Reinforcement effect of geotextiles on shear strength of peat soil: a case study on Urmia peat

Peat soil is a soft material from the group of organic soils. This soil has different behavioral characteristics than other nonorganic soils. One of its weaknesses is insufficient shear strength. Therefore, any construction and loading on it require special measures such as reinforcement. The present study aims to experimentally investigate the shear behavior of peat soil reinforced with geotextiles. In this research, first undisturbed samples of the Urmia peat soil were collected from in situ road construction site of Urmia to Tabriz. After determining its initial physical characteristics, direct shear tests under vertical stresses of 10, 20, and 30 kPa with changing strain rate of 0.9 mm/min and 0.1 mm/min were conducted on two types of peat soils with average organic material content of 33% and 72%, respectively. In the second part, direct shear test was performed between peat samples and two types of geotextiles with tensile strengths of 30 and 6 kN/m. The results showed that the percentage of organic materials in peat plays a significant role in its friction angle (phi), and the peat with higher rate of organic materials has higher frictional behavior and less cohesion (c). Also, the application of geotextile, depending on its tensile strength and the amount of organic materials in the peats, has different results in increasing the peat friction angle. The test results show with higher amount of organic materials in peat and the greater tensile strength of the geotextile; frictional resistance between peat and geotextile may be greater than in peat alone.