Geoscience Reference
In-Depth Information
Unfortunately, such a solution has a cost; typically, it doubles the quantity of
geosynthetics.
A more practical solution would be to use short secondary layers. That is, in
addition to full-length primary reinforcement (say, at every 40 cm), use
intermediate short reinforcement layers (say, 1m wide at “unused” interface
between blocks). Such secondary layers will serve to reduce the tributary area
considering the connection only. The end result would be an increase in break and
pullout factors of safety for the connection. It should be noted that this
arrangement would not typically reduce the load carried by the primary
reinforcement at the slip surface (T max ). Such an arrangement of reinforcement is
similar to the use of intermediate layers in steep slopes to improve compaction
and erosion control. The increase in overall global stability of the slope due to
such layers is normally ignored; however, their increase of superficial stability is
effective and significant.
The overall cost associated with the actual installation of secondary layers
is not only offset by increasing the connection strength, but also by an improved
quality of construction. This is, because intermediate layers are placed, better
compaction near the facing is possible without causing misalignment of blocks.
Once again, this benefit is completely analogous to the use of intermediate
reinforcement in steep slopes where better compaction of the sloping face can be
achieved.
Proper “manipulation” of MSEW software allows for assessment of the
effects of secondary layers on the connection. If the layers are too short (i.e.,
typically at higher elevations), the program will indicate that there is no rear-end
pullout resistance. However, it will allow these layers to carry some of the
connection load. Figure 3b shows a few secondary layers added near the top of
the wall. Table 5 presents the resulting factors of safety (note that the
geosynthetic and block data in Table 4 were also used for Table 5). Comparing
Tables 5 and 4, one realizes that except for the uppermost layer, all connection
safety factors have increased significantly. The pullout connection of the
uppermost layer, located only 20 cm below the crest, is “hopelessly” small. Bear
in mind that traffic load exists in this problem and, hence, the weight of one block
would be too small to generate sufficient frictional resistance. Note that CRs
under 20 cm are negligibly small. However, at extremely low confining pressure,
the connection is likely to have pullout strength larger than predicted by pure
friction. For example, if due to minor interlocking with stacked blocks CRs equal
0.02 for the upper layer, the computed pullout safety factor will increase from
0.75 to about 3.0. MSEW software allows the designer to assess values producing
safe structures and thus make an informed judgment.
Alternatively, the MSEW program allows the user to specify a function
relating connection loads to the calculated maximum reinforcement force
(T 0 /T max ) versus depth. Currently, Demo 82 recommends a default value of 1.
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