Retaining Wall Calculator

Retaining wall calculator - structure stability and calculation of materials

Retaining walls are key engineering structures whose main task is to protect the area against landslides in places with significant differences in levels (slopes, embankments, garden terraces, entrances to underground garages). These structures must resist the enormous forces of earth pressure and rainwater collected behind the wall. The construction of a stable wall requires precise design of its dimensions (height, width of the foundation footing), concrete class and appropriate steel reinforcement. Our free online retaining wall calculator is a professional engineering and cost estimation tool that allows you to calculate the volume of concrete, formwork area, weight of reinforcing steel and estimate the structure's resistance to earth pressure.

Thanks to this, you will efficiently plan the purchase of building materials in a concrete plant, correctly verify the initial design assumptions and safely secure slopes on your plot.

Types of retaining walls and their characteristics

Depending on the height of the slope, type of soil and aesthetic and economic considerations, various technologies for erecting retaining walls are used. The table below compares the most popular solutions:

Retaining wall physics – earth pressure and stability formulas

From the point of view of soil mechanics, the key parameter when designing a wall is **active soil pressure** ($P_a$), which tends to shift or overturn the wall. To calculate this pressure (according to Rankine's theory), the following formulas are used:

Active soil pressure coefficient ($K_a$):

$$K_a = \tan^2\left(45^\circ - \frac{\phi}{2}\right) = \frac{1 - \sin(\phi)}{1 + \sin(\phi)}$$

Where:

• $\phi$ – angle of internal soil friction in degrees (e.g. for medium sand it is approx. $30^\circ - 35^\circ$).

The resultant force of active soil pressure ($P_a$) acting on a linear meter of a wall with a height of $H$ is:

$$P_a = \frac{1}{2} \gamma H^2 K_a$$

Where:

• $\gamma$ – volumetric weight of the soil (standard assumption is approx. $18 \text{ kN/m}^3$ or $1.8 \text{ t/m}^3$).
• $H$ – total height of the wall including the part placed in the ground ($m$).

The designer must check two basic limit state conditions:

1. The condition for protection against displacement (slip):The friction force of the foundation footing against the ground must be greater than the earth pressure force ($P_a$) multiplied by the safety factor (usually $\ge 1.5$).
2. Condition for protection against rotation (overturning):The moment holding the wall (generated by the self-weight of the concrete and the soil above the footing) must exceed the overturning moment (generated by the earth pressure acting on the arm $H/3$) while maintaining a safety factor (typically $\ge 1.5$).

How to use the retaining wall calculator? Step-by-step instructions

Our tool allows you to quickly estimate the necessary building materials and the geometric dimensions of the angular wall. To perform the calculation:

1. Enter the geometric dimensions:Enter the length of the wall ($L$), the above-ground height ($h_n$), the depth of the foundation ($h_f$, below the ground frost zone) and the thickness of the vertical wall wall.
2. Specify the footing parameters:Enter the footing width ($B$) and its thickness ($t$). Remember that in corner walls the footing should protrude more towards the backfill soil.
3. Enter the density of the reinforcement:Enter the estimated weight of reinforcing steel per cubic meter of concrete (for engineering structures, the standard range is 80 to 120 kg/m³).
4. Click "Calculate":The calculator will immediately display the volume of concrete mix needed in cubic meters (m³), the estimated cost of concrete (given the unit price), the area of ​​formwork (OSB boards/formwork) in square meters and the total weight of reinforcing bars in kilograms.

Frequently asked questions (FAQ)