Sheet pile shoring systems are walls that are formed in progressive manner within the ground by constructing a sequence of piles along the outline of the site and used to laterally retain ground including soil, rock and groundwater. The design of the shoring varies with depth of excavation and prevailing nature of the ground and potential surcharge loads imposed outside the shoring, the allowable deflections and whether the shoring system is permanent or temporary in purpose.
Bored Contiguous Concrete Sheet pile Walls
A contiguous bored sheet pile shoring wall is an earth retaining system formed by installing closely spaced (nearly touching), bored concrete piles and thus not suitable when a water-tight wall structure is needed. To improve water tightness of contiguous sheet pile shoring walls, a combination of temporary dewatering, shotcreting, surface mortar seal applications and at times; local grouting may be needed. Sheet piles are constructed alternately to avoid disturbance to freshly casted neighboring piles.
Either all piles are reinforced or else alternately reinforced depending on strength and stiffness requirements of the system. Contiguous sheet pile walls are either designed as a cantilever or else supported by one or more level of supports (braces, props and/or tie-backs). The wall at its top is normally fully encapsulated with a continuous RC capping beam and the piles bay be joined at several levels with steel or RC waler beams (continuously or intermittently as needed).
Bored Secant Concrete Pile Walls:
A secant pile wall is very similar to its contiguous pile wall counterpart except that adjacent piles are constructed overlapping in plan along the full depth of adjacent piles. And depending on the extent of overlap in plan, the wall is rendered water-tight to different extents. Due to the overlap, normally female (primary) piles are not reinforced and are constructed using modest, strength and well retarded concrete (to be easily over-cut during constructing the male piles), Male (secondary) piles are on the other hand are usually heavily reinforced and constructed using high strength concrete.
Nonetheless, with changing the outline geometry of reinforcement in alternating piles, all piles could be reinforced if strength and stiffness requirements deem so. Water-tightness could also be improved by a combination of mortar repairs, local grouting and shotcreting. Normally secant pile walls are needed for exceptionally deep excavations and high groundwater levels.
A sequence of I / H steel soldier beams of selected section moduli are normally vibrated (or dropped into pre-drilled holes and gravel backfilled) to the designated depth below excavation level and in a manner that the respective flanges of adjacent soldiers are oriented to line up with each other. The soil is thin gradually excavated as timber lagging or precast concrete panels are sled down the cannels formed between the flanges and webs of mutually adjacent soldiers and the process continues in stages until full excavation depth is reached. Berlin walls may be cantilevered or constructed with supports (braces and/or tie-backs) depending on; the prevailing ground conditions, depth of excavation supported and preferred design/construction details.
Depending on the prevailing ground conditions, normally 5.0-7.5m excavation depths seem to be the upper limit in the vicinity supported using this system. Berlin walls are naturally not water tight and therefore can’t be used without extensive external and internal dewatering systems provisioned. Length, section and spacing of the soldiers are determined in the design to ensure strength, stiffness and overall stability of the wall which could be analyzed and determined. Likewise, strength and section properties of the lagging and/or concrete panels must be designed as well, so should the supports, if any (including bearing plates and waler beam sections).
In the case of temporary Berlin walls, and once the permanent construction is completed and the excavation backfilled, the beams are normally extracted by conventional vibratory pile extracting methods.
Sheet Pile Walls:
Sheet pile shoring wall systems are flexible, hot rolled structural steel retaining wall sections; coming in different shapes, dimensions, strength and stiffness. The sections are driven by conventional vibrating or hammering systems into the soil or else pre-bored and driven into rock. The common-most of sheet pile types used in the area are Larsen, Z, U, straight, angled and other standard sections. Normally, sheet piles are rolled in mild steel version or in their high tensile counterparts. They are also rolled in a range of alloying elements to suite the environment in which they serve. Traditionally, sheet piles come in 12m long sections and may be either cut to shorten or spliced to lengthen as needed. Sheet pile sections come with strong interlocking clutches to join adjacent sections of piles together to compose a wall that is rather water tight. Clutches could be mortar filled or grouted with different materials to be made fully water-tight. Sheet pile walls may be combined with other structural steel sections or concrete piles for added strength, stiffness and attain the outline shape required as needed.
Sheet piles walls are constructed by establishing a steel guide frame ensuring the wall is controlled in alignment and verticality and that the sections do not declutch during driving. Driving is normally achieved by standard hydraulic vibrating hammers systems fixed to the booms of a rig or suspended from heavy crawler cranes. Sheet piles when well clutched and penetrate sufficiently below excavation levels form water tight shoring wall systems. Sheet pile walls may be designed as cantilevers or may be tied-back, propped and waled. And all these elements need to be designed for strength and stiffness and dimensioned carefully.
This article comes from spectrageotech edit released