Ground improvement is the modification of foundation soils or project earth structures to provide better performance under operational loading conditions. Ground improvement methods are used increasingly for new projects to allow utilization of sites with poor subsurface conditions and to allow design and construction of needed projects despite poor subsurface conditions which formerly would have rendered the project economically unjustifiable or technically not feasible. In this article we are going to do detail description Ground Improvement Using Encased Vertical Stone Column.
India has large coastline exceeding 6000kms. In view of the developments on coastal areas in the recent past, large number of ports and industries are being built. In addition, the availability of land for the development of commercial, housing, industrial and transportation, infrastructure etc. are scarce particularly in urban areas.
This necessitated the use of land, which has weak strata, wherein the Geo-technical engineers are challenged by presence of different problematic soils with varied engineering characteristics. Many of these areas are covered with thick soft marine clay deposit, with very low shear strength and high compressibility. Structures constructed on soft soil experience several problems like excessive settlements, large lateral flow of soft soil beneath the structures and loss of global or local stability.
The popular remedial measure to overcome these problems is to improve the soil with the insertion of stone columns (also called granular piles) in regular grid. Soil reinforcing for bearing capacity augmentation, soil shear strength improvement, foundation settlement decrease, safety factor increase against fill slopes and earth dams stability, reduction of shrinkage and swelling properties of soil and so on. The results of such studies are useful in reinforced soil for dams, foundations, buildings, retaining walls, bridge piers and water reservoir.
Out of several techniques available for improving the weak strata, stone columns have been used to a large extend for several applications. In the conventional stone Column, the Bearing Capacity of the treated ground is mainly derived from the passive resistance offered by the surrounding soil due to lateral bulging of Stone Column material under axial load.
In the present work modifications to existing stone column technique proposed are carried out to evaluate the behavior of stone column as Vertical reinforcement to improve bearing capacity of soft clays. In addition to this the Encasement of Geo-synthetic is suggested for enhancing the load carrying capacity of the Stone Column in treated ground. The stone columns are nothing but vertical columnar elements formed below the ground level with compacted and uncemented stone fragments or gravels or sand.
Stone columns are considered one of the most versatile and cost-effective ground improvement techniques. Stone columns have been used extensively in weak deposits to increase the load carrying capacity, reduce settlement of structural foundations and accelerate consolidation settlements due to reduction in flow path lengths. Another major advantage with this technique is the simplicity of its construction method. Geo-textile is used for encasement of stone column to provide horizontal stiffness to column.
Geosynthetics have been increasingly used in geotechnical and environmental engineering for the past 4 decades. There are a significant number of geosynthetic types and geosynthetic applications in geotechnical and environmental engineering. Geosynthetics have become well established construction materials for geotechnical applications in most parts of the world. Geosynthetics is a generic term which includes geotextiles, geomembranes, geogrids, geonets, and geocomposites and all other similar materials used by civil engineers to improve or modify soil or rock behavior.
Geosynthetics have found an important place in engineering and construction Projects. They have become an integral part of the solution to many civil engineers’ problem. The re-use of waste materials is an essential step in creating a sustainable future, and research into the reuse of different byproducts has often led to new materials that provide superior service or greater economy than those traditionally used.
Waste material has been defined as any type of material by product of human and industrial activity that has no lasting value. The growing quantities and types of waste materials, shortage of landfill spaces, and lack of natural earth materials highlight the urgency of finding innovative ways of recycling and reusing waste material additionally; recycling and subsequent reuse of waste materials can reduce the demand for natural resources, which can ultimately lead to a more sustainable environment. Crushed concrete debris is used as a waste material in absence of natural aggregate.
Abstract of Ground Improvement Using Encased Vertical Stone Column:
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 geo-synthetic is one of the ideal forms of improving the performance of stone columns.
This type of encasement by Geo-synthetic 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 Geo-synthetic 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 Geo-synthetics 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 Geo-synthetic encasement for the given load and settlement.
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