Absorption and discharge capacity tests on natural prefabricated vertical drains

Abstract

ABSTRACT: This paper reports absorption and discharge capacity tests conducted in the laboratory on four types of newly developed and fabricated band-shaped prefabricated vertical drain (PVD) made from natural geotextiles and commercially available polymer-based prefabricated vertical drains (PPVDs). The natural PVDs are made from single-layer woven or nonwoven geotextile jute sheath wrapped around a core of coir ropes or coir mats, designated as natural prefabricated vertical drains (NPVDs 1, 2, 3 and 4). Short-term, rubber-membrane-confined discharge capacity tests were conducted at different compressive stresses and hydraulic gradients. The tests were carried out for a better understanding of the influence of NPVD configuration, compressive stress and hydraulic gradient on discharge capacity. The test results for the NPVDs are compared and discussed, together with the results from PPVDs. NPVD 4, which is made of woven jute sheath and corrugated coir mat core, has a greater discharge capacity than the other NPVDs at all the normal stresses and hydraulic gradients studied. The core configuration of NPVD 4 supports the jute sheath better, to prevent it from collapsing into the core as the compressive stress is increased. Although nonwoven jute sheath is a better water-absorbing geotextile than woven jute sheath, the lowest discharge capacity is observed in NPVD 2, which is made from nonwoven jute wrapped around coir ropes. Flow conditions through all the NPVDs are linear at all hydraulic gradients, satisfying the theoretical requirement of PVDs.