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Design of Rigid Inclusions for Embankment Support considering Load Transfer and Installation Effects

Description:

Rigid inclusions are grouted or cemented columns used to improve soft soils. They have been increasingly used in practice in the United States, mostly for embankment support in transportation applications. There are several types of equipment available in the market to install rigid inclusions with different trade names (e.g., controlled modulus columns, grouted impact piers, cast-in-place ground improvement elements, and augered pressure grout columns). Installation of some of these columns causes full displacement of their surrounding soils, while others result in partial displacement. Installation procedures for rigid inclusions and their effects on soils depend on the type of equipment and the type of soil and are therefore different. Rigid inclusions are often installed under a load transfer platform to support embankment loads. Different equipment and installation procedures may cause ground subsidence and/or heave as well as lateral displacement; change the properties of the surrounding soils at different distances and depths; and affect load transfer of rigid inclusions in these soils. Downdrag forces often exist within the upper portion of rigid inclusions under embankments. The distribution of the downdrag forces is hard to determine. Rigid inclusions under the slopes of embankments are subjected to lateral thrust in addition to axial and downdrag forces. Bending resistance of rigid inclusions is one of the design issues. Unfortunately, no well-accepted design methods are available to consider load transfer in rigid inclusions subjected to vertical and/or lateral loads and installation effects on their surrounding soils. No well-established design guidelines are available for the thickness of the load transfer platform and the engineering properties of platform fill. Research is needed to quantify installation effects from different equipment on different soil types and develop design methods considering their effects in load transfer analysis of rigid inclusions in soils.

Objective:

The main objective of the proposed research is to quantify installation effects of different equipment on different soil types and develop a design method considering their effects in load transfer analysis of rigid inclusions in soils subjected to vertical and lateral loads from embankments. The design method will take into consideration ground movement during installation, changed properties of the surrounding soils after installation, load distribution along rigid inclusions, including toe and side resistance including downdrag forces, lateral resistance of rigid inclusions in slope stability analyses, and the effect of the load transfer platform.

Benefits:

The benefits of developing the design method for rigid inclusions for embankment support include

  • Providing appropriate means to quantify ground movement during installation by different equipment in different soils

  • Considering improved properties of the surrounding soil to create a more economical solution

  • Improving safety through comprehensive and consistent design considerations (e.g., downdrag force and bending resistance) using rigid inclusions

Related Research:

Basu et al. (2010) presented the common practice and design of drilled displacement piles. Simon (2012) provided a brief summary of definition, functions, installation techniques, advantages and drawbacks, load transfer mechanisms, design considerations, and points requiring further research for rigid inclusions*. *ASIRI (2013) developed recommendations for the design, construction, and control of rigid inclusion ground improvements, mainly for building applications. BS 8006-1: 2010 (2010) developed a detailed procedure for designing load transfer platforms over rigid inclusions considering underlying voids, which is very conservative. This RNS calls for the development of a similar document for rigid inclusions for transportation applications.

Tasks:

The proposed research consists of the following tasks:

Task 1: Review Literature and Assess Current Practices

This task includes a comprehensive review of national and international practices for use of rigid inclusions in building applications and transportation earthworks, categorizes different installation equipment and methods, and identifies gaps in understanding of installation effects and load transfer and design of rigid inclusions for embankment support.

Task 2: Evaluate Installation Effects on Surrounding Soils

Perform appropriate studies to evaluate installation effects of rigid inclusions by different equipment and installation methods on different soils (clay and sand). The studies can be physical model tests, field tests, and/or numerical analysis. The evaluation should include but not be limited to ground movement at different distances and depths and changed properties (e.g., density, strength, and modulus).

Task 3: Evaluate load transfer of rigid inclusions under embankments

Perform appropriate studies to evaluate load distributions along rigid inclusions in soils after installation subjected to vertical and lateral loads. The studies should include but not be limited to toe resistance, side friction (including downdrag force), axial capacity, bending resistance of rigid inclusions, and effects of load transfer platforms on load transfer. Field monitoring of a constructed embankment on rigid inclusions is desired.

Task 4: Develop a design method for rigid inclusions under embankments

Develop a comprehensive design method for use of rigid inclusions in soils for embankment support. The design method should include but not limited to ground movement during installation, changed properties of surrounding soils after installation, layout and length of rigid inclusions, load distribution, axial capacity, bending resistance of rigid inclusions, and settlement and stability of embankments.

A budget of $450,000 is estimated.

Implementation:

This research will serve as a basis for development of an implementation plan to be included in FHWA GEC 13 Ground Modification Methods - Reference Manual and design and construction guidance to be included in the AASHTO Bridge Specifications.

Relevance:

Federal and State DOTs, Researchers; representatives from the following departments have indicated this RNS is a critical need: Louisiana Department of Transportation and Development, Ohio Department of Transportation, New Mexico Department of Transportation, Illinois Department of Transportation, and Minnesota Department of Transportation.

Sponsoring Committee:AFS10, Transportation Earthworks
Research Period:Longer than 36 months
Research Priority:High
RNS Developer:Jie Han, University of Kansas; Antonio Marinucci, V2C Strategists, LLC; Jesse Rauser, Louisiana Department of Transportation and Development
Source Info:Cosponsoring Committees
AFS20 Standing Committee on Geotechnical Instrumentation and Modeling
AFS30 Standing Committee on Foundations of Bridges and Other Structures
AFS40 Standing Committee on Subsurface Soil-Structure Interaction
Date Posted:03/28/2019
Date Modified:04/18/2019
Index Terms:Embankments, Soil structure interaction, Load transfer, Installation, Columns,
Cosponsoring Committees:AFS20, Geotechnical Instrumentation and Modeling; AFS30, Foundations of Bridges and Other Structures; AFS40, Subsurface Soil-Structure Interaction
 
Subjects    
Highways
Construction
Design
Geotechnology
Bridges and other structures

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