Analysis Of Pore Water Pressure Characteristics Of Soil Core Wall

Due to its many advantages,earth-rock dams have been rapidly developed in recent years.The heights of a series of earth-rock dams under construction and proposed in China have also reached 300 m or more.Therefore,the safety and stability of high earth-rock dams have received extensive attention.Because the pore water pressure of soil core wall is difficult to dissipate effectively and control and influence the stability of the dam body during construction,the pore water pressure of the core wall during the impoundment period has abruptly changed and is an important indicator to study the hydraulic fracturing of the core wall.Therefore,there are many experts and scholars have conducted extensive research on the stress deformation and the pore water pressure of the core wall of the high earth-rock dam during the construction period and the impoundment period.On the basis of previous research results,this article will use the existing Pubugou core-wall rockfill dam as an engineering example,based on the Duncan Chang E-B constitutive model and the basic theory of unsaturated soil and unsteady seepage theory,using the MIDAS/GTS finite element software to establish the three-dimensional finite element model calculates and analyzes the static analysis of the stress and deformation during the construction period and the impoundment period,the pore water pressure formation mechanism,characteristics and influencing factors during the construction period,the pore water pressure characteristics and influencing factors of the core during the impoundment period,and got the following main conclusions:(1)During the construction period and the impoundment period,the dam body deformation is basically reasonable,the stress distribution of the dam body is even,the dam body is under pressure,and there is no tensile stress in the core wall.During the construction period,the stress of the dam body is symmetrical along the axis of the dam.In the impoundment period,due to the effect of water pressure on the upstream surface of the dam body,the overall stress value on the upstream surface of the dam body is larger than the completion period.(2)The vertical stress and the first principal stress of the dam in the construction period and the impoundment period are in a hump-shaped distribution,and the arch effect coefficient is the smallest near the axis of the 1/3 dam height,and the arch effect of the core wall is most intense near the axis of 1/3 dam height and weakest at the crest.The arch effect only affects the vertical stress and the first principal stress of the dam,and has no influence on the third principal stress of the dam.At the same elevation of the core,the upstream water pressure is less than the stress of the core wall,the stress resistance of the core wall against hydraulic fracture is better,and no hydraulic fracturing occurs.(3)The problem of the generation and dissipation of pore water pressure during construction is very complicated.The generation of pore water pressure is caused by the continuous increase of the total stress of the soil during construction,the soil is compressed,the void ratio is reduced,pore water cannot dissipate timely and effectively,and assumes a part of earth pressure,causing the pore water pressure to increase continuously.When the construction is completed,the earth pressure is not increasing,the pore water pressure begins to dissipate,and the dissipation rate is slow.Within a few years or even more than ten years after completion,the pore water pressure is still high and should be given sufficient attention.(4)The distribution of pore water pressure in the core wall is basically similar during the construction period when the core wall has different drainage conditions,different water content,different permeability coefficients and different construction rates.The pore water pressure of the entire core wall gradually decreases from the largest point to the surrounding,showing a closed circular equipotential line distribution,under different conditions,the maximum pore water pressure of the core wall appears near the height of the core wall by 1/3 to 1/2.(5)The pore water pressure during the construction period is affected by the main factors such as earth pressure,seepage diameter,drainage conditions,water content,permeability coefficient and construction rate;the earth pressure is the mechanical condition that affects the pore water pressure,diameter and core wall drainage conditions are boundary conditions that affect pore water pressure,the water content and the permeability coefficient are the material conditions that affect the pore water pressure,the construction rate is the external condition that affects the pore water pressure.(6)The pore water pressure distribution rules of the core wall are basically similar under the two conditions of different impoundment periods without considering and considering the construction process;the soaking lines within the dam shell are basically horizontally distributed,and the soaking lines within the core wall is inclined.Extending to the downstream of the core wall,the pore water pressure in the core wall has abruptly changed.Without considering the influence of the construction process,the greater the impoundment speed,the more obvious the hysteresis of the soaking line,the steeper the change,and the lower the pore water pressure in the core wall;when considering the influence of the construction process,the pore water pressure and saturation area of the core wall all have been reduced.The greater the impoundment speed,the steeper and steeper the soaking line of the core wall,The pore water pressure equipotential lines in the core wall is abruptly changed and the phenomenon of concentration is more obvious.(7)There are many factors that affect the pore water pressure in the core during the impoundment period,including the impoundment rate,the permeability coefficient of the core wall,the infiltration path,and the stress field generated during the construction process.