Use of steel and polypropylene fibers to improve flexural performance of deep soil–cement column

In this study, steel and polypropylene fibers are used to improve flexural performance of soil–cement pile. Deep cement mixing (DCM) technique has been used for decades in Thailand to improve the strength of soft clay in Bangkok and vicinity. However, since it is made of about 10–20% of cement, it also shares similar properties as the harden cement such as good compressive strength, low permeability, and poor tensile and flexural strengths (brittle). In several occasions when subjected to bending moment caused by horizontal loadings (induced by large embankment), the poor flexural strength can lead to a failure of the soil–cement column. In order to improve its flexural strength and brittleness, a technique of mixing short fibers (similar to that used in conventional concrete) is introduced to the soil cement mixture. Two types of fiber are used to produce the fiber reinforced soil cement (FRSC): polypropylene and steel fibers at three different volume fractions of 0.5%, 0.75% and 1.0%. Flexural performance of the FRSC is carried out according to ASTM C1609. Results show improvements in the flexural performance as seen by the increase in the equivalent flexural strength ratio and the residual strength when the fibers are incorporated into the mix. The polypropylene fiber is found to perform better than the steel fibers. With the increasing volume fraction, the toughness is also increase.