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Introduction Motivations: There are hundreds of miles of retaining wall systems that exist in western United States Their routine design for static applications has been practiced by many public and private sectors However, seismic design of these retaining walls has not been extensively developed with a lack of accurate and reliable guidelines in existing design codes and specifications Objectives: To develop improved and validated rational guidelines for seismic design of retaining walls to overcome the drawbacks in existing Caltrans design specifications and tools Two full-size semi-gravity reinforced concrete cantilever walls designed according to the typical plans in current Caltrans design specifications tested at NEES Large High- Performance Outdoor Shake Table at the Englekirk Structural Engineering Center of UCSD Experimental Investigation Test Specimen: Two retaining walls that had a stem 1.83 m (6 ft) tall, footing was 2.36 m (7.75 ft) wide and 2.69 m (8.83 ft) long First retaining wall that was tested did not have a sound wall Second retaining wall that was tested did have a sound wall on top of the retaining wall Dimensions of the sound wall were 1.83 m (6 ft) high and 2.64 m (8.67 ft) in length Sound wall was constructed from masonry blocks that were filled with grout Experimental Configuration: Both tests have same set-up configuration on shake table Each test specimen backfilled with typical Caltrans soil and contained in steel laminar soil box Soil box was fixed to shake table and restrained laterally to act as a rigid box, allowed for unidirectional movement Backfill had zero slope and 95% compaction using gasoline powered whackers References California Department of Transportation. (2004). Bridge Design Specification (BDS), Structure Design Manual, August. California Department of Transportation. (2008). Section 14 – Retaining Walls with Soundwalls. In: Bridge Standard Detail Sheets. http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/bridge -standard-detail-sheets/sec14.html. Cited 23 July 2010. http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/bridge -standard-detail-sheets/sec14.html Observations Both tests formed cracking at joint where the footing and stem meet Sound wall was still intact after all of the ground motions in test with sound wall Cracking of the joint between the retaining wall and sound wall Reinforcement connected the retaining wall and sound wall together kept sound wall from collapsing during the shaking More disturbance in the soil from high frequency shakes (Northridge earthquake and Takatori earthquake) Most of the early cracking seen closer to retaining wall Cracks in soil started opening up towards middle length of backfill in 150% and 200% Northridge shakes (both tests) Figure 3: Retaining wall with the sound wall in the steel laminar soil box on the shake table Figure 1: Retaining wall without the sound wallFigure 2: Retaining wall with the sound wall Results Similar trends seen in both tests Acceleration at top of retaining wall was greater than the bottom Slightly larger acceleration in soil near wall with translation of wall Bending of stem with greater displacements near top of stem and smaller displacements near bottom of stem Dynamic pressure trend along height of stem (from pressure cells): Low pressure near top with increase of pressure near middle, decrease of pressure near the bottom in test without sound wall Pressure was greater near top of stem than any other location of the pressure cells along height of stem in test with sound wall Figure 11: Crack pattern in the backfill after the test without the sound wall was tested Figure 12: Crack pattern fin the backfill after the test with the sound wall was tested Input Motions 1994 Northridge (US-CA) earthquake, 1999 Kocaeli (Turkey) earthquake, and 1995 Takatori (Japan) earthquake were used All 3 earthquakes were performed at 25% intervals increasing to 100% (25%, 50%, 75 %, and 100%) 150% and 200% of Northridge were performed after 100% of all 3 earthquakes Figure 5: Compacting soil with gasoline powered whackers Figure 6: Northridge Input Motion Figure 7: Kocaeli Input Motion Figure 8: Takatori Input Motion Figure 4: Dumping the soil into the steel laminar soil box Figure 9: Cracking at the joint between the stem and footing of the retaining wall Figure 10: Cracks in the sound wall after testing Conclusions Larger relative displacements of the retaining wall in 150% and 200% of the Northridge motion from test with the sound wall while test without the sound wall had larger relative displacements for other ground motions performed More dynamic pressure near top of stem test with sound wall and greater dynamic pressure towards middle and bottom of stem for test without the sound wall for all motions High frequency earthquake (Northridge and Takatori) had more of effect on test specimens than low frequency earthquake (Kocaeli) Figure 13: Dynamic pressure along the height of the stem for Northridge earthquakes Figure 14: Dynamic pressure along the height of the stem for Kocaeli earthquakes Figure 15: Dynamic pressure along the height of the stem for Takatori earthquakes Test without the Sound WallTest with the Sound Wall Figure 16: Dynamic pressure along the height of the stem for Northridge earthquakes Figure 17: Dynamic pressure along the height of the stem for Kocaeli earthquakes Figure 18: Dynamic pressure along the height of the stem for Takatori earthquakes