Why at-rest pressure and not active pressure on a basement wall?

Active pressure is the lower value a soil falls to when the wall moves away from it far enough to let it shear. A basement wall propped by the ground-floor slab cannot move, so the soil stays at rest, and IBC 1610.1 says so directly: walls restrained at the top are designed for at-rest pressure. At a friction angle of 30 degrees the difference is 0.5 against about 0.33 — half as much again.

Why is the water carried separately instead of using the saturated unit weight?

Because water has no shear strength, so no earth-pressure coefficient reduces it. Below the water table the soil pushes with its buoyant weight times the coefficient and the water pushes at full pressure on top. On three metres of saturated soil at a coefficient of 0.33 that is 10.1 kPa (211 psf) of soil and 29.4 kPa (614 psf) of water. Putting the saturated weight on the soil line counts the water twice; using the moist weight and forgetting the water altogether gives less than half the real load.

What does the overconsolidation ratio change?

Ground that was once under more load than it carries now holds more of its horizontal stress. Eurocode 7 raises the at-rest coefficient by the square root of the ratio, so an OCR of 2 lifts it by about 41 per cent. Placed and compacted fill is normally taken as 1; an overconsolidated clay is a figure for the ground investigation to give.

Where does the thrust act?

At the height of the resultant shown in the breakdown. A triangle of pressure acts a third of the way up, a uniform surcharge half way up, and a wall with water against it has more of its load low down, which moves the resultant towards the base. The bending in the wall and the reactions at the slab and the base follow from that height and the span.

Materials & Quantities

Basement Wall At-Rest Earth Pressure Calculator (with Groundwater)

At-rest earth pressure on a propped basement wall, with surcharge and groundwater carried separately: base pressure, thrust per run and where it acts.

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Retained Height

The height of soil against the wall, from the base slab to the ground surface behind it.

Take it from the underside of the base, or the level the wall is designed to span from, to the finished ground behind the wall — not to the top of the wall where it stands proud of the ground.

Earth Pressure Coefficient

At rest for a wall held by the floor at its head; an entered value for anything else the designer has set.

A basement wall propped by the ground-floor slab cannot move away from the soil, so the soil stays at rest and the at-rest coefficient applies. Enter a coefficient instead where the design has fixed one — an active coefficient for a wall genuinely free to rotate, or a value from the ground investigation.

Effective Friction Angle φ′ (degrees)

The drained friction angle of the retained soil, from the ground investigation.

A well-graded granular backfill commonly sits in the low to mid thirties and a clay lower. It is the effective, drained angle — the one that governs a wall in the long term — and it comes from the report or the fill specification, not from a table chosen afterwards.

Overconsolidation Ratio (OCR)

1 for normally consolidated soil and placed fill; higher for ground that was once under more load.

Eurocode 7 raises the at-rest coefficient by the square root of the OCR and warns against the formula at very high ratios, which is why this field stops at 4. A heavily overconsolidated clay behind a wall is a question for the geotechnical engineer rather than a larger number here.

Moist Unit Weight Above the Water Table (γ)

The weight of the retained soil as it is in service, water in the pores included.

The moist, not the dry, figure: backfill in service is never oven-dry, and the dry figure from a compaction report leaves the pore water out of the driving load. The soil phase relationships calculator converts a laboratory sheet into it.

Saturated Unit Weight Below the Water Table (γsat)

The weight of the soil with its voids full, used below the water table.

The page takes the buoyant weight from it — the saturated figure less the unit weight of water — for the soil below the water table, and carries the water as its own load.

Depth to the Water Table Below the Ground Surface

How far below the retained surface the design water level sits; the full height or more means no water on the wall.

The DESIGN water level, which is a decision rather than the level seen in the excavation on the day: the highest the water can credibly reach against the finished wall, from standpipe readings over a season, flood levels and the site's drainage. Zero puts the water at the surface.

Uniform Surcharge at the Surface

A load spread over the ground behind the wall — a drive, stored material, a building's floor.

It adds the coefficient times the surcharge at every depth, a rectangle on the pressure diagram rather than a triangle. A line load or a strip footing close to the wall does not spread like that and needs its own treatment.

Total thrust on the wall per unit run

3,450 lbf/ft

Medium confidence

At rest: the soil stays where it was placed, which is the state of a wall propped by the floor at its head. A wall genuinely free to lean away could use the lower active coefficient, but only if it can move enough to earn it. Below the water table the soil contributes only its buoyant weight times the coefficient, and the water acts on top of it at full hydrostatic pressure.

At-rest coefficient K0: 0.5
Soil pressure at the base: 464.55 psf
Water pressure at the base: 312.25 psf
Total pressure at the base: 776.8 psf
Soil thrust per unit run: 2,673.27 lbf/ft
Water thrust per unit run: 780.62 lbf/ft
Height of the resultant above the base: 3.13 ft

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

BS EN 1997-1 (Eurocode 7), 9.5.2: for a horizontal ground surface the at-rest coefficient is K0 = (1 − sin φ′) × √OCR, not to be used for very high overconsolidation ratios; with OCR = 1 it is Jaky's relation, K0 = 1 − sin φ′
Effective-stress earth pressure with the pore water on its own line: horizontal pressure = K × σ′v on the soil skeleton plus γw × depth below the water table, the water taking no earth-pressure coefficient because it has no shear strength (Craig's Soil Mechanics; CIRIA C760); IBC 1610.1 requires at-rest pressure for walls restrained from moving at the top

Inputs used

Retained Height: 10 ft
Earth Pressure Coefficient: At rest, from the friction angle (Eurocode 7 9.5.2)
Effective Friction Angle φ′ (degrees): 30
Overconsolidation Ratio (OCR): 1
Earth Pressure Coefficient K: 0.5
Moist Unit Weight Above the Water Table (γ): 120.95 pcf
Saturated Unit Weight Below the Water Table (γsat): 127.32 pcf
Depth to the Water Table Below the Ground Surface: 5 ft
Uniform Surcharge at the Surface: 0 psf

Intermediate steps

At-rest coefficient K0: 0.5
Soil pressure at the base: 464.55 psf
Water pressure at the base: 312.25 psf
Total pressure at the base: 776.8 psf
Soil thrust per unit run: 2,673.27 lbf/ft
Water thrust per unit run: 780.62 lbf/ft
Height of the resultant above the base: 3.13 ft

Final result3,453.89 lbf/ft

Confidence note: At rest: the soil stays where it was placed, which is the state of a wall propped by the floor at its head. A wall genuinely free to lean away could use the lower active coefficient, but only if it can move enough to earn it. Below the water table the soil contributes only its buoyant weight times the coefficient, and the water acts on top of it at full hydrostatic pressure.

What this calculation does not cover

Characteristic, unfactored pressures for a screening check. A design applies the partial or load factors of the code in force, and the structural engineer sets the design water level and the coefficient the wall is designed to.
Horizontal ground behind the wall. A slope rising away from the wall increases the at-rest coefficient — Eurocode 7 multiplies it by (1 + sin β) — and is not modelled here.
Compacting backfill in layers against a propped wall can lock in pressures above the at-rest figure near the top of the wall. AASHTO LRFD 3.11 and CIRIA C760 set out methods for it; this page does not add them.
The water is static and the soil's cohesion is ignored. Seepage towards a drained wall changes the pore pressures, and a line load or strip footing close to the wall adds pressure that a uniform surcharge does not represent.

Add the equipment this sizes

This result is a specification — 3,450 lbf/ft — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

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Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-22 · v1.0.0

Regulatory standards & verification citations2

BS EN 1997-1 (Eurocode 7), 9.5.2: for a horizontal ground surface the at-rest coefficient is K0 = (1 − sin φ′) × √OCR, not to be used for very high overconsolidation ratios; with OCR = 1 it is Jaky's relation, K0 = 1 − sin φ′
Effective-stress earth pressure with the pore water on its own line: horizontal pressure = K × σ′v on the soil skeleton plus γw × depth below the water table, the water taking no earth-pressure coefficient because it has no shear strength (Craig's Soil Mechanics; CIRIA C760); IBC 1610.1 requires at-rest pressure for walls restrained from moving at the top

Which documents these citations point at

Eurocode 7 — Geotechnical design (BS EN 1997) (European (EN))Foundations, retaining structures and slopes, and the ground investigation they rest on.
International Building Code — 1610.1 (United States)Buildings other than the dwellings the IRC covers — occupancy, egress, fire resistance and structural provisions.

A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Backfilling Against Waterproofinguses this calculator
Filling is the one operation that can destroy a membrane without leaving a mark: board it, place it in lifts, and prove the drain takes what arrives.
Reading a Soil Reportuses this calculator
A lab sheet gives specific gravity and dry density; a wall check wants moist and buoyant unit weight. The conversion between them, and where it goes wrong.
Tanking a Basement Wall Against Standing Wateruses this calculator
Below the table a wall has to hold head, not shed it: set the design water level, work out what the ground delivers, then confine the bentonite.

How to calculate basement wall at-rest earth pressure (with groundwater) in 10 steps

Retained HeightThe height of soil against the wall, from the base slab to the ground surface behind it.
Earth Pressure CoefficientAt rest for a wall held by the floor at its head; an entered value for anything else the designer has set.
Effective Friction Angle φ′ (degrees)The drained friction angle of the retained soil, from the ground investigation.
Overconsolidation Ratio (OCR)1 for normally consolidated soil and placed fill; higher for ground that was once under more load.
Earth Pressure Coefficient KThe coefficient the design uses, applied to the effective vertical stress.
Moist Unit Weight Above the Water Table (γ)The weight of the retained soil as it is in service, water in the pores included.
Saturated Unit Weight Below the Water Table (γsat)The weight of the soil with its voids full, used below the water table.
Depth to the Water Table Below the Ground SurfaceHow far below the retained surface the design water level sits; the full height or more means no water on the wall.
Uniform Surcharge at the SurfaceA load spread over the ground behind the wall — a drive, stored material, a building's floor.
Total thrust on the wall per unit runThe tool computes the total thrust on the wall per unit run from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

Why at-rest pressure and not active pressure on a basement wall?: Active pressure is the lower value a soil falls to when the wall moves away from it far enough to let it shear. A basement wall propped by the ground-floor slab cannot move, so the soil stays at rest, and IBC 1610.1 says so directly: walls restrained at the top are designed for at-rest pressure. At a friction angle of 30 degrees the difference is 0.5 against about 0.33 — half as much again.
Why is the water carried separately instead of using the saturated unit weight?: Because water has no shear strength, so no earth-pressure coefficient reduces it. Below the water table the soil pushes with its buoyant weight times the coefficient and the water pushes at full pressure on top. On three metres of saturated soil at a coefficient of 0.33 that is 10.1 kPa (211 psf) of soil and 29.4 kPa (614 psf) of water. Putting the saturated weight on the soil line counts the water twice; using the moist weight and forgetting the water altogether gives less than half the real load.
What does the overconsolidation ratio change?: Ground that was once under more load than it carries now holds more of its horizontal stress. Eurocode 7 raises the at-rest coefficient by the square root of the ratio, so an OCR of 2 lifts it by about 41 per cent. Placed and compacted fill is normally taken as 1; an overconsolidated clay is a figure for the ground investigation to give.
Where does the thrust act?: At the height of the resultant shown in the breakdown. A triangle of pressure acts a third of the way up, a uniform surcharge half way up, and a wall with water against it has more of its load low down, which moves the resultant towards the base. The bending in the wall and the reactions at the slab and the base follow from that height and the span.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.