K. Rajagopal

Bio: K. Rajagopal is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Geosynthetics & Pile. The author has an hindex of 21, co-authored 48 publications receiving 2125 citations. Previous affiliations of K. Rajagopal include Central Building Research Institute & Indian Institute of Science.

Studies on the Behavior of Single and Group of Geosynthetic Encased Stone Columns

Abstract: The stone columns (or granular piles) are increasingly being used as ground reinforcement elements for supporting a wide variety of structures including buildings and flexible structures. The stone columns derive their load capacity from the confinement offered by the surrounding soil. In very soft soils this lateral confinement may not be adequate and the formation of the stone column itself may be doubtful. Wrapping the individual stone columns with suitable geosynthetic is one of the ideal forms of improving the performance of stone columns. This type of encasement by geosynthetic makes the stone columns stiffer and stronger. In addition, encasement prevents the lateral squeezing of stones in to the surrounding clay soil and vice versa, preserves drainage function of the stone column and frictional properties of the aggregates. In spite of many advantages, the behavior and the mechanism of the geosynthetic encased stone columns is not thoroughly understood. This paper investigates the qualitative and quantitative improvement of individual load capacity of stone column by encasement through laboratory model tests conducted on stone columns installed in clay bed prepared in controlled condition in a large scale testing tank. The load tests were performed on single as well as group of stone columns with and without encasement. Tests were performed with different geosynthetics for the encasement of stone column. The results from the load tests indicated a clear improvement in the load capacity of the stone column due to encasement. The increase in the axial load capacity depends very much upon the modulus of the encasement and the diameter of the stone column. The increase in the stress concentration on the stone columns due to encasement was also measured in the tests. The results from the tests were used to develop the design guidelines for the design of geosynthetic encasement for the given load and settlement.

Model tests on geosynthetic-encased stone columns

Abstract: Stone columns (or granular piles) have proven to be ideal ground reinforcement for supporting flexible structures such as embankments and storage tanks. Stone columns installed in very soft soils will have very low lateral confinement: hence they undergo excessive bulging, leading to undue settlement and limited load-carrying capacity. In these situations, the strength and stiffness of the stone column can be enhanced by encasing the individual stone columns with a suitable geosynthetic. The encasement improves load transfer to deeper depths of soil. This paper investigates the qualitative and quantitative improvement of load capacity of individual encased stone columns through laboratory model tests. These tests were performed in a rigid unit cell that represents the stone column and the soil within the contributary area around the stone column. The load tests indicated a clear improvement in the load capacity of the stone column due to encasement. Encasement with geosynthetics having higher modulus resu...

Numerical Investigation of the Effect of Vertical Load on the Lateral Response of Piles

Abstract: The laboratory and field test data on the response of piles under the combined action of vertical and lateral loads is rather limited. The current practice for design of piles is to consider the vertical and lateral loads independent of each other. This paper presents some results from three-dimensional finite-element analyses that show the significant influence of vertical loads on a pile's lateral response. The analyses were performed in both homogeneous clayey soils and homogeneous sandy soils. The results have shown that the influence of vertical loads on the lateral response of piles is to significantly increase the capacity in sandy soils and marginally decrease the capacity in clayey soils. In general, it was found that the effect of vertical loads in sandy soils is significant even for long piles, which are as long as 30 times the pile width, while in the case of clayey soils, the effect is not significant for piles beyond a length of 15 times the width of the pile. The design bending moments in the laterally loaded piles were also found to be dependent on the level of vertical load on the piles.

Closure to “Load Transfer for Axially Loaded Piles in Clay”

Abstract: An analytical method for developing a theoretical load-settlement curve for axially loaded piles in clay is presented. The method is based on the correlation of the ratio of load transfer to soil shear strength as a function of pile movement. The results of studies of field tests of instrumented piles and laboratory tests of small piles in clay are used to obtain the desired correlation. The correlation is presented in the form of a family of curves that are obtained when the ratios of load transfer to soil shear strength versus pile movement are plotted as a function of depth. The validity of the family of correlation curves is checked by comparing computed and actual load-settlement curves for some typical field tests. Results obtained by this method indicate that the method may be used effectively to determine load-carrying capacity for axially loaded piles in clay.

Studies on the Behavior of Single and Group of Geosynthetic Encased Stone Columns

Abstract: The stone columns (or granular piles) are increasingly being used as ground reinforcement elements for supporting a wide variety of structures including buildings and flexible structures. The stone columns derive their load capacity from the confinement offered by the surrounding soil. In very soft soils this lateral confinement may not be adequate and the formation of the stone column itself may be doubtful. Wrapping the individual stone columns with suitable geosynthetic is one of the ideal forms of improving the performance of stone columns. This type of encasement by geosynthetic makes the stone columns stiffer and stronger. In addition, encasement prevents the lateral squeezing of stones in to the surrounding clay soil and vice versa, preserves drainage function of the stone column and frictional properties of the aggregates. In spite of many advantages, the behavior and the mechanism of the geosynthetic encased stone columns is not thoroughly understood. This paper investigates the qualitative and quantitative improvement of individual load capacity of stone column by encasement through laboratory model tests conducted on stone columns installed in clay bed prepared in controlled condition in a large scale testing tank. The load tests were performed on single as well as group of stone columns with and without encasement. Tests were performed with different geosynthetics for the encasement of stone column. The results from the load tests indicated a clear improvement in the load capacity of the stone column due to encasement. The increase in the axial load capacity depends very much upon the modulus of the encasement and the diameter of the stone column. The increase in the stress concentration on the stone columns due to encasement was also measured in the tests. The results from the tests were used to develop the design guidelines for the design of geosynthetic encasement for the given load and settlement.