Overburden Pressure Calculator
Free Overburden pressure Calculator for soil & sediment mechanics. Enter variables to compute results with formulas and detailed steps.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
Effective Stress = Total Stress - Pore Water Pressure
Total overburden stress at depth z equals the sum of unit weight times thickness for each layer above. Below the water table, pore water pressure equals the unit weight of water (9.81 kN/m3) times the depth below the water table. Effective stress, which controls soil behavior, is total stress minus pore water pressure (Terzaghi principle).
Worked Examples
Example 1: Stress Profile at 10 m with Water Table at 3 m
Problem:Calculate total, pore, and effective stress at 10 m depth. Dry unit weight = 18 kN/m3, saturated unit weight = 20 kN/m3, water table at 3 m.
Solution:Total stress = 18(3) + 20(7) = 54 + 140 = 194 kPa\nPore pressure = 9.81(7) = 68.67 kPa\nEffective stress = 194 - 68.67 = 125.33 kPa
Result:Total = 194 kPa, Effective = 125.33 kPa
Example 2: Dry Soil Profile (No Water Table)
Problem:Calculate overburden at 5 m depth with unit weight 17 kN/m3 and water table deeper than 5 m.
Solution:Total stress = 17 * 5 = 85 kPa\nPore pressure = 0 kPa\nEffective stress = 85 kPa
Result:Total = Effective = 85 kPa
Frequently Asked Questions
What is overburden pressure and how is it calculated?
Overburden pressure, also called geostatic stress, is the vertical stress at a point in the ground caused by the weight of the soil above it. It is calculated by multiplying the unit weight of the soil by the depth. When multiple soil layers are present, you sum the product of each layer thickness and its unit weight. Total overburden pressure includes the full weight of soil and water, while effective overburden pressure subtracts the pore water pressure, which is crucial for understanding soil strength and consolidation behavior.
How does the water table affect overburden pressure?
The water table position dramatically affects the effective stress profile. Below the water table, soil pores are saturated and pore water pressure increases linearly with depth. This pore pressure reduces the effective stress, making the soil weaker and more compressible than the same soil above the water table. For example, at 10 meters depth with the water table at 3 meters, the pore pressure is about 68.7 kPa, which subtracts directly from the total overburden. Rising water tables from rainfall or construction dewatering can significantly reduce effective stress and trigger settlement or instability.
What is the coefficient of lateral earth pressure at rest (K0)?
K0 is the ratio of horizontal effective stress to vertical effective stress in soil that has not been laterally deformed. For normally consolidated soils, K0 is commonly estimated using the Jaky formula: K0 = 1 minus the sine of the friction angle. Typical values range from 0.4 to 0.5 for sands and 0.5 to 0.7 for clays. Overconsolidated soils have higher K0 values because past loading has locked in horizontal stresses. K0 is essential for designing retaining walls, basement walls, and tunnel linings where lateral earth pressure must be resisted.
How is atmospheric pressure measured and what does it indicate?
Atmospheric pressure is measured in millibars (hPa) or inches of mercury (inHg) using barometers. Standard sea-level pressure is 1013.25 hPa or 29.92 inHg. Falling pressure indicates approaching storms, while rising pressure suggests fair weather. Pressure decreases approximately 12 hPa per 100 meters of altitude gain.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy