Rigid Stratum Research Articles

Neoteric Direct Physical Approaches in TDDS: A Boon for Permeation Enhancement

Abstract: Human skin has been tremendously explored for decades as a potential route for the delivery of various substances. It has shown great applications to deliver drugs to systemic circulation as well as has provided adequate advantages to treat local manifestations over the skin. However, the rigid stratum corneum layer has served as the biggest barrier in transdermal drug delivery; various methods have been designed to overcome the stratum corneum layer and make the molecule pass through this. These methods were then broadly classified into chemical and physical approaches. The below study is an overall review of the physical approaches being used in transdermal drug delivery for overcoming the stratum corneum layer. Physical approaches also include direct and indirect methods; we will be physically considering the direct approaches herein.

Caissons in Cohesionless Soils Considering 3D Wedge under Earthquake Loading

Ultimate soil resistance that acts on a seismically induced caisson foundation and its distribution along the caisson height have been formulated by considering passive wedge failure analysis for both dry and submerged conditions. The method for limiting the equilibrium of forces acting on a three-dimensional idealized passive wedge developed due to seismicity has been adapted in this study. Using this process, seismic inertia forces will be computed by considering the surrounding soil as a viscoelastic material that overlays a rigid stratum subjected to a harmonic shaking. For a very large value of caisson width, the comparison of this analysis with a 2D seismic earth pressure problem illustrates the compatibility of this methodology in the plane strain condition. Variation in earth pressure coefficients and their distribution for different seismic acceleration coefficients, soil properties, excess pore pressure ratios, and caisson aspect ratios will be discussed in this analysis. The reasonable agreement of the distribution of total passive pressure along the wedge height under the submerged condition with the experimental results shows the applicability of the proposed formulations as a design approach for caissons in sandy soil.

Analytical Solution for Axially Loaded Piles in Two-Layer Soil

AbstractAn analytical elastic continuum model is developed for the settlement of end-bearing piles in a two-layer soil over a rigid stratum. The model has its roots in the point-load solution of We...

Effect of Stratum on the Interfacial Stress and Structural Integrity of Cement Sheath

In order to determine the method of protecting the cement sheath structural integrity in oil and gas wells, the finite element mechanics models of the Casing-Cement sheath-Stratum Combination Body (CCSCB) were established based on different stratum action mechanism. The effect of stratum type, well depth, crustal stress and stratum elastic modulus on the interface stress and structural integrity of cement sheath were researched. The results show that, in the creep stratum, the interface contact pressure of cement sheath increase and the circumferential stresses reduce with the increase of crustal stress. There is no effect of the crustal stress on the interface stress in the elastic and rigid stratum. In elastic stratum and low crustal stress creep stratum, circumferential tensile stress would be generated at cement sheath when loading. The cement sheath is easy to crack by this tensile stress and the structural integrity is destroyed when the load was higher. The effect of stratum elastic modulus on the interface stress is related to the stratum and stress type. There is no influence of the elastic modulus on the interface stresses in the rigid stratum. The influence of the elastic modulus on the interface contact pressure is obvious in the elastic stratum, and the effect on the circumferential stress is obvious in the creep stratum.

The effectiveness of a pile barrier for vibration transmission in a soil stratum over a rigid bedrock

The potential use of pile barriers as a ground vibration mitigation measure is analysed through an efficient numerical model. The soil is modelled as an elastic half space, using the reciprocity theorem and specific Green’s functions for the layered half space, while the piles are treated as beam elements. After benchmarking the proposed model against a Boundary Element model, it is used to study this type of barrier, with particular focus on how the presence of a rigid bedrock alters its performance. A significantly different behaviour when compared to the case of the half space is found if the piles reach the rigid stratum, increasing the barrier performance around the layer second natural frequency.

Seismic Active Thrust on Rigid Retaining Wall Using Strain Dependent Dynamic Properties

An analytical model is proposed for the evaluation of seismic active thrust on retaining wall resting on sandy soil. Foundation and backfill soil is idealized as Kelvin-Voigt solid. The governing differential equation of vertically propagating shear wave is solved by maintaining the displacement continuity and stress compatibility at the interface between backfill and foundation soil. Nonlinear distribution of accelerations induced in the backfill soil is then used to compute the seismic inertia force. Total seismic active thrust is obtained by solving the force equilibrium equation of the triangular failure wedge. The present method computes the strain-dependent shear-wave velocity and damping ratio of sand from its modulus reduction and damping ratio curves using an iterative scheme. Amplification and deamplification of the input excitations in the foundation soil and backfill soil are compared with results of dynamic centrifuge tests reported in the literature. An increase in the magnitude of seismic active thrust is observed when the retaining wall is situated on sandy soil in place of the rigid stratum, and the percentage increase is 18% in comparison to the latest method available in the literature. The seismic active thrust values for long period input excitations are nearly 13 to 17% higher compared to short-period input excitations. The parametric study reveals that depth of backfill and foundation soil, impedance ratio, amplitude, and frequency of input motion dominate the response of the backfill soil under seismic condition. (C) 2018 American Society of Civil Engineers.

Effect of dynamic soil properties and frequency content of harmonic excitation on the internal stability of reinforced soil retaining structure

The effect of dynamic soil properties and frequency content of harmonic excitation on the internal stability of reinforced soil retaining structure is investigated. Arc of a log-spiral is considered as the failure surface in the present limit equilibrium analysis. Backfill and reinforced soil is modeled as a visco-elastic material. The whole structure is considered to be resting on a rigid stratum. Backfill soil and the reinforced soil retaining structure are subjected to harmonic shaking at the base. Present methodology satisfies the stress boundary condition at the ground surface. In the present study, amplitude and phase of the horizontal and vertical seismic accelerations change with depth and the variation of accelerations along the depth is found to be time dependent and nonlinear. All the four possible combinations of horizontal and vertical seismic inertia force directions are considered to determine the total reinforcement force and critical length of the reinforcement. In the present study, amplification of accelerations towards the ground surface depends on the dynamic soil properties and frequency content of input excitation. Detailed parametric study is done to understand their implications on the solution. An algorithm is proposed at the end of this paper which uses strain dependent equivalent linear values of shear wave velocity (Vs) and damping ratio (ξ) to compute the total reinforcement force and critical length of the reinforcement. The limitation of equivalent linear based approach is that it only considers vertically propagating shear wave. Comparison of present method with other theories is also presented showing the merit of the present study.

Seismic passive earth resistance using modified pseudo-dynamic method

In earthquake prone areas, understanding of the seismic passive earth resistance is very important for the design of different geotechnical earth retaining structures. In this study, the limit equilibrium method is used for estimation of critical seismic passive earth resistance for an inclined wall supporting horizontal cohesionless backfill. A composite failure surface is considered in the present analysis. Seismic forces are computed assuming the backfill soil as a viscoelastic material overlying a rigid stratum and the rigid stratum is subjected to a harmonic shaking. The present method satisfies the boundary conditions. The amplification of acceleration depends on the properties of the backfill soil and on the characteristics of the input motion. The acceleration distribution along the depth of the backfill is found to be nonlinear in nature. The present study shows that the horizontal and vertical acceleration distribution in the backfill soil is not always in-phase for the critical value of the seismic passive earth pressure coefficient. The effect of different parameters on the seismic passive earth pressure is studied in detail. A comparison of the present method with other theories is also presented, which shows the merits of the present study.

Experimental Analysis of Embankment on Ordinary and Encased Stone Columns

AbstractThis work investigated the behavior of embankment models resting on soft soil reinforced with ordinary and encased stone columns (ESCs). Model tests were performed with different spacing distances between stone columns and two length-to-diameter ratios (L/d) of the stone columns, in addition to different embankment heights. A total of 39 model tests were performed on soil with an undrained shear strength of ≈10 kPa. The system consisted of a stone column–supported embankment at different spacing-to-diameter ratios (s/d) of stone columns. Earth pressure cells were used to measure directly the vertical stress on the column for all models, and another cell was placed at the base of the embankment between two columns to measure directly the vertical stress in reinforced soft soil. For embankment models constructed on soft clay reinforced with ESCs, it was found that whether a column was floating or end bearing (resting on a rigid stratum), encasement of the column by a geogrid was most effective in im...

Seismic Uplift Capacity of Horizontal Strip Anchors Using a Modified Pseudodynamic Approach

The uplift capacity of shallow horizontal strip anchors embedded in cohesionless soil has been obtained under seismic conditions. The limit equilibrium approach with log spiral failure surface together with modified pseudodynamic seismic forces has been adopted. In this modified pseudo dynamic approach, the soil is assumed to behave as a viscoelastic material overlying a rigid stratum and subjected to harmonic horizontal acceleration. This modified methodology satisfies the zero-stress boundary condition at the free ground surface. In the present methodology, the amplification of seismic acceleration depends on the soil properties and can be evaluated; hence, there is no need for assumption of any amplification value as is usually done in the literature. It is observed that the seismic acceleration distribution along the depth is highly nonlinear. The net seismic vertical uplift capacity factor for a unit weight component of soil (Fγd) is estimated. The results under static and seismic conditions are determined for various combinations of input parameters, such as soil friction angle, embedment ratio, and seismic acceleration. It is observed that the design value of Fγd decreases significantly with an increase in seismic acceleration. As expected, the seismic uplift capacity increases with an increase in embedment ratio and soil friction angle. Results in terms of nondimensional net seismic uplift capacity factor are presented in graphical form. In addition, the present results are compared and found to be in good agreement with a very few available similar results in literature. The present study reveals the lowest critical design values of seismic uplift capacity factor that may be used in seismic design of shallow strip anchors.

Aspectos morfoanatômicos e fisiológicos de sementes e plântulas de Amburana cearensis (Fr. All.) A.C. Smith (Leguminosae - Papilionoideae)

Os objetivos deste trabalho consistiram em descrever e ilustrar os aspectos morfoanatômicos de sementes e plântulas de Amburana cearensis, relacionando o desenvolvimento dos tecidos às fases de germinação das sementes, para verificar as mudanças que ocorreram durante esse processo. Os ensaios foram conduzidos no Laboratório de Estudos em Meio Ambiente da Universidade Católica de Salvador (LEMA/UCSal). O delineamento experimental utilizado foi o inteiramente casualizado com quatro repetições de 25 sementes por tratamento. A curva de embebição foi elaborada com base no peso fresco das sementes durante o processo de embebição, em períodos variando entre 0 e 318 h. Para análise morfológica das sementes e plântulas, ambas foram observadas a olho nu e ao microscópio estereoscópico, a fim de confeccionar a prancha. As secções anatômicas foram feitas com o auxílio do micrótomo rotativo, utilizando-se para tal as sementes durante as fases da germinação. Quanto à análise morfológica, as sementes são esternospermáticas e o embrião axial, sendo a germinação do tipo epígea e fanerocotiledonar. Quanto aos aspectos anatômicos, pôde-se verificar que as sementes de A. cearensis são bitegumentadas e exotestais e apresentam os cotilédones como principal tecido de reserva. O tegumento é composto por um estrato de macroesclereídes e por estratos de osteoesclereídes e possui compostos fenólicos, o que confere às sementes certo grau de dormência por impermeabilidade do tegumento, dificultando, assim, a absorção de água.

Transient kinematic pile bending in two-layer soil

The dynamic response of piles to seismic loading is explored by means of an extensive parametric study based on a properly calibrated Beam-on-Dynamic-Winkler-Foundation (BDWF) model. The investigated problem consists of a single vertical cylindrical pile, modelled as an Euler–Bernoulli beam, embedded in a subsoil consisting of two homogeneous viscoelastic layers of sharply different stiffness resting on a rigid stratum. The system is subjected to vertically propagating seismic S waves, in the form of a transient motion imposed on rock outcrop. Several accelerograms recorded in Italy are employed as input motions in the numerical analyses. The paper highlights the severity of kinematic pile bending in the vicinity of the interface separating the two soil layers. In addition to factors already investigated such as layer stiffness contrast, relative soil–pile stiffness, interface depth and intensity of ground excitation, the paper focuses on additional important factors, notably soil material damping, stiffness of Winkler springs and frequency content of earthquake excitation. Existing predictive equations for assessing kinematic pile bending at soil layer interfaces are revisited and new regression analyses are performed. A synthesis of findings in terms of a set of simple equations is provided. The use of these equations is discussed through examples.

The mechanics and dynamics of sills in layered elastic rocks and their implications for the growth of laccoliths and other igneous complexes

The recent experimental work by Kavanagh et al. [Kavanagh, J.L., Menand, T. and Sparks, R.S.J. (2006). An experimental investigation of sill formation and propagation in layered elastic media. Earth Planet. Sci. Lett. 245, 799–813.] shows that lithological discontinuities and rigidity contrasts can control the formation and dynamics of sills at interfaces separating upper, rigid strata from lower, weaker strata. The present paper extends this work and focuses on its implications in terms of the length- and time-scales associated with the development of laccoliths and other igneous complexes. Sill formation controlled by rigidity contrasts is shown to provide a growth mechanism for laccoliths. The formation of a sill provides favourable rigidity anisotropy for the emplacement of subsequent sills so that laccoliths grow by over-accretion, under-accretion or even mid-accretion of successive sills. In accord with field data, this model predicts that laccoliths grow mainly by vertical expansion, representing the cumulative thickness of their internal sills, while maintaining a comparatively constant lateral extend. The model also predicts that the time-scale over which laccoliths form is essentially determined by the cumulative time between successive sill intrusions. Also, sill dynamics are controlled by viscous dissipation of the fluid along their length, which have consequences for the size and shape of sills. Viscously-controlled dynamics would enable sills to propagate further and thus to grow thicker than dykes of similar magmas. These dynamics would also enable sills to propagate faster and thus to induce non-elastic deformations in surrounding rocks that could deviate them from the interface they originally follow. This would allow them to feed new sills along other interfaces and could assist in the formation of the step structures and saucer-shapes that are commonly observed in sill complexes.

3D seismic response of a limited valley via BEM using 2.5D analytical Green's functions for an infinite free-rigid layer

This paper presents analytical solutions for computing the 3D displacements in a flat solid elastic stratum bounded by a rigid base, when it is subjected to spatially sinusoidal harmonic line loads. These functions are also used as Greens functions in a boundary element method code that simulates the seismic wave propagation in a confined or semi-confined 2D valley, avoiding the discretization of the free and rigid horizontal boundaries. The models developed are then used to simulate wave propagation within a rigid stratum and valleys with different dimensions and geometries, when struck by a spatially sinusoidal harmonic vertical line load. Simulations are performed in the frequency domain, for varying spatial wave numbers in the axial direction of the valley. Time results are obtained by means of inverse Fourier transforms, to help understand how the geometry of the valley may affect the variation of the displacement field.

Bearing capacity of a strip foundation on a sand layer overlying a smooth rigid stratum

The effect of a smooth rigid stratum, located beneath a dense sand layer, on the bearing capacity and settlement of surface and shallow strip footings is investigated using an advanced experimental model. A theoretical analysis is presented for the bearing capacity of surface footings. The results indicate that the bearing capacity reaches a minimum value at a specific sand-layer thickness. Any increase in the layer thickness above this value causes an increase in the bearing capacity up to that corresponding to a continuous media.

Interaction analysis of strip footing resting on a non-homogeneous elastic medium

In this paper, a plane stress solution for the interaction analysis of strip footing resting on (i) a non-homogeneous elastic half-plane and (ii) a non-homogeneous elastic layer resting on a rigid stratum has been presented. The analysis has been done using a combined analytical and FEM method in which the discretization of the half-plane is not required and thereby minimizes the computational efforts considerably. The contact pressure distribution and the settlement profile for the selected cases of varying modulus half-plane, which has more relevance to foundation engineering, have been given. Experimental verification through a photoelastic method of stress analysis has been carried out for the case of footing on Gibson elastic half-plane, and the contact pressure distribution thus obtained has been compared with the theoretical results.

Discrete layer analysis of axially loaded piles and pile groups

This paper presents a simple discrete layer approach for the settlement analysis of axially loaded piles and pile groups. The soil profile may be arbitrarily layered and underlain by either a stiff or rigid stratum. The pile-soil-pile interaction is determined using a modified form of Mindlin's solution for finite soil depth. Good agreement between the present approach and more rigorous finite element and boundary element approaches is observed for the analysis of piles and pile groups embedded in finite soil layers. Settlement predictions obtained from the present approach also agree reasonably well with measurements from a number of published pile tests. Although the emphasis of this paper is on linear elastic solutions, it can easily be extended to include non-linear response.

Appalachian Structural Style in Southern New Brunswick

The strain geometry of southern New Brunswick can be analyzed in terms of four major structural sub-divisions, which mark a variation in style from tilting and translation of rigid strata, single-phase cylindrical folding by flexural slip, polyphase folding by flexural flow, to extreme cataclastic flow with attendant transposition of early planar fabrics. Shallow dips of planar elements and shallow plunges of hinge lines occur in distinct zones, Maximum strain occurred along the northeast-trending Lubec-Belleisle zone, where vertical attitudes of planar and linear elements prevail. Cataclastic fabrics are regionally developed together with narrow mylonitic zones.Rock heterogeneity in part influences structural style, with early granitic plutons tending to act as rigid buttresses, but the major sub-divisions are not controlled by lithologic boundaries. The structural sub-divisions transgress the present position of fault boundaries.Southern New Brunswick is probably a relict continental margin. If regional folding, cataclasis, and later faulting can be attributed to the closing of the Proto-Atlantic seaway in Middle Devonian to Carboniferous times, the localization of intense strain in southern New Brunswick and particularly along the Lubec-Belleisle zone may be accounted for by assuming that stress concentrations would occur in the region of the shelf slope margin.

Essai d'une theorie mecanique de la structure cone-in-cone

Abstract Summarizes data and observations supporting the concept that cone-in-cone structures are the product of mechanical processes. The structures are considered due to deformation, by traction, of plastic material intercalated between more rigid strata.