Large triaxial compression tests on geosynthetic-encased granular columns

Large triaxial compression tests are performed on geosynthetic-encased granular columns (GEGC) with gravels in dense state. The stress-strain characteristics of GEGC with different strengths of polypropylene woven geotextiles and different confining pressures are investigated. The theoretical formulas to compute the strength and modulus of GEGC are then proposed. The results show that the GEGC exhibits dilative shear failure under triaxial compression, and mainly the horizontal textile slices at the shear band break. The shear angle is close to the rupture angle of the Mohr-Coulomb strength theory. The stress-strain curve of GEGC at the preliminary loading stage is concave down, then its stress approximately increases linearly up to a peak stress, and subsequently decreases to a stable value, showing strain softening characteristics. The axial strains corresponding to the strengths of GEGC with the same reinforcement strength under different confining pressures are even close. The quasi-cohesion of the GEGC has a good linear relationship with the strength of reinforcements, and it is much larger than that of the gravels, but the strength of reinforcements has little effect on the internal friction angle of the gravels of GEGC. Theoretical formulas are established to compute the strength and modulus of the GEGC. The formulas are verified through the test data, and the correction factors for the formulas are obtained. The results of the modified formulas agree well with the test ones.