Behaviour of Stone Columns Research Papers (original) (raw)

Soft clayey soils present a geotechnical challenge due to their low shear strength and high compressibility. The finite element package, ABAQUS, is used to perform a comprehensive numerical analysis on stone columns. The study investigates the bearing capacity and vertical and lateral deformations of soft clayey soils due to installing stone columns in them. The numerical model using the unit cell concept investigates the influence of varying two main physical parameters, i.e. the stone column material strength (ϕ), and the native soil cohesion (c). Moreover, this study utilizes variable numerical models to study the effect of the ratio between column length and its diameter, (L/d), on the efficiency of stone columns as a soil-enhancing method for weak clayey soil conditions. The influence of the stone column length on the occurred failure mode was studied. The outcomes demonstrated that using stone columns improves the behaviour of soft clayey soil, where the bearing capacity is enhanced and the soil surface settlement is reduced. Furthermore, using stone column filling materials with higher friction angles enhanced the stability of the system, and the optimum values of native soil cohesion and stone column materials friction angle are 30 kPa and 40°, respectively. Also, the outcomes illustrated that increasing the applied pressure controls the bulging length of SC, where the bulging length was 2.5d, 3d, and 3.5d for the applied pressure of 50.0 kPa, 100.0kPa, and 150.0 kPa, respectively.

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- Soil Reinforcement, Numerical solution using ABAQUS, Stone Column, Soil Improvement
- by Hisham Mohamad
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- Civil Engineering, Geology, Geotechnical Engineering, Bearing Capacity

The foundations at the Huey P. Long Bridge in New Orleans presented special challenges for construction due to the requirements for very deep drilled shafts in the Mississippi River beneath the existing bridge structure. Drilled shafts were constructed to depths of approximately 200ft in alluvial soils using a rotator system with full-length segmental casing, and base grouted to improve axial resistance. This paper describes the design and construction of the work platform to provide access to the restricted-access site beneath the existing bridge, the approach used to construct the drilled shafts, and the results of a load test program to verify the axial resistance.

- by Peter Faust
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This study investigates the effectiveness of encapsulated polypropylene (PP) column in enhancing the undrained shear strength of kaolin (soft clay). The usage of PP in treating problematic soil is a more sustainable and cost-effective alternative compared to other materials. The installation of granular column can be done by using vibro-replacement method. Several geotechnical tests to determine the properties of materials were conducted. The shear strength of treated kaolin sample was examined by using Unconfined Compression Test (UCT). There are seven (7) batches of soil sample in total which included a control sample, three (3) batches of 14 mm and three (3) batches of 20 mm diameter PP column. Different diameters of PP column were examined with 60 mm, 80 mm and 100 mm height, respectively with soil sample of 50 mm in diameter and 100 mm in height. The shear strength improvement of kaolin is 33.82%, 46.51%, and 49.88% when implanted with a PP column with a 7.84 area replacement ratio and 0.6, 0.8 and 1.0 penetration ratio. The soft soil treated using 16.00 area replacement ratio with 0.6, 0.8 and 1.0 penetration ratio has a shear strength increment of 25.22%, 33.39% and 37.59% respectively. In short, the shear strength improvement of the kaolin clay depends on the parameter of the PP column used to reinforce the sample.

- by Dominic Ong
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- Civil Engineering, Geology, Geomechanics
- by Jorge Castro
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- Civil Engineering
- by Ali Zahmatkesh
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- Civil Engineering, Ground Improvement, Soil Heterogeneity, Bearing Capacity
- by Mukul Bora
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- by emma yuliani
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- by CHRISTIANNE DE LYRA NOGUEIRA
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- by Sujit Kumar Dash
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In geotechnical engineering, the analysis of small footing founded on limited number of stone columns is normally treated as 3D problem. However, the 3D analysis requires extensive computational effort and time compared to 2D analysis. Therefore, in this study, a series of numerical analyses are performed to investigate the reliability of the 2D axisymmetric concentric ring model to be used in problems where stone columns are adopted as ground improvement method to support a small foundation. In this approach, a group of stone columns was modeled as a series of concentric rings of the same area replacement ratio as actual columns. The results of the 3D finite element model for stone column reinforced foundation provide the basis for this numerical comparison. End bearing column system was tested first followed by floating column system. The deformation characteristic of the footing under different geometry configuration and area ratio demonstrate the feasibility of the concentric ri...

- by Kok Shien Ng
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The emphasis of current work is on assessing the settlement improvement ratio, which is described as the ratio between the settled soils treated with a stone column and the settlement of the non-treated soil (Sr = Streated/Suntreated). The research was conducted using a 300 mm diameter and 300 mm high stone-column container testing model. On 14 modeled stone columns made only from crush stones and using various backfill content, model tests including static axial compression tests were performed. The substance used in the stone backfill column had been changed by sand or lime or cement percentages. The shear strength prepared by the containers varied between 5.5 kPa and 13.5 kPa. Results show that the settlement ratio values, Sr achieved with crush stone, crushed stone +50% sand, crushed stone +5% dry lime, crushed stones +10% dry lime, crushed stone +2.5% cement +5.0% crushed stone +5.0% cement, respectively, was 0.23, 0.12, 0.16, 0.15 and 0.09. In other words, there is a drop in the settlement from 77% to 91%.

Sabkha soils are widely distributed throughout Saudi Arabia, especially along the coastal areas. Typical problems encountered in foundations and structures built over Sabkha beds. The use of stone columns as a technique of soil improvement is frequently implemented in Sabkha soils. Besides, their use in Sabkha soils has been found to provide moderate increases in load carrying capacity accompanied by significant reduction in settlement. In this paper a case study chosen from the Eastern Saudi Arabia is studied in detail to investigate the performance behavior of ground improved with stone columns. The stone columns were constructed using the wet method. Comparison between Pre-and Post-Cone Penetration Test CPT was conducted in this study to discuss different methods that are used to assess the improvement of the soil layers upon installation of stone columns.

- by IJERT Journal
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- Engineering, Civil Engineering

Stone columns have proved to be the most suited technique for improving the bearing capacity of weak or soft soils. Being cost effective and environmental friendly, stone columns are used worldwide for supporting flexible structures such as embankments, oil storage tanks etc. which can tolerate some settlements. However, when the stone columns in very soft soils are loaded; stone columns undergo excessive settlement due to low lateral confinement provided by the soft soil, leading to the failure of the structure. The excessive settlements may be avoided or at least reduced to a great extent, when the columns are encased with a suitable geosynthetics. In the present study, the effect of reinforcement on bearing capacity of composite soil has been investigated by conducting laboratory plate bearing tests on model floating and end-bearing single stone columns of 30 mm diameter and 300 mm length. The columns were reinforced by providing geosynthetic encasement over varying column length...

- by Kausar Ali
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The stone columns improve the performance of foundations on soft and loose soil due to the ability of composite ground to sustain increased structural loads under reduced settlements. The interaction between the two basic elements: the ambient subsoil and installed column, present a complexity of behaviour, both in terms of applied stresses and resulting strains. Moreover, as the same is provided in-group in a regular array beneath foundations, the performance of an individual column is likely to be influenced by the presence of neighbouring columns. The present paper addresses this very issue. Analysis of reported field hydro-test data of large diameter oil storage tanks in soft ground in reference to some existing theories led to the development of the stone-column ‘group efficiency factor’. In order that such factor is of general use, it was felt necessary to examine the applicability of the factor to different sizes of groups under varied subsoil conditions. With this in view, some model test results reported in literature of single and group of columns have been analysed and in the process an explicit relationship regarding the stone-column ‘group-effect’ could be established.

The stone columns improve the performance of foundations on soft and loose soil due to the ability of composite ground to sustain increased structural loads under reduced settlements. The interaction between the two basic elements: the ambient subsoil and installed column, present a complexity of behaviour, both in terms of applied stresses and resulting strains. Moreover, as the same is provided in-group in a regular array beneath foundations, the performance of an individual column is likely to be influenced by the presence of neighbouring columns. The present paper addresses this very issue. Analysis of reported field hydro-test data of large diameter oil storage tanks in soft ground in reference to some existing theories led to the development of the stone-column 'group efficiency factor'. In order that such factor is of general use, it was felt necessary to examine the applicability of the factor to different sizes of groups under varied subsoil conditions. With this in view, some model test results reported in literature of single and group of columns have been analysed and in the process an explicit relationship regarding the stone-column 'group-effect' could be established.

–In finite element analysis, mesh size is a critical issue. It closely relates to the accuracy, computing time and efforts required for meshing of finite element models, which determines their complexity level. This paper presents study of the effects of mesh size on accuracy of numerical analysis results. Based on these results the guidelines for choosing the appropriate mesh strategy in finite element modelling are provided. The static and buckling analysis is carried out to know the effects of mesh sizes by using Femap and NX-Nastran. The model under study is of a structure made up of steel plate. Index Terms— Finite element analysis, mesh size, static analysis, buckling analysis. I. INTRODUCTION In finite element analysis (FEA), the accuracy of the FEA results and required computing time are determined by the finite element size (mesh density). According to FEA theory, the FE models with fine mesh (small element size) yields highly accurate results but may take longer computing time. On the other hand, those FE models with coarse mesh (large element size) may lead to less accurate results but smaller computing time. Also, small element size will increase the FE model's complexity which is only used when high accuracy is required. Large element size, however, will reduce the FE model's size and is extensively used in simplified models in order to provide a quick and rough estimation of designs. Due to its importance, in generating FEA models, the foremost problem is to choose appropriate elements size so that the created models will yield accurate FEA results while save as much computing time as possible. The objective of this paper is to present guidelines for choosing optimal element size for different types of finite element analyses. In order to achieve that goal, in this study, a series of static, and buckling analyses were performed on a structure model made up of plates to reveal the effects of the element size on the accuracy of the FEA results. The solver NX-Nastran and Femap pre and post-possessor, used for modeling and analyses involved in this work.

- by rocky j
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The inclusion of granular columns in soft clay deposits leads to improvements in bearing capacity and overall stiffness, along with a reduction in consolidation settlement. Many laboratory investigations have focused on aspects of bearing capacity, but published data on settlement performance are limited. This paper reports on some interesting findings obtained from a laboratory model study with respect to these issues. In this investigation, 300 mm diameter by 400 mm long samples of soft kaolin clay were reinforced with single or multiple granular columns of various lengths using the displacement and replacement installation methods. The experimental findings revealed that, for the same area replacement ratio, limited settlement reduction was achieved for single long floating columns and end-bearing column groups. Marginal improvements in settlement performance were also achieved for columns installed by the displacement method. No settlement reduction was achieved for short single floating columns, whereas short floating granular column groups produced increased settlements. These observations were verified using contact pressure measurements between the footing and column/surrounding clay.

- by Bouassida Mounir
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- Geotechnical Enginnering

GEOTILL Engineering (www.geotill.com) is Geotechnical Services Provider of comprehensive, and cost effective Civil and Geotechnical Engineering services for clients located throughout the Midwest in Indiana, Illinois, Michigan, Ohio, Kentucky and Missouri. Provides Geotechnical Engineering - onshore, nearshore and offshore foundations; excavations, slopes, retaining structures, tunnels, ground improvement. Numerical Analysis in 2D and 3D for the optimized design and assessment of ground displacements and soil-structure interaction.
Tunnel Engineering – investigation, planning, design, documentation and construction supervision of tunnels for roads, rail, power supply, water supply and sewerage systems.

- by Janko Logar
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- Civil Engineering, Linear Elasticity, Design method, Parametric Study
- by Bryan A . McCabe
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- Civil Engineering

This study investigated the behaviour of single rammed stone columns. Prior to this assessment, the load – settlement and bulging responses of the columns were evaluated by conducting laboratory tests using a specially designed bench scale tank. The latter was a mild steel cylindrical tank which represented unit cells reinforced with single stone columns. The testing technique enabled the evaluation of the influence of variation of column diameter on stone column deformation responses and also provided data that was compared with the numerical results. In the numerical analysis, Mohr-Coulomb and modified Drucker-Prager models were used in the idealization of the behaviour of the column and soil materials respectively. Results revealed that the bigger the column diameter, the higher the loading capacity of the columns. Increasing the column diameter,D by 1.5, 2 and 3 times its initial size generally led to improved load carrying capacity by approximately 2, 4 and 10 times the initial strength respectively. The radial expansion of the columns was prominent in their upper parts with the highest value being experienced at a depth of about 0.5D from the ground surface.

- by Thi Dung Do
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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.

- by ABHIJIT SAHA, Ph.D., P.E.
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The study presents a mechanistic model backed by a detailed analysis of dilating granular column in soil-stone column interaction in ground improvement technology. For an optimal design of stone column, an optimum stress concentration on the column is required and the column material used being generally dense gravel with/ or without sand, the vertical stress on the stone column is often close to its peak strength and the granular material dilates. The effect of this dilatancy is investigated by incorporating a dilatancy factor in the proposed model. The results reflect the beneficial effect of dilatancy within the optimal range or economically feasible domain of area ratio. The settlement predictions are compared with Van Impe & Madhav’s (1992) model of dilating stone-column along-with measured settlement reduction of stone-column reinforced ground at different subsoil conditions reported in literature. The significance of inclusion of such refinement in the ‘unit-cell’ model to explain the reported settlement reduction of treated ground is highlighted.

- by ABHIJIT SAHA, Ph.D., P.E.
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Despite the widespread use of stone columns, present design methods are largely based on empirical data and / or simplified concepts of the action of columns. Nevertheless, this method has emerged as a powerful and effective means of ground improvement technique. The field application of the technology has developed much faster than the design methodology because the mechanism of interaction of load sharing between the two basic elements- the installed column and the native soil is complex, both in terms of induced stresses and resulting strains. As such, the soil-stone column interaction in field situations calls for a rational understanding, since the output behavior is influenced by the interdependence of the external stress level, the material properties of host soil and backfilled column, the column dimensions, construction procedure and its installation array. The present investigation analyzes some full-scale load test results in available literature (Prakash et al, 2005) on rammed stone columns installed in a wide range of alluvials ranging from loose to medium dense sands / silty sands and clayey silt / silty clays with and without fill over them. The back analysis is in the light of theoretical concepts and mechanistic models developed by the author (Saha, 2007). The extensive load tests and penetration tests prior to and after construction of columns and the extent of improvement achieved have been critically examined in the light of theoretical concepts encompassing the relevant design parameters, and some interesting findings are reported.

- by ABHIJIT SAHA, Ph.D., P.E.
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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