| At present,China is in the stage of rapid urbanization.Large-scale construction of underground spaces in various cities have produced huge amounts of excavated soils.The amount of excavated soils produced in China reaches 2 billion tons per year.It is expected that the annual output of construction waste will increase in the next ten years,and the huge amount of excavated soils disposal has become a difficult problem in China.At present,the disposal method of excavated soils is mainly landfill,which not only takes up a lot of land resources,but also the unreasonable design and operation of some landfills lead to increasing the risk of landslides in the landfill.The Shenzhen landslide accident reflects our lack of in-depth understanding of the engineering characteristics of excavated soils and the safe landfill technology.At the same time,the use of excavated soils for backfilling pits needs to break through the technical problems of post-construction settlement of backfilled foundations,and the use of excavated soils for landscaping needs to break through the technical problems of soft soil foundation treatment and prevention and control of landslides.The solution of these problems requires an in-depth understanding of the deformation,strength and permeability characteristics of excavated soils,especially pore pressure generation and dissipation in the rapidly-filled different excavated soils.Through the centrifugal model tests,pore pressure generation and dissipation in the rapidly-filled completely decomposed granite(CDG)from Shenzhen province and excavated mucky soils from Zhejiang province under were studied.Through numerical calculation,the influence of water content,the landfill ways,the landfill rate of the excavated soil and the water level on the slope stability was analyzed.The main research works and conclusions are listed as follows(1)Through the centrifugal model test,the pore pressure generation laws in the rapidly-filled CDG soils from Shenzhen province with different initial saturation was studied The test results show that the higher the initial saturation of CDG soils,the higher the pore pressure and the greater the pore pressure coefficient.When the acceleration is 100 g,the model corresponds to a height of 90 m,the maximum pore pressure at the bottom of the model on the high water content side is 1068 kPa,and the maximum pore pressure at the bottom of the model on the low water content side is 629 kPa;the average saturation of the CDG soils in the high water content area side is from 70%increased to 93%,and the average saturation of CDG soils on the side with low water content increased from 50%to 71%.The pore pressure coefficient at the non-interface increases with the centrifuge acceleration,and the pore pressure coefficient of 10 g to 100 g varies from 0.62 to 0.71 at the high water content area,and the pore pressure coefficient of 10 g to 100 g varies from 0.07 to 0.43 at the low water content area.The pore pressure coefficient at the interface of the soils layer is significantly lower than that at the non-interface.(2)Through the centrifugal model test,the pore pressure generation laws in the rapidly-filled excavated mucky soils from Zhejiang province was studied.The test results showed that the pore pressure and pore pressure coefficient of excavated mucky soils were increased with the landfill height without drainage measures.The increase rate of pore pressure coefficient decreases gradually with the increase of the landfill height.During the rapidly filling of excavated mucky soils,the pore pressure coefficient varies from 0.72 to 0.84.When the height reaches 60 m,the maximum pore pressure at the bottom is about 918 kPa.Setting geocomposite drainage network can accelerate the dissipation of pore pressure.The shorter the drainage distance,the more significant the dissipation of pore pressure.At 316 days,the pore pressure dissipation percent at the center of the 5 m thick soil layer is about 9%,and at 5 years,the pore pressure dissipation percent at the center of the 10m thick soil layer is 21%under double-sided drainage.The amount of water and the undrained shear strength of the soils have been improved(3)Through the centrifugal model test,the pore pressure dissipation laws in the rapidly-filled excavated mucky soils from Zhejiang province was studied.The test results showed that laying a horizontal drainage network and setting up an upward drainage channel in the soils can effectively dissipate the excess pore pressure.The smaller the spacing of the horizontal drainage network,the more significant the dissipation of excess pore pressure.Under the condition of double-sided drainage,the dissipation percent of excess pore pressure at the midpoint of 10 m thick soil layer after 16.8 years is 91%?96.7%,and the dissipation range of excess pore pressure at the center of 15 m thick soil layer is 24%?30.4%The dissipation range of excess pore pressure at the center point of 20 m thick soil layer is only 15%.Laying horizontal drainage nets and setting down drainage channels in the excavated mucky soils can effectively dissipate the pore pressure and significantly shorten the pore pressure dissipation time.The smaller the horizontal drainage net spacing,the more significant the pore pressure dissipation percent.Under the condition of double-sided drainage,the pore pressure dissipation percent at the center of 10 m thick soil layer after 7.7 years is 87.8%? 91.5%,the pore pressure dissipation percent at the center of 15m thick soil laye is about 35%,and the center of 20m thick soil laye is only 14.1%.Setting geocomposite drainage network can significantly reduce the moisture content of the soils,and the undrained shear strength of the soils is significantly improved.It is recommended that in the actual landfill project of excavated mucky soils,the horizontal drainage network can be combined to insert vertical drainage plates,and the blind drainage ditch can be used to dissipate the pore pressure of the soils.The horizontal spacing of the drainage network should not exceed 10m,and 5m is suitable.(4)Based on the law of pore pressure generation in the rapidly-filled CDG soild from Shenzhen province and excavated mucky soils from Zhejiang province,the stability of the slopes of Shenzhen Hongao landfill and Ningbo Shanyin'ao was analyzed.The stability analysis results of Hongao landfill indicate that:the pore pressure obtained from the input pore pressure coefficient,and the sliding surface obtained by the effective stress method is located on the third step,which is basically consistent with the site survey.The analytical model established by calculation is reliable,and the pore pressure coefficient accurately reflects the pore pressure of the slope of the rapidly-filled excavated soils.The stability analysis results of Ningbo Shanyin'ao Landfill indicate that the design slope of the landfill is in a stable state.(5)According to the limit equilibrium analysis method,the influence of factors such as soil moisture content,landfill ways,landfill rate and water level on slope stability was analyzed by numerical calculation.The analysis results show that:controlling the moisture content of excavated mucky soils at a low level can improve the slope stability,and the excavated soils filling method needs to be adjusted.When the filling rate is too fast,even the soil moisture content is low,the stability of the slope will still be significantly reduced.When there is high moisture content excavated soils in the slope,the slope can still be stabilized by controlling the filling rate.No excess pore pressure in the early stage of the slope body,but in the later stage,the water level rises due to external water entering the slope body,which will still significantly reduce the slope stability.The landfill should take reasonable and effective measures to ensure the safety of construction and operation according to the safety level,surrounding environment,engineering geology and hydrogeology.Stability and safety control should focus on the control of excavated soil moisture content,landfill rate and water level within the slope.At the same time,the horizontal displacement,settlement,water level and excess pore pressure of the slope shall be monitored for a long time. |
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