Investigation of creep behavior of soft soil during and after vacuum preloading

Soft soil has been a major problem in the northern part of Java for the last decade, and several areas have been improved using the preloading method. In Indonesia, the improvement of soft soil using this method has already been regulated in several codes, such as SNI 8460:2017 and Geotechnical Manual series 4. However, these codes did not mention the effects of creep on post-settlement. In addition to creep, several factors influence the amount of post-settlement during the operational period, such as the thickness of the soft soil, load ratio, soil compression ratio, and the drain spacing and pattern. Larger spacing or pattern, higher compression ratio, greater secondary compression index (C_α), and increased soft soil thickness induce more post-settlement. In contrast, a higher load ratio resulted in less post-settlement. It was discovered that the load ratio of 1.20 stated in SNI 8460:2017 did not meet the requirement of a maximum yearly settlement of 20 mm as specified in Geotechnical Manual series 4. This research showed that with and without creep, the load ratio required should be in the range of 1.30 to 1.50, with an average value of 1.375. Furthermore, this study proposed a new coefficient, the load ratio coefficient (C_LR), that accounts for various factors influencing post-settlement. The proposed coefficient can be utilized along with a period of interest to estimate the post-settlement due to creep. It was also observed that the load ratio heavily affects the post-settlement.