Analysis of a Prefabricated Vertical Drain (PVD) Soil Improvement Project

Abstract

A settlement analysis has been carried out for several sectors of a rail station yard improved with prefabricated vertical drains (PVD) in Istanbul, Turkey, that exhibited prolonged consolidation beyond the predicted values in certain sectors of the treated zone. Final settlement and End of Primary (EOP) settlement times have been estimated theoretically as well as using the Asaoka graphical procedure. The compliance of settlement-time curves with in-situ measurements and Asaoka solution has been investigated. A geotechnical model was developed for finite element and three-dimensional consolidation analyses. The settlement curves obtained by varying horizontal-vertical permeability coefficient ratio (kh/kv) and in-situ measurements have been compared, and kh/kv values corresponding to 90% degree of consolidation has been computed for all sectors. The effect of drain spacing (sdrain) as well as drain length (Ldrain) on the rate of consolidation have been examined for each sector, keeping the specified ratios constant. The times corresponding to 95% degree of consolidation (t95) have been calculated using the theoretical solution and compared to in-situ measurements. Calculated t95‘s have also been compared to their estimated values by varying the spacing (sdrain) and the length (Ldrain). Additionally, the required intervals of sdrain and Ldrain have been obtained corresponding to the calculated t95 times.