ASDIP RETAIN is a structural engineering software for the design of retaining walls. It includes the design of counterfort retaining walls based on the IBC / ACI 318, AASHTO, or CSA provisions, either supported on ground or supported on piles. This document is a step-by-step design example of a typical counterfort retaining wall supported on piles per the ACI 318, using ASDIP RETAIN.
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Counterfort retaining wall on piles example
As an example, consider the counterfort retaining wall on piles shown below, which retains a flat backfill load. Due to the wall height of 25 feet, the use of counterforts has proven to be a more economical solution than a cantilever wall. The soils report has recommended 12" round concrete piles with the allowable capacities shown below. The backfill density is 115 pcf and the internal friction angle is 34 degrees. Design the counterfort retaining wall.
In the Geometry tab enter the preliminary geometric dimensions of the wall. In this case, the stem height is 25'-0". Let's try a stem thickness of 10" and a footing thickness of 44" to allow 6" pile embedment. Typical counterfort spacing is about 10-ft. As a rule of thumb, the counterfort length at the bottom should be about 0.4 H = 10-ft long, therefore let's specify the heel length = 12-ft. The toe length will be determined by the pile loads.
The At-a-Glance tab shows a summary of the design for a quick overview of your work as you go. The Condensed tab shows a more complete set of results grouped by topic, great for a more detailed overview of your design. The Detailed tab shows a complete set of step-by-step calculations with exposed formulas and with references to the ACI code.
Specify the applied loads
Go to the Loads tab and enter the loads on the wall. The backfill will be a select material with density = 115 pcf and internal friction angle = 34 deg. We will use the Rankine theory to calculate the active lateral soil pressures. The water table is set to zero. No surcharge or concentrated loads were given as part of the problem. The Stability tab shows graphically the pressures and forces on the wall, as well as the stability safety factors per load combination.
Note that in this example a toe length =2-ft has provided the required distance between the rows of piles to keep the pile loads under the allowable limits. To do so, the piles at the heel side are spaced 6-ft apart, and the piles at the toe side are spaced 3-ft apart. In addition, the toe piles must be battered at 15 degrees in order to resist the lateral loads.
Specify the material properties
Use the Materials tab to specify the material properties, which include the allowable capacity of piles, and the concrete and steel strengths. The Stem tab shows the pressures acting on the stem, and the shear and moment diagrams when the stem is subjected to the lateral pressures, considering the counterforts as the supports.
The Footing tab shows the pile cap in plan view with the pile distribution, and also an elevation view with the shear and bending moment diagrams of the pile cap for the selected load combination, as shown below.
Optimize the reinforcement
Specify the rebars sizes and spacing for the stem, counterforts, and footing. ASDIP RETAIN has multiple options to specify the rebars, stirrups, bar spacing, and concrete cover. The Construction tab shows the final counterfort retaining wall on piles. In this example, the stem has been reinforced with #4 @ 12" at each face, and the counterforts have been reinforced with bars #6 as the main reinforcement, and stirrups #4 in both directions. The pile cap has been reinforced with rebars #8 @ 9" top and bottom, as shown below.
ASDIP RETAIN includes the design of counterfort retaining walls on piles, with multiple options and tools to optimize the design easily. This example shows that the design can be completed and optimized in minutes using ASDIP RETAIN.
Detailed information is available about this structural engineering software by visiting ASDIP RETAIN. For engineering background, see the blog post Cantilever Retaining Walls: Overview of the Design Process
. For our collection of blog posts about retaining walls please visit Structural Retaining Wall Design.
Javier Encinas, PE
ASDIP Structural Software