Research On Design And Application Of Backfilling Metro Station Pit With Construction Waste

All kinds of buildings(structures)above the roof of metro station occupy the backfilling space of the foundation pit of the station.The backfilling space of the foundation pit is narrow and difficult to drain.The backfilling construction is difficult to meet the requirements of the specifications.In general,the backfilling quality of the foundation pit is difficult to meet the design requirements.The backfilling of the foundation pit needs to adopt backfilling with high strength,easy rolling and good water stability in accordance with local conditions.As a new type of recycled material,construction waste has been applied in many subgrade and foundation treatment projects.It has the advantages of high strength and easy rolling,but there is no relevant gradation design and construction technology standards to follow.In order to reduce the backfilling quality of the foundation pit of the metro station and to study the technical economy of backfilling the foundation pit with construction waste,the gradation design,backfilling construction technology,construction quality acceptance after construction and long-term settlement monitoring of the construction waste mixture are studied relying on the Juyuanzhou Station of Fuzhou Metro Line 2.The main contents and conclusions of this paper are as follows:(1)The basic properties of building waste,fine sand and fill are tested through laboratory tests.There are a lot of sawdust in the fine grains of building waste,which exceed the standard requirements.The fine grains of building waste can be replaced by filling or fine sand,and mixed with coarse grains of building waste to form a mixture for backfilling of subway foundation pit.(2)Vibration density of coarse aggregate of building waste with different gradation is analyzed according to filling vibration test.By comparing with the result of voidage calculation,the optimum gradation of coarse aggregate of building waste is 100:25:25.(3)Through standard compaction test and CBR test of subgrade backfilling,the influence of gradation,different admixtures and different admixtures on the density and CBR value of the mixture is analyzed.The results show that mixing fine sand and filling soil has a great effect on improving the maximum dry density and CBR value of building waste.The optimum mixing amount of fine sand and filling soil with maximum dry density is 30% and 20%,while that of fine sand and filling soil with CBR value is 30% and 20%.The optimum dosage is 30% and 10%~15%.(4)The results of field backfilling test and dynamic resilience modulus test show that the backfilling of construction waste mixture is convenient and efficient,and the thickness of loose pavement can be relaxed to 600 mm.When each layer is rolled six times,the deflection value of the left and right wheels of the subgrade is only about 1/4 of the design value,and the resilience modulus of the top surface of the subgrade is about 4 times of the standard value.(5)The results of one-year pavement settlement monitoring show that the settlement of construction waste roadbed is consistent with that of filling roadbed and tends to be stable after 180 days,but construction waste can reduce the settlement of roadbed by about 28%.