2015 Michigan Bridge ConferenceMDOT Geotechnical Perspective

Ryan Snook, P.E.MDOT Foundation Analysis Engineer

Geotechnical Engineering

• What is it?– Geotechnical engineering is the branch of

civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but also has applications in military, mining, petroleum and other engineering disciplines that are concerned with construction occurring on the surface or within the ground. (Ref. Wikipedia)

Geotechnical Engineering

• How does this relate to transportation?– All constructed items are supported on soil or

rock.• Roads, bridges, walls, culverts, signs, tunnels, ITS,

utilities, etc.– Need to provide adequate support for each

structure throughout it’s life in order for it to operate as intended.

Geotechnical Engineering

• How does this relate to bridges?– Must provide adequate support throughout

the 100 year design life. – Must account for events during the design life,

such as flooding, downdrag and scour.– Check design for extreme events such as the

500 year scour event.

MDOT Process

• Design– Early preliminary engineering– Preliminary Engineering

• Construction• Maintenance

COMMUNICATION!!!!!!!

Early Preliminary Engineering

• Used primarily on larger projects or projects where there is limited to no soil information.– Site visit– Perform limited number of soil borings– Provide preliminary/conceptual

recommendations for the proposed project

Preliminary Engineering• Road

– Task 3510 – Roadway Geotechnical Investigation

• Bridge– Task 3325 – Geotechnical Structure Site

Characterization– Task 3530 – Geotechnical Foundation

Engineering Report– Task 3815 – Geotechnical Structure Design

Review

Task 3325 – Site Characterization• Review the structure study.• Review existing plans, soil borings, lab

data, and construction records.• Talk to maintenance personnel. Are there

any recurring issues?• Perform a site visit. Walk the entire site.• Take soil borings.• Perform laboratory testing.• Provide geotechnical data report.

Soil Borings

• Number and depth as indicated in the MDOT Geotechnical Investigation Requirements for Structures– Minimum 1 soil boring at each substructure– Minimum 20 ft beyond the estimated pile tip

elevation– Deep enough to adequately analyze spread

footings for bearing capacity, settlement and overall (global) stability (minimum 50 ft or to rock).

Soil Borings

• Determine state plane coordinates for each soil boring

• Determine an elevation for each soil boring

• Prepare and provide soil borings in MicroStation format in accordance with MDOT requirements

Soil Borings

• Special Considerations– Artesian groundwater conditions

• Install piezometer to identify static groundwater elevation

– Peat/Marl/Very soft clay• New construction• Widening

– Part-width construction• Should perform additional soil boring near stage

line

Task 3530 – Foundation Report

• Review the scour analysis report• Communicate with the bridge engineer

and hydraulic engineer– Is the proposed structure going to work?– Are there any modifications to the structure

that can provide more cost effective foundations?

Task 3530 – Foundation Report

• Provide geotechnical recommendations in accordance with AASHTO, FHWA and MDOT requirements– New projects – AASHTO LRFD– Widening projects – AASHTO LFD

• Review guidance in the Michigan Bridge Design Manual

Task 3530 – Foundation Report• Provide information for standard pay items

– Pile size, pile lengths, pile points, etc.• Use standard pay items whenever

possible.• Provide any Unique Special Provisions

– Use Previously Approved Special Provisions when possible.

– Modify PASP special provisions when possible

– Submit unique special provisions for review as early as possible

Task 3530 – Foundation Report• Construction Considerations

– Are pile driving vibrations a concern? Does it need to mitigated, monitored or both?

– Is steel sheet piling needed? If so, should it be left in place or removed?

– Groundwater control– Are undercuts necessary?– Slope angles for excavations– For part width construction can it be done.

Are there any special procedures needed to keep the existing bridge in service.

Task 3815 – Design Review

• Review the OEC plans to make sure recommendations are incorporated correctly.

• Look over the construction staging. – Can it be built? – What are the risks? – What mitigation measures are needed.

• Review pay items and quantities.

Construction

• Geotechnical engineering doesn’t end with design.

• Need to be involved in construction in order to confirm or adjust geotechnical recommendations.– Is the piling being installed correctly and near

the estimated pile tip elevation?– Is there adequate soil bearing capacity? Are

undercuts necessary?

Construction

• Construction assistance contracts for geotechnical engineering consultants should be established.

• Need access for e-construction.

Maintenance• Need to consider how geotechnical

engineering affects maintenance– Will there be continual settlement over time?

• Are steps needed to limit future settlement?– Drainage/seepage– Rideability– Safety– Ability to mow steep slopes– Long term aesthetic issues (turf

establishment, cracking/differential movement, etc.)

Questions?