Sheet pile retaining walls are widely used for waterfront construction and consist of interlocking members that are driven into place. Individual sheet piles come in many different sizes and shapes. Sheet piles have an interlocking joint that enables the individual segments to be connected together to form a solid wall.
Many different types of design methods are used for sheet pile walls. below Figure shows the most common type of design method. In below Fig. , the term H represents the unsupported face of the sheet pile wall. this sheet pile wall is being used as a waterfront retaining structure and the level of water in front of the wall is at the same elevation as the groundwater table elevation behind the wall. For highly permeable soil, such as clean sand and gravel, this often occurs because the water can quickly flow underneath the wall in order to equalize the water levels.
, the termD represents that portion of the sheet pile wall that is anchored in soil. Also shown in above Fig. is a force designated as Ap. This represents a restraining force on the sheet pile wall due to the construction of a tieback, such as by using a rod that has a grouted end or is attached to an anchor block. Tieback anchors are often used in sheet pile wall construction in order to reduce the bending moments in the sheet pile. When tieback anchors are used, the sheet pile wall is typically referred to as an anchored bulkhead, while if no tiebacks are utilized, the wall is called a cantilevered sheet pile wall.
Sheet pile walls tend to be relatively flexible. Thus, , the design is based on active and passive earth pressures. For this analysis, a unit length (1 m or 1 ft) of sheet pile wall is assumed. The soil behind the wall is assumed to exert an active earth pressure on the sheet pile wall. At the groundwater table (Point A), the active earth pressure is equal to kA yd1, where kA=active earth pressure coefficient from Eq. (the friction between the sheet pile wall and the soil is usually neglected in the design analysis), yt= total unit weight of the soil above the groundwater table, and d1= depth from the ground surface to the groundwater table. At Point B in the figure Fig. 6.38, the active earth pressure equals kA ytd1 + kA yb d2, where yb= buoyant unit weight of the soil below the groundwater table and d2 depth from the groundwater table to the bottom of the sheet pile wall. For a sheet pile wall having assumed values of H and D , and using the calculated values of active earth pressure at Points A and B, the active earth pressure resultant force (PA), in kN per linear m of wall or lb per linear foot of wall, can be calculated
The soil in front of the wall is assumed to exert a passive earth pressure on the sheet pile wall. The passive earth pressure at Point C in the above Figure. is equal to kp bD, where the passive earth pressure coefficient (kp) can be calculated from Eq. . Similar to the analysis of cantilever retaining walls, if it is desirable to limit the amount of sheet pile wall translation, then a reduction factor can be applied to the passive pressure. Once the allowable passive pressure is known at Point C, the passive resultant force (Pp) can be readily calculated. As an alternative solution for
the passive pressure, Eq. can be used to calculate Pp with the buoyant unit
References:
- BUILDING DESIGN AND CONSTRUCTION HANDBOOK for Frederick S. Merritt & Jonathan T. Ricketts