BOND VALUES OF SCREW-IN GROUTED DISPLACEMENT PILES-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines bond values and performance of screw-in grouted displacement piles. These piles are installed by rotating helical displacement elements into the ground, then filling the resulting space with grout or concrete. Claimed benefits include limited spoil generation, reduced cleanup and disposal, relatively rapid installation, and moderate-to-high axial capacity.<br /><br />Ten piles of different sizes were installed and tested at sites in Missouri, Minnesota, and Florida, in clay and sand. Compression and tension tests followed ASTM procedures, with stepwise loading and four-minute holds. Installation measurements included effective torque, grout volume, and grout-take efficiency.<br /><br />Measured grout-to-ground bond values exceeded theoretical estimates at all reported sites. In clay, tested values ranged from 2.95 to 3.74 ksf. In sand, values ranged from 2.07 ksf in Missouri to 5.35–5.53 ksf in Minnesota, and 3.43 ksf in Florida. Grout-take efficiency was about 100–115% in cohesive soils and above 140% in non-cohesive soils; the presenter suggests sand mixes into the grout during installation.<br /><br />Load-deflection results indicate that pile capacity is derived largely from shaft friction, and installation requires substantial shaft torque. The measured bond values were considered consistent with certain Type B soil ranges in FHWA micropile guidance. The presenter emphasizes that further testing is needed, particularly in additional non-cohesive soils and very soft cohesive soils.

Keywords

bond values

screw-in grouted displacement piles

helical displacement elements

axial capacity

shaft friction

grout-to-ground bond

compression and tension tests

grout-take efficiency

ASTM procedures

FHWA micropile guidance