| Taking the typical urban subway and the underground engineering construction of comprehensive pipeline gallery as the research object,we thoroughly analyzed the source characteristics of the construction waste in underground engineering construction site at the project level,based on the idea of the quantification of construction process,as well as the integration method of in-site investigation and literature review.Then,a quantitative prediction model for the classification of the construction waste at the project level was proposed.According to the shortcomings of construction waste management and control in China,the corresponding improvement measures were highlighted.The main conclusions of this paper are as follows:(1)The results of the investigation and the development of underground engineering construction site show that construction wastes mainly include engineering dregs,engineering garbage,engineering mud and abandoned steel bars,which accounts for more than 99%of the total construction wastes.Specially,engineering dregs and engineering mud are the difficulty of construction site management because of their large volumes.Waste timber,waste waterproofing materials and waste paint barrels can be recycled.Therefore,we suggest that supervision should be strengthened at the construction site to avoid potential safety hazards(fire protection)and environmental risks.Meanwhile,in the process of construction,a high correlation was observed between the amount of construction waste and the construction scale,design basis,construction technology,as well as construction level.(2)Taking the engineering dregs and slurry produced by the construction of X city subway as the example,we analyzed the characteristics of resource attributes so that the disposal methods of construction waste can be put forward.We found that the produced miscellaneous filling soil during the construction of subway foundation pit can be used for hill-piling and landscaping after sorting.Sandy silt and salty clay with clay silt can be fired by adding other materials.Silt can be used for foundation reinforcement and roadbed filling.Fine sand can be used as aggregate with high resource,and sandy clay can be fired directly for recycled bricks.The moisture content of shield dregs in metro tunnels reaches 30%.If it is directly landfilled,there will be greater environmental risk.Therefore,the shield dregs should be dried before disposal and fine sand as aggregate should be given priority in the disposal of the dried dregs.Engineering mud is mainly used on site or disposed after abandonment.The optimum disposal method is determined by testing the specific gravity,viscosity,pH value,water loss,colloid ratio,mud thickness and sand content of engineering mud.At the construction site,the waste mud is mixed with the dregs and soil,and the water content reaches 40%.If it is directly landfilled,it will be at greater environmental risk.Therefore,the engineering mud needs to be dried before disposal,and the dried mud can be used for mountain landscaping.(3)Based on the study of the characteristics of construction waste,the underground construction waste was classified and analyzed,which was mainly divided into loss type construction waste and non-loss type construction waste.Specially,loss type construction waste can be divided into two following categories,i.e.,obvious quantity characteristics are and nonobvious quantity characteristics.Considering this situation,we constructed the prediction models of engineering dregs,engineering garbage,engineering slurry and abandoned reinforcing bar occurrence and transportation,respectively,based on the principles of key control,key prominence,in-situ reuse and feature classification.At last,the reliability of the prediction model is verified by using relative error index.(4)Taking the underground construction of H city comprehensive pipe gallery as the example,the model was used to classify and quantitatively predict the occurrence of construction waste.The results show that the predicted occurrence of construction waste was 124537.57m3,the predicted transportation was 145903.18m3,and the relative error was 2.58%compared with the actual transportation of 149776.00m3.The predicted amount of engineering waste was 5019,06m3,the transportation volume was 7945.34m3 compared with the actual transportation volume of 8164.32m3,and the relative error was 2.68%.The predicted mud volume was 20634.57m3 and the predicted transportation volume was 23317.07m3,compared with the actual transportation volume of 22678.00m3,the relative error was 2.81%.The predicted occurrence of abandoned reinforcement was 447.8lt.and the relative error was 4.10%compared with the actual occurrence of 435.18t.The predicted relative error of all kinds of construction waste was less than 5%.Those results indicate that the classification prediction model of construction waste has good accuracy.(5)By investigating the current situation of construction waste management and control in typical demonstration cities,we found that there are some drawbacks in domestic construction waste management and control,such as the lack of classification standards and vague quantitative characteristics as well as the lack of corresponding incentives for resource utilization.Therefore,this paper highlights the importance of drawing lessons from the advanced management experience both at home and at abroad,and puts forward construction site construction waste management strategies covering macro-and micro-levels. |
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