Large-scale Laboratory Tests Research Articles

Mechanistic Analyses of Geosynthetic Reinforced Aggregate Road Test Sections

Large-scale laboratory box tests and a full-scale traffic test were performed by the U.S. Army Engineer Research and Development Center to evaluate the performance of geosynthetic reinforced aggregate road sections constructed with marginal base materials over a typical subgrade. The large-scale laboratory testing and full-scale test section included eight different instrumented aggregate road sections including three different aggregate base materials and two different geosynthetics. Mechanistic analyses of each pavement section were conducted using linear elastic, nonlinear elastic, and nonlinear anisotropic models to predict the critical pavement response parameters. The analyses show that mechanistic tools can be effectively used to estimate the critical pavement response parameters for unpaved roads.

Improved performance of ballasted tracks at transition zones: A review of experimental and modelling approaches

Abstract Track transitions such as bridge approaches, road crossings and shifts from slab track to ballasted track are common locations where track degradation accelerates due to dynamic and high impact forces; as a consequence there is higher differential settlement. These types of discontinuities cause an abrupt change in the structural response of the track due mainly to variations in stiffness and track damping. Track transition zones are prone to an accelerated deterioration of track material and geometry that leads to increased maintenance costs. Track deterioration also leads to vehicle degradation due to enhanced acceleration, low frequency oscillation, and high frequency vibrations. While ballast deterioration is a major factor affecting the stability and longevity of rail tracks, the cost of tackling transition related problems that detract from passenger comfort is also high. A good transition zone lessens the impact of dynamic load of moving trains by minimising the abrupt variations in track stiffness and ensuring a smooth and gradual change from a less stiff (ballasted track) to a stiff (slab track) structure. This paper presents a critical review of various problems associated with transition zones and the measures adopted to mitigate them; it also includes critical review of research work carried out using large-scale laboratory testing, mathematical and computational modelling and field measurements on track transition zones.

Development of Smelting Technology of Complex Ferroalloy with the Use of High-ash Coals

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Acetic acid application as an activating reagent in the intensive cyanidation of gravity concentrates

The well-known technology of intensive cyanide leaching of gravity concentrates, which allows to bring part of gold into commercial products with obtaining high-purity Dore alloy, requires the use of expensive reagents and high temperature (80 °С) leaching. Studies have been carried out on intensive leaching of gold-containing gravity concentrate in a drum-type apparatus at low concentrations of sodium cyanide with the addition of a new reagent-activator. It is proposed to conduct intensive cyanidation of enriched gravity concentrate using acetic acid as an effective activator reagent. Improving the efficiency of cyanide leaching by introducing activators into the reagent system is achieved by dissolving passivating films on the surface of gold grains. Studies on the intensive leaching of gold in the enlarged laboratory tests. The results of the large-scale laboratory tests on the intensive cyanide leaching of the gravity concentrate using acetic acid as an activating agent activator were fully confirmed by the data of laboratory studies.

Influence of Permeability on the Rate of Fire Spread over Natural and Artificial Pinus radiata Forest Litter

The rate of fire spread is of paramount interest in order to prevent and control wildland fires. It has been extensively studied under laboratory conditions, but little research has been made regarding the differences between artificially constructed and natural litter. By using a specially designed sampling method, in this study differences in the rate of spread between natural and constructed pine needle litter samples are assessed using a combustion tunnel with controlled wind speed. A total of 68 experiments were conducted with four levels of wind speed and six levels of permeability (five for constructed samples and one for the natural sample). It was found that permeability has a strong influence on the rate of spread when wind speeds are high (2.1–3.6 $${\hbox {m}} \cdot {\hbox {s}}^{-1}$$ ). It was also found that while wind speed and permeability have a strong influence on the rate of spread, their combined effect is not significant. Thus, both variables may be treated independently from one another. Lastly, it was found that constructed samples with permeability of $$1 \times 10^{-7}$$ m $$^2$$ behave similarly to natural samples in terms of the rate of spread. This suggests that it is possible to use constructed samples in the laboratory by matching their permeability, and, thus, obtain realistic values for the rate of fire spread. This could be of use for medium and large scale laboratory tests, where it is not possible to use undisturbed litter samples.

Study on the Formation Law of the Freezing Temperature Field of Freezing Shaft Sinking under the Action of Large-Flow-Rate Groundwater

Taking into account moisture migration and heat change during the soil freezing process, as well as the influence of absolute porosity reduction on seepage during the freezing process, we construct a numerical model of hydrothermal coupling using laws of conservation of energy and mass. The model is verified by the results of large-scale laboratory tests. By applying the numerical calculation model to the formation of artificial shaft freezing temperature fields under the action of large-flow groundwater, we conclude that groundwater with flow rates of less than 5 m/d will not have a significant impact on the artificial freezing temperature field. The maximum flow rates that can be handled by single-row freezing pipes and double-row freezing pipes are 10 m/d and 20 m/d, respectively, during the process of freezing shaft sinking. By analyzing the variation of groundwater flow rate during freezing process, we find that the groundwater flow velocity can reach 5–7 times the initial flow velocity near the closure moment of the frozen wall. Finally, in light of the action characteristics of groundwater on the freezing temperature field, we make suggestions for optimal pipe and row spacing in freezing pipe arrangement.

Experimental study to examine the role of under sleeper pads for improved performance of ballast under cyclic loading

The degradation and deformation of ballast critically affect the track geometry, safety, and passenger comfort. The increase in axle loads and train speed increases the stress applied on the ballast and exacerbates the rate of ballast degradation. This situation is more critical when tracks are built on stiff subgrades (e.g. bridges, tunnels and crossings), hence the use of energy absorbing (damping) layers in track substructure is a countermeasure to minimize track damage. In this study, a series of large-scale laboratory tests using the track process simulation testing apparatus (TPSA) is carried out to assess the performance of under sleeper pads (USP) to reduce ballast degradation and to decrease permanent deformation. When placed beneath the sleeper, the energy absorbing nature of USP reduces the energy transferred to the ballast and other substructure components. Subsequently, the ballast layer experiences less deformation and degradation. Innovative tactile surface sensors (matrix-based) are used to measure the pressure and contact area between sleeper and ballast. The measured data show that an increase in contact area between sleeper and ballast decreases the stress applied on ballast, and thus a reduction in ballast breakage and corresponding reduced ballast deformation can be achieved. Furthermore, the influence of the USP stiffness is examined and the measured data offer an insightful understanding of the role of USP for given track and loading conditions in terms of energy dissipation and reduced ballast deformation.

Laboratory Study on Single Stone Columns Reinforced with Steel Bars and Discs

Stone columns are widely used as an effective and environmental friendly improvement method for increasing the load-carrying capacity of soft clay soils. In very soft clay soils, reinforced stone columns are used because of the lack of the lateral confinement created by the surrounding soil. To provide lateral additional confinement, geosynthetics are usually used. This study intends to evaluate the use of vertical steel bars and horizontal steel discs as an alternative way to geosynthetics to investigate the effect of reinforcement on the footing load-carrying characteristics. Therefore, some large-scale laboratory tests were conducted on stone columns with diameters of 80 and 100 mm and a length to diameter of 5. The results show that changing the arrangement of the bars to a higher stiffness leads to increase in load-carrying capacity. Reinforcing the full-length of the stone columns with the bars in comparison to half-length reinforced has significant influence in capacity. However, in the case of horizontal discs, this increase is negligible. Also by decreasing the space of the discs, load-carrying capacity increases. Moreover, the performance of the vertical reinforced stone column seemed to be better than the horizontal reinforced stone column. The increase of load-carrying capacity in reinforced stone columns with vertical bars or horizontal discs is higher than geotextile reinforcement in the same conditions.

Relatively Large-Scale Experimental Study on Behavior of Compacted Lime Mortar (CLM) Columns: Influence of Moisture Content

Various materials have been utilized for ground improvement techniques based on geoenvironmental compatibility. The application of lime mortar in soil has been catching the attention of researchers and engineers. However, there is a lack of research on the variation of moisture content in soil affecting the mechanical behavior of lime mortar. In this study, large-scale laboratory tests were conducted on approximately thirty specimens to evaluate the size effect on stiffness and load bearing capacity of compacted lime mortar (CLM) columns and clayey soil under different saturation conditions. In addition, approximately forty small-scale laboratory tests were carried out on dry clay, dry CLM column and lime mortar specimens to evaluate the unconfined compressive strength (UCS). According to results, UCS of CLM column under small-scale condition was higher than that of the large-scale. Moreover, high moisture content had a significant influence on the stiffness of improved ground and the bearing capacity of CLM columns. Finally, validation of results indicated that numerical model predictions are in agreement with experimental results.

Laboratory performance of steel mechanically stabilized earth reinforcements

ABSTRACT Mechanically stabilized earth (MSE) techniques have proven to offer reliable and cost-effective solutions to many poor and unstable ground problems. However, till now there are many uncertainties regarding the selection of appropriate types of reinforcement and the evaluation of design parameters for MSE wall structures. This paper presents the results of a significant programme of large-scale laboratory tests conducted to examine the performance of two types of soil reinforcement namely smooth plain steel and ribbed steel strips. The reinforcements were subjected to a series of axial static and slow repeated loading under different levels of normal stress and their ultimate pullout capacity were determined. The mechanics of load mobilization at the soil-reinforcement interface and the failure modes of the reinforcements were analyzed. In general, the results showed that ribbed steel strips are more load efficient and safer reinforcements than smooth steel strips under both static and repeated loading.

Load and Deformation Mechanisms in Geosynthetic-Reinforced Piled Embankments

Geosynthetic-reinforced piled embankments have been increasingly used to stabilise embankments over soft soils. The presence of the reinforcement reduces the stresses transferred to the soft foundation and improves the efficiency of the transference of loads to the piles. Therefore, significant reductions in fill settlements and in lateral displacements of the soft soil can be obtained. However, the design of this type of work is still complex and simple theoretical approaches are commonly employed in practice. This paper investigates the load transference and deformation mechanisms in reinforced piled embankments by means of large-scale laboratory tests. Four types of geosynthetics, including a geogrid and three geotextiles, were tested with varying values of tensile stiffness. Surcharges on the fill surface of up to 40 kPa (200 kPa under prototype conditions) were applied. Test measurements were compared with predictions from some currently employed analytical methods. The results obtained showed the benefits of using geosynthetic reinforcement in this type of work and that significant variations among predictions by analytical methods and measurements may occur. It is recommended that sound engineering judgement be exercised when using analytical solutions in the design of geosynthetic-reinforced piled embankments on soft subgrades.

Scale effect on hydraulic conductivity and solute transport: Small and large-scale laboratory experiments and field experiments

Hydraulic conductivity (K), dispersivity (α) and partition coefficient (Kd) can change according to the measurement support (scale) and that is referred to as scale effect. However, there is no clear consensus about the behavior of these parameters with the change in the scale. Comparison between results obtained in different support of measurements in the field and in the laboratory can promote the discussion about scale effects on K, α, and Kd, and contribute to understanding how these parameters behave with the change in the scale of measurement, the main objectives of the present paper. Small and large-scale laboratory tests using undisturbed soil samples and field experiments at different scales were performed. Results show that for the same measurement condition, K, α, and Kd increase with scale in all studied magnitudes. Caution should be taken when using K, α, and Kd values in numerical models with no concern about the scale effect. The lack of consideration of the difference of scale between field and laboratory measurements and numerical model may compromise the reliability of the predictions and misrepresent the responses.

Interactions of Alumina-Based and Magnesia-Based Refractories with Iron Melts and Slags: A Review

A novel flash ironmaking technology (FIT) based on the direct reduction of iron ore concentrate with a reductant gas (such as hydrogen, natural gas, coal gas, or a combination thereof) in a flash furnace is being developed at the University of Utah. This technology which is undergoing large-scale laboratory testing aims at overcoming the limitations of blast furnace ironmaking by bypassing the problematic pelletization/sintering and cokemaking steps.[1–5] Refractory selection is expected to play an important step in the development of FIT and its proposed scale-up. For nominating an appropriate refractory for the FIT, understanding the interactions of candidate refractories with iron/iron oxide and slags under H2/CO/CO2/H2O environments is necessary. This work is undertaken to review the existing literature on the interactions of important refractories with iron melts and relevant slags with an emphasis on two of the most commonly used refractories in ironmaking and steelmaking applications: the alumina-based refractories (used widely in blast furnace operations) and the magnesia-based refractories (used extensively in primary as well as secondary steelmaking). First, a comprehensive review on the interactions of alumina-based refractories with iron melts and slags has been done. Next the existing literature on the interactions of magnesia-based refractories with iron melts and relevant slags has been reviewed. Summaries have been included after each section and sub-section along with comments and critical insights from the authors. Finally, in the concluding remarks the differences in operating conditions between existing iron and steelmaking practices and the novel FIT have been highlighted. On the basis of these differences, it has been argued that the results and conclusions available from previous studies on refractory–metal–slag interactions are of little significance to flash ironmaking. Thus, there exists a need to carry out laboratory experiments for evaluating refractory performance in flash ironmaking under conditions relevant to the current process (FIT).

Experimental and numerical study on structural performance of reinforced concrete box sewer with localized extreme defect

An experimental and numerical investigation into the structural performance of reinforced concrete box sewers with typical corrosion-related extreme defects localized at the ceiling was conducted. Firstly, during the large-scale laboratory test, some key structural responses were captured and evaluated, including the crack width development process (via digital image correlation measurement), ceiling deflection, and material strains of both complete and typical defective boxes. The failure modes and load-carrying mechanism throughout the specimen loading phases were analyzed. Furthermore, the specimen failure process was simulated using a damage-based finite element method, and a related parameter sensitivity analysis was performed. The results indicate that the defective ceiling cracked at mid-span under a low load value, but the bending capacity loss can be substituted by two shoulders and carry three to five times more load before completely collapsing. The simulation matched the lab test qualitatively, and with the suggested set strategy of material parameters, the load-deflection feature curve could provide a practical prediction of the ultimate bearing capacity of the defective sewers, with a 10–15% error on the safe side.

Load-settlement response of shallow square footings on geogrid-reinforced sand under cyclic loading

To study the settlement and dynamic response characteristics of shallow square footings on geogrid-reinforced sand under cyclic loading, 7 sets of large scale laboratory tests are performed on a 0.5 m wide square footing resting on unreinforced and geogrid reinforced sand contained in a 3 m × 1.6 m × 2 m (length × width × height) steel tank. Different reinforcing schemes are considered in the tests: one layer of reinforcement at the depth of 0.3B, 0.6B and 0.9B, where B is the width of the footing; two and three layers of reinforcement at the depth and spacing both at 0.3B. In one of the two double layered reinforcing systems, the reinforcements are wrapped around at the ends. The footings are loaded to 160 kPa under static loading before applying cyclic loading. The cyclic loadings are applied at 40 kPa amplitude increments. Each loading stage lasts for 10 min at the frequency of 2 Hz, or until failure, whichever occurs first. The settlement of the footing, strain in the reinforcement and acceleration rate in the soil have been monitored during the tests. The results showed that the ultimate bearing capacity of the footings was affected by the number and layout of the reinforcements, and the increment of bearing capacity does not always increase with the number of reinforcement layers. The layout of the reinforcement layers affected the failure mechanisms of the footings. Including more layers of reinforcement could greatly reduce the dynamic response of the foundations under cyclic loading. In terms of bearing capacity improvement, including one layer of reinforcement at the depth of 0.6B was the optimum based on the test results. It is found that fracture of geogrid could occur under cyclic loading if the reinforcement is too shallow, i.e. for the cases with the first layer of reinforcement at 0.3B depth.

Experimental Investigation of Propellant Fracturing in a Large Sandstone Block

SummaryPropellants have been used in oil and gas wells to assist with perforating and creating near-wellbore stimulation. Propellants are electrically ignited in the wellbore at the perforated interval. Upon ignition, they rapidly create a large amount of gas, and the pressurization leads to breakdown of the formation. It has been postulated that the pressurization leads to creation of multiple fractures in the formation. This paper describes an experimental study with a new propellant and aims to understand the pattern of fracture creation with these propellants. The results are also compared with an older generation of propellant tested by Wieland et al. (2006).A large-scale laboratory test was performed in a sandstone block (30×30×54 in.) with a 2-in.-diameter vertical centralized wellbore extending the full block height. The block was loaded in a polyaxial stress frame. A propellant cartridge was positioned in the center of the wellbore. Small holes were drilled in the rock to intersect the expected primary fracture and were instrumented with high-resolution pressure gauges to enable fracture-timing and -growth-rate analysis. Anisotropic stresses representative of field conditions were applied on the block, and the wellbore was pressurized before ignition.The propellant ignition produced an initial peak pressure of 5,790 psi in 1.4 ms followed by an oscillatory pattern of pressure increase to a maximum pressure of 6,660 psi before decaying because of fracture growth and gas leakoff. The block was removed from the test frame and cut vertically and horizontally to examine the fracture pattern generated by the propellant. A dominant planar fracture was observed on either side of the wellbore, which propagated in the direction perpendicular to the minimum-horizontal-stress direction. It was verified that the propellant had a much-higher burn rate than the propellant tested by Wieland et al. (2006).The large-scale block test provides critical insights and data that can serve as inputs to calibrate physics-based models for modeling propellant ignition and stimulation. The results help in understanding the benefits and limitations of using propellants for stimulation.

Editorial: Large-Scale and Full-Scale Laboratory Test Methods for Examining Wind Effects on Buildings

Editorial: Large-Scale and Full-Scale Laboratory Test Methods for Examining Wind Effects on Buildings

Asphalt wearing course optimization for road traffic noise reduction

Nowadays traffic noise and air pollution are as important as durability parameters, what leads to the need of more comprehensive approach when planning, designing, constructing and maintaining road pavements. Having in mind country differences in traffic volumes, climate conditions and financial capabilities it is not easy to transfer various solutions from country to country. Due to such peculiarities, large research study was initiated in Lithuania seeking to develop efficient and effective low noise pavement solution for specific regional climate conditions. This paper presents research of commonly used asphalt concrete (AC), stone mastic asphalt (SMA), porous asphalt (PA) and a concept of noise reducing asphalt mixtures. As part of this study large scale laboratory testing of acoustical and mechanical performance, durability and resilience to climate were performed. The paper also presents analysis of laboratory testing results which were positive and followed with the pilot implementation of developed asphalt mixtures for further research activities under real traffic and climate conditions.

Experimental Investigation on the Bearing Capacity of Stone Columns with Granular Blankets

Using stone columns is an efficient method to increase the bearing capacity of soft soils. This has led to an increased interest in further developing and improving the method. In addition, granular blankets are used to increase the bearing capacity of the stone columns. In this research, the bearing capacity of stone columns, granular blankets, and a combination of both methods in reinforced and unreinforced modes was examined using large-scale laboratory tests. A scale factor of 1–10 is used for the geometry of the models, and the stone columns are a floating type that are 60 mm in diameter and 350 mm in length. These columns are either reinforced with vertical encasement of a geotextile or they are unreinforced. The granular blankets are either reinforced by using a biaxial geogrid or they are unreinforced with 40 and 75 mm thicknesses. In general, 16 large experimental tests have been carried out. Results indicate that using all these variations (granular blankets, stone columns, and a combination of both) improves bearing capacity. Using geogrid as the reinforcement of granular blankets and geotextile as stone-column encasement increases the efficiency of granular blankets and stone columns significantly. The maximum bearing capacity was obtained when reinforced granular blankets and reinforced stone columns were combined. The stress-concentration ratio and bearing capacity increased as geotextile encasement was used in the stone columns.

Performance of Geosynthetic-Reinforced Soils Under Static and Cyclic Loading

This paper investigates and discusses the composite behavior of geosynthetic reinforced soil mass. It presents the results of a series of large-scale laboratory tests supported by analytical methods to examine the performance of geogrid reinforcement subjected to static and cyclic pullout loading. The testing equipment and procedures used for this investigation are outlined. The results show that geosynthetic reinforcement can mobilize great resistance to static pulling load under high confining pressures. The reinforcement exhibits gradual deformation under cyclic loading showing no sign of imminent pullout failure for all levels of applied loads. In general, the results demonstrate that geosynthetic can be used in situations where loads are non-static, although care will be required in ensuring that appropriate factors of safety are applied to control the resulting deformation. A simplified analytical model for calculating the pulling capacity of geosynthetic reinforcement is proposed.