Diaphragm cell structures consist of a series of two circular arcs
normally joined by 120-degree junction piles and straight transverse
sheet pile diaphragms.
With this layout, the cells are not self-supporting during the
construction phase, which makes it difficult to build such a cofferdam
in water, without constructing an embankment beforehand.
Nevertheless, the diaphragm cell layout has a key advantage:
•• As the length of the common wall within the straight diaphragm
does not impact the tensile force in the sheet piles, its length is
not limited. This solution is therefore an alternative to circular
cells when the maximum diameter allowed by the interlock
resistance is exceeded. Tensile forces in the 120 degree Y-type
junction piles are balanced.
The intermediate sheet piles transfer horizontal loads to the pipe
piles. The sheet piles can be shorter than the pipe piles. The third
element in the combined wall is the connector that enables the
sheet piles to connect to the pipe piles. The connector is usually an
extruded or cast piece, matches the lock of the intermediate sheet
piles and is welded to the pipe pile.
The intermediary sheet piles only have an earth-retaining and
load transfer function and transfer the soil and water pressures to
the pipe piles, which carry most of the load. The sheet piles are usually
shorter, with lengths from 60% up to the length of the pipe pile.
The pipe piles are often designed to carry substantial vertical loads
in addition to bending loads.
A key advantage of a Pipe-Z combined wall system compared
to, for example, Beam-Z systems is its efficiency in terms of
strength to weight ratio.
Beam-Z systems increase strength by adopting a heavier and
deeper beam; however, the overall width of the system doesn’t
change. Therefore, the strength gain as the beam size is increased
is proportional to the increase in weight.
The Pipe-Z increases strength by increasing pipe thickness and
diameter, meaning the system width increases. The increasing
system width offsets the weight gain per square foot. This can be
particularly noticeable when high strength walls are needed and
double beams are combined with intermediate sheet piles.
For example, a double beam-Z with a section modulus of 387
ins3/ft at 93 lbs/ft2 can be matched by a Pipe-Z with section modulus
of 396 in3/ft at 80 lbs/ft2. This represents a 16% weight saving.
The Pipe-Z will also have a much higher stiffness.
Beam-Z combined wall systems
As with other combined wall systems, beam-Z systems are composed
of interlocking king piles and intermediate sheet piles. The
sheet piles transfer the earth and water pressure to the king piles,
which carry most of the load, through connectors that either
interlock or are welded to the beams. In most cases, single beam
systems are used, but double beam walls and continuous beam
walls can be used to increase the bending capacity of the wall.
There should not be more than one pair of sheets in between the
king piles.
Single, double and continuous beam systems with
interlocking connections
STEEL SHEET PILING
Pipe-Z combined wall systems
Pipe-Z combined wall systems are used when higher capacity is
required over that offered by regular sheet piles. A combined wall
combines pipes (primary elements) with intermediate sheet piles
(secondary elements). Structurally, the pipes fulfil two functions.
First, as retaining elements for horizontal loads from soil and
water pressures and, second, as bearing piles for vertical loads.
The pipe piling is usually formed by spiral welding from coil to
produce a wide range of size and capacity options. With thicknesses
up to one-inch thickness and an almost infinite range of diameter
possibilities up to around 120 inches enables precise targeting
of design capacity and tailor made solutions.
Production process for spiral welded pipe
Transversal
bevelling and
transversal
welding
centring
1 2 3
4 5
6
7
10
inside
welding
8 9
11
12
13
14
cutting
bevelling main drive
outside
welding
US testing
weld seam
plasma
cutting
de-coiling
levelling
and centring
edge
cutting
three-roll
forming
pipe
body
testing
106 | ISSUE 4 2020 www.piledrivers.org
/UnitedRentals.com
/www.piledrivers.org
/www.piledrivers.org
