Impact of compaction level and depth of fill on the pullout resistance of ribbed strip MSE reinforcement

Current AASHTO specifications for MSE wall construction require granular backfill used in wall construction to be compacted to achieve 95% of the maximum dry density as determined by AASHTO T-99. However, the degree of compaction specified above is rarely achieved in the field on a consistent basis. Lower compaction levels can adversely impact the pullout resistance capacities of soil reinforcements embedded in the backfill. This paper documents findings from a large scale laboratory test program in which a total of 99 ribbed strip type MSE reinforcement were tested in a sandy backfill to evaluate the impact of compaction level on the pullout resistance of reinforcements. The tests were conducted using a test box with dimensions of 3.6 m×3.6 m×1.2 m (12 ft×12 ft×4 ft). Test specimens of lengths 1.2 m (4 ft), 2.4 m (8 ft) and 3.6 m (12 ft) were tested at overburden pressures equivalent to 1.5 m (5 ft), 3m (10 ft), 6 m (20 ft) and 12 m (40 ft) of backfill at two different levels of backfill compaction. The data collected were then used to calculate the pullout resistance factor (i.e. F) for each reinforcement. Subsequently, appropriate statistical analyses (ANOVA) were conducted on the calculated Fto evaluate the significance of the degree of backfill compaction on F. Results from ANOVA show that compaction is a highly-significant variable (p=0.000). Moreover, review of Fdata collected show that "slight" under-compaction can lower MSE pullout resistance for ribbed strips significantly. Data for the under-compacted pullout tests approached the AASHTO reference line for Fwhile data for the properly compacted tests yielded F values that were significantly higher. The influence of the compaction level on F decreased as the depth of fill increased.