Calculate reference slope-back or geometric depth for a simple excavation slope in feet or meters. These values do not establish excavation safety.

Calculate the horizontal offset for a simple slope.

Reference geometry only. A competent person must assess soil and site conditions. Simple soil slopes are limited to 20 ft (6.096 m); deeper sloping or benching systems require a registered professional engineer.

Related Calculators

Excavation Slope Formula

For a simple slope with ratio r measured horizontally to vertically, use:

H = r × D; D = H / r (r > 0)

Variables:

  • H is horizontal slope-back per side; D is vertical depth; r is the horizontal:vertical ratio
  • The angle from horizontal is θ = arctan(1/r); stable rock is vertical and is distinct from Type A soil

OSHA general simple-slope ratios are 0.75:1 for Type A, 1:1 for Type B, and 1.5:1 for Type C at depths up to 20 ft (6.096 m). A competent person must classify the material and assess site conditions; deeper sloping or benching systems require a registered professional engineer. Distress, surcharge loads, water, or layering can require a different design. This calculation excludes benching and short-term Type A exceptions.

What is an Excavation Slope?

An excavation slope refers to the inclined boundary surface created during excavation work, such as digging a trench, pit, or other depression in the earth’s surface. The angle of the slope is determined by the stability of the soil or rock being excavated and is designed to prevent the sides of the excavation from collapsing. The slope’s angle can vary from vertical to horizontal, depending on the soil type, moisture content, and other factors. The Occupational Safety and Health Administration (OSHA) provides guidelines for the maximum allowable slopes to ensure worker safety during excavation work. These guidelines take into account the type of soil (such as solid rock, Type A, B, or C soil) and the depth of the excavation.

How to Calculate Excavation Slope?

The following steps outline how to calculate the Excavation Slope.

  1. First, obtain the soil or rock classification from a competent person.
  2. Next, choose whether to solve for slope-back or geometric depth.
  3. Enter the known vertical depth or horizontal slope-back per side.
  4. Calculate the reference geometry using H = r × D or D = H / r.
  5. Confirm the protective-system design and actual site conditions separately; the calculator does not certify safety.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Classified Type C soil; vertical depth D = 4 meters

Reference slope-back H = 1.5 × 4 = 6 meters per side; two sloped sides add 12 meters to the bottom width