Foundation Design Workflow for Structural Engineers

The Shared Design Boundary

Foundation design crosses structural and geotechnical responsibilities. The structural engineer defines reactions, stiffness, load path, concrete or steel capacity, and compatibility with the supported structure. The geotechnical engineer defines the ground model, resistance, movement, earthwork, groundwater, and construction requirements.

Problems arise when one number crosses that boundary without its assumptions. An allowable bearing pressure is incomplete unless its load level, net or gross basis, footing size, embedment, settlement criterion, groundwater condition, and bearing material are understood.

Step 1: Read The Geotechnical Report As A Design Document

Identify the recommended foundation systems and the conditions attached to each. Trace the recommendations to boring logs, laboratory data, groundwater observations, fill limits, and site grades.

Record:

• Required bearing material and founding elevation.
• Allowable or factored resistance and design format.
• Net versus gross pressure convention.
• Footing width or depth limits used in settlement evaluation.
• Estimated total and differential settlement.
• Sliding, passive, uplift, and lateral parameters.
• Frost, expansive-soil, collapse, liquefaction, scour, and seismic requirements.
• Earthwork, drainage, observation, and proof-testing requirements.

Issue a request for clarification when structural loads, grades, or foundation geometry fall outside the report scope.

Step 2: Organize Reactions At A Common Reference

Create a foundation reaction schedule containing service and factored combinations. Include axial compression, uplift, two shears, two overturning moments, and torsion where relevant. State the reference point and elevation.

Do not combine the maximum value of every component from unrelated combinations. Preserve the simultaneous reaction set for each governing case.

Moving reactions from column base to footing base requires equilibrium:

Include pedestal height, footing thickness, shear offset, self-weight, backfill, and buoyancy as required by the design basis.

Step 3: Select And Size A Trial Foundation

Use service loads with allowable pressure for preliminary area:

Lay out practical dimensions that respect property lines, utilities, pits, adjacent footings, slopes, and excavation access. For exterior columns, consider combined or strap footings before accepting severe eccentricity.

For deep foundations, establish a trial element type, section, length range, spacing, and cap arrangement using project-specific resistance data and installation constraints.

Step 4: Check Contact Pressure And Stability

For shallow foundations, calculate full biaxial corner pressures and kern status. Use partial-contact analysis where needed. Check sliding, overturning, and uplift with explicit assumptions about interface friction, adhesion, passive resistance, anchors, and drainage.

Service pressures should be compared with compatible allowable criteria. Factored soil reactions used for concrete design should satisfy equilibrium with the factored structural actions and the selected contact model.

Step 5: Check Movement

Review geotechnical settlement estimates against the actual footing dimensions and reactions. Compare total settlement, differential settlement, and rotation with structural, architectural, facade, equipment, piping, and utility tolerances.

Where the report provides only a general estimate, identify whether the foundation layout needs a project-specific settlement profile. Mats, tower-podium systems, heavily unequal columns, and variable fill frequently need more coordination.

Step 6: Complete Structural Design

For spread footings, check punching shear, one-way shear, flexure, bearing, dowels, anchors, development, cover, durability, and minimum reinforcement. For combined footings and mats, include longitudinal distribution, two-way plate behavior, stiffness, joints, and concentrated reactions.

For deep foundations, check the pile or shaft section, reinforcement, driving or handling stresses where applicable, unsupported length, connection to cap, group layout, cap shear and flexure, anchorage, seismic detailing, and durability.

The structural capacity should not exceed the geotechnical resistance or acceptance framework without coordinated revision.

Step 7: Coordinate Drawings And Specifications

Foundation documents should show plan dimensions, elevations, material strengths, reinforcement, reactions or schedules, founding criteria, required observation, groundwater assumptions, and actions for unsuitable conditions.

Avoid ambiguous notes such as "verify soil" without defining who verifies it, what acceptance means, and what happens if conditions differ. Reference the geotechnical report correctly and resolve conflicts between drawings, specifications, and report recommendations.

Step 8: Plan Construction Verification

Define hold points and records before construction. Shallow-foundation verification may include excavation observation, proofrolling, density testing, elevation survey, and concrete preplacement inspection. Deep-foundation verification may include installation logs, dynamic monitoring, integrity testing, static load testing, material tests, and acceptance criteria.

Design changes during construction should be checked against the original ground model and load path, not approved as isolated field dimensions.

A Compact Review Checklist

• Compatible service and strength design formats.
• Reactions resolved at foundation level.
• Net or gross pressure basis stated.
• Final geometry used for pressure and settlement.
• Groundwater and buoyancy included.
• Full-contact or partial-contact assumption stated.
• Total and differential movement reviewed.
• Structural strength and detailing completed.
• Construction and acceptance requirements shown.
• Geotechnical and structural documents coordinated.

References And Further Reading

• FHWA Checklist and Guidelines for Review of Geotechnical Reports and Preliminary Plans and Specifications.
• FHWA GEC 6, Shallow Foundations.
• FHWA GEC 15, Acceptance Procedures for Deep Foundations.
• Current governing load, concrete, steel, and bridge standards as applicable.

FAQ

Can structural design begin before the geotechnical report is final?

Preliminary studies can begin with clearly labeled assumptions, but final geometry and detailing should be reconciled with the completed ground model and recommendations.

Which loads should be sent to the geotechnical engineer?

Provide simultaneous service and factored reaction sets, including compression, uplift, shear, and moments at a stated reference elevation. Also provide movement criteria and likely foundation dimensions.

Who checks settlement compatibility?

The geotechnical engineer estimates ground movement; the structural engineer evaluates how that movement affects the structure and its components. The conclusion requires coordination between both.