Initial Lateral Pressure Research Articles

Hyperbolic stress-strain behaviour of sandy soil under plane strain unloading condition and its application on predicting displacement-dependent active earth pressure

This study investigates the displacement-dependent lateral earth pressure of sandy soil in active state. 3D DEM numerical simulations of plane strain unloading test (unloading in the minor principal stress direction) are carried out firstly to acquire the hyperbolic stress–strain relationship of sandy soil. The initial modulus of sandy soil is observed to increase with the increasing of major principal stress, initial lateral earth pressure coefficient and relative density, while the failure ratio is little influenced by these factors. A simplified hyperbolic model calibrated by the DEM results are then developed to calculate the displacement-dependent active lateral earth pressure of sandy soil. It was found that the hyperbolic model can well predict the variation of lateral earth pressure distribution at intermediate active state of T- (Translation) and RB- (Rotate about the base) mode of retaining structure movement. But it can hardly capture the lateral earth pressure distribution on retaining structure under RT- (Rotate about the top) mode due to significant rotation of principal stress direction. According to the theoretical analysis, the required retaining structure displacement leading to the limiting active state is varied along the retaining structure, and it also dependents on the initial stress state as well as the relative density.

Numerical Study of Fracture Characteristics of Deep Granite Induced by Blast Stress Wave

To study the characteristics of rock fracture in deep underground under blast loads, some numerical models were established in AUTODYN code. Weibull distribution was used to characterize the inhomogeneity of rock, and a linear equation of state was applied to describe the relation of pressure and volume of granite elements. A new stress initialization method based on explicit dynamic calculation was developed to get an accurate stress distribution near the borehole. Two types of in situ stress conditions were considered. The effect of heterogeneous characteristics of material on blast-induced granite fracture was investigated. The difference between 2D models and 3D models was discussed. Based on the numerical results, it can be concluded that the increase of the magnitude of initial pressure can change the mechanism of shear failure near the borehole and suppress radial cracks propagation. When initial lateral pressure is invariable, with initial vertical pressure rising, radial cracks along the acting direction of vertical pressure will be promoted, and radial cracks in other directions will be prevented. Heterogeneous characteristics of material have an obvious influence on the shear failure zones around the borehole.

Analytical and numerical study of a circular cavity subjected to plane and cylindrical P-wave scattering

Dynamic stress concentration has been widely considered as an important factor that dominates the damage of underground cavities. To obtain the influence of wavefront curvature on the dynamic response around the circular cavity, the dynamic stress concentration near the cavity caused by the plane P-wave and cylindrical P-wave scattering is investigated based on the wave function expansion methods and Fourier transform. A three-dimensional numerical finite element model is subsequently established to simulate the dynamic damage and its influencing factors, including the period t0 of the incident wave and the initial lateral pressure coefficient γ, around the underground cavity subjected to plane P-wave and cylindrical P-wave. The results indicate that an obvious dynamic stress concentration occurs around the cavity under dynamic stress disturbance. The dynamic stress concentration factors (DSCFs) caused by the cylindrical P-wave is larger than that caused by the plane P-wave, and the obvious tensile stress concentration, which is equivalent to the compressive stress concentration, only occurs under the cylindrical P-wave. Furthermore, the failure characters of the cavity under different initial static stresses and dynamic incident loadings are simulated using the multiphysics software LS-DYNA, indicating that the dynamic failures are related to the initial static pressure coefficients, period of incident wave, and incident wavefront curvature. The plastic failure under the plane P-wave appears initially at the compressive concentration areas while the initial failure caused by the cylindrical P-wave occurs at the tensile concentration areas.

Deep Cement Mixed Walls with Steel Inclusions for Excavation Support

Deep cement mixed (DCM) walls are widely used in supporting excavations in many parts of the world. In this paper, a case study of an excavation supported by a DCM wall with steel inclusions is analysed using a three-dimensional finite element model and based on the coupled theory of nonlinear porous media. The DCM wall is constructed with wide flange steel inclusions. The stress–strain behaviour of the DCM wall section is simulated using an extended version of the Mohr–Coulomb model, which considers the strain-softening behaviour of DCM columns beyond yield. The computed lateral deformations are compared with the field measurements to validate the numerical modelling procedure. Using the same case study, the internal stability of the wall against bending and shear failure modes is investigated. In addition, the lateral pressure distribution along the wall length is investigated because in practice design is carried out considering a uniform pressure distribution assuming rigid wall movements. A parametric study was carried out to investigate the viability of DCM walls in supporting excavations by varying the spacing between steel inclusions, wall thickness and initial lateral earth pressure. Based on the results of the parametric study, guidelines are proposed to select the most efficient geometric arrangement of steel inclusions within DCM walls.

Dynamic ultimate strength of outer bottom stiffened plates under in-plane compression and lateral pressure

An investigation in conducted on the dynamic ultimate strength of ship bottom stiffened plates under uniaxial compression and lateral pressure. The nonlinear finite element method is adopted, considering both material and geometric non-linearities. The dynamic ultimate strength of a tested specimen is calculated based on the nonlinear finite element method, and the comparison with test results shows the applicability of the present numerical method. The static ultimate strength of stiffened plate structures obtained with the numerical method is compared with an empirical formulation and the error is within the allowable range. Then, the influence of modes and magnitudes of initial imperfections, boundary conditions, lateral pressure, strain rate and structural dimensions, on the dynamic ultimate strength are discussed.

Effect of Formwork Characteristics on SCC Lateral Pressure

Lateral pressure exerted on vertical formwork by fresh self-consolidating concrete (SCC) controls its design. Several factors, including material properties, placement conditions, and formwork characteristics, can affect formwork pressure. This paper presents the influence of formwork width (0.20–1.0 m), shape (circular versus square), and surface material (PVC, plywood, steel, and polyester filter membrane) of formwork on lateral pressure characteristics. The diameter of the pressure sensor used to evaluate lateral pressure characteristics is also investigated. The results showed that the increase in formwork width can increase the initial lateral pressure and delay the time needed for the formwork removal. Correction factors accounting for the changes in the formwork width on the initial pressure and pressure decay were developed. The formwork surface materials did show significant effect on initial formwork pressure, and different pressure decay responses were observed for each formwork material. The longest time for pressure cancellation was obtained for the steel formwork, and the shortest one for the polyester filter membrane.

Effect of placement characteristics on SCC lateral pressure variations

Lateral pressure exerted by fresh concrete on vertical formwork systems controls significantly the design of the formwork systems. Several factors including, material properties, placement conditions, and formwork characteristics can affect formwork lateral pressure. This paper presents the results of an extensive experimental work aimed at studying the influence of concrete temperature (10–32°C), casting depth (up to 13m), placement rate (2–30m/h), waiting period between successive lifts, as well as concrete thixotropy on lateral pressure characteristics. The increase of concrete temperature is shown to accelerate the stiffening rate of the concrete leading to reduction in initial lateral pressure. For highly thixotropic SCC mixture even at very high casting rate of 30m/h, the initial lateral pressure is limited to 26% of the equivalent hydrostatic pressure at casting depth of 10m and to 70% at the shallow casting depth of 3m. These pressure values can drop further (about 25%) when the casting rate reduces from 30 to 2m/h. Interruption of concrete casting with a waiting period of 30min can reduce lateral pressure up to 15%, especially for highly thixotropic concrete.

Fresh concrete lateral pressure decay: Kinetics and factorial design to determine significant parameters

Abstract The design of vertical formworks is governed by the lateral pressure exerted by fresh concrete; while maximum lateral pressure is the key parameter for formwork design, the rate of pressure decay and the time needed for pressure stabilization is important for determining formwork removal time; the complexity of the problem is due the large number of factors which affect the rate of pressure decay. This works describes an experimental investigation of columns to determine the variation in the initial lateral pressure decay and in the time needed for pressure stabilization with the following variables: coarse aggregate concentration (different sand to total aggregate ratios were used), the use of a plasticizer, the presences of reinforcement and concrete temperature. In the last part of this work a correlation between setting time and maturity functions with the time needed for pressure stabilization was done. The results show that both thixotropic linked to cement grains nucleation and consolidation and cement hydration influences in lateral pressure decay to the point of stabilization. In references with the initial pressure decay, the presence of reinforcement seems to have a major influence. On the other hand the time needed for pressure stabilization could be correlated with the maturity functions.

Nonlinear Analysis of Large Deflection of Elastically-Bossed Sensor Plate under Initial Tension

The nonlinear problem of large deflection of an elastically-bossed layered plate under pretension due to lateral load is studied. The approach follows von Karman plate theory for large deflection for a symmetrically layered isotropic case. The thus derived nonlinear governing equations are solved using a numerical finite difference method with the aid of an iteration scheme. For a nearly monolithic plate with a thin boss, the obtained solutions correlate well with those available in literature for a single-layered flat plate, thus validates the presented approach. For three layered symmetric plates made of typical silicon based materials, various initial tension and lateral pressure are implemented. The results indicate that, edge behavior may appear at both the boss edge and the clamped end of the plate, thereby revealing severe variations for the structural responses. Varying the central boss size and relative thickness may have a sensible influence upon the behavior of the bossed layered plate. Furthermore, lateral pressure appears to have a sensible effect upon the nonlinear behavior of the bossed layered plate. For a relatively large initial tension, however, the pretension effect dominates, yielding a total membrane behavior for the bossed plate, regardless of the size of the center boss, except in the vicinity of the clamped edge.

Nonlinear study of large deflection of simply supported piezoelectric layered-plate under initial tension

The nonlinear problem of large deflection of a simply supported piezoelectric layered plate under initial tension is studied. The approach follows von Karman’s plate theory for large deflection for a symmetrically layered isotropic case including a piezoelectric layer. The nonlinear governing equations are solved using a finite difference method, by taking the associated linear analytical solution as an initial guess in the numerical iteration procedure. The results for a nearly monolithic plate under a very low applied voltage are found to correlate well with available solutions for a single-layered case under pure mechanical loading and thus the present approach is validated. For three-layered plates made of typical silicon based materials, various initial tension and lateral pressure are considered, and different applied voltages up to a moderate magnitude are implemented. No edge effect was observed, in contrast to the cases of clamped plates in literature. In additions, varying the layer moduli seems to have an insignificant effect upon the structural responses of the layered plate. On the other hand, the piezoelectric effect tends to be apparent only in a low pretension condition. For a relatively large pretension, the effect of initial tension becomes dominant, yielding nearly unique solutions for the structural responses, regardless of the magnitudes of the applied voltage and the lateral pressure.

The effect of pretensioned FRP windings on the behavior of concrete columns in axial compression

This paper presents the results of an experimental investigation of concrete columns confined by wound pretensioned epoxy-impregnated carbon filament yarns. The yarn winding equipment, with the ability to set the desired pretension force and thereby to produce confined concrete specimens with different initial lateral pressure, was developed at the Institute of Polymer Mechanics. It is shown that the pressure in creases the axial stress at which intense internal cracking of concrete develops.

Effect of Mixture Consistency on Formwork Pressure Exerted by Highly Flowable Concrete

An experimental program was undertaken to evaluate the effect of a mixture’s consistency on the lateral pressure that can be developed by highly flowable concrete. Six mixtures, with various contents of high-range water-reducing admixtures, were tested and had consistency levels varying between a slump of 220 mm and a slump flow of 750 mm . The mixtures had similar water-to-cementitious materials and sand-to-total aggregate ratios of 0.40 and 0.46, respectively. Depending on the mixture consistency, the maximum initial pressures varied between 75 and 98% of hydrostatic. Concretes with lower consistency were shown to exert lower initial lateral pressure and had faster rates of pressure drop with time. This can be attributed to the increased degree of shear strengths that enables the fresh concrete to further resist vertical stresses, hence precluding the development of high lateral pressure. Self-consolidating concrete mixtures made with standard CSA Type 10 cement exhibited higher initial pressure and low...

Effect of w /cm and High-Range Water-Reducing Admixture on Formwork Pressure and Thixotropy of Self-Consolidating Concrete

An experimental program was undertaken to evaluate the effect of water-cementitious material ratio (w/cm) and type of high-range water-reducing admixture (HRWRA) on the development of form-work pressure that can be exerted when using self-consolidating concrete (SCC). Pressure variation was monitored using an experimental column measuring 2800 mm in height. The tested mixtures were proportioned with a similar initial slump flow consistency of 650 ± 15 mm. Three w/cm of 0.36, 0.40, and 0.46 and three types of HRWRA (polycarboxylate, polynaphthalene sulphonate, and polymelamine sulphonate) were investigated. Variations in lateral pressure were related to the thixotropy of the concrete. Test results show that the variations in lateral pressure and thixotropy of SCC are significantly affected by the w/cm. Irrespective of the HRWRA type, mixtures proportioned with 0.46 w/cm exhibited greater initial pressure and lower thixotropy compared with mixtures made with a w/cm of 0.40 and 0.36. This is related to the higher water content and lower coarse aggregate volume in concrete proportioned with the higher w/cm, which can lead to a reduction in shear strength properties of the plastic concrete. The rate of pressure drop and increase in thixotropy with time, however, were greater in mixtures made with a higher w/cm. This is attributed to the lower HRWRA demand that can lead to sharper fluidity loss with time. For any given w/cm, the type of HRWRA appears to have a limited effect on initial lateral pressure. Compared with naphthalene-and melamine-based HRWRA, the use of polycarboxylate-based HRWRA in SCC resulted in lower rate of pressure drop with time. This is reflected by the greater fluidity retention of the mixtures containing the polycarboxylate-based HRWRA. The incorporation of a water-reducing agent in mixtures made with polynaphthalene sulphonate-based HRWRA is shown to increase lateral pressure development of the plastic concrete over time.

Numerical simulations of simple shear with non‐coaxial soil models

AbstractThis paper investigates the effects of a non‐coaxial model on simulated stress–strain behaviour of granular materials subject to simple shearing under various initial conditions. In most cases, a significant difference of predictions between coaxial and non‐coaxial modelling is found during the early stage in shearing. With the increase in shearing, non‐coaxial simulations approach and tend to coincide with coaxial simulations. It is also found that the roles of non‐coaxial modelling in simulating simple shear behaviour are considerably influenced by hardening rules, flow rules, initial static lateral pressure coefficients. In some cases, the non‐coaxial modelling gives a similar simulation as the coaxial modelling. In other cases, the non‐coaxial modelling decreases the hardening response or softening response of materials, compared with the coaxial modelling. Under certain conditions, the predicted peak strength of materials with non‐coaxial modelling is larger than that for coaxial modelling. Some of these observations can be attributed to the amount of principal stress rotation in various cases analysed. Others can be attributed to the difference between the directions of the non‐coaxial plastic flow and those for coaxial plastic flow. Copyright © 2005 John Wiley & Sons, Ltd.

Effect of Coarse Aggregate Characteristics on Lateral Pressure Exerted by Self-Consolidating Concrete

This article reports on a study undertaken to determine the influence of concentration and nominal size of coarse aggregate on the development of lateral and pore water pressures of self-consolidating concrete (SCC). The study evaluated 9 mixtures prepared with sand-total aggregate ratios (S/A) varying between 1.0 and 0.30. An experimental column measuring 2800 mm in height and 200 mm in diameter was used to determine lateral pressure and pore water pressure during the plastic stage of cement hydration. Results show that lateral pressure is significantly influenced by the S/A value. The pore water pressure affects the development of lateral pressure of SCC in the plastic stage. The authors conclude that the lateral pressure developed by the plastic concrete is directly related to internal friction resulting from the coarse aggregate concentration. The greater the degree of increase in internal friction, which corresponds to mixtures made with relatively low S/A values, the lesser the magnitude of initial lateral pressure becomes and the faster the drop in pressure.

Variation of Formwork Pressure with Thixotropy of Self-Consolidating Concrete

An experimental investigation was carried out to determine the influence of thixotropy on the development of formwork lateral pressure. Five self-consolidating concrete (SCC) mixtures prepared with different combinations of cementitious materials and set-modifying admixtures were evaluated. An experimental column measuring 2100 mm in height and 200 mm in diameter was used to determine lateral pressure distribution using five pressure sensors mounted at 50, 250, 450, 850, and 1250 mm from the base. This paper offers a comprehensive review of key factors affecting formwork pressure developed by fresh concrete and presents the results pertaining to the influence of thixotropy on variations in lateral pressure of SCC. The results show that the lateral pressure exerted by the plastic SCC is directly related to thixotropy. With the increase in thixotropy, the initial lateral pressure registered following casting decreases, and the rate of drop in lateral pressure is accelerated. This is attributed to the reversible effect of the thixotropy which enables the material to regain its shear strength, internal friction, and cohesion when left at rest without any shearing action. Immediately after casting, any decrease in lateral pressure was attributed to the increased internal friction resulting from the use of ternary cement and greater concentration of coarse aggregate. The use of a set-retarding agent resulted in a delay in cement hydration that led to a slower rate of drop in lateral pressure. Conversely, the incorporation of a set-accelerating agent resulted in an increase in the rate of pressure drop.

An Axisymmetric Model for Ultimate Capacity of a Single Pile in Sand

ABSTRACT Conventional theories for predicting the capacity of a single pile in sand have not been able to support the undisputed experimental results, which originated the concept of the critical depth (Kerisel, 1961; Vesic, 1967; Tavenas, 1971). Furthermore, the predictions obtained from these theories are wide (Poulos and Davis, 1980). An axisymmetric model was developed to predict the capacity of a single, vertical pile in sand, subjected to axial loading. The proposed model incorporates salient features previously neglected in conventional theories, viz. the interaction between the shaft and the tip resistance, coupled with a punching shear mechanism as a unique mode of failure. This model signifies a distinct departure from existing methods, which calculate the shaft resistance, based on a mechanism independent of tip resistance. The model is also capable of accounting for the effects of the sand density, the initial lateral earth pressure and the relative depth and the roughness of the pile shaft. In the proposed model, the concept of the critical depth is theoretically established, through a variable failure mechanism and the degree of shear mobilization along the pile-soil interface.

Postbuckling of free edge Reissner–Mindlin plates elastically supported on a two-parameter foundation and subjected to biaxial compression and transverse loads

A postbuckling analysis is presented for a rectangular Reissner–Mindlin plate with all four free edges subjected to biaxial compression combined with a transverse central patch load and resting on a two-parameter (Pasternak-type) elastic foundation. The lateral pressure is first converted into an initial deflection and the initial geometric imperfection of the plate is also taken into account. The formulations are based on Reissner–Mindlin plate theory considering the first order shear deformation effect, including plate-foundation interaction. The analysis uses a mixed Galerkin-perturbation technique to determine the buckling loads and postbuckling equilibrium paths. Numerical examples are presented that relate to the performances of perfect and imperfect, moderately thick plates with all four free edges under combined loading conditions and resting on two-parameter elastic foundations from which results for Winkler elastic foundations are obtained as a limiting case. The effects played by foundation stiffness, transverse shear deformation, plate aspect ratio, loaded area parameter and initial lateral pressure are studied. Typical results are presented in dimensionless graphical form.

Nonlinear analysis of simply supported Reissner–Mindlin plates subjected to lateral pressure and thermal loading and resting on two-parameter elastic foundations

A nonlinear analysis is presented for a simply supported, Reissner–Mindlin plate subjected to a transverse central patch load and thermal loading and resting on a two-parameter (Pasternak-type) elastic foundation. The two cases of thermal postbuckling of initially pressurized plates and of nonlinear bending of initially heated plates are considered. The temperature fields considered are associated with a non-uniform parabolic distribution over the plate surface and a linear through-the-thickness temperature gradient, respectively. The material properties are assumed to be independent of temperature. The formulations are based on the Reissner–Mindlin plate theory, considering the first order shear deformation effect and including the plate-foundation interaction and thermal effects. The analysis uses a perturbation technique to determine the thermal postbuckling and nonlinear bending response of the plate. The numerical illustrations concern the thermal postbuckling and nonlinear bending behavior of moderately thick plates resting on two-parameter elastic foundations from which results for Winkler elastic foundations are obtained as a limiting case. The effects played by foundation stiffness, plate aspect ratio, transverse shear deformation, thermal load ratio, loaded area and the amount of initial lateral pressure as well as initial thermal bending stress are studied.

Nonlinear analysis of composite laminated thin plates subjected to lateral pressure and thermal loading and resting on elastic foundations

A nonlinear analysis is presented for a simply supported, composite laminated thin plate subjected to a uniform lateral pressure and thermal loading and resting on a two-parameter (Pasternak-type) elastic foundation. The two cases of thermal postbuckling of initially pressurized plates and of large deflection of initially heated plates are considered. The temperature fields considered are associated with a nonuniform tent-like distribution over the plate surface and a linear through-the-thickness temperature gradient, respectively. The material properties are assumed to be independent of temperature. The formulations are based on the classical laminated plate theory, and including the plate-foundation interaction and thermal effects. The analysis uses a mixed Galerkin-perturbation technique to determine the large deflection and postbuckling response of the plate. The numerical illustrations concern the large deflection and thermal postbuckling behavior of antisymmetrically angle-ply and symmetrically cross-ply laminated plates resting on two-parameter elastic foundations from which results for Winkler elastic foundations are obtained as a limiting case. The effects played by foundation stiffness, the plate aspect ratio, the total number of plies, fiber orientation and initial thermal bending stress as well as initial lateral pressure are studied.