Laboratory-scale Physical Model Research Articles

Laboratory and numerical simulations of infiltration process and solute transport in karst vadose zone

Groundwater in karst systems is a vital resource, which is often highly vulnerable to contaminants that infiltrate through the vadose zone. Understanding the processes of water and contaminant infiltration in the vadose zone is extremely important for protecting and managing karst water resources. A laboratory-scale physical model based on a typical conceptual model of the karst vadose zone was constructed to characterize the influence of the rainfall intensity and internal structure on the infiltration process and solute transport in the karst vadose zone under controlled conditions. Five factors, including the rainfall intensity, the surface slope, the degree of karstification, the thickness of the transfer zone, and the existence of epikarst, were considered in laboratory experiments. A corresponding lumped-parameter model was subsequently developed to further analyze and investigate the water and solute infiltration processes in the laboratory scale physical model. Recession- and breakthrough curves generated from the lab experiments and the water and solute loss from each reservoir generated from the simulation results were analyzed. The downward trend of breakthrough curves' peak value and the variation of solute loss's proportion in three rainfall events demonstrate that both the increase in thickness and karstification degree will intensify the buffer effect of the karst vadose zone, and this buffer effect is mainly affected by the slow flow system which can be inferred from the increasing percentage of cumulative discharge of slow reservoir (qS). With increasing karstification degree, the recession coefficient (α) exhibits opposite trends depending on the existence of epikarst or not, indicating the karstification degree has a more significant effect on hydraulic conductivity (K) when an epikarst is present while affecting effective porosity (φ) more noticeably in the absence of epikarst. The rainfall intensity affects the results of both experimental and numerical simulation most significantly. The percentage of discharge and solutes flowing from the slow reservoir (qS and msoil_S) have negative correlations with rainfall intensity, suggesting a greater influence on fast flow with increasing rainfall intensity.

Terraced slope metasurface in granular media

SUMMARY In this work, the propagation and attenuation of vertically polarized surface waves when interacting with terraced slopes is studied experimentally and numerically. To validate the devised simulation, a laboratory-scale physical model is tested in order to examine the attenuation properties of this well-known artificial landform. The experiment involves formation of a terraced slope, in a laboratory setup, via use of an unconsolidated granular medium made of silica microbeads. This granular medium exhibits a gravity-induced power-law stiffness profile, resulting in a depth-dependent velocity profile. A piezoelectric actuator was used to excite vertically polarized surface acoustic modes localized near the surface of the medium. The three components of the particle velocity field of these modes were measured by means of a 3-D laser Doppler vibrometer. In accordance with the terraced slope, a simple inclined plane was further tested to investigate and highlight the differences in terms of wave propagation along these two different ground formations. The results of this research provide significant experimental evidence that the terraced slopes form mechanisms which attenuate low-frequency surface waves, thus acting as metasurfaces. This work suggests the use of laboratory-scale physical models to investigate the wave propagation in different landforms, which extend beyond typical horizontal ground morphologies, and which could be linked to atypical wave propagation properties, possibly even influencing propagation of seismic waves.

Reliability of Runoff Hydrograph Model for Extreme Rainfall Events using HEC-RAS 2D Flow Hydrodynamics Rain-On-Grid

Hydrological modeling is a valuable tool for analyzing water resources and predicting the impacts of extreme rainfall events, particularly for flood risk mitigation. Accurate results from hydrological models rely heavily on detailed input of watershed characteristics, including morphometric factors, land cover, and slope. In the face of the increasing frequency and severity of floods due to climate change, hydrological modeling has become an essential tool for disaster risk mitigation and management. HEC-RAS is a widely used software for river flow modeling and floodplain analysis. HEC-RAS 2D with the rain-on-grid meteorological model is a powerful tool for simulating flood events in complex river systems. The rain-on-grid method enables the simulation of spatially distributed rainfall events and their impact on runoff, which is crucial for modeling extreme runoff hydrographs. Previous studies have demonstrated the accuracy and effectiveness of HEC-RAS 2D with rain-on-grid in modeling extreme runoff hydrographs. This study aims to validate the reliability of HEC-RAS 2D hydrodynamics in simulating unsteady flow with meteorological data will be examined within a laboratory-scale physical model of the watershed. Additionally, the performance of HEC-RAS 2D will be evaluated in a observed watershed, specifically the Bangga watershed in Central Sulawesi to assess the performance of the HEC-RAS 2D Hydrodynamics model. The runoff hydrograph reliability model using HEC-RAS 2D rain-on-grid yielded close results when compared to a laboratory-scale physical model with a rainfall simulator and HEC-RAS 2D simulation using meteorological input data. The error in Time of Peak (Tp) and Peak Discharge (Qp) between the physical and numerical models was 7% and 3.5%, respectively. Additionally, in the HEC-RAS 2D simulation, a Manning roughness coefficient value of 0.04 closely matched the results of the physical model, while there was some variability when comparing HEC-RAS 2D results with measured data in Bangga watershed of Central Sulawesi. However, the numerical model exhibited relatively approaching result with the HEC-HMS SCS hydrograph model.

Assessment of managed aquifer recharge in saline confined aquifers for freshwater storage and improved recovery: A 3D tank study under various operational conditions

Aquifer Storage and Recovery (ASR), a subset of Managed Aquifer Recharge (MAR) techniques, is a promising technique to address water scarcity issues by recharging depleted aquifers. The application of ASR in saline groundwater regions is challenging due to mixing of recharged freshwater with the ambient saline groundwater, decreasing the recoverable amount of freshwater. This paper aimed to investigate the feasibility of ASR techniques for freshwater storage and recovery in saline confined aquifers using a laboratory scale physical model (100 cm length x 30 cm width x 60 cm depth). The study then explored the impact of operational factors (freshwater storage duration, injected freshwater volume, number of injection/extraction cycles etc.) on freshwater recovery from an applied ASR. Firstly, the behaviour of stored freshwater in a saline-confined aquifer was investigated, and in the next step, the impact of ASR operational parameters on the recovery efficiency (RE) was evaluated. Along with the physical model, these effects were studied using a mathematical model (MODFLOW linked with SEAWAT) for the representative aquifer system. The movement and spreading of the stored freshwater were monitored over time. The experimental results presented in this study suggested that several factors significantly influence the efficiency of ASR systems. A negative correlation between ambient groundwater salinity and average recovery efficiency (ARE) was confirmed, with decreasing ARE observed as the salinity level increased. The injection volume of freshwater was found to have a positive influence on ARE, although the relationship was non-linear, a polynomial trend was observed. The longer freshwater was stored in the aquifer, the lower ARE was reported, indicating a negative impact of storage duration on ASR performance. Finally, the number of successive cycles of ASR operation was found to have a positive influence on ARE, but the effect decreased with each subsequent cycle. This research provided valuable insights into the application of ASR techniques for freshwater storage and its enhanced recovery in saline confined aquifers.

Experimental study on waste foundry sand as partial replacement of retaining wall backfill

Waste foundry sand (WFS) is a sustainable backfill geomaterial with potential to be used in retaining structures. In the present study, 28 distinct laboratory-scale physical model experiments are performed on a 0.5 m high retaining wall. The backfill sand is replaced with WFS at different replacement concentrations. The retaining wall model is reinforced with biaxial polyester geogrid to quantify the effect of reinforcement. The interaction properties of soil with soil, wall and geogrid are measured by a series of drained direct shear tests using a shear box of 300 mm × 300 mm × 150 mm is used. The model retaining wall study includes both at-rest and active cases of walls. The effect of WFS content, the relative density of backfill, static surcharge and reinforcement on earth pressure and lateral displacement of the wall is quantified. Backfill with 40% of WFS is observed to provide maximum values of interaction properties. The results of interaction studies are consistent with model tests. The earth pressure reduces by 22% with 40% WFS backfill compared to the control case of 100% sand. The lateral displacement reduces by 30% and 50% corresponding to single and double geogrid layers, respectively.

Dynamic Motions of Piled Floating Pontoons Due to Boat Wake and Their Impact on Postural Stability and Safety

Piled floating pontoons are public access structures that provide a link between land and sea. Despite floating pontoons being frequented by the public, there is limited data available to coastal or maritime engineers detailing the dynamic motions (acceleration and rotation) of these structures under wave action and the impact of these motions on public comfort and safety to inform their design. This contribution summarises results from a set of laboratory-scale physical model experiments of two varying beam width piled floating pontoons subjected to boat wake conditions. Observed accelerations and roll angles were dependent on beam-to-wavelength ratio (B/L), with the most adverse motion response observed for B/L ~0.5. Internal mass of the pontoon played a secondary role, with larger mass structures experiencing lower accelerations for similar B/L ratios. Importantly, these new experimental results reveal the complex interaction between the piles and pontoon that result in peak accelerations more than six times the nominated operational safe motion limit of 0.1g. Root mean square (RMS) accelerations were more than three times the nominated comfort limit (0.02g) and angles of rotation more than double what would be perceived as safe (6 degrees) for the boat wake conditions tested. The frequency of acceleration also suggests patrons standing on these platforms are likely to experience discomfort and instability. Laboratory results are compared against a series of field-scale experiments of pontoon motion response and patron feedback. The dynamic motion response of pontoons tested in both field-scale and laboratory experiments compared well.

Geometric and material attenuation of surface acoustic modes in granular media

SUMMARYGranular materials can be used in laboratory-scale physical models to simulate and study seismic wave propagation in various unconsolidated, porous heterogeneous media. This is due to the diverse available grain configurations, in terms of their shape, size and mechanical parameters, which enable the physical and geological modelling of various complex substrates. In this work, an unconsolidated granular medium, made of silica microbeads, featuring a gravity-induced power-law stiffness profile is experimentally tested in a laboratory setting. The objective is to investigate the attenuation mechanisms of vertically polarized seismic waves traveling at the surface of unconsolidated substrates that are characterized by power-law rigidity profiles. Both geometric spreading and material damping due to skeletal dissipation are considered. The understanding of these two attenuation mechanisms is crucial in seismology for properly determining the seismic site response. An electromagnetic shaker is employed to excite the granular medium between 300 and 550 Hz, generating linear modes that are localized near the surface. A densely sampled section is recorded at the surface using a laser vibrometer. The explicit solution of the geometric attenuation law of Rayleigh-like waves in layered media is employed to calculate the geometric spreading function of the vertically polarized surface modes within the granular material. In accordance with recent studies, the dynamics of these small-amplitude multimodal linear waves can be analysed by considering the granular medium as perfectly continuous and elastic. By performing a nonlinear regression analysis on particle displacements, extracted from experimental velocity data, we determine the frequency-dependent attenuation coefficients, which account for the material damping. The findings of this work show that laboratory-scale physical models can be used to study the geometric spreading of vertically polarized seismic waves induced by the soil inhomogeneity and characterize the material damping of the medium.

Power absorption modelling and analysis of a multi‐axis wave energy converter

A point absorber wave energy converter (WEC) which converts wave energy into electrical energy with a multi-axis power-take-off (PTO) system is considered here. Previous wave tank trials have proved the ability of the multi-axis WEC to absorb wave power. In this study, the boundary element method (BEM) based software Ansys@ AQWATM was applied to model and analyze the power absorption performance of the multi-axis WEC for a wider range of regular and irregular waves. To verify the numerical model, a laboratory-scale physical model was manufactured and tested. Results show that the multi-axis WEC can absorb more power from the incident regular wave power compared to single-axis WECs and the efficiency reaches up to 45%. It is found that the wave frequency and incident angle significantly influence the amount of absorbed power from different motion modes and PTO axes. Then the numerical model is simulated at 12 nearshore locations in East and South China Sea. The results indicate that the multi-axis WEC can absorb up to 5 kW and the efficiency can reach up to 29% at the most energetic site Shengshan. In addition, considerable differences of mean absorbed power efficiency can be found between sea states.

Analytical solution for a strong free-surface water vortex describing flow in a full-scale gravitational vortex hydropower system

Strong free-surface water vortices are found throughout industrial hydraulic systems used for water treatment, flow regulation, and energy generation. Previous models using the volumetric flow rate as a model input have generally been semi-empirical, and have tended to have some limitations in terms of the design of practical hydropower systems. In this study, an analytical model of a strong free-surface water vortex was developed. This model only requires the water head and geometric parameters as its inputs and calculates the maximum volumetric flow rate, air-core diameter, and rotational constant. Detailed experimental depth–discharge data from a full-scale gravitational vortex hydropower system, unavailable in the relevant literature, were obtained, and the simulated results showed excellent agreement with the experimental observations. These data could be used to verify similar models using laboratory-scale physical models in order to investigate the scaling effects. In contrast to previous models, this model does not assume a constant average velocity across the vortex radius and allows precise calculation of the resultant velocity vectors. Therefore, this model presents advantages in turbine design for energy generation systems.

Reduced-scale geosynthetics retaining walls: deformation prediction by an expedited method

Reinforcement of earth retaining walls dates back to antiquity, although a considerable evolution has occurred over the past decades. Reinforcement materials have evolved from natural to metal and finally to geosynthetic materials. These materials are extensible and the reinforcement effect develops through the soil–reinforcement interface, which is dependent on the deformation of the wall, the soil and the reinforcing elements. It is important to control deformation in order to avoid functional and structural problems. This paper contributes to the accurate prediction of the deformation of retaining walls reinforced with geosynthetics using data from laboratory-scale physical models. The feasibility of a simple method to calculate the deformation of the face and earth pressures is evaluated from the data of reduced-scale model walls previously tested in a laboratory: a brick-faced wall and a more flexible geotextile-wrapped wall. The calculated horizontal deformation of the face compares well with the physical measurements and, therefore, the proposed method can be taken as a valid and expedited tool to predict the deformation of retaining walls reinforced with geosynthetics.

Analysis of Carbon Monoxide Gas Dilution on Horizontal Tunnel Front using Laboratory Scale Physical Model

Potential hazards that often occur in underground tunnels are dangerous and toxic gases, one of which is carbon monoxide (CO) which can be found in underground tunnels for example as a result of imperfect detonation on work surfaces. CO gas is very poisonous so it can cause death. This study aims to determine the spread of CO gas when diluting with tunnel ventilation in the horizontal front. This research was conducted on a physical model of the laboratory with a ratio of 1:10 compared to the actual tunnel, that is at the cross section of the model in the laboratory 40 cm x 40 cm. The effectiveness of dilution or dilution is indicated by the value of the diffusion coefficient, where the greater the diffusion coefficient, the more diffused the CO gas concentration, so the faster the CO gas concentration decreases. The parameters of the test conditions are the ratio of the duct to face distance (L/D) and the Reynolds number (Re) which shows the variation of air velocity in the tunnel work surface. Test results from the distribution of CO gas showed the influence of the configuration of the forcing duct and exhausting duct distances on the working front to the CO gas dilution. In this study also found the influence of Reynolds numbers on the value of the diffusion coefficient, that the greater the value of Re, the greater the value of E.

Feasibility study on the use of geosynthetics to reinforce buried HDPE pipes subjected to localized ground subsidence

Abstract Failures of High Density PolyEthylene (HDPE) pipes caused by the localized ground subsidence were reported. However, the literature about the protection of buried pipes subjected to localized ground subsidence is not available. Four laboratory-scale physical model tests were conducted in this study to investigate the feasibility of the use of geosynthetics to reinforce pipes subjected to localized ground subsidence. Two types of geosynthetics including woven geotextile and biaxial geogrid were adopted. The test results demonstrated that (1) both woven geotextile and geogrid underneath the pipe could limit the pipe vertical displacement; (2) earth pressure at the pipe top for all cases increased with the lowering of the moveable plates. The soil arching ratio at the pipe top in the case with woven geotextile underneath the pipe was the minimum of 1.7, while the ones of other cases were all greater than 2.2.

Production optimization for water flooding in fractured-vuggy carbonate reservoir – From laboratory physical model to reservoir operation

Conventional physical model experiments of carbonate reservoirs are limited to the investigation of production patterns and mechanisms for a single well or a well group, and cannot effectively optimize the oil production at the reservoir scale. For an actual fractured-vuggy reservoir in Tahe Oilfield, China, seismic and drilling data were first analyzed to obtain the distributions of fractures and vugs, and the dynamic tracer monitoring was used to determine the type of connection between fracture-vug units. Then, according to shape similarity, the real fracture-vug units are simplified into 12 visualized physical models made of transparent acrylic plates with a scale of 300:1. Different physical models were further combined together with the connectivity modes derived from dynamic tracer monitoring, thus embodying the entire complex carbonate reservoir to a laboratory-scale physical model for the first time. Experiments were then carried out with these models and results showed that changing the injection and production parameters and increasing the number of flow channels between injector and producer have little effect on the displacement efficiency, while altering the water flow direction and converting injector into producer achieved better effect, due to the increasing fracture-vug units that can be displaced. In the field production, the output of TK652, TK605CH and TK608 wells increased from 11, 5, 1 m3/d to 18, 18, 19 m3/d, respectively, by closing well TK659 and converting well TK6100 (two high water-cut producers) to change the direction of water flow. The laboratory physical modeling technique illustrated in this study provides a simplified and unified way for the production optimization of fractured-vuggy carbonate reservoirs.

Geoelectrical characterization and monitoring of slopes on a rainfall-triggered landslide simulator

In this paper, we present the results of time-lapse electrical resistivity tomography (ERT) monitoring of rainfall-triggered shallow landslides reproduced on a laboratory-scale physical model. The main objective of our experiments was to monitor rainwater infiltration through landslide body in order to improve our understanding of the precursors of failure. Time-domain reflectometry (TDR) data were also acquired to obtain the volumetric water content. Knowing the porosity, water saturation was calculated from the volumetric water content and we could calibrate Archie's equation to calculate water saturation maps from inverted resistivity values. Time-lapse ERT images proved to be effective in monitoring the hydrogeological conditions of the slope as well as in detecting the development of fracture zones before collapse. We performed eight laboratory tests and the results show that the landslide body becomes unstable at zones where the water saturation exceeds 45%. It was also observed that instability could occur at the boundaries between areas with different water saturations. Our study shows that time-lapse ERT technique can be employed to monitor the hydrogeological conditions of landslide bodies and the monitoring strategy could be extended to field-scale applications in areas prone to the development of shallow landslides.

Physical Modeling on Time Domain Induced Polarization (TDIP) Response of Metal Mineral Content

The Induced Polarization (IP) methods is an extension of resistivity method by adding ability of the ground in storing electrical charge. One of the measurement technique is done in time domain, hereinafter referred to as Time Domain Induced Polarization (TDIP). TDIP responses measured on the surface are affected by the physical properties of the subsurface. Research in TDIP response modeling studies is performed to obtain a quantitative relationship between response to metallic mineral content at subsurface. The relationship can be obtained by forward and physical modelling. The forward modeling produces a curve that connects TDIP response to the subsurface parameters and an array. The laboratory-scale physical model is performed on the sand-box size (200x100x70) cm3 by varying iron-ore content in a sphere target. TDIP response measurements on physical models is done using Dipole-dipole and Wenner configuration. The relationship between the TDIP response and metal mineral content is obtained by comparing the results of measurements on physical modeling and forward modelling. There is good appropriatement between the theoretical curves and measuring results of the physical modelling. The greater of iron-ore content on the target, increasing in the TDIP response.

The fracturing characteristics of rock mass of coal mining and its effect on overlying unconsolidated aquifer in Shanxi, China

Due to coal mining taking place on a large scale in northern China, it is inevitable that wide-spread dewatering occurs in the aquifers overlying the resulting goaf. The purpose of this paper is to protect the groundwater of overlying unconsolidated aquifers. Based on physical model experiment, seepage experiments, and numerical simulation, this paper determines the patterns and distribution of the overburden rocks in the goaf, establishes the correlation between the fracture ratio and the hydraulic conductivity of the rock mass, and characterizes the groundwater flow pattern. The results show that (1) the residual fracture occurring ratio within the residual fracture zone is approximately 1.82 times that of the fracture compaction zone and 1.93 times that of the coal wall support zone; (2) the hydraulic conductivity of the rock mass in different parts of the goaf increases with increasing fracture ratio, the relationship of the two follows a power curve; (3) the predicted groundwater levels from numerical simulation is good fit with the measured and indicates that the hydraulic conductivities derived from seepage experiments are rational. We demonstrate how a laboratory-scale physical model can be used effectively to verify existing conceptual models in such a way that the impact of coal mining on groundwater resources can be predicted for similar regions.

Development and Comparison of Two New Methods for Quantifying Uncertainty in Analysis of Flow Through Rockfill Structures

Although extensive researches have been conducted in the analytical and numerical analysis of flow through rockfill structures, one of the main issues in these analyses which still needs attention is uncertainty quantification. In this research, first, it was investigated and shown that the nature and source of uncertainty in rockfill hydraulic parameters can be different indicating random and fuzzy parameters. Then, uncertainty analysis of gradually varied flow computations in rockfill structures was conducted using proposed hybrid and transformation methods in order to quantify the uncertainty in computed water surface profiles resulting from uncertainty in the model hydraulic parameters. Although the proposed methods can be applied to any equation that quantifies the head loss in flow through rockfill structures, two commonly used equations, i.e., Stephenson and Wilkins equations, were used in this study. The methods were applied to a laboratory-scale physical model, and the numerical results were compared with the corresponding measured water surface levels. Three main conclusions drawn from this study were: (1) the results of the two different uncertainty analysis methods did not show significant differences, but the transformation method was rather simple and computationally efficient in comparison with the hybrid method, (2) for both Wilkins and Stephenson equations, the experimental data were within the 90% confidence intervals resulting from both uncertainty analysis methods and (3) the proposed approach and methodologies in this study can be used by hydraulic engineers in analysis and design of real-life rockfill structures.

Moraine dam breach and glacial lake outburst flood generation by physical and numerical models

Summary The areas of glacial lakes in the Himalayas continue to increase alarmingly due to global warming with consequent risk of glacial lake outburst flood (GLOF). The outburst is most common for moraine-dammed lakes as a result of a failure of the dam by overtopping and erosion or piping due to seepage. In the present context, GLOF events, especially for the moraine dam failure process needs to be predicted to assess the drastic and detrimental impacts on the downstream river valley. This study focuses on validating an integrated model for simulating the failure of moraine dam by overtopping and erosion using a coupled numerical simulation model. The proposed numerical methodology is validated with the data from experiments in laboratory scale physical models. The results of the model are compared for both the erosional profiles during collapse of the dam and the resulting outflowing flood hydrograph. The primary finding is that the moraine dam height and the volume of the lake upstream of the dam are the most sensitive parameters influencing the GLOF peak. The model is also applied to the field problem of the Tangjiashan lake outburst and dam failure and shows reasonably good agreement with observations. The validated model is also run for the South Lhonak glacial lake in the Sikkim Himalayas, India to obtain the probable flood hydrograph in case of failure of the moraine dam.

Laboratory-scale model studies on corduroy-reinforced road embankments on peat foundations using transparent soil

Abstract Test sections of a road embankment on peat were instrumented to investigate their performance and to develop more economical means of construction method. One test section was constructed with only geotextile at its base and another with both geotextile and corduroy. Laboratory-scale physical model tests were undertaken to improve the understanding of the operating mechanisms involved in the performance of the two test sections. Artificial transparent soil that has similar deformation properties of natural clays and peats was used as foundation material. It allows determination of spatial displacements beneath the embankment using Particle Image Velocimetry (PIV) technique. The load-settlement behaviour of the test sections were reasonably simulated in the laboratory-scale physical model tests. Displacement patterns from PIV indicate that embankment with geotextile layer and corduroy has less settlements and lateral movements in the foundation compared to that of the embankment with geotextile layer only.

Modelling a Highway Embankment on Peat Foundations Using Transparent Soil

Laboratory-scale physical modelling was conducted to understand the behaviour of highway embankments constructed on peat foundations. Artificial transparent soil was used to simulate the deformation properties of the peat foundation. The use of a transparent soil allows the determination of spatial deformations underneath the modelled embankment using Particle Image Velocimetry (PIV). The load-settlement behaviour in the field is reasonably simulated in the laboratory-scale physical model. This paper presents the results of a modelled embankment with a geotextile fabric across its base.