| Scenario | Rule of Thumb | | :--- | :--- | | | End bearing (kips) = SPT N-value x 4 (for closed end pipe). | | Driven Piles (Clay) | Skin friction (psf) = ( S_u ) (undrained strength in psf). | | Auger Cast Piles | The torque during drilling (ft-lbs) divided by 10 approximates the allowable load (tons). | | Concrete Volume | Always add 10% to your volume calculation for over-excavation and bulbous piles. | | Groundwater | If you find water at depth "D" in the borehole, expect the seasonal high water table to be at the surface (0 depth). | | Expansive Clay | Heave potential is negligible if the plasticity index (PI) is less than 15. | | Liquefaction | If SPT N-value < 15 and groundwater is within 30 feet, check for liquefaction. | | Footing Depth | In frost-prone areas, depth must be > frost line. In stable rock, 1 foot is enough. | | Compaction | You cannot compact wet clay. Maximum dry density occurs near Optimum Moisture Content (OMC). | | Rock Quality (RQD) | RQD < 25% is "very poor" rock; treat it as soil. RQD > 75% is "excellent" rock. |

Geotechnical engineering is a vital branch of civil engineering that deals with the behavior of earth materials, such as soil and rock, and their applications in construction and design. Geotechnical engineers play a crucial role in ensuring the safety and stability of various structures, including buildings, bridges, tunnels, and dams. One of the essential tools for geotechnical engineers is a comprehensive guide to calculations and rules of thumb, which helps them to analyze and design various geotechnical systems. In this article, we will provide an in-depth overview of geotechnical engineering calculations and rules of thumb, along with a downloadable PDF resource.

If you are looking for specific formulas or ready-to-apply data, these resources are industry standards: Geotechnical Engineering Calculations and Rules of Thumb

Qu=Qs+Qb=fsAs+qbAbcap Q sub u equals cap Q sub s plus cap Q sub b equals f sub s cap A sub s plus q sub b cap A sub b : Unit skin friction along the pile shaft Ascap A sub s : Surface area of the pile shaft : Unit tip bearing capacity Abcap A sub b : Cross-sectional area of the pile tip Rules of Thumb for Piles Space friction piles at a minimum of the pile diameter center-to-center. Driven Pile Capacity: Estimate ultimate capacity in kN as for sands.

Many of today's rules of thumb exist because of famous failures: Geotechnical Engineering Calculations and Rules of Thumb