Methods to Improve Vertical Drain Design and Performance

摘要

Laboratory and field research results are provided with recommendations tc modify vertical drain design practice to more reliably estimate field performance and avoid costly delays where vertical drains are considered to be cost-effective. The foregoing research was implemented as a result of inconsistencies in field performance as compared to design expectations. The construction of Chek Lap Kok Airport in Hong Kong is reviewed as a case where accepted design practice indicated vertical drains were cost-effective, yet a Test Section installed to verify the design showed the drains did not perform as expected. Final airport design involved excavating compressible subsoil in areas of Airport operation, and backfilling with sand to insure stability. Laboratory research later showed that pore pressure induced during mandrel advance for wick drain installation did not dissipate on mandrel withdrawal. As a result of field research, an empirical expression was developed which included such variables as time for mandrel induced pore pressure to dissipate for any given soil, the size of mandrel used as well as drain spacing.