Experimental and Numerical Investigation of Uplift Capacity of Membrane-Confined Stem-Grouted Piles

Conventional deep foundations with high uplift resistance, such as enlarged base/belled/underreamed piles, pose significant challenges in terms of quality control and assurance. Specifically, the collapse of enlarged/reamed zones during the construction process is inevitable in sands and saturated fine-grained soil mass. This study evaluated the suitability of a membrane-confined stem-grouted pile as an alternative foundation under the uplift loading scenarios through experimental and numerical investigations. The stem-grouted pile is essentially a bored cast-in-situ pile with a nearly spherical grout bulb formed by membrane-confined pressure grouting. The experimental studies revealed an enhanced soil stress state around the grout bulb, as well as improved skin and bearing resistances due to stem grouting. Based on the failure mechanism observed from the finite-element modeling, an analytical method for predicting the uplift resistance of stem-grouted piles was developed. The study affirms that the stem-grouted pile can overcome the collapse and stress relaxation issues inherent with the aforementioned piles and offers significant uplift resistance. Moreover, pressure grouting with membrane confinement is possible at any depth, even under unfavorable soil conditions (problematic soil, high water table, etc.), unlike the limitations associated with the reaming operation.