--- title: "Methods of determining bearing capacity" subject: "Building Technology" chapter: 2 key: "semester_6/building_technology:bc-determination-methods" source: https://www.bctengineer.com/q/semester_6/building_technology/bc-determination-methods site: BCT Engineering --- # Methods of determining bearing capacity Building Technology · Chapter 2: Foundations - Asked in: 2075 Bhadra, 5 marks; 2072 Magh, 8 marks (asked 2 times) - Video: [How to Calculate the Bearing Capacity of Soil? Understanding Terzaghi's bearing capacity equations](https://www.youtube.com/watch?v=tr0yOf4JaYU) — Civil Engineering Tutor - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/bc-determination-methods - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-2 ## Question Explain the different methods of determining bearing capacity of soil for design purpose (with sketches). ## Short answer Bearing capacity is determined by presumptive code tables for small buildings, Terzhaghi's analytical formula using c, φ and γ, field plate load tests measuring settlement, and Standard Penetration Test (SPT) N-values correlated to safe capacity, with static cone tests providing continuous profiles. ## Answer Bearing capacity of soil for design is determined by the following methods. #### 1. Presumptive values from codes Safe bearing capacity (SBC) is read from tables in IS 1904 (also used in Nepal): for example, hard sound rock about 3240 kN/m², soft rock 440, gravel 440, medium sand 245, medium clay 245, soft clay 100 kN/m². These values are used for small, light buildings. #### 2. Analytical (theoretical) methods These use the soil properties $c$, $\phi$ and $\gamma$ from lab tests. Terzaghi's equation for a strip footing: $$ q_u = cN_c + \gamma D_f N_q + 0.5\gamma B N_\gamma $$ and $q_{safe} = q_u / FS$. Other methods are those of Meyerhof, Hansen, and Skempton (for clay). #### 3. Plate load test A steel plate (300 to 750 mm square) is loaded in stages in a pit at the foundation level, with the settlement measured by dial gauges, until failure or a settlement of 25 mm; a load-settlement curve is then plotted. It gives a direct field estimate, but tests only a shallow depth (about 2 times the plate width). ```text Load frame / kentledge | jack | ====[ plate ]==== ground dial gauges ``` #### 4. Standard Penetration Test (SPT) A split spoon sampler is driven 450 mm by a 63.5 kg hammer falling 750 mm; the number of blows for the last 300 mm is N. SBC is correlated with N (Terzaghi and Peck charts, Meyerhof). #### 5. Static / dynamic cone penetration test (SCPT, DCPT) A cone is pushed or driven into the soil, and the resistance gives its strength; this is good for a continuous profile. #### 6. Other Laboratory tests on undisturbed samples (triaxial, direct shear, unconfined compression), pile load test, and geophysical methods (seismic refraction, resistivity). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In Terzaghi's equation, which soil properties are needed? A. c, phi and gamma B. Only N value C. Only plate settlement D. Only grain size Answer: A. q_u = cNc + gamma Df Nq + 0.5 gamma B Ngamma uses c, phi, gamma. (Key point: Terzaghi) 2. What is a limitation of the plate load test? A. It cannot measure settlement B. It tests only a shallow depth, about twice the plate width C. It needs no loading D. It tests very deep soil Answer: B. The pressure bulb is limited to about 2 times plate width. (Key point: Plate load test) 3. In the SPT, how is the N value taken? A. Blows for the first 150 mm B. Blows for the full 450 mm C. Blows per metre D. Blows for the last 300 mm of a 450 mm drive Answer: D. Blows for the last 300 mm give N. (Key point: SPT) 4. Where do presumptive SBC values come from? A. Triaxial tests on site B. Plate load tests only C. Seismic refraction only D. Code tables such as IS 1904 and NBC Answer: D. Presumptive values are read from codes, used for small light buildings. (Key point: Presumptive) ## Related in Building Technology - [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 - [Soil exploration, safe bearing capacity, improvement](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexploration-bc-065s) — Building Technology, chapter 2 - [Sub-soil exploration, improving bearing capacity](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asubsoil-exploration-improve) — Building Technology, chapter 2 - [Factors affecting foundation design, improving bearing capacity](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Afactors-design-improve-bc) — Building Technology, chapter 2 - [Methods of improving bearing capacity](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aimproving-bc) — Building Technology, chapter 2, asked 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 ## Related in other subjects - [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× - [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× - [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