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This paper presents a preliminary study of time evolution and spatial accumulation of progressive failure for ancient landslide deposits in Xinhua slope. According to the geological response after impoundment, the Xinhua slope has shown the spatial accumulation of deformation, such as ground cracks in the rear edge, toe collapse, local shallow slides in intense rainfall, and progressive creep displacement. Approximately 2 years of monitoring was performed for the Xinhua slope with the assistance of the global navigation satellite system (GNSS), unmanned aerial vehicles (UAVs), and field investigations. The deformation process of a reservoir landslide is considered to be a comprehensive and complicated combination of geological influence from various adverse factors. Field investigations and monitoring indicate that the major serious influence after completion of dam construction comes from the initial large-scale impoundment, the fluctuation of water level, and the existence of a flood season. The creep/slip deformation of slope deposits is a result of integration with adverse hydraulic conditions, e.g., strong rainfall, intense currents and transient seepage flow inside the slope deposits, and activation by water level fluctuation, which can be verified from the twofold evident deformation in the flood season. For the reservoir with daily regulation ability, the occurrence of evident deformations in July highlights that the regulation plan for water level in the flood season is important for controlling the deformation of slope deposits, where the fluctuation of the water level is no more than 10 m in the operation period.

This article presents the results of numerical modeling of seepage in an earth dam with a clay-cement concrete diaphragm for assessing the seepage strength of soils in transition zones at the contact with the diaphragm in the case of the occurrence of a vertical or horizontal crack in its body.

Due to the significant differences in development modes and operation rules of underground gas storage (UGS) and gas reservoir, the design of UGS construction has its own particularity and complexity. Key evaluation techniques in the process of gas reservoir being converted into underground gas storage were proposed and field application was analyzed. The construction and operation experience of the first batch commercial UGS in China was summarized, the mechanisms of multi-cycle injection and production with large flux in short-term was examined and some concepts were proposed such as the dynamic sealing of traps, the effective pore volume of UGS and the high velocity unstable seepage flow with finite supply. Four key technologies of UGS, i.e., trap sealing evaluation, gas storage parameter design, well pattern optimization and monitoring programs design were created. Preservation condition, storage capacity, effective injection & production and safe operation technology problems of UGS were solved respectively. The geological program design technology system of UGS construction in a gas field was gradually enriched and improved. These technologies have successfully guided geological plan design and implementation of UGS construction in a gas reservoir, the effects of gas storage and peaking capacity of the ramp-up cycles were great, and the actual dynamic was very consistent with design indicators. Key words: underground gas storage in gas field, dynamic sealing, gas storage parameter, productivity evaluation, injection-production well pattern, monitor scheme

Heterogeneous artificial core plate models with low permeability are designed, made and evaluated based on similarity theory of heterogeneous reservoir with low-permeability physical simulation by artificial core plate model; then, simulative experiments for seepage flow patterns can be carried out. Pressure data are obtained by pressure transducers symmetrically arranged in artificial core plate models to study on the seepage flow patterns in heterogeneous reservoirs with low permeability. Experimental results show that the pressure gradient around injection and production points is high, and the pressure gradient of diagonal corner is very low. The distribution of pressure gradient changes as plane heterogeneity of artificial core plate models changes. The higher permeability increases the spread range of pressure, but the enhancement of heterogeneity has a negative effect on pressure transmission at the same time. The effect of permeability is greater than the negative impact of heterogeneous when the overall permeability of plate model is at a very low level. Non-seepage flow section becomes smaller with the increase in permeability, and the proportion of quasi-linear seepage flow section which is more conducive to fluid flow raise as seepage flow section becomes larger.

Strong heterogeneity does exist in engineered heat reservoirs of enhanced geothermal systems (EGSs) due to different rock formation, pre-existence of natural fractures and uncertainties associated with the stimulation processes. Exploring the influence of reservoir heterogeneity on EGS heat extraction is of considerable importance to predict and fully evaluate the performance of EGSs. In this work, we take the reservoir as equivalent to a porous medium and employ a previously self-developed numerical model to conduct a series of simulations of the long-term heat extraction process of EGSs with different reservoir porosity distributions. Based on a detailed analysis to the effects of fluid seepage flow field on the heat extraction performance, we establish a method to quantify the heat extraction performance of EGSs with heterogeneous reservoirs using the seepage distribution data. We numerically test this method by taking a wide variety of heterogeneous reservoirs for EGSs. The method proves to have the capability of predicting the heat extraction performance of EGSs with miscellaneous heterogeneous reservoirs.

A distinction can usefully be made between suffusion, which describes the removal of fine particles by seepage flow from a body of soil without volume change, and suffosion, which is characterised by the removal of fine particles, accompanied by contractive volume change. Four pairs of gap-graded specimens were prepared, each pair comprising one glass bead specimen and one soil specimen with sub-angular particles, with nominally identical particle size distributions. The reconstituted specimens were isotropically consolidated to the same confining stress, and then subject to multi-stage upward seepage flow in a flexible wall permeameter. The glass beads and soil specimens with a finer fraction content of 0·20 exhibited suffusion. It appears that the susceptibility to suffusion of these specimens was not governed by particle type. Suffosion was evident in glass bead specimens with a finer fraction content of 0·35, but it was not triggered at an equal, or even larger, hydraulic gradient in soil specimens with nearly identical gradations. Particle type thus appears to be a factor governing the susceptibility to suffosion and should be considered when investigating this phenomenon.

Research on the permeability and pressure distribution characteristics of the roadway surrounding rock in the excavation damaged zone (EDZ) is beneficial for the development of gas control technology. In this study, analytical solutions of stress and strain of the roadway surrounding rock were obtained, in which the creep deformation and strain softening were considered. Using the MTS815 rock mechanics testing system and a gas permeability testing system, permeability tests were conducted in the complete stress-strain process, and the evolution characteristics of permeability and strain were studied over the whole loading process. Based on the analytical solutions of stress and strain and the governing equation of gas seepage flow, this paper proposes a hydro-mechanical (HM) model, which considers three different zones around the roadway. Then the gas flow process in the roadway surrounding rock in three different zones was simulated according to the engineering geological conditions, thus obtaining the permeability and pressure distribution characteristics of the roadway surrounding rock in three different zones. These results show that the surrounding rock around the roadway can be divided into four regions-the full flow zone (FFZ), flow-shielding zone (FSZ), transitive flow zone (TFZ), and in-situ rock flow zone (IRFZ). These results could provide theoretical guidance for the improvement of gas extraction and gas control technology. Keywords: Roadway, Excavation damaged zone, Viscoelastic-plastic analysis, Gas flow model, Permeability

This paper presents the effectiveness of the CO 2 injection process at different periods during gas-condensate reservoir development. Taking a real gas-condensate reservoir located in China's east region as an example, first, we conducted experiments of constant composition expansion (CCE), constant volume depletion (CVD), saturation pressure determination, and single flash. Next, a series of water/CO 2 flooding experiments were been investigated, including water flooding at present pressure 15 MPa, CO 2 flooding at 25.53 MPa, 15 MPa, which repents initial pressure and present pressure respectively. Finally, the core flooding numerical model was constructed using a generalized equation-of-state model reservoir simulator (GEM) to reveal miscible flooding mechanism and the seepage flow characteristics in the condensate gas reservoir with CO 2 injection. A desirable agreement achieved in experimental results and predicted pressure volume temperature (PVT) properties by the modified equation of state (EOS) in the CVD and CCE tests indicated that the proposed recombination method can successfully produce a fluid with the same phase behavior of initial reservoir fluid with an acceptable accuracy. The modeling results confirm the experimental results, and both methods indicate that significant productivity loss can occur in retrograde gas condensate reservoirs when the flowing bottom-hole pressure falls below dew point pressure. Moreover, the results show that CO 2 treatment can improve gas productivity by a factor of about 1.39 compared with the water flooding mode. These results may help reservoir engineers and specialists to restore the lost productivity of gas condensate.

The multi-physical processes during embankment breaching due to overtopping are complex and known to depend upon seepage flow through the embankment. A numerical breach model for progressive embankment breaching is proposed, taking the seepage flow into account including its influence on slope stability due to apparent cohesion effects. Overtopping and embankment surface erosion are computed using finite-volume methods applied to the 2D shallow-water and the Exner equations. The seepage flow is modelled using a Lattice–Boltzmann approach solving the 3D Richards’ equation. The modules are executed in a coupled manner with dynamically adapted boundary conditions. The breach side wall failures are considered using a geometrical approach based on critical failure angles. This approach is enhanced to account for apparent cohesion effects by dynamically adapting the critical failure angles as a function of the water saturation in a heuristic way, as a major enhancement compared to previous approaches. T...

When only limited borehole data are available, making optimum use of the existing data is crucial for performing a preliminary assessment of the investigated site. In this paper, the relationships between the borehole data and the permeability coefficient were first analyzed. These relationships were then used to establish a model for estimating the permeability coefficient of rock mass that takes into account the influence from the confining pressure on the seepage flow. The proposed model can reduce the number of hydraulic tests which are time consuming and very costly and allow the determination of change in the permeability coefficient throughout the borehole. The flow model could assist in providing important references for selecting an appropriate permeability coefficient in hydrogeological simulation and in evaluating the condition of large cracks developed in boreholes. In general, the seepage flow model developed in this study will contribute to the design practice of a tunnel project constructed in fractured rock masses.

The present study discusses a free boundary problem arising from the steady two-dimensional seepage flow through a rectangular dam. The free boundary location, the potential velocity field, and the pressure field have been found using successive linearisation method (SLM) by solving a nonlinear partial differential equation arising as a governing equation for this problem. The SLM is a newly developed method, which is a very efficient and reliable method to handle nonlinear problems. The numerical and the graphical representation of the solution has been discussed using MATLAB under the certain valid assumption.

Daily precipitation in Japan is currently increasing. River levees are constructed by compacting various natural materials. Internal erosion can be induced by suffusion, in which fines within the soil skeleton are transported to the toe of levee or outside the levee in an accordance with seepage flow. There are very few studies that refer to the effects of internal erosion on macro deformation and the instability of a levee. In this study, modeling tests of a levee were carried out to simulated floods in a 30g centrifugal field. Two types of material were prepared based on Kenny’s diagram, one classified as “stable” and the other as “unstable”. For stable soil, surface erosion could be observed on the landside of the levee. When the flood level was increased to overtop the crest, the levee caused catastrophic failure. Whereas, for unstable soil, tension failure was observed the toe, whereby, catastrophic larger circular slip was able to be confirmed.

Two suggestions are provided for expanding the scope of LEAP project for the next stage. The first suggestion is to perform undrained cyclic shear tests with addditional static deviator stress to represent more realistic stress conditions in soil-structure systems during earthquakes. The other suggestion is to perform centrifuge model tests with non-homogeneous soil layer such as mildly sloping ground of liquefiable sand overlain by a less permeable capping crust layer, leading to a unlimited flow failure of surface crust. Effects of void ratio redistribution and seepage flow will be studied in detail in this type of cetrifuge tests.

Fuzzy synthetic evaluation method has become increasingly crucial in deciphering reservoir dynamics by using an enormous amount of data that field operators acquire. These data contain valuable information about the subsurface process. Dominant seepage flow channel which can not be effectively evaluated and identified in fractured horizontal well–vertical well combined injection–production pattern is one of the most significant aspects of subsurface characterization in tight oil reservoir which can impact a project success. In this study, we present novel techniques to quantify dominant seepage flow channel by applying fuzzy synthetic evaluation method. First we construct dynamic and static indexes that affect the producing and developing of dominant seepage flow channel based on the characteristics of the relationship between fractured horizontal well and injection–production well. Second combined with the comprehensive fuzzy evaluation theory and the analytic hierarchy process, we build up a system to identify dominant seepage flow channel between fractured horizontal well and vertical water injection well and obtain the weight of the index evaluation to determine the S-type or inverted S-membership of each index function. The validity of using fuzzy synthetic evaluation to determine dominant seepage flow channel is verified by the interference well testing analysis results of fractured horizontal well pairs SP6 in Changqing oil field. The dominant seepage flow channel information based on the above method can provide strong basis for the comprehensive water control scheme of developing tight oil reservoir with water injection.

High groundwater flow velocity is a major challenge in many artificial ground freezing (AGF) projects, especially in groundwater control projects. That condition may be unfavorable for the ...

The polymer solution for oil displacement is subjected to strong shear action in practical application, and this action will affect its percolation characteristics in porous media. The effects of mechanical shearing on the solution properties and seepage characteristics of modified hydrophobically associated polymers and dendrimers with two different aggregation behaviours were studied. The results showed that mechanical shearing did not affect hydrophobic microzones. Polymers can re-associate to restore part of the network structure, thereby improving shear resistance (dendritic hydrophobically associating polymers > hydrophobically modified partially hydrolysed polyacrylamide). Polymers with ‘cluster’ aggregation behaviour enhanced solution performance, enabling them to establish higher resistance coefficient (RF) and residual resistance factor (RRF) in porous media but also bringing about injection difficulties. Increasing the injection rate would increase the injection pressure, but the established RF and RRF showed a downward trend. Mechanical shear pretreatment effectively improved the injectability of the polymer. To achieve polymer injection and flow control, pre-shearing polymer solution and low-speed injection can be used in field applications.

Seepage analysis is very important issues that should be considered at designing of an earthen dam. For this purpose, a research study was conducted on Harreza dam, which is an earthen dam located at about 15 km, south-west of El-Khmiss city, Algeria. In the study, the amount of seepage through and under body of the main dam is computed; profile of phreatic line is simulated for different scenarios and compared with the observed data. For this study, SEEP/W, the sub-program of Geo-Slope software is used. Data pertaining to design parameters and dam geometry are given as input to the software to compute the unknown parameters. Validation of the model is made by comparing simulated results against the observed ones; this is done to ensure model applicability. The comparison shows a high efficiency and good fitness.

Sediment transport is a geophysical phenomenon in which sediment particles are driven to move in streamwise and vertical directions by various forces. Almost all existing formulas of sedime...

In geotechnical engineering seepage of diaphragm walls is an important issue which may cause engineering disasters. It is therefore of great significance to develop reliable monitoring technology to monitor the leakage. The purpose of this study is to explore the application of a distributed optical fiber temperature measurement system in leakage monitoring of underground diaphragm walls using 1 g model tests. The principles of seepage monitoring based on distributed optical fiber temperature measurement technology are introduced. Fiber with heating cable was laid along the wall to control seepage flow at different speeds. The temperature rise of the fiber during seepage was also recorded under different heating power conditions. In particular the effect of single variables (seepage velocity and heating power) on the temperature rise of optical fibers was discussed. Test results indicated that the temperature difference between the seepage and non-seepage parts of diaphragm wall can be monitored well using fiber-optic external heating cable. Higher heating power also can improve the resolution of fiber-optic seepage. The seepage velocity had a linear relationship with the final stable temperature after heating, and the linear correlation coefficient increases with the increase of heating power. The stable temperature decreased with the increase of flow velocity. The findings provide a basis for quantitative measurement and precise location of seepage velocity of diaphragm walls.

The coefficient of permeability (k value) is an important parameter in civil engineering practice, in hydrology and hydrogeology. It can be determined by field test or by means of laboratory testing. The goal of this paper is to assess this parameter by creating a laboratory model and by validating its results using finite element computer code. The model tests provide that can be applied for estimating permeability of different soils. In a physical model medium-grained sand was tested in the laboratory, for understanding the effects of different flow rates on the validation of the measurement result, the numerical simulation of the physical model was constructed using FEFLOW. Two model variants were developed and both variants were calibrated and validated. Subsequently, the results were converted to real variables based on the model laws. The physical model provides the flow rate of the well in medium-grained sand with sufficient accuracy if the real size of the drawdown is between 0,5 and 1,7 m.

In Southwest China large-scale hydropower projects, the hydraulic conductivity and fracture aperture within the rock mass of a reservoir bank slope has dramatically undergone a time series of evolution during dam abutment excavation, reservoir impounding and fluctuation operation, and discharge atomization. Accordingly, seepage control measures by hydro-structures such as drainage or water insulation curtains should be guided by scientific foundation with a dynamic process covering life-cycle performance. In this paper, the up-to-date status of studying the evolution mechanism of seepage characteristics relating to fractured rock hydraulics from experimental samples to the engineering scale of the rock mass is reviewed for the first time. Then, the experimental findings and improved practice method on nonlinear seepage flow under intensive pressure drives are introduced. Finally, the scientific progress made in fractured rock seepage control theory and optimization of the design technology of high-steep slope engineering is outlined. The undertaken studies summarized herewith are expected to contribute to laying a foundation to guide the further development of effective geophysical means and integrated monitoring systems in hydropower station construction fields.

Suffusion is a typical form of the internal erosion, which leads to worldwide failures of embankment dams. Extensive investigations have been carried out to characterize suffusion process. However, less research has been focused on the lasting heterogeneity development by suffusion physically and quantitatively, despite the phenomenon been found in literatures. This paper proposes a vertical layered theoretical model based on the force balance of movable particles under one-dimensional upward seepage on gap-graded specimens. In the model, the finer particles loss was deduced respectively in every layer, combined with the coupled calculation including the seepage flow, the soil particles movement and the soil structures changes. The model was verified with experiments and showed a good consistency in the critical hydraulic gradient, layered water head, seepage velocity, finer particle loss and hydraulic conductivity. Finally, suffusion induced soil grading changes and the implications to the suffusion development are discussed quantitatively. The results indicate that the theoretically modeled soil heterogeneity changes are consistent with the suffusion phenomenon and the experimental observations. The outlet and inlet are more sensitive to suffer suffusion under upward seepage, as the two layer have more violent fine particles loss and soil grading coarsening. The layered model can theoretically simulate the development of suffusion with the sequential changes of the soil structures and serves as a new approach to understand the process in cohesionless soil.

Seepage flow through embankment dam is one of the most influential factors in failures of them. Thus, the monitoring and accurate measuring of seepage are crucial for the safety and construction cost of an embankment dam. In this study, an efficient data-intelligence paradigm comprised of Extended Kalman Filter integrated with the Feed Forward type Artificial Neural Network (EKF-ANN) scheme, as the main novelty, was developed for precise estimation of the daily seepage flow through embankment dam in Fontaine Gazelles Dam in Algeria. Here, three robust machine learning approaches, namely the Multilayer Perceptron (MLP) Neural Networks, Radial Basis Function-Neural Networks (RBF-NN), and Random Forest (RF), were examined for evaluating the capability of the EKF-ANN in the prediction of seepage flow. According to the obtained results, the EKF-ANN paradigm outperformed the MLP, RF, and RBF-NN, respectively. Besides, the leverage approach was applied to report the applicability domain of provided models.

The mechanism of gas-water two-phase percolation was previously characterized based on percolation experiments. However, the changes in the gas-water interface and the volume fraction of the two phases in the process of gas-water percolation in porous media cannot be accurately described by experiments. This paper uses core casting thin sections and AutoCAD software to establish a digital core. Based on the idea of level set, a two-dimensional gas-water seepage model in microscopic pores is established. The finite element numerical simulation software is used to solve the model to describe the gas. The changes of the water two-phase interface are visually displayed. At the same time, Darcy’s law is used to compare the relative permeability curve obtained from the gas-water two-phase seepage experiment with the relative permeability curve obtained from the gas-water two-phase seepage finite element simulation. The results show that the gas-water two-phase seepage experiment and the gas-water two-phase seepage finite element numerical simulation have basically the same characterization of the seepage ability of porous media. There is obvious fingering phenomenon in the process of gas flooding, and the gas preferentially passes through the large pore throat. The smaller the pore throat, the greater the velocity of gas passing through the pore throat. The gas-water two-phase interface change described by the numerical simulation of the gas-water two-phase flow based on the digital core is more reliable.

In cold regions, frequent incidents of soil slope failures occur due to snowmelt and rainfall. These failures are triggered by an increase in the degree of saturation of soil due to infiltration of water derived from rainfall and snowmelt. This study investigates a soil slope failure occurred on November 27, 2015 at a cut slope of an expressway in Hokkaido, Japan. The soil slope failure is investigated using a recommended stability assessment approach considering non-isothermal coupled seepage flow simulation followed by a limit equilibrium slope stability analysis. It is concluded that at the thawing period, the slope stability is affected by rainfall and snowmelt water infiltration and later in November the failure happened due to overflow of water from a drainage ditch.

Problems concerning the extraction of the fluid from an oil well under conditions of a constant pressure drop or a constant flow rate are considered on the basis of a model describing a seepage flow in a fracture located in an oil or gas reservoir. Exact solutions are obtained and, on the basis of these solutions, the effect of the collecting characteristics of the reservoir and the fracture is analysed as well as the effect of the rheological properties of the saturating fluid on the evolution of the pressure in the fracture, the output from the oil well and the dynamics of the pressure in the oil well.

The head difference between the inside and outside of an excavation leads to seepage flow into the excavation. High seepage velocities lead to high seepage pressures that decrease the effective stresses. In extreme cases, the soil fluidizes and cannot sustain the seepage forces, which causes the soil-water mixture to flow into the excavation site. The problem of hydraulic failure is simulated using the Material Point Method (MPM). The ability of MPM to simulate this phenomenon is shown and some concluding remarks are presented.