The design of minipiles, a specialized type of deep foundation, involves two distinct approaches in determining their load-carrying capacity:
Neglecting Grout Resistance: This conservative method assumes that the grout surrounding the steel bars does not contribute to the axial load-bearing capacity. Consequently, the entire design load is supported solely by the steel bars. This approach necessitates the use of high-strength steel bars, such as Dywidag bars, to ensure adequate capacity. However, it’s important to note that minipiles are not designed to resist bending moments due to their slender geometry.
Considering Combined Resistance: In this approach, both the grout and steel bars are considered to contribute to the axial load-bearing capacity of the minipile. This method is more comprehensive as it accounts for the interaction between the two materials. However, it requires careful consideration of strain compatibility between the grout and steel to ensure their combined performance is optimized.
The choice between these two approaches depends on various factors, including the geotechnical conditions, design loads, and the desired level of conservatism. The first approach, while simpler, may lead to overdesign and increased costs due to the use of high-strength steel. The second approach offers a more accurate representation of the minipile’s behavior but necessitates a more detailed analysis of strain compatibility.
Ultimately, the appropriate design approach should be selected based on a comprehensive evaluation of the specific project requirements and constraints. By understanding the advantages and limitations of each method, engineers can make informed decisions to optimize the design and performance of minipiles.