ANALYSIS OF DILATING GRANULAR COLUMN IN SOIL-STONE COLUMN INTERACTION (original) (raw)

Experimental Study on Load-Settlement Behaviour of Granular Stone Column in Expansive Soil

Lecture Notes in Civil Engineering, 2021

In today’s construction industry as land reclamation is increasing rapidly so ground improvement has become necessity. Ground improvement is carried out by increasing vibration, structural fill or reinforcement, vegetation, admixtures, etc. out of all the methods, the stone column technique is a very effective method of improving the strength parameters of soil like bearing capacity and reducing settlement, particularly, for the construction of flexible structures, such as road embankments, oil storage tanks on soft soils. It offers a very economical and sustainable alternative to piling and deep foundation. The model test was performed on untreated soil and treated soil with 40 mm, 60 mm, 80 mm diameter stone column. The investigation focused on the influence of diameter of granular stone column. The tests were conducted on granular stone column having l/d ratio equal to 10. From the studies, the performance of smaller diameter stone column is superior to that of bigger diameter st...

ANALYTICAL METHOD OF STONE COLUMNS COMPARED WITH AN ANALYSIS AS PER ROWE DILATANCY THEORY

Two analytical closed-form elastic-rigid-plastic solution methods to predict the rigid foundation behaviour on stone-column reinforced soil are compared, both of which takes into account the stone material yield within the host soil according to stress-dilatancy theory. These are the mechanistic methods developed by the author (2004, 2005) [that presently incorporates the dilatancy angle as per Schanz and Vermeer (1996)] and that developed by Pulko and Majes (2006), that takes into account the column yield as per Rowe dilatancy theory. Since optimal design of stone column necessitates optimum stress concentration on column, which is generally composed of dense gravel with/or without sand, the vertical stress on granular column is often close to its peak strength and the material dilates. To arrive at closed-form analytic solution to this complex soil-stone column interaction problem, some common assumptions like axi-symmetric soil-stone column 'unit-cell', elastic host soil and rigid-plastic Mohr-Coulomb stone column material are combined with equilibrium and kinematic conditions. The results reflect the beneficial effect of dilatancy within the optimal range or techno-economic domain of area-ratio. The settlement predictions are compared with other analytical methods available in literature as well as with measured settlement reduction of stone-column reinforced ground at different subsoil conditions around the globe reported in literature.

LIMITS OF APPLICABILITY OF STONE-COLUMN IN GROUND IMPROVEMENT

Proceedings of Indian Geotechnical Conference, IGC-2010, (Vol.-II), GeoTrendz, Mumbai, India, 2010

Ground improvement by installation of stone columns has emerged as a powerful and effective means of ground improvement technique. The field application of the technology has developed faster than the design methodology because the mechanism of interaction between the two basic elements- the installed column and the native soil is complex, both in terms of induced stresses and resulting strains. The output behaviour of the ‘unit-cell’ comprising of the column and soil is influenced by the interdependence of the external stress level, the material properties of host soil and backfilled column and its dimensions, the construction procedure and its installation array. An effort has been made in the present paper to predict the upper and lower bounds in application of this technology for optimal cost effectiveness in terms of the area ratio of unit-cell and height-diameter ratio of column for a given set of material properties. For validation of the model, the results are compared with some field tests reported in literature, and the salient interesting findings are discussed

The Use of Stone Columns to Reduce the Settlement of Swelling Soil Using Numerical Modeling

Journal of Civil Engineering and Materials Application, 2017

The existing soils in the nature that is used for construction cannot necessarily bear the loadings on the structure. For example, in granular soils, the natural soil may be very loose and show a lot of elastic settlement. Sometimes, there are soft layers, saturated clay and swelling soils at the lower depths, which may cause significant settlement in the structure in terms of foundation load and clay layer thickness. To avoid such settlements, it is necessary to use certain techniques to improve the soil condition. One of the methods that have recently been widely used to reduce the settlement of soft soils and swelling soils is stone columns or single piles. In this research, first of all, the parameters in need for the analysis will be gained by using the experimental data, and then, the static and dynamic behavior of the confined stone columns is examined with geotextile and without geotextile by a group and single manner as in two-dimensional form using Plaxis numerical method of the finite element and the impact of the following parameters will be investigated in both static and dynamic modes: Column length, column diameter, single and group behavior of columns, and soil cohesion effect on the behavior of the confined stone column in geotextile and reduction of soil settlement during use of stone columns. The results of this research indicate correct understanding of the use of geotextile (Woven Geotextile with a specific elastic normal strength) to prevent the camber and the settlement of the column and increase of the strength and bearing capacity of the column.

Ground Improvement with Stone Columns - Methods of Calculating Settlement Improvement Factor

Ground Improvement with Stone Columns - Methods of Calculating Settlement Improvement Factor, 2014

Stone Column is a technique used in civil engineering to improve and stabilize soils considered weak as soft clays or silts and loose sands, enabling the construction of highway facilities, storage tanks, embankments, bridge abutments and so on. This technique uses columns filled with a well compacted coarse grained material, which are allocated all over in the in situ soil. Because material of the columns is stiffer, more permeable and has a higher shear strength then the natural soil, we end up with an improvement of the soil properties: increase of the bearing capacity due to shear strength increase; reduce of total and differential settlements due to stiffness improvement; decrease time for the settlements to occur and reduce of liquefaction potential of cohesive soils due to increase of the soil mass permeability acting as a vertical drain. In this research we are interested mainly in the potential of Stone Columns to reduce settlement. When it comes to constructions which the main problem is reducing the settlement, this technique is a very common solution applied by Ground Engineering Companies for being considered as a low cost alternative, effective and ease of installation. Once this technique is pretty much common among industry, there are many studies to improve the design method in order to make the calculation process simpler and to get more accurate results helping engineers to predict the behaviour of the soil due to the insertion of stone columns realistically and driving to reliable conclusions about the degree of improvement achieved. The design process for Stone Columns allows to estimate the reduction in the settlement in terms of a Settlement Improvement Factor (η) which can be obtained by dividing the settlement of the soil without columns by the settlement of the soil with columns. The inverse of this value is the Settlement Reduction Factor (β). There are four published methods to obtain these factors: 1) Simple Elastic Method, described by Castro & Sagaseta (2008), although originally developed much earlier; 2) Elastic Method, published by Ballam & Booker (1981); 3) The Priebe’s Method, published originally in german by Priebe (1976) and described by Priebe (1995); 4) The Elasto-Plastic Method, published by Pulko & Majes (2005) with some slight changes published by Pulko, Majes & Logar (2011). In all four methods the calculations are based on the area ratio (plan area of stone columns divided by the total plan area), the in situ soil properties and the properties of the fill in material used in the columns. So we can expect that the results are implicitly influenced by the origin of the parameters values used for the soil and by the use of the correct equipment and procedures on the installation of columns as specified in the designing to guarantee that the columns properties correspond to the values used, meaning that the reliability of data used for the soil and column as input parameters will imply the reliability we can get in the results obtained for the Settlement Improvement Factor. Another aspect that has great influence over the accuracy of results is the constraints and assumptions made for the calculations, and once we have four different methods, each one with different assumptions and constraints, we have then four different results for the Settlement Improvement Factor, even when considering the same values for the input parameters. One of the aims of this research is to compare those results and try to identify conditions that may converge the results of two different methods in order to try to point out one of them as a general method to be used with a good level of reliability and that is also in favour of safety. Meanwhile, we expect to show in which cases some of the methods have similar results and which ones have totally different results in order to make clear for the users the implications of each method’s results in the designing in terms of safety and costs. We also intend to investigate and understand, for the four existing methods individually, how each one of the input parameters considered in the equations for the Settlement Improvement Factor calculation affect the output results. As mentioned before, Stone Column is a common technique used and one of the goals of designers is to simplify the calculations, that’s why one of the aims of this particularly paper is to search for a way to simplify the representation of the equations used for the Settlement Improvement Factor calculation, in order to facilitate their understanding and application in practice, using dimensionless input parameters and pointing out which of these parameters must be calibrated with a high precision for having a great influence on the final results. Doing so we expect to help improving the designing process by pointing out which of these parameters are worthwhile spending time and money for investigations and laboratory tests and for which ones can be set a standard value without losing reliability and significant precision on final results. By the end of this paper we’ll analyse a case of an embankment construction over a soil improved with Stone Columns using fictional data for the input parameters in order to be able to compare the methods and how the results would impact the design process. We’ll also analyse a case with real field data to try to illustrate and understand how each method influences the final results and which one wold get closer to the value obtained in practice for η.

MODELLING THE FIELD RESPONSE STONE-COLUMN REINFORCED SOIL

Proceedings of Indian Geotechnical Conference, IGC-2005, Ahmedabad, INDIA, 2005

Reinforcement of ground by granular “pinning” are becoming increasingly popular and has been identified as an effective means of ground improvement technique. The composite mass has been found to carry higher loads at reduced settlements than virgin ground. The strain propagation along the cylindrical unit of soil encapsulating a stone column at the center being envisaged to be non-linear, full scale instrumented columns were load tested at two sites for multistoried buildings founded on stone column reinforced ground in Kolkata. The installation procedure followed rammed stone column technique. Four numbers of strain recorders were embedded within the test column along its axis at suitable depths to measure the shortening of the column under increasing stress levels. The load displacement data along-with the segmental strains, diametrical strain (2dh/d), column bulge (dh), proportion of axial-strain (dvz/dv), axial strain (dv/dz) are all plotted against normalized depths (z/H) for increasing stress levels. The stress-strain response believed to be site-specific and problem-geometry oriented, some interesting features of the response could be identified.

Investigation on Behavior of Stone Columns in Soils under Predominant Settlement

International Journal for Research in Applied Science & Engineering Technology (IJRASET), 2023

Recent advances have made stone columns more efficient and effective for addressing soil instability and improving the load-bearing capacity of weak soils. The present study aims to show that the behavior of stone columns can support most of the load transferred to the soil. The use of innovative materials, such as recycled glass, plastic, or tire shreds, as a replacement for traditional stone fill, has been investigated in recent years and has shown promising results in cost and sustainability. The development of advanced numerical modeling techniques, such as finite element analysis, has enabled engineers to understand the behavior of stone columns better and optimize their design for specific soil conditions. The load-displacement characteristics are considered governing parameters for understanding the capacity of stone columns. The study reveals that, stone column method significantly increases strength with the use of concrete waste lo demolished waste rather than stone aggregate, which can overcome this soil behavior. Additionally, stone columns are helpful for soil stabilization in areas with high water tables when other stabilization techniques are ineffective.