Unit Cell Testing of Reinforced Soils - Reinforced Soil Engineering: Advances in Research and Practice - page 56

Figure 11 Relationships between strength ratio and aspect ratio. (From Ingold, 1979.)

Ingold and Miller (1982a) also conducted a study on reinforced clay under
undrained conditions. Kaolin clay, Boulder clay, and London clay were used. The
reinforcements used were porous sintered polythene, needle-punched felt, and
heat-bonded geotextiles. A series of triaxial compression tests was performed.
In the unconfined test at a large spacing where the inverse aspect ratio was
less than 4, a negative reinforcement effect was found. Ingold and Miller (1982a)
believed that it was due to the longer drainage path. They also reasoned that the
large pore water pressure generated in the inner part of the specimen caused a
premature failure. However, when a larger inverse aspect ratio was used, the
strength obtained was close to that at the drained condition. A separate paper by
Ingold (1983a) reports results of a similar study.

3.2 Direct Shear Test

Ingold (1981, 1983b) conducted direct shear tests to investigate the adhesion
factor between reinforcements of different roughness and the clay in which they
were embedded. The undrained shear strength of reinforced soil, c uR , is due to the
true undrained strength of soil, c u , and increment due to reinforcement, Dc u .
Consider the arrangement of reinforcement as in Fig. 12a ; the mobilized tensile
force in it is determined as

T ¼ 2ac u Lb ð 35 Þ