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Chapter 11
Rock Fall Protection IIRock Sheds
Reinforced concrete rock sheds have been developed to provide a highly reliable level of
protection on major transportation routes, and at tunnel portals. Rock sheds are used exten-
sively in Japan and Europe; Figure11.1 shows a variety of concrete shed congurations
used in Switzerland (Vogel et al., 2009). However, sheds are less common in North America
where the trafc volumes are not as high and lower cost protection methods such as barriers
and fences are generally accepted.
11.1 TYPES OF ROCK SHEDS
The most common type of rock shed is precast reinforced concrete; Figure11.2 shows a
typical structure in Japan. This shed comprises a cast-in-place concrete retaining wall back-
lled with gravel on the mountainside, with precast columns on the valley side and precast
roof beams that support a layer of sand to absorb impact energy. Essential features of these
structures are their energy-absorbing components that include cushioning material on the
roof and exible elements in columns and roof slabs as discussed in Section 11.2.4.
Reinforced concrete sheds are usually used at locations with frequent, hazardous rock falls
and where very reliable protection is required for facilities such as high-trafc-volume high-
ways and high-speed trains where service interruptions cannot be tolerated. The advantages
of concrete sheds are that they can be designed to withstand a specic impact energy capac-
ity that can be greater than most types of wire rope fences and barriers (see Figure10.1).
Furthermore, concrete sheds have a long service life and require little maintenance.
The main disadvantage of sheds is their high construction cost. Cost items include com-
plex, precast reinforced concrete beams and slabs, as well cast-in-place concrete founda-
tions and walls. In order to withstand the substantial dead and live loads of the structure,
high-capacity foundations are required, particularly on the valley side of the structure. In
steep mountainous terrain, the valley-side slope may be unstable and deep foundations such
as rock socketed piles may be needed to transfer the loads to stable bedrock. Furthermore,
construction of a shed on an active highway or railway will probably require construction
during short duration trafc closures (“work windows”) with the result that productivity of
the work crew will be low.
Where it is not possible to construct adequate foundations on the valley side of the struc-
ture, even more costly cantilevered sheds may be required as described in Section 11.3.
The roofs of most sheds are near horizontal, with a slope of about 5° for drainage, since
this conguration limits the span of the roof beams and helps maintain a uniform layer of
sand. For sheds below steep slopes, the design will be based on direct impact of rock falls
landing on the roof at an angle close to 90° resulting in all the impact energy being absorbed
by the structure. In contrast, for sheds below atter slopes, the rock falls will tend to roll
194 Rock Fall Engineering
across the roof with little impact energy being absorbed by the structure. In some cases it
may be possible to construct a shed with a roof at the same angle as the slope such that rocks
will roll across the roof with limited impact energy, and it is possible to use a lightweight
structure; Section 11.4 discussed sheds that redirect rock falls.
Although steel sheds have superior energy-absorbing properties due to their greater ex-
ibility than concrete sheds, steel sheds are rarely used due to their higher maintenance costs
and shorter service life.
(a) (b)
(c) (d)
(e)(f)
Figure 11.1 Variety of rock fall shed congurations. (From Vogel, T. et al., 2009. Rock fall protection as an
integral task. Structural Engineering International, SEI 19[3], 304–312, IABSE, Zurich, Switzerland,
www.iabse.org.)

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