Every industrial facility, energy plant, and capital project is only as sound as the ground it sits on. Soil conditions vary dramatically from site to site, and often within a single site, based on geology, depositional history, groundwater, and prior land use. What lies beneath the surface is invisible until someone goes looking. And the consequences of not looking can be severe: overloaded foundations, unexpected settlement, costly mid-construction redesign, and schedule overruns that compound through every downstream phase of a project.
Soil analysis, or more precisely geotechnical investigation, is the systematic process of characterising those subsurface conditions before design begins. By determining the engineering properties of in-place soils and rock, a well-executed investigation gives the entire project team a reliable picture of what they are building on. For engineering firms working on complex capital projects in the energy and industrial sectors, geotechnical data is one of the earliest and most consequential inputs to structural and civil engineering design.
Vista Projects, a multi-disciplinary engineering firm serving the energy and industrial sectors from offices in Calgary, Alberta and Houston, Texas, has integrated geotechnical investigation findings into foundation design, earthworks planning, and structural decisions across capital projects in both regions, and that hands-on context informs this article.
What Is Soil Analysis in Geotechnical Engineering?
Soil analysis, in the context of geotechnical engineering, is the systematic investigation of subsurface conditions to determine the engineering properties of soil and rock at a project site. The process involves collecting samples and in-situ measurements through field investigation programs, including boring programs and cone penetration tests, followed by laboratory testing to establish the physical and mechanical characteristics of the subsurface materials. The outputs of soil analysis include bearing capacity, compressibility, shear strength, moisture content, and soil classification, all of which inform foundation design, earthworks planning, and risk assessment for construction and capital projects.
Soil analysis in geotechnical engineering is a distinct discipline from agricultural soil testing, and the two are frequently confused by those outside the construction industry.
Geotechnical Soil Analysis vs. Agricultural Soil Testing
Agricultural soil testing evaluates nutrient content, pH, organic matter, and biological activity to inform crop production decisions. Geotechnical soil analysis works with an entirely different set of properties: how strong the soil is, how much it will compress under load, how it drains, and how it behaves under different moisture conditions. That data informs engineering design, not agriculture. The two disciplines use different test methods, different laboratories, different standards, and serve entirely different purposes.
Why Soil Analysis Matters for Construction and Capital Projects
No two sites behave identically. Soils that appear uniform at the surface can transition sharply at depth: competent sand giving way to compressible clay, natural ground becoming historic fill, dry conditions turning into a perched water table. These transitions are not visible without investigation, and they have direct implications for how a structure must be designed and built.
Without a geotechnical investigation, foundation design is an exercise in assumption. Assume too conservatively, and the project is overengineered, with unnecessary cost embedded in oversized foundations. Assume too aggressively, and the consequences range from unacceptable settlement to structural failure. Neither outcome is acceptable on a capital project where the stakes are high and the margins for error are narrow.
Three specific failure modes follow from inadequate soil analysis:
Unexpected settlement. When compressibility is underestimated or undetected, structures settle more than anticipated. That settlement may be uniform, which can sometimes be tolerated, or differential, which places the structure under unplanned bending and shear stress. Differential settlement between adjacent foundations is among the most damaging outcomes of inadequate subsurface characterisation.
Foundation shear failure. When bearing capacity is insufficient for the design loads placed on it, the soil beneath a foundation can fail in shear. The ground yields, and the structure above it moves. This failure mode is uncommon with proper analysis, but can be catastrophic when it occurs.
Construction rework. When unexpected soil conditions are discovered during excavation, including weak zones, fill deposits, or high groundwater, the project team is forced to redesign under schedule pressure. An emergency geotechnical investigation is commissioned after work has already started. Foundations already designed must be redesigned. This pattern is one of the most consistently cited sources of cost overruns on capital projects.
The cost of a thorough soil analysis program is a fraction of the total project cost. The cost of discovering what should have been known before construction began is orders of magnitude larger.
Key Soil Properties Measured in a Geotechnical Investigation
A geotechnical investigation measures a defined set of physical and mechanical soil properties, each one serving a specific purpose in engineering design.
Bearing Capacity
Bearing capacity is the maximum load per unit area that a soil can support without undergoing shear failure. Geotechnical analysis distinguishes between ultimate bearing capacity (the theoretical maximum) and allowable bearing capacity, which applies a factor of safety to produce the design value used by engineers. Bearing capacity is the primary criterion for determining whether a shallow foundation system (spread footings, mat foundations) is viable at a given site, and it defines the maximum structural loads those foundations can safely carry. It is derived from shear strength parameters and foundation geometry, using bearing capacity equations attributed to Terzaghi and extended by Meyerhof and Hansen.
Compressibility and Settlement Potential
Compressibility describes a soil’s tendency to reduce in volume under applied load. In coarse-grained soils, gravels and sands, volume reduction occurs almost instantaneously as load is applied, and the magnitude is small. In fine-grained soils, particularly clays, volume reduction occurs gradually through a time-dependent process called consolidation, during which water is slowly expelled from the soil voids. The rate and magnitude of this consolidation settlement can be substantial and may continue for years after construction. Compressibility parameters, the compression index (Cc), the recompression index (Cs), and the coefficient of volume compressibility (mv), are determined through laboratory consolidation testing and form the basis of settlement predictions.
Shear Strength
Shear strength is the soil’s resistance to sliding or shearing failure along an internal plane. It is defined by two components: cohesion (c), which represents the intrinsic bonding between soil particles, and the internal friction angle (φ), which represents the resistance generated by particle interlocking and friction. Cohesive soils, clays and silts, derive much of their shear strength from cohesion and are sensitive to changes in moisture content and stress history. Cohesionless soils, sands and gravels, rely primarily on internal friction. Shear strength data is essential for slope stability analysis, retaining wall design, lateral earth pressure calculations, and bearing capacity estimation.
Moisture Content
Moisture content is the ratio of the weight of water to the weight of dry soil in a sample, expressed as a percentage. In geotechnical engineering, moisture content is more than a simple measurement. It is an indicator of soil state. For fine-grained soils, moisture content relative to the Atterberg limits reveals whether a clay is in a solid, plastic, or liquid state, which directly affects its strength and compressibility. For construction purposes, moisture content governs compaction behaviour: fill soils must be placed and compacted at or near their optimum moisture content to achieve the target density. In northern climates such as Alberta, moisture content also informs frost-susceptibility assessments, since water-saturated fine-grained soils are vulnerable to ice-lens formation and frost heave during freeze-thaw cycles.
Grain Size Distribution and Plasticity
The distribution of particle sizes within a soil sample, determined by sieve analysis for coarse fractions and hydrometer analysis for fine fractions, defines the soil’s texture and influences almost every other engineering property.
For fine-grained soils, particle size alone is insufficient to characterise behaviour. Plasticity, measured through the Atterberg limits (liquid limit, LL, and plastic limit, PL), describes the range of moisture content over which the soil exhibits plastic behaviour. A high plasticity index (PI = LL − PL) indicates a soil that undergoes significant strength and volume changes with changes in water content, which has important implications for foundation design and earthworks.
How a Geotechnical Investigation Is Conducted
A geotechnical investigation is structured in two complementary phases: field investigation to collect samples and in-situ data, and laboratory testing to analyse those samples under controlled conditions. Together, the two phases produce a comprehensive picture of subsurface conditions that neither could achieve alone.
The Boring Program
A boring program involves the systematic drilling of boreholes at planned locations and depths across a project site. A rotary drill rig or hollow-stem auger advances the borehole while soil samples are collected at regular depth intervals, typically every 1.5 metres in variable soils, using a split-spoon sampler driven into undisturbed soil ahead of the borehole. The recovered samples are logged by a geotechnical professional on-site, classified visually, and sealed for laboratory shipment. In rock, continuous core is recovered using a core barrel, and the rock quality designation (RQD) is recorded as a measure of fracturing and integrity. Boreholes typically extend to the depth of the competent bearing stratum or to a predetermined depth below the anticipated foundation level, whichever governs.
Within the boring program, the Standard Penetration Test (SPT) is the most widely used in-situ test in Canadian and North American geotechnical practice. It is performed by driving the split-spoon sampler 450 mm into the soil using a standard hammer drop, and counting the number of blows required to advance the sampler the final 300 mm, the SPT N-value. The N-value provides a direct empirical measure of soil density and consistency and is correlated to bearing capacity, compressibility, and soil classification through established published relationships.
The Cone Penetration Test
The cone penetration test (CPT) is an in-situ testing method in which a steel probe fitted with a conical tip is pushed into the ground at a controlled rate, typically 20 mm per second, using a hydraulic push system. As the probe advances, it continuously measures tip resistance (qc), sleeve friction (fs), and, in the piezocone variant (CPTu), pore water pressure (u2). These measurements are recorded at intervals of 20 mm or less, producing a near-continuous soil profile that reveals stratigraphy, relative density, and soil type with exceptional resolution.
The cone penetration test is faster and more cost-effective than boring in suitable soils, and it eliminates sample disturbance, a limitation of physical sampling that can affect the accuracy of certain laboratory testing results. Its primary limitation is that it does not recover a physical soil sample, which means it cannot provide the particle size, plasticity, or consolidation data that only laboratory testing can deliver. For this reason, most comprehensive geotechnical investigation programs use CPT and boring programs in combination: CPT for continuous profiling and efficient coverage, borings for targeted sample recovery and laboratory testing.
Laboratory Testing
Soil samples recovered during the boring program are transported to a geotechnical laboratory for controlled testing. Laboratory testing transforms raw samples into the quantitative engineering parameters that foundation design requires. A standard geotechnical investigation for an industrial facility includes some or all of the following tests, depending on soil types encountered and design requirements:
- Grain size analysis (sieve and hydrometer): establishes grain size distribution and soil texture
- Atterberg limits (liquid limit and plastic limit tests): determine the plasticity of fine-grained soils
- Moisture content determination: measured on all recovered samples
- Consolidation test (oedometer): measures compressibility parameters (Cc, Cs, mv) and preconsolidation pressure
- Triaxial compression test: measures shear strength parameters (c, φ) under controlled drainage conditions
- Direct shear test: an alternative method for measuring shear strength, particularly useful for granular soils and interfaces
- Compaction test (Proctor): determines the optimum moisture content and maximum dry density for fill placement, required for earthworks design
- Permeability test: measures hydraulic conductivity for drainage and dewatering design
Preliminary vs. Detailed Geotechnical Investigation
A geotechnical investigation is rarely a single event. Investigation programs are staged to match the project lifecycle.
A preliminary investigation is conducted early, at the feasibility or pre-FEED stage, with a relatively coarse borehole grid intended to establish broad site characterisation, identify major subsurface features or hazards, and support site selection comparisons. The findings inform early foundation design concepts and flag any unusual conditions warranting further study.
A detailed investigation follows during detailed engineering, with a refined borehole layout targeted at confirmed foundation locations, higher-load areas, and zones identified as potentially problematic in the preliminary program. This investigation delivers the design-level parameters that structural and civil engineering teams need to finalise foundation design, earthworks specifications, and settlement predictions.
Soil Classification: Making Sense of the Data
Raw soil descriptions and test results are only useful within a standardised framework. Without one, there is no consistent way to compare conditions across projects, regions, or engineering teams. The Unified Soil Classification System (USCS) provides that framework and is the dominant soil classification system in North American geotechnical practice.
The USCS divides soils into two primary groups. Coarse-grained soils, gravels (G) and sands (S), are classified primarily based on grain size distribution: well-graded soils contain a broad range of particle sizes (GW, SW), while poorly graded soils are dominated by particles of similar size (GP, SP). Fine-grained soils, silts (M) and clays (C), are classified based on plasticity using the Atterberg limits. Low-plasticity clays are designated CL (lean clay). High-plasticity clays are designated CH (fat clay). Organic soils carry their own designations (OL, OH, Pt) and are problematic for foundation design due to high compressibility and low shear strength.
The USCS symbol derived from soil classification allows engineers to reliably reference published design parameters, empirical correlations, and engineering tables associated with that soil type, a shorthand that connects the site-specific investigation data to a broader body of geotechnical knowledge.
From Soil Analysis Data to Foundation Design Decisions
The purpose of soil analysis is not the data itself. It is the engineering decisions that data enables.
Foundation Design Type Selection
The most consequential decision that soil analysis data informs is the selection of foundation type. Shallow foundations, spread footings, combined footings, and mat (raft) foundations, bear load directly onto near-surface soil and are viable when bearing capacity is adequate at shallow depths and anticipated settlement is within acceptable limits. Deep foundations, driven piles, drilled shafts, and caissons, transfer load through weak or compressible near-surface soils to a deeper stratum capable of supporting the applied loads. The choice between shallow and deep foundation design is not a minor design detail on an industrial facility or energy project: deep foundation systems can cost five to ten times more than equivalent shallow systems, and the decision turns almost entirely on what the soil analysis reveals. Getting this decision right or wrong has a direct and material impact on the Total Installation Cost of the project.
Foundation Depth
Beyond the type of foundation, soil analysis establishes the appropriate bearing depth, the elevation at which foundations must bear to reach competent soil. Boring logs and CPT profiles reveal the depth to the competent bearing stratum, and this depth directly controls excavation volume, concrete quantities, and construction method. In Alberta and other northern Canadian project locations, frost depth considerations impose an additional constraint: foundations must bear below the depth of seasonal frost penetration to avoid heave from ice lens formation in frost-susceptible soils. Frost depth data is incorporated into foundation design alongside bearing stratum depth to establish the governing foundation level.
Settlement Predictions
Structural engineers and equipment manufacturers specify maximum allowable settlement values for their designs, limits that, if exceeded, could impair structural integrity, equipment alignment, or operational function. Soil analysis provides the compressibility parameters needed to calculate both total settlement (the absolute vertical displacement under design load) and differential settlement (the variation in settlement between different foundation elements). Differential settlement is the governing criterion. A structure that settles uniformly can absorb more total movement than one that settles unevenly. Calculated settlement predictions are compared against allowable limits, and if they are exceeded, the foundation design is modified: enlarged bearing area, increased foundation depth, or a switch to a deep foundation system.
Earthworks Design
Soil analysis data extends beyond the foundations themselves to govern earthworks design across the site. Excavation slope angles are determined from shear strength parameters. Stronger, cohesive soils allow steeper slopes. Loose sands and soft clays require shallower ones. Fill specification and compaction requirements are derived from Proctor test data. Groundwater management and dewatering system design depend on permeability measurements and groundwater elevation data collected during the boring program. Each of these design elements traces directly back to the geotechnical investigation.
The Geotechnical Report
The primary deliverable of a geotechnical investigation is the geotechnical report, also referred to as a subsurface investigation report or geotechnical engineering report. This document translates raw field data and laboratory testing results into engineering conclusions and foundation design recommendations.
A standard geotechnical report for a construction project contains the following components:
- Project description and investigation scope: defines the project, the investigation program, and the limitations of the data
- Field investigation methodology: describes the boring layout, drilling methods, sampling procedures, and in-situ tests performed
- Boring logs and CPT profiles: the primary data record, a depth-by-depth description of soil and rock conditions at each test location
- Laboratory testing results: tabulated results for all tests performed on recovered samples
- Soil profile interpretation: the geotechnical professional’s synthesis of all data into a coherent stratigraphy and subsurface model
- Engineering analysis: bearing capacity calculations, settlement predictions, and other design-level analyses
- Foundation design recommendations: specific guidance on foundation type, bearing depth, allowable bearing capacity, and design parameters
- Limitations and assumptions: identification of data gaps, areas of uncertainty, and conditions under which the recommendations may not apply
The geotechnical report is used by the structural and civil engineering team to develop foundation design and earthworks specifications, by the project owner to understand and manage subsurface risk, and by the contractor to plan excavation, shoring, and earthworks construction.
An important limitation: the geotechnical report reflects conditions at the specific locations tested. Subsurface conditions between boreholes are inferred through interpolation, a judgment exercise that carries inherent uncertainty. Where variability is high or the consequence of encountering unexpected conditions is severe, a denser investigation program reduces, but does not eliminate, this uncertainty.
When to Commission a Soil Analysis
Soil analysis should be initiated as early as feasible in the project lifecycle. The earlier the investigation, the greater its value, and the lower the cost of acting on its findings.
At the feasibility or pre-FEED stage, a preliminary geotechnical investigation can inform site selection by comparing subsurface conditions across candidate sites. Discovering a deep soft clay deposit or an extensive fill zone early, before a site has been selected and design has begun, is far preferable to discovering it during excavation.
At the FEED and detailed engineering stage, a detailed geotechnical investigation delivers the design-level parameters required to finalise foundation design, earthworks specifications, and settlement predictions. This investigation should be completed, and the geotechnical report reviewed by the engineering team before foundation design drawings are developed. Investigating in parallel with foundation design, or worse, after foundations have been designed, eliminates the opportunity to incorporate findings into design and forces reactive, costly changes.
On capital projects in the energy and industrial facility sector, geotechnical investigation is a standard scope item under civil engineering. It is not an optional add-on or a cost reduction target. It is a prerequisite to defensible foundation design.
Planning a capital project in the energy or industrial sector? Vista Projects’ civil engineering and multi-disciplinary engineering services integrate geotechnical investigation findings into foundation design, earthworks planning, and structural decisions from the earliest project phases, including feasibility and pre-FEED.
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What Happens When Soil Analysis Is Skipped or Inadequately Scoped
The consequences of insufficient soil analysis are well-documented in the geotechnical and project management literature, and they are consistently expensive.
Under-scoped investigation programs, too few boreholes, insufficient depth, or missing laboratory testing, leave significant portions of the site uncharacterised. When excavation begins, and reality diverges from assumptions, the consequences land in the construction phase, where they are most difficult and costly to address.
Common outcomes:
Construction rework is the most immediate consequence. Foundations designed for assumed soil conditions must be redesigned when actual conditions are encountered. Additional geotechnical investigation is commissioned under schedule pressure, adding both direct cost and delay. Every day of schedule slip in a construction phase carries its own indirect cost through extended overhead, equipment idling, and downstream contract impacts.
Structural distress is a longer-term consequence. Structures built on inadequately characterised soil may perform acceptably for years before differential settlement or degradation of bearing capacity manifests as cracking, misalignment, or, in severe cases, structural compromise.
The geotechnical investigation cost for any capital project represents a fraction of one per cent of the total project cost. The potential cost consequences of inadequate investigation can exceed that investment by a factor of one hundred or more.
Frequently Asked Questions About Soil Analysis
What is the difference between soil analysis and soil testing?
Soil analysis and soil testing are often used interchangeably in geotechnical practice. Strictly speaking, soil testing refers to specific laboratory or field investigation procedures performed on soil or rock samples, including a triaxial shear test, a consolidation test, or the Standard Penetration Test, while soil analysis refers to the broader interpretive process of collecting data through multiple tests and using it to characterise subsurface conditions and derive engineering design parameters. In practice, a geotechnical investigation integrates both testing and analysis as inseparable components of a single process.
How many boreholes are needed for a geotechnical investigation?
The number and layout of boreholes in a boring program depends on the project footprint, the anticipated foundation design type, expected site variability, and the consequence of encountering unexpected conditions. For a preliminary geotechnical investigation of a large industrial facility site, a minimum grid spacing of 30 to 60 metres is common practice, with additional boreholes targeted at high-load locations, including major equipment foundations or process vessels. Detailed investigations refine this layout with boreholes positioned at confirmed foundation locations. There is no universal borehole count standard. Program design is a professional judgment exercise guided by the project’s risk profile, applicable standards, and the geotechnical professional’s assessment of site variability.
What is the difference between a cone penetration test and a boring program?
A boring program involves physically drilling into the ground and extracting soil samples for laboratory testing, while simultaneously performing the Standard Penetration Test at intervals to measure in-situ soil resistance. A cone penetration test pushes an instrumented probe into the ground continuously, measuring tip resistance, sleeve friction, and pore pressure in near-real time, without extracting a physical sample. The cone penetration test provides a faster, more continuous soil profile with less sample disturbance than boring, but cannot deliver the physical samples required for laboratory testing of grain size distribution, plasticity, compressibility, and shear strength. Most comprehensive geotechnical investigation programs combine both methods: cone penetration tests for efficient continuous profiling and the boring program for targeted sample recovery and laboratory testing at critical locations.
Can soil analysis predict foundation failure?
Soil analysis cannot guarantee against foundation failure, but it reduces the risk by providing the data needed to design foundations that perform within acceptable limits under anticipated loads. When a geotechnical investigation is thorough, appropriately scoped, and interpreted by a qualified geotechnical professional, the probability of unforeseen geotechnical failure is low.
In Alberta, geotechnical investigations must be conducted or directly supervised by a Professional Engineer registered with APEGA. Equivalent registration requirements apply through provincial regulators in other Canadian jurisdictions. Residual uncertainty exists because subsurface conditions between test locations are inferred through interpolation rather than directly measured. That is why investigation program density, borehole depth, and laboratory testing scope all matter. The goal of soil analysis is not certainty. It is the reduction of geotechnical risk to a level consistent with the project’s consequences of failure.
Is soil analysis required for all construction projects?
Soil analysis is standard practice for any project where foundation design performance is critical, including industrial facilities, energy infrastructure, bridges, and any structure where settlement or bearing capacity failure would have significant safety, operational, or financial consequences. For small, low-risk structures on well-characterised sites with established local geotechnical practice, engineers rely on published presumptive bearing capacity values or historical records from nearby investigations. For capital projects in the industrial and energy sectors, a formal geotechnical investigation is standard practice and a specified deliverable under the civil engineering scope. Bypassing soil analysis on a capital project transfers geotechnical risk from the investigation budget, where it is relatively cheap to manage, to the construction phase, where it is expensive and disruptive to resolve.
Engineering Decisions Start with Ground Truth
On industrial and energy sector capital projects, geotechnical data is one of the earliest and most consequential inputs to engineering design. The structural and civil engineering work that follows is only as reliable as the soil analysis that precedes it.
Vista Projects integrates geotechnical findings into a connected, multi-disciplinary engineering environment, so that what the ground reveals at feasibility shapes every foundation, earthworks, and structural decision through to detailed design. That continuity, across civil, structural, mechanical, process, and instrumentation and controls disciplines, carried forward in a Single Source of Truth environment, is what protects project budgets and schedules. It is also what prevents the costly mid-construction surprises that follow fragmented, siloed execution.
Contact Vista Projects to discuss your capital project.
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.