Study On Key Technologies For Construction Of Xudong Underground Substation

With the rapid development of the national economy and the acceleration of the urbanization process,the urban power load is increasing day by day,and more and more substations are going into the urban area.However,due to the shortage of land resources in urban areas and the concentration of various pipelines in the air,the underground substation which can not only ensure the safe and reliable use of electricity,but also alleviate the shortage of land came into being.At present,many underground substations have been built at home and abroad.Due to the special geological environment conditions,there is no successful case in Wuhan.The main structure of the underground substation is built in the complex geological environment,and there are many technical problems in its construction process,such as the deformation control of the soil near the foundation pit during the excavation of the large-scale deep foundation pit;the temperature crack control during the pouring of the mass concrete;the stress and deformation control of the main components of the structure during the hoisting and transportation of the heavy equipment,etc.Based on the background of Xudong underground substation in Wuhan,this paper studies the key technologies in the construction process,such as deep foundation pit support technology,mass concrete temperature crack control technology,heavy equipment hoisting and transportation scheme.The main work and resultswere as follows:(1)Research on support technology of deep foundation pit under special conditions.The foundation pit of the project is large in scale and deep in excavation,close to main roads and important buildings,and the surrounding environment is complex.Considering that buildings have relatively high requirements for deformation of surrounding environment,it is the key point of engineering control to effectively control deformation of surrounding buildings in the process of foundation pit construction.According to the surrounding environment and stratum conditions of the site,according to the principle of technical feasibility,economic rationality and advanced technology,the preliminary selection of foundation pit support structure scheme.Based on MIDAS/GTS software,the finite element model of the primary scheme is established,and the step-by-step excavation simulation calculation is carried out,the deformation control effect is analyzed,and the better supporting scheme of deep foundation pit is determined.(2)Research on temperature crack control technology of mass concrete.The base plate of this project is thick and long in vertical and horizontal directions.During the whole pouring,the concrete will produce shrinkage cracks due to hydration heat,which will endanger the performance of the structure.Controlling the temperature cracks of the base plate concrete has become another key technical problem of this project.First of all,mix proportion tests are carried out for concrete with different parameters of fly ash,slag powder,expansion agent,water reducing agent and other additives to select the mix proportion of concrete that is not sensitive to temperature;based on this,two disposal schemes of setting post pouring belt and expansion strengthening belt are selected,and numerical simulation analysis is carried out by using MIDAS/civil software to further determine the better temperature control scheme for the bottom plate.(3)Research on lifting scheme of heavy equipment in underground multi-layer frame structure.In this project,the three-story three span cast-in-place reinforced concrete rectangular frame shear wall structure is adopted,and the transformer weight.The safety verification and evaluation of the main structural components in the whole hoisting process is also one of the main technical problems of this project.According to the mechanical characteristics of underground multi-layer frame structure and combined with the site construction conditions,two schemes of flat car transportation and track sliding methodare selected.Using MIDAS/civil software to establish spatial frame model,carry out transportation process simulation analysis,and determine the better lifting scheme.For the selected implementation,design the monitoring scheme,arrange the stress and deformation monitoring points,and monitor the main structural members,beams,plates and columns.Compared with the results of monitoring and calculation simulation,all indexes are in line with the requirements of specifications,ensuring the construction safety.