Estimation Of Undrained Shear Strength Of High Water Content Waste Soils During Rapid Landfilling And Stability Analysis

As the rapid development of urbanization process,the large-scale development and construction of underground space in various cities has produced a huge amount of construction waste.And a large amount of soil is generated during the excavation of various types of buildings,structures,pipe networks and other foundations,which is called waste soils.Delivery to the landfill around the city is the main disposal method of waste soils.As the yield exceeds the capacity of disposal,many of the waste soils dumps have the problems of fast filling,lack of drainage facilities,overload of landfill capacity and over height.These irregular operations reflect the instability mechanism of unsaturated soil during rapid landfilling is not yet clear and the poor understanding of the strength growth law of the high saturation degree waste during rapid landfilling,which make it difficult to reasonably assess the stability of the waste dump.First,in order to explore the strength growth law of unsaturated waste soils during rapid landfilling,this paper carried out the undrained and exhausted triaxial test of the Shenzhen granite weathered soil(CDG)fill and the Zhejiang muddy soil.The results show that with the increase of saturation,the greater the pore pressure generated in the isotropic compression stage,the lower the undrained strength.The undrained shear strength of the sample increases nonlinearly with the increase of confining pressure,and under high confining pressure tends to be constant.Secondly,based on the principle of effective consolidation stress method,combined with Hilf pore pressure formula and modified Cambridge model,a method for estimating the undrained shear strength of unsaturated waste soils is proposed.This method is divided into three steps:isotropic compression pore pressure estimation,effective consolidation stress estimation and undrained strength estimation,among which the required parameters Cs?????c'??' and SWCC curve can be obtained through routine tests.This method can better reflect the non-linear growth law of the shear strength with the overburden.The relationship curve between the undrained strength determined and the normal stress of the failure surface by this method can be directly applied to the limit equilibrium analysis of the total stress method.The undrained strength evaluation method is used to predict the results of the unsaturated triaxial test,and compared with the test results,it was found that the estimation method has a more accurate prediction of the undrained strength of high-saturated soils,while for low saturated soil,the estimated strength is lower than the test result.Finally,for the landfills undergoing complex stress paths,this paper proposes a method to analyze the stability of landfills based on the evaluation method of undrained strength,and uses this method to calculate the stability of the Shenzhen Hong'ao landfill,the result of which is basically consistent with the stability calculation result using the bilinear strength index by UU test.For the case where the source of the dump is relatively single,the soil nature is relatively uniform,and the stress path is simple,the undrained strength index obtained through the test can be directly applied to the analysis of total stress stability.The method is used to calculate the stability of the Ningbo Shanyinao dump and the Beijing Guanzhuang dump.The total stress intensity index cu and ?u obtained by the fast direct shear test are used to analyze the slope stability of the waste dump and the result verifies the practicability of this method.