Eco-friendly rice straw as vertical drains for dredged slurry treatment as construction fill

Abstract

This paper presents an experimental study on the feasibility and effectiveness of using the eco-friendly rice straw as vertical drain (SVD) in place of the traditional prefabricated vertical drain (PVD) in the treatment of dredged slurry at higher water contents via the vacuum preloading method. A series of laboratory tests including water discharge tests, straw rope tensile tests, and negative vacuum consolidation tests were conducted on different types of SVDs treated dredged slurries. The effects of woven types of rice straws and standing time on the water discharge capacity, volume deformation, and tensile properties of SVDs were systematically investigated and compared with PVD. Results showed that the logarithm of water discharge rate almost reduces linearly with the confining pressure for all the SVD specimens. SVD specimen of the four core straw braids with a single spiral rope (C4S) shows a better water discharge capacity than that of four core braids and four spiral ropes (CS4). The water discharge capacity of SVD at relatively lower confining pressure (within 160 kPa) is comparable to that of PVD. SVD shows the elasto-plastic volume deformation behavior. The higher the standing time, the lower is the cumulative volume deformation at a given confining pressure. The peak tensile force of a single straw rope reduces nonlinearly with the increase of standing time. The tensile strength of SVD is comparable to that of PVD. The settlement of SVD treated dredged slurry under vacuum preloading reduces significantly from the beginning and reaches more than 85% of the total settlement at the time of 1000 h. Some of the SVD treated samples show a similar or larger consolidation settlement than PVD treated indicating the effectiveness of SVD. The improved form of SVD is recommended as an effective substitute for PVD to treat high water content dredged slurry using the vacuum preloading method.