PhD Thesis on Stone Column Embankments

Questions and Answers

What are stone columns used for?

Ground modification and load bearing support

What is Lithomargic clay?

A type of clay used in geotechnical applications

Which of these is a geosynthetic material?

Reinforced concrete

Steel beam

Wooden planks

Geogrid (correct)

What is the main purpose of geocells?

Reinforcement of soil structure Signup and view all the answers

What does the stress concentration ratio (SCR) measure?

The distribution of stress in soil or foundations Signup and view all the answers

Geosynthetic encased stone columns can increase load-bearing capacity.

True Signup and view all the answers

What is the unit cell concept used for?

Arrangement of stone columns in the field. Signup and view all the answers

What is the Mohr-Coulomb model primarily used for?

Stress-strain analysis Signup and view all the answers

What is the lateral deflection of GESC from the axisymmetric analysis?

Measured response of GESC under load. Signup and view all the answers

What does 'UCS' stand for in the context of foundation settlement?

Unconfined Compressive Strength Signup and view all the answers

The arrangement of stone columns is always in a square layout.

False Signup and view all the answers

What is the effect of drainage layer thickness on foundation soil settlement?

It can influence the amount of settlement. Signup and view all the answers

Match the following models with their primary purpose:

Axisymmetric model = Simplified analysis of cylindrical structures 3D column model = Detailed analysis of column behavior Geosynthetic encasement = Reinforcement of weak soils Full 3D model = Comprehensive analysis of complex interactions Signup and view all the answers

What does the term 'improvement factor' indicate?

The effectiveness of reinforcement methods. Signup and view all the answers

What is the full title of the research thesis?

Performance Evaluation of Encased Stone Column Supported Embankments with Geosynthetic Materials as Basal Reinforcement Signup and view all the answers

Who is the author of the thesis?

Vibhoosha M.P. Signup and view all the answers

What is the register number of the author?

165017CV16F19 Signup and view all the answers

Which materials were evaluated for basal reinforcement in the study?

All of the above Signup and view all the answers

A single geogrid encased stone column improved the load-carrying capacity of lithomargic clay by 180%.

True Signup and view all the answers

What effect did geogrid encasement have on column bulging?

Reduced bulging by 82% Signup and view all the answers

Which software was used for numerical modeling in the research?

ABAQUS Signup and view all the answers

What was the percentage reduction in foundation surface settlement with geocell-sand mattresses?

80% Signup and view all the answers

Which infill material was considered the best suited in the study?

Aggregates Signup and view all the answers

What does GESC stand for?

Geosynthetic Encased Stone Column Signup and view all the answers

What was the maximum bulging visible depth in both cases for bulging of stone columns?

3.5 D Signup and view all the answers

What are geocells used for?

Geocells are used for applications like pavements, foundations, embankments, slope protection, and erosion control. Signup and view all the answers

Geocells are eco-friendly and have a low strength-to-weight ratio.

False Signup and view all the answers

What is a primary benefit of using geocells?

All of the above Signup and view all the answers

What did the studies by U.S. Army Engineer Waterways Experiment Station in the late 1970s focus on?

They focused on various soil reinforcement methods for improving the movement of military vehicles over weak subgrade. Signup and view all the answers

Which materials were found to perform better than conventional base courses according to Webster and Watkins (1977)?

Sand base course reinforced by isolated plastic tubes Signup and view all the answers

The proposed system in this research is a Geosynthetic Reinforced _______ System (GRPES).

Piled Embankment Signup and view all the answers

What role does the three-dimensional honeycomb structure of geocells play?

It confines the soil present in the pockets, allowing for increased stability and stiffness. Signup and view all the answers

What are stone columns commonly used for?

Stone columns are used for supporting embankments, liquid storage tanks, raft foundations, and other low-rise structures. Signup and view all the answers

Encasement of stone columns does not provide any additional benefits.

False Signup and view all the answers

Which of the following is NOT a method of ground improvement discussed in the document?

Excavation Signup and view all the answers

What is the significance of the three-dimensional confinement provided by geocells?

It restricts lateral movement of infill soil, resulting in increased shear strength and stability. Signup and view all the answers

What advantage does footing on geocell reinforced soil exhibit compared to unreinforced soil base?

Higher bearing capacity and reduced settlement. Signup and view all the answers

Geocells are ineffective for embankment construction over soft soil.

False Signup and view all the answers

Which methods are commonly used for remedial actions on embankment construction over weaker subgrades?

Chemical treatment Signup and view all the answers

What occurs when geocells are used in reinforced railway ballast?

Significant reduction of vertical deformations. Signup and view all the answers

Match the following applications with their effectiveness of geocell reinforcement:

Soil erosion control = Retards surface runoff Embankment construction = Distributes loads effectively Railway ballast = Reduces vertical deformation Slope stability = Increases factor of safety Signup and view all the answers

What is the optimum footing diameter ratio relative to geocell cell width according to Rea and Mitchell?

1.5 to 2.0 times cell width. Signup and view all the answers

Geocell height has no effect on its load-bearing capacity.

False Signup and view all the answers

What pocket size of geocell is considered optimum according to Dash et al.?

0.8 times the footing diameter. Signup and view all the answers

Which material properties affect the performance of geocell reinforcement?

All of the above Signup and view all the answers

What is the main benefit of using textured geocells over smooth-walled ones?

Higher degree of frictional interaction. Signup and view all the answers

Which of the following are ground modification techniques? (Select all that apply)

Dynamic compaction or vibration Signup and view all the answers

Geocells are a planar soil reinforcement system.

False Signup and view all the answers

What does ECA stand for?

Equivalent Composite Approach Signup and view all the answers

What are the two main components of the term 'geocell'?

geo and cell Signup and view all the answers

The ______ is a vertical column element formed below the ground level with compacted stone fragments.

stone column Signup and view all the answers

What is one benefit of using geosynthetic encased stone columns?

Higher degree of compaction Signup and view all the answers

What does the abbreviation GESC stand for?

Geosynthetic Encased Stone Column Signup and view all the answers

What is the maximum depth for problematic soil replacement?

3 m Signup and view all the answers

Which material is commonly used as an admixture for soil modification?

Fly ash Signup and view all the answers

The load-bearing mechanism of the stone column involves lateral ______ of columns into surrounding soil.

bulging Signup and view all the answers

What is the advantage of stone columns over conventional piling solutions?

Cost and time savings Signup and view all the answers

Which type of footing does Rea and Mitchell (1978) study?

Circular footing Signup and view all the answers

What is the shape of the opening studied by Mandal and Gupta (1994)?

Hexagonal Signup and view all the answers

What is the width of the rectangular footing according to Mhaiskar and Mandal (1996)?

0.625B Signup and view all the answers

Which pattern is associated with the strip footings in Dash et al. (2001b)?

Chevron Signup and view all the answers

What is the width of the chevron circular footing studied by Dash et al. (2003)?

2.1D Signup and view all the answers

What type of footing does Latha et al. (2006) research?

Strip footing Signup and view all the answers

Sireesh et al. (2009) studied a circular footing.

True Signup and view all the answers

The width of the square footing according to Davarifard and Tafreshi (2015) is ______.

0.2D Signup and view all the answers

What is the opening shape for the footing discussed by Biswas et al. (2016)?

Circular Signup and view all the answers

Match the researchers with their corresponding footing types:

Rea and Mitchell (1978) = Circular footing Mandal and Gupta (1994) = Strip footing Mhaiskar and Mandal (1996) = Rectangular footing Latha et al. (2006) = Chevron Strip footing Signup and view all the answers

Study Notes

Research Overview

Thesis titled "Performance Evaluation of Encased Stone Column Supported Embankments with Geosynthetic Materials as Basal Reinforcement."
Submitted by Vibhoosha M.P. for a PhD in Civil Engineering at NIT Karnataka in December 2021.

Declaration and Certification

Research work confirmed to be original and not submitted elsewhere.
Supervised by Dr. Sitaram Nayak and Dr. Anjana Bhasi, both from Civil Engineering departments.

Acknowledgments

Expressed gratitude to advisors, colleagues, family, and the broader academic community for support.
Acknowledged contributions from faculty members, research committees, and laboratory staff.

Abstract Insights

Focus on lithomargic clay found in the Konkan belt of India, which faces strength issues when saturated.
Investigation of the effect of different designs of geogrid encased stone columns on the performance of lithomargic clay, using both experimental and finite element analyses.

Key Findings

Load Carrying Capacity:
- Single geogrid encased stone column with a basal geogrid layer increased load capacity by 180%.
- Three geogrid encased stone columns with the same surface area enhanced load capacity by 210%.
Column Bulging:
- Geogrid encasement reduced maximum column bulging by 38%.
- Bulging was further reduced by 82% with a basal geogrid layer compared to ordinary stone columns.
Geocell Reinforcement:
- Geocells demonstrated superior reinforcement capabilities due to cost-effectiveness and three-dimensional confinement.
- 3D numerical modeling was essential due to the complexity of geocell structures.
Performance Improvement:
- Adding a geocell layer improved stress concentration ratio by 47% at the end of consolidation compared to GESC alone.
- Foundation surface settlement reduced by 80% with geocell-sand mattresses.

Stress and Deformation Analysis

Minimal arching behavior observed in reinforced columnar structures.
Numerical models indicated overestimation of stress concentration ratio and bearing capacity when using equivalent composite approach.

Settlement and Bulging Reduction

Vertical settlement reductions of 78% and 79% achieved with single and double basal geogrids, respectively.
Maximum bulging reduction of 69% in GESC versus ordinary stone columns with a single basal layer; reductions of 52% and 54% for two basal layers and geocell, respectively.

Material Suitability

Aggregates found to be the most suitable infill for optimal stress concentration ratios and vertical settlements.
Mobilized tensile stress in geocell was highest for aggregates and lowest for quarry dust.

Proposed System

Encased stone columns with geocells at the embankment base resemble a Geosynthetic Reinforced Piled Embankment System (GRPES).
Time-dependent analyses showed that GESC plus one basal layer reduced lateral deformation near the toe by 87% compared to unreinforced structures.

Design Method Comparisons

Terraza’s method and BS 8006 exhibited closer predictions for stress reduction ratios than other methods for low height embankments.
Guido et al. (1987) method provided good alignment with full 3D model results for basal geogrid tension, indicating a more reliable design approach.

Overall, the thesis demonstrates significant advancements in understanding and improving the performance of embankments supported by encased stone columns and geosynthetic materials.### Ground Modification Techniques

Various methods used to enhance the engineering properties of soil.
Stone column technique is a common method for improving load-bearing capacity.

Stone Columns

Function by transferring loads from the structure to deeper, more stable soil layers.
Load-bearing mechanism is crucial for their effectiveness.

Geosynthetic Encased Stone Columns (GESC)

Innovative design that integrates geosynthetics to enhance the performance of stone columns.
Provides improved lateral confinement and overall load distribution.

Geocells

Reinforcement structures made of polymeric materials, creating cellular configurations.
History of use in geotechnical engineering for increasing load distribution and decreasing settlement.
Mechanism involves soil confinement, preventing lateral movement and increasing shear strength.

Lithomargic Clay

A type of clay that plays a significant role in foundation stability.
Specific behavior under load, which affects the performance of stone columns and geocells.

Finite Element Method (FEM)

A numerical method for solving complex engineering problems, particularly in continuum mechanics.
Key advantages include flexibility in modeling complex geometries and loading conditions.
Disadvantages include high computational costs and the need for expertise in modeling.

Numerical Analysis

Critical for understanding soil-structure interaction and predicting settlement behavior.
Case studies and models help validate design approaches and assess performance.

Experimental Studies

Focus on understanding stress concentration ratios and load settlement behaviors of stone columns.
Investigate the effects of column configurations on load-bearing capacities and stress distribution.

Parameters Influencing Geocell Performance

Factors such as stiffness, drainage layer thickness, and material properties influence the effectiveness of geocell reinforcements.
Improvement factors indicate the enhancement in load capacity achieved with geocells.

Key Concepts

Stress Concentration Ratio (SCR): A measure of how stress is distributed in the soil and structures, critical for predicting failures.
Soil Arching: A phenomenon where soil redistributes stresses, enhancing overall stability.

Load Transfer Mechanisms

Effective load transfer from superficial or soft soils to more competent layers through stone columns and geocells.

Future Research Directions

Continued exploration into the efficiency of various reinforcement techniques.
Development of improved models and methods to predict real-world performance under varying conditions.### Overview of Structural Analysis Techniques
Stone columns arrangement includes unit cell concept and tributary area considerations.
Mesh discretization is critical for accurate modeling of soils and structures, ensuring precise analysis.

Mohr-Coulomb and Modified Cam Clay Models

Mohr-Coulomb model utilized to depict stress-strain behavior and yield surfaces in principal stress space.
Modified Cam Clay model shows yield surfaces in q–p' plane, key for understanding soil mechanics.

Geosynthetic Reinforcement and GESC

GESC (Geogrid Encased Stone Column) systems enhance stability in embankment constructions.
Different layout configurations (square and triangular) for stone columns affect load distribution and settlement behavior.

Finite Element Analysis (FEA) Applications

Various FEA models developed include axisymmetric and 3D representations, aiding in the simulation of complex interactions.
Use of membrane elements for reinforcement modeling evaluates the performance of geosynthetics in soil stabilization.

Lateral Deflection and Strain Analysis

Analysis identifies lateral deflections and hoop strain in GESC for different modeling approaches, highlighting structural response under loads.

Soil Properties and Performance Testing

Properties of lithomargic clay and stone aggregates significantly influence foundation behavior and consolidation.
Compaction and gradation curves are essential for understanding material performance under structural loads.

Loading Mechanisms and Settlement Response

Load tests on stone columns reveal detailed pressure-settlement responses, crucial for foundation design validation.
Improvement Factors (IF) gauge the effectiveness of reinforcement methods across single and group configurations of columns.

Stress Concentration Ratios (SCR)

SCR variations provide insights into load resilience and structural integrity under various design and layering conditions.
The geogrid's inclusion significantly alters stress distribution across embankment systems, enhancing support capacity.

Effects of Reinforcement and Configuration

Different arrangements of reinforcement layers lead to varied structural performance, indicating optimization through design complexity.
The study explores effects of geogrid stiffness, drainage layer thickness, and modular ratio on settlement and stress responses.

Consolidation and Time-Settlement Analysis

Time-settlement graphs highlight the relation of consolidation with geosynthetic reinforcement and emergent settlement patterns.
Variations in excess pore water pressure are monitored to assess drainage effectiveness during and after loading conditions.

Arching Effects in Embankments

Arching phenomena are analyzed to understand load transfer mechanisms, critical for the design of effective geosynthetic systems.
The study outlines interactions between lateral bulging and vertical stress distributions under different loading scenarios.

Summary of Analytical Techniques and Findings

The document provides comprehensive tables summarizing parameters, properties, and results critical to understanding soil reinforcement interactions.
A full range of graphical representations elucidates complex relationships between design parameters and structural performances.

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Description

Explore the performance evaluation of encased stone columns used in embankments, with a focus on geosynthetic materials as basal reinforcement. This thesis presents findings relevant to civil engineering and offers insights into contemporary practices in terrain stabilization.