LIMITS OF APPLICABILITY OF STONE-COLUMN IN GROUND IMPROVEMENT

Proceedings of 13th Asian Regional Conference in Soil Mechanics & Geotechnical Engineering, Kolkata, India, 2007, 2007

An in depth study of the load-settlement behavior of stone column treated ground has been made encompassing all the relevant parameters governing design and performance including material properties of the in-situ soil and backfilled stone column, the external vertical stress level and geometry of column installation under different sets of assumptions and boundary conditions. The predictions based on the proposed method are compared with existing theories and ultimate column capacities reported in literature. The stress concentration on column and settlement reduction of composite ground developed by the proposed model has been presented, and results compared with other approaches available in literature. Finally, back analysis of published full scale load test results on ultimate column capacities available in literature has been done by the proposed model, and significant findings presented.

Stone columns are commonly employed for ground improvement in geotechnical projects. This paper studies the problem of stone column settlement in the context of uncertainty and, in particular, the amount of deferred settlements that will occur after a specified time. An improved theoretical solution to the coupled column compression/consolidation problem that considers the influence of the radial deformation and yielding of the column on the (radial only) consolidation analysis is employed. In addition, reliability methods are used to consider the effects that uncertainty and variability have on computed settlement estimates and, hence, on the probability of failure. Uncertainties and variabilities considered include those related to column "as-built" properties and also those related to soil properties. Reliability is estimated using First Order Reliability Methods, and simulation methods are employed to double-check the validity of the results. Results indicate that uncertainties could have a significant effect on the reliability of stone column designs.

Proceedings of the 4th World Congress on Civil, Structural, and Environmental Engineering, 2019

Stone columns repeatedly used for stabilization of soft soils. For the support of different structures, use of stone columns is increasing day by day. Stone columns are used for the improvement of settlement and bearing capacity of soft soils in reasonable fare and friendly towards the environment. In present paper, a review to analyse the behavior of stone columns used in different types of constructions such as oil storage tanks, embankments, buildings etc. The consequence of without encased and encased stone columns on several types of construction is studied. The effect of various diameters with various depths in ground also reviewed. For the encasement different types of geosynthetics are used for improvement of the results. For the prediction of the settlement of foundations reinforced with stone column number of numerical and physical approaches are done. This paper deals with several theories exist from past to present which helps in understanding the enhancements by stone columns in boosting soft soils. In development of geotechnical properties physical modelling has an important role.

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.

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.

2009

Proceedings of the ICE - Geotechnical Engineering, 2009

nternational Journal of Scientific Research in Engineering and Management (IJSREM), 2021

Stone column ground stabilization involves adding columns filled with stone into the ground to a depth of at least 4m below the ground surface. Compacted gravel layer can then be put over the top of the columns, ready for the construction of new house foundations. This method is quick to construct and can be done at any time of the year. Stone columns are widely used to improve the bearing capacity of soil and reduce the settlement of structures which are built on them. It increases the strength and decreases the compressibility of soft, loose fine graded soils, accelerating consolidation effect and reducing the liquefaction potential of soil. These columns consist of either compacted gravel or crushed stone arranged by a dynamic vibrator. This article shows its installation methods, design and its failure modes.

The electronic journal of geotechnical engineering, 2013

Nowadays, diminish in suitable sites for constructions become a big challenge for engineers and encouraged them to consider improving of the in situ soils. Out of all methods for ground improvement, stone column became more popular these days according to its simple construction and economic consideration. Installation of stone column especially in loose and fine graded soil causes increase in load bearing capacity and settlement reduction. On the other hand installation of stone column in very soft soils faces to some limitations and the soft soil particles may not clog into the stones successfully so further development in stone column installation is reinforcing the columns with geosynthetics or geogrids. This paper introduces the assumptions, procedures and results of the numerical analysis for simulating the behaviour of un-encased versus geogrid encased stone column in soft clay. Settlement and bearing capacity of stone columns and geogrid encased stone columns in terms of various diameters were selected as criteria for judgment and comparison of the behaviour of the Vol. 18 [2013], Bund B 316 ordinary and geogrid encased stone columns. The proposed evaluation is conducted with the aid of finite element software, PLAXIS V.8, and a reasonable agreement obtained between the experimental investigation and the finite element method.

European Journal of Environmental and Civil Engineering, 2020

This paper presents results of experimental tests on soil specimens reinforced by stone columns. The experimental investigations have been conducted by setting up a laboratory scale model. The main objective is to evaluate the effects of various reinforcing materials and stone columns configurations on the axial deformation during a vertical loading test of cylindrical samples of unreinforced and reinforced soil. The findings have been compared to existing experimental results proposed in literature. The specimens of soil consisted in an analogic material of poly-dispersed glass beads with a grain size smaller than 50 µm. Two reinforcing materials have been considered as ballasts: crushed sand and coarser granularity glass beads (0.7-1.0 mm). The results show that the material type and spacing between columns in a triangular or square configuration can greatly affect the reinforcement efficiency. The proposed results are applicable to predict the improvement of granular soils of medium density when subjected to the vibrocompaction technique.