Decomposed bedrock near south lot building foundation up of cemented sand mixed with concrete and brick at an El. of approximately 37± ft (11.3 m), whereas a test pit on the western facade exposed a concrete footing extending to El. 36± ft (10.9 m). Based on the varying foundation types, particularly the sections composed of cemented stones, the foundation might have begun to disintegrate once undermined by underpinning efforts. Decomposed Rock Decomposed rock found above the bottom of the site excavation subgrade would have greatly limited the production of handexcavated pit underpinning piers. The decomposed rock posed an issue for even the large excavator implemented for the bulk excavation work performed on site. The soil broke apart in flakey chunks that required buckets to scrape rocks away from the virgin soil material. Digging through this soil by hand underneath the building would have required workers to implement chipping hammers to break apart the soil and rock fragments. Soil Nail Wall Implementation The geotechnical report indicated that the Carnegie Building rested on top of a dense soil layer with standard penetration testing (SPT) N-values as high as 99 blows per foot and fines content ranging from 25% to 35%. More specifically, laboratory testing conducted on retrieved samples found that the soils under the building had a unified soil classification system (USCS) classification of SM and had at least 25% of the soil grains passing through the No. 200 18 * DEEP FOUNDATIONS * MAR/APR 2020 Active soil nail wall illustration (cross-section) Carnegie soil nail wall