Realistic constitutive ground models are critical in the evaluation of soil‐structure interaction problems and the assessment of key design parameters in the seismic analysis of infrastructure ...systems. In the present study, the modified pseudo‐dynamic lateral earth pressures acting on retaining structure with granular backfill of depth‐varying damping ratio are evaluated adopting the lower bound limit analysis in conjunction with the finite element (FE) discretization method using second‐order cone programming (SOCP). The earthquake loading is simulated by the propagation of shear and primary waves through non‐constant inertia forces in the horizontal and vertical directions, respectively. The influence of varying damping ratio alongside the retaining wall height on the seismic active and passive lateral earth pressures is effectively taken into account by adopting well‐established formulas published in the literature. It is shown that failing to consider the damping variation with depth while performing the modified pseudo‐dynamic analysis could lead to precarious, unrealistic estimates of design parameters.
AbstractIn the literature, the influence of spatial variability of the undrained shear strength of foundation soils on the bearing capacity of footings is limited to footings seated directly on the ...foundation. This is an unlikely arrangement in practice. This paper revisits the footing problem by considering a thin granular layer between a strip footing and soft foundation soil using analytical and stochastic numerical modeling. The analyses are extended to the case of a geosynthetic-reinforced granular layer and to the idealized case of no granular layer. The study shows that the probability that the ultimate bearing capacity for the footing is smaller than the deterministic design value is greater for all three scenarios with randomly uniform clay soil than for the same soil with isotropic or anisotropic spatial variability of strength at practical levels of reliability index β (e.g., β≥3.09 for a permanent footing). The reason for this outcome, which may appear counterintuitive, is explained. Design charts are provided to estimate the deterministic design bearing capacity of a rigid strip footing required to meet a range of target reliability index for the three footing scenarios examined in this study.
The influence of expanded polystyrene (EPS) beads inclusion on the shear stiffness of a quartz-based material and a calcareous-based material has been examined by performing a comprehensive series of ...non-destructive bender element tests. To this end, siliceous-based Firoozkooh and calcareous-based Hormuz sands are mixed with different percentages of expanded polystyrene beads and then tested with a bender element apparatus embedded in a triaxial cell. Accordingly, the influences of confining pressure, void ratio, grain size distribution, and different percentages of expanded polystyrene beads on the small-strain shear modulus of siliceous and calcareous sands are thoroughly studied and discussed. For all mixtures of both sands, the maximum shear modulus increases with increasing confining pressure, but decreases with increasing void ratio and expanded polystyrene beads content in the mixture. The contribution of expanded polystyrene beads to the reduction of small-strain shear modulus is observed to be more pronounced for the quartz-based aggregate as compared to the calcareous-based aggregate. The confining pressure is also observed to have no influence on the small-strain shear modulus of the composites at high expanded polystyrene bead contents due primarily to the notably high compressibility of soft beads diminishing the augmented interparticle contact forces caused by increasing isotropic confinement. Using the results of experiments, different small-strain shear modulus expressions are developed for quartz-based and calcareous-based compacted fill-expanded polystyrene beads composites, which can be utilized for design purposes in earthen structures.
Abstract
This paper aims at analyzing the active and passive lateral earth pressures exerted on retaining walls due to the anisotropic medium of dry and noncohesive backfill subjected to the modified ...pseudodynamic earthquake loading. To this end, the well-established lower bound limit analysis in conjunction with the finite-element discretization method using second-order cone programming is exploited to evaluate the corresponding states of seismic earth pressures on the retaining structure. The earthquake loading is simulated by the propagation of the shear and primary waves through nonconstant inertia forces in the horizontal and vertical directions, respectively. The inherently anisotropic behavior of the soil medium is also accounted for by differentiating between the internal friction angles in different directions. Results generally show that, unlike the active state, inherent anisotropy bears a notable influence on the passive earth pressure; however, the effect of seismic loading on the lateral earth pressure is more pronounced in the active state. The dominant influence of anisotropy occurs at the critical state of seismic loading, i.e., the resonance condition. Using the results of numerical simulations, the influence of internal friction angle, soil–wall roughness, imposed wavelength, material damping, and inherent anisotropy on the lateral earth pressures is thoroughly evaluated and discussed.
AbstractThe bearing capacity of strip footings on anisotropic soils was examined by using the method of lower-bound-limit analysis coupled with the finite elements and linear programming technique. ...The governing equations were first used assuming anisotropic soil shear strength, followed by some modifications to make them applicable for this particular problem. The method was applied to inherently anisotropic soils under a static loading condition, but it can be extended to other problems. The modifications lead to an iterative procedure that solved stability problems assuming shear-strength anisotropy. This iterative procedure is, in fact, a procedure by which the shear-strength parameters are incrementally updated to attain a stationary and converged solution. In this study, the focus was on the bearing capacity of surface footings on anisotropic soils, and eventually, design charts were developed for the problem under study. A few comparisons were also made to show the practical advantages of the results and the verification.
Zeolite is often exploited to reduce the consumption of lime in the treatment of problematic clays and to help further enhance the soil stabilisation process in pavement base and subbase courses. For ...the mix design of the proposed pavement materials, 8% lime was first opted, according to pH tests, as the optimum content and its different portions were then replaced by zeolite inclusion. A comprehensive set of Atterberg limits, standard Proctor, unconfined compression and unconsolidated undrained (UU) triaxial tests was performed on lime and zeolite stabilised specimens. Zeolite addition into the mixture increased the maximum dry unit weight and decreased the optimum moisture content. The least plasticity index and the highest unconfined compressive strength were attained at 25% of lime replacement with zeolite, deemed to be the optimum mixing content. Results of UU triaxial tests on the optimum mixtures also confirmed the marked improvement of shear strength parameters.
The limit load in stability problems in soils is often influenced by the inherent anisotropy. Accordingly, it can be more or less misestimated if an anisotropic soil is simply assumed as being ...isotropic. In this research, the static and seismic active and passive earth pressures of vertical retaining walls in anisotropic sands are investigated by the use of the lower bound limit analysis method in conjunction with the finite elements and linear programming optimization technique. In this regard, the effect of friction angle anisotropy on the limit pressure was considered. To do so, an iterative procedure was made to incorporate the effect of soil anisotropy. In the proposed iterative procedure, the friction angle was incrementally updated after each iteration. After sufficient iterations, a converged solution and a consistent field of friction angle is achieved which satisfy the convergence criteria of the direction of the major principal stresses and the limit load, as well as a stable stress field. It is worth mentioning that the pseudo-static approach was considered in order to apply the seismic condition. The results were compared with those found in the literature and some design charts were developed. Findings indicate that the passive earth pressure coefficient is much more influenced by the degree of anisotropy than the active earth pressure coefficient.
Strength and compressibility characteristics of problematic soils such as loose sands and extra-sensitive clays need to be enhanced for the construction purposes which is due in part to the ...population growth and society’s ever-expanding requirements. Accordingly, cemented soils are being used as a world-renowned soil stabilization practice in all geotechnical engineering applications, yet the high energy consumption and cost of cement is to blame. Therefore, various types of binders have been proposed to partially or even totally supplant the cement, whilst fibers have emerged to be used as composite reinforcement. The current study provides a simple literature review on cemented composites, common non-conventional stabilizers, reinforcing fibrous inclusions and the simultaneous use of a stabilizer and a reinforcing agent. It encapsulates highlighted studies which are stated in a logical sequence to introduce the most practical mixtures used for the stabilization purposes. Moreover, microstructural analysis and measurements regarding variable properties of mortar-like and cemented granules composites will be discussed. Eventually, future works such as an appropriate use of weight–volume relationships as well as adopting an objective qualitative assessment for the selection of the additives will be recommended.
Lightweight sand–EPS beads composite is a new artificial geo-material, which has been recently found applications in geotechnical engineering projects. A series of laboratory tests were carried out ...using a large-scale cyclic direct shear test apparatus to evaluate the monotonic, cyclic and post-cyclic behaviour of an interface between EPS-sand mixtures and a Polyfelt geogrid. EPS were added to sand at 0%, 0.5%, 1%, and 2% by weight. Tests were conducted under three different vertical stresses (30 kPa, 60 kPa and 90 kPa). The influences of cyclic shear semi-amplitude, number of cycles and normal stress on interface properties are investigated. The test results revealed that for a given strain level, interface shear stiffness decreases and damping ratio was shown to increase with increasing EPS content. Hardening behaviour was observed with the number of cycles under different normal stress levels and EPS contents. The EPS-sand-geogrid specimens did not develop clear peak shear stress at monotonic and post-cyclic direct shear tests. The EPS-sand-geogrid mixtures represent an overall contraction behaviour in monotonic, cyclic and post-cyclic stages. The apparent adhesion of interface was shown to increase and the friction angle of interface to decrease with EPS content.
Abstract
This paper aims to assess the lateral limit load (H) of a pile embedded in cross-anisotropic clay deposits by a three-dimensional (3D) finite-element lower bound theorem in association with ...the second-order cone programming method. The lower bound solutions for a laterally loaded pile that is embedded in an anisotropic soil deposit can be found by formulating the element equilibrium, discontinuity shear and normal stresses equilibrium, boundary conditions, yield function, and optimizing the objective function using the second-order cone programming method and an iterative-based update procedure. The calculation procedure ceases when the discrepancy between the successive solutions satisfies the convergence criterion. Three different anisotropy models that include linear, sine, and cosine functions will be exploited to address the effect of cross-anisotropy. A parametric study will be conducted to capture the coupled effects of anisotropy degree (β), embedment length (L), and adhesion factor (α). The findings of this paper will be compared with those reported in the literature. The comparative analyses illustrated that the sine and cosine anisotropy functions yielded the least and most H predictions with β lower than 1, respectively. However, for soils with β higher than 1, the linear and the sine functions provided the lowest and the highest H predictions, respectively.
