This module is focused on the process for which simple, shallow/spread foundations for bridge abutments are designed from a geotechnical aspect. The module will focus on geotechnical design practices related to foundation bearing capacity, allowable foundation bearing pressure, total and differential settlement, and related design aspects. At the conclusion of this packet, students should have a functional understanding of the geotechnical design development process for bridge foundations, within the context of the entire geotechnical and project design process.
Your firm has been selected to provide geotechnical design recommendations for a stream restoration project along Paradise Creek, through the UI campus in Moscow, Idaho. Your client is Mr. Art Vandelay, P.E., Esq. with Vandelay Industries, Inc. (Vandelay). The project has many facets. One of which is a new pedestrian bridge that must be constructed across the new stream alignment. The bridge will be prefabricated and shipped to the site. However, concrete bridge foundations will be constructed at the site, to support the prefabricated structure. A preliminary site plan is attached, which shows the currently planned bridge configuration. Project funding requires the structure be designed according to AASHTO LRFD Bridge Design Specifications (assume the version provided is the most current, although it is not)
Your firm has performed geotechnical exploration at the site. Laboratory testing has been accomplished on the samples obtained during exploration. This data is attached in Appendix A. AJ Abrams, the EOR has tasked you with performing geotechnical analysis and providing recommendations for typical shallow foundations planned to support the bridge. Vandelay needs allowable bearing pressure recommendations to complete their footing design (recall the requirement to follow AASHTO bridge design specifications)
Deliverable: This single document to be titled “Analysis and Recommendations Summary” should be addressed to the project EOR (your “internal client” with ATeam). This document will not be provided to the client, but will be used as a design tool as the “design development” process evolves.
This single document to be titled “Analysis and Recommendations Summary” should be addressed to the project EOR (your “internal client” with ATeam). This document will not be provided to the client, but will be used as a design tool as the “design development” process evolves.
Analysis/Recommendations Summary (memo and calculations packet)
1. ADMINISTRATIVE ITEMS
a. Not to exceed 15 total pages unless otherwise approved in advance.
b. Page content may include, but is not limited to a combination of text, figures, calculations, sketches, photos, notes, tables, or related visual aids. Create a succinct “package” (practice good engineering synthesis)
c. Use 8.5”x11” format, color and/or B&W, no font restrictions;
d. All drawings to scale, or labeled otherwise;
e. Submit DM-2 deliverable electronically (BbLearn) and as a single .pdf document clearly labeled.
f. Tables, lists, bullets encouraged
g. File documentation quality (not formally submitted to client) HOWEVER, aspects of this document (some text and figures) may be used during meetings and communications with the design team and should be reasonably neat, presentable and professional
h. Your deliverable should be clear, legible, and of sufficient organization befitting your selected career path (hint: you want to be an Engineer someday). Your document may be created and organized as you see fit, but should describe and outline the “assignment’s” goals, your thought process, engineering judgment, analysis results and your findings/recommendations, such that years from now, a person unfamiliar with the project can easily ascertain the basis for the geotechnical design on this project.
2. CONTENT ITEMS – Required or “highly suggested” aspects of memo:
a. Brief introduction and project description (site description, structure description, ATeam’s and your (SE) role, etc.)
b. Explanation of the submittals “goals” (i.e. why are you putting this together and what is the expected outcome?)
c. Analysis approach and available information.
i. What design specifications are your following? What do you know about the site and project? What are they building and what soil/conditions are impacted?
d. Available data summary and synthesis (logs, plans, lab results, crosssections, etc.)
i. Summary, discussion, and selection of engineering parameters (. . . for site model).
ii. Site model and subsurface characteristics
1. General soil condition description;
2. Subsurface geometry, groundwater, proximity/overlay with proposed structures, etc.
3. Selected engineering parameters within the model
e. Engineering calculations and analysis “findings”
i. describe analysis steps and approach;
ii. discuss parameter and output sensitivity
iii. present reasonable predictions/recommendations for the following:
1. Ultimate and allowable bearing capacity (strength limit state)
2. Predicted settlement, both total and differential.
3. Discuss bearing pressure and footing widths (i.e. optimize both service and strength limit states)
4. Coefficient of foundation base siding friction (fs)
5. Equivalent Fluid Pressure (EFP) for the abutment backfill and recommended soil/gravel material.
6. Other geotechnical parameters or information that may be required by Section 10 of the AASHTO Bridge Design Specifications
iv. Summarize your analysis findings to support the ATeam’s final recommendations (to be included in final report, not this internal document).
f. Summary and Geotechnical Recommendations
i. Discuss/summarize/present/outline your overall recommendations for the bridge foundations only (do not include any geotechnical project aspects not directly related to the abutment foundations). Your recommendations/summary should include, but may not be not limited to items such as:
1. footing bearing depth
2. recommended bearing pressure and corresponding settlement estimate
3. any recommended changes or modifications to foundation geometry that are “geotechnically opportune”
4. geotechnical design differences between each abutment, if any.
5. Foundation design alternatives, if applicable.
Paradise Creek Pedestrian Bridge Structural Load Data and Performance Criteria
Structural Loads (what loads the structural engineer estimates will transfer to the foundation system (spread footing)
Pedestrian Bridge Foundation Reactions
o Vertical Dead Load (DC) = 17,000 plf
o Vertical Live Load (LL) = 3,300 plf
o Ignore moments and lateral loading
Requested Design Criteria (what the structural engineer needs from ATeam):
Bearing Capacity (strength limit state):
o Reference AASHTO Bridge Design Specifications