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Vertical Impermeable Barriers (Cutoff Walls)

 

 

2.4.    Sheet Pile Walls

Theoretical Background/Applicability

In general, sheet pile walls may consist of steel, precast concrete, aluminum, wood, among others (Pearlman, 1999; USEPA, 1984). For containment of contaminants steel is the most applicable material. The sheets are assembled before installation and can be either driven or vibrated into the ground, in either case, the sheet is lowered a few feet at a time (Pearlman, 1999). A major advantage of using sheet pile walls is that it provides strength (McMahon, 1995). A continuous wall is constructed by joining the sheets together. These joints are considered to be the major weakness of sheet pile walls (McMahon, 1995; Pearlman, 1999). Another concern is potential corrosion of the steel due to long-term exposure to some chemicals (McMahon, 1995).

Traditional sheet pile walls are widely used for civil engineering projects but their use in geoenvironmental applications is limited due to leakage between the panel interlocks (McMahon, 1995). Several innovative designs have been developed to address the problem of leakage between the interlocks including the Waterloo Barrier which is shown in Figure 11.  The Waterloo barrier is able to achieve hydraulic conductivities of less than 10-8 cm/s (Pearlman, 1999 previously from Mutch et al., 1997) by sealing the joints between each sheet.

                                      

figure 10

Figure 11: Waterloo Barrier Schematic (Mutch et al., 1997 as presented by Pearlman, 1999)

 

Advantages (Sharma and Reddy, 2004)

  • Damaged wall section can be easily removed and replaced
  • Depths of 50 to 100 ft can be reached depending on conditions and equipment
  • Installation is very rapid when compared to other types of cutoff wall construction
  • These walls have high strengths which is ideal for durability or if any type of reinforcement is required
  • Little to no waste materials are generated during constuction
  • Transport through means of diffusion is greatly reduced

Disadvantages (Sharma and Reddy, 2004)

  • Steel walls are generally susceptible to salts and acids
  • Interlock leakage can be quite significant for standard sheet pile joints
  • Steel is very expensive when compared to other construction materials
  • Piles can be hard to drive if boulders are present and also hard to key into low permeable layers
  • Standard sheet pile walls usually do not have hydraulic conductivity values greater than 10-7 cm/s

Cost (as presented by Pearlman 1999)

The cost of a sheet pile barrier ranges from $15 – $40/ft2 depending on the depth, equipment used, type of joint, and type of sealant.

Field Setup/Process Involve

Sheet pile walls are fairly easy to install and do not require any previous excavation. Interlocking sheet piles, typically made of steel, are simply inserted into the ground one by one. The piles are either driven or more commonly vibrated to the necessary depth. For greater depths, additional piles are simply welded to the piles already inserted into the ground. If sealable joints are used, the joint cavities are flushed of all soil and debris and then a sealant is injected into the cavity (Pearlman, 1999).

 

 

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