Research On The Impact Of Reinforcement Actions Of New Construction In The Protective Area On The Deformation Control Of Subway And The Carbon Emissions And Costs

Urban rail transit has solved the demand of public transportation in big cities,and it also undertakes the important task of driving urban development.There are more and more new engineering along the subway,and the city is prosperous because of the subway.However,a large number of engineering projects near the subway cause the deformation of the subway structure and affect the safety of the subway during the construction.When building new constructions in the protective area of the subway,construction measures need to be adopted to ensure the deformations of the subway structure do not exceed the limit.The deformation control effect and cost of the reinforcement measures are the first two elements to be considered in the design.In addition,the carbon emissions generated by these construction measures cause innovative problems for the whole life cycle carbon emission evaluation system of the subway.Based on two new engineering cases in the protective area of Beijing subway,one is adjacent to and the other one is upper section structures,firstly this paper analyzes the control effect of the construction measures on the deformation of subway section structure.Secondly,this paper analyzes the costs and carbon emissions of construction measures.The main research contents are as follows:（1）The three-dimensional model of"existing subway section structure+soil+new construction project"was established by using Plaxis 3D finite element software.Based on the models,this paper firstly analyzed the control effect of the construction measures of the new engineering on the deformation of the subway section structure.In addition,and the scope of application of the construction measures under the change of the spatial position parameters of the new engineering and the subway was analyzed:1)The case 1is adjacent to subway section structure,for the foundation pit,the initial scheme adopted single row pile and anchor pole for support.The reinforcement scheme adopted underground continuous wall and internal support in northern area,meanwhile,it adopted double row pile and anchor pole in southern area.The results showed that the underground continuous wall and internal support system reduced the maximum horizontal displacement of the section structure by 39.51%,and the maximum vertical displacement was reduced by 10.18%.The double-row pile and anchor support system reduced the maximum horizontal displacement of the section structure by 13.37%,and the maximum vertical displacement was reduced by 29.76%.When the horizontal distance between the new engineering and the section structure was 18.5m～58.5m,the horizontal and vertical displacement of the section structure were less than the limit value,and the construction measures were effective.When the vertical distance between the new engineering and the section structure was 6-11m,the horizontal displacement of the section structure exceeded the limit,and the existing measures could not meet the requirements.2)The case 2 is upper span the subway section structure.For the foundation pit,the initial scheme adopted the method of soil nail wall support and divided the excavation area to 3 parts.The reinforcement scheme also adopted the method of soil nail wall support but divided the excavation area to 10 parts.After the excavation of every part,the reinforcement scheme used some loads on the bottom of foundation pit.The results showed that increasing the number of excavation parts and loading measures reduced the maximum horizontal displacement of the section structure by 78.08%,and the maximum vertical displacement was reduced by 84.61%.When the vertical distance between the new engineering and the section structure was a certain,the horizontal distance is 0m～40m or when the horizontal distance is a certain,and the vertical distance is 3.0m～7.4m,the horizontal and vertical displacement values of the section structure were less than the limit value,and the construction measures were effective.3)When dividing the scope of the subway protective area,in addition to considering the horizontal space parameters,the influence of the vertical space parameters should also be considered.（2）A carbon emission calculation model generated by the construction measures of the new engineering in the subway protective area was established,and the added carbon emissions incurred by the construction measures in two cases were calculated by using the carbon emission calculation method based on the quota.The results showed that the carbon emissions incurred by the construction measures in Case 1 were 1642.72 t CO₂eq,which increased the carbon emissions of the initial scheme by 43.06%;In Case 2,the carbon emissions incurred by the construction measures were 156.71 t CO₂eq,which increased the carbon emissions of the initial scheme by 28.09%.（3）Using the quota valuation method,the additional economic costs incurred by the construction measures in the two cases were calculated.The results showed that the costs incurred by the construction measures in Case 1 were 3,012,100 yuan,which increased the costs of the initial scheme by 34.71%.In Case 2,the costs incurred by the construction measures were 832,200 yuan,which increased the costs of the initial plan by 90.32%.A consistent analysis of the increased cost and carbon emissions was carried out,and the results showed that the increases of costs and carbon emissions incurred by the construction measures represented the linear relationship.（4）Based on the expected cost theory and the reliability theory based on the displacement criterion,considering the influences of soil parameters and different measures,the expected carbon emission added value and the expected cost added value calculation model of the new construction measures based on the probability of failure were established,which used the methods of Monte-Carlo Importance Sampling and Kriging agent models.By this model,the effects of the common change of horizontal distances and excavation depths on the expected carbon emissions added value and the expected costs added value were analyzed.The calculation results showed that when the excavation depth of the foundation pit were more than 8 meters and the horizontal distances between the foundation pit and the of the subway section structure were fewer than 4 meters,the probability of failure was at a high level,the expected costs added value of construction measures is more than 400,000 yuan,and the expected carbon emissions added value is more than 400 tCO₂eq.