Analysis of geotechnical instrumentation to assess foundation performance of I-15

The reconstruction of Interstate 15 in Salt Lake City, Utah required extensive high fills and high retaining walls over soft foundation soils to both raise and widen existing embankments and to construct new embankments. The paper describes the type and interpretation of geotechnical instrumentation used to assess foundation performance during construction. Data are presented for a 9.5 in high embankment and a 16 in high MSE wall both treated with prefabricated vertical drains (PVD) and geotextile reinforcement. The methodology finally adopted to assess foundation stability focused primarily on the time rate of maximum horizontal displacement (dh(m)/dt) and changes in the deformation ratio (DR = dh(m)/ds), where s is the settlement under the embankment, as a function of the fill height. The installation of PV drains at spacings of 1.5 m or less caused significantly more settlement and lateral displacement without increasing the rate of consolidation.