Review of Calibration Methods for Scheimpflug Camera

The Scheimpflug camera offers a wide range of applications in the field of typical close-range photogrammetry, particle image velocity, and digital image correlation due to the fact that the depth-of-view of Scheimpflug camera can be greatly extended according to the Scheimpflug condition. Yet, the conventional calibration methods are not applicable in this case because the assumptions used by classical calibration methodologies are not valid anymore for cameras undergoing Scheimpflug condition. Therefore, various methods have been investigated to solve the problem over the last few years. However, no comprehensive review exists that provides an insight into recent calibration methods of Scheimpflug cameras. This paper presents a survey of recent calibration methods of Scheimpflug cameras with perspective lens, including the general nonparametric imaging model, and analyzes in detail the advantages and drawbacks of the mainstream calibration models with respect to each other. Real data experiments including calibrations, reconstructions, and measurements are performed to assess the performance of the models. The results reveal that the accuracies of the RMM, PLVM, PCIM, and GNIM are basically equal, while the accuracy of GNIM is slightly lower compared with the other three parametric models. Moreover, the experimental results reveal that the parameters of the tangential distortion are likely coupled with the tilt angle of the sensor in Scheimpflug calibration models. The work of this paper lays the foundation of further research of Scheimpflug cameras

Elastoplastic Model Framework for Saturated Soils Subjected to a Freeze–Thaw Cycle Based on Generalized Plasticity Theory

The failures of soil slopes during the construction of high-speed railway caused by the soil after the freeze–thaw (F–T) cycle and the subsequent threat to construction safety are critical issues. An appropriate constitutive model for soils accurately describing the deformation characteristics of soil slopes after the F–T cycle is very important. Few constitutive models of soils incorporate the F–T cycle, and the associated flow rule has always been employed in previous models, which results in an overestimation of the deformation of soil exposed to the F–T cycle. Generalized plasticity theory is widely used to predict the performance of geotechnical materials and is especially well adapted to deal with this type of generalized cyclic loading (such as a freeze–thaw cycle), and it overcomes the shortcomings of the associated flow rule that causes larger shear deformation. To this end, an elastoplastic model framework based on generalized plasticity theory with double yield surfaces for saturated soils subjected to F–T cycles was developed. Two types of plastic deformation mechanisms, i.e., plastic volumetric compression and plastic shear, were considered in this elastoplastic model. It was found that this model can accurately predict the mechanical behavior and deformation characteristics of saturated soils after F–T cycles

Frost heave performance of a foundation at an overhead transmission line in the alpine seasonal frozen regions

The Manzhouli 500 kV electrical transmission line travels more than 218 km through seasonal frozen regions, which result in many freezing soil engineering problems with respect to the transmission tower foundations. Physical model tests of independent reinforced concrete foundations at various temperatures were conducted and verified by numerical simulation to investigate the frost-heaving characteristics of the reinforced concrete foundation in an alpine seasonally frozen region. The evolution of the temperature field, frost-heaving force, and water migration of frozen soil were studied in an open water refill environment with a dead load. The heave force in the foundation soil increases as temperature decreases. The horizontal heave force in the middle and upper parts of the foundation can reach 540 kPa. However, the maximum tangential frost-heaving force becomes 3.83 kN, and the maximum frozen depth of the frozen soil was 240 mm. During the freezing process, the frost heave of the foundation was significantly more noticeable. The correlation between experimental and simulated values is good, and each parameter’s variation error is less than 5 %. Finally, control measures of frost heave were proposed to guide engineering practice based on experimental and numerical studies

Numerical study of ice loads on different interfaces based on cohesive element formulation

Abstract With the increase of marine activities in the Arctic area, the demand for reliable design of marine structures is growing. Numerous publications can be found regarding simulations of ice action on structures using cohesive element models of the ice. However, previous studies have rarely discussed the influence of structural form, that is, the form of ice-structure interaction interface, on the ice load. Thus, a more comprehensive understanding of the ice load on structures with different interface geometries needs to be explored. In the present paper, three-dimensional finite element models with the cohesive element method are developed to investigate the ice load on different structures. The numerical results are validated based on in-situ testing data and the results of the previous numerical model. Parametric studies considering structure widths, inclination angles, ice velocity as well as structure roughness are conducted to explore the horizontal force and failure process of the ice sheet. The process of ice-structure interaction and ice loads on different structural forms were discussed and simplified diagrams of ice load distribution on the interface were developed

Stress–Strain Model for Freezing Silty Clay under Frost Heave Based on Modified Takashi’s Equation

In analyzing frost heave, researchers often simplify the compressive modulus of freezing soil by considering it as a constant or only as a function of temperature. However, it is a critical parameter characterizing the stress–strain behavior of soil and a variable that is influenced by many other parameters. Hence, herein several one-dimensional freezing experiments are conducted on silty clay in an open system subjected to multistage freezing by considering the compressive modulus as a variable. First, freezing soil under multistage freezing is divided into several layers according to the frozen fringe theory. Then, the correlation between the freezing rate and temperature gradient within each freezing soil layer is investigated. Takashi’s equation for frost heave analysis is modified to extend its application conditions by replacing its freezing rate term with a temperature gradient term. A mechanical model for the stress–strain behavior of freezing soil under the action of frost heave is derived within the theoretical framework of nonlinear elasticity, in which a method for determining the compressive modulus of freezing soil with temperature gradient, overburden pressure, and cooling temperature variables is proposed. This study further enhances our understanding of the typical mechanical behavior of saturated freezing silty clay under frost heave action

On the optimized design of interfacial configurations in a highly thermal conductive graphite flakes/aluminum composite

International audienc

Bearing Properties and Stability Analysis of the Slope Protection Framework Using Recycled Railway Sleepers

The slope protection framework developed using recycled railway sleepers offers a novel sustainable solution for slope protection. However, this has been inadequately reported, and its force and deformation, its protective effect, and the bonding characteristics between sleepers are still unclear. The slope protection framework project of a recycled railway sleeper embankment slope on the Beijing–Tongliao railway was numerically analyzed using three typical recycled railway sleeper slope protection structures. The bearing properties and the slope stability of rectangular, rhombic, and herringbone framework structures were determined. The results show that the stress state, stress level, and failure mode of the three types of slope protection structures are similar on average. The slope protection skeleton’s stress concentration position and failure area are all concentrated at the sleeper connection node at the slope base. The rectangular and rhombic framework structures have better stability than the herringbone framework. This study proposes applying a slope protection framework constructed entirely using recycled railway sleepers. Furthermore, it allows for proper disposal of recycled railway sleepers and a reduction in stone mining

Investigation of the Effect of Graphene Oxide on the Properties and Microstructure of Clay-Cement Composite Grouting Materials

Reductions in bleeding rates and bulk shrinkage of grouting repair materials comprise the key to solving the leakage of earth–rock dams. In this paper, an anti-seepage grouting material for earth–rock dam was developed by introducing mineral admixtures and graphene oxide (GO) nano sheets into low-cost clay–cement grouting materials and by adding polycarboxylate superplasticizers (PCs) to improve slurry viscosity. The experimental results show that the shear stress and viscosity of the slurry increase with the increase in GO concentration, and the slurry has a certain thixotropy. GO can provide a platform to promote the formation of hydration products and fill the pores of clay particles due to its high specific surface area and low volume; in this paper, the microstructure of clay–cement–graphene oxide (CCGO) grouting materials were improved. Therefore, the bleeding rate, bulk shrinkage rate, setting time and unconfined compressive strength (UCS) of the sample were macroscopically improved. In particular, the bleeding rate and bulk shrinkage rate were shown to be 0% when the content of GO reached 1.08 g/kg. Thus, the grouting anti-seepage and reinforcement performance of CCGO grouting materials were improved