Evaluation Of Passive Force On Skewed Bridge Abutments With Controlled Low Strength Material Backfill
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Author | : Kevin Bjorn Wagstaff |
Publisher | : |
Total Pages | : 129 |
Release | : 2016 |
Genre | : |
ISBN | : |
To determine the relationship of passive force versus backwall displacement for a CLSM backfilled bridge abutment, two laboratory large-scale lateral load tests were conducted at skew angles of 0 and 30°. The model backwall was a 4.13 ft (1.26 m) wide and 2 ft (0.61 m) tall reinforced concrete block skewed to either 0 or 30°. The passive force-displacement curves for the two tests were hyperbolic in shape, and the displacement required to reach the peak passive resistance was approximately 0.75-2% of the wall height. The effect of skew angle on the magnitude of passive resistance in the CLSM backfill was much less significant than for conventional backfill materials. However, within displacements of 4-5% of the backwall height, the passive force-displacement curve reached a relatively constant residual or ultimate strength. The residual strength ranged from 20-40% of the measured peak passive resistance. The failure plane did not follow the logarithmic spiral pattern as the conventional backfill materials did. Instead, the failure plane was nearly linear and the failed wedge was displaced more like a block with very low compressive strains.
Author | : Aaron Kirt Marsh |
Publisher | : |
Total Pages | : 176 |
Release | : 2013 |
Genre | : Electronic dissertations |
ISBN | : |
Accounting for seismic forces and thermal expansion in bridge design requires an accurate passive force versus backwall deflection relationship. Current design codes make no allowances for skew effects on the development of the passive force. However, small-scale experimental results and available numerical models indicate that there is a significant reduction in peak passive force as skew angle increases for plane-strain cases. To further explore this issue large-scale field tests were conducted at skew angles of 0°, 15°, and 30° with unconfined backfill geometry. The abutment backwall was 11 feet (3.35-m) wide by 5.5 feet (1.68-m) high, and backfill material consisted of dense compacted sand. The peak passive force for the 15° and 30° tests was found to be 73% and 58%, respectively, of the peak passive force for the 0° test which is in good agreement with the small-scale laboratory tests and numerical model results. However, the small differences may suggest that backfill properties (e.g. geometry and density) may have some slight effect on the reduction in peak passive force with respect to skew angle. Longitudinal displacement of the backfill at the peak passive force was found to be approximately 3% of the backfill height for all field tests and is consistent with previously reported values for large-scale passive force-deflection tests, though skew angle may slightly reduce the deflection necessary to reach backfill failure. The backfill failure mechanism appears to transition from a log spiral type failure mechanism where Prandtl and Rankine failure zones develop at low skew angles, to a failure mechanism where a Prandtl failure zone does not develop as skew angle increases.
Author | : Tyler Kirk Remund |
Publisher | : |
Total Pages | : 110 |
Release | : 2017 |
Genre | : |
ISBN | : |
It was observed that the cellular concrete backfill mainly compressed under loading with no visible failure at the surface. The passive-force curves showed the material reaching an initial peak resistance after movement equal to 1.7-2.6% of the backwall height and then remaining near this strength or increasing in strength with any further deflection. No skew effects were observed; any difference between the two tests is most likely due to the difference in concrete placement and testing.
Author | : Jaycee Cornwall Smith |
Publisher | : |
Total Pages | : 110 |
Release | : 2014 |
Genre | : Electronic dissertations |
ISBN | : |
Bridge abutments are designed to withstand lateral pressures from thermal expansion and seismic forces. Current design curves have been seen to dangerously over- and under-estimate the peak passive resistance and corresponding deflection of abutment backfills. Similar studies on passive pressure have shown that passive resistance changes with different types of constructed backfills. The effects of changing the length to width ratio, or including MSE wingwalls determine passive force-deflection relationships. The purpose of this study is to determine the effects of the wall heights and of the MSE support on passive pressure and backfill failure, and to compare the field results with various predictive methods.
Author | : Amy Fredrickson |
Publisher | : |
Total Pages | : 196 |
Release | : 2015 |
Genre | : Electronic Dissertations |
ISBN | : |
Test results in both sets of backfills confirmed previous findings that there is significant reduction in passive force with skewed abutment configurations. The reduction factor was 0.58 for the gravel backfill and 0.63 for the GRS backfill, compared to the predicted reduction factor of 0.53 for a 30° skew. These results are within the scatter of previous skewed testing, but could indicate that slightly higher reduction factors may be applicable for gravel backfills.
Author | : Rebecca Eileen Black |
Publisher | : |
Total Pages | : 89 |
Release | : 2018 |
Genre | : |
ISBN | : |
The cellular concrete for the 0° skew test had an average wet destiny of 29 pounds per cubic food and a 28-day compressive strength of 120 pounds per square inch. The cellular concrete for the 30° skew test had an average wet density of 31 pounds per cubic foot and a 28-day compressive strength of 132 pounds per square inch. It was observed from the passive force deflection curves of the two tests that skew decreased the peak passive resistance by 29% , from 52.1 kips to 37 kips. Various methods were used to predict the peak passive resistance and compared with observed behavior to verify the validity of each method.
Author | : Azadeh Bozorgzadeh |
Publisher | : |
Total Pages | : 265 |
Release | : 2007 |
Genre | : |
ISBN | : |
Bridge abutments provide resistance to deformation and earthquake induced inertial forces from the bridge superstructure. In order to limit the inertial forces transmitted into the abutment walls and piles, the abutment walls are designed to be sheared off in major seismic events. Therefore, the force-resistance mechanism of bridge abutments in the longitudinal direction is mainly provided by backwall-soil interaction. Current design practice in California makes use of bi-linear load-deformation curve and does not account for the structure backfill properties. An experimental and an analytical research program were conducted at UCSD to further investigate such structure backfill interaction characteristics. In order to meet the objectives of this research project, a field investigation was conducted to develop a proper characterization of the soil types used for abutment structure backfills. The experimental program included five large-scale tests. In the first phase of the experiment, an abutment wall (without a foundation) was built at 50% scale of a prototype diaphragm abutment. The second phase of this research program was performed on a backwall sheared off from wingwalls and stem in seat-type abutments. The specific aims of the experimental program were to examine the effect of structure backfill soil type, backfill height, vertical movement of the wall, and pre-existing cut slope in backfilling on stiffness and capacity of the abutments in the longitudinal direction. An analytical model was developed for evaluating the response of bridge abutments loaded longitudinally. The approach involves calculating maximum passive resistance of the structure backfill material, and creating p-y curves to predict the force-displacement relationship of longitudinally loaded bridge abutments. The finite element program Plaxis 2D was used to model the abutment wall experiments. The procedure was validated by comparing the finite element results with the experimental results. In conclusion, the study indicates that the response of bridge abutments in the longitudinal direction is nonlinear and a function of several factors which need to be considered. The passive resistance of the structure backfill is controlled by the soil shear strength and the interface friction angle. Finally, the vertical movement of the wall has a significant effect on post-peak behavior of abutments.
Author | : Kyle M. Smith |
Publisher | : |
Total Pages | : 186 |
Release | : 2014 |
Genre | : Electronic Dissertations |
ISBN | : |
A comparison of passive force per unit width suggests that MSE wall abutments provide 60% more passive resistance per unit width compared to reinforced concrete wingwall and unconfined abutment geometries at zero skew. These findings suggest that changes should be made to current codes and practices to properly account for skew angle in bridge design.
Author | : Scott Karl Snow |
Publisher | : |
Total Pages | : 109 |
Release | : 2019 |
Genre | : Electronic dissertations |
ISBN | : |
The finite element models generally confirmed the findings of Smith (2014). The results of the 11- and 38-foot abutment finite element models confirmed that the wingwall on the obtuse side of the 45° skewed abutments experienced approximately 4 to 5 times the amount of horizontal soil pressure and 5 times the amount of bending moment compared to the non-skewed abutment. Increases in the pressures and bending moments are likely caused by soil confined between the obtuse side of the abutment and the wingwall.
Author | : Kyle M. Rollins |
Publisher | : |
Total Pages | : 88 |
Release | : 2010 |
Genre | : Reinforced soils |
ISBN | : |
Approach fills behind bridge abutments are commonly supported by wrap-around mechanically stabilized earth (MSE) walls; however the effect of this geometry on passive force development is unknown. This report describes the first large-scale tests to evaluate passive force-deflection curves for abutments with MSE wingwalls. A test was also performed with fill extending beyond the edge of the abutment wall for comparison. The abutment wall was simulated with a pile supported cap 5.5 ft high, 11 ft wide, and 15 ft long in the direction of loading. The backfill behind the pile cap consisted of clean sand compacted to 96% of the modified Proctor maximum density. As the pile cap was loaded laterally, pressure on the MSE wall led to pull-out of the steel reinforcing grids and the MSE wall panels moved outward about 2% of the wall height when the ultimate passive force developed. Despite pullout, the passive force per effective width was 28 kips/ft for the pile cap with MSE wingwalls compared to 22.5 kips/ft for the cap without wingwalls. Nevertheless, the passive force with the MSE wingwalls was still only 76% of the resistance provided by the cap with fill extending beyond the edges. The pile cap with MSE walls required greater movement to reach the ultimate passive force (deflection of 4.2% of wall height vs. 3%). The Caltrans method provided good agreement with the measured passive resistance while the log spiral method required the use of a higher plane strain friction angle to provide reasonable agreement.