Mark J. Farrow, P.E.¹ & Michael D. Roland²

Grapevine Mills Mall is a 2 million square foot single level mall located in Grapevine, Texas. The surficial site soils consist primarily of clay and sandy clay soils having plasticity indices (PI’s) ranging from about 15 to 30. Layers of highly plastic clay and shaley clay with PI's of over 40 are also present within areas on the site. Construction began in the summer of 1996 after one of the most severe droughts in the Dallas-Fort Worth Metroplex. As a result, the overburden clay and sandy clay soils were extremely dry and potentially highly expansive to depths of about 12 feet at the start of construction. Preliminary recommendations for pier foundations and structural floor systems were cost prohibitive. The developer requested that subgrade preparation requirements be developed to achieve a balanced cut/fill, with minimal imported select fill, yet suitable for shallow foundation support. On-site clay soils were over-excavated and placed in 'a moisture-conditioned-controlled manner to minimize soil swell yet provide adequate compressive strength to allow the use of shallow foundations. This paper presents the details associated with design and construction of the building pad and the shallow foundation system used at this site.