RNS
Browse Projects > Detailed View

Soil Structure Interaction Construction Dynamics of Transportation Earthworks and Structures

Description:

Background

Today’s computational modeling tools and associated visualizations allow for a more comprehensive understanding of soil mechanics problems than the simplified analytical solutions of the past. Yet many relatively common geotechnical situations have not been re-explored in either parametric studies or investigated using step-wise construction sequences. An improved understanding of the behavior of embankments, slopes, and foundations when modeled through various construction and life-cycle events can be gained if relatively simple foundation elements and geotechnical features are more fully explored using current powerful computational modeling tools. Exploring the influence of geometry, material properties, reinforcing elements, construction events, or life cycle changes and the subsequent impact on geotechnical and geo-structural performance, can lead to new insight and reveal areas for additional research and practice improvement.

Research Description

Research is needed to examine, and in some cases re-explore, “real world” geotechnical situations, assessed analytically in the past, using modern computational modeling methods. This will allow new insight on deformable-body behavior especially when changes in geometry, material properties, structural components, extent of excavations and fills, and effects of the actual construction loading sequence can be included allowing the subsequent impacts on performance, risk, reliability, and safety to be examined in more comprehensive detail and in the current LRFD framework, rather than a single “safety factor” which may not appropriately capture service limit state or other performance considerations. Improved understanding of stress/force and strain/displacement characteristics will help improve geotechnical practice by relating performance to LRFD strength and service considerations.

Objective:

The proposed project has the following significant objectives:

Apply computational modeling tools to several basic transportation construction features, examining how the soils and structures interact and react to construction and life-cycle events with time, with an emphasis on stress and deformation characteristics relating to LRFD strength and service considerations.

Study the impact of construction sequence and methods on geotechnical behavior, comparing results with traditional analytical methods, where they exist.

Through investigation of basic problems of bearing capacity, soil-structure interaction, and slope stability, use computational modeling to reveal the impact of changes in geometry, material properties, time, deformation, reinforcing and structural elements, and sensitivity to site changes over time (such as from erosion, scour, man-made excavations, soil stockpiles and surcharges, and similar external effects).

Provide modeling to use as a comparison to real world case histories and project observations from State DOT and other experience.

Make the models available to educators and professional groups to aid in teaching and continuing education.

Benefits:

An improved understanding of the impacts of superposition of effects and construction sequencing, through computational models, will aid in the effective establishment of appropriate service limit state and strength limit state performance criteria in the LRFD framework (e.g. use of spread footings based on construction point methodologies; improved understanding of dragload; and performance of embankments with various side slopes and/or reinforcing).

Results for various cases could be compared against guidance in manuals (NAVAC, state DOT) for established geometric cases (such as loading and situations with slopes or live vehicle load).

The visualizations of construction sequencing and the mechanics of how foundations and geotechnical works perform while being constructed has not been well investigated generally- although it certainly has been for complex project specific cases- these cases however seldom are referenced or provided for use in general geotechnical training and education.

Computer modeling output and visualizations of stress and strain (load and deformation) can be very effective teaching and educational aids for use in college curriculums and for continuing education FHWA/NHI etc.

Related Research:

A literature review would need to be conducted, but to the best of our knowledge a general analysis of several types of transportation foundations during the construction and service life has not been conducted.

Tasks:

The research tasks to include the following:

An examination using computational modeling tools to investigate stress/strain and load/deformation of the following six areas:

  1. An assessment of soil stresses/deflections on a ‘typical’ dimension of a bridge spread footing as seen from a construction sequence standpoint (e.g. foundation, stem, backfill, beams, deck, rail, service etc.) [6+ construction stages and both soft and stiffer foundation soils]. Continue the model to simulate at least 2 possible modes of failure (e.g. due to soil loss or erosion of the foundation or overstressing).
  2. An assessment of soil stresses/deflections on a foundation on piles or shafts of a bridge as seen from a construction sequence standpoint (e.g. foundation, stem, backfill, beams, deck, rail, etc.) to investigate positive and negative side friction distribution and end-bearing under different conditions of soil strength and pile toe stiffness. [several construction stages and several soil types for side resistance and base resistance; potentially also multi-layered systems or external effects, such as liquefaction]. Continue the model to simulate at least 2 possible modes of failure (e.g. due to soil loss or erosion of the foundation or overstressing).

  3. An assessment of soil stresses/deflections on a shallow foundation placed over a column supported embankment using auger-cast or controlled modulus columns or similar foundation elements for a bridge as seen from a construction sequence standpoint (e.g. foundation, stem, backfill, beams, deck, rail, etc.) [dragload]

  4. What do stress and displacement profiles look like below cantilever walls, MSE walls, GRS-IBS walls, and other types of complex soil reinforced structures or those supported on deep foundations?

  5. What are the impacts of drainage clogging [failure] on cantilever walls (if hydrostatic pressure builds)? Continue the model to simulate at least 2 possible modes of failure (e.g. due to soil loss or erosion of the foundation or overstressing).

  6. Examine the deflection below a new 30ft. embankment over soft ground as it is constructed in stages. Include an examination of reinforced 1H:1V side slopes; unreinforced 2H:1V side slopes, with internal reinforcing; unreinforced 2H:1V side slopes without internal reinforcing; and unreinforced 3H:1V side slopes without internal reinforcing. Continue the model to simulate at least 2 possible modes of failure (e.g. due to soil loss or erosion of the foundation or overstressing).

The research tasks may also include:

An examination of the following additional subject areas:

  1. Compound movements- construction of a bridge abutment in two stages, or construction of a new embankment adjacent to an existing embankment [modeling performance of new construction’s impacts on original construction].

  2. What are the impacts of excavation in front of a retaining wall supported on piling. How do displacements differ depending on the slope of the excavations.

  3. How are stresses distributed in column-supported-embankments with different amounts of soil cover above the columns?

  4. How does settlement below a foundation react to use of prefabricated vertical drains [triangular and square spacing]?

  5. Active, Passive, At-rest pressure on earth walls. What if a cantilever wall is constructed on compressible fill and the system rotates backward? What are the global impacts?

  6. What are the impacts of changing the friction angle of soils in the backfill of cantilever walls?

  7. How do retaining walls behave when either the slope above or below the wall changes from flat to various inclinations?

  8. How do retaining walls on piling react to different degrees of slope in front of the wall?

  9. How does settlement occur below a foundation above variable soils (different deformation character)?

  10. Are loads from impacts to traffic barriers on tall walls (MSE or cantilever) transmitted to foundation elements?

  11. How do traditional and integral abutments comparatively behave due to thermal cycles?

Implementation:

Departments of Transportation and other infrastructure owners (such as FHWA Federal Lands) can immediately benefit from the work, improving training guides and educational materials.

Any insights from the work can also be immediately used to improve policy and procedures and/or focus new and additional research efforts.

The most significant benefit is through an improved understanding of service limit and strength limit performance considerations. Computational modeling can aid in providing visualizations which show how performance is impacted at service limit and strength limit thresholds, which could be used to adapt the code to better reflect construction sequence and the impacts of other external life-cycle events.

Relevance:

Geotechnical engineering is complicated and frequently there can be a superposition of measured effects such that unexpected results are observed from expected events. The geotechnical and geo-structural engineering communities will benefit from this research, in addition to teachers and educational institutions. The improved understanding through the thoughtful examination of ‘common’ transportation soil mechanics “problems” in a computational modeling setting will provide a valuable basis for geotechnical education- whether for undergraduate students first learning or practicing engineers in a continuing education setting. Force, deflection, settlement, creep, pore-water-pressure dissipation and structural elements of various strengths and stiffnesses interacting- considering changes in geometry, construction staging, and construction practice- will be examined to show the impact of various influences.

Sponsoring Committee:AKG60, Geotechnical Instrumentation and Modeling
Research Period:12 - 24 months
Research Priority:High
RNS Developer:Derrick Dasenbrock, PE, D.GE, F.ASCE Geotechncial Engineer Federal Highway Admiration, Resource Center 12300 W. Dakota Ave, Lakewood, CO, 80228 202.923.0972 derrick.dasenbrock@dot.gov
Source Info:Committee members and friends.
Date Posted:07/21/2020
Date Modified:02/10/2021
Index Terms:Soil structure interaction, Earthwork, Computer models, Geotechnical engineering, Load and resistance factor design,
Cosponsoring Committees: 
Subjects    
Highways
Construction
Design
Geotechnology
Bridges and other structures

Please click here if you wish to share information or are aware of any research underway that addresses issues in this research needs statement. The information may be helpful to the sponsoring committee in keeping the statement up-to-date.