--- title: "Limitations of classical bearing theories" subject: "Foundation Engineering" chapter: 6 key: "semester_5/foundation_engineering:classical-theory-limitations" source: https://www.bctengineer.com/q/semester_5/foundation_engineering/classical-theory-limitations site: BCT Engineering --- # Limitations of classical bearing theories Foundation Engineering · Chapter 6: Bearing Capacity and Settlement of Shallow Foundations - Asked in: 2076 Asoj, 3 marks - Video: [Terzaghi's Theory of Bearing Capacity | Most important Theory | Foundation | Strip footing](https://www.youtube.com/watch?v=_mwvfaQiyPU) — Sudip Dhakal - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/classical-theory-limitations - Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-6 ## Question Explain the limitations of different classical bearing capacity theories. ## Short answer They assume strip footing, homogeneous isotropic soil, and general shear. Rankine and Bell ignore footing width and base friction. Prandtl and Reissner neglect soil weight. Terzaghi ignores shear strength above the base, assumes Df ≤ B, and handles local/punching shear only by empirical reduction. Nγ values vary among authors. Compressibility is ignored, so settlement is not predicted. Eccentric, inclined, or dynamic loads are not originally included, and water table effects are approximate. ## Answer Classical bearing capacity theories (Rankine, Prandtl, Reissner, Terzaghi) have several limitations. - **Strip footing assumed.** Plane strain is assumed, so shape effects for square, circular and rectangular footings are put in by empirical factors rather than being derived. - **Homogeneous, isotropic soil.** Real soil is layered, variable and anisotropic, and the theories cannot deal with it directly. - **Rankine's and Bell's theories** ignore the width of the footing and the friction on the base, so they are approximate and conservative. - **Prandtl's theory** assumes weightless soil and no surcharge; **Reissner's** still neglects soil weight. - **Terzaghi's theory** ignores the shear strength of the soil above the base (treated only as surcharge) and assumes a rough base and $D_f \le B$, so it is not suited to deep footings. - **General shear assumed.** Local and punching shear are handled only by an empirical two-thirds reduction of $c$ and $\tan\phi$. - **Load conditions.** Central, vertical, static load only. Eccentric, inclined and dynamic loads are not included in the original form. - **Nγ values differ** between authors (Terzaghi, Meyerhof, Hansen, Vesic) because of the uncertainty in the failure surface, giving different results for the same soil. - **Compressibility is ignored.** The soil is treated as rigid–plastic, so settlement is not obtained. Settlement may govern the design. - **Water table effect** is accounted for only approximately by correction factors. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How are square and circular footing effects included in the classical theories? A. They are derived rigorously B. By empirical shape factors, since the theories assume plane strain C. They are ignored D. By using a higher factor of safety Answer: B. Plane strain strip footing is assumed, so shape factors are empirical. (Key point: Shape effects) 2. Why do classical theories not give settlement? A. Settlement is zero for general shear B. Water table effects cancel it C. Soil is treated as rigid-plastic, so compressibility is ignored D. They assume soil is elastic Answer: C. Rigid-plastic soil gives only failure load; settlement may still govern. (Key point: Compressibility) 3. Why do Ngamma values differ between authors? A. Uncertainty in the failure surface assumed B. Different units are used C. Different footing widths D. Different water tables Answer: A. Each author assumes a different failure surface, giving different results. (Key point: Ngamma variation) ## Close variants set in other exams - [Development of classical bearing capacity theories](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aclassical-bearing-theories-development) — Foundation Engineering, chapter 6, asked 2× ## Related in Foundation Engineering - [Factors affecting bearing capacity; water table](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Abearing-capacity-factors-water-table) — Foundation Engineering, chapter 6, asked 5× - [Mat bearing capacity: cohesive vs cohesionless](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Amat-bc-cohesive-vs-cohesionless) — Foundation Engineering, chapter 7, asked 2× - [Terzaghi's bearing capacity theory](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aterzaghi-theory-assumptions) — Foundation Engineering, chapter 6 - [Skempton's findings on clay bearing capacity](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Askempton-net-safe-bc) — Foundation Engineering, chapter 6 - [Bearing capacity from plate load curve](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Abc-from-load-settlement-sand) — Foundation Engineering, chapter 6 ## Related in other subjects - [Methods of improving bearing capacity](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aimproving-bc) — Building Technology, chapter 2, asked 2× - [Methods of determining bearing capacity](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Abc-determination-methods) — Building Technology, chapter 2, asked 2× - [Soil exploration and improving bearing capacity](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asoil-exploration-improving-bc-nepal) — Building Technology, chapter 2 - [Safe and ultimate bearing capacity, improvement](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Abc-define-improve-066j) — Building Technology, chapter 2