This is the height of retained earth measured from top of footing to the top of soil behind the stem (over the heel). When the backfill is sloped, the soil will slope away and upwards from this height.
The actual retained height used for overturning and soil pressure calculations will be the retained height projected at the vertical plane of the back of the heel, but for stem moments, no such increase will be made.
Using the spin-buttons you can vary this in 0.25-foot increments (or you can type in any number). After each entry you can press the tab key to advance to the next entry, or use your mouse to position the cursor in the next input field.
Wall Height above Retained Soil:
Use this entry to specify if the wall extends above the retained height. This entry is typically used to define a "screen wall" projection. This extension can be used as a weightless "Fence" or a concrete or masonry stem section without any soil retained behind it. You can enter wind load on this projection using the entry "Wind on Stem above soil" on the "Loads" tab. We'll handle the fence when we get to the STEM design screen. TOTAL HEIGHT OF WALL = “RETAINED HEIGHT” + WALL HEIGHT ABOVE RETAINED SOIL”.
Height of Soil over Toe:
Measured from top of footing to top of soil on toe side, this may vary from a few inches to a few feet depending upon site conditions. (Note that it is input in inches.) It is used to calculate passive soil resistance (but its effective depth can be modified by the "Ht. to Neglect" entry on the Footing > Key Dimensions & Sliding tab). This depth of soil is also used to calculate a resisting moment, and reduce net lateral sliding force. You can negate the latter effects on the Options screen.
You may enter any backfill slope behind the wall. Use the drop-down menu or type the slope as a ratio in the form of Horiz/Vert. The soil must be level or slope upward. Negative backfill slopes (grade sloping downward, away from the wall) are not allowed.
The program will use this slope to 1) include the weight of a triangular wedge of soil over the heel as vertical load, and 2) compute overturning based upon an assumed vertical plane at the back face of the footing extending from the bottom of the footing to ground surface – a steeper slope will result in a higher overturning moment. The program will not accept a backfill slope steeper than the angle of internal friction.
When the EFP method is used, the program will NOT change the EFP based on soil slope. All it does with the slope is:
•calculate the retained height at the back of the heel, which might be greater because of the sloped soil, and
•add a surcharge due to the weight of the triangular prism of soil on top.
When the Coulomb method is used, the final calculated pressures do include the effect of the slope on those Coulomb equations.
Water Table Height over Heel:
If a portion of the retained height is below a water table, the active pressure of the saturated soil will increase below that level. This additional pressure for the saturated soil is equal to the pressure of water, plus the submerged weight of the soil (its saturated weight - 62.4), plus the surcharge of the soil above the water table. The program does not collect a saturated weight of soil, so instead it conservatively approximates the buoyant or submerged weight of a soil as 65% of its dry unit weight.
If you want to design for a water table condition, enter the maximum height from bottom of footing to water table level. The program will then compute the added pressures for saturated soil on the heel side of the footing, including buoyancy effect, to calculate increased moments and shears on the stem, and overturning. Don’t enter a height more than the retained height, and keep in mind that this feature automatically assumes that the liquid is water. If the water table is near the top of the retained height, it may be advisable to use the saturated soil density and active pressure for the full retained height instead of specifying a water table height.
Top Lateral Restraint Height:
This will appear if you are designing a restrained wall. Enter the distance from the bottom of the stem to the point of lateral restraint.