Foundation Design

The Foundation Engineering Process

Foundation design begins with the geotechnical investigation report — the soil boring logs, lab test results, and bearing capacity recommendations provided by the geotechnical engineer of record. From this data, we determine foundation type, depth, bearing area, and reinforcement for the specific column loads, wind base shears, and seismic overturning moments produced by the structural system above.

Foundation design cannot be separated from the superstructure analysis. Foundation loads — axial compression, uplift tension, biaxial bending, and shear — are extracted directly from the structural model. This ensures that the foundation is sized for the actual load combinations that govern, not conservative rule-of-thumb estimates.

Shallow Foundations

Spread Footings

Individual spread footings support single columns or rows of columns where soil bearing capacity is adequate at shallow depth. Design involves sizing the bearing area for allowable soil pressure, checking for overturning and sliding under lateral load combinations, and designing the footing thickness and reinforcement for flexure, punching shear, and wide-beam shear per ACI 318-19 Chapter 13.

Spread footings are the most common foundation type for steel column bases in our portfolio of tower and support structure projects. The base plate and anchor rod system connects the steel column to the concrete footing, and the design of both elements — base plate and footing — must be coordinated so that the load transfer is complete and the concrete can accommodate the anchor rod embedment forces without splitting or pullout failure.

Combined and Strap Footings

When adjacent column loads are eccentric relative to available bearing area, or when the soil pressure from individual footings would overlap, combined footings or strap footings resolve the problem by distributing load across a larger bearing area. Their design is statically more complex, requiring combined pressure distribution analysis and reinforcement design for the resulting moment and shear diagrams.

Mat Foundations

Mat foundations (raft foundations) distribute the total structural load across the entire building footprint, reducing unit soil pressure and eliminating differential settlement between column points. They are appropriate for weak soils with low bearing capacity, closely spaced columns, or structures where differential settlement must be strictly controlled. Mat design involves soil-spring modelling using the modulus of subgrade reaction and finite element analysis to determine moment and shear demands in the mat slab.

Deep Foundations

Pile Foundations

When shallow bearing strata are inadequate — either due to low bearing capacity, deep groundwater, or consolidating fill — loads must be carried to deeper competent strata through piles. Driven steel pipe piles, precast concrete piles, and timber piles are all applicable depending on soil profile, load magnitude, and local construction practice. Pile design involves axial capacity (both end bearing and shaft friction components), lateral load capacity (Broms method or p-y curve analysis), pile group efficiency, and negative skin friction where consolidating fill is present.

Drilled Shafts (Bored Piles)

Drilled shafts (caissons) are cast-in-place concrete elements formed by rotary drilling to bearing depth. They can carry very high axial loads and are particularly effective in cohesive soils. For tower structures carrying significant overturning moments — such as the Dammam 150 ft steel tower — drilled shafts with enlarged bells or socketed into rock provide the uplift resistance and moment capacity that shallow spread footings cannot achieve economically.

Geotechnical Report Interpretation

Geotechnical reports vary enormously in format and completeness across the fourteen countries we serve. A Saudi Arabian geotechnical report will reference Saudi Aramco Engineering Standards for sabkha soil conditions; a Canadian report will classify seismic site class per NBC 2020 Table 4.1.8.4; a Japanese report will present N-values from standard penetration tests in a format calibrated to JIS standards.

We interpret geotechnical reports from any jurisdiction, extracting the design parameters needed for foundation sizing, and where reports are incomplete, we identify the additional investigation required before foundation design can proceed responsibly.

Multi-Country Soil Conditions

Soil conditions across our project footprint range from the expansive sabkha (salt flat) soils of Saudi Arabia's Eastern Province, which are highly corrosive to unprotected steel and subject to collapse upon wetting, to the earthquake-prone ground conditions of Antalya, Türkiye, where seismic site amplification can double the design spectral acceleration at the surface compared to bedrock values. Florida's coastal geology presents high water tables and variably cemented limestone that requires sonic core sampling for reliable bearing capacity data. Each jurisdiction demands a different approach to geotechnical assessment and foundation design.

What Clients Receive

• Foundation design calculations — Bearing capacity checks, settlement estimates, reinforcement design with ACI-318 clause references, and governing load combinations.
• Foundation layout drawings — Plan locations, dimensions, reinforcement layout, and anchor bolt patterns for every footing.
• Geotechnical parameter summary — Documentation of the soil parameters used, their source in the geotechnical report, and any conservatism applied.
• Recommendations for additional investigation — Where available soil data is insufficient for confident design decisions.