Experimental Study On Solidified Use Of Underground Excavation Soil In Nanjing

At present,China vigorously develops urban construction and advocates the development and utilization of underground space.The amount of waste muck produced by the excavation of underground tunnels and foundation pits is rising at an alarming rate every year.Although there are a variety of disposal methods for waste soil,the current treatment in China is still dominated by centralized landfill.In order to avoid the dust and road pollution caused by the transportation of the foundation pit muck and the hidden danger of environmental safety caused by the disorder and random stacking of the foundation pit muck,combined with the prospect of the reclamation of the foundation pit muck,this paper carried out relevant experimental research on the solidification and utilization of the foundation pit muck.Specific research contents and results are as follows:1)Investigate the status quo of muck utilization at home and abroad,and analyze the existing problems and deficiencies.Based on the investigation of the composition types of foundation pit muck in nanjing,the distribution of the soil is mainly silty silty clay,silty soil and silty sand.On this basis,low-liquid-limit clay,sand-containing low-liquid-limit clay and clayey sand were used to simulate different types of foundation pit residual soil for solidification test.2)Explore the influence of different molding conditions on the strength and dry density of three kinds of soil samples,including initial moisture content,molding pressure,cement content and other factors.The results show that the compressive strength and the initial moisture content are parabola,and the best initial moisture content is ω’＝0.053+0.0039W_L-0.0014N.The compressive strength of the block is linearly related to the forming pressure,and the splitting tensile strength is positively related to the forming pressure.The affects of final soil liquid limit>the affects of molding pressure>the affects of initial moisture content.3)Study the influences of added activator admixture FSC,polypropylene fiber and rice husk on the properties of pressed blocks were studied.The results show that adding polypropylene fiber or rice husk has a negative effect on clayey sand.Rice husk can improve the compressive strength of sandy clay with low liquid limit,and polypropylene fiber can improve the strength of clay with low liquid limit.For the sample with polypropylene fiber added,the affects of initial water content>>the affects of soil liquid limit>the affects of fiber content.For the addition of rice husk samples,the affects of initial moisture content>>the affects of fiber content>the affects of soil liquid limit.4)Combined with dry and wet cycle test to evaluate the durability of pressed block.The results show that the compressive strength increases with the number of cycles.The addition of polypropylene fiber will lead to an increase in the strength loss of clayey sand,and the addition of rice husk and activator FSC can improve the durability of sandy clay with low liquid limit,while the addition of polypropylene fiber can improve the durability of clay with low liquid limit.After the dry and wet cycle,the overall dry density trend is consistent with the compressive strength trend,showing a trend of rise and then fall.The results show that the three kinds of muck can be reused.Using cement as curing material combined with activator and fiber can make blocks with certain strength and basic durability.