or damage of piled wharf, which are all problems that should be paid attention to in the application of high-piled wharf.
Analysis of common problems in reconstruction project of high-piled wharf
Crack problem
In mass concrete, the surface temperature or temperature difference is also relatively large. In such a place, concrete is prone to cracks. Because the volume of ordinary concrete is relatively large, a lot of heat after hydration is concentrated in concrete, which is not volatile, which will lead to a sharp rise in the internal temperature of concrete and a faster heat dissipation on the surface of concrete. The large temperature difference between the inside and outside will also cause the inside and outside to expand when heated and contract when cooled, which will cause a certain tensile stress on the concrete surface. When the tensile stress inside concrete is greater than the tensile strength of concrete, cracks will occur on the surface of concrete.
Temperature cracks are generally irregular and have different sizes, which are affected by temperature.
Main preventive measures: ordinary portland cement below 450kg/m3 should be selected as far as possible, coarse aggregate should be crushed stone or pebble, fine aggregate should be medium sand, and high-quality Class I fly ash and wood calcium water reducer with small fineness, light color, low carbon content and stable quality should be selected to reduce the hydration heat at early stage and enhance the strength at later stage. Adding retarder during mixing can slow down the setting time of concrete and reduce the concentrated generation of hydration heat. Adding a small amount of steel bars or fiber materials to concrete will control the temperature cracks of concrete within a certain range. The damage degree of reinforced concrete cracks to high-piled wharf is uncertain. If the situation is serious, it may affect the normal use and safety of the wharf. Various problems will affect or destroy the wharf structure along the wharf front structure, reduce the bearing capacity of high-piled wharf, and may cause various inclinations, settlements, rotations or displacements.
Corrosion of reinforcement and carbonation of concrete
Steel corrosion and concrete carbonization often occur in reinforced concrete high-piled wharf, which is more serious. With the corrosion of steel bars, concrete may peel off and crack, which leads to the loss of adhesive force between steel bars and concrete, the reduction of cross-sectional area of steel bars and the reduction of bearing capacity, thus affecting the structural safety of high-piled wharf and leaving hidden dangers of safety accidents. According to relevant investigation data, if the carbonation depth is close to or has exceeded the thickness of the concrete protective layer, it proves that most of the steel bars in the concrete structure have been corroded. If there are many cracks in concrete, it shows that the corrosion of steel bars is serious and needs to be paid attention to.
Key points of optimization measures for high-piled wharf
Construction control of bored pile
In the process of cast-in-place pile construction, firstly, the control of pile casing sinking is strengthened, and the control of pile position is strengthened by using the right angle intersection in front to meet the requirements of the code. In the process of sinking, vertical ball is used to detect the verticality change of casing and adjust the deviation in time. In the process of drilling cast-in-place pile, the center line of drilling rig and casing should be on the same straight line. After drilling, the thickness of sediment and the specific gravity of mud should be detected, and the steel skeleton should be installed after the detection is qualified. Generally, the conduit method is used to complete the concrete pouring of cast-in-place piles, accurately measure the first tank of concrete, ensure continuous pouring and avoid pile breakage.
Bank slope stability control
During the construction period, it is very important to control the stability of the bank slope. In addition to strictly controlling the layered and segmented dredging, the control of the excavation process is also very important. Reasonable piling construction arrangement can effectively reduce the influence of piling vibration on the bank slope, and at the same time, strengthen monitoring in the construction process, find out the changes of the bank slope in time, and optimize and adjust the construction efficiency.
Pile sinking construction
First of all, according to the design report, check the soil layer distribution, soil quality of each layer, the range, soil quality and thickness of hard interlayer one by one, and if there is any objection, make up the drilling; Secondly, if the bearing capacity of a single pile is determined according to the test results, it must be ensured that the model of the tools used for pile sinking, the elevation and strength of the pile tip entering the soil layer are consistent; Thirdly, if the bearing stratum is hard, and there is neither test pile nor test data to refer to, we can consider doing tests before pile sinking; Finally, in the process of determining the pile length, the irregularity of soil layer change should be considered, and the elevation of soil layer should be determined by drilling.
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During the construction of high-piled wharf, it is necessary to strengthen the on-site construction supervision, formulate solutions in time when problems arise, especially in the case of poor construction and geological conditions, and strengthen the on-site supervision to ensure the engineering quality.
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