Shallow Foundations

When a structure is built, its loads don’t stop at grade. Every column, wall, and slab transfers weight downward through the substructure and into the ground. Shallow foundations are the structural systems that do this work, distributing building and equipment loads to soil layers near the ground surface. They’re the most widely used foundation system in construction, selected when competent soil exists close to the surface and loads fall within the range that near-surface bearing strata can reliably support.

A shallow foundation is a load-bearing substructure element that transfers structural loads from a building or facility to soil or rock near the ground surface, typically at a depth (D) less than or equal to the foundation width (B). Common forms include spread footings, strip footings, mat foundations, and combined footings, each selected based on load distribution requirements and soil bearing capacity.

The team at Vista Projects, a multi-disciplinary engineering firm serving energy and industrial capital projects across Calgary, Alberta and Houston, Texas, has specified and coordinated shallow foundation systems across dozens of industrial facilities. This work has given the firm direct insight into how foundation selection ripples through civil, structural, and geotechnical disciplines simultaneously.

How Shallow Foundations Work

A shallow foundation spreads the incoming load over a larger soil contact area than the structural element above it. A column carrying a concentrated load, for example, bears on a footing with a significantly larger footprint, reducing the load per unit area (or bearing pressure) that the soil must resist.

The defining characteristic of a shallow foundation is its embedment depth. By convention, a foundation is considered shallow when its depth (D) is less than or approximately equal to its width (B), expressed as D ≤ B, though some references accept D up to 2B depending on soil and loading conditions. This distinguishes shallow foundations from deep foundations such as driven piles or drilled shafts, which bypass weak near-surface soils to transfer loads to competent strata at greater depth.

Types of Shallow Foundations

Shallow foundations aren’t a single form but a family of substructure elements, each suited to different load configurations and site conditions.

Spread Footings (Isolated Footings)

A spread footing, also called an isolated footing or column footing, is a discrete pad of reinforced concrete placed beneath a single column or support point. Its geometry is typically square or rectangular, sized so that the total column load, spread across the footing’s base area, produces a net bearing pressure within the soil’s allowable bearing capacity. The footing is thicker at the column face and may be stepped or tapered depending on depth and load requirements.

Spread footings are the most common form of shallow foundation. They’re cost-effective to design and build, work well for structures with regular column grids, and are standard across a wide range of industrial support structures, from process building columns to equipment pedestals carrying moderate concentrated loads.

Strip Footings (Continuous Footings)

A strip footing, also referred to as a continuous footing, is an elongated reinforced concrete element that runs continuously beneath a load-bearing wall or a closely spaced row of columns. Rather than serving a single point of load, the strip footing distributes wall loads or line loads uniformly along its length, transferring them to the soil over a broad, linear contact area.

Strip footings are the standard foundation type for load-bearing masonry and concrete walls, perimeter foundations of industrial buildings, and pipe rack bases where columns are closely spaced.

Mat Foundations (Raft Foundations)

A mat foundation, also called a raft foundation, is a single, continuous reinforced concrete slab that extends beneath an entire structure or a substantial portion of it. Rather than concentrating bearing pressure beneath individual footings, the mat spreads the total structural load across the full slab area, producing a lower and more uniform net bearing pressure on the supporting soil.

Mat foundations are specified when individual spread footings would cover more than roughly half the building footprint (at which point a full mat becomes more economical), when soil bearing capacity is relatively low but still adequate for shallow founding, or when differential settlement between column locations must be controlled. In industrial construction, mats are common beneath large compressor buildings, process modules, control buildings on variable soil, and structures carrying heavy, distributed equipment loads.

Combined Footings

A combined footing serves two or more columns on a single footing element. It is used when columns are spaced too closely for individual isolated footings to function independently without overlap, or when an exterior column sits near a property line and cannot be centred on its own footing. The combined footing is designed so that its centroid aligns with the resultant of the combined column loads, producing a uniform bearing pressure distribution across the soil contact area.

Combined footings are less common than isolated or strip forms, but a practical solution in constrained industrial facilities and multi-story structures.

Bearing Capacity: The Governing Design Factor

The viability of any shallow foundation depends on the soil’s ability to carry the load imposed on it. Bearing capacity is the measure of that ability, defined as the maximum load per unit area a soil can sustain without experiencing shear failure or unacceptable settlement.

Geotechnical practice distinguishes between two values. The ultimate bearing capacity is the theoretical maximum at which the soil fails in shear. The allowable bearing capacity applies a factor of safety (typically 2.5 to 3.0) to that value, producing a working pressure that accounts for uncertainty in soil properties and load estimation. Foundation design is governed by the allowable value.

In practice, settlement governs more often than outright shear failure. Even when bearing pressures remain well within allowable limits, compressible soils will consolidate under sustained load, producing downward movement. Differential settlement (uneven settlement between foundation elements) is particularly damaging, inducing bending stresses in structures not designed to accommodate them.

Embedment Depth and Frost Considerations

Minimum embedment depth is governed by several factors that vary by climate, soil type, and applicable building code.

The most critical factor in cold climates is frost depth, the depth to which the ground freezes seasonally. Foundations must bear below the local frost line to avoid frost heave. In Alberta, frost depth varies significantly by region. Southern Alberta, including Calgary, sees frost depths of approximately 1.2 metres. Central Alberta, including Edmonton, typically requires 1.5 metres. Far northern communities can reach 2.4 metres or more. These regional differences directly set minimum embedment depth requirements regardless of bearing capacity considerations, and designers should verify the applicable frost depth with local authorities having jurisdiction. In warmer climates, such as Houston, where frost isn’t a governing factor, minimum embedment still applies for soil stability and protection from surface disturbance.

Beyond frost, adequate embedment depth ensures sufficient overburden pressure on the bearing stratum, which contributes to bearing capacity and provides protection from surface erosion and construction disturbance. Minimum depth requirements are governed by the National Building Code of Canada, applicable provincial codes, and local jurisdiction requirements.

When to Use Shallow Foundations, and When Not To

Foundation selection is ultimately driven by soil conditions, load characteristics, and project economics. Shallow foundations are the preferred choice when conditions support them. They’re faster to construct, require less specialised equipment, and cost substantially less than deep foundation systems.

Use shallow foundations when: competent soil with adequate allowable bearing capacity exists at or near the surface; structural or equipment loads are light to moderate; settlement risk is within acceptable tolerances for the structure type; the site is not subject to problematic conditions such as expansive soils, collapsible soils, or a high groundwater table that would compromise construction or long-term performance; and project economics favour a cost-effective, near-surface solution over the greater expense of deep foundations.

Avoid shallow foundations when: near-surface soils are weak, soft, or highly compressible, including soft clays, organic soils, and uncontrolled fills, and cannot provide adequate bearing capacity at practical depths; imposed loads are heavy enough that the required footing area becomes impractical; differential settlement cannot be tolerated by the structure or the equipment it supports; groundwater is high enough to require extensive dewatering during construction or to reduce effective soil bearing pressure over time; or site investigation reveals conditions such as expansive clays or collapsible soils that would cause unacceptable movement regardless of footing size.

When conditions are borderline, ground improvement combined with shallow foundations is sometimes evaluated as an intermediate option.

Shallow Foundations in Industrial and Energy Projects

Industrial facilities, including process plants, compressor stations, tank farms, pipe rack structures, and auxiliary buildings, rely heavily on shallow foundations for a broad range of support functions. Where site investigation confirms adequate bearing capacity in near-surface soils, shallow foundations are the default specification for cost efficiency and constructability.

In the energy sector, particularly in western Canada, where glacial till, dense gravels, and other competent near-surface soils are common, shallow foundations are regularly used for:

• Structural column footings for process buildings, maintenance facilities, and warehouses
• Equipment pads supporting pumps, heat exchangers, air coolers, and moderate-load compressor skids
• Pipe rack footings carrying piping, cable trays, and instrument conduit
• Control building and electrical substation foundations on competent ground
• Tank annular ring foundations and ring wall foundations for above-ground storage tanks

On complex energy and industrial capital projects, civil foundation design integrates with structural framing, equipment layout, process requirements, and site grading. These disciplines must work from shared data and aligned assumptions to avoid costly coordination errors downstream. 

Vista Projects’ multi-disciplinary engineering model coordinates civil, structural, mechanical, electrical, and instrumentation disciplines from a single data-centricA data-centric outlook is a core concept in digital project execution architecture where data is viewed as the most important and perpetual ... platform, adding direct value to capital project execution. This integrated approach supports informed decision-making across disciplines and helps protect total installation costThe total installed cost refers to the final cost of designing, fabricating and building a capital project or industrial asset. Various phas... by reducing the coordination gaps that drive rework and schedule overruns.

Limitations of Shallow Foundations and Failure Considerations

No foundation system works everywhere, and shallow foundations carry specific vulnerabilities that need to be recognised during site evaluation and design.

Settlement is the most frequently encountered performance issue. Even where bearing pressures remain within allowable limits, compressible soils consolidate under sustained structural load over time. Differential settlement, where one part of a structure settles more than another, induces bending and shear stresses that can crack walls, distort framing, and damage equipment connections.

Expansive soils, specifically clay-rich soils that absorb moisture and swell then shrink as they dry, pose a serious risk to shallow foundations, particularly in Alberta and the Canadian prairies. Seasonal volume changes in expansive clays can exert significant uplift pressure on footings, causing heave and structural distress that accumulates over multiple cycles.

Collapsible soils, which are dry, loosely structured soils that consolidate rapidly when wetted, present the opposite problem: sudden, large-magnitude settlement when surface water or irrigation introduces moisture to the bearing stratum.

High groundwater reduces the effective unit weight of soil above the water table, lowering bearing capacity, and can create hydrostatic pressure complications both during construction and over the life of the foundation.

Frost heave results from inadequate embedment depth relative to the local frost line, allowing seasonal ice formation to lift foundation elements.

Bearing failure (actual shear failure of the soil mass) occurs when applied bearing pressure exceeds the soil’s ultimate bearing capacity. It’s less common than settlement-related issues in well-designed foundations, but it remains a governing limit state that geotechnical investigation and conservative design factors are specifically intended to prevent.

Geotechnical Investigation: The Foundation of Shallow Foundation Design

No shallow foundation system should be specified without a preceding geotechnical investigation. The type, depth, and dimensions of any foundation element are determined by soil conditions at the specific project site, and those conditions must be measured, not assumed.

A geotechnical investigation involves soil borings or test pits, in-situ testing (such as standard penetration tests or cone penetration tests), and laboratory analysis of recovered samples to characterise soil strength, compressibility, and groundwater conditions. The output is a geotechnical report that provides allowable bearing capacity values, settlement predictions, minimum embedment depth recommendations, and any site-specific constraints that govern foundation design.

On any well-managed capital project, the geotechnical engineer’s recommendations drive foundation selection. Civil and structural foundation design proceeds from those recommendations.

In Alberta, geotechnical engineering services are delivered under the oversight of APEGA (Association of Professional Engineers and Geoscientists of Alberta). Engineering services in other provinces are governed by their equivalent provincial regulators. Clients should verify the applicable authority having jurisdiction (AHJ) for their project location.

Frequently Asked Questions

What is the difference between shallow foundations and deep foundations?

Shallow foundations bear at or near the ground surface, with an embedment depth (D) generally less than or equal to the foundation width (B). They rely on near-surface soil to provide bearing capacity. Deep foundations, including driven piles, drilled shafts, and caissons, extend through weak near-surface soils to transfer loads to competent bearing strata at greater depth. The choice between them is governed by surface soil conditions, load magnitude, and project economics. Where near-surface soils are competent, shallow foundations are substantially more cost-effective. Where they are not, deep foundations are required regardless of cost.

What soil conditions are required for shallow foundations?

Shallow foundations require competent soil, specifically soil with sufficient allowable bearing capacity, at or near the surface. Suitable conditions include dense sands, well-graded gravels, stiff clays, dense glacial till, and bedrock at shallow depth. Problematic conditions that typically preclude shallow foundations include soft clays, organic soils, loose fills, expansive clays, and collapsible soils. Groundwater at or near the proposed bearing elevation also warrants careful evaluation. The geotechnical investigation for each project determines whether surface soils are adequate for shallow founding.

When should a mat foundation be used instead of spread footings?

A mat foundation is typically preferred when: individual spread footings would cover more than approximately 50% of the building footprint, making a continuous slab more economical; soil bearing capacity is low enough that spreading the total load across a larger area is necessary to stay within allowable limits; or differential settlement between column locations must be minimised, since a rigid mat distributes loads more uniformly than discrete footings. Mat foundations are also used where column spacing is irregular or where the structure carries heavy, distributed loads over a large area.

What is the role of embedment depth in shallow foundation design?

Embedment depth determines how far below grade a shallow foundation bears. It is governed by frost depth in cold climates, as foundations must bear below the local frost line to prevent frost heave, as well as minimum overburden requirements for bearing capacity, protection from surface disturbance, and applicable building codes. In Alberta, frost depth requirements vary by region, from approximately 1.2 metres in southern areas such as Calgary to 1.5 metres in central Alberta and greater depths in far northern communities. These values directly control minimum embedment depth independent of load considerations. Embedment depth also affects the bearing capacity of the supporting soil, since deeper bearing generally provides greater confinement and higher resistance. 

What is a geotechnical investigation, and why is it required for shallow foundations?

A geotechnical investigation is a structured site investigation program that characterises subsurface soil conditions through soil borings, test pits, in-situ testing, and laboratory analysis. For shallow foundation design, it provides the critical inputs that cannot be assumed: allowable bearing capacity at the proposed bearing elevation, expected settlement under design loads, groundwater conditions, frost depth, and identification of any problematic soil types that would preclude shallow founding. Without a geotechnical investigation, foundation design has no reliable basis, as soil conditions vary substantially across sites and cannot be inferred from regional generalisation.

What are the main limitations of shallow foundations?

The primary limitations of shallow foundations are: dependence on competent near-surface soil, which is not present at every site; vulnerability to settlement, particularly differential settlement, under sustained loading on compressible soils; susceptibility to expansive soils that cause heave through seasonal moisture-driven volume changes; risk of frost heave in cold climates when embedment depth is insufficient; reduced performance in high groundwater conditions; and load magnitude constraints, as very heavy concentrated loads may require bearing areas that are impractical at shallow depth, making deep foundations more appropriate.

Conclusion

Shallow foundations, including spread footings, strip footings, mat foundations, and combined footings, represent the most cost-effective foundation system available when site conditions support them. Suitability depends on soil bearing capacity near the surface, load magnitude and distribution, settlement tolerance, and site-specific constraints such as frost depth, groundwater, and soil type. When those factors align, shallow foundations deliver reliable, economical load transfer without the cost and complexity of deep foundation systems.

Foundation selection is never purely a design exercise. It requires geotechnical investigation, discipline coordination, and engineering judgment specific to each project. Vista Projects is a multi-disciplinary engineering firm with over 40 years of experience delivering integrated engineeringThe process of integrated engineering involves multiple engineering disciplines working in conjunction with other project disciplines to e... services for energy and industrial facilities across Canada and the United States. If your project requires coordinated civil and structural engineering expertise as part of a broader capital project scope, we would be happy to show you how our team approaches complex project execution.

Note: Certifications and licensure requirements vary by jurisdiction. This article reflects Canadian standards and Alberta provincial regulations. For projects in other provinces or jurisdictions, verify requirements with the appropriate provincial authority having jurisdiction.