Installation of 10 Feet Diameter CIDHS in Soft Clay Using Rotator/Oscillator on Trestle-Paper

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The paper describes the design of a temporary trestle over Moanalua Stream in Honolulu to construct five 10-foot-diameter cast-in-drilled-hole (CIDH) piers. Elevated 20 feet above grade to clear an existing bridge, the trestle supported heavy construction equipment while spanning approximately 150 feet of very soft recent alluvial clay over stiff to hard older soils.<br /><br />The main design challenge was resisting substantial lateral forces from casing-installation equipment without exceeding the manufacturers’ two-inch displacement limit. A BUMA rotator could impose up to 260 kips of lateral load, while an oscillator could impose up to 580 kips. Reaction piles, connected by bracing and cap beams, were incorporated into the trestle to resist these forces alongside the gravity-support system.<br /><br />Because the geotechnical report’s soil Young’s modulus values were empirical and potentially unreliable, the authors developed a process to estimate and verify soil stiffness. First, they matched single-pile results from LPILE and PLAXIS, calibrating the upper clay layer’s modulus from the recommended 1 ksi to 4.9 ksi. They then calculated depth-varying modulus values using seismic CPT shear-wave velocities, maximum shear modulus, and clay modulus-reduction relationships. These values were simplified into three depth zones and used in PLAXIS models of the full reaction frames.<br /><br />The calibrated and calculated soil-stiffness models produced broadly consistent pile-deflection predictions. The analyses showed that lateral pile movement occurred mainly near the ground surface and diminished rapidly with depth. They also indicated that soil stiffness increases with depth, so modeling it as a constant can overpredict deflection. The study emphasizes that realistic soil-modulus estimates are essential for reliable lateral pile and trestle design.

Keywords

temporary trestle

Moanalua Stream

CIDH piers

cast-in-drilled-hole

lateral load

reaction piles

soil stiffness

PLAXIS modeling

LPILE calibration

geotechnical design