Single Stone Column Research Articles

The Kushite temple in Soniyat after the 2016 season

Archaeological fieldwork in the Kushite temple in Soniyat (Tergis 40) was conducted from 1997 to 2001 with an additional short season in 2013. A team supervised by Bogdan Żurawski returned to the site in 2016 to continue the excavation of the southern section of the complex. Remains of substantial mud-brick architecture were discovered together with large quantities of small finds (potsherds and objects made of metal, stone and faience) and faunal remains. A compact layer of Nile alluvial deposits, about 0.10 m thick, covering the remains represented evidence most probably of a flood. A single stone column was visible at that level. The spatial distribution of the discovered architectural features matches the temple orientation; they can be interpreted as the remains of a pylon with an entrance flanked by columns

Investigation of the Effect of Dimensional Characteristics of Stone Column on Load-Bearing Capacity and Consolidation Time

One of the best methods for rehabilitating loos and soft soils is the application of stone columns. This method enhances the soil properties by increasing its load-bearing capacity, decreasing the soil subsidence, and accelerating the consolidation rate. In the present paper, numerical analysis of a stone column of 10 m in length into a clayey soil using ABAQUS software is presented. The stone column was modelled based on the concept of unit cell, i.e. a single stone column with the surrounding soil. In this respect, material of the stone column was modelled using the elastoplastic behavioural model of Mohr-Coulomb, while Cam Clay behavioural model was used for the surrounding clayey soil. Furthermore, throughout the analyses performed in this study, effects of different parameters (e.g. applied load on rigid foundation, and the stone column length and diameter) on the subsidence and consolidation time of the rigid foundation were examined. The results indicated that, construction of a stone column into clayey soil decreases the subsidence and consolidation time of the soil considerably. In additions, increases in length and diameter of the stone column were found to significantly contribute to reduced subsidence and consolidation time of soil.

Effect of Vibro Stone-Column Installation on the Performance of Reinforced Soil

AbstractEmpirical design methods for stone-column foundations are often on single stone columns or as a homogeneous medium of soil and column. These methods underestimate the capacity of the compos...

Numerical study on bearing capacity of single stone column

Stone columns are an efficient ground improvement technique for treating problematic soils. The confidence in the prediction accuracy of bearing capacity remains unsatisfactory. This paper aims to investigate the bearing capacity of single stone column using three-dimensional numerical analysis. Failure modes were observed and the effect of key parameters such as column’s friction angle, undrained shear strength of surrounding soil and modular ratio were investigated. Numerical results showed bulging and a combination of bulging and punching are two dominant failure modes for the single stone column. Ultimate bearing capacity is mainly influenced by the column’s friction angle and the undrained shear strength of the surrounding soil. Based on the results, a new prediction method is developed and compared reasonably well with the existing analytical solution and the field measurements.

Experimental simulation and mathematical modelling of clogging in stone column

In this paper, time-dependent clogging is studied considering a unit cell consisting of a single stone column interacting with the surrounding soft clay. Clogging is assessed quantitatively and the corresponding void space of the column is determined using computed tomography. It is observed that the extent of clogging is substantial in the upper part of the column, but diminishes rapidly with depth. The soil properties in the clogged zone are determined indirectly through additional tests of clay–aggregates mixtures with various clay fractions. An equal strain consolidation model based on the principle of unit cell analysis is developed to capture both the initial and time-dependent clogging. The model accounts for a reduction in permeability and an increase in compressibility of the column. This current model, as expected, offers identical results to some previous studies if clogging is ignored, while the comparison with other selected models demonstrates the influence that clogging of the stone column can have on the consolidation of the surrounding soil. Furthermore, load–settlement predictions from the proposed “equal strain” model are also compared with the consolidation response of a previously developed “free strain” model.

Three-Dimensional Discrete-Element Method Analysis of Stresses and Deformations of a Single Geogrid-Encased Stone Column

Three-Dimensional Discrete-Element Method Analysis of Stresses and Deformations of a Single Geogrid-Encased Stone Column

Three-dimensional DEM analysis of single geogrid-encased stone columns under unconfined compression: a parametric study

Three-dimensional discrete element method (DEM) was employed in this study to analyze the behavior of single geogrid-encased stone columns under unconfined compression. Four important parameters were investigated to understand and evaluate their effects on the behavior of the encased columns by seven DEM models. The biaxial geogrid used as an encasement material for stone columns was simulated using parallel-bonded particles, and the aggregate in the stone column was simulated using graded particles. Both the macroscopic responses (e.g., vertical pressure–strain curves) and the microscopic interactions (e.g., contact force, coordination number, and sliding fraction) of the columns under unconfined compression were analyzed and are presented in this paper. The numerical results show that the geogrid encasement with high tensile stiffness could provide high confining stresses and then effectively increased the bearing capacity of the column. The short column yielded quickly even though its column modulus at a small deformation was relatively high. The modulus of the column slightly decreased with an increase in the column diameter due to high circumferential strains mobilized in the geogrid encasement. The column with large aggregate was stiffer and deformed less than the column with small aggregate. Selecting aggregate with a size larger than the geogrid aperture size was an effective way to achieve better interlocking between the aggregate and the geogrid and to minimize mass loss for the geogrid-encased stone column under loading. Due to limited deformation allowed by the geogrid encasement, a coefficient of radial stress equal to half of the coefficient of passive earth pressure was suggested to estimate the ultimate bearing capacity of the geosynthetic-encased stone column.

General Analytical Model for Consolidation of Stone Column–Reinforced Ground and Combined Composite Ground

AbstractFirst, this paper develops a new analytical model for the consolidation of stone column–reinforced ground by introducing multiple stone columns into the unit cell for analysis. Governing equations and analytical solutions are obtained for a time-varying surcharge loading, which includes four special loading schemes. The analytical model is then discussed and compared with a conventional analytical model with a single stone column in the unit cell. The results show that the conventional analytical model is a special case of the present model because they predict almost the same average degree of consolidation. This verifies the correctness of the proposed analytical model. Compared with the conventional analytical model, an apparent advantage of this analytical model is that multiple stone columns are introduced into the new unit cell, which makes it possible to extend it to solve the consolidation of a combined composite ground stabilized by impervious piles along with vertical drains with some mo...

Uncertainty analysis of safety factor of embankment built on stone column improved soft soil using fuzzy logic α-cut technique

Uncertainty in safety factor (FS) of slope stability is a main subject in geotechnical engineering. Uncertainties are associated with shear strength parameters of the soil, their complex nature, numerical analysis methods, etc. The main aim of this research was to improve the model used by other researchers for determination of FS of embankments built on stone column improved soft soils, and compare the results with what was found in literature using α-cut fuzzy technique (FAC). The results showed that the highest and lowest uncertainty occurred at equivalent area with existence of underground water, and for single stone column with no underground water respectively. A reduction factor proposed to amend the FS calculated using the equivalent area method. In the equivalent area model, the equivalent parameters were used. This contribution might have real and more precise behavior in comparison with what was suggested by other researchers in literature. In addition, with applying of membership functions, the height of embankment had the most effect on the values of FS obtained using finite element (FE) and finite difference (FD) methods.

Coupled discrete element–finite difference method for analysing the load-deformation behaviour of a single stone column in soft soil

Experimental studies and numerical modelling of the deformation of soft clay stabilised by stone columns have been conducted over the past few decades. Continuum-based numerical models have provided valuable insight into the prediction of settlement, lateral deformation, and stress and strain-rate dependent behaviour of stone columns at a macroscopic scale, but because they consist of granular material such as crushed rock, gravel, and waste rock aggregates, their behaviour is influenced by inter-particle micromechanics and cannot be modelled properly using these models. In this paper a novel coupled model of the discrete element method (DEM) and finite difference method (FDM) is presented to study the deformation of a single stone column installed in soft ground. In this coupled discrete–continuum method, PFC2D and FLAC were used to model the interaction between the stone column and surrounding clay, respectively. The contact forces at the interface between the two zones were determined through a socket connection that allows the DEM to transfer forces and moments to the FDM and vice versa. The predicted results were comparable to the data measured experimentally, showing that the coupled discrete–continuum model proposed in this study could simulate the load-deformation behaviour of a stone column installed in clay. The contact force distribution and shear stress contour developed in the stone column and surrounding clay were captured to provide a better understanding of the load-deformation behaviour of the stone column.

Factors Affecting the Settlement Estimation of Stone Column Reinforced Soils

The ground improvement technique of stone columns has been effectively used over the last decades in order to accelerate the consolidation rate of soft soils by providing a drainage path, reduce foundation settlements, improve the bearing capacity of the soil, and limit the risk of liquefaction due to seismic activity. Because of the time consumption of a three dimensional (3D) calculation, most stone column projects are presently studied by axisymmetric finite element computations. Otherwise, it is the analytical method of Priebe that is commonly used to predict the final settlements of a single stone column and the corresponding settlement reduction factor. Both methods, axisymmetric finite element analysis and Priebe’s analytical method make use of the axisymmetric theory of unit cell. The main objective of this study is to examine and compare the three dimensional response of stone column reinforced soils with the axisymmetric analysis results. A proposed analytical method, governed by the failure mechanism of a cylindrical cone is also presented. The comparison between these different approaches is studied and evaluated in conjunction with in situ measurements. It is proved that the beneficial effect of this ground improvement technique, especially on the foundation soil with the lower strength characteristics, is more pronounced. Also, it is concluded that due to unit cell theory, the settlement reduction factor is usually under predicted and the failure of the composite system is impossible, even under high applied pressures. The proposed analytical method of the cylindrical cone failure mechanism is proved to be in good agreement with the 3D results.

Bearing Capacity of a Group of Stone Columns in Soft Soil

Installation of stone column is a viable, cost effective, and environmentally friendly ground-improvement technique. Columns are made of compacted aggregate and are installed in weak soil as reinforcements to increase the shear resistance of the soil mass and, accordingly, its bearing capacity. While a single stone column mostly fails by bulging, a group of stone columns together with the surrounding soil may fail by general, local, or punching shear mechanism, depending on the soil/columns/geometry of the system. The mode of failure of the reinforced ground could be identified based on the ground geometry and strength parameters of both stone column and soft soil. This paper presents an analytical model to predict the bearing capacity of soft soil reinforced with stone columns under rigid raft foundation subject to general shear-failure mechanism. The model utilizes limit-equilibrium method and the concept of composite properties of reinforced soil. The proposed theory was validated for the case of bearing capacity of footings on homogenous soil and via the laboratory and numerical results available in the literature for this case. Design procedure and charts are presented for practicing purposes.

Experimental evaluation of stress concentration ratio of model stone columns strengthened by additives

The main objective of this paper is to find an experimental base for the value of the stress concentration ratio by manufacturing a model of a single stone column with rigid instrumented loading plates such that the total load applied to the model footing, and the load applied to the stone column can be measured alone. Model tests of soil treated with a single stone column and groups of two, three and four stone columns were tested. In addition, model tests were prepared with 10% cement as additive to backfill material for the columns. The backfill material was also modified by mixing 30% sand by weight with 70% crushed stone. It was found that the addition of the sand to the crushed stone indicated a marginal effect on stress concentration ratio in soil of shear strength cu = 12 kPa, but no clear effect was noticed during addition of sand to stone in treated soil having a shear strength cu = 6 kPa.

Mode of Failure of a Group of Stone Columns in Soft Soil

AbstractThe design of stone columns is currently based on theories developed for a single column, ignoring the group interaction and therefore the group efficiency. Whereas single stone columns mainly fail by bulging, a group of stone columns may fail by bulging or shear of the entire soil/columns mass. A numerical model was developed to simulate the case of a single stone column and a group of stone columns installed in soft clay. The model establishes the level of interaction between individual columns and therefore determines the mode of failure of a given geometry, soil, and loading condition. The model was validated with the available experimental data in the literature and used to generate data for a potential mode of failure. This parametric study is conducted to examine the effect of the parameters believed to govern the mode of failure and includes modulus of elasticity of the stone column material and the clay, column diameter, and the spacing and angle of shearing resistance of the column mater...

Vibro-Stone Column Reinforcement Mechanism and Numerical Analysis

Numerical simulation of vibro-stone column is taken to simulate the installation of vibro-stone column. A relationship based on test is adopted to calculate the excess pore pressure induced by vibratory energy during the installation of vibro-stone column. A numerical procedure is developed based on the formula and Terzaghi-Renduric consolidation theory. Finally numerical results of composite stone column are compared single stone column.

Vibro-Stone Column Reinforcement Mechanism and Numerical Analysis

Numerical simulation of vibro-stone column is taken to simulate the installation of vibro-stone column. A relationship based on test is adopted to calculate the excess pore pressure induced by vibratory energy during the installation of vibro-stone column. A numerical procedure is developed based on the formula and Terzaghi-Renduric consolidation theory. Finally numerical results of composite stone column are compared single stone column.

Compression/tension load capacity of stone column anchors

Stone column anchors are a newly developed innovative method of resisting vertical tension and compressive loads on very soft ground such as reclaimed land. In the stone column anchor system, the ground slab is connected to an anchored frustum at the base of the column by a steel bar. This enables the stone column anchor to resist tension loads, while the shaft of the stone column and the surrounding soil form a composite foundation to resist compressive loads. This paper examines the vertical compression/tension load-carrying capacity of single stone column anchors tested under repeated loading. The results show that stone column anchors can be used to provide an increased tension and compression ground load-carrying capacity. The system has been implemented on reclaimed land for the construction of a new sewage treatment plant.