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This study investigates the behaviour of basal-reinforced embankments under seepage flow. For this purpose, physical embankment models with dimensions of 195 cm long, 100 cm wide and 110 cm high were constructed in the laboratory. The seepage gradient within the embankment was generated by applying a constant water head of 100 cm at the water compartment located behind the models. The unreinforced embankment experienced seepage erosion at the toe section which triggered deep-seated global failure. Due to the limited transmissivity of the non-woven geotextile, the geotextile-reinforced embankment exhibited similar pore-water pressure distribution to that of the unreinforced embankment, which resulted in lateral spreading failure between the base of the embankment and the non-woven geotextile. In contrast, the geocomposite drain, which has a higher in-plane flow capacity compared to that of the geotextile, significantly alleviated the pore-water pressures within the embankment. The behaviour of the physical models was verified numerically by variably saturated flow modelling conducted for a wide range of in-plane permeabilities for the basal reinforcement. The effect of increasing in-plane permeability of the basal reinforcement layer on pore-water pressure reduction was quantified irrespective of the geosynthetic type.

Silty sand slopes are prone to damage due to seepage or rainfall. A partial reinforcement method using short polypropylene fiber and sand mixtures was proposed to protect silty sand slopes from seepage flow failure. The effects and the reinforcement mechanism were explored. First, triaxial tests were performed on sand samples reinforced with fiber lengths (6 and 12 mm) and contents (0.25 and 0.50%) to verify the reinforcement effect. Then, model tests were conducted on sand slopes under lateral seepage flow and the failure mode with different fiber contents and reinforcement method were examined. The results showed that the cohesion and shear strength of sand were significantly improved with the increase of fiber content and length. The suction of unsaturated sand was also enhanced by the fibers. The change in stress-strain behavior from strain softening to strain hardening indicated that static liquefaction could be effectively prevented. The failure mode and extent of slope damage depended on the fiber content. However, it was noted that the slope surface with small reinforcement range performed similarly to that with large reinforcement range. In conclusion, the partial reinforcement method with short discrete synthetic fibers can be used as an effective alternative for slope reinforcement.

Internal instability or suffusion is one of the mechanisms of internal erosion in cohesionless soils, which is described by the loss of integrity of soil by seepage flow and is associated with the migration of finer particles. The contribution of the non-plastic finer fraction in a material is a key factor governing internal instability susceptibility. This study presents the experimental investigation of the influence of the fines content on the onset of internal instability of gap-graded sands using a pressure-controlled triaxial erosion device. The results indicate that the finer fraction in the soil has a significant influence on the hydraulic gradient at the onset of erosion. The underfilled soil with fines content less than 30% is vulnerable to suffusion at a relatively small hydraulic gradient. The transitional soil, whose fines content is between 30 and 35%, also exhibits suffusion, but the erosion onset hydraulic gradient significantly increases with increasing fines content. The overfilled soil with fines content larger than 35% exhibits suffosion or internal stability at a larger hydraulic gradient. The results also highlight the necessity of the multiple indices, such as mass loss, volumetric change and change in permeability, in evaluating the onset of various instability phenomena.

This paper presents a unified semi-analytical solution to investigate the passive earth resistance of unsaturated soils retained by a rigid wall in the framework of limit-equilibrium approach based...

The Loess Plateau can be considered as a landslide-prone area in northwest China. The genera consensus about the interaction between landslide deposit and terrace sediments is not well studied; this paper summarised 40 loess landslides in the South Jingyang Platform, Shaanxi Province, China to help understand of this issue. Four of the loess landslides with high mobility have been analysed in detail. Three trenches T1, T2 and T3 dug after the loess landslides LD37, LD11 and LD38 highlighted the landslide-induced changes in geomorphology and internal geometry of geology, respectively. Furthermore, observation of upwards seepage flow on the profile of trench T3 is believed to be the trigger of the high speed, and long runout flowslides in the study area. A newly developed sandbox apparatus is used to reproduce the landslide kinematics due to a mass travelling over an inclined plane. The sandbox experiments show that the sediments are sheared and pushed upwards after the collision with the deposits. The deposits are then wrapped in a space between sediments, which tends to form the ‘sandwich’ structure. The distal sediments are thrust when the loess deposits’ kinetic energy consistently dissipates, developing the accumulated folded strata. These results reveal the deposits’ interactions with the sediments in the study area and provide key guideposts regarding prevention and mitigation of loess landslide hazards.

In the basin of western China, four different kinds of lithological reservoirs are developed, including low-permeability sandstone, sedimentary tuff, shale and volcanic rock. There is generally a large difference in the micropore structure characteristics and distribution laws due to different reservoirs. The reserving capacity as well as the porous flowability, mechanism and laws are determined by the micropore structure characteristics and distribution laws of hydrocarbon reservoirs. Low-temperature nitrogen adsorption and desorption technology, high-pressure mercury injection experiment and nuclear magnetic resonance (NMR) testing technology are applied to study the micropore size, quantity, structure and distribution laws of four different kinds of lithological reservoirs as well as their similarities and differences of corresponding relation with macroporosity–permeability physical parameters. This paper also studies the movable fluid and nonlinear seepage flow characteristics of four different kinds of lithological reservoirs.

In this study, a novel apparatus was developed for the study of horizontal suffusion behavior of compacted soils under vertical stress. The apparatus consists of a permeameter chamber to accommodate specimen preparation and testing, a pressurized water supply system to generate horizontal seepage flow, a vertical loading system to apply and maintain the vertical stress onto the specimen, a pore water pressure measuring system and a soil–water collection system both to capture the characteristics of the suffusion. The apparatus is featured with a tailor-made flexible pressure bladder for vertical stress control and a modified vacuumizing method for specimen saturation. It has been verified to well perform during the horizontal suffusion, in terms of the specimen uniformity and repeatability of test results. Preliminary tests with this apparatus have been carried out to investigate the suffusion behavior of a gap-graded cohesionless soil. It can be found that suffusion can heterogenize the soil specimen along the seepage direction and that the level of vertical stress significantly affects the horizontal suffusion, such as the initiation and failure hydraulic gradient for suffusion as well as accumulated eroded weight.

Estimation of the magnitude and location of the lateral earth thrust on a retaining wall considering seepage flow effects within the backfill is necessary to examine the failures of such walls. In ...

A modified triaxial shear test apparatus was used to investigate the factors influencing the onset of suffusion (migration of fine particles from soil without a change in volume) and suffosion (migration of fine particles from soil with a change in volume or a local collapse of the soil structure). A new criterion was developed to predict the seepageincited internal instability phenomena of suffusion or suffosion. A flexible wall permeameter, a seepage flow control system, and volume change measurement instrumentation were designed and manufactured for the study.

This paper presents a formula to estimate the stable weight of a rubble mound for breakwaters, considering the tsunami-induced overflow and seepage flow, based on the theoretical force balance among the frictional resistance of the rubble mound, the tractive force of the water flow over the caisson to the rubble mound and the seepage force of the rubble mound through the breakwaters. A series of hydraulic model tests was conducted on the scale of 1/100 for the Kamaishi Harbor Mouth Breakwaters in order to confirm the effectiveness of the proposed formula. Using the test results, the stability of rubble mounds for breakwaters was evaluated from the geotechnical engineering and hydrodynamical points of view.

The purpose of this study was to determine the displacement and dynamic distribution characteristics of the remaining oil in the two development stages of water flooding and subsequent alkaline surfactant polymer (ASP) flooding. The well pattern types in the water and ASP flooding stages are a long-distance determinant well pattern and short-distance five-point well pattern, respectively. The type A displacement characteristic curve can be obtained using the production data, and the slope of the straight-line section of the curve can reflect the displacement strength of the oil displacement agent. A numerical simulation was carried out based on the geological model. The results revealed that the injected water advances steadily with a large-distance determinant water-flooding well pattern. The single-well water production rate increases monotonically during water flooding. There is a significant positive correlation between the cumulative water-oil ratio and the formation parameter. Differential seepage between the oil and water phases is the main factor causing residual oil formation after water flooding, while the residual oil is still relatively concentrated. The effect of the chemical oil-displacement agent on improving the oil-water two-phase seepage flow has distinct stages during ASP flooding. The remaining oil production is extremely sporadic after ASP flooding.

Suffusion is defined as the migration of fine particles caused by seepage flow through pre-existing pores of a soil structure made of coarse particles. This particle transportation changes the fine particle content and its distribution, possibly impacting the mechanical behaviour of eroded soil. Although limited research has been conducted on the post-erosion mechanical consequences under monotonic shearing, little attention has been paid to the impact of suffusion on the cyclic resistance and liquefaction potential of internally unstable soils. This paper investigates the cyclic and post-cyclic behaviour of a gap-graded cohesionless soil using combined triaxial-erosion apparatus. An internally unstable soil was chosen for the erosion test and was subjected to different seepage flow velocities and durations followed by cyclic loading and post-cyclic shearing. During cyclic loading, the eroded specimens with different residual fine contents behaved in a similar manner to a soil specimen constructed only of coarse particles. Regardless of the seepage velocity and duration, the erosion of fine particles resulted in significant increase in cyclic resistance. It is understood that eroded specimens with lower intergranular void ratios show higher resistance during cyclic loading, highlighting the importance of the intergranular void ratio in understanding the post-erosion mechanical behaviour of soils.

The uplift capacity of buried plate anchors depends on the tension sustained beneath the anchor. This study provides a detailed treatment of interface tension and the associated seepage flow and gap formation below the anchor. This behaviour is explored via large deformation finite element analysis using a thin highly compressible porous layer for the gap. The observed seepage effect is captured by a simple model using Hvorslev's intake factor, validated across a wide parameter range. This model for uplift capacity at various pull-out rates provides a simple basis for the effect of seepage on plate anchor capacity under sustained loading.

The scouring of seabed beneath an unburied pipeline under regular waves was investigated in a large wave flume. Sands and silts were employed for the contrast experiment and the results obt...

Embankment structures are important to protect against flooding damage. Suffusion, in which fine particles within the soil are transported and washed away following the seepage flow, intensifies the instability of embankment structures. Therefore, it is possible that some embankment structures that repeatedly experienced flooding and rainfall penetration have been deteriorated. However, there is little research investigating the relation between seepage flow histories and deterioration within the embankments. In this study, small-scale modeling tests duplicating a river levee were conducted under different seepage flow histories: (i) short term-critical ground water level, (ii) continuous-high ground water level and (iii) repeatedhigh ground water level. The work in this paper investigates changes in “drainage flow rate”, “height of ground water level” and “particle size distribution” during the seepage tests, and evaluates the effects of seepage flow histories on them. Soils gradually showed lower permeability under the first seepage experience in each cases. In the case of relatively longer flooding duration, the drainage flow rate is gradually increased. Fine particles were eroded, regardless of the seepage flow histories; “the number of fluctuations” and “height” of ground water level could particularly be a trigger of suffusion.

Suction buckets are becoming established as a viable foundation solution for offshore wind turbines. In sand, suction-induced seepage flow reduces effective stresses at the skirt tips, whic...

As a typical form of internal erosion, suffusion refers to the detachment and migration of fine particles through voids among coarse particles driven by seepage flow. This paper studies the...

The suction anchor becomes more popular for offshore oil and gas industry in deeper water. For suction anchor–soil interaction, the prediction of hydraulic conductivity of porous materials is a lon...

Using an assumed vertical retaining wall with a drainage system along the soil–structure interface, this paper analyses the effect of anisotropic seepage flow on the development of passive earth pressure. Extremely unfavourable seepage flow inside the backfill, perhaps due to heavy rainfall, will dramatically increase active earth pressure while reducing passive earth pressure, thus increasing the probability of instability of the retaining structure. A trial and error analysis based on limit equilibrium is applied to identify the optimum failure surface. The flow field is computed using Fourier series expansion, and the effective reaction force along the curved failure surface is obtained by solving a modified Kötter equation considering the effect of seepage flow. This approach correlates well with other existing results. For small values of both the internal friction angle and interface friction angle, the failure surface can be appropriately simplified with a planar approximation. A parametric study indicates that the degree of anisotropic seepage flow affects the resulting passive earth pressure. In addition, incremental increases in the effective friction angle and interface friction angle both lead to an increase in passive earth pressure.

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.

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.

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.

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 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.

We characterize seepage flow in porous media via a series of three-dimensional (3D) direct numerical simulations (DNSs) of Navier-Stokes flows in representative volume elements (RVEs) at the pore level. The immersed boundary method with a fixed staggered grid is employed for calculations based on the finite difference method in the pore domain formed with spatially arranged rigid particles in RVEs. The numerical results of the DNSs with different particle sizes and different seepage flow velocities are volume-averaged over the RVEs to evaluate the permeability coefficients of the seepage flows and are ordered according to the Reynolds numbers for porous media. After the numerical scheme is validated with a simple RVE model, the transition from Darcy to non-Darcy flow, for which experimental results have reported in the literature, is demonstrated in terms of the calculated permeability coefficients and examined based on the pore-level flow characteristics to clarify the mechanism of the permeability change, i.e. the macroscopic behaviour of RVEs related to the Reynolds number.

The seepage beneath a concrete dam causes an upward force acting to the dam foundation, known as uplift. Previous literatures show that implementation of drainage wells in gravity dam foundations causes a reduction in uplift forces. The main aim of these wells is to drain excess seepage flow bypassed from the cutoff wall and to reduce the uplift force. The location of the drains in the foundation plays a key role in reducing the pressure. In the present study, effect of the location of drain pipes from the upstream face of the dam (s), space among them (n) and drain’s diameter (d) in uplift force reduction is investigated. The processes of the study have been performed by the Seep/w software based on the finite element method. Results show that the use of a drain system reduced the uplift forces developed beneath the floor of the structure. If the drain is located close to the face of the dam, it may not be effective in reducing the uplift. On the other hand, shifting it too much away from the upstream face of the dam will lead to increased total uplift. It is, therefore, desirable to find out the location of the drain such that the total uplift is optimum. Optimum location of the vertical drains is not fixed, and by increasing vertical drains distances from each other and also decreasing drain diameter, optimum location would be shifted to the downstream. For example introduction of system of pipe drains to the floor of gravity dams reduced the uplift force acting on the floor by up to 80% for d/l = 0.0004, n/l = 0.024 and s/l = 0.08. This reduction in uplift becomes up to 65% for d/l = 0.0004, n/l = 0.048 and s/l = 0.12. The best location of the drain is such that the total uplift is minimum and this is presented in both design charts and algebraic equations in this study.

Even though a large number of large-scale arch dams with height larger than 200 m have been built in the world, the transient groundwater flow behaviors and the seepage control effects in the dam foundations under difficult geological conditions are rarely reported. This paper presents a case study on the transient groundwater flow behaviors in the rock foundation of Jinping I double-curvature arch dam, the world's highest dam of this type to date that has been completed. Taking into account the geological settings at the site, an inverse modeling technique utilizing the time series measurements of both hydraulic head and discharge was adopted to back-calculate the permeability of the foundation rocks, which effectively improves the uniqueness and reliability of the inverse modeling results. The transient seepage flow in the dam foundation during the reservoir impounding was then modeled with a parabolic variational inequality (PVI) method. The distribution of pore water pressure, the amount of leakage, and the performance of the seepage control system in the dam foundation during the entire impounding process were finally illustrated with the numerical results.

Recent physical model studies of landslide behaviour in loose, granular slopes have illustrated that the soil at the base of a slope may be of heightened risk of liquefaction as this area is located directly in the path of monotonic shearing events (i.e. localised toe failures) and is often saturated by groundwater. The objective of this paper is to further investigate the factors that influence the possible transition of a small toe slide to a larger and higher mobility liquefaction flow failure. Specifically, this paper investigated the influence of stress-level and soil-layer thickness between two different laboratory testing methods in controlling whether a slide transitions to a flow in physical model flume tests. Observations from two flume experiments were contrasted: one in which suction stresses were designed to dominate (a 0.33 m soil layer in a large-scale 1 g test) and a second enhanced gravity test performed in a geotechnical centrifuge where the body stresses are more representative of field scale landslides (i.e. behaviour representative of a 1.5 m thick soil layer). While the centrifuge test was brought to widespread liquefaction failure under increasing seepage flow, the 1 g flume test experienced liquefaction, but only displaced 25 mm. The results from this study highlight the dominant effect matric suction can have on the mobility of landslides, and provides a clear demonstration of the danger of misinterpreting the behaviour observed in small scale 1 g models as being fully accurate representations of larger field-scale landslide behaviour.

In view of the gap between the inflow-performance forecasted by the traditional equation and the actual inflow-performance, experiments of gas-gas alternating seepage flow and gas-water alternating seepage flow were carried out, and a modified equation of inflow-performance relationship considering gas permeability change due to water invasion was established. This equation was verified by example analysis. The experimental results show that: gas permeability of net pay, when water-invaded reservoirs are converted into underground gas storage, is different from that during actual gas field development, in that the value of permeability decreases gradually in gas-water zone while the value increases gradually and even higher than that of original gas field in gas zone as a result of gas water alternative flooding in gas storage. Then one parameter describing the extent of permeability change when gas reservoirs are converted into gas storage was defined based on the result of the experiments, and eventually the traditional equation of inflow-performance relationship was modified to forecast inflow-performance in gas storage based on data from field development. Example analysis result shows that: the modified equation considers the effect of changing permeability, its results agree with the actual inflow-performance, while the result of traditional equation differs greatly from the actual inflow-performance. Key words: underground gas storage, well inflow-performance, percolation experiment, permeability change, gas-water zone, gas zone

Lightweight expanded polystyrene (EPS) geofoam (geofoam block) is used in slope remediation works as a soil substitute fill to reduce driving forces that can lead to global instability. On the other hand, the presence of seepage flow requires special attention because geofoam block slope systems are vulnerable to seepage-induced lateral forces. In this study, the effect of an internal drainage system on the alleviation of piezometric pressures within the back-slope of a geofoam block slope system was investigated. For this purpose, laboratory experiments were conducted using a small-scale lysimeter with dimensions of 60 cm height, 20 cm width, and 200 cm length. The slope was compacted with sand to obtain an overall dry unit weight of 14 kN/m3. The constant piezometric head boundary conditions of 25, 38 and 50 cm generated the necessary hydraulic energy gradient for the seepage flow directed from the water reservoir of the lysimeter to the 45° angle slope face. The slopes were remediated by using geofoam blocks assembled in an embankment-type configuration at the toe of the slope. The internal drainage system consisted of grooved geofoam blocks that formed the 10, 15 and 22.5 cm high embankments. Deep-seated failures of the non-remediated slope were prevented except for the experiments with 10 and 15 cm high embankments under 50 cm pressure head boundary conditions. In general, the internal drainage system alleviated the piezometric pressure conditions within the back-slope by lowering the phreatic surface using the active drainage channels observed during laboratory experiments. These drainage channels provided a convenient passageway for seepage flow. The coupled numerical variably saturated flow modelling and slope stability modelling predicted the factor of safety for global stability which confirmed the observed physical conditions in the laboratory. The use of the internal drainage system increased the factor of safety of the geofoam block slope system under seepage conditions.

This paper described medium scale test results for bucket foundation installation. The campaign includes both, the jacking and the suction installation tests in the sand. Results allow for better understanding of the interaction between the soil and the bucket skirt. Such observations are desired as there are many issues concerning the suction installation. The suction applied under the bucket lid results in seepage flow inside the surrounding sand. The seepage flow plays a pivotal role in the reduction of the penetration resistance and, therefore, allows for the full penetration despite of the initial large soil resistance. On the other hand, the loosening of inside soil plug might become problematic when the soil approaches its failure stage. The failure happens as a result of soil piping or due to extensive soil heave inside the bucket foundation. All aspects are still not fully understood and challenging, while capturing them into the design, therefore, they are addressed in this paper. Additionally, measurements of pore pressures around the bucket skirts are compared with results of numerical simulations. This allows for validation of the FE-model and enables the analysis of the soil behavior around the skirt.

Biogrouting is a new ground improvement method that has been studied in recent years. This method involves mainly the use of a microbially induced calcite precipitation process to bind soil particles to increase the strength or to fill in the pores of soil or joints of rock for seepage control. There are two major challenges in the use of biogrout for seepage control through rock joints. The first is how to inject the biogrout solutions, and the second is to understand the mechanisms for the formation of calcite under seepage flow. In this paper, a study on the injection of biogrout solution and the formation of precipitates along a circular 1D flow channel is presented. To minimize the influence of flow, a new one-phase injection method to inject bacterial solution and cementation agents simultaneously was adopted in this study. Factors affecting the formation and distribution of precipitates along the flow channel such as flow velocity, flow rate, and aperture of flow channel were investigated. The experimental results indicated that less calcite was precipitated at locations further away from the injection point due to depletion of the reactants’ concentrations along the flow path. Using the one-phase injection method, the bacterial activity had a major effect on the accumulation of the calcite on the inner surface of the flow channel. The total calcite precipitated on the surface of the flow channel increased slightly with increasing bacterial activity or flow rate. An equation to predict the distance travelled by the biosolution has been derived based on the testing results. Ministry of National Development (MND) We would like to acknowledge that this study is supported by Grant No. SUL2013-1 by the Ministry of National Development, Singapore. We would also like to thank the anonymous reviewers for the good comments which helped in the improvement of this paper.

During the construction of an excavation pit, the main problem is often dominated by seepage flow into the excavation pit. The pore water pressure developed by the seepage flow may lift the excavation base, and thus, may lead to the stability loss of the excavation pit, which is known as seepage failure by heave. In this study, based on the results of three-dimensional steadystate groundwater flow analyses, design charts are given to evaluate the safety against heave of circular-shaped sheeted excavation pits constructed within homogeneous isotropic soil layers of limited or unlimited thicknesses. The given design charts consider the various conditions of water level on both up- and downstream side of an excavation pit. It means that they can be used for excavation pits constructed in both urban areas and open water.

Suffusion describes the phenomenon whereby finer particles are eroded through the voids of coarse particles by the seepage flow. This may cause the deterioration of the hydraulic structure and, in the worst case, result in the failure of the hydraulic structure. The suffusion process is presented in this paper in an embankment under transient and steady seepage conditions. A series of physical model tests on seepage-induced suffusion on a small-scale model embankment is performed under constant boundary head conditions. A binary mixture, consisting of two Silica sands (Silica sands Nos. 3 and 8), which is categorized as “internally unstable material” by several previous criteria for the seepage-induced internal stability, is used for the model embankment. The cumulative eroded soil mass and the discharged rate of water are recorded during the seepage tests. The spatial extent of the variation in erosion-induced fines contents is discussed through sieve analyzes on subdivided areas of the model embankment after seepage testing. The test results reveal that a decrease in fines propagates along the phreatic surface from downstream in the embankment. Below the phreatic surface, the eroded fines not only move laterally by the seepage flow, but also vertically due to the gravitational force, and are deposited in the foundation. This deposition of the fines results in the expansion of the fine-rich region in the foundation and causes a decrease in the permeability of the whole embankment.

To investigate the relationship between the structural characteristics and seepage flow behavior of rough single rock fractures, a set of single fracture physical models were produced using the Weierstrass–Mandelbrot functions to test the seepage flow performance. Six single fractures, with various surface roughnesses characterized by fractal dimensions, were built using COMSOL multiphysics software. The fluid flow behavior through the rough fractures and the influences of the rough surfaces on the fluid flow behavior was then monitored. The numerical simulation indicates that there is a linear relationship between the average flow velocity over the entire flow path and the fractal dimension of the rough surface. It is shown that there is good a agreement between the numerical results and the experimental data in terms of the properties of the fluid flowing through the rough single rock fractures.

Suffusion is a selective erosion of fine particles under the effect of seepage flow within the matrix of coarser particles. This complex phenomenon appears as a combination of three process...

ABSTRACT: Lightweight expanded polystyrene (EPS) block geofoam (geofoam block) is commonly used as a replacement of the heavy in situ soil during slope remediation in order to reduce driving forces. The design procedure requires the use of permanent drainage systems to alleviate hydrostatic pressures in geofoam block slope systems. In this study, small-scale laboratory lysimeter experiments investigated the behavior of a stabilized sandy slope with a geofoam block slope system experiencing seepage. An internal drainage system was incorporated by grooving dual drainage channels (weep holes) on the top and bottom side of the geofoam blocks. A lysimeter with dimensions of 60 cm height, 20 cm width, and 200 cm length was constructed in the laboratory. Slopes were constructed by compacting sand. The geofoam blocks (2.5 cm height, 5 cm width, and 15 cm length) were placed on the sandy slope face with an angle of 45° in ‘one row' and ‘two rows' configurations. The experiments were conducted under constant water pressure heads (25-, 38-, and 50-cm pressure head boundary conditions) in the water reservoir located at the opposite end of the lysimeter from the geofoam blocks. In general, the lightweight geofoam blocks could not resist earth and hydrostatic pressures under seepage. The back-slope was not self-stable under seepage conditions, and deep-seated global stability failures were observed, except for the remediated slope at the 25- and 38-cm pressure head boundary conditions. The internal drainage system was ineffective at dissipating piezometric pressures at the higher seepage gradients investigated at this lysimeter scale. Numerical slope stability modeling confirmed these observations, predicting a factor of safety below the critical value for global stability in cases where failure was observed. More elaborate geofoam block configurations and/or drainage systems should be used to increase resistance against global stability failure caused by higher seepage gradients.

Stability of sheet-pile walls is often very sensitive to seepage flow. In the presence of seepage flow, the reduction in passive pressure on one side and increase in active pressure on the other side of the wall increase the risk of the instability that may precede instabilities due to piping or ground heaving. In this research the earth pressure behind sheet-pile walls in granular soils is studied. The flow field is computed by the finite-element method and the slip lines (stress characteristics) method is utilised to compute the associated stress field required to compute the effective passive pressure. The same finite-element mesh and interpolation functions are used to solve the flow field and to interpolate the seepage forces in the stress field solved by the stress characteristics method. Comparisons are made to verify the numerical results with those values available in the literature; these show reasonable agreement. The stability of sheet-pile walls is then analysed for a number of different problems with varying geometries and boundary conditions. These different geometries and boundary conditions are expressed in terms of non-dimensional factors and results are plotted.

The present paper investigates the problem of the stability of the tunnel face under seepage flow conditions based upon the so-called “method of slices”. This computational model improves the limit equilibrium method of Anagnostou and Kovari (1996) by treating the equilibrium in the wedge consistently with the overlying prism, i.e. without an a priori assumption concerning the distribution of the vertical stresses. Furthermore, it shows that tensile failure of the wedge may be more critical than shear failure, if the gradient of the hydraulic head in the ground ahead of the face is high. For an approximate distribution of the hydraulic head in the ground around the tunnel face, we derive a closed-form solution for the necessary face support pressure. In addition, we provide normalized diagrams, which allow for a quick assessment of the stability of the tunnel face.

Stress sensitivity plays an important role in the development of a tight low-permeability gas reservoir. With the constant low-permeability reservoir exploitation, formation pressure drop, rock net effective coverage pressure increase, the rock pore is resulted in deformation and the seepage flow of fluid in a low-permeability reservoir no longer followed Darcy flow law. With the further exploitation of reservoirs, reservoir stress sensitivity is enhanced, so evaluation on the stress sensitivity on reservoir development was a burning question. The authors present results of those experiments that simulated the permeability changes via the net confining pressure in the lab and give the influencing factors of stress sensitivity.

Seepage flow renders tailings dams vulnerable to failure during their staged construction. Draining is one of the most effective measures in improving dam stability. In this study, a stepwise-coupled hydro-mechanical model is employed to examine the effect of seepage control on the stability of a tailings dam during its staged construction. The settlement and deformation of the tailings under gravity load are modelled using the Duncan–Chang non-linear elastic E–B model, and the seepage flow through the tailings with drains is characterised by a variational inequality formulation of Signorini’s condition. The Kozeny–Carman equation is calibrated to illustrate the dependence of hydraulic conductivity on the porosity and volumetric deformation of the tailings. The proposed model was applied to assess the performance of the drains designed for the Luogou tailings disposal in Luanchuan County, Henan Province, China. Numerical results show that the stress-induced variation in tailings permeability could be of 1...

With the permeability of reservoirs becoming lower, the non-Darcy flow phenomenon becoming more obvious. The rules of fluid flow in low permeability reservoirs need to be researched through experimental method. The authors get the function relation between the ratio of resistivity and the concentration of solution through core experiments. The authors performed the single-phase fluid displacement experiment in low permeable natural sandstone plate model, then calculated the spreading condition of fluid in the model by recording the change of resistivity between measuring points. The application of resistivity method is verified the feasibility of measuring seepage flow field.

Artificial ground freezing (AGF) is a reliable technique for ground improvement to address adverse geotechnical engineering conditions. The formation of a freezing curtain during the AGF process is crucial as it serves to control groundwater flow and enhances the strength of the soil. However, groundwater flow has a considerable influence on the formation of the freezing curtain because it provides a continuous source of heat. Thus, to investigate the influence of water flow on the freezing process during AGF, a moisture–heat coupling model was proposed considering ice/water phase transition to quantify the temperature distribution in soil during the freezing process. The proposed numerical model was further validated using thorough laboratory tests under various seepage flow conditions. Finally, a numerical simulation of AGF was conducted for the end well of the Harbin metro station in China. Five representative monitoring points on the end well were selected and continuously monitored for 30 days to predict the formation of a freezing curtain. It was observed that the temperature results obtained using the proposed model are consistent with actual field monitoring data.

Internal erosion involves selective loss of fine particles within the matrix of coarse soil particles under seepage flow, which affects the hydraulic and mechanical behavior of the soil. In this research, extensive laboratory internal erosion tests were conducted under complex stress states following three stress paths: isotropic, drained triaxial compression, and triaxial extension stress paths. These tests were designed to investigate the initiation and development of internal erosion and the effect of stress state on critical hydraulic gradients. The entire erosion process can be divided into four phases: stable, initiation, development, and failure. Accordingly, three critical gradients termed as initiation, skeleton-deformation, and failure hydraulic gradients, can be defined. These critical gradients correspond to the onset of erosion of the fine particles filling the large pores of the skeleton, the buckling of the strong force chains formed by the coarse particles, and the soil failure, re...

Stability of a levee and its foundation soil during flood is governed by seepage forces. In this study, the seepage forces in the flow domain have been determined using conformal mapping technique. Stability of foundation soil has been studied for a levee with and without cut-off wall on permeable soil of infinite depth. In situ effective normal and shear stresses due to self-weight, additional induced stresses due to levee structure and ponded water on upstream sloping face have been determined by assuming soil to be elastic. Besides, components of seepage stress acting at a point on two orthogonal planes, i.e., on vertical and horizontal planes, are considered and the Mohr’s circle is drawn. Mohr–Coulomb failure envelope is drawn for the foundation soil with known effective cohesion ( $$c^{\prime}_{1}$$ ) and angle of internal friction ( $$\varphi^{\prime}_{1}$$ ), and then the stability of the foundation soil has been assessed. Probable zone of general shear failure considering seepage flow has been identified. Zones vulnerable to foundation failure for different width of levee and depth of cut-off wall have been computed. The hydraulic unstable zone in downstream side of the levee resembles a log spiral. The provision of cut-off wall restricts the progress of failure zone only in the downstream side; otherwise, the zone of failure will enter the foundation of the levee. The stability of the foundation soil of an existing ring levee along the rivers Ganga, Sone and Punpun, near Patna (India), has been evaluated.