Construction Technology of Beam-Slab Overhead Track Foundation in Land Bulk Cargo Yard
1 Project Overview
Beam-Slab Overhead Track Foundation
For a bulk cargo terminal project, the project covers an area of about 247,000 ㎡ , uses a shoreline of about 346m, and builds three 1,000t-class (3,000t-class) bulk cargo berths (1 berth for grain import, 1 berth for bulk cargo import, 1 cargo export berth), with a designed annual passing capacity of 5.88 million tons; the land area of this project is 347m in length and 408m in depth and is divided into two platforms. The front top elevation of the first-level platform is 275.2m, the depth is 310m, and the longitudinal slope is 1%; the front top elevation of the second-level platform is 283.3m, the front length is 290m, the rear length is 347m, the depth is 98m, and the longitudinal slope is 1%. Overhead track foundation.
2. Structural characteristics of beam-slab overhead track foundation
The crane rail track foundation occupies a small area, which has an obvious effect on saving the storage area. The drainage ditches, auxiliary equipment, dust removal sprinkler, track foundation, and part of production water installed vertically in the yard are combined and arranged, which effectively improves the use efficiency of the track foundation.
The track foundation has a certain drainage performance, and a part of the drainage load in the storage yard is reduced, so that the problems of a blocked drainage ditch, difficulty in cleaning, and water accumulation in the bulk storage yard are effectively solved. There is a lot of dust and debris in the bulk cargo yard, causing the drainage ditch to be often blocked. Therefore, it is necessary to set the drainage ditch at the edge of the storage area. There are not too many drainage ditches in the storage area, which greatly reduces the drainage function. For the drainage ditch of the beam-slab overhead track foundation, the drainage ditch is usually set in the overhead area under the track foundation platform, the drainage ditch is slightly lower than the surface of the yard, and the filter layer of bagged gravel is set at the root of the outer side of the track beam Location. The drainage ditch is set under the track foundation platform so that the drainage area of the storage yard is continuously increased, the drainage capacity of the storage yard is improved, and the usable area of the storage yard is not occupied, which plays an important role in improving the water accumulation problem of the bulk cargo storage yard. enhancement. In order to make it easier to clean the impurities and debris filtered out of the outer root of the track beam, you can use a net cage or a mesh bag as a bagged gravel filter layer, which will be more convenient for replacement and cleaning. When cleaning impurities and debris, construction personnel and vehicles can directly enter under the track foundation platform, so that the drainage ditch can be effectively maintained and cleaned, and the drainage can be smoother.
Install, operate and maintain ancillary facilities. Under normal circumstances, the pipelines of supporting equipment will be buried underground in the storage yard, and the pipelines will often be damaged due to uneven settlement of the foundation. When installing and maintaining pipelines, it is necessary to excavate along the buried position of the pipelines, which makes the cost continue to rise. The power, water, and communication main lines supporting the stacker reclaimer are buried in the overhead area under the track foundation platform, which will be more convenient for the installation and maintenance of the pipeline in the future, and the cost will be effectively controlled. It is better to set the ladders at the manhole of the aisle door and near the horizontal aisle door along the direction of the track beam so that it will be more convenient for the staff to enter and exit the track foundation, and it will be more convenient for the staff to enter the track foundation platform to maintain and repair other equipment.
It has strong feasibility and rationality. The vertical drainage ditch is set under the beam-slab overhead track foundation so that the land acquisition cost of the total land area of the yard can be effectively controlled, the installation and maintenance costs of supporting pipelines can be controlled, the problem of structural settlement can be effectively avoided, and the number of maintenance during the operation period can be effectively controlled. It has been continuously reduced, and the use efficiency of the stacker reclaimer has been continuously improved, thereby continuously improving the economic benefits of the terminal.
3 Design beam-slab overhead track foundation structure
3.1 Layout structure
The vertical overhead arrangement is the main form of the track beam pile foundation structure, as shown in Figure 1. The purpose of optimizing the track foundation structure is to better reflect the layout scheme of the overhead beam-slab structure. ① The vertical type is the main form of the structural section, which effectively reduces the area occupied by the storage yard. ②Rainwater and sewage on the foundation platform can be directly discharged to the bottom of the track beam and discharged out of the yard through the drainage ditch at the bottom of the track beam. The drainage ditch is not directly exposed outside, and impurities, etc. will not fall into it, so as to ensure smooth drainage and no water accumulation in the storage yard. ③Professional supporting pipelines are set under the track foundation platform, which does not need to be buried during installation, which makes the inspection and maintenance of the pipelines more convenient in the later stage. The pipelines are all hidden in the overhead area, and the overall aesthetics of the yard will not be affected in any way.
Figure 1 Schematic diagram of the overhead beam and slab structure
3.2 Design scheme
The track foundation of the bucket-wheel stacker-reclaimer in the bulk cargo yard uses a structural model combining pile foundation and beam-slab overhead. The sequence from bottom to top is pile foundation, cast-in-place track beam, cast-in-place panel, cross brace, and QU80 Steel rails, etc., the overhead area is formed between two parallel track beams, and the drainage ditch is set on the ground.
There are three main components of the superstructure, namely reinforced concrete panels, cross braces, and cast-in-place reinforced concrete track beams. The plain concrete surface and crushed stone cushion are the main structural forms of the pavement in the elevated space. The length of the track foundation structure section is usually 30m. PHC piles are the main form of the pile foundation, and the spacing is about 5m. Strengthening nodes are set at the middle and end positions of the structure section. In order to effectively resist the horizontal load generated during the operation of the bucket wheel stacker-reclaimer, it is necessary to add inclined piles. Since the foundation of each stacker-reclaimer is relatively long, if the yard construction personnel want to quickly cross the track foundation, they need to set the aisle door at the position where the two sections of the track are connected, with a distance of 100m. Set a vertical straight ladder at the position of the passage door, which will make it more convenient for the staff to go to the foundation platform to overhaul the belt conveyor equipment. Reinforced concrete steps are set at both ends of the track foundation, and cast-in-place panels are used for the connection between the track foundation platform and the manhole to lay.
The load-bearing bracket adopts bowl buckle-type steel pipes, and the load-bearing and channel functions should be erected separately. The poles are at a distance of 0.6m under the beam body, and the rest are 0.9m. In order to balance the load distribution, at least 3 rows of vertical poles are guaranteed when the beam is lowered. The horizontal rod step distance is 1.2m. The scissors’ support shall be set according to the specification requirements.
The bracket adopts bowl-buckled steel pipe scaffolding, in which the length of the vertical pole is 6.0m, 3.0m, 2.4m, 1.8m, 1.2m, 0.9m, 0.6m, the horizontal pole is 0.6m, 0.9m, and the vertical pole Adjustable seat, pole adjustable support and other specifications of rods.
The erection of rods adopts layer-by-layer erection and layer-by-layer acceptance. A layer of sweeping rods is required 30cm above the ground, and a layer of horizontal rods is required 30cm below the formwork.
3.3 Rational analysis of pile foundation selection and pile length
(1) When selecting pile foundations, it is necessary to use the information shown in the geological profile as the basis. The soft soil cover layer at the track foundation position is relatively thick. When piles are cast on land pile foundations, the construction method of on-site drilling and grouting is usually used, which can effectively reduce construction noise and make construction more convenient. However, the drilling time of this construction technique is very long, and inclined piles need to be installed in places where the soft soil cover layer is very thick. When setting inclined piles, it is easy to cause hole collapse, which is very difficult to control the construction quality. The load on the track foundation is very heavy. After careful analysis of previous successful construction cases, it is best to use 800mm PHC piles, that is, B-type piles, when selecting the diameter of the pile foundation. During pile foundation construction, the construction method of on-site splicing is adopted. The analysis is carried out according to the construction standard of the elastic long pile, and the bending moment below the characteristic depth of the pile foundation is ignored so that the problems of poor assembly quality on-site and weak bending resistance of joints can be well solved. The length of the first pipe joint of the pile foundation in this project is set to 12m, the characteristic depth of the pile foundation is set to 5m, and the effective distance between the characteristic depth of the pile foundation and the joint is 7m, so as to ensure that the bending moment will not affect the pile body structure.
(2) When calculating the internal force of the pile foundation, it is necessary to fully consider the horizontal force perpendicular to the direction of the track, the vertical wheel pressure of the bucket-wheel stacker-reclaimer on the track foundation, and the lateral earth pressure caused by uneven loading. After a lot of practice, the limit value of the pile foundation bearing capacity was finally obtained, and the maximum pile body bending moment value and maximum axial pressure value was calculated in detail.
(3) Through the investigation of the pile length and the geological conditions of the pile foundation bearing layer, it is found that the construction site can be selected as the pile foundation bearing layer: ⑥silty sand layer, ④silty clay layer, ③-3 powder fine sand layer, and ③-2 silt layer. ③-3 The distribution of the silty fine sand layer is relatively continuous and stable, the average thickness is deep, and the strength is relatively high. PHC piles cannot pass through this layer, so it is selected as the bearing layer of the pile foundation. After a lot of practice, the pile length is about 25m, and the axial bearing capacity of a single pile is about 3200kN, which can reach the maximum design value of the pile force. In order to make the designed pile length more scientific and reasonable, and make the hammer ability of the pile foundation meet the design requirements, several points can be selected at different positions of the pile for detection, and the specific pile sinking information and the corresponding final average penetration Make a note. After careful analysis, the designed pile length and the hammer ability of the selected pile type all meet the design standards, making the pile foundation construction smoother, and the bottom elevation of the pile foundation meets the design requirements. During the construction, part of the pile foundations was inspected, and the inspection results showed that most of the pile foundations met the Class I standard.
A comprehensive analysis of all the above situations shows that the design standards for pile length and pile foundation selection are relatively ideal, which makes the track foundation construction smoother, and at the same time provides a lot of technical support for the smooth construction of the track foundation, ensuring the later construction Meet the design requirements.
4 Conclusion
To sum up, this paper takes the actual project as an example to analyze and discuss the construction plan of the beam-slab overhead track foundation of the land bulk cargo yard and makes a reasonable design of the pile foundation structure. After the completion of the project construction, it experienced The scouring of many heavy spots of rain did not affect the normal use of the yard and the track and achieved good application results.
