Terzaghi shallow foundation cheat‑sheet

EngInfinityCo circulated a one-page Terzaghi shallow-foundation reference sheet in an X post on June 2, 2026, packaging bearing-capacity equations for strip, square and circular footings into a single field-style layout. The sheet groups the classic Terzaghi terms for cohesion, surcharge and soil-weight contribution, then adds local-shear variants and water-table adjustments for quick checks. The post drew 257 likes and 104 bookmarks, according to the social briefing supplied for this story. The formulas themselves match the standard Terzaghi framework still used for preliminary shallow-foundation checks in engineering calculators and teaching references. ### Which equations are on the sheet engineers keep sharing? Terzaghi’s 1943 bearing-capacity method expresses ultimate capacity as the sum of three components: a cohesion term, a surcharge term at footing level, and a soil-unit-weight term tied to footing width. For strip, square and circular footings, the differences come through shape factors applied to the cohesion and unit-weight terms, with strip footings commonly taken as 1.0, square footings using higher shape factors, and circular footings using a different pair again. (calctree.com) GeoCalc’s Terzaghi formulation page says the method it presents follows Braja M. Das’s *Principles of Foundation Engineering* and lists the same footing-shape distinctions: strip foundations with \(s_c=1\) and \(s_\gamma=1\), round foundations with \(s_c=1.3\) and \(s_\gamma=0.6\), and square foundations with \(s_c=1.3\) and \(s_\gamma=0.8\). CivilWeb’s summary describes the same three-part structure and says Terzaghi’s equations were later adapted from the original strip-footing analysis to square and circular cases. (geocalc.app) ### Why do general shear and local shear both appear? CalcTree’s Terzaghi calculator says it evaluates both general shear failure and local shear failure, reflecting the way engineers separate dense or stiff soil behavior from weaker or more compressible conditions. General shear uses the classic bearing equation, while local shear uses modified strength parameters and corresponding factor tables, the site says. (geocalc.app) That distinction matters because a footing can look acceptable under a general-shear assumption and much less comfortable once local shear is considered. Educational and calculator references commonly present both forms for exactly that reason: the same footing geometry can produce different capacities depending on how the soil is expected to fail. ### Why is the water table on a cheat sheet at all? Water-table position changes effective stress, which changes both surcharge and the unit-weight term in Terzaghi’s equation. (calctree.com) CalcTree says its Terzaghi tool switches among cases with water above the footing base, at the base, and below the base, adjusting surcharge and unit-weight terms for each. GeoCalc likewise says it computes an average effective unit weight beneath the footing based on the depth to groundwater below the base. A one-page sheet is useful because water is one of the easiest inputs to misread during a quick review. A footing that clears a dry-soil check can lose capacity when the groundwater line rises into the failure zone, especially in sands or mixed soils where the unit-weight contribution is material. That is why many Terzaghi calculators now include groundwater position as a standard input rather than a side note. (calctree.com) ### Is this enough to design a footing from scratch? Turn2Engineering’s Terzaghi calculator says the method is best used for preliminary shear bearing-capacity checks and “not final foundation design.” The same page notes that settlement can govern allowable pressure before shear failure does. CivilWeb says Terzaghi’s method was the first widely adopted analytical method and has since been extended by later approaches. (calctree.com) In practice, that leaves the cheat sheet most useful as a verification aid: a fast way to sense-check a consultant output, compare footing options, or review a tender-era assumption before moving to fuller bearing, settlement and code-based checks. (turn2engineering.com) ### Why did a compact sheet get traction with practitioners? The social briefing for this story recorded 257 likes and 104 bookmarks on the EngInfinityCo post, a pattern consistent with reference material engineers save rather than just react to. The sheet condenses footing shape, failure mode and groundwater adjustments onto one page, which is the kind of format commonly used during site meetings, hand checks and early design reviews. (civilweb-spreadsheets.com) The next place readers can inspect the material is EngInfinityCo’s June 2, 2026 X post, which is the source cited in the social briefing. Related Terzaghi tools from CalcTree and GeoCalc also show the same strip, square, circular and groundwater cases for users who want to test numbers against the reference layout. (calctree.com)