After sand liquefaction, buried underground structures may float, leading to structural damage. Therefore, implementing effective reinforcement measures to control sand liquefaction and soil deformation is crucial. Stone columns are widely used to reinforce liquefiable sites, enhancing their resistance to liquefaction. In this study, we investigated the mitigation effect of stone columns on the uplift of a shield tunnel induced by soil liquefaction using a high-fidelity numerical method. The liquefiable sand was modeled using a plastic model for large postliquefaction shear deformation of sand (CycLiq). A dynamic centrifuge model test on stone column-improved liquefiable ground was simulated using this model. The results demonstrate that the constitutive model and analysis method effectively reproduce the liquefaction behavior of stone column-reinforced ground under seismic loading, accurately reflecting the time histories of excess pore pressure ratio and acceleration. Subsequently, numerical simulations were employed to analyze the liquefaction resistance of saturated sand strata and the response of a shield tunnel before and after reinforcement with stone columns. Additionally, the effects of densification and drainage of the stone columns were separately studied. The results show that, after installing stone columns, the excess pore pressure ratio at each measurement point significantly decreased, eliminating liquefaction and mitigating the uplift of the tunnel. The drainage effect of the stone columns emerged as the primary mechanism for dissipating excess pore pressure and reducing tunnel uplift. Furthermore, the densification effect of stone columns effectively reduces soil settlement, particularly pronounced around the stone columns, i.e., at a distance of three times the diameter of the stone column.

With the growing need for efficient mitigation strategies in liquefaction-prone regions, ensuring both seismic resilience and sustainability of infrastructure has become increasingly significant. This paper presents a datadriven probabilistic seismic demand model (PSDM) prediction and sustainability optimization framework to mitigate liquefaction-induced lateral deformation in regional mildly sloping ground improved with stone columns. The framework integrates finite element (FE) simulations with machine learning (ML) models, generating 1,200 ground FE models based on the key site attributes, such as ground inclination, soil properties, and stone column configurations. The performance of the selected ML models is evaluated through hyperparameter tuning by k-fold cross-validation, with the artificial neural network (ANN) outperforming other models in accurately predicting the PSDM. Subsequently, this framework is applied to a set of representative mildly sloping ground sites, enabling rapid PSDM prediction for each site with varying site attributes. Moreover, by incorporating cost and sustainability metrics, multi-objective optimization is performed using the developed ANN predictive model to maximize seismic performance while minimizing total carbon emissions and costs associated with ground improvement. Overall, the framework allows for rapid and accurate PSDM prediction and regional optimization, facilitating the identification of the optimal stone column configurations for efficient and sustainable liquefaction mitigation.

This paper presents a comprehensive case study on the numerical analysis of stone columns as a ground improvement technique for an expressway embankment. The primary objective is to assess the effectiveness of stone columns in enhancing the performance of predominantly fine-grained soils using Finite Element Method (FEM) analysis. To achieve the objective, detailed numerical models are developed in both three-dimensional (3D) and two-dimensional (2D) plane strain configurations to simulate embankment conditions accurately. Key geotechnical parameters, including the modulus of elasticity and hydraulic conductivity of the stone column material, are incorporated to account for the improved stiffness and drainage effects. The installation process considers critical factors such as vibration-induced changes and horizontal displacement to capture the evolution of soil stress conditions. A staged construction approach is implemented to realistically simulate the sequential embankment construction process and its impact over time. To ensure model reliability, validation is performed by comparing numerical results with field measurements obtained from horizontal inclinometers installed beneath the embankment. The analysis focuses on key performance indicators such as settlement behaviour, the generation and dissipation of excess pore water pressure, and overall stability assessments. The results demonstrate a strong correlation between numerical predictions and field observations, confirming the accuracy of the developed models. This study provides valuable insights into the performance of stone column-reinforced embankments, highlighting significant improvements in load-bearing capacity, reduction in settlement, and overall ground stability. By evaluating the role of stone columns in accelerating consolidation and enhancing the stiffness, strength, and stability of fine-grained soil layers, the research contributes to the optimisation of design and construction methodologies for ground improvement. Additionally, a comparative assessment of 3D and 2D plane strain numerical models is conducted to evaluate their predictive capabilities in representing real embankment behaviour. The findings support the advancement of safer and more resilient infrastructure solutions.

When stone columns or vertical drains are applied to improve soils, it is common to face situations where the soft soil layer is too thick to be penetrated completely. Although consolidation theories for soils with partially penetrated vertical drains or stone columns are comprehensive, consolidation theories for impenetrable composite foundations containing both two types of drainage bodies have been few reported in the existing literature. Equations governing the consolidation of the reinforced zone and unreinforced zone are established, respectively. Analytical solutions for consolidation of such composite foundations are obtained under permeable top with impermeable bottom (PTIB) and permeable top with permeable bottom (PTPB), respectively. The correctness of proposed solutions is verified by comparing them with existing solutions and finite element analyses. Then, extensive calculations are performed to analyze the consolidation behaviors at different penetration rates, including the total average consolidation degree defined by strain or stress and the distribution of the average excess pore water pressure (EPWP) along the depth. The results show that the total average consolidation rate increases as the penetration rate increases; for some composite foundations with a low penetration rate, the consolidation of the unreinforced zone cannot be ignored. Finally, according to the geological parameters provided by an actual project, the obtained solution is used to calculate the settlement, and the results obtained by the proposed solution are in reasonable agreement with the measured data.

Tunnels embedded in liquefiable soil are frequently subjected to uplift and sustain serious damage during major earthquakes. Mitigation methods to prevent the flotation of these tunnels must be developed and implemented in the natural environment. For this purpose, this study proposes a new method that uses stone columns to enhance soil drainage and mitigate soil liquefaction around tunnels. A circular tunnel in liquefied soil is simulated using a 2D finite element model, PLAXIS 2D, and subjected to a sinusoidal input motion. The tunnel's pre-construction and post-construction scenarios are examined. Parametric studies are carried out to investigate the effect of changing several parameters, such as the distance between stone columns and tunnel springing, the diameter of stone columns, the spacing between stone columns, the number of stone column rows, and the stone column arrangement patterns on the effectiveness of liquefaction mitigation. The study reveals that liquefaction mitigation is enhanced by using stone columns closer to tunnel springing, with larger diameters, less spacing, and more rows of stone columns that are arranged in a square pattern. It also emphasizes the importance of timely implementation of stone columns for maximum benefit.

The application of sites containing low-strength soil deposits is of great concern concerning the rapid increase in urbanization and industrialization. To overcome such difficulties in construction, ground improvement techniques are frequently practiced. So, the provision of the stone column is one of the well-known approaches to improve the weak soil properties. Moreover, the application of reinforced stone columns is chosen over the conventional method of stone columns to enhance the strength and durability parameters of weak soils to a greater extent. In this context, the present article presents a state-of-art review of reinforced stone columns and analyzes their developments, Performance, and Prospects concerning future aspects. This comprehensive analysis includes the most relevant existing studies based on experimental, analytical, and field testing for static and cyclic loading conditions. The present study presents the review chronologically from the beginning of the research on geosynthetic reinforced stone columns. The main aim of this study is to collect the existing outcomes from various research and accumulate them in one resource which will be helpful for future researchers to proceed with the new development with this easily accessible information and data.

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.

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.

Die R & uuml;ttelstopfverdichtung kommt als Baugrundverbesserung weltweit in fein- und grobk & ouml;rnigen B & ouml;den zum Einsatz. Jedoch sind die Zustands & auml;nderungen des anstehenden Bodens infolge des vollverdr & auml;ngenden S & auml;uleneinbaus und der induzierten Vibration noch nicht ausreichend untersucht. Im ersten Teil dieses Beitrags werden daher in einem Feldversuch die Auswirkungen der R & uuml;ttelstopfs & auml;ulenherstellung auf den Zustand des anstehenden Bodens untersucht. Dabei zeigt sich, dass der R & uuml;ttelstopfs & auml;uleneinbau in grobk & ouml;rnigen B & ouml;den zu einer Verbesserung der bautechnischen Eigenschaften des anstehenden Bodens f & uuml;hren kann. Motiviert durch den Feldversuch betrachtet der zweite Teil der Arbeit anhand von simplifizierten Beispielen einen grunds & auml;tzlichen Vergleich verschiedener Hohlraumaufweitungsprozesse. Mithilfe eines hypoplastischen Stoffmodells wird dabei die Aufweitung eines Hohlraums infolge (1) einer monotonen und infolge (2) einer zyklischen Belastung betrachtet. Beide F & auml;lle werden im Hinblick auf eine qualitative & Uuml;bertragbarkeit auf die Modellierung der S & auml;uleninstallation verglichen. Es zeigt sich ein qualitativ unterschiedliches Bodenverhalten: Eine monotone Aufweitung f & uuml;hrt zum kritischen Zustand im Boden, w & auml;hrend eine zyklische Aufweitung in Abh & auml;ngigkeit von der Durchl & auml;ssigkeit zu einer Verdichtung und/oder einer Spannungsrelaxation f & uuml;hrt. Eine vollst & auml;ndige Vernachl & auml;ssigung der R & uuml;ttlervibration in entsprechenden numerischen Modellen erscheint daher nicht zutreffend. Field test on the vibro replacement stone column installation and considerations on cavity expansionVibro replacement stone columns are used for ground improvement worldwide in coarse-grained as well as fine-grained soils. However, the changes in the soil's state due to the stone column installation including the induced vibration have not yet been investigated sufficiently. In the first part of the article, the effects of the stone column installation are investigated using a field test. It is shown that the installation in coarse-grained soils can lead to an improvement in the structural properties of the surrounding soil. Based on the field test, a theoretical comparison of different cavity expansion processes is presented in the second part of this paper using simplified numerical examples. For that purpose, the expansion of a cavity in the soil due to (1) a monotonic and (2) a cyclic loading is investigated using a hypoplastic constitutive model. Both cases are compared to investigate their ability to simulate the column installation process. However, a qualitatively different soil behaviour is observed: A monotonic expansion will result asymptotically in the critical state of the soil, while a cyclic expansion leads to a compaction and/or a stress relaxation depending on the permeability. Therefore, neglecting the cyclic deformation of the soil in simulating the stone column installation seems to be inappropriate.

Recycled concrete aggregate (RCA) is a voluminous solid waste material derived from the construction sector and is typically stockpiled in landfills. In recent years, the ground improvement industry has grappled with challenges stemming from the depletion of natural quarry materials, resulting in a skyrocketing of their prices and increased project costs. This research investigated the feasibility of using RCA stabilized by one-part geopolymers to produce an innovative semi-rigid inclusion column system for ground improvement of soft soils. Na2SiO3anhydrous was used as a sole solid activator for the activation of fly ash (FA), slag (S) or a binary precursor (FA+S) in the stabilization of RCA. The unconfined compressive strength (UCS) and microstructure of the stabilized mixtures have been examined with respect to different binder formulations and curing conditions. The permanent deformation characteristics of mixtures under cyclic loading were evaluated through repeated load triaxial (RLT) tests to replicate the moving wheel loads imposed on the semi-rigid inclusion columns. In addition, the cost and environmental impacts of the optimum mixtures suggested in this research were studied. The test results indicated that stabilizing RCA with as low as 5% one-part alkali-activated FA, S or (FA+S) met the minimum strength requirement (1.034 MPa) for ground improvement work. Compared with standalone FA and S geopolymer stabilized RCA mixtures, (FA+S) geopolymer stabilized RCA mixtures were identified as preferred industrial formulations due to their prolonged setting time for ease of mixing and handling when used in stone column applications. It was found that curing temperature and duration played a pivotal role in the strength gain of the mixtures. The RLT test results demonstrated that implementing the optimum RCA + 5%(FA+S) mixture as identified in this study for semi-rigid inclusion columns, led to a reduction in permanent strain values by approximately 90% compared to conventional unbound stone columns. The comparison between the optimum mixture highlighted in this study with other stabilization methods showed that the semi-rigid inclusion columns had great potential to enable large-scale production, cost and emission reduction in future ground improvement projects.