624618619

Technical report; Sept. 2006-Aug. 2008.

University of Texas at Austin. Center for Transportation Research

NTL-HIGHWAY/ROAD TRANSPORTATION-Soils and Geology

PDF

This research addressed two key issues:

1) Will verification cores holes fill during concrete backfilling? If so, what are the mechanical properties of the

filling material? In dry conditions, verification core holes always completely fill with concrete whose

compressive strength is of equal strength to the concrete in the drilled shaft column. In wet conditions, the

bottom half of the verification core hole fills with non-cemented gravel-sand mixture (φ = 52°), while the upper

half of the verification core hole filled with weakly cemented material (Vp = 2000 fps).

2) When drilling in materials, such as shales, susceptible to degradation: does this degradation specifically around

shaft verification core holes affect point bearing capacity? The shear strength of Del Rio Clay and Eagle Ford

Shale is not affected by drying-duration, but is related to water content; the shear strength of Taylor Marl and

Navarro Shale decreases considerably as drying-duration increases. The elastic modulus of all four clay shales

drops significantly when clay shales are dried and then wetted.

When shales are first dried and then rewetted and concrete is poured in the wet, the verification core hole reduces tip

capacity by a maximum of 10% (14% for Taylor Marl). In all other cases, the verification core does not decrease the

tip capacity.

US Transportation Collection

0-5825