Highways Research on Hawaii’s First GRS-IBS
By: Kurt Sanehira
Dr. Phillip Ooi, UH Professor of Civil and Geotechnical engineering and former research assistant, Arshia Taeb, conducted innovative and extensive research on Kauaula Stream bridge, a new 110-foot long geosynthetic reinforced soil integrated bridge system (GRS-IBS) in Lahaina, Maui.
is the likelihood of inducing cyclic-induced deformations of the GRS abutment. A numerical simulation of the bridge confirmed the magnitude of the field measured pressure fluctuations.
James Fu, HWY-DB section head is the project sponsor for this research project. This bridge was instrumented to measure superstructure strains and vertical pressures below the footing. Research and Findings
FHWA currently suggests limiting the span length of GRS-IBS to 140 ft because the longer the span, the more severe the thermal effects and hence GRS settlement will be. A second objective was to analyze the thermal effects on the bearing pressure fluctuation of a similar bridge twice as long. With modifications to the Kauaula Stream Bridge finite element model, the peak-to-trough cyclic bearing pressures of the 220-ft-long bridge remained within the backfill’s shakedown limit, the largest cyclic load at which the GRS backfill will stop settling continuously after the first few cycles.
When subjected to ambient daily temperature fluctuations, the GRS-IBS was observed to undergo cyclic straining of the superstructure. The upper and lower reaches of the superstructure experienced the highest and lowest strain fluctuation, respectively.
The results of this study showed that GRS abutments in Hawaii with similar temperature fluctuations are capable of supporting similar type GRS-IBS with a span longer than the 140 ft.
These non-uniform strains impose axial loading and bending of the superstructure, which in turn cause the vertical pressures beneath the footing to fluctuate cyclically. Measured vertical footing pressures closest to the stream were found to fluctuate significantly.
GRS-IBS in Hawaii has many advantages and benefits over traditional concrete abutment bridges as follows:
The larger the pressure fluctuation, the greater PAGE 12
See GRS-IBS page 13
