Factors affecting field settlement assessment and back-analysis by the Asaoka and hyperbolic methods

Thick deposits of marine clay are commonly present in the coastal regions of the tropics. Land reclamation on this marine clay formation will require some form of ground treatment works to accelerate the consolidation process. The aim of the ground treatment works is to negate settlements under the fill load, future dead and live loads. The use of prefabricated vertical drains with preloading option is the most widely-used ground improvement method for the improvement of marine clays in land reclamation projects. Surcharge of equivalent working load after taking into account submergence effect and settlement of the reclaimed land is placed until the required degree of consolidation of the marine clay is obtained. As such, the assessment of the degree of consolidation of the marine clay is of paramount importance prior to the removal of preload. The most suitable means of carrying out this assessment is by means of field settlement monitoring. During the process of consolidation, the field settlement monitoring data can be analysed by means of the Asaoka and hyperbolic methods to predict ultimate settlement and degree of consolidation of the underlying soft marine clay. There are various factors that affect the predictions by these methods such as the period of assessment after surcharge placement as well as the time interval used for the assessment. The aim of the paper is to highlight the significance and impact of these factors in the field settlement assessment and back-analysis of coefficient of consolidation due to horizontal flow of soft clays and with special regard to coastal marine clays.