Thread Content
The Phase III wharf project at Bayuquan Port is located in the Bayuquan Port area of Yingkou City, Liaoning Province. The wharf has a total length of 897.384 m and is a gravity-type wharf with four layers of concrete blocks and a load-reducing slab; the volume of each concrete block or slab ranges from 33.5 to 75.01 m3, with a concrete grade of C35F300. The water depth at the front edge of the wharf is -14.0 m, the elevation of the bottom of the foundation trench is -17.2 m, and the thickness of the rock fill foundation is 3.2 m. 1. Natural conditions: 1.1 Water level: Extreme high water level +5.13 m, extreme low water level -1.34 m. Design high water level +4.03 m, design low water level +0.26 m. 1.2 Waves: This project is located in an unprotected area near the coast, and is greatly affected by wind and waves, especially by southwest and northwest winds. 1.3 Geology: The riprap foundation rests on a sub-clay stratum with a SPT count of greater than 40, which serves as the bearing stratum. 2. General construction details: 2.1 Dredging of the foundation trench: The owner subcontracted the task of dredging the foundation trench to the Shanghai Waterway Bureau, with suction dredgers being used for the dredging work. In accordance with the current industry standards, the foundation trench is allowed to be 0.4m deeper than specified, and 1.5m wider on each side. By strictly controlling the excess depth and width of the foundation trench, the cost of laying stones in the foundation bed can be **reduced**. Therefore, by maintaining timely communication with the owner, the supervisor, and the Shanghai Waterway Bureau, the project team sent a technician and a quality inspector to the suction dredger. Whenever the dredger dug out the foundation trench for a particular berth, the technician and quality inspector would assess the progress of excavation based on the water level at that time, and provide feedback on the quality of the excavation to the operator of the dredger, enabling them to adjust the elevation of the dredging cutter as needed. Through the joint efforts of technicians, quality inspectors, and the operators of the cutter suction ship, the foundation trench was made 0.2m deeper on average and 0.6m wider on each side on average. 2.2 Bedrock riprap: Due to the tight deadline set by the client, using traditional civilian ships for riprap placement would not only fail to meet this deadline but also introduce various negative aspects to the management of bedrock riprap placement. Therefore, the project team attempted to use the rock dumping technique employed for western breakwaters for filling the foundation bed; on land, surveyors used total stations to determine the positioning of the barges, while underwater, excavators and barges were used to dump the rocks. Given that the water depth ranges from 18m to 22m and tidal currents are strong, it was determined after typical construction trials that rough dumping should be carried out during high and low tides, while fine dumping should be done at slack tide ； Before throwing the stones, the technician determines the number of stone dispensers required for each throwing section based on the amount of stones loaded onto the barges used for throwing and the cross-sectional area of the underwater bed. After the stones are thrown, the workers use weights to check the water level and make minor adjustments to the number of stone dispensers for each section as needed. Tests in the subsequent processes have proven that the stone-throwing technique using excavators and barge teams is highly feasible. The elevation of the compacted subgrade surface is on average 17.9 cm lower than the designed elevation, achieving the desired outcome. This not only meets the owner’s deadline requirements but also avoids various drawbacks associated with traditional methods of using civilian ships to transport stones, such as difficulties in measuring the amount of stones to be used and managing the stone-laying process on site. 2.3 Compaction and leveling of the foundation bed: Compaction is carried out using a 6.35-t hammer lifted by a 65-t crawler crane. Due to limitations imposed by the construction site provided by the owner, it is not possible to set up markers for the direction and distance of compaction at the site; therefore, a total station used for positioning the rock-throwing vessel is employed to locate the compaction boat. During the compaction process, strict control is exercised over the drop height of the hammer as well as its vertical and horizontal distances from other elements. The average settlement of the foundation bed resulting from compaction was 2.1 cm (with the standard requiring this value to be no more than 3 cm). During the leveling process of the foundation bed, divers from the project team periodically conduct underwater inspections to assess the quality of work done by the subcontractors responsible for leveling. Through strict management ； Careful construction ensured that the qualification rate for leveling measurement points reached 98%, earning recognition from the owner, the supervisor, and the port quality inspection agency. 2.4 Prefabrication of blocks and unloading plates: The concrete design grade for these blocks and unloading plates is C35F300, with each block requiring 75.01 m3 of concrete. This constitutes large-volume, high-grade concrete; once the concrete has set, common quality issues such as cracks, sand spots, and sand lines can occur, affecting the appearance of the concrete and causing permanent defects in the structure. To eliminate cracks in concrete, we took a series of measures: (1) First, we focused on controlling the amount of stone dust in the coarse aggregates used in concrete. To reduce construction costs, we used circulating water to wash the gravel, and installed sunshades during summer to lower the temperature of the aggregates before they were put into the mixers ； (2) Under the premise of meeting design and specification requirements, test mix concrete mixtures without the use of cement, and select the optimal concrete mixture from them ； (3) Strictly control the concrete mixing time and the concrete slump ； (4) Early-strength cement is used in spring and autumn, while ordinary cement mixed with retarding agents is used in summer ； (5) Strictly control the concrete vibration time, the spacing between vibration rods, as well as the time for compacting the concrete and removing the formwork ； (6) Embed \"pseudo horse legs\" within the blocks and unloading plates, then fill them with fresh water; change the water in these \"pseudo horse legs\" every 2–3 hours in order to reduce the temperature inside the blocks and unloading plates and thus minimize the temperature difference stress between the interior and exterior of the concrete ； (7) Concrete curing work after adding the QC modulus (establish a concrete curing team). With the adoption of the above measures, the appearance quality of prefabricated components such as blocks and unloading plates has been further improved. Common quality issues such as cold joints, sand lines, and bubbles have been effectively controlled, especially the cracks on the water-facing side of the unloading plate have been eliminated. It has received praise from the owner, supervisor, and quality inspection station. 2.5 Installation of square blocks and unloading plates: To reduce project costs, the traditional method of using a crane ship to lift the measurement platform has been replaced by directly using a crane ship to suspend weight balls; the installation of the square block lines is carried out during low tide. To ensure the installation quality of the blocks underwater, during the installation process, divers from the project team conduct random inspections from time to time of the installation joints, misalignments, and height differences on the top surfaces of these blocks. A weight suspended above the water is used to pull the blocks up to the surface via steel cables, and total station devices on land are employed to determine positions and measure distances in order to assess the installation quality of the blocks. Through strict management and multiple quality control checks, the actual length of the dock turned out to be 30 cm greater than the designed length (the specifications allow a range of -45 to +300 cm), thus achieving the preset control objectives. 2.6 Prism dumping: As this project spans multiple years and is affected by factors such as weather, the work can be suspended from November 2001 to March 2002. During these five months, silt deposition has occurred at the tops of the installed blocks and at the backfill prisms; it is necessary to remove the sediment from these areas. According to traditional methods, a hopper crane – lifting unit is required to carry out this dredging work. At that time, the crawler cranes available in the project department were in short supply; in order to reduce construction costs, the project department carried out technical innovations and process optimizations. The “Jinfu sludge suction” method was used to remove the silt completely, ensuring high quality in underwater silt removal and keeping the project schedule on track. During the construction of the mixed filter layer, divers from the project team are sent underwater to check the thickness of the gravel in the mixed filter layer at the base of the mud surface ； Before laying the geotextile, divers went underwater to inspect each area in order to ensure the flatness of the slope surface and thus guarantee the quality of the installation. The strict area-by-area inspection and control of these concealed works won the trust of the supervision engineer. 2.7 Construction of the breast wall: The designed bottom elevation of the breast wall is +2.1m, and construction must be carried out during low tide. Before starting the construction of the breast wall, relevant personnel are gathered to discuss the construction techniques, with an emphasis on optimizing these techniques to ensure the quality of the work. Quality assurance measures should be established; after typical construction tasks are completed, on-site meetings should be held promptly to summarize construction experience and improve construction techniques. During the construction process, strict adherence to procedural standards is maintained, with frequent inspections and testing to strive for excellence; any issues identified are not tolerated, and corrective actions are taken promptly. It effectively ensured the quality of concrete pouring, resulting in a 100% excellent quality rate for the cast-in-place breast wall concrete, and was praised by experts from the Ministry’s Quality Supervision Station. 3. In terms of technical management: In line with the overall requirements of the \"Striving for Departmental Excellence Project,\" the following measures were taken in construction management: (1) Concentrated efforts were devoted to carefully preparing the construction organization plan, which was submitted for review in a timely manner ； (2) Given the geological complexity of the project, the unfavorable natural conditions, and the owner’s strict deadline requirements, it is essential to focus on providing technical training for the staff ； (3) Thoroughly study the design documents, establish key construction technical points, and strengthen technical briefings for construction ； (4) For key processes or projects, a combination of workers, technical personnel, and managers is employed to work together in teams to tackle the challenges ； (5) For major technical issues, hold seminars attended by the project owner, design unit, and construction unit ； (6) New processes and technical changes during construction are carried out in accordance with the requirements of the “Design Modification Notice” and the “Technical Coordination Form”. 4. Quality management: Since March 2001, the project team has regarded project quality as a symbol of the company’s reputation; in terms of quality management, the following measures have been taken: (1) A quality leadership team composed of the project manager, the technical supervisor, the deputy production manager, as well as those responsible for production scheduling and project quality, was established to take overall responsibility for project quality and ensure the proper and effective operation of the quality management system ； (2) In work, properly handle and balance the relationship between project progress and project quality, adhering to quality first ； (3) Hold regular quality meetings (once a month) to diagnose the quality of the work, formulate corrective actions, assign them to specific teams or individuals, and set deadlines for implementation; show no leniency toward employees within one’s own department or subcontractor teams ； (4) Establish a quality reward and penalty system as well as a system for timely rectification ； (5) Strictly implement the self-inspection and specialized inspection systems during on-site construction ； (6) The requirement to strictly follow the rule that construction can proceed to the next stage only after approval is given by the owner’s representative and the supervision engineer’s representative during on-site construction. Thanks to the proper implementation of the above two measures, the construction quality of the Phase 3 terminal project has been reliably ensured. 5. Remaining issues: 5.1. Concrete crack issue: Although a range of measures have been taken for large-volume, high-strength concrete, cracks still exist in some blocks and unloading plates. The width of these cracks is within 0.3 mm, and their length ranges from 50 to 100 cm (the cracks are mainly found in the mortise sections of the blocks and at the joints where the semi-circular holes in the unloading plates meet). Experts from the quality inspection station have classified these cracks as harmless, but they have not been completely eliminated. If conditions permit, replacing ordinary Portland cement with dam cement might help to reduce the occurrence of such cracks. 5.1. Rust prevention of embedded parts in the upper structure of the pier: All iron embedded parts in the upper structure of the pier were galvanized. After completion of construction, it was found that all of these galvanized iron parts had developed rust. We conducted an urgent inspection of the factories where the galvanizing was carried out, and there were no issues with either the process or the methods used for galvanizing. The likely cause of the rusting was damage to the iron parts during transportation and installation, coupled with the fact that the embedded parts were exposed to the humid environment of seawater, which led to rust formation on those galvanized iron parts. If conditions permit, galvanizing could be replaced with chromium plating.