Abstract:Seepage-induced failure may disable the bearing capacity of foundations in dams and embankments. However, the evolution mechanism of the seepage failure process in granular soils is not well understood. In this paper, a series of laboratory hydraulic tests were performed to investigate the seepage failure process in sandy gravels and fine-grained sands. Seepage behaviors of the hydraulic gradient, seepage flow velocity, and permeability coefficient were observed, and then, the Reynolds number was obtained to d… Show more
“…The study of the seepage evolution model is a critical technological issue for the construction and O&M (operation and maintenance) of important facilities located on the earth's surface and underground [78], such as infrastructure embankments [79,80], tailings ponds and dams [81,82], and tunnels and pipelines [83,84]. However, when considering seepage problems in the loess region, it is always based on the macroscopic piston flow based on Darcy's law [85].…”
Section: Discussion 41 the Formation Process Of The Seepage Evolution...mentioning
confidence: 99%
“…Furthermore, since the voids are filled with contrast agents, the initial voids become intermediate apertures (2.0~5.0 mm). The voids in this interval are in a dynamic change of expansion, develop-ment, and destruction accompanied by seepage erosion [82]. Therefore, there is not much fluctuation in the number and volume of voids.…”
Section: Evidence For the Seepage Evolution Modelmentioning
Preferential flow is widely developed in varieties of voids (such as macropores and fissures) in loess areas, affecting slope hydrology and stability and even leading to geological disasters. However, the model of seepage evolution with dynamic preferential flow is not clear, which obstructs the disclosure of the mechanism of landslides induced by the preferential flow. This study aimed to capture the seepage and occurrence status of water in loess voids, explain the variability characteristics of the loess pore structure, and reveal the seepage evolution model of dynamic preferential flow. Preferential infiltration experiments were conducted by combining X-ray computed tomography (X-ray CT) nondestructive detection with contrast techniques under dynamic seepage conditions. Three-dimensional (3D) visualized reconstruction, digital image correlation (DIC), image processing, and quantitative analyses were performed in AVIZO 2019.1, including two-dimensional (2D) and 3D characteristics of preferential flow distribution and macropore changing, dynamic variation of the porosity, pore number, volume, dip angle, and connectivity. Results showed that (1) preferential flow exists under saturated and unsaturated conditions in loess with strong uniformity and anisotropy; (2) preferential flow not only migrates into existing connected macropores, but also connects the original isolated pores into channels and forms larger percolation groups of contrast medium under the gradually increased high pressure; (3) the seepage develops with the evolution model of ‘preferential flow–piston flow–preferential piston mixture flow–piston flow’ in the dynamic process. The new insights into the characteristics of the seepage evolution in undisturbed loess under dynamic preferential flow will enrich the understanding of loess seepage and provided an important reference for future research on the slope instability of the loess induced by preferential flow.
“…The study of the seepage evolution model is a critical technological issue for the construction and O&M (operation and maintenance) of important facilities located on the earth's surface and underground [78], such as infrastructure embankments [79,80], tailings ponds and dams [81,82], and tunnels and pipelines [83,84]. However, when considering seepage problems in the loess region, it is always based on the macroscopic piston flow based on Darcy's law [85].…”
Section: Discussion 41 the Formation Process Of The Seepage Evolution...mentioning
confidence: 99%
“…Furthermore, since the voids are filled with contrast agents, the initial voids become intermediate apertures (2.0~5.0 mm). The voids in this interval are in a dynamic change of expansion, develop-ment, and destruction accompanied by seepage erosion [82]. Therefore, there is not much fluctuation in the number and volume of voids.…”
Section: Evidence For the Seepage Evolution Modelmentioning
Preferential flow is widely developed in varieties of voids (such as macropores and fissures) in loess areas, affecting slope hydrology and stability and even leading to geological disasters. However, the model of seepage evolution with dynamic preferential flow is not clear, which obstructs the disclosure of the mechanism of landslides induced by the preferential flow. This study aimed to capture the seepage and occurrence status of water in loess voids, explain the variability characteristics of the loess pore structure, and reveal the seepage evolution model of dynamic preferential flow. Preferential infiltration experiments were conducted by combining X-ray computed tomography (X-ray CT) nondestructive detection with contrast techniques under dynamic seepage conditions. Three-dimensional (3D) visualized reconstruction, digital image correlation (DIC), image processing, and quantitative analyses were performed in AVIZO 2019.1, including two-dimensional (2D) and 3D characteristics of preferential flow distribution and macropore changing, dynamic variation of the porosity, pore number, volume, dip angle, and connectivity. Results showed that (1) preferential flow exists under saturated and unsaturated conditions in loess with strong uniformity and anisotropy; (2) preferential flow not only migrates into existing connected macropores, but also connects the original isolated pores into channels and forms larger percolation groups of contrast medium under the gradually increased high pressure; (3) the seepage develops with the evolution model of ‘preferential flow–piston flow–preferential piston mixture flow–piston flow’ in the dynamic process. The new insights into the characteristics of the seepage evolution in undisturbed loess under dynamic preferential flow will enrich the understanding of loess seepage and provided an important reference for future research on the slope instability of the loess induced by preferential flow.
“…Many scholars have studied the effects of physical and mechanical properties of soil on the seepage and bank-slope stability of flood control dikes. Based on the change in the microstructural arrangement of soil particles, the microscopic change in the permeability coefficient of soil is studied experimentally [45][46][47]. The coupling equation of seepage and erosion shows that the pore water pressure in soil increases until the hydraulic gradient is greater than the critical hydraulic gradient, and the fine particle phase migrates and loosens from the soil, resulting in deformation and instability [48][49][50][51].…”
Flood-controlled ancient dikes play a significant role in flood control and have received widespread attention as historical and cultural symbols. Flood-controlled ancient dikes often undergo disasters, and research on their repair is receiving increasing attention from experts and scholars. This article studies the control of seepage and bank slope instability in flood-controlled ancient dikes. Starting from the repair of ancient dike materials, three types of work are carried out: a test of soil’s mechanical properties, finite element numerical simulation, and repair technology research. The research results show that the soil of the ancient dike site has hardened after being contaminated with waste oil from catering. The strength index of the ancient dike soil decreases and shows brittleness when the water content is 15% and the oil content exceeds 6%. The strength index and permeability coefficient of oil-contaminated soil improved using modified lime mortar (MLM), which was achieved using the method of MLM to repair oil contaminated soil. When the MLM content was 10% and the oil content was 6%, the friction angle of the soil sample reached its maximum value. When the MLM content was the same, the higher the density of the soil sample, the greater the friction angle and cohesion and the smaller the permeability coefficient. Establishing a finite element numerical model, through comparative analysis, it was found that after MLM remediation of oil-contaminated soil, the extreme hydraulic gradient of the ancient dike decreased by 31.3%, and the extreme safety factor of the bank slope stability increased by 31.2%. MLM pressure grouting technology was used to improve the soil during the remediation of contaminated soil at the ancient dike site. Through on-site drilling inspection, the effective diffusion radius of MLM grouting was obtained, and the plane layout and grouting depth of MLM pressure grouting were determined. The on-site water injection permeability test showed that using MLM pressure grouting technology can effectively repair oil-contaminated soil in the ancient dike while reducing the permeability coefficient by 8–15%.
Monitoring the seepage field is essential to characterize the operation of the earth dam. However, conventional seepage monitoring typically involves the use of a piezometer tube or pressure sensor for point distribution. A mathematical model incorporating the feedback of the temperature field on the seepage field was proposed based on experimental test observations. First, a theoretical analysis of the mathematical model is conducted, which includes examining the relationship between the variation of temperature field and factors, such as hydraulic gradient, water and soil temperature difference, hydraulic conductivity, thermal conductivity, specific heat, and time. Second, a homogeneous earth dam model is constructed in the laboratory with a distributed temperature sensor system to obtain synchronous information of the seepage–temperature field. Finally, the parameters of the mathematical model are quantified using observations from experimental tests, demonstrating good agreement between calculated and measured values. The experimental results indicate the feasibility of inferring seepage field monitoring information from the temperature field and elucidation of the interaction mechanism of the coupled fields. The quantitative mathematical model of the temperature field feedback on the seepage field is validated for its applicability in earth dams.
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