Under the prospect of social and economic sustainable development, the quality requirements of substation construction project are higher than other civil engineering projects. However, due to quality requirements, such as geological conditions of site selection, the civil engineering of substations is restricted in many places, so it is very important to discuss the foundation construction technology of civil engineering of substations.
1 analysis of foundation characteristics of substation civil engineering
1. 1 Substation civil engineering has high investment cost and technical requirements.
Substation civil engineering involves many contents, among which power equipment, automation equipment and intelligent equipment account for a high proportion, which requires high equipment accuracy. Therefore, it is determined that the capital cost and technical requirements of substation civil construction will be high.
1.2 The substation construction site is affected by the substation system.
Because the substation is irreplaceable in the power system, the civil construction of substation is usually located in the relative center of power load to ensure the normal operation of substation. In substation construction, there are many aspects that need to be considered, such as whether there are large-scale projects around the substation, the probability of lightning strikes, and the transportation of substation engineering materials. Therefore, the construction of substation civil engineering is difficult and often has to be carried out on poor foundation.
1.3 substation has comprehensive civil functions and occupies a small area.
The civil construction of substation requires less land area, but the substation building contains comprehensive related functional equipment, such as substation room and power distribution room. For transformers, foundation construction, such as fire pool and drainage pool, needs to be completed. The operation of civil engineering needs to ensure the independence of substation structures and buildings, meet the functional requirements of substation electrical appliances, and ensure the daily functions of the system on the premise of meeting the functional requirements of substation electrical appliances. Substation requires high quality of civil construction, but it will encounter some natural factors, leading to many problems such as poor foundation, which poses a great test for substation civil engineering.
2 Common causes of poor foundation
In the construction of substation site selection, it is easy to have poor foundation. The common factors that cause poor foundation are alluvial flat at the bottom of the slope, and the surface is relatively flat. However, due to the short formation time, it is easy to be attacked by mountains and rivers, which leads to poor foundation, or when the substation is located in the terrain with large elevation difference, it needs to be excavated and compacted to balance the terrain. However, it is likely that the deep soil layer is not covered due to the deep fill and short compaction project.
3 Technical measures of substation civil foundation construction under bad foundation conditions
3. 1 Suggestions for improvement of substation foundation building
Most substations have main control building, high voltage distribution room and other related buildings. When planning the overall layout of the substation, designers will give priority to the outgoing direction of each level of voltage, so as to follow the electrical layout and arrange buildings in places with relatively good geological conditions, but often some buildings will be arranged in places with poor foundations. Therefore, before the design and construction, it is necessary to conduct all-round geological exploration of the station. In most cases, independent piles and other pile foundations are selected for the foundation of substation buildings. However, when the bearing capacity of the station site foundation cannot meet the design requirements, pile foundation and other suitable foundation methods should be adopted for foundation construction.
During the construction process, when the foundation pit elevation is reached, it is necessary to carry out a penetration test on the foundation, and the test results must meet the requirements of foundation bearing capacity before the project can continue. If it can't meet the requirements, it needs further treatment. Common treatment methods are as follows. (1) By observing the earthwork map and topographic map, we can see whether the foundation is in the shallow position of the fill layer. For the filled soil layer, excavation should be carried out, and the soil layer should be dug to a bearing layer 0.5m below the old soil layer to meet the design requirements, and carefully built to the design elevation with cement mortar and flaky with strength of M 10 to meet the design requirements. (2) When the bearing capacity of strip foundation is lower than the difference of design requirements, it is necessary to expand the calculation of basement area and expand the foundation according to the results. Independent column foundation can reduce the elevation of basement below the original soil, and the volume of bottom column will increase accordingly. At this point, you should trim the results of the bottom column.
3.2 Substation Transformer and Frame Foundation Treatment
Transformer and frame foundation in substation are independent foundations, which are connected by pipes. According to relevant regulations, the settlement range must be controlled within10 mm. When the building foundation condition is poor, according to the actual construction situation, it is necessary to adopt flaky cushion and dynamic compaction to deal with the situation that most of the foundation is in deep fill area.
3.3 Foundation Treatment of Cable Lighting and Drainage Pipes in Substation
Cable trenches and drainage pipes in substation buildings are mostly strip foundations, which are characterized by light weight and long length. On the bad foundation, the local flaky cushion and the method of expanding the base area can be used for treatment. If this method is adopted as a whole, the project cost will increase greatly. Therefore, in addition to the above methods, the common methods to deal with bad foundation are: lime-soil cushion method. For the soft soil layer with the thickness of 1~4m, the lime-soil cushion treatment method is usually adopted. By digging out the soft soil layer below the foundation within a quantitative range, filling in a proper proportion of lime soil, and backfilling or tamping in layers under the optimal moisture condition. During tamping or compaction, attention should be paid to confirm the bearing capacity.
Under the condition of manual compaction or 3: 7 lime-soil cushion compaction, when the compaction coefficient is limited to 0.97 and the dry soil weight is not less than 14.5 ~ 15.0 kn/w, the bearing capacity of lime-soil cushion can reach at least 300Pa. If the lime-soil cushion ratio is 2: 8, the compaction index is 0.97 and the dry soil weight is not less than/kloc. Dynamic compaction method. Dynamic compaction is usually used to treat fragile foundations such as gravel soil, sandy soil and low saturation silt. However, in the case of high saturated silt, the site suitability should be tested when backfilling gravel in the rammed pit. Before the construction of dynamic compaction method, it is necessary to find a representative test area on the spot for test construction. The tamping strength of dynamic compaction method should be comprehensively determined according to various factors such as the type, structure and size of foundation soil. In most cases, coarse-grained soil can be 1000~3000kN? ; M/m2, fine-grained soil desirable 1500~4000kN? ; Square meters.
3.4 How to cooperate with electrical engineering should be considered in substation civil engineering.
Electrical engineering should be considered in the construction of substation civil engineering, and the cooperation between them plays a great role in the stability and safety of the whole substation. The construction between them must be carried out in accordance with the specifications, and there are relevant specifications and standards in the construction process of substation, which strictly shows that the quality of civil engineering must be controlled accurately. If there are nonstandard factors in civil engineering and inappropriate factors in electrical engineering in substation engineering, it will destroy the whole civil structure and lead to the stability and safety of functions. In the process of electrical construction, functional equipment is usually connected through pipes, so if electrical engineering and civil engineering are properly coordinated, the damage of the whole building can be greatly reduced.
3.5 Strengthen the quality control of civil foundation construction.
In the foundation construction of substation civil engineering, it is essential to detect the engineering quality. The standards for detecting the construction quality of civil engineering foundation include the positioning of structural foundation, welding state control of steel raw materials, concrete soil quality and so on. The testing standards are strictly stipulated, and the whole detail quality of the project must be tested according to the regulations.
4 conclusion
For the construction of substation, we must design projects that can be well matched with each other according to relevant specifications, so as to improve the quality of substation. If there is any situation that is not conducive to the foundation construction of substation, it should be analyzed and handled in time with the correct method. After repeated revisions, we can ensure that all requirements can meet the design needs before we can start the construction of the project.
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