A System with Local Strain for Studying Shear Modulus Degradation of Cement Treated Clay with Fibers-Paper

Paper

Pdf Summary

The study develops and validates a local strain measurement system for assessing shear modulus degradation in fiber-reinforced cement-treated clay. Conventional external strain measurements can underestimate small-strain stiffness because they include deformation and errors from the testing apparatus. The proposed triaxial system uses a floating miniature submersible LVDT attached to the specimen with mounts and stainless-steel pins, avoiding reliance on the membrane.<br /><br />Tests were conducted on 70 mm by 140 mm specimens made with Singapore marine clay, 50% cement, 100% water, 0–1% polypropylene fibers, and seven days of curing. Unconfined compression and undrained triaxial tests were performed, the latter under 300 kPa effective confining pressure. The researchers varied pin diameter, length, and spacing to assess their effects on measurements.<br /><br />A recommended mount configuration uses pins 1.2–1.5 mm in diameter, 12–15 mm long, and spaced 46 mm apart. Local measurements produced substantially higher stiffness estimates than external measurements, while specimen behavior remained repeatable. Results were consistent with resonant column and bender element tests, supporting the system’s reliability under both confined and unconfined conditions.<br /><br />Confining pressure slightly increased small-strain shear modulus and accelerated its degradation. Adding fibers increased shear modulus and reduced degradation at strains up to 0.01%. The system therefore offers a practical way to measure small-strain stiffness in fiber-reinforced cement-treated clay, with potential relevance to ground improvement for foundations and tunnels.

Keywords

shear modulus degradation

fiber-reinforced cement-treated clay

local strain measurement

triaxial system

small-strain stiffness

floating miniature LVDT

undrained triaxial tests

polypropylene fibers

confining pressure

ground improvement