Earth-filled wide-base hollow piers for excavation support

Tiebacks are frequently used to support deep excavations. Installations of tieback systems require certain favorable subsurface conditions as well as skill and experience. When the subsurface conditions are not suitable for tieback installation, an alternative bracing method is needed to achieve the same degree of effectiveness without the use of anchors. This paper presents a method of using earth-filled wide-base hollow piers to brace a deep excavation for construction of Penyun Hotel Building in Shenyang, China. The building covers 16,000 m2 and had a 100-m high main tower with a 24-m high apron building. The depth of excavation varied from 12.3 m to 16.5 m. The foundation site contained a 4.1-m thick fill of construction debris followed by a 0.7-m thick clay, a 5.5-m thick sand, and a very thick gravelly sandy soil stratum. The ground water table was near the foundation base. The design, construction, and performance of the bracing system are presented and discussed. It was concluded that the earth-filled wide-base hollow piers could effectively utilize a portion of unstable backfill to become a part of the retaining structure. As a result, a considerable saving in concrete material was realized. Therefore, it is an effective and economical method for bracing deep excavations when the subsurface condition are not favorable for installation of tieback systems.