Ramyasri Rachamadugu

Bio: Ramyasri Rachamadugu is an academic researcher from Shiv Nadar University. The author has contributed to research in topics: Stiffness & Structural load. The author has an hindex of 1, co-authored 5 publications receiving 1 citations.

Lateral Response of Hollow Circular Caisson Embedded in Nonlinear Soils

Abstract: This paper presents the numerical analysis of the lateral response of hollow circular caisson embedded in nonlinear soils. The caisson–soil system is modeled by a three-dimensional nonline...

Effect of Soil Spatial Variability on Lateral Response of Well Foundation Embedded in Linear Elastic Soil

Abstract: This paper presents, the effect of soil spatial variability on response of laterally loaded well foundation embedded in linear elastic soil medium. The spatial variation of elastic modulus of soil along embedment depth of the foundation is modeled using random field theory. Elastic modulus of soil is considered to be random variable that follows Log-Normal probability distribution. Monte Carlo simulation technique is used to generate various random realization of spatial variability of elastic modulus of soil. Random realization is done for different values of coefficient of variation of elastic modulus with different spatial correlation distance. A finite element model is developed for laterally loaded well foundation embedded in linear soil. The finite element model is then coupled with the random field of elastic modulus of soil to analyze effect of soil spatial variability on the response of well foundation under different values of lateral load. The results obtained from this study indicate that spatial variation of soil elastic properties has small effect on lateral response of well foundation irrespective of magnitude of lateral load.

Issues in Interpretation of Constant Rate of Strain Consolidation Test Data

Abstract: Constant rate of strain (CRS) consolidation test is a fast test method to characterize consolidation behavior of fine grained soils. In this test method, the test specimen is deformed at a constant rate of deformation, and pore water pressure at the base of the test specimen and axial reaction load are measured at successive interval during the test. This test method has several advantages over traditional incremental loading consolidation test. In the present research, a series of CRS consolidation tests have been performed on reconstituted samples of eight different clayey soils with different plasticity indices. The suitable strain rate at which the test is to be performed has been decided considering the criterion given in the literature. The test data obtained from these tests have been analyzed through the method of interpretation given in ASTM: D4186-06 (Standard Test Method for One-Dimensional Consolidation Properties of Saturated Cohesive Soils Using Controlled-Strain Loading. 2008). The present study shows that the existing method of interpretation yields unreliable results for a significant duration at early stage of the test despite of performing the test at recommended strain rate. Analysis of present experimental data and some of the available recommendations to select suitable strain rate indicates that the theory for CRS consolidation which forms the basis for the existing method of interpretation is unable to describe rapid evolution of pore-water pressure at early stage of the test. Because of this, the existing method of interpretation fails to interpret the consolidation parameters accurately throughout the test.

Significance of Interface Modeling in the Analysis of Laterally Loaded Deep Foundations

Abstract: Interface modeling is one of the important components in the numerical modeling of soil–structure interaction problem. It is equally important as material and geometrical modeling. Inaccurate modeling of the interface between the soil and the structure may lead to unreliable results. However, in many cases, interface modeling is overlooked and the interface between the soil and the structure is generally modeled as a rigid connection. In the present paper, we have shown the influence of interface modeling in the analysis of laterally loaded deep foundations. A finite element model of laterally loaded foundation–soil system is developed wherein the foundation is modeled as a linear elastic system and the soil as nonlinear which is defined by the multi-yield surface plasticity model. The interface between the soil and the foundation is modeled using zero thickness contact element, which is defined, by constitutive relationships capable to define sliding and separation mechanisms at the interface. The results obtained from the proposed finite element model are then compared with the conventional approach of interface modeling. The present study indicates that the conventional approach overestimates the lateral load capacity of deep foundation as well as it is unable to explain the mechanisms of the deformation of laterally loaded foundation–soil system.

Comparative Study of Methods for Analysis of Laterally Loaded Well Foundation

Abstract: Well foundation is commonly used in India for road and railway bridges over rivers. It is a massive structure and hence it is generally considered to be safe under laterally loaded condition. Indian Roads Congress Codes (IRC:45-1972 and IRC:78-1983) suggests limit equilibrium approach to determine lateral load capacity of well foundation. It considers well foundation as a rigid body and surrounding soils as elastic in design state and plastic in limit state. Design procedure stated in Indian standard codes determines ultimate lateral load capacity of Well-Soil system. However, it does not yield the magnitude of lateral displacement of a well foundation at the ultimate load. Because of this, it is difficult to decide whether the lateral displacement at estimated ultimate lateral load capacity of a well foundation is allowable or not. Over the years, few methods to analyze the lateral response (both force and displacement responses) of well foundation are developed. These methods consider surrounding soil as linear elastic material which is modeled by linear elastic springs, and well foundation as a rigid body. Recently developed methods consider lateral stiffness as well as rotational stiffness of the surrounding soil and represent soil by parallel combination of lateral linear springs and rotational springs. Some of these methods also consider flexibility of well foundation and model well foundation by Euler-Bernoulli beam element. In this article, we present a comparative study of the available methods of analysis of laterally loaded well foundation. This study indicates significant differences in the response of Well-Soil system obtained from different methods. Validation of existing methods is done with two-dimensional continuum model to identify accuracy in existing models. It highlights the need for proper evaluation of available methods of analysis with realistic incorporation of foundation stiffness and interface effect in modeling the Well-Soil system for pseudo static loading conditions.

Rectification of the Tilt and Shift of Well Foundation: A Numerical and Analytical Solution

Abstract: Well foundation is a common type of foundation normally used in bridge construction to transfer heavy load from superstructure and moving vehicles. During construction, sinking of well at the site poses a lot of challenges due to several reasons, such as heavy mass of well, properties of soil, location of ground water table and velocity of water in river or canal. During sinking, the well may tilt and shift from its original vertical position and thereby affecting its functionality. In the current investigation, the force required to rectify the shift and tilt of a reinforced concrete well of 40.8 m deep located near the bank of river Gandak in the state of Bihar, India was determined by numerical and analytical method based on finite element simulation and earth pressure theory (conventional method), respectively. The outer and inner diameter of the well was 8.0 m and 4.9 m, respectively. In numerical study, a straight well was built and the force required to shift the well equal to the amount observed at site was determined by trial and error method. In the conventional method, the force required for rectification of the tilt and shift of the well was calculated. For both numerical and analytical study, three different depths of soil layer surrounding the well were considered for the study. By comparing the results of numerical and analytical method, the best possible condition was chosen. The soil condition was further modified, and the required force was calculated by conventional method. Further, kentledge load was applied to investigate its effect on rectification of shift and tilt of well foundation. In conventional method, by removing the top two soil layers and entire depth of soil from the surrounding of well, the inclined force was noted to decease about 79 and 99%, respectively. It was also noted that with 10 MN increase in kentledge load, the inclined force decreased by 0.82 MN. Therefore, the application of inclined force is more effective than the kentledge load for well straightening. Hence, greater effort is required for the restoration of tilt and shift due to the overburden pressure and self-weight of the well after sinking of well to a considerably deeper soil stratum. Therefore, rectifying measures should be taken immediately at the site as soon as tilt and shift is observed.

Study of the Lateral Bearing Capacity and Optimization Reinforcement Scheme of an Open Caisson with Consideration of Soil Disturbance

Abstract: The bearing capacity of an open caisson under lateral loads is a key factor affecting the normal operation of an open caisson. It will inevitably have a disturbing effect on the surrounding soil layers during the sinking process of the caisson; that is, a disturbance ring will develop around the caisson. Based on the Jurong Yangtze River water supply project, the lateral bearing characteristics of the open caisson are analyzed by the numerical method with due consideration to soil disturbance, and the reinforcement scheme is optimized. The numerical results show that when the thickness of the disturbance ring is less than 0.5 m the disturbance ring has little effect on the lateral bearing capacity of the open caisson. An arc-shaped cement–soil reinforcement at the loading area can effectively improve the lateral bearing performance of the caisson. The optimized reinforcement thickness is 2 times that of the disturbance ring, and the reinforcement angle is approximately 60°.