Polypropylene (PP) fiber is considered as an innovative
material to enhance the strength parameters of soils under both dynamic and
static loading conditions. This study is an attempt to improve the liquefaction
resistance of loose state sands, which are prone to liquefaction, by the
addition of PP fibers as reinforcement. A series of undrained cyclic triaxial
tests with various initially constant and subsequent cyclic shear stresses were
applied on the saturated sand having a low relative density ranging from 24 to
40%. Tests were carried out on two
different sand samples obtained from two different sites, i.e. Topaktas (Van)
and Akpinar (Istanbul), using cyclic triaxial test apparatus available in the
laboratory. The first one was liquefied on the site during the MW 7.1 Van Earthquake on 23rd
October 2011. Polypropylene fibers were used in two different combinations of
randomly distributed and layered in the second type of sand. In the case of
fibers, the percentages of fibers by weight of dry sand were taken as 0.1 and
1%, respectively. The liquefaction parameters, such as pore water pressure
(PWP) and shear stress, have been measured in cyclic tests at a constant
frequency of 0.1 Hz. Large strain level deformations and liquefaction phenomena
started to occur in the first few cycles of cyclic triaxial tests of
unreinforced samples. Moreover, the results of this study indicate that
increasing the percentage of fiber inclusion decreases the initial elasticity
modulus, Emax; in
contrast, fiber addition makes loose sand more resistant against liquefaction
under dynamic loading.