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ABSTRACT A theoretical and practical review of the utilization of prefabricated vertical drains (PVDs) in geotechnical engineering is presented. Recommended spacing of the PVDs and associated zone of influence are presented along with the general boundary theory normally utilized in soil consolidation analysis. Issues related to the installation process and the disturbance of the surrounding soil are discussed. Work reported in the literature on the effect of well resistance and smear is presented. Geotechnical projects dealing with the use of PVDs for coastal applications are reviewed. Case histories reported by several researchers on the stabilization of coastal dredge material, dissipation of pore pressure in the foundation, and the drainage of sludge material are discussed. Finally, recent developments dealing with the premise of using the PVDs for environmental remediation of contaminated soils is presented. INTRODUCTION Coastal and harbor construction activities often encounter contaminated sediments and dredged soft material. The use of the Prefabricated Vertical Drains (PVDs) for a range of applications in offshore engineering is gaining wide acceptance. In addition to the current usage in soil improvement through accelerated consolidation and vacuum assisted consolidation, as reported by Jacob et al. (1994), an innovative development for using PVDs in environmental soil flushing was presented by Gabr et al. (1995) and Bowders and Gabr (1996). The PVDs, also referred to as wick or strip drains, were originally developed as a substitute for the commonly used sand drains. With the advent of material science, these drains are manufactured from synthetic polymers such as polyproplene and high density polyethylene. PVDs are normally manufactured with a corrugated or channeled synthetic core enclosed by a geotextile filter shown schematically in Figure 1. Installation rates reported in the literature are on the order of 0.1 to 0.3 m per second excluding equipment mobilization and setup time.
- Energy > Oil & Gas > Upstream (1.00)
- Construction & Engineering (0.90)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.68)
ABSTRACT The innovative application of prefabricated vertical drains (PVDs) for enhancement of the in situ soil flushing remediafion technique is presented. Testing was performed to evaluate the internal well resistance as a function of flowrate of the PVDs operating under vacuum pressures. The results indicated an approximate linear relationship between the PVD flowrate versus the total vacuum head as well as the head loss versus flowrate. The zone of influence was characterized by testing the PVDs under vacuum conditions in soils consisting of 100% sand and 80% sand/20% kaolinite mixture. Results of the areal extent of the PVD zone of influence were quantified and showed relationships between the 100°6 sand specimens and the 80% sand/20% kaolinite specimens. Pilot-scale tracer flushing tests demonstrated the feasibility of using PVDs for flushing in the 100% sand and the 80/20 soil. The tracer testing demonstrated that longer flushing times were necessary to achieve 80% dean-up levels as the soil hydraulic conductivity decreased when the kaolin was added to the sand. INTRODUCTION Soil flushing is a treatment technology used to remove contaminants from the subsurface with the aid of solutions. The technology uses drilled injection and extraction wells located within the site's contaminated zone. The injection wells are the source point for introducing the flushing solution into the subsurface soil. The remediation process occurs as the solution permeats through the contaminated soil and desorbing the soil-bound contaminants into solution. This technology is limited to sites having coarse-grained soils (i.e., coarse sands) with hydraulic conductivity ranging 10 "1 cm/s to 10"2cm/s. In the case of fine-grain fraction soils with hydraulic conductivities less than 103cm/s, conventional soil flushing is not always effective for remediation of contaminated soils and the use of pump and treat systems on long term basis may be required.