Overburden Stress Calculator

Inputs

Enter soil layers from ground surface downward. Provide dry and saturated unit weights for groundwater-sensitive results.

Example data table

Example unit weights shown as dry/saturated. Replace with project-specific lab or in-situ values.

Formula used

Total vertical stress at depth z is calculated by summing surface surcharge and the weight of each soil segment:

• σ_v(z) = q + Σ(γ · Δz)
• Above the water table: use γ = γ_dry
• Below the water table (total stress): use γ = γ_sat

Pore water pressure at depth z is:

• u(z) = γ_w · (z − z_wt), for z > z_wt
• u(z) = 0, for z ≤ z_wt

Effective vertical stress is: σ′_v(z) = σ_v(z) − u(z)

How to use this calculator

1. Choose a unit system that matches your project data.
2. Enter the target depth z from finished grade or ground surface.
3. Enter water table depth z_wt to evaluate pore pressure.
4. Add any surface surcharge q from equipment or storage.
5. Define up to three layers with thickness and unit weights.
6. Press Calculate to view total and effective stress results.
7. Use the export buttons to attach outputs to reports.

Overburden stress in construction practice

1) Why vertical stress matters

Overburden stress is the vertical load carried by soil at depth from self-weight and surface loading. It influences bearing performance, settlement, stability of excavations, and uplift checks. On many projects, designers review both total stress and effective stress, because drainage conditions and groundwater control the pore pressure term.

2) Typical unit-weight ranges

Field and laboratory data often show dry unit weight values around 16–20 kN/m³ for many sands and silts, and 17–21 kN/m³ for many compacted fills, while saturated unit weights frequently fall near 19–22 kN/m³. For preliminary estimates, maintaining consistent ranges and verifying against site investigations helps avoid unrealistic stress profiles.

3) Groundwater effect and pore pressure

When the water table is shallow, pore water pressure increases linearly below it. In metric units, γ_w is approximately 9.81 kN/m³, so each meter below the water table adds about 9.81 kPa of pore pressure. Effective stress equals total stress minus pore pressure, so the difference between σ_v and σ′_v can be significant for deep excavations and tunneling works.

4) Layering and construction decisions

Layered profiles are common: engineered fill over natural alluvium, or dense sand over clay. Summing γ·Δz by layer reveals where stress increases rapidly and where it does not. This breakdown supports decisions on dewatering, temporary support, ground improvement, and whether a target founding level should be adjusted to reduce stress-driven risk.

5) Using results for checks and reporting

Use total stress for immediate loading conditions and effective stress for strength and deformation checks tied to soil skeleton behavior. Include any surface surcharge from stockpiles or equipment. Exported summaries are useful for design narratives, calculation packages, and peer reviews, especially when the layer-by-layer contributions are shown.

FAQs

1) What is the difference between total and effective overburden stress?

Total stress includes soil weight and surcharge. Effective stress subtracts pore water pressure, representing stress carried by soil grains. Effective stress governs shear strength and compressibility behavior.

2) What should I enter if the water table is unknown?

If you do not know groundwater depth, leave it blank to treat it as very deep. For conservative checks, run sensitivity cases using a shallow water table and compare effective stress results.

3) Why do I need both dry and saturated unit weights?

Above the water table, soils behave closer to a dry or moist unit weight. Below it, the total stress contribution uses saturated unit weight. This improves realism when groundwater intersects your depth of interest.

4) Can I model more than three layers?

This calculator provides three primary layers plus an automatic “below layers” extension. If your profile is more complex, combine thin sublayers into equivalent layers using thickness-weighted averages for preliminary work.

5) How is surcharge included?

Surcharge is added directly to total vertical stress as q at the ground surface. Typical sources include equipment, traffic, temporary stockpiles, and floor slabs placed near excavation edges.

6) What units are used for the output?

Metric mode reports stress in kPa and unit weight in kN/m³. Imperial mode reports stress in psf and unit weight in pcf. Ensure your input unit weights match the selected system.

7) Are these results suitable for final geotechnical design?

The results support preliminary checks and documentation. Final design should use site-specific laboratory and field data, consider drainage and time effects, and follow applicable standards and geotechnical review procedures.