Three commonly rolled Z-shaped sections are the PZ 22, PZ 27, PZ 35, and PZ 40. In sheet piling nomenclature, “P” denotes that it is steel sheet piling, “Z” denotes that it is a Z-shaped profile, and the remainder denotes the weight per sq ft of wall (Askar, 1988). Straight-web and Z-profile sheet piling as well as high-modulus (combi-wall) systems are readily available in the United States in various steel grades ranging in yield strengths from 39 ksi to 65 ksi.
Straight Web (PS) Sheet Piling
The PS pile provides minimal flexural strength as it is not designed for use in bending. PS piling is the section that is used for construction of cellular sheet pile structures. These sections have high-strength interlocks designed to withstand the tensile forces developed in the wall. A typical PS section is shown in Figure 3-1 with section dimensions and properties provided in Table 3-1.
Figure 3-1. PS sheet pile section
Table 3-1. Section dimensions and properties for commonly rolled PS sections
Section Width Web Maximum Interlock Strength Minimum Cell Diameter Cross Sectional Area Weight Elastic Section Modulus Moment of Inertia Coating Area
Pile Wall Single
Pile
Wall Surface (w) (tw)
in. in. k/in ft in2/ft lb/ft lb/ft2 in3/sheet in4/sheet ft2/ft ft2/ft2
PS 27.5 19.69 0.4 24 30 8.09 45.1 27.5 3.3 5.3 3.65 1.11
PZ 31 19.69 0.5 24 30 9.12 50.9 31.0 3.3 5.3 3.65 1.11
Z-Profile (PZ and PZC) Sheet Piling
Z-profile steel sheet piling provides a section which is designed primarily for resisting flexural loads. They have a higher section modulus and moment of inertia per lb of steel compared to PS sections. A PZ-profile sheet pile section is shown in Figure 3-2a with section dimensions and properties provided in Table 3-2. PZC sections are the most recent generation of sheet piling and have a higher ratio of section modulus to weight than traditional PZ sections. As a comparison, a PZC 17 section has a weight of approximately 80% of a PZ 27 section with both having the same flexural strength. While PZ sections are named for weight per sq ft of wall, PZC sections are
listed by section modulus (a PZC 13 has a section modulus of 1300 cm3/m). A PZC section is
shown in Figure 3-2b with section dimensions and properties provided in Table 3-3.
w
Figure 3-2. Z-profile sheet pile sections Table 3-2. Section properties for commonly rolled PZ sections
Section Width Height Thickness Cross Sectional Area Weight Section Modulus Moment of Inertia Coating Area
Flange Wall Pile Wall Elastic Plastic Single
Pile
Wall Surface (w) (h) (tf) (tw)
in. in. in. in. in2/ft lb/ft lb/ft2 in3/ft in3/ft in4/ft ft2/ft ft2/ft2
PZ 22 22.0 9.0 0.375 0.375 6.47 40.3 22.0 18.1 21.79 84.38 4.48 1.22
PZ 27 18.0 12.0 0.375 0.375 7.94 40.5 27.0 30.2 36.49 184.20 4.48 1.49
PZ 35 22.6 14.9 0.600 0.500 10.29 66.0 35.0 48.5 57.17 361.22 5.37 1.42
PZ 40 19.7 16.1 0.600 0.500 11.77 65.6 40.0 60.7 71.92 490.85 5.37 1.64
Table 3-3. Section properties for commonly rolled PZC sections
Section
Width Height
Thickness Weight Section
Modulus
Moment of Inertia
Flange Wall Wall Elastic
(w) (h) (tf) (tw)
in. in. in. in. lb/ft2 in3/ft in4/ft
PZC 13 27.88 12.56 0.375 0.375 21.7 24.2 152.0
PZC 18 25.00 15.25 0.375 0.375 24.2 33.5 255.5
PZC 26 27.88 17.70 0.600 0.525 31.8 48.4 428.1
PZC 36 24.80 19.93 0.655 0.600 39.6 67.0 667.4
High Modulus Sections
Large lateral pressures caused by surcharge loading may induce significant bending stresses in the sheet piling. The use of standard sheet pile sections would require large sections which may make the use of a sheet pile abutment uneconomical. In such cases, Dondelinger and
w h t t t t h w w f w f a.) PZ b.) PZC
3-3. The disadvantage to these systems is the special fabrication required. Although many steel manufacturers provide specialized wide-flange sections (HZ), adapters are readily available to allow the use of standard W and HP shapes in combination walls (see Figure 3-4).
Figure 3-3. Combination wall using specialized high-modulus shapes
Figure 3-4. Combination wall system using standard shapes with flange adapters
Vinyl Sheet Piling
Although steel is the primary material used in sheet pile construction, other materials are
available which may provide benefits over steel. One alternative is vinyl sheet piling, made from polyvinyl chloride (PVC). In general, vinyl sheet piles are approximately half the cost of steel as well as being about 20% of the weight; these benefits have resulted in the successful construction of several retaining structures utilizing the material (Dutta and Vaidya, 2003).
Although vinyl is lighter and cheaper, steel is the superior material when it comes to structural properties. The average modulus of elasticity of the PVC piles is 300 ksi; vinyl sheet piles will deflect approximately 100 times more than similar steel piles under the same loads.
Special connector Special pile sections Flange adapter PZ or PZC piles W or HP shape
An analysis of the long-term applications of vinyl sheet piling was completed by Dutta and Vaidya (2003). Accelerated aging tests, including testing of ultraviolet radiation exposure and impact resistance degradation, were performed on the piles. Through these tests, severe discoloration from ultraviolet radiation and impact resistance degradation was observed. The primary concern, however, is the visco-elastic properties of the material. Over time the modulus of elasticity will undergo degradation under a static load, causing the piling to creep and show excessive deformation without any failure occurring. Creep is an issue which must be accounted for in the selection of piling; creep modulus information should be available from PVC sheet pile manufacturers (Dutta and Vaidya, 2003). Other concerns that are more prominent for PVC sheet piling than steel are vandalism and fire damage; extra effort must be made to remove
combustible materials from the abutment areas.
Geogrid for GRS Systems
One type of material used for the construction of GRS system is geogrid and is available in uniaxial, biaxial, and triaxial designs; biaxial geogrid was utilized for project TR-568. Uniaxial geogrid provides soil reinforcement in one direction while biaxial provides strength in both the longitudinal cross-machine direction (XMD) and the transverse machine direction (MD). Triaxial geogrid is constructed to have no weak axis and thus provides strength in all directions. A geogrid material with strength in at least two directions is desirable for sheet pile bridge abutment systems to provide reinforcement transversely for the wingwalls.
Biaxial geogrid is stronger in the XMD due to the nature of its fabrication. As can be seen in Figure 3-5, the XMD consists of continuous fibers throughout the length of the material; the MD is not continuous and does not provided the same strength.
Figure 3-5. Diagram of geogrid material depicting MD and XMD
Tensar® International Corporation provides several types of biaxial geogrid; select product
specifications are provided in Table 3-4. The damage resistance of the material is considered to be the percentage of strength retained after installation damage (based on testing performed with gravel).
Table 3-4. Geogrid specifications
Geogrid Type
Tensile strength @ 5% strain Ultimate tensile strength Damage
Resistance MD XMD MD XMD (lb/ft) (lb/ft) (lb/ft) (lb/ft) % BX1100 580 920 850 1300 90 BX1200 810 1340 1310 1970 90 BX1500 1200 1370 1850 2050 90 XMD MD