Fill Heights Research Articles

Progressive development of soil arching and deformations in two- and three-dimensional trapdoor tests

In this study, two- and three-dimensional trapdoor tests were conducted using a newly developed trapdoor test device, to investigate the evolution of soil arching and fill deformation with different relative fill densities and fill heights. The test results show that the trapdoor settlements normalised by trapdoor width required for the soil arching ratios to reach minimum and ultimate values increased with fill height. In tests with dense fill, both the minimum and ultimate soil arching ratios were smaller compared to tests with loose fill at the same fill height. Two symmetrical slip surfaces developed from the trapdoor edges, with their inclination angles dependent on the dilatation angle of the sand. The proposed Gaussian distribution function with fitting parameters well matched the measured fill settlement profile. In the dense fill tests, the settlement trough’s width and volume loss induced by trapdoor settlement gradually decreased with fill elevation due to its strong shear dilation behaviour. Conversely, the loose fill exhibited weaker shear dilation behaviour, resulting in a larger settlement region. The settlement trough width and volume loss ratio, derived from the measured fill deformation, can be used to predict the fill deformation, including the surface settlement.

Discrete Element Modeling of Irregular-Shaped Particles Using an Automatic Generation Algorithm-Based Multi-Sphere Model

Within the Discrete Element Method (DEM) framework, the multi-sphere model capable of creating irregular-shaped particles by several sub-spheres attracts increasing attention. Traditionally, the creation of irregular-shaped particles using the multi-sphere model requires manual determination of the position and diameter of each sub-sphere, which extremely increases the difficulty and workload of DEM modeling of irregular-shaped particles. To tackle this issue, a new automatic generation algorithm that helps to create arbitrary-shaped multi-sphere particles automatically was developed in this study. The quality of created multi-sphere particles can be easily controlled by adjusting the number of sub-spheres and size factor referred to as the size ratio of the smallest sub-sphere to the largest sub-sphere. To verify the effectiveness of the newly developed automatic generation algorithm, two verification tests were conducted in this study: (i) The packing behavior of irregular-shaped particles in a rectangular container and (ii) the mechanical behavior of irregular-shaped particles under the uniaxial compression. The fill heights of the simulations were in line with those of the experiments with an error of less than 8%. The mechanical behavior of irregular-shaped particles under the uniaxial compression can also be well reproduced. Besides, the influence of important parameters on simulation accuracy was also investigated. The results demonstrated that the newly developed automatic generation algorithm can accurately create complex-shaped particles with a small number of sub-spheres. Increasing the number of sub-spheres will improve the simulation accuracy but at the expense of computational efficiency. A larger size factor leads to higher computational efficiency in DEM simulation but is accompanied by a significant loss of accuracy.

Effect of live loads on top slab of cast-in-place reinforced concrete box culverts

Reinforced concrete box culverts (RCBCs) designed according to old codes, using lighter truck weights (e.g., H15), may require posting when rated for current design and permit vehicles. When load ratings are calculated based on current AASHTO Specifications, they can be negatively affected by the conservative live-load attenuation through soil fill. This study evaluates the positive bending strains induced by live-load distribution through soil fill when load rating cast-in-place (CIP) RCBCs. Eighteen (18) single and multicell RCBCs in Kentucky were load tested and the effects of truck live loads analyzed. Fill heights, HF, varied from 0 m (0 ft) to 3.57 m (11.7 ft), clear cell spans, S, from 3.05 m (10.0 ft) to 6.71 m (22.0 ft), and culvert spans from 6.71 m (22.0 ft) to 18.59 m (61.0 ft). Field data were collected using strain gauges attached to the interior surfaces of culverts. Irrespective of how many cells the RCBCs had, strain variations with fill height in the top slabs were similar. At fill heights greater than 3.05 m (10.0 ft), maximum strains in the top slabs measured less than 10 microstrain, a value at which live-load effects are considered negligible. Combining live-load strains measured on the Kentucky culverts with ones from field tests in Missouri and Louisiana, a live-load tensile strain envelope is proposed to load rate the top slabs of RCBCs for positive bending when cell spans are less than 4.6 m (15.0 ft).

Centrifuge and analytical modeling of counterweight retaining walls under translation mode

Counterweight retaining walls (CRWs) are a variant of gravity-retaining walls that feature a pressure relief platform (RP) on the backfill side to reduce total earth pressure, offering a cost-effective option compared to traditional forms. However, the intricate interactions between CRWs and backfill, coupled with the lack of clear design guidelines, have restricted their use. This study examines the behavior of CRWs in translation mode using three different centrifuge model tests, each with varying fill heights. Observations show a slightly concave slip surface through the wall heel and a nearly planar slip surface extending from the edge of the RP to the back of the wall in an active limit state. Backfill movement can be classified into translation, sliding, and stable zones. Earth pressure distribution on the upper wall follows a trapezoidal pattern, whereas the pressure on the lower wall exhibits a triangular distribution. Earth pressure on the RP is approximately linear, peaking near the RP’s edge. Introducing a friction angle mobilization factor for the potential first slip surface improves accuracy in calculating earth pressure. The tests were replicated to validate the analytical model for earth pressure calculations, using the adaptive finite-element limit analysis method.

An Evaluation of Treatment Effectiveness for Reclaimed Coral Sand Foundation in the South China Sea

Mega land reclamation projects have been carried out on the coral reefs in the South China Sea. Coral sand was used as a backfill material through hydraulic filling, with fill heights ranging from 6 to 10 m. To enhance foundation stability, vibro-flotation and impact rolling have been employed. However, the uneven distribution of coral sand, irregular particle shape, lower single-particle strength, and paucity of engineering cases for reference have posed challenges in evaluating the effectiveness of these foundation treatments. In this study, the effectiveness of vibro-flotation and impact rolling on the densification and bearing capacity of coral sand foundations has been investigated. In situ tests, including the plate load test, California Bearing Ratio (CBR) test, density measurements, dynamic penetration test (DPT), and settlement monitoring, were conducted at four distinct zones: an untreated zone, a vibro-flotation zone at a 5 m depth, a vibro-flotation zone at a 10 m depth, and an impact rolling zone. The findings suggest that coral sand exhibits promising characteristics for foundation construction. Seepage and self-weight consolidation following land reclamation formation significantly enhance the compaction degree of the coral sand foundation, thereby meeting the requirements for areas with lower bearing capacity demands. Both vibro-flotation and impact rolling techniques could significantly enhance the foundation-bearing capacity, with marginal differences between them. Since the machinery is simple and construction speed is quick, the impact rolling method is considered to be the most efficient for the treatment of coral sand foundation. The DPT results suggest that the reinforcement effect of both vibro-flotation and impact rolling on the deep foundation is not as substantial as the surface layers. This study provides valuable insights into optimizing foundation treatments for land reclamation projects on the coral reefs.

Determination of Finite Element Modelling Errors for Box Culverts Using Field Load Tests

Buried culverts have been in service more than half a century and their age raises questions about their reliable serviceability for the new standard vehicles. The gross weight and axle spacing of these trucks play an important role on the performance of the buried culverts where the culvert is covered with shallow fill heights. Field live load tests were conducted by driving a loaded truck over some culverts at slow speed while recording data at the critical locations of these culvert. Finite element (FE) models were developed and calibrated using field load test results. Live load distribution formulations were adopted from AASHTO LRFD Bridge Design Specifications for different fill heights. Two- and three-dimensional FE models were modelled and loaded separately to compare the critical section forces. The results showed that the error using two different FE modelling approach yields more than 100% error for the maximum section forces when fill heights is between 60 cm and 120 cm. This study is aimed to highlighting the inherent error in numerical modelling of buried reinforced box culverts for design or rating purposes.

Calculation of Dynamic Amplification Factor for Railway Concrete and Masonry Arch Bridges Subjected to High-speed Trains

The dynamic amplification factor (DAF) is one of the most important parameters to express the dynamic behavior of bridges under moving loads. This parameter is used in bridge design codes instead of exhaustive dynamic analyses. Therefore, the DAF and the possible derived relationships can be good alternatives to dynamic analyses because of time and computational cost savings. Masonry arch bridges are complex infrastructures due to their geometry and structural behavior, and it is troublesome to prepare an accurate numerical model. To conduct dynamic analyses, due to their multiplicity, calculating the DAF of the bridges imposed by high-speed trains can lead to a rapid assessment of these old railway arch bridges. For this purpose, in the present study, the finite element models of two concrete and masonry arch bridges with small fill material heights, which are completely different in terms of geometric and mechanical characteristics, were prepared. In the next step, by performing 378 dynamic analyses based on the 27 different train models, the DAF has been computed. The results show that the calculated DAFs are in the rational range, and bogies interval, axles interval, and span length are recognized as the most important parameters in the DAF changes.

Investigation on the effect of skew angle on dead and live-loads in RC skew box culverts for Road Under Bridge (RUB) design

Skew box culverts are common on railway lines and highways when non-perpendicular crossings are encountered. Although various studies on the influence of skewness on culvert design have been undertaken, the majority of the work has focused on the Road Over Bridge (ROB) design. In the present study, an investigation of the effect of skew angle and topsoil fill height on the live and dead load characteristics of a two-cell reinforced concrete (RC) skew box culvert for Road under Bridge (RUB) design has been carried out. The dead and live loads considered in the present work have been calculated following the Indian Railway Standard (IRS) Bridge rule – 2014, Indian Railway Standard (IRS) Substructures and Foundation of Bridges – 2013, and Indian Standard (IS) 875part 3 – 1987. The soil fill height above the top slab varied from 2 m to 10 m with a 2 m increment for the current investigation, with skew angles ranging from 0° to 75° at intervals of 15°. The influence of skewness and soil fill height is explored in a detailed manner in this work, and the findings are provided in contrast to a straight box culvert. The dispersion diagram showing the distribution of loads is developed for the various skew angles and soil fill heights. The results revealed that the effect of skew has no influence on SIDL, lateral earth pressure, earth pressure from surcharge loads, and live load intensities from wind and footpath. However, the intensity of dynamic loads due to the axle movement of trains, derailment of trains, and Plasser’s Quick Relaying System (PQRS) loads decreases with increased skew angle. But the effect of longitudinal forces caused by the braking and traction of the trains increased as the skew angle increased. Also, the influence of skew is more pronounced at lower fill heights. The Engineers may find the results of this study valuable for building RC skew box culverts for RUB applications.

Effect of relative density of 2D granular materials on the arching effect through numerical trapdoor tests

The relative density and the fill height of granular materials influence the arching effect significantly, from either the overall behavior of granular materials or the formation of the arching effect. In this study, a comprehensive comparison of the arching effect at four fill heights with three relative densities is conducted by numerical trapdoor tests using the two-dimensional (2D) discrete element method. The results indicate that the stick–slip behavior of the arching ratio (the ratio of the average vertical stress on the trapdoor to the overburden stress; the ratio decreases to a minimum value, followed by recovering to the ultimate value) is more obvious for the case with lower fill height at a given relative density or that with higher density at a given fill height. The partial and the full arching can be distinguished by whether the loosen zone propagates to the surface. Two different critical states are identified for the partial and the full arching, respectively. These critical states are insensitive to the relative density. A characteristic height is identified around twice the width of the trapdoor, at which the critical state of the partial arching transfers to that of the full arching with the increase of the relative density.

Investigation of heat and mass transfer behavior of mannitol during vial freeze-drying

The vial design feature, such as the base curvature, acts as the primary heat transfer barrier in the lyophilization process. In this study, heat and mass transport characteristics of mannitol (5%) during vial freeze-drying are numerically investigated by including the vial base curvature effects. The influence of the product fill height, chamber pressure, and the vial base curvature on the product temperature, drying time, and mass transfer resistance is analyzed in detail. The diameter of the vial is taken as 15 mm, while the fill height of the product is varied from 3 to 5 mm. The chamber pressure is maintained between 5 and 50 Pa. The results revealed that the product with a 3 mm fill height experienced a 2.5 °C lower temperature than the product with a 5 mm fill height. As opposed to the flat vial predictions, if the vial base curvature effects are considered, the drying time is increased by 1.96 and 3.8 h for the 3 mm and 5 mm fill heights, respectively. The increased drying time is attributed to the reduced direct contact area between the vial and shelf and the vapor entrainment in the gap. The results showed that the dry layer mass transfer resistance contributes to 95% of the total mass transfer resistance; however, the contribution of semi-stoppered vial resistance is 1–2% only.

Experimental and theoretical analysis of mechanical draft counterflow wet cooling towers

Wet cooling towers have high thermal efficiency and are cost-effective industrial cooling units, used in factories, in energy plants, and in the HVAC market. The working principle of the cooling towers is based on cooling of the hot process water with cold atmospheric air via cooling fills and water distribution systems. This study investigates the pressure losses and thermal performance of mechanical draft counterflow water cooling towers having different cooling fill heights. During the thermal performance tests, the pressure loss through cooling fill was separately measured for each condition. The variation of pressure losses with air velocity was plotted through cooling fills at different loading heights. Performance curves were obtained and compared as graphs relating the liquid–gas ratio (L/G) to the Merkel number for cooling fills at different heights between 1500 mm and 2400 mm. Although the lowest and the highest flow resistances were measured at fill heights of 1500 mm and 2400 mm, the lowest and the highest performances for the cooling tower were calculated at 1500 mm and 2400 mm, respectively.

Multi-super-ellipsoid model for non-spherical particles in DEM simulation

The discrete element method (DEM) is extensively used in the investigation of granular systems and the particle shape has a great influence on the dynamics behaviors of granular material. To describe some kinds of non-spherical particles accurately, a multi-super-ellipsoid model, somewhat similar to the multi-sphere model, is proposed in this paper. With this model, non-spherical particles are modeled by connecting a certain number of super-ellipsoids, and the component super-ellipsoids can overlap with each other. Some non-spherical particles, such as tablets and capsules, can be described accurately by the multi-super-ellipsoid model. To verify the accuracy of the multi-super-ellipsoid model, four kinds of non-spherical particles including three kinds of tablets and one kind of capsule, are adopted in this research. The packing of four kinds of non-spherical particles in a cylinder container and the flow of three kinds of tablets in a horizontal rotating drum are done by both numerical simulation and experiment, and the simulation results are compared with the corresponding experiments. The results show that the simulation can predict the basic characteristics of such kinds of non-spherical particles accurately, including fill heights and the dynamic angles of repose, which show that the accuracy of the multi-super-ellipsoid model is quite high. The computational efficiency of the new model is also tested, and the results indicate that the computational efficiency depends on the particle shape and the number of sub-particles in the composite particle.

Earth Movement Optimization Model in Urbanistic Projects

Urban areascomprising natural terrainare prepared empirically for the urbanistic developmentof cities, causingalterationsto the natural relief and affecting notablythe physical surroundingsas resultof deficient planning in the preparation of the terrainfor urbanism works. Thisstudyseeks to formulate a rational solutionto earth movementsthroughtwomodels, one having to do with simulation and the other being mathematical in contrast with thecurrent empirical methodappliedin numerous works of engineering, where el budgethas an important specific weight. In response to this, modelingofsurfaces emerges, which describesthe process ofphysical and artificial representationof the skin of the earththroughageometric model. Thistype ofmodel permits designing the modificationof a terrain’s topographyto prepare it optimally for a given purpose, considering twofundamental variables: area and volume. As resultof this research, an optimization model was obtained for the designofartificial earth movementsapplicableto the type oftopography prevalent in the citiesin the Colombian Eje Cafetero (coffee growing region). The studyfound that the variables ofarea, volume and cut and fill heights createa model, which determinesthe optimal point and around such, an uncertainty zonecalled design zone, achieving the greatest useful areain the constructionwith the least volumeof earth to move.

Experimental study of soil arching effect under seepage condition

Soil arching effect, which relates to the load transfer and stress redistribution in a soil mass, exists commonly in various geotechnical situations. Many researchers have conducted trapdoor tests and theoretical analyses to study the soil arching and its development in recent years. However, little attention has been paid to the interaction between soil arching and seepage flow, both occurring during the tunnelling of a seabed tunnel. To study the influence of the seepage flow on soil arching, a series of two-dimensional trapdoor tests were carried out considering different fill heights and water level heights. Two subvertical slip surfaces were observed during the tests using the PIV technique. It was found that seepage flow increased the displacement of the particles and the effective vertical stress acting at the top of the trapdoor. However, there was little difference in the development of slip surfaces between the seepage condition and the saturated/no-seepage condition. In addition, a nonuniform distribution of vertical stresses at the top of the trapdoor was observed. The effective earth pressure measured along the centreline of the trapdoor was larger than that on the two edges of the trapdoor. But this nonuniformity decreased with an increasing water level height in the test chamber.

Numerical investigation of heat and mass transfer behavior of freeze drying of milk in vial

The transient heat and mass transfer characteristics of the freeze-drying process of milk in a vial is numerically investigated. The paper reports the influence of semi- stoppered vial on mass transfer resistance and the relative importance of the bottom curvature of the vial on the drying time. Moreover, the variation of product temperature and mass transfer resistance as a function of time is predicted. The study revealed that the vial heat transfer coefficient strongly depends on chamber pressure; however, the effect of shelf temperature is minimal. The analysis is conducted for two fill heights (8.25 and 16.5 mm.) It is observed that the presence of curvature at the bottom of the vial increases the primary drying time but decreases the product temperature. Based on the simulation, it is observed that 16.5 mm product fill height provided higher mass transfer resistance than 8.25 mm fill height.

Probabilistic analysis of reinforced slopes using RFEM and considering spatial variability of frictional soil properties due to compaction

ABSTRACTProbabilistic stability analyses of constructed wrapped-face reinforced slopes (or embankments) using frictional soils were carried out using the random finite element method (RFEM). Soil properties reported in the literature for unsaturated frictional fills compacted to different densities were used in the simulations. Bar elements were added to the RFEM code to simulate extensible geosynthetic reinforcement layers and the Davis approach was used to improve numerical stability for purely frictional soil slopes at collapse. The influence of isotropic and anisotropic spatially variable soil strength was investigated and shown to have a large influence on the variation of maximum mobilised tensile forces in reinforcement layers for the steep 5 m-high slopes in the study. The influence of fill placed at different layer thickness and compacted to different levels was simulated by adjusting the soil strength and unit weight, and the vertical strength correlation length in the anisotropic spatially variable strength field used in each slope realisation. Numerical results showed that vertical strength correlation lengths approaching the magnitude of fill lift heights can control the probability of failure for reinforced slopes constructed with weak fills placed in lift heights close to but less than the wrapped reinforcement spacing used in the study.

Analysis of Box Culvert with Different Aspect Ratio

Box culverts are the default buried structure type, where pipe solutions are not suitable. Their larger openings are often required to provide adequate hydraulic capacity. Box culverts are also frequently used for pedestrian or cattle underpasses. The reinforcement used in concrete box culverts can be either conventional bar reinforcement or welded wire fabric. Welded wire fabric has yield strength slightly larger than conventional bar reinforcement. Standard designs for precast concrete box culverts are available with spans varying from 6 to 16 feet and rises varying from 4 to 14 feet. Standard precast concrete box culverts are characteristically invented in 6 foot sections; however larger boxes are fabricated in 4 foot sections to reduce section weight. The designs utilize concrete strengths are suitable for fill heights ranging from less than 2 feet to a maximum of 25 feet. Box culverts outside of the standard size ranges must be custom designed. Each culvert size has three or four classes. Each class has specified wall and slab thicknesses, reinforcement areas, concrete strength, and fill height range to which it applies. To prevent corrosion at the ends of welded wire fabric, nylon boots are required on the ends of every fourth longitudinal wire at the bottom of the form. A maximum of two layers of welded wire fabric can be used for primary reinforcement. If two layers are used, the layers may not be nested. The first box culverts built in Minnesota were made of cast-in-place concrete. The activity of these structures over the years has been very good. Currently, most box culvert installations are precast due to the reduced time required for plan production and construction. Cast-in-place culverts continue to be an allowable option. Buried structures serve a variety of purposes. They are typically used for conveying water. At other times, they are used to provide a grade separated crossing for pedestrian and bicycle traffic. A variety of structure and material types are used. The most prevalent types are pipes and box culverts. Buried structures with horizontal dimensions less than 10'–0 are not classified as bridges. Typically, these smaller buried structures do not need widespread design and are selected from standard design tables. Buried structures with horizontal dimensions greater than or equal to 10'–0 are considered bridges and require a plan prepared by the Bridge Office. All box culverts need a Bridge Office equipped plan as well. In addition to pipes and box culverts, precast concrete arches, precast three-sided structures, and long-span corrugated steel structures are used as buried structures. Buried structures carry vertical loads through a mixture of internal capacity and soil arching around the structure; this is termed soil-structure interaction. The means by which a buried structure carries vertical load varies significantly between different structure types due to their relative stiffness. Concrete box culverts and rigid pipes are categorized as rigid culverts and are supposed to carry the design loads internally with limited requirements or benefit of the soil. Flexible pipe structures (corrugated steel, thermoplastic, etc.) carry loads through soil-structure interaction. For this reason, material and installation requirements of the pipe and soil are well defined including trench or embankment conditions and backfilling and compaction procedures to ensure that the assumed soil-structure capacity is provided and that settlements are not excessive.

Post-construction performance of induced trench rigid culverts

Induced trench construction is commonly used to reduce earth pressures on rigid circular and box culverts. Most of the reported literature pertains to the performance of induced trench culverts during construction and shortly after construction. This paper addresses the post-construction performance of induced trench culverts. First, results of field inspection reports are presented as an indirect assessment of performance of 90 induced trench culverts installed in New Brunswick that have been in service for up to 24 years. Second, earth pressure measurements are presented from three case studies where prototype installations were monitored over periods ranging from 4 to 9 years. The case studies presented include a single circular culvert, a cast-in-place double-cell box culvert, and a twin circular culvert installation. The fill heights above the instrumented structures varied from 19 to 25 m. All the available data from both the field inspections and earth pressure measurements indicate that the culverts installed in induced trenches are performing in a satisfactory manner.

Interferometric Volume Measurement in Microplates.

Low-coherence interferometry is presented as a method for nondestructive, noncontact, and high-resolution measurement of liquid volumes and fill heights in microplates. A Meniscense (Bolton, MA) prototype system captures both fill height and meniscus shape and combines them into a volume measurement, allowing for the measurement of a wide range of liquids with different meniscus shapes. The system has a liquid fill height resolution of 0.7 µm, corresponding to a volume resolution of 0.02 µL in a typical 96-well plate, demonstrated in an ideal model system. Initial data on the gravimetric verification of volume measurements on aliquots of distilled water between 50 and 350 µL in a 96-well plate suggest an inaccuracy of volume measurement of <2%. The Meniscense system offers accuracy comparable to ratiometric photometry, the only commercially available high-resolution volume measurement system. Its fill height resolution is substantially better than that of ultrasonic ranging, the only other noncontact, nondestructive method for fill height measurement.

A dilation-driven vortex flow in sheared granular materials explains a rheometric anomaly.

Granular flows occur widely in nature and industry, yet a continuum description that captures their important features is yet not at hand. Recent experiments on granular materials sheared in a cylindrical Couette device revealed a puzzling anomaly, wherein all components of the stress rise nearly exponentially with depth. Here we show, using particle dynamics simulations and imaging experiments, that the stress anomaly arises from a remarkable vortex flow. For the entire range of fill heights explored, we observe a single toroidal vortex that spans the entire Couette cell and whose sense is opposite to the uppermost Taylor vortex in a fluid. We show that the vortex is driven by a combination of shear-induced dilation, a phenomenon that has no analogue in fluids, and gravity flow. Dilatancy is an important feature of granular mechanics, but not adequately incorporated in existing models.