Study On Seepage Failure Characteristics Of Sandy Caused By Leakage Of Underground Water Pipe

Ground subsidence accidents caused by leakage of urban underground water pipes are increasing year by year,and their engineering hazards are increasingly prominent,and the accidents are sudden and hidden.In order to understand the occurrence mechanism and evolution law of disasters,and then effectively prevent and cure related accidents,In order to ensure the safety of urban facilities and people's life and property,it is very important to study the soil failure mechanism caused by underground pipe leakage.In this paper,based on the ground subsidence accident caused by underground water pipe leakage,taking non-clay sand as the research object,the relevant leakage test is carried out by using the developed water pipe leakage model device.Based on the different leakage pore size and sand particle gradation sample,the sand layer is described.The evolution process and failure characteristics of sand seepage flow are discussed in combination with the experimental phenomenon and the total head change with the variation of the total water head at the same height with the leakage water pressure.By using Darcy's law to fit the variation of seepage hydraulic gradient,several classical flow soil theories and empirical formulas are used to verify the critical hydraulic gradient of sand seepage,and the evolution process and meso-mechanism of sand soil failure caused by leakage flow are explained.The main results of the study are as follows:(1)The total head of sand seepage over the leakage reaches a peak value with the increase of the leakage water pressure.The "hole" phenomenon in the destruction of sand is observed through the transparent plexiglass box device,and once the critical leakage water pressure corresponding to the peak value is exceeded,The soil skeleton over the leakage is completely destroyed,and the soil above the leakage forms a mixed fluid with the coupling of soil and water.Cavity is the link between seepage and flowing soil.In addition,the experimental results show that the smaller the leak aperture,the greater the critical water head and leakage water pressure to the peak value.(2)Based on the leakage test of different particle gradients,the variation of average hydraulic gradient of sand seepage was fitted.The variation of hydraulic gradient of seepage is similar to that of total head.Based on the physical parameters of the soil,the classical flow soil formula of Taishaji,?.?.???????,Mao Changxi and Shajin xuan are selected to verify respectively.The results show that the ?.?.??????? theoretical formula is more suitable for the critical hydraulic gradient of sand seepage failure caused by leakage flow.(3)Based on the fractal theory of rock and soil particles,the relation between different graded samples and fractal dimension D is solved,and the relationship between the fractal dimension D and critical hydraulic gradient is established.Combining a large number of soil seepage failure tests,the fractal dimension D and the critical gradient are roughly inverse relation.The more accumulation of particles gradually,the smaller the critical hydraulic gradient.(4)In the field of rock and soil seepage fractal field,fractal dimension D also has segmental fractal characteristics.The fractal dimension D is divided into three regions with the boundary of 2.35 and 2.65.In the first region,the critical gradient of most soil samples is greater than 0.8,and the failure type belongs to fluid-soil type.The failure of fluid-soil is in the first range of the first interval,forming mutual corroboration.In addition,in the fractal dimension subsection 2.35 < D < 2.65(second zone),between the critical gradient of one and three areas,the critical hydraulic gradient of most of the critical hydraulic gradient is between 0.5 and 0.7,and the hydraulic gradient fluctuation of fluidization stage is within the range of two zones,combined with the damage of sand caused by leakage flow.The complete destruction of its own soil skeleton has the property of flowing soil,but finally a mixed fluid is formed under the action of soil and water coupling.Therefore,combined with the experimental phenomenon and seepage hydraulic gradient,the fluidization stage is considered to be a transitional type of large area pipeline failure.