Small-scale Laboratory Tests Research Articles

Effects of the impact angle on the coefficient of restitution in rockfall analysis based on a medium-scale laboratory test

Abstract. The reliability of a computer program simulating rockfall trajectory depends on the ascertainment of reasonable values for the coefficients of restitution, which typically vary with the kinematic parameters and terrain conditions. The effects of the impact angle with respect to the slope on the coefficients of restitution have been identified and studied using small-scale laboratory tests. To investigate whether the existing conclusion based on small-scale laboratory tests is valid when the test scale changes as well as the role of rotation in the effect of the impact angle on the coefficients of restitution, this study performed a medium-scale laboratory test using spherical limestone polyhedrons to impact concrete slabs. Free-fall tests are conducted, and the velocities before and after the impact are obtained by a 3-D motion capture system. The comparison of results between our test and the existing small-scale tests verified that several general laws occur when accounting for the effect of the impact angle, regardless of the test scales and conditions. Increasing the impact angle will induce reductions in the normal coefficient of restitution Rn, the kinematic coefficient of restitution Rv and the kinetic energy coefficient of restitution RE, whereas it will lead to increases in the tangential coefficient of restitution Rt. The rotation plays an important role in the effect of the impact angle. A higher percentage of kinetic energy converted to rotational energy always induces a higher normal coefficient of restitution Rn and a lower tangential coefficient of restitution Rt. As the impact angle decreases, the ratio between the rebound angle β and the impact angle α increases, and the percentage of kinetic energy dissipated in rotation as the collision became higher. Considering that the effect of block shape and the detailed impact orientations are not involved in the present study, the test results are valid for trajectory simulation codes based on a lumped-mass model and can be referenced in the trajectory predication of spherical rocks impacting hard surfaces using a rigid body model.

The Effect of High-Intensity Ultraviolet Light to Elicit Microalgal Cell Lysis and Enhance Lipid Extraction.

Currently, the energy required to produce biofuel from algae is 1.38 times the energy available from the fuel. Current methods do not deliver scalable, commercially viable cell wall disruption, which creates a bottleneck on downstream processing. This is primarily due to the methods depositing energy within the water as opposed to within the algae. This study investigates ultraviolet B (UVB) as a disruption method for the green algae Chlamydomonas reinhardtii, Dunaliella salina and Micractinium inermum to enhance solvent lipid extraction. After 232 seconds of UVB exposure at 1.5 W/cm2, cultures of C. reinhardtii (culture density 0.7 mg/mL) showed 90% disruption, measured using cell counting, correlating to an energy consumption of 5.6 MJ/L algae. Small-scale laboratory tests on C. reinhardtii showed bead beating achieving 45.3 mg/L fatty acid methyl esters (FAME) and UV irradiation achieving 79.9 mg/L (lipids solvent extracted and converted to FAME for measurement). The alga M. inermum required a larger dosage of UVB due to its thicker cell wall, achieving a FAME yield of 226 mg/L, compared with 208 mg/L for bead beating. This indicates that UV disruption had a higher efficiency when used for solvent lipid extraction. This study serves as a proof of concept for UV irradiation as a method for algal cell disruption.

A general numerical model for surface waves generated by granular material intruding into a water body

Surface water waves generated by large-scale landslides have been a major concern of many geoscientists and coastal engineers because they may result in disastrous consequences. This study presents an advanced two-phase model for dry granular material intruding into an otherwise still water body as well as their resulting waves. The water-air interface both within and outside the granular material is captured by the volume of fluid method. The inter-granular stresses are formulated based on a general collisional-frictional law developed for underwater granular flows and a modified k−ε model is adopted to describe the turbulence effect of the ambient fluid. Phase interaction is characterized by the drag force caused by the relative motion between the granular particles and the fluid. The effect of the ambient fluid on the restitution coefficient of granular particles is also considered. The newly proposed two-phase model is validated following a reasonable agreement of the numerical results with measured data from small-scale laboratory tests on surface waves caused by collapse of a subaerial granular column and by intrusion of a landslide into water. Generation and propagation of the waves, as well as the motion and deformation of the granular body, are all adequately represented by the numerical model. A relatively more general applicability of the proposed model to the study of waves generated by granular landslides can thus be expected.

Size Effect Analysis for the Characterization of Marcellus Shale Quasi-brittle Fracture Properties

Mechanical characterization of shale-like rocks requires understanding the scaling of the measured properties to enable the extrapolation from small scale laboratory tests to field study. In this paper, the size effect of Marcellus shale was analyzed, and the fracture properties were obtained through size effect tests. A number of fracture tests were conducted on Three-Point-Bending (TPB) specimens with increasing size. Test results show that the nominal strength decreases with increasing specimen size, and can be fitted well by Bazant's Size Effect Law (SEL). It is shown that SEL accounts for the effects of both specimen size and geometry, allowing an accurate identification of the initial fracture energy of the material, Gf, and the effective Fracture Process Zone (FPZ) length, cf. The obtained fracture properties were verified by the numerical simulations of the investigated specimens using standard Finite Element technique with cohesive model. Significant anisotropy was observed in the fracture properties determined in three principal notch orientations: arrester, divider, and short-transverse. The size effect of the measured structural strength and apparent fracture toughness was discussed. Neither strength-based criterion which neglects size effect, nor classic LEFM which does not account for the finiteness of the FPZ can predict the reported size effect data, and nonlinear fracture mechanics of the quasibrittle type is instead applicable.

Technology Focus: Matrix Stimulation (June 2018)

Technology Focus The evolution of horizontal drilling and multistage completions has changed matrix stimulation from the “more acid, better result” belief to effective lateral distribution and deeper penetration with less acid. Large-gallon-per-foot-based treatment became impractical and unnecessary. The constant remains that drilling is blamed for causing formation damage; therefore, matrix stimulation is needed. Underbalanced coiled-tubing drilling aimed at changing this constant, however, has its own drawbacks. For certain lithologies, acid tunneling can be an attractive alternative to rotary-bit drilling. Though the technology was proposed many years ago, its use has been limited. Hardware to control the drilling direction, fluids to dissolve the formation rock efficiently, and jetting dynamics to optimize the rate of penetration have been pushed forward progressively. The goal of stimulation while drilling finally may be achievable. Of course, not all reservoir rock types are readily soluble in chemicals. Cracking the reservoir rock will continue to be the preferred process for sandstone. The first mechanism we think of for rock cracking is hydraulics. Unless full-fledged hydraulic fracturing is required, using high-energy pulses induced by propellant or other chemical reactions can produce sufficient pressure to break the rock past the near-wellbore formation damage. Perfecting the control and job design can lead to efficiency and broader implementation. One question we often ask in the matrix-stimulation domain is “what’s new?” It almost seems that the products and technologies of yesterday have been brought out again and again with minor twists. Indeed, it is amazing how many “new technologies” actually have been around for decades. While most of the industry is busy handling daily operations and logistics, it is encouraging to see universities, government-supported research and development institutes, and even some large service and operating companies studying the science behind the products and technologies. Advanced multiscale, multiphysics mathematical models are used to optimize particle bridging for diverting efficiency; large-scale experimental setups are used to gain insights into differential etching patterns during acid fracturing caused by viscous fingering and heterogeneous reactions, perforation penetration in realistic geometry and stresses, and other phenomena that could not be observed by small-scale laboratory testing. These studies help us appreciate the ingenuity of our predecessors and help us fit the technologies to the right applications better. Recommended additional reading at OnePetro: www.onepetro.org. SPE 185344 Application of Closed-Fracture Acidizing for Stimulation of Tight Carbonate Reservoir in Mumbai Offshore by Dilip Kumar Sarma, Oil and Natural Gas Corporation, et al. SPE 187019 Large-Scale Visual Experiment and Numerical Simulation of Acid Fingering During Carbonate Acid Fracturing by Xiaogang Li, Southwest Petroleum University, et al. SPE 189546 Influence of Transport Conditions on Optimal Injection Rate for Acid Jetting in Carbonate Reservoirs by Dmitry Ridner, Texas A&M University, et al.

Fast falling weight deflectometer as new tool to perform accelerated pavement testing

The development of the falling weight deflectometer (FWD) in the late 1970s made it possible to determine quickly the in situ modulus and critical stresses/strains in pavement structures, which are generally considered the most important input for the ‘mechanistic’ part of the mechanistic–empirical pavement design method. In 2015, the newly designed FastFWD was released and provided the opportunity to speed up the testing procedure and overall productivity significantly. The increased rate of loading prompted the current study into the possibility of performing in situ accelerated pavement testing to predict pavement deterioration, and to fill the gap between the heavy vehicle simulator and small-scale laboratory test methods. Numerous experimental sequences and test sites have been initiated since the start of the research; in the last of these, 1·6 million load applications were applied and the dynamic modulus master curve was back-calculated and used to filter out the viscoelastic response of the asphalt layer caused by temperature changes within the material from the repeated loading. Based on the findings of this research, an incremental-recursive fatigue model has been used to predict accurately the reduction in asphalt modulus as a function of any combination of loads and temperatures for a known material.

Laboratory and Numerical Study of the Behavior of Circular Footing Rested on Sand Contaminated with Oil under the Cyclic Loading

This research studies the behavior of circular foundations rested on the soils contaminated with gas oil and kerosene oil under cyclic loading. The final goal of this study was to determine the influence level of the foundation of the reservoirs rested on oil-contaminated sand due to their filling and discharging. The contaminated sand layers were mixed with different percentages of contamination from 2 to 6 of kerosene oil and gasoline. The effect of the contamination percentage, the value of the applied load, as well as the depth and type of contamination is investigated in this study. To validate the numerical studies performed by finite element software, small-scale laboratory tests is carried out. The results showed that the pollutants could affect the amount of final settlement and the number of loading cycles to reach this value. Increasing depth, the number of load cycles and the contamination content increased the final settlement and the number of loading cycles to reach that level increases. Numerical results showed a good compatibility in the load-settlement charts with the experimental results.

Numerical simulation of slurry fracturing during shield tunnelling

The slurry type shield method is an important tunnelling method, especially for underwater tunnels in soft soil. If the slurry pressure is too high, it may lead to slurry fracturing of the stratum in front of the excavation face and cause water inrush accidents. Controlling the face stability of shallow shield tunnels is difficult owing to the inadequate understanding of the slurry induced fracturing mechanism. Most importantly, understanding the details of the slurry fracturing propagation process is not enough, as the process is especially complicated. However, the propagation process cannot be directly observed in the field or in small-scale laboratory tests because it occurs in bodies of soil. Thus far, an effective approach to investigate the slurry fracturing mechanism in the surrounding stratum of a slurry shield tunnel has not been reported. In this paper, a numerical simulation method for evaluating tunnelling-induced slurry fracturing is presented. The developed numerical model considered the couplings of stress distribution, fluid flows, and fracturing. The fracture initiation, branching, and propagation in the stratum could be reproduced numerically. A series of simulations for different ratios of cover depth to tunnel diameter were carried out to investigate the propagation process of slurry fracturing. The effects of slurry pressure at the tunnelling face and the cover depth above the tunnel were investigated. The results of the fracturing process induced by slurry, such as the fracture propagation velocity, slurry pressure distribution along the fracture, fracture initiation pressure, fracture extending pressure, and stratum deformations, were analyzed.

Experimental and numerical analysis of thick embedded laminated glass connections

Laminated glass components are usually realized by bonding glass plates using interlayer polymers that develop adhesion forces during lamination. Recently, these adhesion forces have been used also to realize special adhesive connections for structural glass components and assemblies. The typical example of such a joining technique is conventionally known as “embedded laminated connection”, where a metal insert is encapsulated in multi-ply laminated glass components.In this study, careful consideration is paid for the investigation of the mechanical behaviour of embedded laminated connections with thick metal insert. To this aim, small-scale laboratory tests, Finite Element (FE) numerical models and analytical considerations are presented. Firstly, the results of experimental investigations at different temperatures are discussed, giving evidence of the geometrical and mechanical parameter effects on the so observed performances. It is observed, in particular, that the temperature affects not only the maximum load carrying capacity but also the failure mode of the studied connection typology. Non-linear numerical simulations are then developed in ABAQUS on FE models, able to account for the geometrical and mechanical properties of the reference connection specimens. Further analytical considerations are also presented, in support of the observed experimental findings. It is shown, in particular, that as far as high temperatures are not attained, the mechanical performance and failure mode of the examined connections is strictly related to glass breakage. In addition, it is also observed that at high temperature, failure mode (i.e. bubble formation) and failure location are in line with the expectations. Rather close correlation can be also found for the same embedded connections between test results, FE numerical simulations and analytical assumptions.

Small-scale trials on passenger microbehaviours during aircraft boarding and deplaning procedures

NRC researchers have recently employed computational tools to simulate airline passenger movement – primarily to examine the impact of different procedures on aircraft boarding times. It was felt that the modelling techniques could be improved by the inclusion of current, relevant and refined data on passenger movement. This article outlines a series of small-scale laboratory tests performed to help quantify individual passenger boarding and deplaning movement with and without the presence of luggage. Test subjects were monitored and video recorded while participants moved through a cabin section enabling observers to quantify the performance of specific micro-behaviours that formed the deplaning and boarding process. These tests were conducted at the National Research Council of Canada's prototype cabin research facility. The trials involved a total of 35 subjects who were each observed performing a series of 12 trials inside the cabin section. These trials were formed from the manipulation of three factors: seat pitch (29 in/31 in/33 in), luggage (present/absent), and instructions (continuous flow/discrete movements). During each trial, participants performed a series of micro-behaviours that included traversing the aisle/row, stowing/collecting under-seat bags, seat belt fastening and unfastening and adopting a brace position. In addition, two trials were conducted for each participant outside of the cabin facility to establish baseline straight line movement speeds with and without luggage. The study indicated that the impact of luggage and seat pitch had a notable, but complex, effect on performance and, more importantly, generated an array of data-sets for use in future simulation efforts. For instance, seat pitch appeared to have a more consistent impact when passenger movement was perpendicular to the seat row, as opposed to along the seat row where the impact was varied. Such data collection is necessary to advance empirical support for current and future simulation efforts.

Large displacement numerical study of 3D plate anchors

This paper presents a numerical study carried out in the context of the development of a new application of plate anchors for landslide stabilisation. The plates are positioned on the slope’s ground surface and linked to a deeper stable layer with a steel grouted bar, thus acting as discontinuous elements contrasting the slope movement. This technique is less expensive compared to standard retaining structures, especially in medium and deep landslides. Moreover, plate anchors can bear large displacements of the unstable moving mass without losing efficiency. Evaluating the stabilising force and its optimisation in relation to the plate shape are of great interest. Numerous studies have investigated the bearing capacity of rectangular and circular thin plates at small strains, but the performance of alternative shapes, such as cones or truncated cones, has never been considered. The numerical study here presented applies the Material Point Method to investigate the behaviour of plate anchors with different 3D shapes at large displacements. The numerical model is validated with the results of some small-scale laboratory tests. The pull-out resistance, the soil stress and displacement fields around the plate and the group effect have been investigated, thus obtaining preliminary indications for the design of these elements.

200 kHz Sonication of Mixed-Algae Suspension from a Eutrophic Lake: The Effect on the Caution vs. Outbreak Bloom Alert Levels

For effective ultrasonic algae removal, several studies have considered the ultrasound equipment linked factors, such as power and frequency. However, studies on the response of mixed algal cultures and associated water quality parameters to ultrasound are limited. In this lab-scale sonication, the removal of cyanobacteria at a pre-set frequency of 200 kHz on mixed algae suspensions collected from a eutrophic lake was investigated. The caution (17.5 µg/L) and outbreak (1450 µg/L) alert levels in terms of chlorophyll-a (Chl-a) concentrations of the initial samples were each sonicated for 10, 15, and 20 min, and then kept in an incubator. Fifteen minutes of sonication resulted in best removal efficiency of 0.94 and 0.77, at an ultrasonic dose of 30 kWh/m3 at the outbreak and caution level concentrations, respectively. Immediately after 15 min sonication, and after standing in the incubator for a day, chlorophyll-a removal efficiencies of 0.28 and 0.90 were achieved in the outbreak level, respectively, and the matching removal efficiencies for the caution level were 0.23 and 0.64. Even though the removal was substantial in both cases, the final 147 µg/L chlorophyll-a concentration of the outbreak, which is itself still in the outbreak level range, shows that ultrasonication is not effective to satisfactorily remove algae from a concentrated suspension. Total dissolved nitrogen and chemical oxygen demand were reduced, overall, due to sonication. However, total dissolved phosphorus of the concentrated level was increased during the treatment. Although sonication needs further replicated experimental testing in whole-lake systems, our results show that 200 kHz sonication was able to reduce chlorophyll-a concentrations in small-scale laboratory tests.

Normalized Curvature Ratio for Damage Detection in Beam-Like Structures

Fiber optic sensors (FOS) offer numerous advantages for structural health monitoring. In addition to being durable, lightweight, and capable of multiplexing, they offer the ability to monitor strain in both static and dynamic mode. FOS also allow for instrumentation of large areas of a structure with long-gauge sensors which helps enable global monitoring of the structure. Drawing upon these benefits, the Normalized Curvature Ratio (NCR), a curvature based damage detection method, has been developed. This method utilizes a series of long-gauge fiber Bragg grating (FBG) strain sensors for damage detection of a structure through dynamic strain measurements and curvature analysis. The main assumption is that the ratios between cross-sectional curvature amplitudes under free vibration remain unchanged given the state of the structure is unchanged. The theoretical development of this method is presented along with an analytical study of a simply supported beam with two damage cases: a loss of flexural stiffness in the span and a change in rotational stiffness of the support. Validation of the method is then performed through two implementations. First, through a small-scale laboratory test with a simply supported aluminum beam subjected to a change in the rotational stiffness of the support. Second, the method is applied to an existing in-service highway overpass with over 5 years of data collection of dynamic strain events. The advantages and limitations of the method are identified and discussed. This research shows encouraging results and the potential for the NCR to be used as a simplistic metric for damage detection.

Reflection and transmission of regular waves from/through single and double perforated thin walls

In this paper, reflection and transmission coefficients of regular waves from/through perforated thin walls are investigated. Small scale laboratory tests have been performed in a wave flume firstly with single perforated thin Plexiglas plates of various porosities. The plate is placed perpendicular to the flume with the height from the flume bottom to the position above water surface. With this thin wall in the flume wave overtopping is prohibited and incident waves are able to transmit. The porosities of the walls are achieved by perforating the plates with circular holes. Model settings with double perforated walls parallel to each other forming so called chamber system, have been also examined. Several parameters have been used for correlating the laboratory tests’ results. Experimental data are also compared with results from the numerical model by applying the multi-domain boundary element method (MDBEM) with linear wave theory. Wave energy dissipation due to the perforations of the thin wall has been represented by a simple yet effective porosity parameter in the model. The numerical model with the MDBEM has been further validated against the previously published data.

NUMERICAL SIMULATION OF SEAWALL- BEACH PROFILE INTERACTION IN RUNUP ZONE

This study aimed to determine beach response in the presence of a vertical wall placed in the run-up zone. The responses of natural beach and the beach with a seawall with two different configurations were studied numerically. The capability and limitation of the cross-shore numerical model CSHORE in simulating the cross-shore transformation and the beach evolution in front of a seawall situated inside the surf zone was examined. Numerical model results were compared with small scale laboratory tests (Yüksel et. al, 2014). Offshore transport was observed in all three tests and the model was shown to predict the same trends in profile evolution. Scour depth in front of the vertical wall was correctly captured by the numerical model.

Site characterisation for the Ballina field testing facility

A soft soil field testing facility has been recently established near Ballina, New South Wales, on the east coast of Australia, which is aimed at improving design and construction methods for transport infrastructure. Several sampling, laboratory and in situ testing campaigns have been performed to characterise the material properties of the soil. High-quality laboratory testing has been performed at one location through the soil profile and a range of geophysics, cone penetrometer, seismic dilatometer, shear vane and permeability tests have been carried out at other locations. The in situ tests have demonstrated that the stratigraphy and test data are reasonably uniform across the site. Seasonal groundwater variations cause the in situ stress state to vary with time. In situ test data have been compared with laboratory tests in order to estimate soil material properties at the locations of the in situ tests. The accuracy of published correlations was variable and site-specific correlations were found to provide a better outcome. The coefficient of consolidation and the water permeability obtained from small-scale laboratory tests shows good agreement with in situ estimations based on piezocone penetration test (CPTu) dissipation tests and BAT tests, respectively. The correlation between laboratory and in situ data is used to develop a robust geotechnical model for the Ballina site.

Bearing capacity of footing supported by geogrid encased stone columns on soft soil

The stone columns are increasingly being used as a soil improvement method for supporting a wide variety of structures (such as road embankment, buildings, storage tanks etc.) especially built on soft soil. Soil improvement by the stone column method overcomes the settlement problem and low stability. Nevertheless, stone column in very soft soils may not be functional due to insufficient lateral confinement. The required lateral confinement can be overcome by encasing the stone column with a suitable geosynthetic. Encasement of stone columns with geogrid is one of the ideal forms of improving the performance of stone columns. This paper presents the results of a series of experimental tests and numerical analysis to investigate the behavior of stone columns with and without geogrid encasement in soft clay deposits. A total of six small scale laboratory tests were carried out using circular footing with diameters of 0.05 m and 0.1 m. In addition, a well-known available software program called PLAXIS was used to numerical analysis, which was validated by the experimental tests. After good validation, detailed of parametric studies were performed. Different parameters such as bearing capacity of stone columns with and without geogrid encasement, stiffness of geogrid encasement, depth of encasement from ground level, diameter of stone columns, internal friction angle of crushed stone and lateral bulging of stone columns were analyzed. As a result of this study, stone column method can be used in the improvement of soft ground and clear development in the bearing capacity of the stone column occurs due to geogrid encasement. Moreover, the bearing capacity is effected from the diameter of the stone column, the angle of internal friction, rigidity of the encasement, and depth of encasement. Lateral bulging is minimized by geogrid encasement and effected from geogrid rigidity, depth of encasement and diameter of the stone column.

Classification of simultaneous multiple partial discharge sources based on probabilistic interpretation using a two-step logistic regression algorithm

In online condition assessment monitoring of high voltage (HV) insulators, it is often required to identify multiple, simultaneously activated partial discharge (PD) sources that happen in the insulation of the HV apparatus. Phased resolved partial discharge (PRPD) patterns are commonly used to identify PD sources. However, multiple, concurrent PD sources sometimes result in partially overlapped patterns, which make them hard to be identified. In this paper, we develop an accurate, reliable algorithm by constructing a novel two-step logistic regression (LR) model to conduct probabilistic identification of multi-source PDs. To this end, principal component analysis is applied on a database to construct a low dimensional space associated with single-source PDs. Samples of multi-source PDs are then projected onto this space and one-class kernel support vector machine is adopted to distinguish multi-source PDs from single-source ones. Finally, classification is performed by estimating the probability (degree of membership) of each PRPD pattern arising from different multi-source PDs following two rounds of LR modeling. To evaluate the performance of our proposed method, we study a number of multi-source PD models to simulate common defects of Gas-Insulated Switchgear (GIS) in small-scale laboratory test cells with realistic SF6 gas condition. Observations are obtained using fingerprints generated by a novel approach from recorded PRPD patterns. Comprehensive performance evaluation of the proposed algorithm and its advantages are conducted and the development of analytical equations is presented. The results of this paper can be used to design a solid basis for an automated multi-source classification system, which facilitates multi-source PD identification in early stages and safe operation of HV apparatus.

Comparative modelling of laboratory experiments for the hydro-mechanical behaviour of a compacted bentonite–sand mixture

A comparative modelling exercise involving several independent teams from the DECOVALEX-2015 project is presented in this paper. The exercise is based on various laboratory experiments that have been carried out in the framework of a French research programme called SEALEX and conducted by the IRSN. The programme focuses on the long-term performance of swelling clay-based sealing systems that provide an important contribution to the safety of underground nuclear waste disposal facilities. A number of materials are being considered in the sealing systems; the current work focuses on a 70/30 MX80 bentonite–sand mixture compacted at dry densities between 1.67 and 1.97 Mg/m3. The improved understanding of the full set of hydro-mechanical processes affecting the behaviour of an in situ sealing system requires both experiments ranging from small-scale laboratory tests to full-scale field emplacement studies and coupled hydro-mechanical models that are able to explain the observations in the experiments. The approach was to build models of increasing complexity starting for the simplest laboratory experiments and building towards the full-scale in situ experiments. Following this approach, two sets of small-scale laboratory experiments have been performed and modelled. The first set of experiments involves characterizing the hydro-mechanical behaviour of the bentonite–sand mixture by means of (1) water retention tests under both constant volume and free swell conditions, (2) infiltration test under constant volume condition, and (3) swelling and compression tests under suction control conditions. The second, more complex, experiment is a 1/10th scale mock-up of a larger-scale in situ experiment. Modelling of the full-scale experiment is described in a companion paper. A number of independent teams have worked towards modelling these experiments using different conceptual models, codes, and input parameters. Their results are compared and discussed. This exercise has enabled an improved modelling of the bentonite–sand mixture behaviour, in particular accounting for the dependence of its retention curve on the dry density. Moreover, it has shown the importance of the technological voids on the short-term behaviour of the sealing system.

A device to study the simultaneous heat and moisture movement in soils

Studies of simultaneous heat and moisture movement in soils are essential to characterise the thermal stability of the medium and to understand the soil water dynamics in the vadose zone. Although, many laboratory, analytical and mathematical models have been developed, small-scale laboratory tests found to be quite useful in understanding the behaviour of model materials and evaluating the influence of various interrelated parameters on heat and moisture movement in the soil mass. This paper presents the usefulness of a simple device (i.e. a thermal probe) that can be employed to study the simultaneous heat and moisture movement in kaolin. The device, which was fabricated in-house, is easy to use, handy and cost effective. It imposes a line-heat source of thermal flux in the soil mass that creates a thermal gradient causing moisture movement to take place from higher to lower temperature regions. It has been noticed that the device is very efficient and quite useful to carry out experiments related to simultaneous heat and moisture movement in soils. Further, attempts were also made to demonstrate the distinct advantage of electrical properties to measure the instantaneous moisture content of kaolin in a non-destructive and non-invasive manner.