Geoscience Reference
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Figure 15 Mohr circle of strain increments.
and 1˙ 3 , and the aand bplanes. The planes are connected to form zero extension
trajectories, which give the potential slip surface in a soil mass.
It is found that the reinforcement should be placed in the tensile arc for it to
be effective, and the optimum direction should be parallel to the 1 ˙ 3 direction. On
the other hand, the reinforcement placed along the zero-extension trajectories
would not function; it may weaken the soil mass under certain circumstances. For
example, if the frictional bond between the reinforcement and soil is less than that
of the soil at the interface, slippage would occur.
With the inclusion of reinforcement, the strain field in the soil mass can be
significantly modified. Figure 16a shows the results by Jewell and Wroth (1987),
in which the increase in strength was realized when the reinforcement was placed
vertically (1˙ 3 -direction), whereas no effect was realized when placed horizontally
(zero-extension direction). Tatsuoka (1986a) performed model tests on the
bearing capacity of footing on unreinforced and reinforced Toyoura sand. Figure
16b shows the strain fields in unreinforced and reinforced foundations at peak
value strength. The modification of strain fields after placing the reinforcement
along the 1˙ 3 -direction was noticed.
In applying strain field analysis to the reinforcement of bearing capacity,
slope, embankment foundation, and so on, it is necessary that experiments be
performed using reduced scale or centrifuge models. A more powerful and
versatile method for this purpose would be that based on the finite-element
 
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