Design of Self-Drilling Micropiles for Permanent Applications-PPT Presentation

PPT Presentation

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The paper examines structural design and durability requirements for self-drilling micropiles used in permanent applications, which may have service lives of 50–100 years. It outlines U.S. design references, including FHWA guidance, AASHTO specifications, and the International Building Code, and reviews common reinforcement types and corrosion-protection strategies.<br /><br />For conventional reinforcement, protection may involve grout-filled sleeves, coatings such as galvanizing, sacrificial steel thickness, or grout encapsulation. Grout alone provides effective protection only when cracking is limited to 0.1 mm. Self-drilling micropiles are installed using rotary-percussive drilling and grout, making additional protective sleeves difficult to apply. As a result, many hollow-bar systems rely on coatings and corrosion allowances to account for steel loss over the design life.<br /><br />The paper distinguishes R-threaded systems from Ischebeck TITAN micropiles. R-threaded bars may develop grout cracks that make grout encapsulation unsuitable as the primary protection method; their design commonly uses coatings and sacrificial corrosion allowances. TITAN’s thread geometry promotes a cracking pattern that limits primary crack widths. Its permanent corrosion protection therefore relies on grout encapsulation, verified by a maximum crack-width limit of 0.1 mm, rather than on corrosion loss allowances.<br /><br />A design example considers permanent uplift reinforcement for a parking structure. The authors calculate a required tensile design load of 389.5 kN per micropile and compare seven reinforcement options; all meet the stated structural resistance requirement after durability factors are considered. The paper concludes that corrosion protection must be integrated into micropile design and tailored to the reinforcement system and ground conditions.

Keywords

self-drilling micropiles

durability requirements

corrosion protection

grout encapsulation

permanent applications

FHWA guidance

AASHTO specifications

International Building Code

sacrificial corrosion allowance

Ischebeck TITAN