Soil Bearing Capacity Calculator

What is Soil Bearing Capacity (SBC)?

Safe Bearing Capacity (SBC) is the maximum contact pressure intensity that soil can safely support beneath a structural footing without undergoing shear failure or excessive foundation settlement. Determining accurate SBC is the first step in foundation design for buildings, bridges, and industrial structures.

Terzaghi Bearing Capacity Formulas

Karl Terzaghi's classical bearing capacity equation for shallow strip footings incorporates soil cohesion ($c$), overburden pressure ($gamma D_f$), and soil unit weight ($gamma B$):

Where $c$ = soil cohesion (kPa), $gamma$ = soil unit weight (kN/m³), $B$ = footing width (m), $D_f$ = footing depth (m), and $N_c, N_q, N_gamma$ are Terzaghi bearing capacity factors dependent on internal friction angle $phi$.

How to Calculate Safe Soil Bearing Capacity

1. Enter the Cohesion $c$ of the foundation soil (in kPa).
2. Enter the Soil Unit Weight $gamma$ (in kN/m³).
3. Enter the Footing Width $B$ and Footing Depth $D_f$ in meters.
4. Select the Factor of Safety (FOS) (typically 2.5 to 3.0).
5. The calculator computes the Ultimate Bearing Capacity ($q_{ ext{ult}}$) and Safe Bearing Capacity (SBC) in kPa.
6. Click Copy Bearing Capacity to export the geotechnical summary.

Worked Geotechnical Example

Practical Geotechnical Engineering Applications

• Shallow Footing Sizing: Determining required pad or strip footing dimensions for residential and commercial columns.
• Retaining Wall Stability: Verifying base soil resistance against bearing capacity failure under overturning loads.
• Site Investigation Reports: Providing SBC recommendations for geotechnical borehole reports.

Limitations & Assumptions

• Assumes shallow foundation conditions where depth $D_f le B$. Deep foundations (piles) require Meyerhof or Janbu pile capacity formulas.
• High groundwater table conditions (submerged soil) require applying a groundwater reduction factor to unit weight $gamma$.