Strip Loading Research Articles

An assumed enhanced strain finite element framework for tensile fracturing processes with dual-mechanism failure in transversely isotropic rocks

We present an assumed enhanced strain finite element framework for the simulation of tensile fracturing processes in transversely isotropic rocks. Fractures along the weak bedding planes and through the anisotropic rock matrix are treated with distinct enrichment, and a recently proposed dual-mechanism tensile failure criterion for transversely isotropic rocks is adopted to determine crack initiation for the two failure modes. The cohesive crack model is adopted to characterize the response of embedded cracks. As for the numerical implementation of the proposed framework, both algorithms for the update of local history variables at Gauss points and of the global finite element system are derived. Four boundary-value problem simulations are carried out with the proposed framework, including uniaxial tension tests of Argillite, pre-notched square loaded in tension, three-point bending tests on Longmaxi shale, and simulations of tensile cracks induced by a strip load around a tunnel in transversely isotropic rocks. Simulation results reveal that the proposed framework can properly capture the tensile strength anisotropy and the anisotropic evolution of tensile cracks in transversely isotropic rocks.

A testing theory for simultaneously determining asphalt mixture’s dynamic modulus in compression and tension by use of IDT test

The compressive and tensile moduli of asphalt mixtures are not equal. As a result, in order to obtain reasonable response calculation results, asphalt pavement mechanical analysis should first determine the compressive and tensile moduli of asphalt mixtures separately. Then, it should assign an appropriate modulus to the FEM element based on the stress state of the element. However, conventional uniaxial compression modulus testing protocol is typically unable to determine the actual asphalt pavement's coring specimen due to the limitation that general dynamic modulus testing protocol requires a larger size of specimen and conventional coring specimen from field usually cannot meet the requirement in regard to specimen size. In this case, the dynamic modulus of the asphalt mixture can only be ascertained using the IDT test method.Nevertheless, the current IDT test protocol is unable to distinguish between the compressive and tensile moduli of asphalt mixtures, and the testing results are usually different from those obtained by using the conventional uniaxial compression or tension method. This is because the current IDT test method for determining the dynamic modulus of asphalt mixtures generally treats asphalt mixtures as a kind of ideal elastic material and considers its compressive modulus is equal to its tensile modulus.Consequently, this paper presents a new theory, based on Ambartsumyan's bi-modulus constitutive relation theory, that can use the IDT test method to simultaneously determine the dynamic modulus of an asphalt mixture in both compression and tension. This theory assumes that the stress-strain relationship of asphalt mixture complies with the bi-modulus constitutive relation, and obtains the vertical deformation or horizontal deformation of the IDT specimen by solving a definite integral for the displacement of a small segment on the vertical or horizontal axis, which utilizes the results of the mathematical analysis of the stress distribution of the IDT specimen under distributed strip load. Then, the specimen's dynamic modulus in compression and tension can be obtained via back-calculating method, if the specimen's vertical and horizontal displacement are measured by a physical test in the lab. Obviously, this theory addresses the limitation of the conventional IDT method that cannot reflect the distinction of compressive modulus with tensile modulus, and can be better utilized to simultaneously determine compressive and tensile modulus of cored specimen from field. The verification test also demonstrates, the dynamic modulus determined by this theory are in line with the results of the conventional uniaxial test and is highly practicable.

Dynamic Response Analysis of Quasi-Saturated Foundation Half-Space under Strip Loading

Dynamic Response Analysis of Quasi-Saturated Foundation Half-Space under Strip Loading

Analytical determination of the dynamic response of layered saturated frozen foundation to moving loads under plane strain conditions

Based on the theory of solid porous media with pores, a calculation model of two-dimensional layered saturated frozen soil foundation is established. The study focuses on the dynamic response of layered saturated frozen soil medium placed on an impermeable rigid bedrock when subjected to a uniform surface moving strip load in motion. Firstly, the governing equation of saturated frozen soil is established. Then, the Helmholtz vector decomposition theorem, coordinate transformation, and Fourier integral transformation are used to decouple the governing equation of saturated frozen soil, and the general solution of the potential function is obtained, and the general solution of the stress and displacement of each layer of saturated frozen soil is derived. Using the transfer and reflection matrix (TRM) method, the semi-analytical solution of layered saturated frozen soil medium in the frequency domain is derived. Finally, the dynamic response of each phase of the saturated frozen soil in the time domain is obtained by the fast Fourier transform. After verifying the accuracy of the solution by comparing the model degradation with the existing literature, the effects of soil shear modulus, load moving speed, temperature, porosity, contact parameter, and frequency on the dynamic response of homogeneous foundation, soft interlayer foundation, and hard interlayer foundation are analyzed in detail. The results show that the stratification of the foundation is of great significance for accurately evaluating the dynamic response of saturated frozen soil.

A Simplified Method for Seismic Behavior of Retaining Walls with Strip Load on the Backfill

A Simplified Method for Seismic Behavior of Retaining Walls with Strip Load on the Backfill

Analysis of layered soil under general time-varying loadings by fractional-order viscoelastic model

Time-varying loading is a frequently encountered loading type in geotechnical engineering. As the deformation of viscoelastic soil is related to its loading history, studying the viscoelastic problems under time-varying loads has important practical engineering significance. In this paper, the stress and displacement of a layered soil with fractional-order viscoelastic model under time-varying loads were solved using the complex variable method and the corresponding principle. Under the assumption of quasi-static and linear elasticity, this paper derives the quasi-static elastic solutions of a layered soil under time-varying strip loads. By introducing the fractional-order viscoelastic model and using the corresponding principle, the Laplace-domain analytical solutions are obtained. Finally, numerical methods are utilized to perform the Laplace inverse transform and obtain the solutions in the physical domain. The correctness of this paper is validated by comparing the numerical results with the ANSYS software, as well as by comparison with previous literature. Based on the experimental data, the material parameters of frozen soil at two temperatures are fitted. The settlement patterns of soil under two engineering loads were analyzed through case studies. By controlling variables, the influence of parameters of the fractional viscoelastic model on elastic aftereffect was investigated.

Orthotropic composite slabs for road bridges

AbstractLarge increases in traffic loads led to extensive fatigue damages to existing orthotropic steel deck slabs of road bridges. Reinforced concrete bridges and conventional composite bridges are less susceptible to fatigue but considerably heavier. The ortho‐composite slab is a lightweight and robust alternative construction method, which retains the advantages of the previously mentioned construction methods, but eliminates their disadvantages. Within the framework of the AiF‐FOSTA research project P1265 [1], the construction of the bridge deck was developed using dowel strips as composite elements with high load‐bearing capacity and fatigue resistance. The principle of area composite with loading of the dowel strips in longitudinal and transverse direction was used. Extensive experimental and structural mechanics studies were conducted, particularly investigating the load‐bearing capacity and fatigue strength of the ortho‐composite slab under local load application. The following article describes the load‐bearing structure of the ortho‐composite slab and the motivation for the research project P1265. It gives an overview of the experimental investigations carried out. Finally, the article presents pilot projects that were carried out to apply the construction method. In further articles on Eurosteel, the experimental investigations and structural‐mechanical calculations are described in more detail (see [2] and [3]).

Finite element analysis of compaction load to investigate the stress-deformation behavior of soil geosynthetic composite mass: A case study

When building Soil Geosynthetic Composite (SGC) walls, fill compaction is normally carried out by operating a compactor in a general direction parallel to the wall face. In other words, a moving point or area load is often used to apply a compaction load on a newly installed soil lift. Pham (2009) and Wu and Pham (2010) demonstrated that the compaction-induced stress (CIS) caused by multiple passes of a compactor moving toward or away from a section can be calculated by taking into account the compaction load applied directly above the section under consideration using a simplified stress path proposed by Duncan and Seed (1986). Additionally, by simulating the compaction, the CIS due to fill compaction may be correctly assessed. The CIS resulting from fill compaction can also be accurately assessed by simulating the compaction load, such as by applying a distribution load on top of each backfill layer or a distribution load at the top and bottom of each soil layer, or by applying various widths of strip load to the top of each backfill layer. The objective of this study was to validate the numerical simulation of the compaction load to stress deformation behavior of SGC mass under operating stress conditions. In order to conduct the numerical analysis, data from both a full-scale instrumented SGC mass based on large-scale soil geosynthetic composite (SGC) experiments and a 6 m-high SGC (Pham, 2009) were employed. This study will examine a few SGC behavior parameters, including reinforcement strains, lateral displacements, and reinforcement strains. The objective of the FE modeling is to demonstrate the effect, emphasize the significance of the compaction conditions to the stress-deformation behavior of SGC mass, and validate the findings from the field-scale experiments and proposed model by Pham (2009) and Wu and Pham (2010).

A numerical analysis on anchored sheet pile wall subjected to surcharge strip loading

Anchored sheet pile walls are practically subjected to a surcharge load that exists on the field in the form of vehicles, buildings, and storage areas, those additional surcharge loads on the ground surface produce additional stress on the wall. In the present investigation, a three-dimensional finite element method is implemented to study the behavior of an anchored sheet pile wall under a uniform surcharge strip load. The influence of surcharge load and foundation soil types on wall deflections, bending moments, anchor forces, and backfill ground settlement are examined. A parametric study is performed by varying the wall stiffness, anchor stiffness, number of anchors and magnitude of surcharge load. The results show that medium dense foundation soil increases the passive resistance, so it reduces wall deflections, bending moments, anchor forces and ground settlement. Moreover, double anchorage effectively reduces wall deflections, bending moments, anchor forces and ground settlement than single anchorage.

The surface bearing capacity of a strong granular layer on weaker sand

Stronger granular layers are often placed as working platforms over weaker sand subgrade. The design of a working platform involves the calculation of a two-layer bearing capacity under rectangular loading. Existing design methods are either overly simplified, based on infinitely long strip loads and validated by a small number of small-scale 1g model tests, or rely on numerous or empirically derived charts that are difficult to use or implement into design software. In this paper a new and highly practical design method is proposed in which the bearing capacity is determined simply from the shear strengths and unit weights of the two soil layers. The method was derived from extensive finite-element analysis and finite-element limit analysis (FELA) parametric studies in both plane strain and axisymmetric geometries. It was validated against published physical model tests, other FELA analyses and existing design methods. It can be applied to all rectangular shape ratios with dry and saturated layers.

Influence of surcharge strip loads on the behavior of cantilever sheet pile walls: A numerical study

Influence of surcharge strip loads on the behavior of cantilever sheet pile walls: A numerical study

A quasi-2D exploration of optimum design settings for geotextile-reinforced sand in assistance with PIV analysis of failure mechanism

Many earlier studies were focused on testing different types of geosynthetics to investigate effect of reinforcement on bearing capacity, but the effect of tensile strength on the failure mechanism has not been examined sufficiently. Within this scope, a test setup was prepared to apply strip loads on densely compacted reinforced sand under the plane strain condition. The tank containing the reinforced sand was a rectangular prism with perfect transparency, and its interior dimensions were 960 × 200 × 650 mm3. Firstly, optimum values of design variables (depth of first sheet, length and number of sheets, space between sheets, tensile strength of sheets) for the woven geotextile reinforced sand were determined experimentally. Then, the failure mechanisms of the soil, which were reinforced with geotextiles of different tensile strengths, were observed and analyzed with particle image velocimetry (PIV) technique. Consequently, the failure mechanism of the sand with a single geotextile reinforcement was similar to general shear failure of unreinforced soil. Contrarily, the failure surfaces were deeper and longer. Additionally, the deep-footing mechanism reached out large depth in the case of four reinforcement layers. The failure mechanism converted into a punching type due to a hypothetic increase in the bearing depth of reinforcement.

MEMORY RESPONSE ON THERMOELASTIC BEHAVIOUR WITH TEMPERATURE DEPENDENT MATERIAL MODULI UNDER MECHANICAL STRIP LOAD

Temperature of the medium has a significant impact on the deformation and stress distribution into the medium. Material moduli is another key component that determines the deformation of the structural element. The present paper deals with the thermal memory response on stress and temperature fields in an isotropic medium. The material moduli of the medium are considered to be varying with temperature. Consequently, the classical heat conduction law is replaced by the memory dependent generalized theory of heat conduction. Analytical solutions of the field functions are obtained in the integral transform domain. The variations of the field functions in the space-time coordinate system are displayed graphically for different empirical constants and kernel functions.

An elasticity solution of laminated cylindrical panel

In this paper, an exact elasticity solution of cylindrical panel under cylindrical bending is presented. The formulation is based on the displacement approach in which 3D elasticity equations are reduced to 2-D equations using plane-strain conditions. In the present formulation, an exact elasticity solution is feasible due to the consideration of simply supported boundary conditions with applied loads expressed in harmonic forms. Single layered and multi-layered orthotropic composite panels subjected to realistic transverse normal loads are analysed. Solutions have been presented for uni-directional, bi-directional, and symmetric three-layered cross-ply laminated composite cylindrical panels. Variation of displacements and stresses through the thickness has been investigated for the panel subjected to single sinusoidal load, uniformly distributed load, hydrostatic load, and strip load. Validation of results is presented using reference results in the literature. The extensive results presented in this paper can be served as benchmark solutions for the assessment of improved panel theories.

Application of artificial neural network for determining elastic constants of a transversely isotropic rock from a single-orientation core

Numerous efforts have been made to determine the five independent elastic constants of transversely isotropic (TI) rocks. Recently, the novel strip load test method combined with the strain inversion method, offering the advantage of requiring only a single-orientation core, was presented (Yim J, Hong S, Lee Y, Min K–B. A novel method to determine five elastic constants of a transversely isotropic rock using a single-orientation core by strip load test and strain inversion. Int J Rock Mech Min Sci. 2022; 154:105115.1). As a follow-up study, this paper suggests artificial neural networks (ANNs) to replace the strain inversion for determining five elastic constants of TI rocks with a strip load test method. The method comprises three main parts; the first was the strip load test experiment, the second part involves training ANNs using numerous datasets, and the final part is the application of trained ANNs to determine the elastic constants. The proposed method was numerically validated based on homogeneous and heterogeneous TI rocks. Experimental validation using Asan gneiss showed that the elastic constants determined from ANNs are in good agreement with those determined by using strain inversion and conventional method. The ANNs suggested in this study can significantly reduce the computing time required for strain inversion by numerical modelling and can be potentially used for other stress analyses of anisotropic rock.

Effect of nearby strip loading on lateral capacity of offshore large-diameter monopiles in clay slope

This study is devoted to investigating the effect of nearby strip loading on the lateral bearing capacity of offshore large-diameter monopiles at the crest of marine clay slope by the finite element limit analysis (FELA) method. After the successive validations by cases of rigid piles and strip footings at the clay slope crest, the safe domains for the laterally loaded large-diameter monopiles are defined by the failure envelopes relating the dimensionless lateral bearing capacity H u/(c u D 2) to dimensionless strip loading q/c u. Particularly, all failure envelopes are depicted by closed-form expressions and design charts can then be given for a quick and straightforward assessment of dimensionless lateral bearing capacity for a wide range of frequently-encountered cases. In addition, the interaction between the pile bearing capacity and nearby strip loading is characterized by introducing the relationship of normalized parameters H u/(c u D 2) and q/c u, then graphically explained by plastic multiplier contour plots. Several kinds of representative curves are given successively to further clarify the effects of dimensionless factors on the interaction.

Centrifuge model and numerical studies of strip footing on reinforced transparent soils

This paper presents the results of centrifuge model tests to investigate the deformation behaviour of unreinforced and reinforced transparent soil foundations under strip loading. A digital image analysis technique was employed to obtain the soil displacement field and strain distribution of reinforcements. Two-dimensional (2D) numerical models were developed and verified using the test results. The soil was modelled as a linearly-elastic perfectly-plastic material with Mohr–Coulomb failure criterion. The reinforcement was characterised using a linearly-elastic model considering rupture behaviour. Moreover, a parametric study was conducted to investigate the load–settlement response of foundations, distribution of reinforcement tension and failure sequence of reinforcements. The experimental and numerical studies show that the results obtained from the numerical simulations are in good agreement with the results of the centrifuge model tests. The 2D finite difference model developed using the user-defined functions coded into the FLAC programme can better simulate the progressive failure of the reinforcement layers in the tests. The failure sequence of reinforcement layers is not affected by the modulus and internal friction angle of soil and the reinforcement length, but is closely related to the combined effect of spacing and number of reinforcement layers and the combined effect of reinforcement stiffness and strength.

Dynamic Responses of Saturated Soil Foundation Subjected to a Moving Strip Load Based on the Nonlocal-Biot Theory

Dynamic Responses of Saturated Soil Foundation Subjected to a Moving Strip Load Based on the Nonlocal-Biot Theory

Model tests on jarofix embankment subject to strip loading

Model tests on jarofix embankment subject to strip loading

A novel method to determine five elastic constants of a transversely isotropic rock using a single-orientation core by strip load test and strain inversion

This study proposes a novel method to determine the five elastic constants from a single-orientation core of a transversely isotropic rock using strip loading and strain inversion. The proposed method can be performed under two test conditions: 1) strip load test and strain inversion (single strip load method) and 2) strip load test combined with Brazilian test and strain inversion (strip load and Brazilian method). Strain inversion was carried out by finite element modeling to determine the elastic constants by minimizing the difference between the measured and numerically modeled strains. The method was validated by numerical and laboratory experiments in comparison with the conventional method that uses two uniaxial compression tests with multiple coring directions. In the numerical validation, elastic constants were estimated with high accuracy for cores with high coring angles by the single strip load method. The strip load and Brazilian method accurately determined the five elastic constants for all ranges of coring angles. Validation using Asan gneiss showed that both the approaches of the suggested method can determine the five elastic constants using a single-orientation core. Most of the experimental results were within the range of variations often observed in rock mechanics experiments. The method combining uniaxial compression and Brazilian tests was additionally proposed even though it required an empirical relation of the second shear modulus for horizontally and vertically layered cores. Further, the experimental results were discussed in terms of heterogeneity, nonlinear stress–strain relationship, and Saint–Venant empirical relation. The existing method using a single uniaxial compression test involving the Saint–Venant empirical relation was also tested, showing limited reliability for low coring angles. The suggested methods using a single-orientation core will contribute to a convenient determination of elastic constants of transversely isotropic rocks.