Thomas A. Williamson’s research while affiliated with University of Illinois, Urbana-Champaign and other places

A 183 m by 122 m prefabricated vertical-drain test section was completed in February, 1993, in the Craney Island Dredged Material Management Area. The test section was constructed to evaluate the effectiveness of prefabricated vertical drains in consolidating the dredged fill and underlying foundation clay, thus increasing the storage capacity of the facility. The feasibility of installing prefabricated vertical drains was questionable because vertical drains had never been installed in an active dredged material management area; a drain length of approximately 50 m was close to the longest vertical drain ever installed, and the installation equipment could exert a ground pressure of only 10.3 kPa to operate on the surface of the soft dredged material. Results show that the dredged fill and foundation clay underwent substantial consolidation settlement (1.8 to 2.7 m in 30 months) after drain installation. In summary, prefabricated vertical drains appear to be an economical technique for increasing the storage capacity of active and inactive dredged material management areas.

This paper describes torsional ring shear tests on interfaces comprised of high-density polyethylene (HDPE) geomembranes/nonwoven geotextiles and a drainage geocomposite. Four textured geomembranes with three different manufacturing techniques are utilized to investigate the effect of geomembrane texturing on interface shear resistance. In addition, the effects of geotextile fiber type, fabric style, polymer composition, calendering, and mass per unit area on textured HDPE geomembrane interface strengths are investigated. The textured HDPE geomembrane/nonwoven geotextile and drainage geocomposite interfaces exhibited a large post-peak strength loss. This strength loss is attributed to pulling out or tearing of filaments from the nonwoven geotextile and orienting them parallel to shear and polishing of the texturing on the geomembrane. At high normal stresses, the strength loss can be caused by damage to or removal of the texturing on the geomembrane surface.

This study investigates the feasibility of installing vertical strip drains to increase the storage capacity of the Craney Island Dredged Material Management Area. The installation of vertical strip drains in the disposal area is technically feasible and will accelerate consolidation of the dredged fill and underlying marine clay. This consolidation will result in a rapid increase in storage capacity and soil shear strength. The shear strength gain will allow the perimeter dikes to be constructed to higher elevations without setbacks or stability berms. The installed strip drains will also accelerate consolidation of the existing dredged fill and marine clay as new dredged material is laced in Craney Island. A preliminary triangular strip drain spacing and cost of installing vertical strip drains in Craney Island is presented. A detailed plan of action and schedule for installing vertical strip drains in the northern compartment of Craney Island is also presented. Strip drains, Dike setback, Vertical drainage system, Craney Island, Horizontal drainage system