Why should a foundation be documented before it is repaired?
A foundation should be documented before it is repaired because crack widths, elevation differences and the visible pattern of distress are the evidence, and patching, regrading or underpinning removes that evidence. This is not an argument against foundation repair — a distressed building sometimes has to be stabilized quickly — but the sequence of documentation and repair matters.
Where foundation repairs have already happened, the investigation is not over, but it is harder. The analysis shifts to pre-repair photographs, invoices describing what was done, and whatever foundation movement can be measured from that point forward.
How should cracks be documented in a foundation investigation?
Cracks in a foundation investigation should be documented as measurements, not merely photographed: useful crack documentation records location, orientation, width, whether the crack passes through or around masonry units, whether the edges are offset out of plane, and the condition of the crack faces. Photographs alone rarely capture crack width or offset; a scale in the frame and a recorded dimension do.
Crack orientation carries information about foundation movement. Diagonal and stair-step cracking generally reflects shear from differential vertical movement; vertical cracking at openings reflects tension; horizontal cracking in a basement wall usually reflects lateral earth pressure rather than settlement.
What does a floor-level survey show in a foundation investigation?
A floor-level survey shows the shape of the floor: a relative elevation survey across the floor plate, taken on a grid rather than at a few convenient points, produces the surface everything else in a foundation investigation is checked against. The floor-level survey shows where the low and high areas are, whether the shape is a bowl or a ridge, and how abrupt the transitions are.
Two cautions apply to a floor-level survey. Floors are not built perfectly flat, so part of any deviation is original construction tolerance rather than movement. And a relative elevation survey establishes shape, not direction — knowing which points moved requires a benchmark outside the structure or a repeat survey.
What do borings and in-situ testing show beneath a foundation?
Borings, sampling and in-situ testing show what a foundation bears on and how that material behaves. Standard penetration testing under ASTM D1586 gives resistance and a disturbed sample at intervals; thin-walled tube sampling recovers relatively undisturbed specimens; cone penetration testing gives a continuous profile and, with pore-pressure measurement, information about drainage.
In a foundation investigation, the depth and spacing of borings matter as much as the method. Borings must reach through the compressible or expansive zone and be distributed across the building footprint, because variation is the question. A single boring at the least-distressed corner can support almost any conclusion.
What does laboratory testing of soil samples add to a foundation investigation?
Laboratory testing of recovered soil samples adds a prediction, independent of the building, of what the foundation soil should have done. Classification under ASTM D2487 and Atterberg limits under ASTM D4318 establish soil type and plasticity. One-dimensional consolidation testing under ASTM D2435 gives compressibility and stress history, supporting an independent estimate of how much settlement the structure’s loads should have caused and over what period. ASTM D4546 measures swell or collapse on wetting directly.
Laboratory soil testing is valuable because it is independent of the building. The laboratory work predicts what should have happened; the floor-level survey records what did. Agreement between the laboratory prediction and the survey is a finding, and so is disagreement.
How do you tell whether foundation movement is still ongoing?
Whether foundation movement is still ongoing is answered only by monitoring: repeating the floor-level survey and the crack measurements over an interval long enough to span a full wet and dry cycle. Repeat monitoring is also the only way to establish the rate of foundation movement, not just whether the movement is still happening. A single set of measurements is a snapshot, and a monitoring interval shorter than a full wet and dry cycle can read seasonal movement as progressive or miss it.
Consolidation theory supplies a second, independent check on whether foundation movement is ongoing: for a soil layer of known thickness and properties, the expected time course of settlement can be estimated and compared against the structure’s age and loading history. Where monitoring and consolidation theory agree, the conclusion is hard to dislodge.
How do you tell old, finished foundation movement from progressive movement?
Old, finished foundation movement is told apart from progressive movement by the condition of the cracks and distortions, by measurable change between visits, and by records that fix dates; much of what a survey finds is old. Cracks patched and not reopened, painted-over separations, weathered and dirt-filled crack faces, and doors planed to fit a distortion that stabilized long ago all indicate finished movement.
Clean crack faces, spalled edges, cracks cutting through prior repairs and measurable change between visits indicate the opposite: foundation movement that is progressive rather than historic. Repair records, listing photographs, permit history and earlier inspection reports fix dates the building cannot supply itself.
What matters in the original geotechnical report when a foundation has moved?
What matters in the original geotechnical report is what it stated and what it did not address. The original geotechnical report is usually the most important document in a foundation investigation file, and it is often read too loosely. What the report stated includes the borings performed and where, the bearing value recommended, the anticipated total and differential settlement, the soil-preparation and fill-compaction requirements, and any conditions attached.
Equally important is what the original geotechnical report did not address — a portion of the site never explored, a moisture condition assumed rather than measured, a recommendation conditioned on drainage being maintained afterward. IBC Chapter 18 sets the code framework for soils and foundations and ASCE 7 the design loads; the geotechnical report is where site-specific conditions enter.
What does the construction record show, and what challenges should a foundation investigation anticipate?
The construction record — compaction test results, special-inspection reports, as-built foundation drawings and change orders — establishes whether what was recommended for the foundation is what got built, and a foundation investigation should anticipate predictable challenges to its own methods. Where the code or the specification called for those construction records, their absence is itself a finding.
The predictable challenges to a foundation investigation are worth anticipating: no stable datum for the survey, construction tolerance never separated from movement, borings too few or too shallow for a variable site, and a monitoring interval too short to see a season. A foundation investigation stating its methods, precision and limits absorbs those challenges. A conclusion offered without them does not.
This article is general technical orientation, not a failure analysis, an engineering opinion, or advice on any specific matter. Determining the cause of a particular incident requires hands-on examination by a credentialed expert.