<p><p><h2>Project Summary/Scope:</h2>The project to retrofit/strengthen the existing footings called for cast-in-drilled-hole concrete piles. Due to unanticipated site conditions and a low overhead height of approximately 6 meters, these proved to be unfeasible and micropiles were used instead. Sixty-four micropiles were installed.</p><p>Subsurface Conditions: Loose to slightly compact fill in the upper 8 meters. Dense to very dense sands and gravels were found below this. The ground water table was approximately located 8 meters below the ground surface.</p><p>Type 1B micropiles were used and were designed for a maximum of 15 mm of movement and to bear a load of 2,225 kN. The total length of the pile was 27 meters. Pipe piles had an outer diameter of 178 mm and a wall thickness of 12.7 mm. The micropiles were reinforced full length with grout and two 35-mm diameter, grade 150 thread bars. The pile bond length extended from 9 to 18 meters below the bottom of the existing footing, which consisted of pressure grouted bond zone. A high torque, low-head room drill rig was used to install the micropiles.</p><p><figure id='attachment_3527' style='max-width:933px' class='caption aligncenter'><img class="wp-image-3527 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic diagrams showing case 1 micropiles used to stabilize slopes." width="933" height="401" /><figcaption class='caption-text'> Case 1 Micropiles (FHWA NHI-05-039; Sabatini et al., 2005)</figcaption></figure><h2>Performance Monitoring:</h2>Cyclic pile load testing and creep load testing were performed. Deformations that occurred during testing proved to be within an acceptable range.<br><h2>Project Technical Paper:</h2>Bruce, D.A. and Chu, E.K. (1995). "Micropiles for Seismic Retrofit" Proc. National Seismic Conference on Bridges and Highways. Sponsored by FHWA and Caltrans. San Diego, CA, Dec. 10-13, 17p.<br><h2>Figure Reference:</h2>Sabatini P.J., Tanyu, B., Armour, T., Groneck, P. and Keeley, J. (2005). “Micropile Design and Construction (Reference Manual for NHI Course 132078).” Federal Highway Administration, Publication No. FHWA-NHI-05-039, December 2005.<br><h2>Date Case History Prepared:</h2>November 2012</p><p>&nbsp;</p></p>