Semirigid Inclusions Research Articles

Feasibility of recycled concrete aggregate stabilized with one-part geopolymers as semi-rigid inclusion columns

Recycled concrete aggregate (RCA) is a voluminous solid waste material derived from the construction sector and is typically stockpiled in landfills. In recent years, the ground improvement industry has grappled with challenges stemming from the depletion of natural quarry materials, resulting in a skyrocketing of their prices and increased project costs. This research investigated the feasibility of using RCA stabilized by one-part geopolymers to produce an innovative semi-rigid inclusion column system for ground improvement of soft soils. Na2SiO3-anhydrous was used as a sole solid activator for the activation of fly ash (FA), slag (S) or a binary precursor (FA+S) in the stabilization of RCA. The unconfined compressive strength (UCS) and microstructure of the stabilized mixtures have been examined with respect to different binder formulations and curing conditions. The permanent deformation characteristics of mixtures under cyclic loading were evaluated through repeated load triaxial (RLT) tests to replicate the moving wheel loads imposed on the semi-rigid inclusion columns. In addition, the cost and environmental impacts of the optimum mixtures suggested in this research were studied. The test results indicated that stabilizing RCA with as low as 5% one-part alkali-activated FA, S or (FA+S) met the minimum strength requirement (1.034 MPa) for ground improvement work. Compared with standalone FA and S geopolymer stabilized RCA mixtures, (FA+S) geopolymer stabilized RCA mixtures were identified as preferred industrial formulations due to their prolonged setting time for ease of mixing and handling when used in stone column applications. It was found that curing temperature and duration played a pivotal role in the strength gain of the mixtures. The RLT test results demonstrated that implementing the optimum RCA + 5%(FA+S) mixture as identified in this study for semi-rigid inclusion columns, led to a reduction in permanent strain values by approximately 90% compared to conventional unbound stone columns. The comparison between the optimum mixture highlighted in this study with other stabilization methods showed that the semi-rigid inclusion columns had great potential to enable large-scale production, cost and emission reduction in future ground improvement projects.

Alkali activation of recycled concrete and aluminum salt slag aggregates for semi-rigid column inclusions

Stone columns develop their load-bearing capacity from the circumferential confinement offered by the surrounding soils. In highly plastic soils, the circumferential confinement provided by the surrounding soft soils may not be sufficient to develop the required bearing capacity. Meanwhile, the ground improvement industry has been keen to explore substitution backfill materials due to the depletion of natural aggregate resources typically used to construct stone columns. This research investigated the viability of using recycled concrete aggregate (RCA) and recycled aluminum salt slag (RASS), stabilized with alkali-activated fly ash (FA), slag (S) and a binary precursor (FA + S), as a novel semi-rigid inclusion column system for ground improvement of soft soils. The effect of the RCA/RASS ratios, additive types and dosages along with different curing conditions on the unconfined compressive strength (UCS) of geopolymer-stabilized mixtures, were evaluated. Various reinforcing mechanisms were suggested through the microstructure characterization of the mixtures. In addition, the permanent deformation responses of mixtures under cyclic loading were studied using repeated load triaxial (RLT) tests that simulate the cyclic moving traffic loads imposed on the stone columns system. The results demonstrated that increasing the RASS contents resulted in a subsequent decline in the UCS of the mixtures. Increasing the additive dosages on the other hand, in general led to higher strengths. The effects of both curing duration and temperature were found to play a vital role in the strength development of the mixtures. Furthermore, 100RCA stabilized by as low as 5% alkali-activated FA, S or (FA + S), met the minimum UCS requirement of 1.034 MPa for ground improvement. The highest reduction in permanent strain of 87.3% was recorded for the stabilized 100RCA + 10%(FA + S) mixture compared to the unbound 100RCA (control group). The practical implications of the findings were also discussed in detail throughout the paper.

Numerical solution of the equilibrium problem for a two-dimensional elastic body with a thin semirigid inclusion

The equilibrium problem for a two-dimensional elastic body containing a thin semirigid inclusion is considered. The inclusion delaminates from the elastic matrix, forming a crack; therefore, the problem is posed in a nonsmooth domain with a cut. The mathematical model of the delaminated thin semirigid inclusion was developed on the assumption that the rigidity of the material differs in different directions. The problem statement is presented both in the form of a variational inequality and in the form of a boundary value problem. The boundary condition on the crack faces has a form of inequality and, as a result, the problem is non-linear. Consequently, the construction of an algorithm for the numerical solution of the problem requires the use of additional analytical methods. The methods of domain decomposition, the method of Lagrange multipliers, and the finite element method are used. An algorithm for the numerical solution of the problem is constructed and a computational example is provided.

On numerical solving of junction problem for semirigid and Timoshenko inclusions in elastic body

The paper considers an example of mathematical modeling of the process of deformation of a structure made of fiber-composite material. Timoshenko’s theory of thin beams is used to describe the reinforcing fiber model. The paper concerns a numerical solving of the equilibrium problem for a two-dimensional elastic body with a thin Timoshenko elastic inclusion and a thin semirigid inclusion. Both inclusions are of a rectilinear shape and delaminate from the elastic matrix. Therefore, the problem is posed in the domain with a cut and conditions of the form of inequalities are specified at the edges of the crack, as on a part of the boundary. These conditions exclude mutual penetration of the crack edges into each other. At the same time, such a formulation leads to the nonlinearity of the problem and the need to use additional mathematical methods to construct an algorithm for the numerical solution of the problem. The inclusions have a joint point at which junction conditions are written out. For the numerical solving of the problem in a domain with a cut, a variational formulation is used using the domain decomposition method and the Uzawa algorithm. To obtain an approximate solution that satisfies the conditions of semirigid inclusion, an additional algorithm is built using methods of mathematical analysis, an example with calculations is given.

Semirigid inclusions in elastic bodies: Mechanical interplay and optimal control

The paper concerns an analysis of an equilibrium problem for 2D elastic body with two semirigid inclusions. It is assumed that inclusions have a joint point, and we investigate a junction problem for these inclusions. The existence of solutions is proved, and different equivalent formulations of the problem are proposed. We investigate a convergence to infinity of a rigidity parameter of the semirigid inclusion. It is proved that in the limit, we obtain an equilibrium problem for the elastic body with a rigid inclusion and a semirigid one. A parameter identification problem is investigated. In particular, the existence of a solution to a suitable optimal control problem is proved.

On the mechanical interplay between Timoshenko and semirigid inclusions embedded in elastic bodies

AbstractIn the paper, an equilibrium problem for elastic bodies with a thin elastic Timoshenko inclusion and a thin semirigid inclusion is analyzed. The inclusions are assumed to be delaminated from elastic bodies, thus forming a crack between the inclusions and the elastic matrix. Nonlinear boundary conditions are imposed at the crack faces to prevent a mutual penetration between the crack faces. The inclusions have a joint point. A passage to a limit is investigated as a rigidity parameter of the elastic inclusion goes to infinity. The limit model is investigated. Junction boundary conditions are found at the joint point for the problem analyzed as well as for the limit problem.

Energy release rates for interfacial cracks in elastic bodies with thin semirigid inclusions

In this paper, we present some rigorous results for an equilibrium problem arising from the study of fiber-reinforced composites. We consider a two-dimensional homogeneous anisotropic linear elastic body containing a thin semirigid inclusion. The semirigid inclusion is an anisotropic thin structure that stretches along one direction and moves like a rigid body possessing both rotational and translatory motion along the perpendicular direction. A pre-existing interfacial crack is subject to nonlinear conditions that do not allow the opposite crack faces to penetrate each other. We focus on a variational approach to modelling the physical phenomenon of equilibrium and to demonstrate that the energy release rate associated with perturbation of the crack along the interface is well defined. A higher regularity result for the displacement field is formulated and proved. Then, taking into account this result, we deduce representations for the energy release rates associated with local translation and self-similar expansion of the crack by means of path-independent energy integrals along smooth contour surrounding one or both crack tips. Finally, some relations between the integrals obtained are discussed briefly.

Junction problem for rigid and semirigid inclusions in elastic bodies

The paper is concerned with equilibrium problems for 2D elastic bodies having thin inclusions with different properties. In particular, rigid and semirigid inclusions are considered. It is assumed that inclusions have a joint point, and we analyze a junction problem for these inclusions. Existence of solutions is proved for each equilibrium problem, and different equivalent formulations of these problems are discussed. In particular, junction conditions at the joint point are found. A delamination of the inclusions is also assumed. This means that we have a crack, and inequality-type boundary conditions are imposed at the crack faces to prevent a mutual penetration between crack faces. We discuss a convergence to zero and infinity of a rigidity parameter of the semirigid inclusion and analyze limit problems.

Embankment on Soft Soil Reinforced by CMC Semi-Rigid Inclusions for the High-speed Railway SEA

The embankment going to Dordogne Viaduct crossed by the LGV South Europe Atlantic SEA is based on 4 000 semi-rigid inclusions (CMC) designed in accordance with ASIRI. Published in 2012, these recommendations are starting to be well known and applied around the world. Depending on the purpose of the CMC (stability or only settlement reduction), CMCs justifications differ. For the first case, verifications are more numerous and more severe. After CMC ground improvement work in 2013, the embankment had been performed and the rail is being installed. A monitoring setting up during project progress has allowed the comparison between predicted deformations and measurements.

Crack on the boundary of a thin elastic inclusion inside an elastic body

AbstractWe propose a model for a 2D elastic body with a thin elastic inclusion in which delamination of the inclusion may take place, thus forming a crack. Non‐linear boundary conditions at the crack faces are imposed to prevent mutual penetration. We prove existence and uniqueness of the equilibrium configuration, considering both the variational and the differential formulations. Moreover, we study the dependence of solutions on the rigidity of the beam and we prove that in the limit corresponding to infinite and zero rigidity, we recover the case of a semi‐rigid inclusion and the case of a crack with non‐penetration conditions, respectively. The convergence of solutions is proved both using variational inequalities and Γ‐convergence.

Large-strain deformation and strain partitioning in polyphase rocks: Dislocation creep of olivine–magnesiowüstite aggregates

Aggregates composed of olivine and magnesiowüstite have been deformed to large strains at high pressure and temperature to investigate stress and strain partitioning, phase segregation and possible localization of deformation in a polyphase material. Samples with 20 vol.% of natural olivine and 80 vol.% of (Mg 0.7Fe 0.3)O were synthesized and deformed in a gas-medium torsion apparatus at temperatures of 1127 °C and 1250 °C, a confining pressure of 300 MPa and constant angular displacement rates equivalent to constant shear strain rates of 1–3.3 × 10 − 4 s − 1 . The samples deformed homogeneously to total shear strains of up to γ ∼ 15. During constant strain rate measurements the flow stress remained approximately stable at 1250 °C while it progressively decreased after the initial yield stress at the lower temperature. Mechanical data, microstructures and textures indicate that both phases were deforming in the dislocation creep regime. The weaker component, magnesiowüstite, controlled the rheological behavior of the bulk material and accommodated most of the strain. Deformation and dynamic recrystallization lead to grain refinement and to textures that were not previously observed in pure magnesiowüstite and may have developed due to the presence of the second phase. At 1127 °C, olivine grains behaved as semi-rigid inclusions rotating in a viscous matrix. At 1250 °C, some olivine grains remained largely undeformed while deformation and recrystallization of other grains oriented for a-slip on (010) resulted in a weak foliation and a texture typical for pure dry olivine aggregates. Both a-slip and c-slip on (010) were activated in olivine even though the nominal stresses were up to 2 orders of magnitude lower than those needed to activate these slip systems in pure olivine at the same conditions.

An Evaluation of Strain Amplification Concepts via Monte Carlo Simulations of an Ideal Composite

Abstract In the modeling of carbon-black filled elastomers it is important to have a good estimate of the state of the elastomer itself, since many nonlinear effects originate in the matrix material. A common notion in such estimates is the idea of a “strain amplification” factor that relates a macroscopically imposed strain state to the average strain state in the elastomer matrix material. In this paper Mullins and Tobin's interpretation of the Guth—Gold and Smallwood's amplification factor, and a more recent proposal by Govindjee and Simo will be examined. All three theories are compared to the results of a series of Monte Carlo simulations on an ideal composite with a Neo-Hookean matrix and semi-rigid inclusions. It is shown that for the idealized material, one can not interpret the Guth—Gold and Smallwood amplification factors as an estimate of the strain state of the matrix material. The theory of Govindjee and Simo, on the other hand, is shown to accurately predict the strain state of the matrix.

The Ainslie Detachment: a regional flat-lying extensional fault in the Carboniferous evaporitic Maritimes Basin of Nova Scotia, Canada

The Ainslie Detachment occurs near the base of the Carboniferous Windsor Group, forming a regional flat-lying extensional fault distributed across 10 000 km2. New mapping has delineated the structure through southwestern Cape Breton Island and into central Nova Scotia. Shearing is concentrated at the top of the basal Macumber limestone along its contact with overlying evaporites and younger allochthonous units. The highly contrasting rheologies of the formations created an anisotropic zone of weakness which acted as an upper crustal stress guide, stratigraphically controlling the trajectory of the detachment through the basin. The detachment is characterized by an approximately 3–10 m thick calc-mylonite zone, with an intense planar fabric featuring alternating very fine grained shear planes and coarser annealed layers. Coarser layers are boudinaged into pinch and swell structures, locally producing segmented augen. Highly strained intraclasts, ooids, and peloids, recrystallized carbonate boudins, and carbonate vein segments are included in the calc-mylonite as semirigid inclusions and rotated porphyroclasts. Thick zones of fault breccia straddle portions of the detachment and overprint the mylonite, demonstrating an evolution to brittle conditions during progressive shear. Listric faults in the hanging wall of the detachment feature a ramp and flat geometry, with an upper detachment occurring along the upper contact of the Windsor Group with the overlying Namurian Mabou Group. Locally up to 2 km of the stratigraphic succession has been removed, with faults cutting downsection in a westerly direction producing rollover in the hanging wall.