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This study investigates the effect of pore water pressure during the vibro-compaction stone column construction in coral reef sand strata. Field tests were conducted at a port project in a Southeast Asian country to monitor the pore water pressure during construction. The study focuses on the impact of vibro-compaction on pore water pressure in coral sand strata at different depths, radial distances, and under various vertical drainage conditions. Results show that the greatest pore water pressure changes occur during the drilling stage, with the area closest to the vibro-compaction head experiencing the highest pressure. The peak excess pore water pressure significantly affects existing stone columns. The liquefaction characteristics of coral reef layers are closely related to the surrounding drainage conditions.

This paper reviews the main modeling techniques for stone columns, both ordinary stone columns and geosynthetic-encased stone columns. The paper tries to encompass the more recent advances and recommendations in the topic. Regarding the geometrical model, the main options are the “unit cell”, longitudinal gravel trenches in plane strain conditions, cylindrical rings of gravel in axial symmetry conditions, equivalent homogeneous soil with improved properties and three-dimensional models, either a full three-dimensional model or just a three-dimensional row or slice of columns. Some guidelines for obtaining these simplified geometrical models are provided and the particular case of groups of columns under footings is also analyzed. For the latter case, there is a column critical length that is around twice the footing width for non-encased columns in a homogeneous soft soil. In the literature, the column critical length is sometimes given as a function of the column length, which leads to some disparities in its value. Here it is shown that the column critical length mainly depends on the footing dimensions. Some other features related with column modeling are also briefly presented, such as the influence of column installation. Finally, some guidance and recommendations are provided on parameter selection for the study of stone columns.

Although the efficacy of stone columns as a ground improvement technique for soft soils is well-established, their effectiveness diminishes in very soft soils ( q u  < 25 kPa) due to insufficient lateral support. In such situations, encasement with geosynthetics may be beneficial. This paper presents the results of model tests on various types of stone columns (floating and end-bearing) with different diameters (40 mm and 60 mm), both ordinary and geogrid-encased, in very soft clay with varying undrained shear strengths. The tests were conducted under monotonic and cyclic loading conditions in a plane-strain configuration. The study evaluates the impact of key parameters, including column length and diameter, base support conditions, undrained shear strength of clay, and geogrid encasement length, on the performance of improved ground through a total of 28 model tests. The results show that regardless of the soil's undrained shear strength, the encasement of stone columns with geogrids significantly enhances ground performance. Under monotonic loading, this improvement ranges from 22 to 140% depending on the length of geosynthetics encasement and base support conditions. Under incremental cyclic loads, the improvement varies from 25 to 50%. It is also observed that the geogrid encasement's effectiveness significantly increases when it encompasses the entire length of the stone columns, as it extends the lateral bulging zone below the encasement length.

Stone-column’s are recently garnered popularity being an effective ground-enhancement technique. This study investigates stone-column’s reinforcement impacts of black cotton soil (BCS) upon consolidation & strength characteristics. The laboratory experiments were performed upon BCS specimens reinforced with three various diameters (50 mm, 75 mm, & 100 mm) of stone-column’s and four slenderness ratios (l/d = 3, 4, 5, and 6). Consolidation characteristics and load-settlement responses of reinforced & unreinforced samples were compared. Results demonstrate how bearing capacity of reinforced soil rises along both column diameter & l/d ratio under end-bearing conditions. Furthermore, key geotechnical parameters which are compressibility coefficient (a v ), void ratio (e), coefficient of consolidation (C v ), volume change index (m v ), & permeability (k) are significantly affected by stone-column geometry. The findings confirm the efficacy of end-bearing stone columns in improving loading-carrying capacity and expediting consolidation in BCS, underscoring their suitability for ground stabilization in expansive soils.

Purpose Sincethe availability of natural aggregates is very sparse, recycled industrial and construction waste provides a sustainable alternative to ground improvement using vibro replacement method. Utilizing recycled building waste caters the requirement for its disposal and offers an effective remedy for the scarcity of natural resources. The aim of this study was to give a sustainable alternative for the natural aggregates as the material for stone column. Materials and methods A good stone column material should be hard, dense, chemically inert and must comply with the size requirement. The utilization of construction debris and spent railway ballast as column material has been the subject of numerous researches. This work focuses on finding the suitability of railway ballast and concrete debris as alternatives for stone column material. A detailed laboratory testing of these materials has been carried to judge their strength requirements as the material for both Ordinary Stone Columns (OSCs) and Geosynthetic Encased Stone Columns (GESCs). The improvement in capacity of both OSCs and GESCs is evaluated by performing California Bearing Ratio (CBR) test in laboratory by creating unit cell stone column models of different recycled aggregates and comparing their load settlement behavior with natural aggregates. Results and discussion Railway ballast, natural aggregates, concrete debris and virgin soil were found to show decreasing order in CBR test results. Loading required for causing settlement in both OSCs and GESCsshowed remarkable increase as compared to that of virgin clay and the maximum load settlement improvement was observed for railway ballast in both the types of stone columns. The CBR values for GESC made from railway ballast, natural aggregates and concrete debris were 54, 49 and 38% respectively. On the other hand, CBR for OSC made from railway ballast, concrete debris and natural aggregates were found to be 25.5, 20.4 and 24% respectively and CBR of virgin clay was found to be just 11%. Conclusion The demonstrated application of sustainable sources in place of natural aggregates provides a crucial pathway for utilizing the recycled aggregates as stone column filler material. Up on encasing the OSC with geotextile the performance of stone columns has improved appreciably in terms of load capacity. Railway ballast and concrete debris can be adopted as an alternate for the natural stone column materials to improve the bearing capacity of site consisting mainly of soft clays.

This paper presents the results of large shaking table tests to investigate the improvement effects of using ordinary stone columns (OSCs), geosynthetic-encased stone columns (GESCs), and surrounded stone columns with filtering material (FSCs) on saturated sand. The internal dimensions of rigid box were 2.35 m and 0.9 m in plan and was filled with 1.1 m Firuzkuh sand using the water pluviation method. The diameters of stone columns (SCs) were 120 mm and 170 mm and the SCs spacing was 300 mm. The embedded lengths of SCs were 1100 mm. The results indicate that, although the increase in excess pore water pressure is not restrained by using OSCs, the use of both GESCs and FSCs are more effective to mitigate liquefaction potential. This is because of the effectiveness of the geotextile and sand filter on preventing the clogging of SCs and allowing permanent drainage of SCs during shaking. It was found that in the cases of unimproved sandy ground and improved sand by OSCs at 0.05 g loading horizontal acceleration, sand became totally liquefied, while in the cases of improved sand by GESCs or FSCs, under approximately 0.2 g acceleration, the soil close to the SCs was not liquefied.

Geosynthetic-encased stone columns (GESCs) effectively improve soft soils where traditional stone columns lack sufficient lateral confinement. The complex interaction among the column, encasement, and surrounding soil necessitates an analytical model for efficient prediction and design. This study presents a simplified semi-analytical iterative solution to evaluate ground reinforced with GESCs. The system is modeled as a unit cell with regularly arranged end-bearing stone columns in soft soil. The stone column is idealized as a rigid-plastic material, yielding at active stress and deforming plastically without volume change, while the geosynthetic encasement is represented as linear-elastic, and the surrounding soil is modeled using semi-empirical assumptions in which horizontal stresses are linearly proportional to vertical stresses. The soil profile is divided into horizontal slices to account for depth-dependent behavior, applicable to both homogeneous and layered soils, and to un-encased, partially encased, or fully encased columns. Validation with field tests and finite element analysis shows that the proposed solution provides comparable results for settlements, stress distribution in both soil and stone columns, and encasement radial expansion. The model is effective across a wide range of area replacement ratios (i.e., 0 to 0.35) and encasement stiffnesses (0 to 5000 kN/m), with optimal stiffness effects calculated between 2000 and 3000 kN/m. Parametric analyses reveal that settlement improvement and stress concentration are most sensitive to the area replacement ratio, encasement stiffness, and soil stiffness, while increasing column diameter beyond an optimal value reduces effectiveness. An optimum partial encasement length ratio of 0.45 was identified, beyond which the Settlement improvement factor (SIF) increases only marginally. The proposed model also provides an analytical design chart for evaluating the settlement of GESC-reinforced soft soils, along with a Python-based code for calculation.

One of the most popular soil improvement methods is the use of stone columns to increase the bearing capacity and decrease settlements of buildings built on soft clay. Due to an absence of lateral confinement, the stone column treatment’s effectiveness is insufficient. The stone column’s bearing capacity is increased, and its amount of settlement is considerably reduced when it is encased with a geotextile. Numerical analyses were conducted to evaluate the effects of column material friction angle, geotextile stiffness, column diameter and spacing on the behavior of a group of encased stone columns (ESC) supporting a square isolated footing on soft clay. The analyses showed that increasing friction angle of the column material resulted in lower settlement reduction ratio (SRR) for ordinary stone columns (OSC), but had minimal impact on SRR for ESC. Increasing geotextile stiffness significantly decreased SRR for ESC, but the benefits diminished once stiffness exceeded 1000 kN/m. ESC also showed much higher stress concentration ratios compared to OSC, along with lower excess pore pressures. The mobilized hoop forces in the geotextile increased with applied stress but remained relatively constant for high column friction angles. The results demonstrate the effectiveness of geotextile encasement in improving the performance of stone column foundations, with the geotextile stiffness playing a more dominant role than the column friction angle. Parametric evaluation of column diameter and spacing demonstrated their significant influence on settlement reduction. The findings provide guidance on selection of appropriate geotextile properties for design of encased stone column ground improvements.

Three different liquefaction mitigation techniques for an earthen embankment resting on saturated loose cohesionless soil have been compared in the present study as densification of foundation soil, stone column mitigation, and hybrid pile-stone column mitigation. Numerical modelling has been done using finite element modelling assuming plane strain condition. Liquefaction behaviour of the foundation soil has been modelled using the effective stress-based elasto-plastic UBC3D-PLM model. All the three mitigation models along with the benchmark model have been analysed under 25 different real ground motions. The maximum embankment crest settlement has been occurred in the Imperial Valley (1979) ground motion having the maximum Arias Intensity. The maximum crest settlement and the maximum excess pore pressure ratio in the mitigation zone below embankment toe found to be increasing with Arias Intensity of ground motions. In case of mitigation using densification of region below the embankment toe, the mitigated zone away from the toe towards the free field liquefies. The stone column mitigation reduces the excess pore pressure more efficiently beneath the embankment toe region than other two mitigation techniques. The hybrid mitigation with a combination of gravel drainage and pile found to be more effective to reduce the excess pore pressure as well as the shear-induced and post-shaking settlement due to the rapid dissipation of excess pore pressure of the foundation soil.

The objective of this investigation is to understand how to use waste tires to surround stone pillars and mix gravel with recycled asphalt pavement (RAP) and stone pillars to provide an environmentally friendly and cost-effective weak layer improvement method. To study the behavior of such stone columns, experiments were conducted in units consisting of a single stone column with recycled asphalt pavement as filling material and a single stone column covered with old tires. To test the effect of different mixing ratios, rapeseed content was selected from 0% to 100%. Elasticity tests were conducted on cladded and nonclad stone column samples. Furthermore, direct shear tests were conducted on samples with different ratios of gravel and rapeseed mixtures. The results of the load-bearing capacity test show that the cover of the stone columns with old tires can significantly increase the load-bearing capacity. Replacing 25% of natural stone column aggregates with RAP increases the load capacity. But as the percentage of RAP in the mixture increases from 25% to 100%, the loading capacity decreases. Another advantage is the reinforced stone column. From the point of view of ecology, an advantage is the use of recyclable materials.