Effect Of Seepage Research Articles

Effect of seepage on soil arching effect in deep shield tunnel

Shield tunneling and post-tunneling steady seepage are accompanied by stress and displacement variations, which could induce and influence the soil arching effect. Although there are many studies on the tunneling-induced soil arching effect, the research about the effect of seepage on soil arching effect is extremely lacking. In this study, a numerical model is firstly established and verified by field data. Then, a series of numerical models, whose simulation method of steady seepage is verified by adopting the conformal mapping technique, are established to study the soil arching evolution of deep-buried tunneling and post-construction steady seepage. The results indicate that seepage leads to an increase in effective vertical stress, which is consistent with the existing theory. The seepage weakens the soil arching effect resulting in the height of the arch zone reducing from 2.38D (D is the tunnel diameter) to 1.25D. The seepage leads to the further development of ground consolidation settlement, but the differential displacement in the soil mass decreases. The ground reaction curve in the steady seepage condition shows a bigger value than that after excavation. It is reasonable to control the ground loss ratio in the range of 0.5–1.0%, which can minimize overburden pressure with moderate ground deformation.

Permeability Coefficient of Concrete under Complex Stress States.

Hydraulic structures are typically subjected to long-term hydraulic loading, and concrete-the main material of structures-may suffer from cracking damage and seepage failure, which can threaten the safety of hydraulic structures. In order to assess the safety of hydraulic concrete structures and realize the accurate analysis of the whole failure process of hydraulic concrete structures under the coupling effect of seepage and stress, it is vital to comprehend the variation law of concrete permeability coefficients under complex stress states. In this paper, several concrete samples were prepared, designed for loading conditions of confining pressures and seepage pressures in the first stage, and axial pressures in the later stage, to carry out the permeability experiment of concrete materials under multi-axial loading, followed by the relationships between the permeability coefficients and axial strain, and the confining and seepage pressures were revealed accordingly. In addition, during the application of axial pressure, the whole process of seepage-stress coupling was divided into four stages, describing the permeability variation law of each stage and analyzing the causes of its formation. The exponential relationship between the permeability coefficient and volume strain was established, which can serve as a scientific basis for the determination of permeability coefficients in the analysis of the whole failure process of concrete seepage-stress coupling. Finally, this relationship formula was applied to numerical simulation to verify the applicability of the above experimental results in the numerical simulation analysis of concrete seepage-stress coupling.

Numerical Analysis of the Effect of Groundwater Seepage on the Active Freezing and Forced Thawing Temperature Fields of a New Tube–Screen Freezing Method

To more comprehensively explore the mechanism of the active freezing and thawing process of a new tube–curtain freezing method in construction, the temperature field of the new tube–curtain freezing process is analyzed using finite element software to establish a numerical model. Six paths were set up upstream and downstream of the model and around the top steel tube to analyze the development of frozen soil curtains during active freezing and forced thawing. The results show that, due to the effect of seepage, the cold energy generated by the upstream frozen pipe will be carried to downstream by water, which leads to the asymmetry of the frozen soil curtain. A greater seepage rate leads to a more pronounced the influence on the development of the temperature field. During the process of forced thawing, the first 15 days of the frozen soil curtain heating rate are fastest; thus, it is necessary to monitor the thawing settlement intensively during this period. By comparing different heads of water and different forced thawing temperatures, it was found that a bigger head of water results in a longer thawing time. At a constant head of water, a higher thawing temperature results in a shorter thawing time, with the thawing time at 50 °C being about 0.5 times that at 5 °C. Low-temperature thawing can be chosen to control the cost; however, when the head of water is large, high-temperature thawing can significantly shorten the thawing time. In addition, the new tube–curtain freezing method has little influence on the surrounding environment, along with a short construction period and low construction cost, in accordance with the concept of sustainable development.

Analytical study on the seepage field of EPBS and preliminary discrimination of spewing

Considering the two-dimensional seepage effect of a soil chamber, the spewing problem of an earth pressure balance shield (EPBS) is analysed by an analytical method. In this paper, an explicit analytical solution of the two-dimensional shield seepage field considering the water level distribution at the cutter surface is derived by using the separation of variables method and the superposition principle, and the unknowns in the analytical solution are solved by constructing a non-homogeneous system of equations. The correctness of the solution is verified by using the experimental and numerical simulation results, and a parameter analysis was conducted to investigate the effect of shield geometry and water head at the center of the cutter surface. The results show that water head on the cutter surface, screw conveyor angle, screw conveyor length and screw conveyor in the water flow and water pressure with an approximate linear relationship, reducing the screw conveyor diameter is most conducive to prevent spewing. On the basis of previous studies, the analytical solution can calculate the critical permeability coefficient for the occurrence of a spewing, and use the undisturbed soil or predicted permeability coefficient to preliminarily discriminate whether a spewing will occur. By comparing with the shield spewing example and with the shield one-dimensional analytical solution, it is proven that spewing discrimination based on this analytical solution is effective and more accurate. Since the analytical solution considers the water level distribution on the cutter surface, it can be used to discriminate the spewing of shields of any size.

Distribution Characteristics of the Geoelectric Field in Waste Dump Slopes during the Evolution of Instability Sources under Rainfall Conditions

To study the evolution of geological hazard sources of waste dump slopes under rainfall conditions, a physical model of a rainfall-affected slope was designed. The apparent resistivity of the slope rock and soil mass at different rainfall times was measured via the high-density resistivity method, and the formation process of internal disaster sources of the rainfall-affected slope was obtained. The variation characteristics of the resistivity of the rain-affected slope were analyzed when it had a weak surface and crack development. Based on the three-water model and Maxwell conductivity formula, the evolution process of geological hazard sources of the rainfall-affected slope was summarized. A resistivity response mechanism equation for rainfall-induced slope hazard sources was derived and compared to the Archie formula, verifying the model rationality. The test results showed that the behavior of the rainfall-affected slope conforms to the saturated–unsaturated dynamic cycle process. The apparent resistivity was positively correlated with the development of slope pores and cracks and negatively correlated with the water content in the slope. The apparent resistivity increased during fracture development and decreased during water seepage. In the slope failure and disaster process, the apparent resistivity varies under the coupling effect of crack development and water seepage. During the formation of geological hazard sources, the apparent resistivity abruptly changes and fluctuates. Therefore, according to the abrupt changes and abnormal fluctuations in the apparent resistivity detected, the development of geological hazard sources of slopes can be determined.

Analytical and Numerical Solutions for the Effect of Seepage on the Bearing Capacity of Rock Masses

Analytical and Numerical Solutions for the Effect of Seepage on the Bearing Capacity of Rock Masses

Size Effects of Rough Fracture Seepage in Rocks of Different Scales

Percolation experiments were conducted on coal samples with various fracture lengths and inclination angles under different stress conditions using a gravity-loaded rock percolation test device. The goals of these experiments are (1) to improve the technology for protecting water resources while mining coal and (2) to enhance the research on how the size effects of fracture affect seepage. A three-dimensional seepage model was constructed using COMSOL numerical simulation software for larger fracture lengths ranging from 1 to 30 m to investigate the seepage pattern under the coupling of fracture roughness, fracture width, and other factors. Multiple regression analysis was used to investigate the effects of different factors on seepage from large and small fractures independently. The results show that, under laboratory conditions, for fracture lengths 10–70 mm (small length), permeability increases non-linearly with an increase in fracture length, and the overall increase is approximately 1.8 times. Whereas, for fracture lengths of 1–30 m (large length) in the simulation, permeability decreases and then increases with an increase in fracture length, and the overall change is approximately 0.03 times. The permeability varies in three stages (1–8 m obvious change, 8–23 m stabilization, 23–30 m stability) under different fracture lengths, widths, and roughness conditions. Acritical size was found to exist. The effect of fracture length on large length fracture seepage and small length fracture seepage was further verified by parameter sensitivity. The results of this study further reveal the mechanism of fracture seepage under coupling of fracture geometry size stress.

A multi-scale coupled productivity prediction model for conflagration compression fracturing of shale

A multi-fracture pressure flow regime coupled productivity prediction model considering shale gas adsorption and desorption, mass transfer and diffusion and cross-scale zoning was established based on cross-scale seepage characterization in unmodified area, interstitial matrix area, main fracture area, branched micro-fracture area and broken damage area formed from by conflagration compression fracturing. Then, geometric similarity, hydropower similarity and coupled iteration were used to build the model and complete the calculation. Finally, the effects of regional cross-scale seepage, number of fractures, production pressure difference, and fracture zone scale on gas well productivity were analyzed. The following results were obtained. First, the seepage flow of shale gas in different fractured areas is a continuous changing process. Among them, the unaffected area is dominated by transition flow and slip flow while continuous flow exists in the microfracture area-wellbore broken area and artificial fracture area. Second, the productivity of gas wells increases with the increase of fracture length and number, but the productivity increase tends to be stable after the fracture length exceeds 2 m. It is worth to mention that the increase of the number of fractures is more conducive to improving the productivity of shale gas under this condition. Third, when the number of high energy gas fractures is 6, its mining capacity is equivalent to that of hydraulic fracturing fractures with a half-fracture length of about 100 m. Fourth, when the production pressure difference exceeds 22 MPa, the free gas production capacity shows a decreasing trend. Therefore, the preferred production pressure difference is about 22 MPa. Fifth, the greater the number of artificial fractures, the greater the contribution of the increase in the diffusion coefficient to productivity, and the existence of wellbore fracture zone is also conducive to the stimulation of gas wells.

Формирование экологического ущерба при складировании сульфидсодержащих отходов обогащения полезных ископаемых

The mining industry is one of the most challenging in ensuring environmental safety. During the last century, the Karabash Copper Smelting Plant was processing sulfide ores and depositing the tailings into storage facilities that now occupy an area of more than 50 hectares. To date, abandoned tailings are a significant source of natural water, air, and soil pollution in the Karabash city district. The article comprehensively examines the environmental impact of the Karabashmed copper smelter, one of the oldest metallurgical enterprises in Russia. The effects of seepage from the two Karabashmed tailings facilities on water resources were assessed. We revealed that even outside the area of the direct impact of processing waste, the pH of natural water decreases to values 4-5. Further downstream, the infiltration water from the tailings pond No. 4 reduces the pH of river water to 3.0-3.5. The presented results of environmental engineering surveys are derived from sampling water and bottom sediments of the Ryzhiy Stream and the Sak-Elga River, sample preparation, and quantitative chemical analysis. The study revealed significant exceedances of the maximum permissible concentrations for a number of chemical elements in the impact zone of the copper ore processing tailings.

Experimental Assessment of Combined Contribution of Coal Mass Diffusion and Seepage to Methane Migration under In Situ Stress Conditions

Gas diffusion and seepage characteristics can reflect the transport capacity of coal mass pores and fracture channels and are also important parameters to determine the mechanism of methane migration. Currently, research on the contribution of diffusion and seepage to methane migration is carried out mainly by fixing one parameter and discussing the effect of the other. However, few studies are focused on the dynamic combined effect of diffusion and seepage on methane migration under in situ stress conditions, which is mainly attributed to difficulties in obtaining the parameters of diffusion characteristics of coal mass under stress. This paper presents a study on the dynamic combined effect of coal mass diffusion and seepage on methane migration under different in situ stress conditions. First, the physical structure model of coal mass under high and low stresses was constructed based on the variations of coal mass porosity, permeability, and computed tomography under different stresses. Meanwhile, based on the methane desorption and diffusion curves of coal mass under different stresses, the diffusion parameters of coal mass were obtained according to the corresponding diffusion model. Furthermore, the coupled multifield model was used to calculate the methane migration in coal mass during the process of borehole extraction with different stresses. The results suggest that the difficulty in methane extraction is directly proportional to the stress, but a huge discrepancy exists in methane migration under high and low stresses principally due to the change of dominant factors in methane migration of coal mass under different stresses. Additionally, given the essential factors controlling the overall methane migration of coal mass under high and low stresses, a joint technical method for promoting methane flow rate under multicoal seam conditions in the same mining area was proposed, i.e., hydraulic fracturing and sand injection (increasing permeability) in coal seams under low stress and simultaneous application of hydraulic fracturing and sand injection and multistage cavitation pressure relief (increasing diffusion) in coal seams under high stress. The research results obtained in this paper provide theoretical support for understanding the methane migration mechanism in coal seams under in situ stress and stimulated gas production.

A Coupled Seepage–Deformation Model for Simulating the Effect of Fracture Seepage on Rock Slope Stability Using the Numerical Manifold Method

Modeling seepage problems in rock fractures is an interesting research approach to evaluating rock slope instability that is attracting increasing attention. In the present study, a coupled seepage–deformation model based on the numerical manifold method (NMM) is proposed, and the flow of groundwater in a fracture network coupled with the effects of seepage pressure and rock deformation are discussed. A global equilibrium equation of the system and a local factor of safety (FoS) of arbitrary rock fractures are derived based on the principle of minimum energy, and a series of verification examples are calculated. The simulation results show the robustness and effectiveness of the proposed numerical model. Finally, a rock slope collapse accident caused by seepage effects is simulated by the proposed method, and the failure process of the slope is reproduced. The simulation results show that excessive hydraulic pressure caused the vertical fractures to open and augmented the rock mass deformation, eventually leading to the failure of the slope. The proposed method possesses the potential to simulate larger-scale engineering problems.

Development of multi-field rock resistivity test system for THMC

Abstract. To study the relationship between rock mechanical properties and resistivity under deep-underground environmental conditions, a rock resistivity test system, which can realize the simultaneous control of temperature, pressure, seepage, and the chemical environment, was developed; further, a corresponding specimen-sealing method was explored. The system primarily comprises a triaxial system, chemical permeation system, temperature control system, and test control system. The reliability of the system was verified through tests and preliminary experiments. The resistivity of fractured granite specimens under coupling of seepage and temperature and the resistivity of unfrozen and freeze–thawed coals during triaxial compression were tested with this test system. The test results show that the temperature-induced resistivity change is greater at low seepage pressures for fractured granites, and the effect of seepage on rock resistivity is greater at lower temperatures. The resistivity change patterns of unfrozen and freeze–thawed coals during triaxial compression differ quite significantly. The resistivity of unfrozen coal specimens exhibits a decreasing trend in the initial compression stage and then gradually increases with rises in the deviatoric stress. After freezing and thawing, the electrical resistivity of coal decreases during the entire compression process.

Study on the Creep Characteristics and Fractional Order Model of Granite Tunnel Excavation Unloading in a High Seepage Pressure Environment

The creep associated with unloading surrounding rock during the excavation of deep tunnels seriously affects the stability of the tunnel, and a high seepage pressure will aggravate the strength attenuation and structural deterioration of the surrounding rock. Based on the background of the excavation-induced unloading of the surrounding rock of a deeply buried granite tunnel with high seepage pressure, in this paper we carry out a triaxial unloading seepage creep test that considers the effects of both excavation disturbance and seepage pressure. We also analyze the mechanism of unloading and seepage pressure leading to sample failure and construct a fractional creep damage constitutive model that considers the unloading effect. The results include the following findings, firstly, seepage pressure will affect the creep deformation of rock for a long time, and the circumferential expansion of the granite creep process is more obvious than the axial expansion. Secondly, a high seepage pressure will reduce the rock bearing capacity. Under 0, 2 and 4 MPa seepage pressures, the long-term strength of the samples are 193.7 MPa, 177.5 MPa and 162.1 MPa, respectively. Thirdly, the rock damage factor increases with increasing seepage pressure, time and deviatoric stress. Finally, the rationality of a fractional-order model that considers the effect of unloading and seepage is verified by the test data. These research results may provide some reference for the stability analysis of surrounding rock during excavation in environments under high-stress and high-seepage-pressure.

Gas-mechanical coupled crack initiation analysis for local air-leakage of compressed air energy storage (CAES) cavern with consideration of seepage effect

The gas-tightness and stability of compressed air energy storage (CAES) cavern (usually with three-layered struction of sealing layer, concrete lining and surrounding rock) plays an important role for ensuring the power-generation efficiency of CAES system. Since the action of the compressed air with high temperature and high pressure would possibly cause the local damage of the sealing layer and lead to the air-leakage from the sealing layer to the surrounding rock, it is necassary to study the gas-mechanical (GM) coupled crack initiation behavior of the surrounding rock in order to provide a scientific basis for anti-cracking design and stability evaluation of CAES cavern. Currently, the GM coupled crack initiation are studied mainly by experimental and numerical methods but little by theoretical method, in which the gas pressure is taken as a static pressure regardless of the seepage effect. In this paper, the calculation formulea of GM coupled Mode I and Mode II SIFs are derived by the superposition principle with the consideration of seepage effect firstly. And then the criterion of GM coupled crack initiation is established based on our K-ratio criterion in order to analyze its mechanism for local air-leakage of CAES cavern. Finally, a gas seepage device is designed to conduct the tri-axial GM coupled compression tests of pre-cracked sandstone specimens on MTS815 hydraulic servo testing machine combined with PCI-II AE instrument to measure the crack initiation stress σi and initiation angle θC. Research results show both σi and θC are decreased with the increasing of gas pressure PG, while increased with the increasing of crack inclination angle β. All of these pre-cracked sandstone specimens have initiation mechanisms of Mode II. The prediction results of initiation angle with consideration of seepage effect is more closer to the test results than those of initiation angle without consideration of seepage effect, which can prove the validity of both our SIFs calculation formulea and the GM coupled criterion with consideration of seepage effect.

Seismic Characteristics of a Geotextile Tube-Reinforced Embankment and Shallow Foundations Laid on Liquefiable Soil

The ground in Saemangeum has a high water level and is mostly composed of silty soil and sand, which makes it susceptible to liquefaction and seepage effects. To investigate the seismic response of a geotextile tube-reinforced embankment and shallow foundations laid on a liquefiable soil, a simple spring type shaking table apparatus was developed. The variation in the response acceleration and shear stress-strain relationship were investigated, and the effect of soil improvement and reinforcement were explored, wherein one of the shallow foundations was laid on a coarse sand layer and reinforced by a polyester geotextile. The results showed that the main cause of damage to the embankment was seepage-induced liquefaction. Excessive surface accelerations were observed in the embankment soil due to lateral spreading, indicating the importance of analyzing the liquefaction potential of soils not only at the site area but also near embankments. Lastly, the inclusion of geotextile reinforcement and soil improvement only resulted in the slight reduction of shallow foundation settlement.

Numerical Evaluation of Slope Stability based on Temporal Variation of Hydraulic Conductivity

Slope failure is a common phenomenon all over the world on both man-made and natural slopes. Prolonged rainfall is one of the climatic factors which is largely responsible for slope failure. During heavy and prolonged rainfall, a part of the rainwater infiltrates through the soil and seeps into the slope. The infiltrated water lowers the matric suction and increases the porewater pressure. Eventually, the generated porewater pressure decreases the strength of the soil which results in slope failures. To evaluate the effect of rainwater seepage on slope stability, it is necessary to investigate the hydraulic conductivity of the slope soil. The objective of this study is to evaluate the effect of hydraulic conductivity on slope failure mechanisms. A finite element analysis of slope stability was conducted using Geo-Studio software. A numerical model was developed and calibrated with field monitoring data. The field monitoring data included the observation of hydraulic conductivity using a Guelph Permeameter. Afterward, the temporal variation of rainfall and hydraulic conductivity was incorporated into the SEEP/W program and the consequent changes in slope stability were evaluated in SLOPE/W. From the numerical analysis, with the identical strength parameters of the soil, different factors of safety were observed when the slope sections retain different hydraulic properties. Based on the numerical analysis, it was observed that hydraulic conductivity greater than 4×10-6 cm/s leads to slope failure. Periodic monitoring of hydraulic conductivity in the field may provide deep insight into rainfall-induced slope failures.

Study on the Seepage Effect of Dewatering for Deep Excavation with Cantilever Curtain in Soft Soil

Study on the Seepage Effect of Dewatering for Deep Excavation with Cantilever Curtain in Soft Soil

Dynamic numerical investigation of the long-term performance of a GSHP system considering groundwater seepage and layered subsurface coupling conditions

This study presents a novel analytical model for ground source heat pump (GSHP) which comprehensively considers the dynamic interaction between building load, borehole heat exchanger (BHE) and heat pump unit, and the BHE under groundwater seepage and layered subsurface coupling conditions, as well as the impact of seasonal ground temperature fluctuation. The model achieved comprehensively reflect the influence of complex geological condition, interaction of unit system and seasonal fluctuation on GHSP performance. The model is utilized to simulate and analyze the long-term dynamic performance and the evaluation index (SCOP) is introduced to evaluate it, the results indicate that, after the 20 years of operation, the SCOP decreases by 9.1% from 4.81 to 4.37. Moreover, by analyzing the influence of load variation on outlet liquid temperature, it can find that the maximum value of the outlet temperature of the circulating fluid and the building cooling load appear at different times, with a difference of 44 days. Finally, the effect of seepage and seasonal ground temperature fluctuates on GSHP performance is investigated, the results reveal that the seepage effect is beneficial to it, and the seasonal ground temperature fluctuate will have an adverse effect on it.

Effects of Hydrostatic Dissolution and Seepage on the Transport and Mechanical Properties of Glauberite

During the development of urban underground space in Chengdu, China, it was found that glauberite rocks in the Guankou formation of the Cretaceous system had extensive dissolution and exerted a serious impact on the safety of the project. At present, research on the transport and mechanical properties of glauberite under hydrostatic conditions in this area is limited. In this paper, the effects of hydrostatic dissolution and seepage on the transport and mechanical properties of glauberite are studied. The results show that the concentration of aqueous solution increases step by step with the increase in the dissolution time of glauberite in still water, indicating that the forward movement of the dissolution front of glauberite rock is not a continuous process and has intermittent characteristics. The dissolution and infiltration of mirabilite seriously deteriorates the physical structure of mirabilite, resulting in a decrease in elastic modulus and an increase in axial deformation, and a decrease in mechanical properties. There are a dissolution layer, dissolution front and undissolved area in the karst infiltration of calcium and mirabilite in the hydrostatic solution, so the mechanism of the calcium and mirabilite karst dissolution process is determined. Because of the dissolution characteristics of mirabilite, underground space development should prevent the uneven settlement of mirabilite, ground collapse, pit and chamber water gushing, corrosive groundwater and other geological problems.

Stability Analysis of the Surrounding Rock-Lining Structure in Deep-Buried Hydraulic Tunnels Having Seepage Effect

To clarify the factors affecting the stability of deep-buried hydraulic tunnels containing pore water, the elastoplastic theory and the Mogi-Coulomb strength criterion were used to derive the analytical solutions of stress on the surrounding rock-lining structure, tunnel wall displacement, and plastic zone radius in surrounding rock under different operating conditions. During this process, the seepage effect and surrounding rock-lining interaction were considered. The influencing rules of seepage action, intermediate principal stress coefficient, lining permeability coefficient, and lining thickness on the stability of the surrounding rock-lining structure were investigated in depth. The results show that the seepage effect significantly changed the stress distributions in the lining structure and surrounding rock, reduced the bearing reaction force, and lowered the tunnel stability. The bearing reaction force was decreased considerably from the intermediate principal stress, and the plastic zone radius in the surrounding rock and the tunnel wall displacement was obviously reduced. Moreover, the bearing reaction force was reduced, and the plastic zone radius in the surrounding rock and the tunnel wall displacement was increased with the decrease of the lining permeability coefficient. With increasing the lining thickness, the bearing reaction force was enhanced, and an apparent restriction on the development of plastic zone in the surrounding rock appeared at the beginning, but the restriction effect weakened subsequently. This research can theoretically provide references for analyzing the stability of hydraulic tunnels containing pore water.