Full Scale Footing Load and Settlement Response Case Study

Several alternatives were evaluated for improving the load carrying capacity of the existing spread footings at a 1-story 9,100 square meter (98,000 square foot) manufacturing facility in Yonkers, New York. Improvements were deemed necessary because a proposed vertical building addition, consisting of 2 additional levels of parking/office space was planned, and because the underlying soils beneath the existing footings consisted of loose to dense sands/silts. Improvement alternatives that were evaluated during design included the installation of micro-piles, jet grouting, and increasing the size of the existing spread footings by forming and pouring symmetrical footing extensions. This latter alternative was determined to be the most cost effective by the Developer/Contractor for limiting the total estimated settlements under the existing and proposed loads to acceptable levels. Because the estimated footing settlements were dependent upon the assumed engineering properties of the underlying sands/silts, specifically the Modulus of Elasticity, E_s, an instrumentation plan was developed to allow the footing load and settlement response to be monitored in the field during construction. This "Observational Approach" was employed to better estimate E_s and the total footing settlement at completion.