The series of laboratory tests have been conducted to investigate the effects of confining drain by clay and different thickness of rubber membrane on discharge capacity of prefabricated vertical drain (PVD). There are two types of PVD were tested namely: Mebra drain and CN drain. The test results indicate that confining the drain by thick rubber membrane is higher discharge capacity than thin rubber membrane confinement. Due to the tension stiffness of rubber membrane, the filter cannot be deform freely as that in clay. When confining the PVD with clay, the discharge capacity yielded much lower discharge capacity than rubber confinement. In addition, the clay particles can enter the drainage channel and the filter jacket can squeeze into the flow channel and further reduce the water flow. From the test results, Mebra drain consistently yielded the higher discharge capacity than CN drain because filter jacket of Mebra drain has higher tensile strength than CN drain. Thus, the tensile strength of filter jacket significantly affect the discharge capacity of PVD. In addition, the field test was constructed in AIT campus using the PVD to recharge and remove the negative piezometric drawdown. The PVD was installed to 10 m below the original ground level in square pattern with 1mx1 m spacing. The sand embankment which served as drainage blanket and construction platform, was constructed to a height of 1.2 m. The piezometric level in PVD area increased and removed the negative drawdown within 28 days after PVD installation. The PVD has successfully removed the negative drawdown in the subsoil. The maximum surface settlement 5.5 mm was observed at 130 days after installation. The settlement prediction by agreed with the field settlement.

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Civil Engineering

Thesis (M.Eng.) - Asian Institute of Technology