Quality Control and Estimation of Axial Resistance by Using an Expander Body, a Large-Scale Pressuremeter-Paper

Paper

Pdf Summary

The paper presents the Expander Body (EBI), a post-grouted steel device installed near the base of bored piles or ground anchors to increase axial resistance. Pressurized grout unfolds the device, expanding its diameter and compacting surrounding soil. This improves soil stiffness and strength, increases the pile’s base and side areas, and enhances soil–pile interaction.<br /><br />The authors compare EBI installation to a large-scale pressuremeter test. Real-time measurements of grout pressure and injected volume produce pressure–volume response curves that indicate soil stress, stiffness, and strength, while also helping identify leakage and estimate the device’s as-built dimensions and nominal axial resistance. The response depends on soil conditions and installation method: denser soils and displacement piles generally mobilize higher pressures sooner than looser soils and non-displacement piles.<br /><br />The paper outlines methods for estimating EBI end and side resistance during design and after installation, using site investigation data and actual grouting measurements. Continuous monitoring can support quality control and help verify or adjust design assumptions.<br /><br />A case history describes 80 full-displacement piles fitted with EBIs for an office development in Santa Cruz, Bolivia. A production pile was tested in axial compression: it carried the design load of 150 tonnes with approximately 8 mm of settlement, and reached 300 tonnes at about 38 mm of displacement. The authors conclude that the EBI both enhances pile performance and provides pile-specific information during construction, potentially reducing uncertainty in foundation capacity and behavior.

Keywords

Expander Body

EBI

bored piles

ground anchors

post-grouting

axial resistance

pressure-volume response

soil stiffness

pile capacity

axial compression test