Drainage Systems

Wick Drains

In conjunction with surcharge loading, wick drains are a time- and cost-effective method of consolidating low permeability soft, compressible soils that if left untreated  take several years to drain. Suitable material includes soft, saturated fine-grained soils, organics, sludge, mine tailing, and dredge fills. When a wick drain system is installed before the surcharge preload is placed, the drainage path of trapped pore pressure is shortened to the nearest drain, effectively decreasing total overall drainage time to months. The drain itself consists of a filter strip with corrugated drainage channels wrapped in geotextile filter fabric to prevent clogging. Prior to wick drain installation, a sand or gravel blanket is placed across the site to provide a stable working platform for equipment. Wick drains are installed in a grid pattern on spacings ranging from 2.5-8 ft on center. The wick drains are fitted with an anchor plate and advanced to depth by means of a mandrel attached to a track-mounted excavator or crane, depending on installation depth. Where dense interlayered strata are present, vibratory energy can be applied during installation. On potentially contaminated sites, the wick drain system can be designed to collect the pore water for treatment.

Advantages

  • Rapid installation process
  • Greatly reduced consolidation time
  • Minimal post-construction settlement

Applications

  • Railway and roadways embankments
  • Bridge approaches and overpasses
  • Dams and levees
  • Seaports
  • Buildings and storage tanks
  • Mine waste and tailings

Earthquake Drains

Earthquake drains, either alone or in combination with other methods, are an economical and effective method of mitigating liquefaction potential in loose saturated cohesionless soils. The large-capacity flexible vertical drains are advanced to design depth with a vibrating mandrel that also affords some soil densification, further aiding liquefaction mitigation. Drains are wrapped with a geotextile filter fabric that provides free access to the drain while preventing clogging. They are typically installed on 3-6 ft centers and to depths of 85+ ft. Tighter drain spacing can allow more rapid dissipation of pore water pressure during a seismic event.

Advantages

  • Effective and economic liquefaction mitigation solution
  • Discharge capacity and flow rate exceeds traditional sand drains
  • Pipe designs and fabric types available for variety of applications and soils

Applications

  • Railway and highway embankments
  • Bridge approaches and overpasses
  • Dams and dikes
  • Seaports
  • Commercial and residential development
  • Seismic retrofit