8
structure used as a wharf where the penetration level of
the piles is close to the bottom of the waterway and piles
are subject to considerable horizontal loads. There, rock
dowels drilled through the hollow dowel ensure the stability
of the retaining structure. Rock shoes with a hollow dowel
are also used at sites where piles are subject to tension
forces. A pull anchor can be installed through the hole.
In conditions of no or few stones, where the pile tip is
designed to bear on soil layers, the tip of the pile can be
protected by a so-called reinforced bottom plate. The
recommended solution for such conditions, however, is to
use standard rock shoes with structural steel dowels.
Open ended piles are often equipped with a so-called
reinforcement ring to protect the lower end. The
reinforcement ring is usually a 150 to 500 mm wide steel
band welded onto the lower end of the pile. The sheet
thickness of the steel band is usually 10, 15 or 20 mm.
Both reinforcement rings and reinforced bottom plates
are manufactured to the client’s project-specific designs.
Rock shoes are preheated before welding and assembly
welding is carried out by robots. The rock shoes are
numbered to ensure the traceability of the manufacture
and raw-materials of the shoes.
The design resistance values of standard rock shoes for
RR large diameter piles are presented in Table 7. The
most important criterion for rock shoes are the end blows
and/or the dynamic load test. Project specific rock shoes
with different capacities are analyzed numerically by the
requirements of Finnish Transport Agency. Moreover, the
installation instructions of Sec. 7.3 must be followed in
installation, especially if the pile tip encounters a boulder
or an inclined rock surface.
At the design stage, however, the maximum impact
resistance of each pile size should be limited to its/the
R
d,L
value.
Figure 3. Shoe types of large diameter RR piles.
Rock shoe with structural
steel dowel
Rock shoe with hardened
steel dowel
Rock shoe with
hollow dowel
Toe
reinforcement
2.4.2 Pile shoes
In soil conditions typical of the Nordic countries,
RR large diameter piles are usually equipped with
RR rock shoes. SSAB's standard rock shoes were
granted the Finnish Transport Agency’s use permission
(565/090/201, 4 October 2011) and the manufactured
rock shoes are CE marked. Rock shoes are used to protect
the lower end of the pile against installation stresses, to
centre the stresses on the pile tip as evenly as possible
across the pile pipe cross-section, and to prevent lateral
sliding of the pile tip.
There are three types of RR rock shoes (Figure 3). The most
common ones are rock shoes fitted with a structural steel
dowel or a hardened rock dowel. SSAB also delivers rock
shoes fitted with a hollow dowel, which allows drilling, for
example, a dowel bar to be grouted to bedrock through the
concrete filled hollow dowel of the rock shoe.
A rock shoe with a structural steel dowel is used in
conditions where the target level of the piles is within
coarse-grained or moraine soil layers, or in conditions
where the bedrock surface is relatively even and there
are supporting compact soil layers on top of the bedrock.
A rock shoe with a structural steel dowel endures well
penetration to the surface of the bedrock and into it.
A rock shoe with a hardened rock dowel is used in
conditions where the bedrock surface is inclined or there
are no compact coarse-grained or moraine soil layers on
top of the bedrock – or the soil layers are thin and the
pile tip is to be driven to the bedrock surface. Rock shoes
with a hardened rock dowel can prevent lateral sliding of
the pile tip in most conditions.
Rock shoes with a hollow dowel can be used in conditions
where it is desired to ensure the staying in place of the pile
tip by a grouted steel dowels drilled through the hollow
dowel into bedrock. A typical application is a combi-wall