Sunita Kumari

Numerical Analysis of Earth Embankment Resting on Liquefiable Soil and Remedial Measures

AbstractLiquefaction-induced ground displacements resulting from earthquake shaking are a major cause of damage to earth structures comprised of, or underlain by, loose saturated granular soils. The present paper describes the results of numerical modeling of an embankment founded on loose liquefiable deposit using PLAXIS three-dimensional finite-element software. Acceleration base-input excitation of the El Centro earthquake has been applied to the model monitoring the displacements, liquefaction potential, and excess pore pressures (EPPs). A modified nonassociative plastic-potential function depending on the Drucker–Prager criterion is used to maintain the coaxiality of stress strain in the deviator plane for a stress path initiated from an isotropic line. The soil-densification rule is also added to predict more realistic EPPs in seismic loading. The countermeasures considered are densification of the sand layer by compaction and sheet pile enclosure. The dynamic behavior of the used embankment-foundat...

Simulation of liquefaction phenomenon in semi-infinite domain under harmonic loading

Abstract A fully coupled dynamic computer code in FORTRAN-90 is developed to predict the liquefaction potential of a semi-infinite saturated sandy layer. The saturated soil system is modeled as a two-phase material based on the Biot’s theory for porous media with u–P formulation to determine the responses of pore fluid and soil skeleton. The variational principle is applied to the field equations of fluid flow in a fully saturated porous elastic continuum, and the finite element method is used to numerically solve the resulting continuity equation and equilibrium equation. The mathematical advantage of the coupled finite element analysis is that the excess pore pressure (EPP) and displacement can be evaluated simultaneously without using any empirical relationship. Generalized Newmark-beta method is employed for integration in time. The soil behavior is modeled by Pastor–Zienkiewicz Mark III to describe the inelastic behavior of soils under isotropic cyclic loadings. The effect of the material non-linearity of the soil grain on liquefaction response is investigated by conducting parametric study. The accumulation of pore water pressure and the reduction of mean effective stress are simulated well. It has been observed that soil properties like permeability and shear modulus have significant effect on liquefaction analysis.

Reliability Analysis of Infinite Slope Using Metamodels

Reliability analysis is an important work to determine the stability of an infinite slope. In this study, four metamodels (Adaptive Neuro Fuzzy Inference System, Gaussian Process Regression, Multivariate Adaptive Regression Spline and Generalized Regression Neural Network) based on First Order Second Moment Method (FOSM) has been used to determination of reliability index (β) of an infinite slope. An example has been taken to show the working procedure of the adopted techniques. The results shows the developed models overcome the limitations of the FOSM. A comparative study has been done between the developed models.

Deterministic and Probabilistic Analysis of Liquefaction for Different Regions in Bihar

The built environment and human life have been regularly affected by earthquakes. One of the most catastrophic earthquake hazards is liquefaction causing failure of embankment, earth structures, foundations, natural slopes and superstructures. In this paper, three methods have been used to predict the liquefaction susceptibility of some of high seismically active regions of Bihar such as Darbhanga, Samastipur, West-Champaran and Araria Sangram. The first method is based on semi-empirical approach, given by Idriss and Boulanger (in: Proceedings of 11th International conference on soil dynamics and earthquake engineering and 3rd International conference on earthquake geotechnical engineering vol 1, pp 32–56, 2006). The stress reduction factor (rd), overburden correction factor for cyclic stress ratios Kσ, earthquake magnitude scaling factor for cyclic stress ratios (MSF) and recently modified relations has been considered in this approach. The result is obtained in form of factor of safety at particular depth beneath the ground surface. The second approach is based on Muduli’s probabilistic method (2013) and third is on relevance vector machine (RVM) method developed by Karthikeyan et al. (Eur J Environ Civ Eng 17(4):248–262, 2013). RVM model has been used to determine the liquefaction potential of soil based on standard penetration test (SPT) blow count. The SPT data has been used as input parameter for the analysis. Site coming under high seismic zone is more susceptible to liquefaction during earthquake. This concludes that earthquake magnitude plays very important role for the assessment of liquefaction, irrespective of soil type and water table of the site. This paper contains the deterministic and probabilistic analysis of liquefaction behavior of soil.

Reliability Analysis of Slope Safety Factor by Using GPR and GP

Reliability analysis of slope is an important aspect of geotechnical engineering practice. However, it is very difficult to assess the estimation of reliability analysis of slope because it include the uncertainty parameters i.e. soil parameters cohesion of soil (c), angle of shearing resistance (φ) and unit weight of soil (γ). In former days, to execute the reliability analysis of slope, several analytical methods were used but at the present days various computer technique (model) are available and among which Gaussian Process Regression (GPR) and Genetic Programming (GP) are part of them. This paper’s primary objective is to survey the fitness of GPR and GP with the help of First Oder Second Moment Method (FOSM) to find out the Reliability analysis of slope. The GP is the non-parametric kernel probabilistic method. It is adequately assigned by its mean function m(x) and covariance function k(x, x′). GP is a standard technique for acquiring computer automatically to resolve a problem from an eminent-level argument of what need to be performed. This study shows that the proposed GPR based FOSM is suitable alternative for reliability analysis of slope.

Numerical Evaluation of Cyclic Response of Shallow Foundation Resting on Liquefiable Soil

As the earthquake events are unpredictable, the accurate estimation of settlement and excess pore pressure is challenging for the soil foundation system against earthquake loading. Therefore, it is essential to study the effect of an earthquake before the construction of any structure on a particular site. In the present paper, response of a shallow foundation resting on liquefiable soil is numerically modeled to evaluate its response under cyclic loading. Two different conditions have been numerically simulated and the effect of spacing in between two foundations has been studied along with light and heavy foundation. The porous media theory based on coupled approach has been considered for analyzing the system. A computer code for finite element analysis has been developed in FORTRAN 90. The inelastic behavior which includes dilitancy and hardening behavior of the soil is modeled using Pastor–Zienkiewicz Mark III model. The settlement and effective pore pressure obtained are validated with centrifuge test results. It is observed that settlements during the cyclic loading time remained almost the same, regardless of the foundations spacing. The post-shaking settlements, however, were different for different spacing. Foundations settled often less when located close to each other.

Analysis of Rigid Pavement Built with Multi-layer Concrete Slabs Resting on Pasternak Foundation

Rigid pavement construction is emerging due to its long term performance and less maintenance cost. Its rigidity and high modulus of elasticity tend to distribute load over a wide area of foundation, resulting in very low deflections under traffic and environmental loading. Thus a major portion of the structure capacity is imparted by slab itself. Multi-layer slab is the composition of several superposed concrete layers of different quality. An idea is that lower quality material can be sandwiched in the neutral axis zone. This paper deals a structural analysis of the three layered structure resting on the Pasternak foundation subjected to traffic loading. The three layered structure is replaced by an equivalent single layered structure. An assumption was taken that the deflection at the surface of the upper layer may be considered to be equal with the deflection at the bottom of the lower layer. The mechanical characteristics of the equivalent structure depend on the mechanical characteristics of the different layers and the various adhesion conditions at the interfaces. Adhesion condition are full slip at each of the interface, full friction at the first interface as well second interface, full friction at both interfaces and partial friction at all interfaces. Analytical solutions are arrived and structural responses are investigated. It has been found that the structural responses for full friction case showed significant results. This study is made towards enhancing current design method and economic construction.

Dynamic Response of Railway track using two parameter model

In the present analysis, an infinite Euler–Bernoulli beam of constant cross-section resting on an elastic foundation is considered. The beam and foundation are assumed to be homogeneous and isotropic. The foundation is modeled using two parameters with damping. The beam is subjected to a constant point load moving with a constant speed along the beam. An effort has been made to find the solution of the governing differential equation analytically. It gives beam deflection under moving load in closed form for damped case. At subcritical speed the absolute value of the deflection of the beam increases with increase of the load velocity. Peak maximum deflection appears when the load travels at the critical speed.