Aggregate Piers Research Articles

Shallow Foundations and Deep Foundations; Drilled Piers, Aggregate Piers and Stone Columns; Design Recommendations, Construction Considerations, and Performance

Shallow Foundations and Deep Foundations; Drilled Piers, Aggregate Piers and Stone Columns; Design Recommendations, Construction Considerations, and Performance

Improved Liquefaction Resistance with Rammed Aggregate Piers Resulting from Increased Earth Pressure Coefficient and Density

Improved Liquefaction Resistance with Rammed Aggregate Piers Resulting from Increased Earth Pressure Coefficient and Density

Design and construction of Rammed Aggregate Piers for Te Kaha - Canterbury's new Multi-Use Arena

Design and construction of Rammed Aggregate Piers for Te Kaha - Canterbury's new Multi-Use Arena

Rammed Aggregate Pier ground improvement trial and the effects on geologically aged soils

Rammed Aggregate Pier ground improvement trial and the effects on geologically aged soils

Finite Element Analysis of Segmental Precast Concrete Panel Reinforced Earth Retaining Wall

Reinforced earth retaining walls are being utilized more frequently in civil infrastructure projects as an alternate design structure to typical reinforced concrete walls and other structures for supporting backfill. The objective of the present study is to model and analyze a 2-dimensional Segmental Precast Concrete Panel (SPCP) wall using the 2-dimensional finite-element tool PLAXIS and analyze the behaviour of the wall concerning the effect of reinforcement type and surcharge loads. The present work also includes the investigations of the effects of reinforcement type and surcharge loads, as well as the influence of different supporting systems on the deformations and ground-surface settlements of the SPCP wall. Ribbed steel reinforcements, Polyethylene Terephthalate (PET) geogrids and Density Polyethylene (HDPE) geogrids are used to evaluate the wall deformations for reinforcement types. For ribbed-steel reinforcement, ground settlements and wall deformations are 14% and 25% less compared to those of PET and HDPE geogrid reinforcements, respectively. With the increase in surcharge on the backfill soil, wall deformations and surface-ground settlements are increased significantly by 150%. To decrease the deformations of walls resting on soft soil, pile foundations and aggregate piers are considered as supporting solutions. In the case of reinforced blocks with pile foundation as supporting systems, the wall deformations and settlement are 60% lesser than for aggregate pier supporting systems. KEYWORDS: Segmental precast concrete panel, PLAXIS, Reinforcement type, Aggregate pier, Pile Foundation, Wall deformation

Artificial intelligence assisted optimization of rammed aggregate pier supported raft foundation systems based on parametric three-dimensional finite element analysis

The increased usage of rammed aggregate piers has demanded optimizing the design parameters of this technique. In this study, numerous parametric three-dimensional finite element analyses were conducted to optimize the parameters of the rammed aggregate pier-supported raft foundation with novel methods. Three-dimensional finite element simulations were validated using a field loading test for a single rammed aggregate pier at Neola, Iowa (USA). After the validation, elasticity modules of the rammed aggregate piers, raft foundation thicknesses, and column spacings were varied. The raft foundation-rammed aggregate pier groups system in 81 different combinations was subjected to parametric three-dimensional finite element analyses to provide data for the optimization study. The effect of the changes in the elasticity modulus of the rammed aggregate piers, the raft foundation thickness, and column spacing on the settlement was investigated. Optimization analyses were performed using the artificial intelligence-supported novel Goal Attainment Method and the Response Surface Method. The novel coding developed in this study, which automatically selects the most reasonable prediction function with the support of artificial intelligence, created a prediction function with a high correlation coefficient used in the optimization analyses. Two different optimization methods specified in the optimization study performed as multi-objectives were compared, and the solution system with the highest desirability value was selected. Therefore, optimum design parameters were reached by using novel methods for general raft foundation-rammed aggregate pier group systems to guide researchers.

3D Numerical Assessment of Rammed Aggregate Pier Performance under Dynamic Loading in Liquefiable Soils

Ground improvement (GI) techniques have shown promise in effective liquefaction mitigation, but the physical mechanisms governing their three-dimensional (3D) response during dynamic loading are not yet fully understood. To evaluate the 3D performance of one GI technique, the rammed aggregate pier (RAP), in-situ site characterization, full-scale field test data, and calibrated baseline constitutive soil model parameters are combined to model the 3D fully coupled hydromechanical response of natural (unreinforced) and improved (reinforced) soil profiles. To the authors’ knowledge, this contribution represents the first 3D model of a columnar-reinforced soil profile being calibrated using full-scale field testing. The field observations from the comprehensive ground improvement testing (GIT) program in New Zealand and insights from two-dimensional (2D) finite-difference analyses using constitutive model parameters calibrated against the field measurements were used. The developed 3D models were subjected to dynamic loads simulating the excitation generated by a vibroseis truck at one of the in-situ test sites of the GIT program, as well as unidirectional and bidirectional earthquake ground motions from the Canterbury Earthquake Sequence events. The 3D simulations showed that the improved soil profiles experienced reduced excess pore pressures and reduced dynamically induced shear strains compared to the natural, unreinforced soil models. The developed 3D finite-element predictions were compared and validated vis-à-vis the field observations of the GIT program. Compared to 2D analyses, 3D analyses provide a more accurate description of actual field conditions, and, for instance, it was observed that multidirectional shaking has a significant effect on liquefaction triggering, particularly for natural soil profiles. Finally, it was shown that soil densification around the installed pier elements and the lateral earth pressure increase within the densified soil and are the primary ground improvement mechanisms contributing to the reduction of dynamically induced shear deformations and excess pore pressure generation during earthquake shaking. It was also found that the permeability and shear stiffness of the installed RAP piers did not have a significant influence on the pore pressure response and shear strains developed along the centerline of the improved area.

Sensitivity Analysis of a Scaled Rammed Aggregate Pier (Geopier) Bearing Capacity

Sensitivity Analysis of a Scaled Rammed Aggregate Pier (Geopier) Bearing Capacity

Influence of Load Test Scale on Prediction of Ultimate Bearing Capacity of Aggregate Pier Reinforced Clay

Predicting the bearing capacity of spread footings on aggregate pier‐reinforced soil is particularly important for ground improvement. Various methods for predicting the bearing capacity of spread footings supported on aggregate pier‐reinforced clay have been proposed. In addition, many fields or laboratory load tests have been conducted to identify the improvement effects of aggregate pier. However, no study has quantitatively compared the effect of the experimental scale on the prediction of bearing capacity. In this study, multiple linear regression analyses were performed for field and laboratory load tests, and the effects of the load test scale on bearing capacity prediction were identified. The sensitivity analysis showed that the prediction model for the laboratory load test (MLRL) exhibited a higher sensitivity for the undrained shear strength than that of the field load test model (MLRF). However, the sensitivity of the area replacement ratio of MLRL was less than half that of the MLRF. As the undrained shear strength increased, the predicted bearing capacity of the MLRL was larger than that of the MLRF owing to the influence of boundary conditions on the experimental equipment.

Gravel impact compaction piers as a method of soil improvement

The purpose of this study was to evaluate the performance of gravel impact compaction piers system (GICPs) in improving a 3.5m thick loose silty sand in a multilayer coastal soil system located in Bushehr, Iran. The liquefiable sandy soil layer was layered on clay layers with moderate to very stiff consistency and below the engineering embankment layer with a thickness of 1.8 m. Implementation of gravel impact compaction piers is a new generation of aggregate piers. Gravel impact compaction piers were used to improve the liquefiable soil layers and to increase the bearing capacity and reduce subgrade settlement to withstand surface infrastructures. The process of making gravel impact compaction piers in a triangular or square-patterned grid was created using three types of special mandrels and feeding and compacting the gravels in the cavity in several stages without removing the soil from the cavities. The experience gained in this case study showed that artificial liquefiable was created immediately after the construction of these piers in a limited area and the soil became unstable. After about 11-14 days, the soil stabilized rapidly. The results of the standard penetration test in the matrix soil around the piers showed that the amount of (N1)60 in compacted soils was in the range of 21-30 and on average 15 times the amount of (1-3) in the initial soil. Also, the relative density of the initial soil was increased from 25% to 75% after soil improvement. Accordingly, by relying merely on the compaction properties of the piers and without relying on other primary soil remediation factors, such as piers drainage and soil texture change, the safety factor of the improved soil is 1.7-1.95 times the minimum required according to the two risk levels in the design.

Explicit soft computing model to predict the undrained bearing capacity of footing resting on aggregate pier reinforced cohesive ground

Explicit soft computing model to predict the undrained bearing capacity of footing resting on aggregate pier reinforced cohesive ground

Numerical modelling of rammed aggregate piers (RAP) in liquefiable soil

Liquefaction poses a significant risk to the built environment, and as a result, ground improvement (GI) techniques are commonly used to mitigate this risk. Liquefaction mitigation strategies continually evolve, and several relatively new techniques, such as Rammed Aggregate Piers® (RAP), have shown promise. While the densification mechanism associated with many of the GI techniques is generally well known, other mechanisms such as reinforcement, lateral stress increase, and improved drainage that are thought to enhance liquefaction mitigation are still not completely understood. Moreover, field performance data for these GI schemes during actual earthquakes is limited. To fill this gap and evaluate the performance of RAP, this study presents the first numerical model on a specific GI technique that uses detailed site characterization, large-scale field test data, and post-earthquake field performance observations to calibrate and qualitatively validate the model. The in-situ characterization and full-scale field test data collected from the Ground Improvement Programme (GIP) performed following the 2010–2011 Canterbury Earthquake Sequence (CES) in New Zealand are used in this study. A set of fully-coupled hydro-mechanical finite difference (FD) models are performed in natural and reinforced conditions. For the unimproved soil profile, the results predict shear strains and zones of high excess pore water pressures reasonably well. For the profile reinforced with RAP, the analyses indicate that the stiffness properties of the RAP have the greatest influence on the reduction of generated shear strains in the soil profile. Finally, the calibrated models are subjected to a set of ground motions with different intensities to assess the efficacy of the RAP under different loading conditions.

Liquefaction Mitigation of Silty Sands Using Rammed Aggregate Piers Based on Blast-Induced Liquefaction Testing

AbstractTo investigate the liquefaction mitigation capability of rammed aggregate piers (RAP) in silty sand, blast liquefaction testing was performed at a soil profile treated with a full-scale RAP...

Prediction of Ultimate Bearing Capacity of Aggregate Pier Reinforced Clay Using Machine Learning

Prediction of Ultimate Bearing Capacity of Aggregate Pier Reinforced Clay Using Machine Learning

Mobilized Bearing Capacity Analysis of Global Stability for Walls Supported by Aggregate Piers

Global stability analysis is a key component of mechanically stabilized earth (MSE) wall design, especially those constructed over marginal soils. When limit equilibrium analysis is used for MSE wall design, incorrect factors of safety can be predicted depending on the shape assumed for the failure surface. The use of ground improvement, such as aggregate piers (AP), further complicates the analysis. A mobilized bearing capacity (MBC) approach is presented which highlights the direct relationship between the factors of safety for global stability and bearing capacity. Results from the MBC approach are compared with finite element strength reduction analyses for a range of MSE wall geometries and AP replacement ratios. The factors of safety match well for global factors of safety between 1 and 1.5, considering both eccentricity and stress concentration. The MBC approach provides a tool to supplement and refine global stability analyses for retaining walls constructed over improved foundations.

Prediction of Ultimate Bearing Capacity of Aggregate Pier Reinforced Clay Using Multiple Regression Analysis and Deep Learning

Aggregate piers have been widely used to increase bearing pressure and reduce settlement under structural footings. The ultimate bearing capacity of aggregate pier-reinforced ground is affected by the soil strength, replacement ratio of piles, and construction conditions. Various prediction models have been proposed to predict the ultimate bearing capacity. However, existing models have shown a broad range of bias, variation, and error, and they are at times unsuitable for practical design. In this study, multiple regression analysis was performed using field loading test results to predict the ultimate bearing capacity of ground reinforced by aggregate piers, and the number and type of the most efficient input variables were evaluated to build a robust predictive model. Accordingly, a multiple regression equation for predicting the ultimate bearing capacity was proposed, and a sensitivity analysis was conducted to identify the effect of input variables. In addition, a deep neural network was applied to estimate the ultimate bearing capacity. The optimal structure was selected on the basis of cross-validation results to prevent overtraining. Prediction errors for two approaches were evaluated and then compared with those of existing models.

Numerical analysis of single rammed aggregate piers installed in stratified soil profiles

In this study, Rammed Aggregate Pier systems are analyzed according to the numerical analysis that are performed by two dimensional commercial finite element analysis software. The focus point of the paper is to identify the effects of pier dimensions, stratification of foundation soil profile and load applying levels on the deformation behavior of interacted rammed aggregate pier-surrounding soil system at the installation stage. Interpretations of the parametrical analyses are focused on the deformation change via loading levels. The relative displacement occurrence between pier and soil matrix is also checked.

Blast-induced liquefaction in silty sands for full-scale testing of ground improvement methods: Insights from a multidisciplinary study

In the engineering geology field increased attention has been posed in recent years to potential liquefaction mitigation interventions in susceptible sand formations. In silty sands this is a major challenge because, as the fines content increases, vibratory methods for densification become progressively less effective. An alternative mitigation technique can be the installation of Rammed Aggregate Pier® (RAP) columns that can increase the resistance of the soil, accounting for its lateral stress increase and for the stiffness increase from soil and RAP composite response. To investigate the influence of these factors on liquefaction resistance, full-scale blast tests were performed at a silty sand site in Bondeno (Ferrara, Italy) where liquefaction was observed after the 2012 Emilia-Romagna earthquake. A multidisciplinary team of forty researchers carried out devoted experimental activities aimed at better understanding the liquefaction process at the field scale and the effectiveness of the treatment using inter-related methods. Both natural and improved areas were investigated by in-situ tests and later subjected to controlled blasting. The blast tests were monitored with geotechnical and geophysical instrumentation, topographical surveying and geological analyses on the sand boils. Results showed the RAP effectiveness due to the improvement of soil properties within the liquefiable layer and a consequent reduction of the blast-induced liquefaction settlements, likely due to soil densification and increased lateral stress. The applied multidisciplinary approach adopted for the study allowed better understanding of the mechanism involved in the liquefaction mitigation intervention and provided a better overall evaluation of mitigation effectiveness.

Under-Slab Utility Installation with Aggregate Piers: It's All About Planning

Aggregate pier ground improvement is commonly used in North America to support buildings. The technology has expanded in the last decade thanks to refinement and introduction of new techniques, more rigorous engineering, improved quality control, and acceptance by the design and construction community. In-place improvement of unsuitable soils offers many advantages, not the least of which is cost savings compared to traditional deep foundations or over-excavation and replacement. Today, thousands of projects in the U.S. are supported on aggregate pier ground improvement.

Bearing capacity of spread footings on aggregate pier–reinforced clay: updates and stress concentration

Aggregate piers represent an economical ground improvement technique used to increase bearing capacity and reduce settlements of weak soils. Several approaches have been developed to estimate the bearing capacity of aggregate pier–reinforced clay, but these models exhibit large prediction bias and uncertainty. This study uses newly developed footing loading test data to investigate the relationship between the bearing capacity and the area replacement and slenderness ratios. The bearing capacity of a single aggregate pier, whether isolated or in groups, below a loaded footing increases as the area replacement ratio decreases due to increase in extent of confined soil surrounding the pier. The length and diameter of an aggregate pier is also shown to result in significantly increased bearing capacity, an effect that diminishes with increasing slenderness. New modifications are proposed to existing simplified and cavity expansion models to account for the effect of confinement, area replacement ratio, and slenderness ratio using a leave-one-out cross-validation technique. The cross-validation analysis resulted in robust bearing capacity models that are more accurate than existing analytical models. Additionally, the stress concentration ratio for shallow foundations supported by aggregate pier–reinforced plastic soils at failure was estimated and compared with the available data, indicating its sensitivity to design variables and showing that this critical design parameter may be predicted using the updated models.